Author Topic: What do you think MIGHT be causing this problem?  (Read 108 times)

Offline fussfeld

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What do you think MIGHT be causing this problem?
« on: December 06, 2018, 07:07:31 PM »
If i get stuck in a LONG traffic jam, say more than 15 mins long.  And it doesn't have to be hot outside, although most every time this has happened, it was at least warm outside.

After we finally get moving, after about 5-10 feet, it stalls out.  You can start it up immediately, but it might move another 5-10 and stall out again.  Repeat, rev it up to 2000-3000rpm(so that the engine will continue to run).  It might do the same a few more times, but eventually it will smooth out and run normally.   With traffic behind me, this can get quite nerve-wracking.

NOTE: this only happens after long traffic jams.  NOT at redlights or stopsigns.    I feel as though i could idle indefinitely, only when we start to move will the engine stall out.

i have a hunch what the problem is, but i want to hear some opinions first

BACKGROUND:

1) Jeg's/Summit reman quadrajet carb, model#15805.  i don't have the carb # offhand at the moment, but i believe these are an 84 1/2 ton truck core.  i have a hunch these are remanned by JET?   It seems to otherwise run ok and pretty smooth (by my standards at least) with the exception of the above problem.

2) The airhorn gasket always seemed to be saturated.  And it appears that fuel is/was coming out of the accelerator pump pushrod hole based on stains/dirt accumulation and saturation in that area.

3) Recent Goodwrench reman LB4  4.3 v-6  everything stock.   Stock iron 4bbl manifold.  YES, some 4.3's came with these on trucks in 85 and 86.

4) Facet DuraLift electric pump advertised as 4.25 to 6.25 lbs.  The reason why i'm running an electric is that the 87 and newer blocks don't have the pushrod hole drilled to take a mechanical pump.

5) i checked float level and it was spot on for that carb# at 13/32"  (Although v-6 might need something else?)

a) i did notice that the needle hook thing was hooked thru one of the holes on the float arm and i heard it shouldn't be like that.   i corrected it.  But could this alone cause possible flooding?

6) Fuel pressure, assuming the gauge is right, was from a little over 3lbs. (generally at idle) to no more than 5.75 lbs.   It generally seemed to go to 5.75 when i let off the throttle not necessarily all the time, but if it did go to the higher side it generally seemed to do so when i let off the throttle.   

7) i do not YET have a regulator with return installed, but plan to soon irregardless.

This setup has run pretty good (in my novice opinion) for the past 2 years with no problems except for the above problem.

« Last Edit: December 06, 2018, 07:14:25 PM by fussfeld »

Offline Cliff Ruggles

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Re: What do you think MIGHT be causing this problem?
« Reply #1 on: December 07, 2018, 03:19:56 AM »
Not a big fan of those carburetors as we have had enough sent here over the years to avoid them completely. 

There could be many issues from heat soak to a very slight leak at the bottom plugs to a small leak at the inlet needle or under the seat at the gasket.

Very slow leaks will cause EXACLTY what you are seeing as the fuel bowl fills up at idle only.  If the leak is a tiny one at the needle or under the seat the fuel bowl fills up so slowly it may actually take several minutes before you see a flooding condition.  The carburetor will typically work OK in all other scenarios when the fuel demand far exceeds the small leak and the fuel level never gets high enough to cause any major issues.

In any case the first thing I'd do is replace the float, needle/seat assembly and the accl pump.  Our SR kit will contain all the correct parts to upgrade those components.  Pay very close attention to the gasket area under the fuel inlet seat and gently remove any material from it and look for damaged areas where it could be leaking even with the gasket tightly compressed.

If you see any potential problem areas install the seat, needle, and fill the bowl with a soap/water solution.  Gently holding down the needle blow some compressed air into the inlet and look for a stream of bubbles.  If it passes that test good to go and look elsewhere for the issues.

While the top is off spend some time with the power piston and make sure the arms are level and EXACTLY even.  Make sure the carburetor has the correct metering rods in it as well, the later SMAB units used "M" series rods.

I've never to date seen one of those that didn't have bend PP hanger arms and many will not have the correct metering rods in them either as they are pretty much a mass produced "generic" unit.  You'll probably find the bypass air holes plugged with lead as well, and often a very generous idle calibration as they are not set up for any specific application and you'll get far fewer complaints/returns being too rich vs being too lean........Cliff

Offline fussfeld

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Re: What do you think MIGHT be causing this problem?
« Reply #2 on: December 07, 2018, 08:59:17 PM »
Thanks so much.  Will order a kit on monday or whenever you are open next.

Beginning to agree with you concerning: Jeg's/Summit remans:  i guess when i first got mine, i was so happy about the way it ran, compared the wornout/used up q-jets sitting on my shelf, that i thought they(the jegs/summit units) were actually pretty good.   But the more and more i work with this carb i see some quality control issues:  Like bent/binding linkages, choke pulloff wrong(?), wrong torque settings etc. that i'm beginning to realize that even these remans probably fall into the "crap" reman category as well.....

i did not realize your turnaround time for rebuilds was only 12 weeks (thought i read somewhere it was much longer?)   In that case, i would more seriously want to locate a correct core for this engine and have you guys rebuild it pretty soon.  Whereas before i was kinda on the fence.

Offline Cliff Ruggles

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Re: What do you think MIGHT be causing this problem?
« Reply #3 on: December 08, 2018, 05:05:31 AM »
Believe me it gives me no pleasure to bad mouth the efforts of others as it appears I'm bashing the competition to steer work in my direction.

Actually I don't want for work these days and could easily work for at least a year without picking up the phone. 

With that said we've taken a stance here to avoid anything commercially "remanufactured" and many "rebuilt" units from other sources.  I've found that it is much easier to start out with a virgin unit that to go back thru something that's "hacked" up.  I've found those carburetors little if any better than something you'd get at Pep Boys or Auto Zone. 

No time and no need to go into great detail, but I've NEVER worked on anything commercially remanufactured in decades that was worth two squirts of duck poop, and it's actually getting worse as the carburetor era comes to an end here. 

Companies currently as pushing electronic carburetors (they call them "fuel injection" but they are TB's and wet-flow) so hard these days folks are jumping onto that band wagon thinking there is something far superior than a carburetor waiting for them in the end.

I've dabbled with that sort of thing enough to know that IF you know how to set up a carburetor, the difference when you are done between than and a TB system is having to "pat" the gas once on a cold start to set the choke.  Carburetors are and always have been an excellent way to go with these older vehicles.  Cripe the manufacturers couldn't even get TB set-ups to work all that well and by 1995 most were gone just like the carburetors they replaced in favor of much better multi-port systems with a dry intake manifold........Cliff

Offline fussfeld

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Re: What do you think MIGHT be causing this problem?
« Reply #4 on: December 14, 2018, 02:57:56 PM »
i didn't get the impression that you were bashing anyone;  You're just telling the truth  :)


My carbed cars (even with remans) actually start faster than my TBI equipped car.  Usually within 1 engine revolution,  whereas the tbi will have to crank for a few seconds.    i think this may be due to the TBI system having to "see" what the crankshaft position is in relation to the engine before it fires the injectors (????  not clear on this)
In all fairness, it (tbi), seems to run ok when warmed up.

Will order a rebuild kit for now (Was unable to on Monday because back went out temporarily).   And then get a good core.   i've already located two.  Just need to go to wrecking yard to pick up.

Offline Cliff Ruggles

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Re: What do you think MIGHT be causing this problem?
« Reply #5 on: December 15, 2018, 03:40:34 AM »
Not a big fan of TBI style fuel delivery systems.  GM must not have been either because they weren't around that long and they ended up going to MPFI......Cliff