Hi guys im trying to set up a single solex c40ddh side draft for a l20b. Im having a couple of issues with backfiring under acceleration. And when you put your foot down it just dies. Any suggestions on what jets and chokes i should run. I also have a double manifold and 3 other solex carbs i just need 1/2" spacers
To run them. Any suggestions would be great thanks.

P.s if anyone has spacers for them that they are willing to sell that would be helpful

in my opinion a single 40 side draft would be pretty useless on an l20b, even a stock one. for the hassle in tuning it id stick with a standard carb for a stock engine.
id put your efforts into setting up the twins
(also what mods do you have on the engine?)

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When the sign says "don't feed the bears", man you better not feed the bears.

Currently i have no other mods but I'm looking at a new cam possibly a stage 2. The engine has had a complete rebuild i was changing the carbs due to the original was completely shot from the previous owner dropped the motor. If i run the twins i had a look 2 x have a 32mm choke jets 150 and 50
And the other 2 have a 28mm choke jets 190-33 and 52
What do you guys think is best to start with

have you tried searching this site for info. there was a thread on this a while back. the following info is taken from ratsun.net I cant say if its any good for your situation or not but probley a pretty good start.


This is the baseline for Mikuni PHH40 with a stock L20B

Carburetors: Twin Mikuni PHH 40
Venturis: 32 mm
pilot jets: 57.5
main air jets: 180
main bleed pipes: T
main jets: 140
pump nozzles: 40
starter jets: 130
pump nozzles: 40

But with a high-RPM (7000 RPM) L20B youll want the largest venturis available: 32mm? PHH44 would be even better with 40mm venturis. The jets used will be proportional to the venturi sizes.

I have twin mikunis solex and I love them

I ran this set on a stock L18 and a L16 with a cam and just bolted them on and the run fine/
160 air 135 main for 40mm

240 air 180 or so is close enought for 44s

make sure the venturis are not loose and the jet blocks installed

I dont like the single sidedraft set up. as it seems the outers never get the right mixture unlkess you have a Lynx manifold. But others say they seem fine.

make sure your distrubutor ignition set up is correct first.

I would run 2 carbs myself so get a manifold.


I also seen the accel pumps not working or installed diaphram backwards that might cause this also

Hi again sorry it took so long to reply. Thanks for all your help guys. Im going to america in april so i might pick up a few weber parts while im there.
The problem i have is all these webers i have are not the jap models they are all off alfas. One main isue i have is when i brought the car the guy warped the head (BIG TIME) i got a new one but its blowing a lot of blue smoke. The compresion is around 140psi in all is this right.
Thanks again