When the truck stops, the carb stops.

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I'm having a low idle problem, I think the loose linkage is part of the problem. I can get the idle down low enough but then when I stomp on it and let off... it dies. I set the idle up high and had been driving it around, a great deal of the time it dies when I come to a quick stop.

heres what I've done:
fuel tank cooked and epoxy coated, new fuel lines, all oldies cleaned out or replaced. fuel pump seems adquite.
Carb rebuilt, pulls 19-20 in of merc. at 800-1000 rpm. float sits just above level I think.

I first thought vacuum leak, can't seem to find one though. maybe my carb job wasn't good enough. I was pretty thorough and cleaned and replaced everything except that one ball bearing that is down that deep hole with a clippy on top. It seemed to run fine this past winter started up and idled well. then I fixed the vacuum leaks and know it wont run right. doesn't make sense. help
 

fjwagon

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Does your rig still have an EGR valve? This could be sticking in the "open" postion. This circuit is only used on the higher rpm band and once it starts idling it should close. Tap on it and see if you can get it to close. Also Check if your linkage is loose or has missing bushings. You can tell if it is loose or if you tap on the gas pedal and you a different response on your idle.
 
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desmogged, choke breaker is not hooked up, vacuum advanceois on the ported side? the side closest to the valve cover. Would the breaker be causing this problem? I wasn't sure how to hook it up and if I even needed it. I'm thinking of sending this thing to Jim C and having having him take a look at it. I'm goona try and fin some more vaccum related prob
 

fjwagon

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I'm not familiar with desmoged carbs. Have you tried looking in the tech section? Sor.com has some good carb diagrams if you think you have a missing bushing. What year is your carb? I fixed a carb that would turn off like you are mentioning but he an intermettent problems with it idling. Sometimes it would be too high and sometimes it would be too low. Stomping on the gas pedal would sometimes fix it. Long story short, he ended up having two problems. The EGR insulator was flipped there for installed wrong(PO). In the flipped position it was blocking the EGR idle circuit and he also had a missing bushing. Good Luck>
 

gladly

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you've got a '75 right?
choke breaker to manifold vacuum, power valve to manifold vacuum
my linkage is cobbled together pretty bad, but it shouldn't effect the idle. if it does, then the idle is being set by the little screw gizmo on the choke breaker linkage, which is pulled out of the way when you hook up the choke breaker to vacuum.
 

gladly

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https://forum.ih8mud.com/showthread.php?t=101664

...
I set the idle speed and cannot figure out if I need a choke breaker or not. No emmissions what so ever, . This is a Non-usa spec. carb do I need the choke breaker? I installed a brand new choke cable from Toyota, worth every penny.
I seem to recall Jim C saying in your previous thread that the choke breaker is one of 'the good things' but that it is maybe on some models part of the ?TPS? or some thing which is one of 'the bad things'... I might be on gas, I'll go see if I can find what was said. ( this is something that I am wondering about too obviously)
btw, mine is a 75 canadian spec

aha!:
CB is good and necessary.
TP is an extra bit of linkage on the CB diaphragm on some years.

Keep the CB, ditch the TP linkage. That way, when throttle is lifted, the engine will slow the truck down.


(from here: https://forum.ih8mud.com/showthread.php?t=80445&page=2 )
which was a link from here:
https://forum.ih8mud.com/showthread.php?t=101247

(I hate it when I can only 'think' I remember something, esp. when paraphrasing the gurus )

and from https://forum.ih8mud.com/showthread.php?t=101247

Does anyone know where the non USA carbs connect the choke breaker hose and Vac advance?

The choke breaker needs full manifold vacuum, so anywhere at or below the throttle plates.

Ed
 
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I'm not familiar with desmoged carbs. Have you tried looking in the tech section? Sor.com has some good carb diagrams if you think you have a missing bushing. What year is your carb? I fixed a carb that would turn off like you are mentioning but he an intermettent problems with it idling. Sometimes it would be too high and sometimes it would be too low. Stomping on the gas pedal would sometimes fix it. Long story short, he ended up having two problems. The EGR insulator was flipped there for installed wrong(PO). In the flipped position it was blocking the EGR idle circuit and he also had a missing bushing. Good Luck>

Wow you might be onto something... I removed the old egr plate and swapped in another plate with no egr provision. Maybe that circut your speaking of could be the problem? I believe it to be mostly a 78 carb.
 

gladly

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don't mean to harp on it...

did you connect the choke breaker to manifold vacuum??/

it may not solve all your problems, but that is one thing in your setup that is definately wrong, and may help you to get to the next step of diagnosis...

BTW, is it up and road legal now? if so :beer: your rig looks to be second only to coolermans for PITA factor, good to see man out-think metal again :D
 
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don't mean to harp on it...

did you connect the choke breaker to manifold vacuum??/

it may not solve all your problems, but that is one thing in your setup that is definately wrong, and may help you to get to the next step of diagnosis...

BTW, is it up and road legal now? if so :beer: your rig looks to be second only to coolermans for PITA factor, good to see man out-think metal again :D

Yeah the ol' bitch is running about, I'm cleaning out my garage this weekend and saying good bye to an old friend, my first car... 73 VW beetle. Off to the scraper to make room for the 4 motorcycles I've got strewn around. I need more room in the shop. it's too hard to work with al the clutter in the way.

The choke break to manifold vac huh ? I'll do that this weekend for sure. I've been promising folks a full set of pics on this ride and need to get them up. its such a pain going through and changing the pic size and stuff.

I've got a new tre set from pector off-the wall and a budbuilt relay rod to go with the tie rod. that's next weekend with the knuckle job, I've be sure to snap some pics along the way. thanks for the help on the carb bit
 
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Choke breaker hooked up and carb retuned with idle and mix... seemed ok but then I put it all together and drove it, running well idle fine, hit the brakes hard or even moderately... It dies. WTF!!??
this is a 78' carb with a 79 carb plate between the base and top helf in order to eleminate the egr stuff. Any ideas? It's going to Jim C if I can't resolve this.
 
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Thanks Jim, for the input is there a way to test that booster? I'm worried about trying to find another booster now.
 
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Disconnect the booster and plug the hose. Drive it around and see if problem persists. But be advised you won't have power brakes anymore.
 
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Update: the idle jet in the primary was the cuplret, it runs like a freakin' top. I just need to figure out the heating at high rpm issue (down the highway). Thanks for all the help Ken
 

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