147 Franklin Airman

Timing set up for crank & cam on 29-25 standard

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Can anyone please tell me how I can check the timing between the crank and the camshaft on my 29-25X?

I have an issue whereby when adjusting the distributor so that the timing light is on the 17 deg Adv mark the engine runs terribly but adjusting manually to get her running smoothly she then backfires through the carburetor.

All the valves have been cut and the valve seats ground, compression is good. Head was skimmed. Fibre timing gear looks good. Carburetor stripped and cleaned, new idle needle fitted.

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A common cause of this symptom is the heat riser having pin holes. Carb running lean would be next.

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23 minutes ago, raydurr said:

A common cause of this symptom is the heat riser having pin holes. Carb running lean would be next.

Thanks Ray, I forgot to mention that I have blanked off the heat riser but the back firing through the carb can be stopped by pulling the choke out a bit. I have been looking at a replacement carb but its the timing that's worrying me.

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Blocking the openings may or may not prevent the rusted sleeve from affecting intake vacuum signal. I doubt that gear timing is off but is possible. Carb blockage and venturi flap adjustment are also a cause. 

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