Author Topic: Riddle me this...  (Read 8927 times)

Offline Monkey Uncle

  • Registered Users
  • *
  • Posts: 128
  • Newbie
Riddle me this...
« on: October 01, 2017, 05:11:05 AM »
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.
« Last Edit: October 01, 2017, 09:25:17 AM by Monkey Uncle »

Offline Henry

  • Frequent Member
  • **
  • Posts: 331
Re: Riddle me this...
« Reply #1 on: October 01, 2017, 12:17:35 PM »
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

Offline Monkey Uncle

  • Registered Users
  • *
  • Posts: 128
  • Newbie
Re: Riddle me this...
« Reply #2 on: October 01, 2017, 04:44:52 PM »
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.

Offline Stewart G Griffin

  • Senior Member
  • ****
  • Posts: 3324
Re: Riddle me this...
« Reply #3 on: October 02, 2017, 09:43:15 AM »
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.

Offline Henry

  • Frequent Member
  • **
  • Posts: 331
Re: Riddle me this...
« Reply #4 on: October 02, 2017, 11:29:48 AM »
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

Offline Stewart G Griffin

  • Senior Member
  • ****
  • Posts: 3324
Re: Riddle me this...
« Reply #5 on: October 02, 2017, 12:45:18 PM »
BTW, on a side note, aren't most carbs on lawnmowers gravity fed?

Offline Augusto

  • New Users
  • Posts: 1
  • Newbie
Re: Riddle me this...
« Reply #6 on: October 02, 2017, 08:31:21 PM »
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


Offline Monkey Uncle

  • Registered Users
  • *
  • Posts: 128
  • Newbie
Re: Riddle me this...
« Reply #7 on: October 03, 2017, 05:39:56 AM »
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.

Offline Monkey Uncle

  • Registered Users
  • *
  • Posts: 128
  • Newbie
Re: Riddle me this...
« Reply #8 on: October 03, 2017, 05:45:45 AM »
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.

Offline Monkey Uncle

  • Registered Users
  • *
  • Posts: 128
  • Newbie
Re: Riddle me this...
« Reply #9 on: October 03, 2017, 05:47:20 AM »
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.

Offline Henry

  • Frequent Member
  • **
  • Posts: 331
Re: Riddle me this...
« Reply #10 on: October 03, 2017, 12:55:17 PM »
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

Offline Monkey Uncle

  • Registered Users
  • *
  • Posts: 128
  • Newbie
Re: Riddle me this...
« Reply #11 on: October 03, 2017, 08:00:19 PM »
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).

Offline Monkey Uncle

  • Registered Users
  • *
  • Posts: 128
  • Newbie
Re: Riddle me this...
« Reply #12 on: October 08, 2017, 02:25:28 PM »
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?

Offline Stewart G Griffin

  • Senior Member
  • ****
  • Posts: 3324
Re: Riddle me this...
« Reply #13 on: October 08, 2017, 03:21:38 PM »
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.

Offline Monkey Uncle

  • Registered Users
  • *
  • Posts: 128
  • Newbie
Re: Riddle me this...
« Reply #14 on: October 08, 2017, 03:33:24 PM »
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.
« Last Edit: October 08, 2017, 03:38:14 PM by Monkey Uncle »