850 commando amal carb jet sizing...

Hey team,

putting together my first 850...first brit bike as a matter of fact... just had a question regarding carb jetting.....i plan on using some aftermarket cone pod filters with a non baffled straight through set of 1.5" pipes....anyone else tried such a configuration? i imagine ill need to up the main jet - just wondering to what kind of number....?

Hi, welcome! Standard 932 concentrics?

thats right......

As far as mains, I'd start with the oem setup - 260 mains - and then do some throttle chop tests and go from there. You can have what by eye appears to be "better flowing" or "less restrictive" but it may not work well with the engine and actually perform less well than a stock muffler.

I believe stock set up should be.
260 main
3 1/2 slides
106 needle jet.
needle in top groove.
You may need to raise the needle by using either the middle or bottom groove to richen the mixture some to compensate for the more open exhuast and air-filter.
Do some plug chops at half throttle position to check for needle position. Probably more important than main jet as that is where most of the every day riding is done.

ianfotheringham said:

Hey team,

putting together my first 850. with a non baffled straight through set of 1.5" pipes........?

Click to expand...

That's most likely to cause more jetting issues than anything else. Pipe diameter and length....stock cam? Stock compression ratio?
It may sound loud as hell, but that doesn't mean its actually performing better than stock. Oh and by the way, if the rear end of the header pipes are not supported in a flexible way like the stock muffler assembly, the header pipes will crack around the bend.

mmm...i've been cognizant of my neighbors potential problems...perhaps a baffle in the custom pipe setup i have will be best.... but am looking for a gritty sound...stretched bobber style and all....

Any relation to Allan Fotheringham?

Glen

ianfotheringham said:

mmm...i've been cognizant of my neighbors potential problems...perhaps a baffle in the custom pipe setup i have will be best.... but am looking for a gritty sound...stretched bobber style and all....

Click to expand...

Now you've done it. Confessed its a bobber with straight pipes?
You shall be exiled to the island of Norton Blasphemy.
Wait....... You can almost here the snide remarks already.

One option you could do is a baffle inside the pipe. My brother did that to his Triumph and it toned it down and added a little mid range, since at the time he was running 1.75 inch pipes.

It could go either way. There are no greater group of motorcycle snobs than the Vincent owners. When you see a goup of vintage mc riders looking at your parked Vincent they are generally saying positive things and admiring the bike. When you see a group of Vincent owners looking at your parked Vincent they are saying things like, "Well somebody is certainly not concerned about using the correct battery box!!!" or,
"My God, ewwww, the number on this rear frame correlates to a Comet and the rest of the bike is a Rapide!!"
So a new Vincent owner in Seattle built his very clapped out Argentinian Rapide into a very nice bobber style machine. The Vincent owners did not know what to do with it, so they liked it! It had so many things about it that were not "correct" that their correction mode was completely overloaded and could not function. :mrgreen:
Who knows, the same thing could happen to the Norton snobs with Norton bobber ( much smaller percentage snobs than in the Vincent community)

Glen

It's always been my intention that if I could ever afford a Vincent (highly unlikely) I'd flame the tank and put high bars on it just to annoy the other Vincent owners.

Baffle in Commando muffler is a well known solution to decrease performance. Increasing exhaust pipe diameter is also causing same effect
stock 1 3/8 and straight through reverse cone are best performer but I 'm a Norton snob

Getting good performance by keeping stock stuff doesn't make you a Norton snob. To do that you would have to keep the stock stuff that either decreases performance or likes to fail at inopportune times. Sorry JRD, you're just not there yet :mrgreen:

Glen