Dieseling, Engine run on, etc.

[muddermilitia]

Last month, my girlfriend and I bought a 1979 Chevy G10 van. We bought it off a friend who only had it a few months. He was doing some work to it, getting it ready to be road worthy but we ended up buying it off him.

So now I'm getting it ready to be road worthy. It has an issue with dieseling after I shut it off. It doesn't happen everytime. But when it does, it's pretty bad.

The van was originally equipped with a straight 6. Somebody swapped in a SBC at some point. It has a quadrajet carb and HEI distributor.

All I've done so far is some cosmetic things and fixed a fuel line leak & replaced the mechanical fuel pump. Our friend did plugs, cap, rotor, and wires before we bought it. Plus brakes, tires, wheels, and some body work started.

Ive never had a vehicle with this issue so any input on how to solve it is greatly appreciated.

 

[Wes Harden]

So dieseling or run on, is caused by gas and air getting into hot cylinders after the shut down. Normally this can be fixed by adjusting the carb. Start out with cleaning all the linkage on both sides of the carb. Then a little lube on the throttle shaft. Check for binding and sticky. Make sure the throttle return springs are good. If there is a throttle dashpot or a/c electric step up solenoid make sure these are not holding throttle open.
Turn the idle speed screw out to slow the idle down, as low as you can with reasonable smooth engine. Adjust idle air mixture screws for best rpm and or highest vacuum.
Set idle speed screw to spec, check and adjust timing. Reset idle speed.
If you still have run on, the pistons probably have carbon build up. Clean off the carbon with sea foam or similar.
This all assumes no vacuum leaks.
Hope this helps

 

[Blue85]

Yeah, what he said. Look at the throttle shaft holes in the carb body to see if they're worn out, giving inconsistent closed position. Also, the problem will be worse if the engine runs hot, so note the temp when it does happen and of course make sure it's cooling right. Oh and update the thread so this song plays every time it's opened:

 

[diesel4me]

Most all carbed engines back then had an idle stop solenoid,that set the idle speed,and let the throttle butterflies close completely when you turn off the ignition..many of these solenoids are now "missing" or do not work as intended..some can still be had new,but prices are insanely high..(over $100 !)..

As noted,idle speed and fuel mixture settings are critical to prevent "run on" without the solenoid...too lean encourages high cylinder temps that'll ignite any fuel still coming out of the carb..too fast an idle will encourage run-on also...as will carbon build up on valves and pistons..timing is also a factor..retarded timing will raise cylinder temps and make it easier for run-on to happen..
One way to make the engine more likely not to run on is to shut it off when it is still in "drive"...but don't forget to shift it into Park after!...

That's a nice van...I have an '81 G-10 that was a 250 six originally,I put a 307 V8 in it from a '73 Chevelle...probably the "worst" SBC I could have gone for,being the last year of production,lowest HP, and first year with an EGR valve,but it was the only carbed V8 I could get around here in 2000 for a reasonable price..

It has a 2:73 rear axle I put in after the original 3:08 10 bolt one hogged out the diff case,making acceleration even more sluggish--sometimes I think it was better off with the 250 six(which also "ran on" even with an idle solenoid !).......but it can pass vehicles on the highway if I drop it into second gear,it tops out about 77 mph in second!...love the looks of the people I pass when I downshifted it into second at 65 mph.....

My van has been parked since 2003,its getting rough from sitting,but isn't rotted out any worse than when I got it,and patched up the door bottoms and lower panels,rear quarters..not sure if it'll ever see the road again now..my ability to work on things is about over....I miss it,I went to TN,and all over the northeast in it to concerts and camped out in it a lot back in the day..

 

[Bent77]

Running crap gas or too much timing can cause it

 

[muddermilitia]

Yeah, what he said. Look at the throttle shaft holes in the carb body to see if they're worn out, giving inconsistent closed position. Also, the problem will be worse if the engine runs hot, so note the temp when it does happen and of course make sure it's cooling right. Oh and update the thread so this song plays every time it's opened:

Lol, funny you post that. The week we bought the van, we watched a movie from the 70s called "The Van" and this song is the theme song, despite the fact that the main character drives a Dodge van.

Thanks for the tips guys. I'm gonna try and work on it some later this week.

Few more pics. We back dated it a little with these side marker lenses. I bought some very hard to find, tail light trim (a dealer option back then) and I'm working on making this chrome tube grill fit.

 

[Wes Harden]

when you reinsulate use this stuff https://shop.havelockwool.com/produ...WY_oG-9L-soVZXR6P37ZmXgBuLFl_5gQaAglqEALw_wcB

It doesn't hold condensation next to the steel body. If I fix my rust and redo the interior I will use this stuff. I have an old 74 E200 Supervan that was done in the 70's. They used fiber glass to insulate it keeps the van cooler in the summer, but there is alot of rust around the roof.

 

[Blue85]

What's the story on the bodywork and what are the plans? The wheels are nice. What's the plan for a rear bumper?

 

[diesel4me]

Those side marker lights were optional on G vans from 1971-82 or so,they were identical to the ones used on some first gen GM pickups (67-72 ?)..
My van has a '78 grille in it ,the original was broken when I got it--sadly some a$$hole busted the '78 grille while it was parked in my driveway,I think a crackhead scrap theif was going to saw out the radiator core with a cordless sawsall,but got scared off before he could get that far..
Mine is a weird duck,it was built in Dec. 1980,but sold as an '81,but had many '80 parts on it including the manual brake master cylinder,the 81's were way different--good thing I cross referenced the casting number off the original one,because the price for a 1980 new master was $20 at Autozone,while an '81 with manual brakes was completely different looking and only available from a few sources for $80 ..I bet there wasn't many built with manual brakes..

..it also has 2 round headlights (6014's),and no one lists new bezels for a round eye van of that vintage,only single square headlights or duals..
The bezels are plastic crap and are all busted up,have chunks missing and I had to tape them together..searched hi & lo in salvage yards and have never found any round eyes vans like mine..