as per title, twin delllorto 40s on 1300 crossflow.

when idling, snapping open the throttle rapidly makes the engine stutter before it picks up.

what is the cause of this? I can think it is the carb. pump supplying too much or too littel fuel - any way to diagnose this in a locost way?

need to do more tests but I think it happens more noticeably when engine is not quite up to temp.

need to try this when driving as this may give more clues.

dunno what the jetting is nor if it is right for the engine.

Not sure if this applies to your Dellortos, but my old alfa did this if the accellerator pump jet was blocked.

Stu

^^^^ well there is a start.

some while back, I did take the filters off and trun the throttle spindle and did see petrol being squirted in; cannot recall if I checked all 4 chokes.

Crossflows like to be woken up gently before they roar!

Try letting it warm up before giving the throttle some welly.....

HTH Fozzie

I can stall my Pug if i dab the throttle rapidly, immediately after start up. Just needs warming up.

With unknown jetting I don't think I would expect it work very well. Just check each choke get fuel pumped in with the a quick opening with engine off then get to a rolling road.

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Originally posted by chriscook
With unknown jetting I don't think I would expect it work very well. Just check each choke get fuel pumped in with the a quick opening with engine off then get to a rolling road.

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First thing to check is that all four pump jets are working as they should.

The earlier pump jets squirt fuel directly down into the carb and can be easily seen by looking into the carb from the trumpets. The later jets, squirt fuel back at the butterflies and aren't so easy to see.

If you operate the throttle slowly (with the engine stopped) you should see fuel squirting simultaneously from all four jets almost as soon as you move the throttle.

It is possible, if someone has adjusted the pump rod nuts, that you might be able to move the throttle some way before the jets begin to operate. This can cause a huge hole in the acceleration to the extent that the engine will almost stop completely if you jab the throttle open.

Of course, on the other hand, you might just have the wrong jets, or as stated maybe you haven't let the engine get up to full operating temp.

Drew

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Originally posted by lotustwincam


It is possible, if someone has adjusted the pump rod nuts, that you might be able to move the throttle some way before the jets begin to operate. This can cause a huge hole in the acceleration to the extent that the engine will almost stop completely if you jab the throttle open.

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I need to spend a few pennies to sort that out and then start looking elsewhere.

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I am having the same problem, symtons are the same. Doesn't matter if its hot or cold, the instant you open up quickly, the engine dies. gradual opening is fine.

my problem however is on the webers not dellortos. I found this diagram http://www.racetep.com/weber/40DCOE151.pdf

pump jet is no 57,

If I remove the screws and take out the pump jets, on the one carb I can see a squirt into the pump jet chamber. On the other carb, it remains dry. if I open it up, the chamber fills up but doesn't seem to get to the pump jet.

I'm not sure what your carbs look like, but try take out the pump jets and see if anything is squirting through will the accelerator is blipped. do this while the car is off.

sorry for hijacking your post but if anyone could point me in the right direction here as well

cheers

looking at literature about this I have found that the lever should be adjusted to rest against the pump base so when the throttle moves, the pump is activated immediately.


that is one thing I will check.

Other thing is to pump the lever 20 times and collect fuel from each barrel and meeasure. Somethwere there is data on how much that should be, then the next size jets, up or down, should be fitted.

There is other stuff that I cannot recall right now.