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78 B210 idle problem


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HI, I just bought a 78 b210 and I'm having a small issue. First off, it's an automatic. I tuned it up (cap, plugs, wires) and put a remanufactured carb on it. Idles perfectly in park, but has issues when put into reverse or drive. If you give it a little gas when putting it in gear it goes in fine, but if you have your foot on the brake and don't give it gas it will stumble and die. Also if you come to a hard stop it stumbles and sometimes dies. Once it's going it pulls nice and runs smooth, it's just when you first put it into gear or when you come to a stop. I'm going to recheck the base timing, but what else should I be looking at. I also want to delete the emission crap. From what I've read, the only thing we really need to keep is the pcv system and the vacuum advance on the distributor. Does that sound right? Any help is greatly appreciated! Don't worry, I'll post pics soon. -Mike

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Be sure the valve lash is set correctly and the timing at factory setting before setting the idle mixture....


Set the idle speed and turn the idle mix screw in till idle quality drops then out untill it stumbles. Select a mid point where it runs smoothest and fastest and adjust the idle down to normal, repeat until you can't improve the idle quality.


If it stumbles only when stepping on the gas while in drive and coming off a stop, the accelerator pump may need replacing. This will not affect idle.


Idle speed may just be too low when in gear and need to be turned up very slightly.


You may have dislodged a vacuum hose, and this will be enough to cause a poor idle with a load in gear.

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Check valve lash too. A tight valve will not allow the valve to close properly and will affect the idle quality.


Over full trans can lift the level to the point that spinning parts will foam the fluid. Foam is compressible and hydraulic pump pressure will be erratic causing it to slip in and out of gear or not shift of go into gear. It shouldn't affect idle.

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Dude you have an air leak somewhere. It might be a cracked hose, but more likely it is one of the vacuum diaphragms. The most common to leak are the distributor diaphragm and the air cleaner flapper door diaphragm.


A small air leak like this can cause the symptoms your have reported. It will run very good with your foot down further on the pedal, but stumble off-idle.


Check it out: Vacuum Leaks







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Definitely could be a hose off or cracked. Won't be the vacuum advance or EGR as there is no vacuum signal at idle. The line to the air cleaner is a good one though and easily dislodged if the air filter is removed.

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Here she is. Will post update this afternoon, hopefully after it's fixed!



Looks good, hope you don't mind, I rehosted it so it would show up inline (your flickr link breaks the reply function)


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Flickr is a great hosting optoin. Just use the URL from flicr that ends in .jpg and the image button here at Ratsun (picture.png).



I re-read your post about five times until I noticed the significance of this:

if you have your foot on the brake and don't give it gas it will stumble and die


Idles good.

Idles good when put in Drive.

Stumbles when you touch the brakes.


That indicate a leak in the power brake booster vacuum circuit. You can test this by removing the booster hose from the intake manifold, then plug the hole in the manifold. If it no longer dies while idling in Drive when you touch the brake pedal, it is confirmed.


I think you have more than one problem. So fixing one won't solve them all. Just be patient and fix them one by one.

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Got a chance to work on her this morning. Brake booster lines were crap. Replaced both then retuned and fixed a couple more small leaks. No more cutting out when put into gear! A little more fine tuning and she should run like a champ! Thanks guys! Glad I joined the forum! I'm sure I'll need more advice in the future and hopefully I'll be able to give some!

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