QuestionQUESTION: I have a 1950 truck that I just rebuilt the carbirator cleaned the gas tank, tuned up with points and plugs, condensor with new vaccum advance. Truck fires right up and runs smooth when it idols, but pops and hesitates when driving. No power
ANSWER: I guess question #1 is why did you do all the work on it? In other words, how did it run before all this?
The reason I ask is that your symptoms suggest a serious vacuum leak, or a non-functioning accelerator pump, or possibly both. It is also possible the engine is out of time, but if it ran good before all this, that is probably not the problem, as long as you did not have a bad backfire or a problem getting the distributer back in correctly.
I'm assuming this is the original 216 Cu. In cast iron wonder engine, AKA "stovebolt" engine. What do you know about the history of the engine, particularly how many miles ago since it had the timing set changed? Have you done a compression or leakdown test?
Get back to me with more info and I'll try to help you.
Dick
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QUESTION: This is a 20 year pull out of the garage deal. How it ran before is unknown. The accelerator pump works well. I've tried the old hand over the carburetor, kills motor. Putting the distributer back in was no problem. Far as I know it is a 216Cu. As far as the history not much. Not sure about the timing set, The truck only has 17,000 org. miles as per the paper work and seller. I have not checked the compression yet.
ANSWER: Well, if you never heard it run until after the work, we'll have to start with the basics.
When you have it running at idle, try this: Very slowly slide a piece of cardboard or the like across the top of the carburetor - if at any point, before it begins to slow down and finally stall, see if there is a point at which it idles faster as you progressivly block more air. If it does, we know there is a vacuum leak. If it doesn't, we can eliminate a whole bunch of things.
Second: If you have a dwell angle meter, measure the dwell - it should be around 30 degrees, and should remain pretty steady as you rev up the engine. If it is off or if you don't have a meter, double check your point gap setting with a feeler gauge. I know you just did this, but something is wrong, we need to doublecheck everything until we find it.
Third thing to try is this (after you know you have the points set right) - with the engine idling, rotate the distributor body (you'll have to loosen the clamp) slowly, a small amount at a time, you should be able to speed up the idle. If you can, set it to as fast as you can make it, then, back off on the distributor rotation to where it pings just a tiny bit, when you are accelerating gently at about 30 MPH in high gear - that will be the best you can to with this adjustment for now.
Next: run a compression test. This will tell us if all the valves and pistons are sealling well. If you have a valve hanging open - that would cause popping back through the carburetor if the sticking valve is an intake valve.
Assuming the very low mileage is correct, don't worry about the valve timing - the timing hardware isn't going to be worn at all. We may come back to this issue after we exhaust all the other thoughts, though.
We'll stay on this until we have it running like it should.
For your information, I drove my almost identical truck (a 51 half ton Chevy with a later model 235 Cu In version of your engine) from 1975 to 1994, and I know you can't expect much in the way of acceleration or power - but in those years I moved some very heavy loads with it (very slowly), and it always did the job for me. I still miss it, in fact. This is not a truck you can ever expect to drive more than about 45-50 MPH (the splash oiling system isn't up to high RPM), so you have to be a patient person to drive one like this.
Dick
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QUESTION: did the cardboard same speed to stall doublecheck points try rotate distributor check compression all have 80 to 95 what does the valves set on shoud they make noise thanks for all the help
AnswerJust to confirm (your report was a bit too brief and I want to be sure I understand)
1. at no point did covering part of the air inlet on top of the carburetor, did the engine speed up, right? OK< then we can forget about a vacuum leak.
2. you doublechecked the points, and the maximum gap is around 0.017", or the dwell is about 30 degrees, and holds steady when you rev the engine. OK< then we can forget about ignition problems.
3. When you rotated the distributor, were you able to make it idle faster? If not, we can eliminate spark timing problems.
4. Your compression is even and pretty high for that engine. So, we can eliminate valves not closing all the way or sticking.
5. You previously checked the accelerator pump and saw a good healthy squirt of liquid fuel down the carburetor barrel every time someone mashes the gas pedal - right? So, we can eliminate a lean mixture on accleration.
That is all the causes for your symptoms I can think of - we've eliminated all the possiblilties - the truck should be running the way it was when it left the factory. If not, we've missed something - and I have no clue what it is. I'd like to look at it and listen to it and drive it - but unless you live in Southern California around Temecula - that is out of the question.
The valves are supposed to be noisy on these engines - it's the quiet ones that you have to worry about. This engine has solid lifters, and they should be adjusted to the specified gap between the rocker arm and the end of the valve stem - if they are set too tight, they will be quiet but the valves will not seat all the way, which will burn the valves. If they are making noise, you know they are not set too tight.
Try one more thing for me:
Take the distibutor cap off, and with a wrench on the big nut at the front of the crankshaft, slowly rotate the engine back and forth while you watch the rotor - see how far you can move the crank back and forth without moving the rotor. This tells us about any wear or looseness in the timing of the camshaft drive. You should watch the pulley on crankshaft to see how far you can move it without seeing the rotor move. Anything up to 5/16 inch is probably OK, but more than that tells me that the valve timing might have jumped a tooth.
If that isn't the case here, I'm afraid I'm out of ideas - you will have to take it to a shop which has an engine analyser and have them check it out.
Dick
