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Old 05-23-2020, 12:09 PM   #1
Auroch
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1970 C10 struggling at shut off, dieseling?

So whenever I drive it over a certain amount of time around (15-20 mins) it struggles to shut off, does a few more cycles before finally stopping. Any ideas? The engine is a new 350 + Edelbrock EPS intake manifold + lightly used Edelbrock 1406 Electric choke. Hopefully you guys can help me out. Thanks.
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Old 05-23-2020, 01:41 PM   #2
tim_mc
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Re: 1970 C10 struggling at shut off, dieseling?

Would over-advanced timing contribute to dieseling? Did you also install a new HEI with the engine? If you are using the vacuum advance, try unplugging it and capping the port and see how it runs. I recently installed a new SBC 350 and a new AC Delco HEI. The vacuum canister on the new HEI pulls 20 (crankshaft) degrees of timing - too much - so I replaced it with one that only pulls 14 degrees total (VC204). I also moved from ported vacuum (which was recommended by both GM and Edelbrock) over to manifold vacuum. So far so good.
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Old 05-23-2020, 02:00 PM   #3
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Re: 1970 C10 struggling at shut off, dieseling?

Also, Edelbrock carbs need to be limited to about 4-5psi of fuel. If you're running a new mech fuel pump, I'd bet that it's putting out more pressure than the 1406 can handle, which could be loading up with fuel on drives longer than a few minutes. My 1405 seemed to load up and I had a strong gas smell before I installed a Mr Gasket 9710. I just added this VDO gauge yesterday to make sure I wasn't dealing with any pressure issues while dialing in my new AVS2 1905 650cfm carb.

Another carb related issue might be that your idle is set too high. Sometimes intial timing may be set too low, so the idle has to be turned up so high that it's running on the main circuit. Once hot, it could still be drawing in fuel and igniting for a revolution or two. By running the vac advance on manifold, it raises the idle by a few hundred RPM and allows you to dial back the idle set screw.
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Last edited by tim_mc; 05-23-2020 at 02:24 PM.
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Old 05-23-2020, 06:12 PM   #4
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Re: 1970 C10 struggling at shut off, dieseling?

This is great information, thanks guys! Looks like I have a few things to work on. I appreciate the pics too. Liking that gauge, very smart.
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Old 05-23-2020, 07:29 PM   #5
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Re: 1970 C10 struggling at shut off, dieseling?

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Originally Posted by Auroch View Post
This is great information, thanks guys! Looks like I have a few things to work on. I appreciate the pics too. Liking that gauge, very smart.
And by Guys I mean you, Tim! Haha. Cheers.
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Old 05-24-2020, 09:34 AM   #6
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Re: 1970 C10 struggling at shut off, dieseling?

Thanks! I hope you figure it out! A fuel regulator is a must for these carbs, and probably a good idea for any carb. One more thought was to check for vacuum leaks that might lean it out. Maybe put a vacuum gauge on your carb's manifold port and make sure you have a steady reading at idle and spray suspect areas with WD40 or carb cleaner to see if there are any leaks.

Update: I've been chasing my own carb demons with this new AVS2 1905 for the past few weeks. Today I took some of my own advice to figure out why I had a lean stumble off cruise. It accelerates fine, but would stumble and sometimes backfire when pressing the pedal a bit, but would then run OK after that. I disconnected the vacuum advance and added a few degrees of timing at the distributor (I have 12 degrees intial timing at the crank). I took it for a drive and WOW, what a difference! So, halfway home I hooked the vac advance up to ported and it still runs great...screams from a dead stop to WOT, and responds instantly mid-throtttle. As much as I wanted to keep the vacuum advance on the manifold, it just didn't seem to run right. So, maybe GM and Edelbrock are right and the ported source for the vacuum advance is the way to go.
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Last edited by tim_mc; 05-24-2020 at 02:23 PM.
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Old 05-25-2020, 10:19 AM   #7
Auroch
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Re: 1970 C10 struggling at shut off, dieseling?

Quote:
Originally Posted by tim_mc View Post
Thanks! I hope you figure it out! A fuel regulator is a must for these carbs, and probably a good idea for any carb. One more thought was to check for vacuum leaks that might lean it out. Maybe put a vacuum gauge on your carb's manifold port and make sure you have a steady reading at idle and spray suspect areas with WD40 or carb cleaner to see if there are any leaks.

Update: I've been chasing my own carb demons with this new AVS2 1905 for the past few weeks. Today I took some of my own advice to figure out why I had a lean stumble off cruise. It accelerates fine, but would stumble and sometimes backfire when pressing the pedal a bit, but would then run OK after that. I disconnected the vacuum advance and added a few degrees of timing at the distributor (I have 12 degrees intial timing at the crank). I took it for a drive and WOW, what a difference! So, halfway home I hooked the vac advance up to ported and it still runs great...screams from a dead stop to WOT, and responds instantly mid-throtttle. As much as I wanted to keep the vacuum advance on the manifold, it just didn't seem to run right. So, maybe GM and Edelbrock are right and the ported source for the vacuum advance is the way to go.
Just got the 9710! Definitely a no brainer. Definitely will be looking for timing issues too. Great trick to find vac leaks, going to see if I have time today and try it out. Huge thanks man, I'm not the most seasoned player in this game. I'm at the culmination of "finishing" this restoration, been a 3 year project of youtubing, asking questions on this forum, and lots of arguments with the wife so far
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