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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: 87K104X4 on February 24, 2007, 06:09:00 pm

Title: Engine diesels after carb swap
Post by: 87K104X4 on February 24, 2007, 06:09:00 pm

I replaced the Q-jet on my truck last weekend with an edelbrock 600 and now when I shut the truck off it diesels (keeps wanting to run). It never did this before the swap and I even replaced the plugs and wires but no help. Anyone know what to look for? I have tried to adjust the timing and this didn't help. Any help would be great. Thanks

Title: Re: Engine diesels after carb swap
Post by: Lt.Del on February 24, 2007, 07:12:00 pm

A lot of times the cause for dieseling is too low of octane used.   A lot of performance engines require more octane.  If you put 92 octane in it, i bet your dieseling goes away.

However, you state it didn't occur with the old carb.  My guess is air is getting through somewhere.  A vacuum leak, carb gasket leak--something like that is the culprit.

For a quick rememdy, turn ignition off when you are still in gear.  It will stop immediately. Then with key half way off (auto trans) put it in park then take key out.  

Grab some WD40 and spray around vacuum lines and gaskets with engine idling.  Just be careful with the stuff, it is flammable.  If rpms go up, you found a leak.

Also, double check your timing and set idle rpms to where they should be--around 750.  

SgtDel
aka "Andy"

www.delbridge.net

1979 Big 10 383 stroker
1991 Blu 'Burb 3/4 ton 4x4

Edited by: SgtDel  at: 2/24/07 7:14 pm

Title: Re: Engine diesels after carb swap
Post by: 75 C20 on February 24, 2007, 08:48:00 pm

my 75 use to diesel a bit after i put my edelbrock carb on it- i set my idle to a lower rpm and that stoped it- it now idles at about 600-650 and she hasnt dieseled since

Title: Re: Engine diesels after carb swap
Post by: 87K104X4 on February 25, 2007, 04:57:00 pm

I tried the wd-40 trick but cannot find a vacuum leak anywhere. One strange thing about the timing was when I hooked the light to it I could not get the mark on the balancer to show up on the tab unless I dialed around 30-35 degrees on my light. The vacuum advance was unhooked so I don't know what would cause that. Got any ideas?

Title: Re: Engine diesels after carb swap
Post by: roundedline on March 01, 2007, 04:41:00 pm

Put the number 1 piston on TDC and check your mark.  If it is off you outer ring has slipped.  You can remark it with some white out and recheck the timing.  

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

Title: thanks
Post by: 87K104X4 on March 01, 2007, 05:22:00 pm

Thanks for the info. As soon as the weather comes around I will try that.

Title: Re: thanks
Post by: VileZambonie on March 01, 2007, 06:49:00 pm

What is your engine idling at? ______RPM

Title: no tach
Post by: 87K104X4 on March 03, 2007, 08:52:00 am

I don't have a tach so I don't know for sure. I am just setting it by ear.