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Hi

I am in the process of rebuilding a 900 carb engine. I have mikuni flatslides and have found that I must run them a bit richer than otherwise ideal to get rid of the popping in the airbox when cold.

I thought the backfiring could be caused by the wasted spark igniting the mixture when the intake valve is open if the mixture fails to ignite at the combustion stroke.

Converting the ignition to single spark would be an interesting experiment and would also reduce the power consumption of the ignition by half.

I am running the ignitech tcip4 so the conversion would be easy if I could fit the timing gears and pickup from an IE engine.

Does anybody know if the gears will "drop in" the carb engine? The place for the pickup hole is there in the alternator cover casting but would have to be drilled open (no big deal).

This mod would also allow more advance to be used at part throttle if I wanted to fit a TPS to the flatslides.

 

[pajazo]

The timing gears are not the same, the carb version has helical gear and the ie engines have straight cut gears. The ie camshaft drive gear has 2 narrower teeth to give the signal to the pickup, which is why they would need to be changed.

I would need to confirm that the shaft diameters and the gear widths are the same to make them fit.

I realize the popping is caused by leanness, but the carb ignition is very sensitive to it, the popping starts already at afr 15:1. If the carbs are tuned to stay lower than that when cold, they run quite rich when warmed up. I thought maybe the single fire ignition would tolerate a bit leaner mixture. Saving about 30 watts of power consumption wouldn't hurt either to keep the battery fully charged.

 

[pajazo]

Tdmr flatslides. There's no air leaks, checked that. The stock carbs did also backfire to the airbox, but the cv design muffles the backfires so much that they're not really noticeable, but there was black soot in the stock carbs too.

I'm not really trying to debug the backfiring with this mod. I can do away with the popping by tuning the carbs rich and have now jetting that does not backfire but is about 11.5-12 afr when warm.

I'm interested in doing this because I want to make the bike run as smoothly as possible and also want to find out if this is a useful mod to achieve it. The cost for doing this would be minimal, the gears can be had for about 25 usd and used pickups are not expensive either.

 

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Dukedesmo: at least they have the pickup on the belt drive gear which rotates half as fast as the crankshaft.

Guess I'll have to find out if the ignitech has a wasted spark when set to the ducati 48-2 pickup type.

 

[pajazo]

When I look at pics of the alt covers, there might be a little difference in the pickup boss position between the ie and carb engines as Brad said. If this is the case, it wouldn't be as straight forward mod to do.