slight hesitation?

[Mark@Sea]

My engine just went back in the truck today after a full rebuild. What a relief to get to this point!
Anyway, it starts and runs fine, but when blipping the gas there is a slight hesitation before rpms pick up. Is this normal, or is some tuning needed?

[cuz]

Kinda depends on how quick you are

blipping

.

If you are doing it really quick IE mili-second jerks of the linkage the accelerator pump circuit may not be able to react quick enough.

If you are kicking the throttle halfway open try doing it while counting 1000-one for example. Time the movement of the throttle from idle to the halfway mark so you can finish saying to yourself "one thousand-one" just as you reach the halfway point. If there's no stumble or hesitation you don't have a problem.

[M-Thrax]

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[MSeriesRebuild]

Question, did all the accessory components get rebuilt and brought to new specs at this same time?

I'm talking carb, fuel pump, starter, generator, distributor, etc. Don't expect the best in performance until all the components are addressed and brought up to new standards.

I don't agree with the hesitation is somewhat normal mindset, it simply doesn't have to be. Performance issue causes can come from many different areas. Other questions could be asked also, such as were the timing chain and sprockets replaced with new during the rebuild? Any sloppy action there will bring out performance issues. Electrical issues could also cause this. I have no idea how thorough your rebuild was done, certainly I'm not suggesting it is lacking, just bringing out a few of the many possibilities that could be involved in a combination of factors that may be causing your issue.

At any rate, the bottom line is this, NO, hesitation is not normal, the nature of the beast, or something you just have to accept because the pump is vacuum operated, etc. This issue is common with many engines, however it can be conquered and laid to rest. Personally, it is a very annoying issue to me and I simply wouldn't put up with it in my engine, especially a new rebuild.

[Mark@Sea]

New camshaft, pistons, valves, timing gears and chain, oil pump, water pump, rebuilt fuel pump, distributor, carburetor, radiator (thanks again, Charles).
The only things not rebuilt are the generator and starter. Timing set to 4* btdc. Cranks instantly with no drama, runs very smoothly. A little exhaust burble. Can't tell you how it runs under load, as the transmission is on the bench awaiting parts (all new seals and bearings, will be here Monday).
I think the issue could be resolved with a bit of carb/governor adjustment, but don't have a really good procedure for this.

[topellis]

I think I had a similar problem and my issue was that the choke was not adjusted properly. Been a couple years ago and Charles told me how to do it.... but may be worth checking.

Mark

[Cal_Gary]

Mine does the same thing but I've bigger issues to tackle right now.
Gary

[Chunk]

Try checking the leather accelerator pump diaphram. Make sure its in good shape...not missing chunks,stiff and not sealing in the bore,etc.

And... make sure the one way check valve at the bottom of the bore isn't stuck,or restricted in its movement.

[shawn085]

I read somewhere that you should check the accelerator pump spring. It seems some rebuild kits could have the incorrect spring. This incorrect spring could be to stiff. This them would require more vacuum than normal to fill the accelerator pump with fuel. Then when the trottle is opened there wouldn't be the correct amount of fuel on hand for the accelerator pump to apply when required. I know mine needs the choke pulled out about a 1/4" to get rid of it's hesitation. But my engine needs to be rebuilt and have a bunch of other work done. So I live with it for now.

[Cal_Gary]

I know this is an old post, but I stumbled (no pun intended) on to a solution for mine that might work for you. I was driving mine at a leisurely pace recently and noticed that I didn't have the hesitation I usually do. Investigating revealed that I had my choke pulled out around a quarter of an inch without realizing it, and as soon as I pushed it in the hesitation returned, so that tells me that a slight choke adjustment is in order, to correct the problem. You might try that (and I know Mark mentioned this in his post, too).
Gary

[Mark@Sea]

Yep, with a half inch of choke knob out, the problem goes away. Has to be an adjustment issue, as everything has been rebuilt.
At this point I'm just waiting for the bodywork guy to finish the bed (much worse than it initially appeared) and it will be back on the road.
Everything else is squared away, except waiting for the stamp set for the replacement data plates, and hoping for divine inspiration (or intervention) getting those draft pads over the clutch and brake pedal.

[Lifer]

It sounds to me like you're both running just a little too lean. I don't think you'll have to back the mixture screw out very far to correct your problems, though. We had a similar "problem" with my 40/8 Voiture's '54 Chevy fire truck. It would be just fine with the choke pulled out about 1/4" but cough and die when quickly opening the throttle from idle. The bigger problem was that we had more than one driver, most of whom would flood the carb at startup when it was properly adjusted. I finally adjusted it back to where it was and learned to live with it.

[cuz]

A choke adjustment is not what's needed. It is the normal function of the choke when pulled out a 1/4" to increase the richness of the mixture. If this increase gets rid of your hesitation then what is really needed is a bit of troubleshooting to determine why your mixture off idle is too lean. Causes of a too lean mixture are many and each should be investigate. They can be either too much air or not enough fuel or a combination of both.

1-Air leak in the induction system from the base of the carb to the intake valve. Extra air getting sucked in will lean the mixture. A propane enrichment style test is the easiest way to locate induction leaks. Check the gasket areas and the throttle shaft ends closely.

2-Not enough gas can be several things.
A-Idle mixture screw set too lean.
B-Float level set too low.
C-Accelerator pump system inoperative.
D-Main metering restricted.
E-Incorrect metering jets.
F-Low fuel pump pressure.