The Stovebolt Site Forums The Shop Area Engine Shop my GMC 305 is overheating

So ok I finally got the truck running after putting in a new timing chain and rebuilt carb. and now its running hot and it desils and a couple times pops through carb also it dose not want to come up to speed very fast when you press on the accelerator (runs more like a desil engine) heres what I have done and possibly someone can tell me what to do next? or is there an order to timing?

timing chain, checked marks and is proper
timed to book at 7 1/2 BTDC
dwell at 31* to 34*
carb set to just run without black smoke from tailpipe (ww stromburg)set mixture screws are at 1 1/4 turns out and choke is set at about 1/2" open when pushed in

Any help greatly appriciated

Hy todjob2000, the timing sounds correct, you set your dwell first then set your timing, [dwell effects timing, but timing doesn't effect dwell]. The firing order is 165432. The choke plate should be fully open when the choke is off [knob pushed in]. You could check your thermostat to make sure it is working properly. You haven't told us how it was running before you did this work?

I'm not exactly sure on how it was running before hand, I limped it home with a worn out timing chain so it was a bugger to get it going to do anything, as soon as you would touch the accelerator it would try to die,I thought it was the carb. so I had that rebuilt, put it on and then it would not start, so then the timing chain was changed, I did put in a new thurmostat on today but it is still running hot and there was still pressure on the top hose, I will re-time it to see what that dose.

Hy todjob2000, when you get it running again, put a vacuum gauge on it, the choke, the poor running, and the overheating are all signs of a lean condition, you may have a large vacuum leak.

Ok I will do that too (This is where I get stupid) where do I attach the vacuum gauge and what am I looking for, after I rent a vacuum gauge that is.

Hy todjob2000, if you have any vacuum accessories, power brakes, vacuum wipers, then tap into those ports/hoses, or remove them and install the vacuum gauge in their place. you should be able to get a reading of around 18", hope that helps.

You said you set the timing to the proper sepc but it sounds to me like it is retarded.With the engine running have the dist clamp bolt just loose enough enough to turn it to the place where it runs best for now as a test to see if you are working on the right area.Please be aware you can have the index marks on the harmonic balancer not where they should be.It is not uncommon for an old balancer (or not so old) to have the outer rim with its marks, slipped from the proper relation to the hub which is keyed to the crank.
See if timing by ear will help it and then we can tell you where to go from there.
We can reestablish the proper relationship for the marks and we can verify the cam timing without a teardown.

Ok I will try that as well, according to a tach what would be a good rpm for this motor? Thank you every one for your help.

I don't know what you mean by "what would be a good rpm for this motor".If you mean a good rpm for setting, just move the dist slowly opposite direction of rotation to advance until the engine seems to be running easier--it will get faster idle in the process so you may have to slow it down and continue.When it has been advanced until it is starting to get rough you have gone too far--but we are trying to prove that your "timing to book at 7 1/2 BTC" is not correct, there could be several reasons for error, but tell us how it reacts to advancing the spark timing until it sounds "happy" and we cn go from there.
Just one step at a time please.

Ok I will get to it tomorrow or the next day ( my days off ) and I will reply then. Thank you.

Ok, I set the choke correctly now and made sure the carb was tight to the intake manifold just to check.

I made sure the points were still at about 32* then I fiddled with the distributor until it was not popping through the carburator or backfiring when I throttled it and seems to be running smoother, however it is still desiling when you shut it off.

Also;
I looked for a vaccum point to attach to and the only one I see is from the vaccum advance to the back of the carburator by a metal hose, will that work if it is unattached to get a proper vaccum test?

Hy todjob2000, yes that location should be fine for hooking up your vacuum gauge line, tee it in place so your distributor still receives its vacuum signal. If your truck is "dieselling" when you shut it off, I would say your throttle is open too far at idle, hope that helps.

ok I can adjust back the throttle then on the carburator and I will check the vaccum then.

Ok, today I started it from cold and it's right back to hesitating and wanting to stall and popping slightly when I take the choke off, I'm waiting on a vaccum gauge to put on it tomorrow, anything I should look into in the meantime?

Hy todjob2000, I just reread all of these posts, and in one you talk about the rad hose being hard. When you run it tomorrow or whenever, take the rad cap off and watch for bubbles in the coolant while it is running, you might have a leaking head gasket. You have verified the timing order is correct?

Getting confusing feedback here.
1) Were you able to make it run acceptably by adjusting the timing to the best running position?
2) Under what conditions does this "popping" occour?
3) are you taking the choke off before the engine has run for a little while or are you modulating it until warm?
4) How does it idle when backed down to say 550-750?
5) When warmed up and running best does it pull ok without missing and bucking at lower speed?
6) Are you able to drive the vehicle or is your testing limited to shop running only?
I reread and see you said "I made sure the points were still at about 32*"
I hope this means 32 degrees and not 32 thousanths/inch.
My old plug chart says gap the plugs @ .030---not many plugs are gapped out of the box @ .030 these days we must always adjust before install.
Just another thought if your parts supplier has convinced you to install the Bosch platinum plugs consider throwing them away but at least try a used set of "took out champion or AC".
I have cured several problems caused by these Bosch when the tiny center platinum electrode material came loose to drift in and out of the insulator varing the gap at random and sometimes going away altogether.But then some of them must be quite alright, after all we know they wouldn't keep on making a flawed product.But really how many users notice 1 erratic plug acting up out of 6 or 8? By gosh WE DO since we are intimate with our machines, not cooped up in that sound proof, climate controlled compartment using mufflers and other creature comforts.But if the owner should happen to notice the intermittant miss the next tune up will probably dismiss it.
Bottom line watch those Bosch plugs.I don't want none.
Hang in there you've already found all these things that are NOT the answer.

Ok, for 3B, I did check for bubbles and found noting in that area of problems. I also checked to see if the distributor was in the correct position and the plugs for timing order and that as well is correct.

and for engine nut;
1) yes I did get it to run smoothly.
2) it will pop when I drop down the choke after it warms up, as long as I do not touch the accelerator it runs fine,other wise it wants to hesitate and or pop, it always hesitates but only pops 1/2 the time I accelerate.
3) I take the choke off about 3 to 5 minuets into the engine run or when it starts running really fast.
4) it idles perfect as long as I do not try to accelerate
5) I have not drivin it yet as far as around the block to get it into second gear or 3rd only in first gear in my yard, it seems to do ok actually driving it as far as not stalling but the hesitatin and popping is still there.

Yes points are at 32 degrees my plugs are AC delco but I have not pulled them to re-gap or see if fouled sisnce I bought it, I did check them when I got it and only have say 4 hours on run time since I got it, however I will pull them to check again for oil foul or? I am getting the vaccum gauge today so I will see where that goes as well.

To all that have and are replying again I want to say thank you for your help.

But I didn't re read very throughly or I would have seen the concern about the point setting answered.
If the popping mentioned is occuring on acceleration when not fully warmed up, it can be caused by our modern gasoline that has been stored long enough for the lighter materials to evaporate.If the fuel smells strong and much like paint thinner please exchange it for fresh before trying to finalize the tuning or you may be confused by the way the engine responds.It would be like adding kerosine or diesel fuel to your gas and would tend to make the plugs foul which can show up as the engine popping under load, especially when not up to proper operating temp.

The gas tank was empty when the timing chain was installed it is all fresh gas. Today I plan to get to the plugs unless I get called to fix someone elses clunker.

You said that the carburetor had been recently rebuilt but it sounds like the accelerator pump may be inactive or giving an insufficient shot of fuel when the throttle is coming off idle.A look down the bore while stroking the throttle just off idle should show a squirt of gas into each barrel.The amount and the point of commencement of delivery is usually adjustable with specs for setting the linkage usually in the carb kit or we can find it in a manual.
Make this observation with the engine off to avoid entertaining the onlookers in case it pops fire in your face.

Ok, I will try to do that today

Ok finally got back to it today, new plugs ( AC ) new wires, checked the accelerator pump and that is working, re-did dwell and did timing by ear (in case harmonic balancer was off)It dose run smoother but I still can't get rid of the desiling, should I use hotter gas or a led supplement? do I have a bent or stuck valve ? I did put MMystry oil to free stuff up. any ideas?

check the vacum advance unit on the dist, if it is not working that may be the problem.

Todjob, If the dieseling you are trying to eliminate is "running on" after the key is shut off then the answer usually is like 3b said--the throttle opening at idle is too great or possibly a vacuum leak.
Set the idle speed down to a minumum and see if that doesn't cure it.
I don't see how timing setting or advance mechanism can affect running on since the spark is stopped when the switch is cut off so distributor timed spark is no longer a factor.
Hot spots in the comb chamber provide ignition after the spark is stopped but closing the throttle to provide minimum air flow therefore lowered compression will shut her down.
In the early emission lowering days the factory provided a way on many engines by solenoid activated throttle stop to allow the throttle plates to close tightly when the switch was cut off to minimize running on (dieseling)but when the solenoid was energized it extended to allow a normal idle speed.Some non automotive engines that usually are not idled down before shutdown have a way of blocking by solenoid the main jet when the key is shut off to prevent running on and backfiring.Look at your larger lawn mower engines like B&S and Kohler.
My guess is abnormally high idle speed.

Ok I will try those next to see what i get, thank you both for the tips.

The only thing that lets an engine run on after the ignition is shut is getting air from somewhere (as said). The idle speed is too fast, you have a vacuum leak, power brake diaphragm is bad, etc.
If all else fails, a curb idle solenoid from a late engine can easily be adapted to your existing throttle stop, powered through the ignition to be hot with key on. Key on activates the solenoid plunger and raises the idle speed slightly (easily adjustable for the exact speed for a good idle), and key off drops it back to nearly closed to prevent dieseling.
Any brand, any carburetor as long as the voltage matches your system.