'78 R80/7 backfiring on deceleration

[r67boxer]

Thanks Rob. They appear to be the same as stock. Having said that though they are noticeably louder compared to the stock /5 on my R75. Is it possible that the baffling is reduced or different? They are quite new by the way.

Kevin

[SteveD]

Thanks Rob. They appear to be the same as stock. Having said that though they are noticeably louder compared to the stock /5 on my R75. Is it possible that the baffling is reduced or different? They are quite new by the way.

Kevin

I don't have decibal readings for any of them.
Over the years I've used "stock" Keihans, the sports "Jim Cray" Keihans and Staintune.
The sports Keihans are noticeably louder than the other two, which seem a tad louder than oem.

They did "crackle" a little on the overrun. Jim Cray suggested 170 main jets and K&N air filter.

https://youtu.be/vTqO1hABIzw?si=oCbqKZDOF5VlSHja

1981 BMW R100RS using Jim Cray mufflers, by Keihan.

The oem 160 main jets replaced with 165's, oem air filter. Mixture screw at near 0.75 turns out from stumble. It was at a 0.5 turn with touring Staintunes on, and the 160 main jet.

Note the popping on deceleration. I'm trying to decrease that, whilst tuning the carbs. I have since tightened the exhaust system a little more. Testing will continue.

Fiimed with a MD-80 spycam clipped to the belt of my jacket and as you saw, facing rearwards. The sound of faster acceleration isn't quite so harsh with a helmet on when riding. They don't sound too obnoxious whilst cruising either, and my neighbours are yet to complain of me waking them at 0630 am when I often leave for work.

[ME 109]

I use a good hill/s and a stubby screwdriver to set mixture in real riding conditions.
Cackling on closed throttle gets an 1/8 turn or less at a time until the cackling/popping ceases, or is just there.
Assuming all else is in order with the carbs and just fine tuning is needed.

[r67boxer]

That worked. I turned both sides out 1/8 turn each. Best overall was a full 1/4 out. I then had to dial down the idle a touch. All good. Thanks to all!

Kevin

[Seth]

I would still keep an eye on the spark plugs, especially after a high speed run. The adjustment you made is for idle only. Mix and high speed mixture is controlled by the main jet and needle. If you had to enrich the idle mixture, chances are you’d need to enrich the higher speed circuits.