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Help please! I have a 42 Chevy bolt with a carter carb. I rebuilt the carb but still have a hesitation when trying to accellerate, any ideas out there would help...

something is not right with the accelerator pump

Ridge,

The common answer is that the accelerator pump is not working properly. With the air filter off, you should be able to see a squirt of fuel in the throat of the carb when you goose the throttle. That squirt gives the engine a little oomph when the vacuum drops suddenly when you accelerate. I would say it's not uncommon for the pump to not work after a rebuild - carbs are fairly complicated critters, what with all the things they're supposed to do under different circumstances. Check your rebuild if you don't have a squirt.

Another possible issue would be timing. If you're timing is off too far, the truck will be sluggish. You can loosen the distributor hold-down bolt while the truck is running, and "tweak" it one way or the other to see if it sounds better. Then tighten it up again, and give it a test-drive. Don't make any major adjustments, unless you are familiar with resetting the base timing. (top dead center, timing mark, timing light, etc.)

Other possibilities are plugged exhaust, inadequate fuel delivery, and towing an overly-large anchor behind your truck . . . ;-)

Check that squirt first and report back.

Hope this helps,

-Michael

Thanks my friend, will let you all know.

Contrary to popular belief, one of the most common causes of hesitation from a dead stop is the idle being set too rich. This often occurs when the idle is set with a vacuum gauge. The overrich mixture combined with little air velocity causes "puddling" in the intake. When the throttle valve is opened, the additional air sweeps the puddles into the cylinders causing an instantaneous overrich condition, and a hesitation.

Another common cause of hesitation is faulty ignition.

And, of course, the accelerator pump certainly can cause a hesitation. However, when I was a kid in the 1940's and 1950's, it was common practice among farmers in rural Missouri to disconnect the accelerator pump completely in an effort to save fuel.

Check the other "possibles" first.

Jon.

Jon,

good point. What's your chosen method for setting the idle mix? Vacuum guage and tachometer, shoot for highest vacuum at proper idle speed (with engine warm)?

Turn both ways until it runs poorly, and adjust it to half-way between?

-Michael

I have the same year, same carb and I too have the same problem. We rebuilt the carb, and now it seems like it is struggling for power. the idle mix screw turned in will cause it to buck pretty bad, and lurch around(causing your body to move forward and back). with the screw turned out quite a bit, it gets much better, but mid 3rd gear, with the pedal pushed all the way to the floor there is a loss of power(i use to have full power), and if i move off the pedal to the half way point it gets power back but its still not right. 2nd gear runs good until the rpms get real high and then it starts the lurch. and then 4th gear there is just minimal power when the pedal is anymore that half way. any suggestions to check first?

Michael - the method I use for setting the idle on any vehicle is quite simple (although at first blush it sounds confusing).

(1) I look up the original manufacturer's RANGE for the idle adjustment. A common range is 3/4 turn to 1 1/2 turns.

(2) I divide this range into thirds. In the above example, one would have 3/4 turn, 1 turn, 1 1/4 turn, and 1 1/2 turn.

(3) How I set the idle depends on the condition of the engine.

(3A) New engine to maybe 500 miles - set idle out 2/3 of the range (in our example 1 1/4 turns).

(3B) Engine broken in, and in good condition - set idle out 1/3 of the range (in our example 1 turn).

(3C) Engine worn out, burns oil, etc - set idle out the full range (in our example 1 1/2 turns).

(4) Once I have set the idle mixture, I start the engine, run at a fast idle until the thermostat opens, and then set the idle RPM with the throttle positioner screw.

Gocart - you are describing a fuel delivery system issue, among other possible issues. Check your fuel pump, fuel filter, tank vent, etc.

And all of the above assumes the carb linkage was checked for wear during the rebuild, and the idle tube was enlarged at the top for sealing purposes.

And if you live in an area where ethanol is served at the pump, the engine MAY be lean. As a test, raise the float 1/16 inch. If the problems go away, you will need to recalibrate the carb for the ethanol, and then reset the float (you don't want to leave it too high, the high setting is just for the test).

And hopefully, you at least looked at this article prior to rebuilding your W-1:

http://www.thecarburetorshop.com/CarterChevroletW1.htm

Jon.

Ok, carbking, I did a lot of tooling around today with the truck. Fuel lines are clear, nice strong stream running out of the fuel tank. I blew the line out with air(just to ensure there were no obstructions) between the fuel pump and fuel tank( i disconnected both ends and let it blow free)

I bypassed the new fuel filter and ran a straight fuel line to ensure there is no restrictions of flow

and lastly, i removed air cleaner to verify the accelerator pump shoots fuel into the carb when i look straight down. its a nice powerful stream kinda goes away as the engine reaches a level rpm.

There have been zero changes. In neutral, i can rev the engine up nicely with it not bucking a bit. but as i get towards the end of third gear, if i dont let off the pedal, it will start to lurch back and forth in the seat.

I will do a fuel pump check soon when i get a 2nd hand, but i cant do both at once right now without my rig catching fire.

Does anyone think this is a timing issue or anything?


Any other suggestions? I did not personally rebuild the carb, but a very good mechanic friend of mine has, i havent talked to him recently but i doubt with his experience that he did anything wrong. Anything however is possible.

How about the end of first gear, and the end of second gear?

If the engine will rev through first and second, but not third; then more than likely the carb has more gas going out than coming in. This may not be an issue in first and second, as you are not in first and second as long as in third.

Jon.

1st and 2nd rev through without an issue. If I hold 2nd gear in for a long period of time(at high revs) it seems like it might want to buck, but i dont ever want to hold the engine at that rpm for that long to create the issue

At this point your suggestion of more gas going out than coming in would be correct. so where does that point me. The discussion I had with several people today points me to two places. Either #1- the fuel pump also has junk lodged in it, or #2 the carb rebuild was messed up in someway shape or form. whether that means that they used the wrong kit, idk.

If the carburetor works well in first and second (also the timing) then it is also good in third.

I would check:

(A) fuel filter
(B) possible clogged tank vent
(C) leak-down test on fuel lines from tank to pump
(D) fuel pump volume test
(E) (stretching here) possible worn fuel pump lobe on camshaft
(F) minor kink in fuel line restricting volume

Jon.

Took off the fuel line at the carb, the engine didnt run long, but it spewed good solid fuel flow into my jar that i had. Vent appears clear as well. again, fuel filter is clear, was even taken off and ran engine without a change. carb linkage is in perfect shape. fuel flow out of tank is great. thinking of possible timing issue, i also get a few backfires/ spits occasionally in the carb.

You might want to take the fuel sender out and take a look inside the gas tank. If its nice and clean then check the fuel line from the tank to the fuel pump for pin holes or cracks. If that checks out I'd try a new fuel pump.

Could be your points.

Kurt

Boy, gotta love the "occasional" problems!

My truck does the "bucking" thing you talk about, but it does it from the get-go in 2nd, or 3rd, or 4th. Pulling the choke out about a third cures it right away. Per Jon, I'm in want of a larger main jet - just haven't gotten to it yet.

Does the choke change anything when you're driving it? (sorry if I've already asked this . . . ) Doesn't really make sense with the 3rd gear only thing, but thought I'd ask anyway . . .

-Michael

You're on the right track. Sounds like the timing might be a bit retarded. Try advancing it about 5 degree. Also, you may want to check the points as Kurt mentions.

I have a vacuum leak at the throttle shaft, is there a seal that wears out? or is this carb shot? spraying carb spray at the throttle shaft causes the engine to smooth right out.

You can have the shaft rebushed and it will last the life of the truck.

John G

I had the shaft re bushed, the truck has more power.
but still have the hesitation in 3rd and fourth gear.
I put a replacement(known good working carb) on and the engine smoothed ride out, idles nice and low, has full power. this eliminates everything but the carb.

Is there a few jets that might be clogged? I just had this carb rebuilt, the truck idles like hell with it, and 3rd/4th run rough. im looking for some pointers. Id love to have a backup known good carb, so when something happens i can be prepared.