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73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: Monkey Uncle on October 01, 2017, 05:11:05 am
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I have a standard push lawn mower with a 5.5 hp Honda engine and tiny one-barrel carburetor. After it sits in the shed from October to April, I can pull it out, set the choke, pull the rope one time, and it starts right up. If my truck (350 with a quadrajet) sits for more than three days or so, I stomp the pedal to set the automatic choke, and I have to hold the ignition over for up to 10 seconds before it will fire. Is it just because the carburetor is so much farther away from the gas tank? Or is there something wrong?
The longer it sits, the longer it takes to fire up. After two days, it hesitates just a bit and then starts; after a week it takes considerably longer. But it always fires if I hold the ignition on long enough.
This is the first carbureted vehicle I've owned in close to 30 years. I don't recall having this issue with my old car, but I probably never let it sit for very long either.
I should add that the mechanical fuel pump and fuel lines are essentially new. I recently had the engine swapped for a remanned 350, but it behaved the same way with the old 350. I re-used the old stock intake. As far as I can tell, there is no charcoal canister.
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Hi Monkey Uncle:
First off, you really cant try to compare the functions and features of a small power tool carb to a sophisticated carb like a Q-jet...the power tool carb is much simpler and hence less to go wrong.
If it has been a long time since the Q-jet was tuned up or re-built, there are a couple of things that could be happening:
-a phenomenon that sometimes occurs when it sits inactive for a while is bleed down of the float bowl. Essentially your float bowl dries up and you need to refill it by cranking until it fills and then can feed the jets and there is enough fuel to be moved around by all the air pressure signals. the longer you wait between using your truck the longer it takes to start. This could be caused by a leaking gasket, leaking welch plugs on the bottom of the carb, looseness between the air horn assy and the float bowl assy, and or a disconnected or broken hose that vents the float bowl to the outside atmosphere.
-another thing is you could also have a misadjusted or gunked up float and needle assy...if the float is adjusted wrong it closes the needle before the float bowl fills up to spec and you never really have enough fuel in the bowl...and it evaporates away quickly between operation.
It just sounds as if you need a carb tune up or rebuild. A tune up can be just the removal of the air horn on the engine and you have access to the float chamber and all the workings...I personally find it too hard on my back to work on the carb in the engine so I just remove the carb completely and work on the garage bench even though it is more disassembly and takes longer.
Regards,
Henry
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Thanks, Henry. I should have noted that when I bought the truck last December, the previous owner reported that the carb was new. I don't have any documentation of that, but I had no reason to doubt him based on the external appearance of the carb. Of course, I have no experience working on carbs and can't tell you anything beyond the external appearance.
It has a disconnected vacuum hose on the passenger side. And presumably the port that should connect to the non-existent charcoal canister is also open. Perhaps one of those holes is where my fuel vapors are going.
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What type of air cleaner assembly do you have?
The next time you try to start it up after sitting for a while, before starting look at the carb primaries while moving the throttle arm. If you can see fuel squirting into the carb then the problem is something else.
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Yes, the test that Stewart suggests should indicate whether or not you are getting fuel or not after not running it for a week or so. When it does start and run, does it restart easily later the same day?
You should get those vacuum connections for the carb sorted out....what year, model, engine size is your truck? Is it a CA truck? Do you have the original air cleaner cover which may help indicate the emissions equip installed? Do you know what model your Q-jet is? Does it have a divorced choke or integral choke? Does it have the idle stop solenoid? A photo of the passenger side of the carb may help identify those hose connections.
Regards,
Henry
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BTW, on a side note, aren't most carbs on lawnmowers gravity fed?
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Q-jets always leak through the welch plugs, even if you epoxy them they'll leak again, I always remove the air cleaner and squirt some gas down the vents to fill the bowl up and it starts right away, this is the reason I'm converting my truck to EFI, to get rid of my pesky q-jet
Enviado desde mi Life One X2 mediante Tapatalk
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What type of air cleaner assembly do you have?
The next time you try to start it up after sitting for a while, before starting look at the carb primaries while moving the throttle arm. If you can see fuel squirting into the carb then the problem is something else.
It has the original air cleaner assembly from the 1978 K-15 chassis/drive train donor truck (body is from an 85 C-10 diesel). The air cleaner does not properly fit the carb, so I presume the carb is a different model from the original carb. The bolt hole is centered in the cleaner lid, but the bolt in the carb is off-center toward the front. Right now I'm using the "bubba" trick of flipping the lid to get a seal all the way around, until I get around to putting an after market cleaner on it. I didn't discover this until after the engine swap when I couldn't get the lid to fit. Apparently the P.O. had the cleaner on there crooked so the lid would fit, which presumably was allowing the carb to suck dirty air in underneath the cleaner.
I'll try the test when I get a chance. Just ran it yesterday, so probably later this week.
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Yes, the test that Stewart suggests should indicate whether or not you are getting fuel or not after not running it for a week or so. When it does start and run, does it restart easily later the same day?
You should get those vacuum connections for the carb sorted out....what year, model, engine size is your truck? Is it a CA truck? Do you have the original air cleaner cover which may help indicate the emissions equip installed? Do you know what model your Q-jet is? Does it have a divorced choke or integral choke? Does it have the idle stop solenoid? A photo of the passenger side of the carb may help identify those hose connections.
Regards,
Henry
It restarts easily up to two days after the last run. Hot restarts are sometimes difficult, although I've mitigated this some by using ethanol-free gas.
As noted, chassis and drive train are from a 78 K-15, body is from an 85 C-10 that originally had a 6.2L diesel in it. The remanned engine is a stock replacement of the original gas 350 that was in the 78 K-15. I do have the original air cleaner cover (from the 78) - any tips on what I should be looking for on that?
I don't know enough about carbs to answer the questions about model, type of choke, and the idle stop solenoid. Will get a photo up if I can figure out how to post it.
Thanks.
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BTW, on a side note, aren't most carbs on lawnmowers gravity fed?
Yes, I believe you are correct. Carb on mine is below the gas tank. Which would answer the original question of why it starts right up after 6 months of sitting.
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Hi:
Well it sounds as if you have a chassis/drivetrain is essentially a 78 1/2 ton 4wd with a 350. If you re-used the intake manifold it is probably the oem cast iron design with all the original emissions connections (and choke coil attachment if it used a carb with a divorced choke). The carb that came with this truck should have been a Rochester (or Carter manufactured) 4 barrel Q-jet of either the 4MV or M4MC model. The 4MV had the divorced choke (coil in the manifold on pass side) and the M4MC had the coil mounted on the pass side of the carb itself. What I find a bit confusing is that you say the threaded rod on the air horn of the carb is not centered on the air horn...I think that both these carbs have the threaded rod centered on the air horn. So maybe you have yet another version (later) Q-jet that I am not familiar with. Anyway, if you have the original air cleaner cover, it should have some decals that indicate the basic emission class of your engine and how to tune the carb...after all these years these decals could be gone by now. Since your truck was a 1/2 ton, it almost assuredly had the ECS cannister and associated hoses that went to the carb and fuel tank. I would not plug either of these hoses until you have done the squirt test to see if your carb dries up after sitting for 3-4 days. The ECS system changed over the years, but basically, one hose to the carb was for vacuum signal (to operate the ECS purge valve) and another was to vent the carb bowl to the ECS charcoal cannister. If the ECS cannister is gone, you would want to plug the signal line and leave the vent line open to atmospheric pressure, but not just open to the engine bay where the fumes can vent and just continue to evaporate the float bowl. Until you can get us some pics of the carb I would not change anything on these hoses for now. These carbs had a lot of hose connections that were used on some model vehicles and plugged on others so it can be confusing. Your truck probably also had EGR which would have been another tangle of vacuum lines that connected to the carb and intake manifold that may be gone now as well.
Regards,
Henry
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Thanks very much for all that information. Please stand by - it may take me a few days to check things out more and get some photos up (busy week at work).
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A few pics of the carb are attached.
I was mistaken when I said earlier that there is a loose vacuum hose on the passenger side of the carb. The hose actually emanates from the underside of the air cleaner. There is something that looks like a little filter in the bottom of the cleaner where the hose is attached. The letters AC are on the little filter. No idea what the other end of the hose is supposed to connect to. It is pointing at the camera in the picture that has the air cleaner mounted on the carb.
Note that the picture with the air cleaner also illustrates how the bolt is off-center relative to the cleaner.
It looks to me like all of the unused ports on the carb are plugged.
The decal on the air cleaner lid says "CCS" for emissions. It says that for all possible engines that were sold in that model truck, from a 250 to a 454.
Stewart - I tried your throttle test after it had been sitting for nearly a week. I could not lean over far enough to look directly down into the primaries. But I could hear what sounded like a squirting noise when I moved the throttle. I presume that means it's getting fuel. So I figured maybe if I pump the pedal a bunch of times before turning the key, it might have enough fuel to start promptly. I pumped the pedal about 10 times and when I turned the key it acted like it was going to fire, close enough that I let off the key. But it didn't keep going, and I then had to turn and hold the key for 5 seconds or so to get it started. But it still seemed like it was a little faster than it usually is after sitting that long.
One of the pics of the driver's side has some numbers visible. Are those useful for determining the model? Or is there something else I should be looking for to help identify an air cleaner that will fit properly?
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You should only have to pump the pedal once before starting when the engine is cold. Also the choke should snap shut when you do this----like in picture 3.
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Does it mean anything that the choke was already closed before I ever moved the throttle or pressed the pedal?
And now that I'm looking at the photos again, it strikes me just how odd it looks with the bolt in that hole between the primaries. Is the opening between the secondaries threaded? Seems to me that's where the bolt should be.
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The choke should not be closed after the truck has been driven a while and warmed up.
Yes, the air cleaner stud SHOULD NOT be there. It should be in the hole right behind the slot where the stud is now.
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The choke should not be closed after the truck has been driven a while and warmed up.
Yes, the air cleaner stud SHOULD NOT be there. It should be in the hole right behind the slot where the stud is now.
It had not been driven prior to those pictures - had been sitting for a week. I did take the pictures after I moved the throttle by hand, but the choke was already closed before I did that.
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Hi:
-From one of the photos, it looks like the Q-jet part number is 17083226. In my reference material I cannot find out exactly which Q-jet this is...the part number is close to the M4M or M4ME carb which was used originally on 1982-83 model trucks. Much different emissions equip than on your 1978 engine. It looks like your air cleaner is original as it has a decal that says emissions equip was CCS. This is "controlled combustion system" which is essentially tuning the carb to a very lean setting to meet the emissions standards at the time, in addition to other things like egr and probably catalysts.
-It looks like your accelerator pump shaft is kinda grungy which indicates that the accelerator pump cup may be on the way south which would either give you some flatness when accelerating or even outright stalling when you hit the accelerator.
-Yes, the air cleaner stud is in the wrong place...thread it out carefully and thread it into the right hole...hopefully nothing is permanently damaged here....now your air cleaner cover should fit properly.
-The air cleaner housing has a snorkel on it which has the hot air vacuum solenoid (door that allows either cold air from the end of the snorkel or hot air from the pass side exh manifold to come in to the carb for cold starting. One vacuum line goes from this solenoid to the temp switch (the little gizmo with "AC" logo) mounted on the bottom of the air cleaner housing. The other vacuum line goes from the temp switch to a source of vacuum which should be at the base of the carb somewhere on the passenger side. This little system is the "thermostatically controlled air cleaner assembly" from the factory to assist in quick warm ups. This hose used to be plugging into your carb somewhere and now the connection is plugged on your carb so the thermo air cleaner system is essentially disconnected and you just get air from the end of the snorkel coming in to the carb at all times. One photo on the passenger side of the carb shows the rear vacuum break assembly but it looks like it is also disconnected...some linkage parts seem to be missing. I think this carb also had a front vacuum break assy that is now missing. I see you have the electric choke and stat assembly on this carb and from the photo I can tell you have the original intake manifold that used to have the thermostatic choke mounted in the manifold (the divorced choke style). I feel a uncomfortable advising you on what to do next with this carb as far as adjustments since it is a much later model than mine (1976 4MV) with some different features. I do think you should call those guys at quadrajetparts.com and verify exactly what model you have and get an illustrated parts picture for it to see what parts are missing...they may or may not be important for it to operate properly.
-In the first photo there is a short rubber hose connected to a metal hose that appears disconnected...is it? this little hose should plug into the carb in the front here somewhere and the other end of the metal hose should have another rubber hose that plugs into the vacuum advance unit of the distributor.
-From your "cold squirt test" your acc pump is probably working just enough to get some fuel into the manifold to start but you still need your primary jets to be working to keep the engine running with the correct fuel/air metering ratio...I dont think these jets are supplying enough fuel and this is probably because the fuel bowl is either dry, gunked up, or too low as I have said before. Your pics of the carb show a lot of fuel seepage on the float bowl assy (the center part of the carb) which indicates that the gaskets are not sealing or the bolts holding the whole thing together are too loose....this could be where the fuel is evaporating when it sits for a week.
-I think it may be time to rebuild/repair this carb or replace it with a carb that came on the engine originally which was probably a 4MV. If you can find a real good old-time mechanic who has experience with multiple models of Q-jets he can probably tune this carb as a basic carb with all the emissions and cold start features disabled...I just dont have enough experience with newer Q-jets such as yours to advise what to do. I am going to be out of town next week but will check in on your situation the following week.
Good Luck!
Henry
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Henry, thanks very much for all that detailed information. I'll check that apparently disconnected hose again. I thought everything looked like it was connected, except for the hose on the cleaner. But maybe I missed something.
I'll definitely check out quadrajetparts.com. Although I doubt I'll be working on the carb myself, the parts diagram will come in handy whenever I have someone else work on it.
I'll soon be taking the truck back to the guy who did the engine swap so he can (hopefully) fix some oil leaks. While he himself admits to not knowing how to tune carbs (young guy), he says he has an older friend that he can call in to tune the carb.
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Got the air cleaner stud back where it belongs. It was a bit of a pain to back it out, as the hole it was in isn't threaded (well, it sorta kinda is now, LOL). Not sure what would possess a person to put the stud where it was. They obviously had to work pretty hard to get it in there. Amazingly, the threads on the stud weren't boogered up.
The end of the stud that was in the carb smelled strongly of gasoline when I pulled it out. I leaned way over the carb and sniffed, and could get a faint whiff of gasoline. I'm wondering if that hole that the stud was in is supposed to be plugged with something.
I checked out the short rubber hose that is connected to a metal tube (in the first photo), and it is indeed hanging loose. The metal tube runs around to the passenger side, where it is held in place by a small clip on the intake. That end of the metal tube is also loose, so the whole thing is disconnected at both ends and is just sitting there doing nothing. Perhaps it used to connect to the original divorced choke?
Despite my earlier assertion that all the open ports were plugged, I did notice that there appears to be an unplugged port on the back of the rear section of the choke. Could this be where the loose hose on the breather is supposed to connect? (Edit: according to a quadrajet service manual I found that has a picture of a M4ME model, the unplugged port is on the rear vacuum break.)
I appreciate everyone's help, especially Henry and Stewart. At this point I'm probably done fiddling with it until I can (1) get a proper parts diagram, and (2) have someone who knows carbs look at it person.
Thanks again, guys.
Update: Based on the ID chart here, http://www.chevyhardcore.com/tech-stories/choose-your-quadrajet-number-identification-guide/, the carb is a 1983 model built for a Chevrolet with an automatic transmission.
Another update: Here's the 1981 quadrajet service manual that I found: http://www.generationhighoutput.com/Quadrajet_Service_1981.pdf. It has the M4M and M4ME models in it.
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We can help; i apologize---i'm very busy and probably can't discuss it in-depth until the weekend, but i don't think there's a need to wait for someone who knows carbs to actually physically appear in order help you (although it probably would be helpful if you do know someone).
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We can help; i apologize---i'm very busy and probably can't discuss it in-depth until the weekend, but i don't think there's a need to wait for someone who knows carbs to actually physically appear in order help you (although it probably would be helpful if you do know someone).
Thanks, Stewart. No need to apologize. I very much appreciate any help you can give, but don't feel like it's your responsibility to do so.
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In the third pic part of your choke linkage is not hooked up. Look behind choke thermostat the linkage going into the pull off is not hooked up also above the linkage is a eyelet with nothing in it.
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I'd didn't see where you mentioned how it runs other than the hard starting after sitting more than a couple days.
The air cleaner stud was int the slot just above the float bowl/float, as long as the float wasn't damaged by the stud you should have no issues now u moved it to the correct location.
The later carbs like this one 1983 can have a front and rear pull off, just a rear pull off, just a front pull off.
There's a linkage missing from the rear pull off to the 2ndary air flaps that has been mentioned. Due to the type of connection at the 2ndary air flaps the rear pull off belongs and probably never had a front pull off due to the vacuum port arrangement.
Buuut no telling with a remanufactured carburetor.
Some even had a rear pull off that had a fast idle pull off feature that worked off of vacuum and water temp, but that's not the case here.
Without that missing linkage I would expect a bog going into the the 2ndaries. The pull off slows the initial opening of the 2ndary airflaps preventing to much air vs fuel and hence a bog.
The choke linkage is probably not adjusted correctly to allow full opening of the choke flap.
Even looks like the link to be too straight just below where the linkage connects with to flap.
Vacuum ports, large port lower front pvc. Distributor appears to be connected to manifold vac but not positive.
Lower passenger side is probably for egr, its ported vac with a bleed off to limit vac.
The larger angled port at the front is a vent for emissions.
The lower drivers side front could be ported or manifold Vacuum used for various applications such as vac advance or emissions.
On the rear upper middle is for the air cleaner.
And there should be another port rear lower passenger side which is manifold vac and used for whatever needs manifold vac.
Remember that carb was for a later engine with more ports for emissions than yours and not needed.
Nothing wrong with that carb and with preferable electric choke.
The later single main air bleed carbs use different calibrations, jets and rods.
They can be easily jacked up by commercial rebuilders as well as any other Qjet.
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I'd didn't see where you mentioned how it runs other than the hard starting after sitting more than a couple days.
It runs reasonably well, other than a few quirks: (1) Idle can be a bit erratic - sometimes it seems a little too fast, sometimes a little rough. The fastest idle tends to occur around the time the thermostat is opening, although sometimes it persists a little longer. Fast idle will not kick off when I tap the pedal. Idle gets slower and rougher when the engine is warmed up fully (i.e., after 5+ miles of driving). (2) Gentle acceleration from a dead stop produces a split-second flat spot before the truck starts moving. Gentle acceleration while the truck is moving does not cause any hesitation.
There's a linkage missing from the rear pull off to the 2ndary air flaps that has been mentioned. Due to the type of connection at the 2ndary air flaps the rear pull off belongs and probably never had a front pull off due to the vacuum port arrangement.
Buuut no telling with a remanufactured carburetor.
Some even had a rear pull off that had a fast idle pull off feature that worked off of vacuum and water temp, but that's not the case here.
Without that missing linkage I would expect a bog going into the the 2ndaries. The pull off slows the initial opening of the 2ndary airflaps preventing to much air vs fuel and hence a bog.
I get a little bit of bog when I punch the pedal, but it picks up pretty quickly (less than a second). I'm not really sure what's normal and what's not, as I am used to fuel injected engines that respond instantaneously. Acceleration seems a bit slow to me even with the secondaries fully engaged, but again, I'm not used to carburetors and am not sure what I should expect.
The choke linkage is probably not adjusted correctly to allow full opening of the choke flap.
Even looks like the link to be too straight just below where the linkage connects with to flap.
The pictures were taken when the engine was cold. I had the breather off later when the engine was warm, and the primary flap appeared to be fully open.
The truck is currently in the shop to fix lingering oil leaks from the engine swap. The mechanic is having his older friend who knows carbs come to the shop today to attempt a tune. Unfortunately I can't be there to observe (I've got a brisket on the smoker and can't leave the house for 14 hours). I'll pay close attention when I get the truck back and see if the rear pull-off linkage and the air cleaner vacuum hose have been re-connected.
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Hi:
If your engine is timed correctly, your distributor is correctly set up, your carburetor tuned properly, you will not notice any difference in performance compared to fuel injection except for cold starting where you have to manually use the gas pedal to do the cold start routine. Acceleration and throttle response in all speed regimes should be instantaneous. The only things modern fuel inj has over carbs is better emissions control, better fuel economy, lower maintenance intervals, and hands-off cold starts.
I have taken a couple of photos of my engine so you can see what some of the things we have been discussing should look like. The photos are too large for this website but if you give me your e-mail I can send them to you:
1. First photo shows what the hole in the carb where you had the air cleaner cover stud threaded in looks like: it should have a flat blade of metal in the center of the hole and I am not sure what it does but it is not a removable part for rebuild...I would be concerned what happened to it...is it jammed down the hole?....or just removed?
2. The second photo shows what the thermostatic air cleaner assy (THERMAC) hose connections are to the carb.
3. The third and fourth photos shows that rubber and metal hose (clipped to the pass side intake manifold) connected to the carb and vac adv assy of the distributor. What kind of distributor do you have?...is it the original HEI unit with vac adv? Gotta have distributor advance for it to run right.
Considering the missing parts on your carb and the installation of the air cleaner cover stud, I would be suspect of what has been done the the inside of the carb for rebuild...this is a delicate instrument with some fine internal assembly and adjustments (float assy) and if these are not done correctly by a pro or a knowledgeable shade tree mechanic you can have driveablility problems like you seem to be having. You definitely need to get the cold start features of your carb fixed or it will annoy you to no end starting the truck...especially in cold weather. My carb has been recently rebuilt and when it sits for 7 days it takes 6-7 seconds of cranking to start. When it sits overnight it takes 2 seconds of cranking. Starting in the same day is instantaneous. Dead cold start with high idle takes about 4-5 minutes and then it can be kicked down to the lowest idle and runs fine in 75F weather. It will run fine cold at high and mid level idle if I want to drive away instantaneously from a cold start...it just is hard clunks shifting into gear because of the high idle. Throttle response when driving when engine is warm or cold is instantaneous with no flat spots or hesitation. The choke opens up completely when the water temp gauge is at 1/4 on cold engine. On semi-cold engine the choke is opened up completely at 1/8 water temp gauge reading. You notice on my photos that the choke plate is fully vertical when the engine is off and cold before a start is attempted. I expect it to all be this way for 2 years of routing driving (5,000 miles/yr) and then the carb will need to be tuned up (filter change, linkage adjustment, float adj and cleaning of float chamber, tightening of attachment bolts).
Regards,
Henry
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Thanks, Henry. I'll send you a PM.
Edit: your inbox is full and won't accept the message. Let me know if you clean it out, or you can try compressing the photos and posting them here.
Here are some instructions for using Paint to compress images: http://www.ctimls.com/Support/KB/How%20To/Reduce_Image_Size.htm
Scroll down to "reduce image file size."
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something else to think about is a bad fuel pump. a bad pump will allow fuel to drain back into the tank. do a search on here for the words "bad fuel pump" by "bd"
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The only thing turned by a search for "bad fuel pump" is your post...
The fuel pump is another part that was advertised as "new" by the previous owner. It is bright and shiny and looks new, as do all the fuel lines. But I guess it could have been just cleaned up really well. And I suppose even a new one could be defective. Is there any way to confirm that short of replacing it?
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did you use the search button in the middle top of the screen?
should bring up window that takes you to this screen
http://forum.73-87chevytrucks.com/smforum/index.php?action=search