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Spitfire Spitfire backfire, timing or carb?

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roofman

roofman

Jedi Knight
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Well I got my choke cable readjusted, and starting is more normal than before. Took the car out for a ride and have a small backfire after shifting.
1980 1500 Spitfire, I just added new cap, rotor, wires, pertronix ignition and flamethrower coil. Has Weber carb. Does the backfire come from timing, or carb?
 
My guess would be the carb, but there's no use in fooling with carb adjustments until you are sure that the valve clearance and especially the timing is correct.
 
is the pop back through the carb, or is it exhaust?

If it's through the carb, it sounds to me like the carb was never set up, the fact that the choke linkage wasn't set, pops back, find someone with a mixture set up, either one of those O2 sensor ones, or one of the spark plug things where you can see the color of the flame.

What is the timing set to?
 
It is from the exhaust, not the carb.
 
Oops, sorry, totally missed the line about the Weber. Never mind.
 
I did add alot of parts at one time so maybe that did it. Am I supposed to open the plug gap with the pertronix?
 
roofman said:
Am I supposed to open the plug gap with the pertronix?
Click to expand...
Some people do, but I would suggest at least getting it running right first, before you start playing with plug gaps. It should run perfect with the stock gap.

And opening up the gap increases electrical stress on components like the rotor, which can lead to other problems.
 
roofman said:
I did add alot of parts at one time so maybe that did it. Am I supposed to open the plug gap with the pertronix?
Click to expand...

:iagree:Randal

Yes if you retained the original coil open the plug gap to 0.35" . If using Pertronix or Lucas sport coils you can possibly go to 0.40". However, secondary stress is going to go up simply due to the switching efficiency of the Pertronix and breaking the plug gap down is easily handled.---Keoke
 
If its a standard downdraft webber for a spitfire, then there really is not that much you can adjust on it. Idle speed, and idle mixture is about it from what i recall. Adjust the mixture screw to give you your faster/smoothest speed, then adjust the idle screw to bring idle down to where is should be.
Is this a new carb installation?
 
The carb was on it when I bought it but suspect by the condition it is not too old. It is the single downdraft 36 something type. It had a choke cable but it broke. I put a new one on and initially had it so it wasn't pulling the arm back 100% but I have that corrected. It starts much better, but have the slight backfire. I didn't get instructions so I ordered a weber tuning book that should be here any day. I don't have either a timing light nor a carb balancing tool so will have to look into that. May try turning the distributer ever so slightly one way the the other to see if that helps. I can't be that far off.
 
What octane are you using? Its recommended Premium for these cars 93 octane.87 octane is not good.If your using low octane gas go out & buy a can of octane booster & see what happens,your timing is probably off too.....Another question does the engine experience PREIGNITION :pukeface: when it shuts down.
 
I usually have used mid grade gas, no preignition at shut down.
 
Um, Ok, came at it from the wrong direction, hate when that happens.

The Weber 32/36 DGV is very adjustable, you do however need to change emulsion tubes and jets in order to do it. A jet kit for those of us who like to tinker is invaluable.

A pop back through the exhaust on overrun could be something very simple, like a small leak allowing air into the pipe. or it could just be the Spitfire "burble". If the air system is removed, double check that all the plugs are tight.

The new carb should make the bypass valve irrelavent. Try playing with the mixture 1/2 turn or so either way, it does make a difference in this case.

It sounds like a good excuse for happily playing in the driveway for an afternoon.
 
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