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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: bob77 on September 11, 2008, 10:28:37 am
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Long story short, I need a replacement carb.
My 77 Inline 250 has been getting horrible fuel mileage and in an attempt to rebuild the carb yesterday, I found that the Power Piston Rod Link was mising causeing the Power Piston and Meter Rod assembly to kind of float free and jam itself between the float and the roof of the air horn. I could probably find some pieces and parts and try to rebuild my carb, but I am just going to buy a new/remanufactured one. I'm trying my best to make a good purchase but I would like a little advice.
The number on the mojonet is 17057001. This carb has a holley remaufactured sticker on it, so obviously it had been replaced sometime in the past. Obviuosly there are mulitiple carb 3's available for the 77 250, I was just wondering if someone could give me some advice on choosing one if a suitable 17057001 is not available. I know that some of the numbers seem to correspond with elevation and such. (perhaps depending on where the vehicle was sold new, determined what kind of carb setup.) I am within an hour of the oregon coast, so I barely live a few hundred feet above sea level. I want to purchase the right carb, but I kind of need it soon as this truck is my daily driver.
Any ideas?
Thanks
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I'm kind of shocked. I have called every salvage yard within 20 miles of me and NOBODY has a monojet for a late 70's chevy.
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You can get one from autozone
http://www.autozone.com/N,14900169//shopping/partTypeResultSet.htm
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That's not as bad of a price as NAPA. I'm at the point where it is probably my only option. I have what may be a silly question. Obviously I know that I have a manual transmission. That part I have down. But other options include California/ Non-California. Of course I imagine this is an emissions thing. The california carbs cost significantly less. I certainly do not need a carb rated for higher altitudes either.
I'm sure the California carbs are cheaper because they are far less desireable due to the emissions controls and such.
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You should put the money into a V8 upgrade and not put $ into that 250.
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You should put the money into a V8 upgrade and not put $ into that 250.
Amen. It seems a six works awfully hard to push around 4800 lbs of metal. Whereas a V8 may n ot require such pressure from your right foot.
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Yeah Bob, solve your gas mileage issue by installing a 350 :D!
Don't listen to 'em Bob! The 250 inline is a classic, man! They came in 3/4 tons for years, not exactly an anemic engine. They've got torque out the ying-yang and get good mileage to boot (yours will soon!). Enough room in the engine bay to take a nap or hide from the old lady! Check out Leo Santucci's book "Chevrolet six cylinder power manual", a good read even if you're not planning on modifying your engine.
350's are great, but if you want to save gas and still have a real stump puller stick w/ the 250!
If the truck is your daily driver buy the monojet from Autozone, thats the quickest, easiest solution. It's a little pricey, but less than a car payment and should pay for itself in better gas mileage in no time.
A few other ideas if you feel like doing a project.....you could swap out your itegral head for a non-integral setup & carb from a pre '77 truck. I'd be really surprised if you're not able to do that dirt cheap at a junkyard, it would be a pretty simple job. They should have several to chose from, and you wouldn't have to worry about future trouble w/ the integral head. If you do the head switch you could get an adapter ($15) to run a Holley-Weber progressive 2bbl carb ($65!) from Langdons (http://stoveboltengineco.com/catalog.htm) that should get you better mileage than the monojet. Just a few ideas...
Try posting your question over at Stovebolt.com there are some amazingly knowledgeable inline guys over there...
Jason
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Jason,
I appreciate all the good advice. The new (reman.) monojet from Auto Zone will be in on Tuesday. I have to say that I am quite excited about it. And let me assure you, if the engine blew up tomorrow, I would be out looking for another 250. Nothing against the 350's. They have their place. That place just isn't in my truck. After checking my compression last tuesday and finding that I am between 155 and 170 in all cylinders, I am going to trickle some money into the rest of the motor when I can. I have already been looking for a pre-75 head and intake. My plan is to locate one as inexpensively as possibly and rebuild it in my spare time and with some spare money (anyone have any spare money?). After the carb is installed and tuned well, my next aim will be at some smaller things such as new hoses and probably a new water pump. I think the water pump that is on it now was pressed together too far when it was built because the water pump pulley seems to sit too far back and the belt is misaligned. I am going to try over the next few weeks to locate me an electric fan setup based on your recommendations.
Thanks again as always to everyone.
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http://www.cliffordperformance.net/Merchant2/merchant.mvc?Screen=CTGY&Store_Code=CP&Category_Code=C250
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Bob, just a thought. If your belts are mis-aligned check your harmonic balancer (on crankshaft). When I got my truck the two pieces of the balancer were coming apart and causing my belts to be very crooked. That balancer isn't something you want flying off on the highway!
Jason
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Don't knock th V8 potential with power vs economy. Just a mild TBI V8 will kill the 250 all around which is why I suggested the V8. You can replace the carb with a reman unit but don't expect phenomenal results in fuel efficiency. If you wanna keep the 250 for Nostalgia I totally understand but if you're going to pump a lot of $ into it expecting good results you'll be quite disappointed.
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i don't forsee needing to pump ALOT of money into it at all. The carb at $230 will by far be the single most expensive item I drop onto the engine for quite a while. I'm not expexting miraculous results. I just know that 10 mpg is just not right for a 250. Especially for one that has practicially "Like New" compression. Between the new carb, possibly a new distributor and an electric fan setup, I expect I can see 15 mpg. I am hoping anyway. I am certainly going to be keeping an eye out for a seperate head and intake setup on which I can mount a 2-barrel. This may be 6 months or a year down the road, but it is my plan.
I will double check the harmonic balancer, but I can tell for certain that the water pump is pressed together too far. The pulley actually rubs the water pump itself just slightly. And, the balancer and the alternator line up just fine.
And believe me, I understand that a proper setup on a small block can yield very respectable fuel efficiency results. But that also requires not driving a small block in the manner in which it was intended to be driven. (I wouldn't stay out of the pedal, it just wouldn't seem right).
I have a thing for those 250's. This is the 4th one I've owned. My very first truck when I was 19 was an 84 short box with the 250 and a 3 on the tree. If I hit the lottery tomorrow, I would build myself a huge shop/garage and start a collection of Chevy short boxes with inline 6's. I've already explained this to my wife. She doesn't seem as excited about the idea as I am. I already located hers. Craigs list here in Salem the other day had one listed. A 77 or 78 short box with the 250, power steering, power brakes and air conditioning. Again.... she didn't show much enthusiasm. But, she puts up with me and treats me like a king. So, I suppose I will have to carry the chevy short box excitement for the both of us.
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The pulley actually rubs the water pump itself just slightly.
That may account for a couple of mpg's
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How difficult is it to change the harmonic balancer? I'm going to do the water pump, hoses, and probably the electric fan sometime in the next month and I would like to change out that harmonic balancer. Mine does look like it is kind of coming apart.
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Just use a puller like this.
Click Here (http://www.sears.com/shc/s/p_10153_12605_00947626000P?vName=Automotive&cName=Tools&Equipment&sName=Automotive%20Specialty%20Tools&psid=FROOGLE01&sid=IDx20070921x00003a)
Remove the crank pulley and the bolts. Just don't press against the crankshaft threads. insert a smaller bolt to push off of.
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I'm replacing my carb today. I can't find any specifications on a torque for installing the carb. Any suggestions or just tighten it to what feels right?
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Question:
What would the difference be between a "Fed" carburetor and a "Heavy Duty Cycle Emissions" carburetor. There are monojets with both of these descriptions. The "Fed" carburetor is also described as a High Altitude carburetor on one website. As I am barely above sea level, I didn't opt for this carburetor. But now I am second guessing my choice. I haven't seen my replacement yet. I am to pick it up this afternoon. I will never have to pass any emissions testing, so will the "Heavy Duty Cycle Emissions" carb work? I hope I didn't jump the gun when I made my purchase.
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You want Federal emissions.
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As far as I can tell, the difference is in the vacuum line connections, EGR valve. Essentially, the EGR valve is bypassed on the NON-Federal carburetor. Aside from the obvious excess emissions and pollution, what would be the performance/driveability positives and negatives to the Heavy Duty Cycle Emissions setup?
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Bob,
My '84 GM shop manual suggests torquing each mounting nut to 37 in. lbs., then retorquing to 16 ft. lbs. for the 1ME. That should be in the ball park at least. My guess is that you are right about the 'heavy duty' carb lacking some vacuum lines,etc. I doubt that it is jetted any differenly.
If your crankshaft is not drilled and tapped (some 250's aren't) putting the new balancer on can be a little hairy. I carefully 'press fit' mine because a GM dealer told me to 'just hammer it on with a pipe', but I didn't fell good about it. Better to have it drilled and tapped and use an installer tool.
Jason
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Just picked up the new carb. Surprisingly, the vacuum fittings are about the same. Close enought that if I put a "T" on one, I could hook the thing up exactly as it was before, including the EGR. (I'm going to experiment a bit without it). There is actually even an "Extra" one compared to the current carb. All fittings have tight caps on them. It appears to me that Holley has kind of generalized some of these carbs for multiple applications. Leaving options for different setups. I was a little put off that the bracket that holds the throttle return spring to the carb was tweaked, but the fella at the auto parts store gave me a pair of pliers and let me straighten it before I signed for it. I could swap it for the old one if I felt like it.
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Replaced the carb. Still had to back the idle mixture screw out about 3 turns to get the truck to idle somewhat smooth. It has this odd little rough spot in the idle, but as soon as you get to about 1200 or 1400 rpm's it goes away. I put new plugs, wires, cap, and rotor, and adjusted the timing. I'm wondering if I don't have another issue with the distributor. And I had to stay in the throttle this morning to keep it running until it got warmed up. I need to tinker with the choke.
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I am also going to trace and check all vacuum lines....again. Does anyone know where I might find a complete engine schematic/parts breakdown for the 250. I would like to crawl over it front to back and see if anything is missing or out of place.
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vacuum schematics should be displayed on a label on your radiator support or other place on the truck itself. It should be a silver-like color decal.
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Yeah. I got the vacuum schematics. I'm stumped. I have to have the idle mixture screw almost 4 turns out to make the thing run decently. It seems to me that I MUST be getting air sucked in from somewhere. When I rev the thing, it smooths out and runs well. But I can't make the thing idle at all without having that idle mixture screw pulled way out. And it idles a bit rough at that. I had to pull the idle stop solenoid off of the old carb and install it on the new one as it didn't come with one. Is it possible that I need to drive that thing in further? I couldn't find any decent information on where to set the idle stop when comissioning a new carb.
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Ok. I have one other bit of info that I probably should have shared earlier/ payed closer attention to. When I picked this truck up, the throttle linkage had been replaced. And by replaced, I mean that there is a bent piece of a wire coat hanger or something in place of the throttle linkage. The chances of this linkage being the exact right length I'm sure are slim to none. So, I believe that I need to set the idle and such before even connecting the throttle cable. Maybe the throttle linkage being too short is holding the throttle plate open slightly and allowing more air to the carb at idle, thus causing the need to have the idle mixture screw set out further than what it should have to be.
Once again, I could be completely off base on my assumption.
So... If I were to disconnect the throttle linkage (coat hanger), what would be a good point at which to start with the idle stop? Just barely touching the throttle? Slightly pushing in on the throttle?
I appreciate everyone's help and continued advice.
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What happens if you cup your hand over the carburetor with it running?
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She will stall out.
I do get a pretty good whistle from the carb when it is idling.
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I just happened on some information that could be dead wrong, but I will throw it out here. Almost everything I have read and been told is that the idle mixture screw should never need to be more than 1 1/2 to 2 1/2 turns out. I just read one bit of information (on some website that I found through an AutoZone link I think) that mentioned that 4 full turns out is a good starting point on a monojet. That's right about where it was at it's running best. I gathered that this meant I definitely had some issue so I have been trying to make it run well without having the idle mixture screw out more than 2 - 2 1/2 turns. How far out will that thing actually go?
I apologize for the constant asking of maybe silly questions, but I am just a bit frustrated on why I can seem to get the truck to run smooth. Good compression, good spark, timing set, can't find a vacuum leak (doesn't mean there isn't one), remanufactured carb from Holley, yet it has a rough spot in the idle and It seems I need to have the idle mixture screw out too far to make it run...... Oh the frustration... :-[
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You can set the idle mixture screw all day long but if you have vacuum leaks it will do you no good. Use propane around the intake, in the crankcase, around the carb etc to see if it has any effect.
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You can also spray WD-40 around to try and find a vacuum leak, if propane is not handy. My shop manual says 4 turns out is the starting point for that carb, so if you think you have a vac leak just because you are that far out don't worry.
I'm sure you've got it down by now, but just in case here's what I found on adjusting idle on the 1ME:
You may want to do this with the throttle linkage disconnected, and see if it connecting it when you are done increases rpm and adjust the linkage as necessary....
A: Set "Curb idle" First
1.) Adjust timing with vac. advance hose to distributor plugged (if equipped)
2.) Prepare carb per your emissions label that sgtdel was talking about. It will tell you what hoses to plug and what to leave hooked up.
3.) Engine should be warm, AC off, choke fully open, idle cam follower off steps of cam (see emissions label)
4.) Seat mixture screw and then back off 4 turns.
5.) Buy or borrow a tachometer. With selenoid energized (lead attached), turn the nut at the end of the idle stop selenoid using a hex wrench. Adjust until the rpm listed on the emissions label is reached for curb idle.
6.) Now adjust your idle mixture screw to get the highest rpm at the idle setting you dialed in for the selenoid.
B: Now set "Fast idle"
1.) Place cam follower tang on the high step of the cam.
2.) Support the lever with a pair of pliers and bend the tang to obtain the high idle speed specified on the emissions label.
A Haynes manual (mine is for 67-87 pickups) covers the 250 pretty well. You should be able to pick up a real life GM shop manual for your specific year of truck for around $40-50. I bought mine from Amazon.com, the seller was 'tacbook' I believe. It will have ALL of the wiring, vacuum diagrams, trouble shooting guides, correct procedures, etc. A good investment, and you get a good workout just carrying it around! :)
Hope this helps, good luck! Don't get too frustrated, you're almost there!
Jason
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Jason,
I can't tell you how much I appreciate it. I was chasing my tail it seems trying to get the Monojet to run well at only 2 turns out on the idle mixture screw. Things are making more sense and are certainly running better. More to come........
Bob
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Well, seems like the choke is working well and the carb is doing what it is supposed to be doing. Now to watch the fuel gauge. I am still having that bit of a rough idle. You can notice it more visually looking under the hood. I'm wondering if perhaps a bad motor mount may be part of the problem. The passenger side kind of looks suspect.