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Re: Carburetor junk
pockets #734622 April 03rd 2018 10:55 am
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If the engine is original to the van it should have hydraulic lifters. Those lifters need to not be sticky or you will have problems. The sticking lifter may be causing the fluctuating vacuum reading.

Does your fast idle cam work properly? If the choke is closing then the fast idle screw should be set on the second highest step of the fast idle cam and your cold/fast idle should be around 1200 RPM. What does it idle at once it is warmed up?

I usually start the idle mixture screw at two turns out. Turn it out or in to achieve maximum idle speed then turn it in 1/4 turn. Verify your idle speed is about 700-750 RPM out of gear (with the dist. hose removed and plugged from the dist.).

That being said, in the 80s Chrysler built some carbs with an internal governor on the idle enrichment circuit where the idle mixture screw will not allow the idle mixture to get richer than a predetermined point. I wonder if you got one of those.


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Re: Carburetor junk
pockets #734624 April 03rd 2018 11:06 am
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The idle cam is working as it should. Played with that setting for days before I got that right. Warm up, let it cool, warm up, let it cool. Oh the fun.

Once it warms up it idled at 700 give or take. It's not a perfect steady idle per say but it does have 121000 on it.

Is there a way to tell if the carb has one of those governor's on it?

I hope the sticky lifter is the problem. It's been getting better with the mmo in the oil changes. Changing the oil monthly right now.

Re: Carburetor junk
pockets #734626 April 03rd 2018 11:37 am
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Out for another drive. Started up idled low. Once warmed up it acts as though nothing is wrong. I still don't get what can cause it to idle low cold but idle fine once it's warmed up and driven. Thanks for you assistance on this too. I know you have your own things to deal with.

Re: Carburetor junk
pockets #734642 April 03rd 2018 2:12 pm
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Cold idle quality is controlled by the choke and the fast idle screw. If the engine is cold the choke should be fully applied and the fast idle cam should be under the fast idle screw and the fast idle should be much higher than the curb idle.

Can you turn the cold idle speed screw in to get it to idle higher when it is cold? It sounds like your problem. You don't need to wait for the engine to cool down. You can just put the fast idle speed screw on the second highest step of the cam and set the fast idle speed to about 1200 RPM, even if the engine is warm. In fact, all adjustments, timing, idle mixture, fast and curb idle speeds, etc... should be set with the engine fully warmed up.

Have you verified if your engine has adjustable rocker arms or not? Slant sixes went to hydraulic lifters in 1981, but that was 37 years ago. Who knows if a prior owner swapped in an older slant or switched from hydraulic to solid valvetrain. If you find you DO have adjustable rocker arms, try setting the valve lash to .012 intake and .022 exhaust with the engine idling and HOT.

Try increasing the curb idle to 750 RPM and then play with the curb idle mixture. Once you get those settings nailed so it idles smooth with maximum vacuum at 750 RPM, put the fast idle screw on the second step of the fast idle cam and adjust it so the engine is idling at 1200 RPM.

The only way I know of to tell if the carb has an idle mixture restrictor is to have the list number of the carb and look it up OR open the carb up and inspect the idle circuit very carefully.


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Re: Carburetor junk
pockets #734644 April 03rd 2018 2:50 pm
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It just occured to me that you could have a misadjusted choke vacuum pulloff. When the motor is cold and not running, a single depression of the accelerator pedal should open the throttle and the choke thermostat should shut the choke fully. At the same time, the fast idle cam linkage should pull the fast idle cam up under the fast idle speed screw. As soon as the engine is started, the choke vacuum pulloff should open the choke ROUGHLY 1/4 inch, but the fast idle linkage should be adjusted so the fast idle cam stays under the fast idle sped screw. As the motor warms up the choke thermostat slowly pulls the choke the rest of the way open and the fast idle cam is slowly lowered until the carb controls idle speed with the curb idle speed screw, not the fast idle cam. If the vacuum pulloff is misadjusted, it can open the choke completely as son as the engine is started. This defeats the choke and fast idle functions of the carb.


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Re: Carburetor junk
pockets #734646 April 03rd 2018 3:27 pm
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Ok. I'll play around with the choke more then. It does shut and open 1/4 inch when the engine starts and slowly opens till warm. Maybe I need to set it to open slower. I'll try adjusting it more. My van is an 82 and definitely has hydraulic valvetrain. I had to replace the valve cover gasket so i got a look at that. Ill be taking the valve cover off again to take a look at how the mmo in the oil has been at cleaning some of it up. It wasn't horrible just some build up from 36 years of use. I'll take the numbers off the carb later. Been raining here. Hopefully spring will come soon.

Re: Carburetor junk
pockets #734778 April 06th 2018 12:07 pm
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Ok. Finally got a chance to get the numbers off the carb. Played with the choke a bit more and got it to run better. Still a little idling issue though. Unable to move the idle mixture screw with out it stumbling. These are the number on the side of the carb in their order.

6R 5785 R

4213712

9153 2221

Not sure if you can tell much from them or not. Thanks

Re: Carburetor junk
pockets #734780 April 06th 2018 2:38 pm
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Those aren't the list numbers. The list number would have been on a little stamped aluminium tag that was secured by one of the float bowl screws. It is almost certainly no longer present.

Can you post some pictures of the carb?

If it heps, here is a Chrysler training video about the 1945 carb:

https://www.youtube.com/watch?v=gBti9Y-5g60

It sounds like you know what you are doing and you are doing everyhting right, but it never hurts to double check.

Here is another thought- the problem might not be carburetor related at all. What was the source of the distributor you are using? Have you verified the air gap on the reluctor for the pickup? Are you using a relay to power the HEI module?


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Re: Carburetor junk
pockets #734782 April 06th 2018 5:28 pm
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Ya, No tag. What are those numbers anyways? They were stamped on the side of the carb. I actually did check the air gap and ignition sources before I posted my problem. Even replaced the cap and rotor and checked the plugs. I even replaced the air filter. Had to make a small adjustment to the choke pull off after work but other than that it's running much better now. Now if I could get more adjustment from the idle mix screw I think I'd be set. Picture will be difficult but the top one is the exact carb i have rockauto

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