View Full Version : Spitfire Spitfire tuning problem

Simon TR4a
08-26-2004, 04:04 PM
I have recently purchased a 1979 Spit with 40 dcoe Weber, but otherwise stock.
The car starts well and runs fine at very small throttle openings then misses and splutters as I try to gently accelerate.
The vacuum advance has been disconnected but a strobe shows the weights in the distributor are not stuck, the charcoal canister has been removed and a manifold fitting has been sealed by threading a bolt into the end of a rubber hose.
I have checked jets, chokes, air correction jets and emulsion tubes against Tegler and other internet sources and all now correct.
Any help appreciated! Simon. /ubbthreads/images/graemlins/nopity.gif

08-26-2004, 05:29 PM
Diapraghm in the accelerator pump of the Weber leaking or perished?

Never tinkered with a weber but I've had a couple cars with Accelerator Pump style carbs that did the same thing -

I guess a rebuild kit would be a last resort

I'm sure somebody with more knowledge will stop by shortly -

Good Luck!

Bob M.

Simon TR4a
09-01-2004, 10:16 AM
After weeks of messing about I figured it out last night and feel like a genius!
After freeing up the choke cable which would not close all the way, resetting the timing changing pugs and playing around trying to rig up vacuum advance the car was running worse than ever.
Last night I took off the air filter and the caps over the progression holes and shone a light into the carb intake to check the holes were clear and the throttle butterflies in the proper position. All was o.k., but I noticed the secondary venturis were not "clocked" correctly so the holes didn't line up with the jets. Corrected that and there is a huge improvement, even the clutch judder is gone, obviously it was caused by the engine stumbling as I tried to get going.
A little final tuning and it will be great! Now I can enjoy the rest of the summer.

09-02-2004, 12:25 AM
Good job, Simon.
Hope to see the Blue Flame here soon.

Bring a SLEDGE for my WEDGE while you're at it.

09-02-2004, 08:03 PM
Simon, take the "Grub screws" out that hold the venturis in place, and drill them for safety wire. I've seen these back out and cause the exact problem you had. A nickels worth of safety wire will prevent that from ever happening again.

Simon TR4a
09-03-2004, 10:15 AM
Thanks Jeff, they are secured in fact by a locknut, so I think they must have been installed less than carefully. On the other hand I have got a roll of stainless wire that I will likely not use up in my lifetime!