can't get my 1600 crossflow to run properly. it has got a dgav twinchoke carb and lumenition ignition. i've experimented with the ignition timing; it's at 6'btdc static now, but i've tried advancing and retarding it; no differance. i discovered today that i'd got the main jets the wrong way round, putting them in the right holes made........no differance. the engine will tick over at about 1100revs and when i 'blip' the thottle, it will rev to about 3000 or until it uses the fuel that the accelerator pump delivered then cuts out. it won't rev unless you keep blipping the throttle. i don't know iof it is related, but the engine gets very hot and the plegs aren't sooty. any help would be grateful as this is really holding the project up! cheers martian

Main jets too small? - running too lean on the main circuit,
Could also be lean on the idle jets.
How is your float level - could be too low

Cheers

hi, i just rebuilt carb with new diaprahms, seals, etc. the float height is correct, as for jets, they are marked 125 and 170 (if my memory is correct!)

It does sound too lean - mind you don't damage your engine!

I would also recommend that you check the float level, and that the float actually does... float, that is.

Other than that, do you have a good flow of petrol to the carb? No filters blocked or anything? Don't forget to check the filter on the carb's fuel inlet.

Are all jets, ports and other orifices clean?

If all these are OK, then you're into jets and the like - hard to recommend fixes remotely!

HTH,
David

Here are my weber settings for a similar setup:

P=primary, S=secondary

Auxiliary venturi: P 3.5, S 4.5
Main jet: P 130, S 130
Air correction jet: P 165, S 120
Emulsion tube: P F66, S F66
Idle jet: P 45, S 45
Pump jet: 2
Needle valve: 200

These have been rolling-road tested.

HTH,
David

I don't know your carbs well at all but had the same problem as you with my webbers.

Turned out i had put the aux vents in the wrong way round.

thanks guys! i'm thinking that fuel can't be getting to the main jets cos changing them round didn't make any differance. if the float height was wrong i don't think it would be as bad as it is? btw does anyone know how many turns out the mixture screw should be?

You may find this link useful...

Weber tuning

BTW: an incorrect float level can have a significant effect - can stop the carb working properly.

[Edited on 16/7/07 by David Jenkins]

Mixture screw about 2-2&half turns out.

Are you getting enough fuel & pressure from the pump??

Grrrrrrrr.........spent most of morning taking carb to bits and couldn't find any blockages or anything. tried several different float heights; no joy. out of frustration i opened the throttle fully and discovered the engine will run at 2 speeds; tickover or 6000revs! any other throttle position, it stops.