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philleech

Carburettor accelerator pump adjustment

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I have been driving the car for about 100 miles now after a complete engine rebuild and there is no acceleration . I suspected either timing or incorrect settings of the nuts under the carbs that adjust the accelerator pump. It turns out that I hadnt adjusted these nuts correctly as having looked underneath the carbs whilst pushing the throttle linkage to simulate acceleration I thought the pump lever got pulled up but thats completely wrong. The normal position for the pump lever looks like it should be up and then pressing the throttle pedal releases the sprung accelerator rod and the pump lever goes down. My question is how far up this rod should I adjust the nuts? Am I aiming for maximum movement of the pump lever when the throttle is pressed? Ive re read my rebuilding dellorto carbs book and it doesnt mention it.

Ive adjusted the nuts about 10mm up the rod now and hey presto Ive got some power now but Im not sure if Ive done enough or too much?

Phil

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I've had a peer at the Des Hammill Meisterwerke...and you're right, nothing specific about adjusting the operating arm for the accelerator pump. Since it is operated by the spring in the system, I would suggest that you adjust the two nuts so that the arm is just about to move the diaphragm...in which case, the slightest movement of the accelerator should result in the accelerator pump jets giving a bit of a squirt. That ought to be OK, imho...(!) There is a photo on page 98 which could be used as a guide...

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I think Des says don't undo them to start with.

 

I did too and I done mine by sitting them on a fixed chair and operating the pump and adjusting so all four squirt the same distance approx. 1 meter marked on the floor.

 

Buddsy

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I also have to adjust mine as I took the carbs completely to bits to re-plate all the metalwork. It would be nice to know how they should be adjusted if you have to and Mr Hammil's "don't take them apart" comment isn't very helpful :(

 

Of course I wasn't smart enough to measure them beforehand!! And one of them broke the rod as it was so rusty and just to add insult to injury they don't make the rods I have any more, which is really useful.

 

Edit: Just found this after a quick Google http://www.or600.laverda-club.com/content/tips/carbs/dhla/content_e.html ...

Accelerator pump
Adjust the accelerator pump injection quantity by fitting the carburettor to the special support with the proper gasket and connect the carburettor to a reservoir so that it is continuously supplied with fuel.
Put the two graduated measuring tubes, each having a capacity of 10 cc, under the drain pipes on the support in order to collect all the fuel pumped out. Open and close the throttle completely 20 times, with a few seconds break in between each time, and check that the amount of fuel collected in the tubes corresponds with the correct specification and is the same for both barrels. It not, adjust the pump delivery by resetting the nut and locknut fitted on the pump operating rod; remember that screwing the nuts up increases fuel delivery and vice versa. It there is any difference in volume between the two barrels, remove the pump jets and blow through them vigorously to correct this. Recheck until the correct setting is obtained and then ensure that the nut and locknut are retightened.

 

Not sure what the correct quantity of fuel is though?

 

Paul.

Edited by Paul Coleman

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I tried squirting mine and catching the fuel....not as easy as you might think. Someone on here went to a great deal of effort to make a fixture to clamp, collect and measure the fuel but as long as they are all roughly the same it will be ok. Any excess fuel doesn't get burnt and comes out the tail pipe. Its only to fuel the engine in the period before the air starts flowing if you bang your foot down hard.

 

Buddsy

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