carb/engine troubles

[MannyDantyla]

Sorry you guys, I bet these sort of threads get started all the time, but I don't have much experience and I'm hoping that it's something simple. I'll do my best to list all the information needed for a diagnosis.

Engine is 350 from late 70s or early 80s (painted blue, idk) and heads are seemingly off a 305 according to the casting numbers. Carb is an edelbrock 1400 performer. sm365 tranny, not sure if that matters. Edelbrock duel-plane intake, Hedman racing headers.

It's not running very well, not as well as when I first bought it (like a month ago). It's started to diesel when I stop the engine and it's getting worse. Here is all the symptoms:

• Dieseling
• Poor power, especially at low RPMs and idle.
• Seems rich. spark plugs are black as coal. It starts very easily when cold, but when warmed up it doesn't fire to life as well.
• Either the vacuum advance or electric choke is sticking and it causing a high idle. when I'm at a stop light and I give it a quick burst of throttle, the idle goes back down to normal. Then at the next light the idle is too high again, like the choke is engaged.
• When the idle is low (by doing the trick with the throttle), the engine stumbles a little like some of the pistons are missing, it's especially bad when the engine is cold.

Here's what I've done so far:

• installed a fuel regulator to make sure the carb bowl wasn't overflowing. I thought that was the issue but it didn't change anything. fuel pump is brand new also.
• Cleaned the carb with lots of carb cleaner but didn't take it apart. new air filter.
• replaced the spark plugs and wires
• have NOT checked the timing yet, but a friend just told me that he has a timing light I can borrow. Tomorrow will be a good day to do it.
• have NOT checked compression. yet.
• pretty sure all the vacuum lines are good.
• new thermostate
• sprayed under the distributor cap with WD40. That was BEFORE all these problems started happening. (I was making sure no moisture got in it after an engine wash)

So after all of that, the engine is still running poorly. I'm still driving it around every day. I mostly drive very small distances at a time (I work like half a mile away from home, lol) and keep the RPMs down to get better MPG.

Any ideas?

[enaberif]

You said "dieselling" that means there is probably a build of carbon or your timing is out to lunch amongst a few other things.

[Kren420]

My truck seemed to idle high everytime I came to a stop.  Turned out my throttle return spring was wearing out.  I doubt that would fix your other problems though

[MannyDantyla]

You said "dieselling" that means there is probably a build of carbon or your timing is out to lunch amongst a few other things.

Yes I'm starting to believe there are mutliple little things that need to be corrected. Because I have 35" tires and a 3.42 gear ratio, the engine really struggles at low RPMs and that could be when the carbon is building up. I drove to work this morning and did my best to keep the RPMs higher than I normally would and, no dieselling when I turned off the engine. Next I'll drive real low RPM and see if it makes a difference.

Also, the timing... now I know that once the ignition is turned off then there is no spark going to the cylinders then timing of the spark shouldn't matter. But could a poorly timed engine aid in the build up of carbon? What should the timing be?

My truck seemed to idle high everytime I came to a stop.  Turned out my throttle return spring was wearing out.  I doubt that would fix your other problems though

Oh yeah, forgot to mention, installed brand new throttle cable and throttle springs a few weeks ago.

It's also been very cold here and maybe the electronic choke is never happy with the engine temp. Although yesterday I had the water temp up to 210 F and the high idle was still an issue.

[78BIG-TEN]

verify choke is completely open after warm up and choke linkage is not binding\sticking

[MannyDantyla]

verify choke is completely open after warm up and choke linkage is not binding\sticking

If it's sticking, what do you recommend I lube it with? I sprayed it all down with WD40 before this problem started, now I'm wondering if it actually made it worse.

With the air cleaner off, the choke plate moves without too much force but it's not real smooth either. I'll try to get a picture of what it looks like before I start the engine to drive home today.

[FlatBlack77]

i had a handful of those problems with my 79 K10. took me 10 months to track down those problems aswell as a few others.

the timing has to be set correctly. it will diesel if its too far out of whack. it has to be set with the vacuum advance unhooked and capped off. youll have to play with the timing to see what the engine likes best. id start at eight degrees advance and play around from there.

BUT you may not be able to ever get it running and timed correctly if the distributor is shot or the timing chain is stretched. i had both of those problems. i could get good timing readings at idle but other than that it was all over the place and nothing i could do helped it run well. the mechanical advance on my distributor was shot it wouldnt spring back and the timing chain was stretched so far i could rotate the engine from noon to 4oclock before the rotor moved.

and the deal with the choke was the final fix for my truck. i just unplugged it. runs like a champ now along with all the other fixes. im not saying it will solve your problem but its a quick easy thing to try

[MannyDantyla]

I've solved the problem!

The electric choke wasn't getting 12 volts! I don't know what was wrong but it was getting 1 volt at most. I replaced the whole wire and plugged it into a keyed 12-volt source in the fuse box. Viola! I've fixed the truck!! Earlier the choke was ALWAYS engaged and was literally choking the engine. When trying to drive, the only thing I could do was flog it with more throttle which caused the spark plugs to fawl and carbon to build up. Also, the engine is much more likely to diesel a little bit when it's idling at 2k rpm when the engine is shut off.

I'VE MENDED SOMETHING!! I'VE MENDED IT!

https://www.youtube.com/watch?v=s2a1z4iFc9o
[youtube]https://www.youtube.com/watch?v=s2a1z4iFc9o[/youtube]
[youtube]s2a1z4iFc9o[/youtube]

edit: well that ^^^ just isn't working at all...

[78BIG-TEN]

What year is your truck?Does it have a choke light?Wiring to a switched ignition is ok as long as you don't leave the key in the on position without the engine running.This will burn out the choke coil.

[rich weyand]

What year is your truck?Does it have a choke light?Wiring to a switched ignition is ok as long as you don't leave the key in the on position without the engine running.This will burn out the choke coil.

Why would that burn out the choke coil?  The choke coil is normally on whenever you are driving, which can be 10-12 hours a day.

[MannyDantyla]

edelbrock user manual just says to use a keyed 12-volt source. Keyed meaning 12 volts with the key in the on position.

[timthescarrd]

The only issue with using Keyed 12v for electric choke, is if you turn the key to ON without starting the engine, and it hasn't been ran to full operating temp yet, it will open the choke and cause hard cold starts.

[rich weyand]

The only issue with using Keyed 12v for electric choke, is if you turn the key to ON without starting the engine, and it hasn't been ran to full operating temp yet, it will open the choke and cause hard cold starts.

Yup, that's true.  The advantage is that if you park the vehicle in cold weather long enough for the choke to cool down, but not for the engine to cool down, you can turn the choke on for a few minutes to match it to the engine and not flood the darned thing.

[MannyDantyla]

ugh,

how hard is it to switch to manual choke? lol

[roundhouse]

The electric ones work fine usually

Only issue is like mentioned
If its cold and you switch the ign on but don't start the car the choke will heat up and pull off but that's the only issue


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