Hesitation on Partial Throttle Opening

[Stuart+2]

Lately I've noticed that, after a trailing throttle on the move, if I touch the accelerator by just a small amount (say down 1 inch), I get distinct hesitation.

It's fine if I stamp on the pedal - no hesitation at all - so the pump jet is working under that circumstance. Timing, etc is fine.

The only thing I can think of is that the pump jets are worn in that first few millimetres of movement.

Any suggestions welcome.

Thanks

[RotoFlexible]

Webers?

I had the same situation with my newly rebuilt engine. It was set up on an engine dyno but it's hard to get the slow running jets perfect. After consulting dusty tomes, I experimented by opening the mixture screws 1/4 turn - leading to improvement - meaning I had a lean stumble. So I went up one size on the slow running jets, 50F8 to 55F8, which required 1/4 turn less on the mixture screws to get a good idle. The problem isn't completely solved - I still have a slight misfire in that transition zone - but driveability is improved. The mileage appears to be a little worse (as would be expected) but I'm still getting a handle on that.

This is a work in progress, and of course your situation might be completely different. Good luck!

[65 Lotus]

There is a check valve at the bottom of the float bowl that activates when the accelerator pump is operated. If it is worn (i.e., not sealing well) or sticking in the open position, I can see how that would do it.

[Verve]

Hi . Like Andrew`s done , it`s usually the "Progression Jet" , if you are on Webers ( assuming everything else is good , including timing not too retarded & using good strong fuel ) .

I`ve even had to go up to 60 F8`s to get super , silky , light throttle response on one of my Elans ( they are all different ... and the heavier plus 2 will be more prone ) .... so plug & play ( it`s easy to change the jet ) ... the results will be worth it ... and when you get it right you will still have good idle & economy ... plus a big smile ; ) .

Verve .

[Stuart+2]

Thanks Andrew, Scott & Verve

I'lll get into it.