85 d100 won't idle after warmup

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dodgebry

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1985
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225
I have a 85 d100 6 cylinder w carburetor; bought it about two years ago. It had sat idle for several years. Changed oil; spark plugs and wires, new entire front brake system, new clutch, new fuel pump and she was ready to roll. After a few months it started to stall when idleing. Sporatically at first, then all the time. Replaced clogged fuel filter didn't help. It cranks and idles fine at first but after 5-7 minutes it starts to slowly die down and eventually it dies now matter how hard I pump the gas. If I let it set for about 30 minutes it cranks again and goes through the same cycle. Any ideas?
 

crazzywolfie

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do you know if it has the lean burn system with the computer on the air filter or in the fender behind the battery?
 

michael.frushour

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wow this is scary

i have the exact same truck with the exact same problems. my truck was also sitting for several years and with the exeption of changing the carb i replaced all the same stuff. imagin my surprize when i saw your thread. please dodgebry contact me let me know what you found to be the trouble. i cant afford to throw parts at it till i figure it out thanks
 

b7labelle

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318
Hi all,

I have a 87 W150 318/727 2bbl with a very similar, if not identical problem. It starts and idles fine on high idle, but after it warms up and I put a small load on the engine (going into D or R) the engine struggles and the idle begins to drop. If I let it continue without applying throttle, it will eventually stall.

I checked the choke operating this morning...appears to be working correctly (ie closed when cold, opens as engine temp increases).

If i remove the load and let the engine idle in N, the engine resumes normal idle behavior.

When engine load is higher, say when driving, the engine behaves normally. In stop and go traffic, it is a nightmare and I have had it stall on the road several times.

This truck did also sit for 2 years. I replaced the battery and all was well for about a month then one day it started displaying this behavior. I did also try cleaning the carb up by spraying some carb cleaner in the carb around all the jets and other little holes I could see.

Any thoughts/suggestions?
 

NYCruiser

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Sounds like the idle circuit in the carb is acting up. Have you tried running sea foam in the fuel for a bit and seeing if it clears it? Short of that, get the carb rebuilt. Or get a kit and do it yourself. Spraying carb cleaner around the jets isn't going to help.
 

b7labelle

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Hi NYCruiser,
Thanks for the suggestion. Another note that I wanted to add is that it does not act up immediately on low idle...I took it down the drive after it warmed up and let it idle in drive without any issues. Went back down the drive and back again, and when I stopped the idle issue returned. This is what makes me unsure about having clogged idle jets.

ALSO....when I first fired up the truck to check the timing, I couldn't even see the timing notch on the crank pulley. When I kicked it off high idle, the timing notch suddenly appeared at about 2* BTDC. I adjusted this back to about 7-8* BDTC.

This behavior confuses me...when is the timing moving like that? That does not sound normal, unless there is some sort of vacuum advance system that is supposed to do that. When I restarted the truck later, the timing notch was still at about the 7-8* BTDC. I took it for the above mentioned spin down the drive and all went well until I returned. When I came to a stop the issue resumed...I tried to re-hook up the timing light I purchased from Harbor Freight, and go figure, the tool no longer worked (Or i have a bigger issue on my hands). Good thing I kept my receipt.

So I think tomorrow I will return the timing light and pick up a nicer one else where, and replace the plugs/wires, as they are going on 3 years old.


I can also try some SeaFoam...can always hope its the simplest solution that works..
 

crazzywolfie

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did you unplug the vacuum advance when setting the initial timing? it sounds like you left the vacuum advance hooked up while checking the timing.
 

NYCruiser

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Yeah, should have vacuum advance. Need to disconnect the vacuum line and plug it up with a screw or something when you set the timing. There should be an idle mixture adjustment on the carb too. Could be set too rich so the warmer air after warmup upsets the idle. Sounds like you're on the right track.
 

b7labelle

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did you unplug the vacuum advance when setting the initial timing? it sounds like you left the vacuum advance hooked up while checking the timing.

Nope, looks like i'll be out there today rechecking that.

Question...I can't locate that idle adjustment screw. Do you guys know where it is located? Someone told me it might be INSIDE the casting and that I might have to cut part of it off...no way in hell i'm doing that even if it is where it is located lol

-B7
 
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