Engine dies under load.

[Kerzy]

Hello, the truck starts but only when you prime it with gas down the carb,it will idle nicely but when you hit the gas or try to drive it dies right away, you can hear what sounds like lots of air then if you let off the gas it will come back and idle, so I bought a carb kit from Mikes carb parts and rebuild the factory Rochester single barrel, that did not help, same exact problem. New points, new plugs all with in spec, timed properly, the fuel pump works fine but it sounds like the carb is starving for fuel? I had an old farmer come over to see if he could help, he took apart the carb I just rebuilt and said everything looks good. I’m at a loss. Any info is greatly appreciated. Thanks!

1965 GMC 910
230

[FetchMeAPepsi]

Sucking air maybe? There's a filter under the passenger side cab that can have the seal rot out if it's not changed in years. My guess would be that, or the fuel pump is wearing out and not pumping enough or holding pressure. You did change the float needle, right?

[Kerzy]

I ordered a new fuel pump, gasket and push rod, I’ll give that a try.
Where is this filter under the cab you’re talking about?

[Funky61]

Hello Kerzy, if you have the fuel filter it will look like this:

[Kerzy]

Ok, nope nothing like that on my unit. I just have a small inline fuel filter that I just replaced. Hopefully the new fuel pump solves the issue.

[Kerzy]

Sucking air maybe? There's a filter under the passenger side cab that can have the seal rot out if it's not changed in years. My guess would be that, or the fuel pump is wearing out and not pumping enough or holding pressure. You did change the float needle, right?

Yes, brand new float needle. Pretty much everything is new inside the carb. Float, springs, gasket, check !Bork!!Bork!!Bork!!Bork!!Bork!, accelerator pump etc.

[AZKen]

1. Why did you say the fuel pump works fine?
2. Any vacuum leaks, hoses, fittings, hard lines. Check the rubber lines carefully. Difficult to find a leak by just looking.
3. What exact motor? and what timing setting do you have?
4. Is vacuum advance working? Hose hooked up?
5. It does sounds like the carb bowl is empty. Recheck float level dimension and float drop dimension.
6. Choke working? Not stuck?
7. Let us know what new fuel pump does, but you can check the one you have now. Do you know how? If it works OK or the new pump does not fix it, that's OK. It narrows it down to few other areas.

[FetchMeAPepsi]

Yeah, my guess is the fuel pump. Ken has some good questions too. When you change the fuel pump, fuel will pour out of the line so be prepared for that. You also may need to prime the pump to get it to pull right.

On Cecilia I have to get a funnel tied to the fuel line in a position above the gas tank and pour gas down the line until it goes back to the tank almost completely. It's a pain to prime.

Hopefully yours won't lose too much and it'll prime itself easily. Good luck!

[65GMCKV4000]

I had a partially plugged fuel tank suction line that caused the same thing on mine. Now first thing I make sure of on all these old rigs is a clean tank and unrestricted suction line. Also replace rubber lines. Saves me a lot of time and parts.

[Kerzy]

I’m running it off of a Jerry can and Hose for now till I can clean the factory tank and lines.

[Kerzy]

So I added the new fuel pump and distributer which made no difference.
I sprayed some ether around the intake/exhaust manifold and the engine idle did speed up. Could a leaky manifold cause it to die under load like it is?
I thought it was a bad fuel pump which it wasn’t then I thought the vacuum advance wasn’t performing on the old stock dizzy so I replaced the whole dizzy which didn’t make a difference. I took the carb apart again and went through the instructions which I’m 99.9% sure it’s put together properly.

[FetchMeAPepsi]

So I added the new fuel pump and distributer which made no difference.
I sprayed some ether around the intake/exhaust manifold and the engine idle did speed up. Could a leaky manifold cause it to die under load like it is?
I thought it was a bad fuel pump which it wasn’t then I thought the vacuum advance wasn’t performing on the old stock dizzy so I replaced the whole dizzy which didn’t make a difference. I took the carb apart again and went through the instructions which I’m 99.9% sure it’s put together properly.


Did you remember to prime the line after installing the fuel pump? If you don't prime it it'll just suck air.

[AZKen]

With all due respect, I have never had to prime a fuel pump.
Kerzy, is all this latest data you gave us running off of a jerry can? Does it start without squirting can into carb? Are you driving it with jerry can? What exactly is it doing now?
What you did with ether is a sign of a vacuum leak. Identify exactly where it is leaking by using a hose on the ether stem to keep the spray controlled. The Rochester carb bodies can warp. Do you have a Model B? Did you take carb completely apart, including power piston? Did you get the right b a l l s in the right place?
I can advise further if I get these answers.

[FetchMeAPepsi]

With all due respect, I have never had to prime a fuel pump.
Kerzy, is all this latest data you gave us running off of a jerry can? Does it start without squirting can into carb? Are you driving it with jerry can? What exactly is it doing now?
What you did with ether is a sign of a vacuum leak. Identify exactly where it is leaking by using a hose on the ether stem to keep the spray controlled. The Rochester carb bodies can warp. Do you have a Model B? Did you take carb completely apart, including power piston? Did you get the right b a l l s in the right place?
I can advise further if I get these answers.

Me either, until this truck. If I didn't prime it after changing the pump I couldn't get her running. Then once primed, she ran great. Just my 2 cents. Your mileage may vary.

[AZKen]

:thumbsup:

[Kerzy]

Yes, I’m currently running off a Jerry can because the factory tank is getting cleaned.
The truck starts now if I choke it, no need to put gas down the carb, but it will still stall if you hit the gas, I need to feather it slowly to increase the rpm in order to drive it; then when I let out the clutch I will want to die so I need to feather it some more. Sometimes it does stall. If I hit the gas hard you can hear air and then it will want to stall.

I removed the power piston in the Rochester B carb, cleaned it up, installed the new return spring and check ball and small spring. It did move freely by hand but maybe it’s getting stuck somehow? I’m very sure I put all the correct check !Bork!!Bork!!Bork!!Bork!!Bork! in the right places. I followed mike carb parts rebuild video on YouTube as well as the print out sheet from his web site.

With the new fuel pump and dizzy the truck is running better and will idle very nice but it is still not running “right”

I’m sitting at 8° timing with the dwell at 30. Plugs are gapped properly.

I will spray some ether to see if I can determine if/where the leak is coming from.

[James]

With you feathering the throttle it sound like the accelerator pump not pumping fuel into the carb throat. Look down into the carb (with the engine not running) and work the throttle. You should see fuel squirting in each barrels. If not that why it is stalling or if it is getting fuel it might need more fuel. Just my though.

[AZKen]

I am now leaning AWAY from fuel delivery. Every thing sounds so right. Carb check several times. New pump tested. Not running off tank or lines. New filter.
I would:
1. Get a new condenser. 50% or more are bad right out of the box.
2. Set the points more carefully.
3. Retest motor
No result? Try 4 deg to 12 deg timing, in intervals.

Still no result? Try a coil.

These can all be tested, but the prices are low and it's easy to replace these things.

Be sure all vacuum hoses, fittings, clamps and ports are not leaking. Take off all rubber hoses and check them for cracks and holes in good light. Also there are several gasket in the kit for carb mounting flange. Double check correct gasket and that it is oriented correctly. (slots/holes)

MORE QUESTIONS: Did this start happen when running off the tank and still did it after switching to jerry can? When did this start happening? Out of the blue or after work being done? If there was work done, what was it exactly? Do you understand float level AND float drop measurements? These are BOTH VERY important with your issue.
It is pretty common that a B carb can be warped and will suck air. It takes an expert to "fix" that. After all the above fails, next time you have carb apart, set the sections on a flat surface and make sure there is to wobble and no space between carb surface and flat surface. Glass is a good test surface.

[Kerzy]

It’s my grand fathers truck, was sitting in the barn for 20plus years. I just decided to get it running again. Been running off the Jerry can since I started to play around with it. I measured the float level as per the carb rebuild instruction sheet but I’ll check it again.

[AZKen]

Jerry can must have a breather hole or open top. Try a new batch of fresh gas. Make sure the hose you are using is genuine gas hose, not something laying around. Do the other stuff I mentioned. Just to repeat: there is "float level". There also "float drop". Do you understand what that is? Carb upside down with float hanging down and take measurement. You have to get them both right. Make sure you are reading the paper gauge correctly. What is your experience with motors and carbs?

[Quigley]

I'm betting it is either the condenser or the coil. 2cents worth. Dave

[Kerzy]

https://youtu.be/0-EVW0YIJL0

Here’s a video of what it’s doing.
Yes yes I have a water leak from the thermostat gasket. Lol.

[AZKen]

Take that feakin air cleaner off so it gets more air and so you can see that the choke is open. See if there is any rev difference. Better or worse.
If no change then use your hand as a partial choke, or the choke lever, in various amounts of close-off and see if anything changes.
If none of that produces, get a spray bottle of gas and, between mist and squirt, it down the carb throat with one hand and throttle it to see if you can maintain that rev up.

[Kerzy]

Yes, I had the air cleaner off this whole time. I just cleaned it and wanted to see how it looked on the carb. The engine was warmed up and running with the choke wide open. I will have to spray some fuel down the carb and see how it reacts. I will let you know. Thanks for the help so far!

[AZKen]

If the squirting has no effect, go to the electrical list above.

[AZKen]

Well?

[Kerzy]

Ok. New condencer, no change
Points gapped within spec
New coil, no change
Re checked the carb float level, no change
Re checked the power piston no change
Installed the factory gas tank, no change
Removed the fuel filter at the fuel inlet of the carb, no change
Played with the timing on different °‘s no change.
With the choke fully closed, it will rev perfectly
squirting gas down the carb it revved perfect but would back fire a bit here and there. I did not get a chance to take it for a drive as it’s been raining for a few days here.

[AZKen]

It's kind of good news it runs. Probably eliminates electric if you have it timed, points set and condenser is actually good. So keep that in mind as we move forward. It now sounds like a vacuum leak, kind of a big one. You said you did ether and it responded. Better investigate ALL hoses, fittings, lines, gaskets and report any messing around you did recently.

Not to repeat my self but back a few post ago I said "What you did with ether is a sign of a vacuum leak. Identify exactly where it is leaking by using a hose on the ether stem to keep the spray controlled". ..............I kind of like repeating myself. It's sounds so good.