Getting the carbs correct

[neilbardsley]

I've had an issue with my 912 since it had new carbs and a top end rebuild. It back fires when taking my foot off the accelerator when over 3000rpm. I got this back from the place that did the work

"Well, I finally managed to coax a little pop out of her on the over run whilst on my way back from a drive to Guildford.

I reckon it's a weak cut due to jetting.

I'd like to replace the chokes with a larger size and increase the jetting of both main and idle circuits - Should cure your pop and give a mild performance increase too."

Sounds to me like this carb setting up is an iterate process so would be better done on a rolling road? I tempted to leave as is or take to the rolling road that Steve Wright used. I had a quick chat with him and he has been doing this type of set up for a long time. Maybe using a road we can get it set up nicely in a couple of hours v many more trips to the garage/road tests? Or I introducing another person into problem so more variable and more confusion?

Also I seem to remember that the carbs where replaced so that we could fit in smaller chokes and now we are moving back to large chokes.

Opinions?

[Lightweight_911]

The important thing is to get it looked at/set up by someone who's experienced with these engines.

'Backfires' can be caused by a multitude of different problems - ignition faults, air leaks, timing, etc - the cause needs to be correctly identified & rectified rather than guessing/fiddling ...