Re-jetting

[keith m 131]

Hi All,

I have a 34 ADF carb on my 2ltr twin cam with timing set to 10 deg BTDC, Facet electric fuel pump and K&N filter. The jets fitted are as original spec 122 for primary main, 130 for secondary main, air corrector jets are 170 main and 175 secondary.

The engine is flat out at 80mph, so if I were to increase the main jets to say 130 or 135 and secondary to 135 or 140 would this make the engine run too rich so as to run like a bag of bolts or would it increase the power but reduce my mpg?

If I increase the main jets then would I also need to increase the air corrector jets too? Or do I only need to increase the secondary jets as that is the venturi that takes over after half throttle is achieved on the primary? If I were to leave the primary as is would that retain fuel consumption for daily driving up to half throttle?

Regards

Keith

[TOAD]

  Don't forget the air jets trim or compensate for a main jet,  but I'm not that much into jetting but this may get a response from those with more knowledge than me on this.

[Tas131]

What makes you think the jetting is wrong? What is the stock jetting for that carb? Has someone previously played with the jetting? Simply running it richer won't mean it makes more power.

[miro-1980]

I would be very hesitant to change the jetting at this stage.

Have you taken the carb off and see what shape t is in ?

What about the condition of the plugs, compression, or such elements as valves, rings ...

Have you dynoed the car recently and tested the exhaust fumes ?   

Time for re-jetting is after you rebuild the engine modifying it for more power. 

If you give it bigger jets you will only tend to flood it and waste gasoline for no power effect

Miro