jet sizes ?

[littledave]

hi lads
i have been giving my old very tired r65 a cafe racer makeover this winter and was wondering if anyone can give a idea where to start  with jetting the carbs I'm running k&n style filters and a straight through exhaust i still have the original 135 jet in but it seams a bit lean dose anyone have a similar set up and possibly give me a idea of what jet size they are using
cheers Dave

[Barry]

Have you tried the standard roll off test for main jet size.

Apply full throttle in 4th or 5th with minimum 4000 - 5000 rpm on a quiet and safe stretch of road. When the engine has been pulling steadily for several seconds roll off the throttle a touch.  If the engine pulls better when you role off it's running weak, if it hesitates your rich, no change then the jet is fine.

[montmil]

Can't get no darned simpler than that. [smiley=thumbup.gif]

[steve hawkins]

I am running a set of pod filters on my carbs with a non-standard exhaust.  I found that when I mistakenly richened the mixture by fitting larger jets, that the bike very quickly developed a flat spot or hesitation at around 4000rpm, I went back to standard jets and have not looked back.  However although my pipes are non-standard, they do have a spoon baffle in them and some back pressure as a result.  Without the silencers - i.e. free flowing - all bets are off!

[Jmo]

My 83 LS also has pod filters, with Supertrapp exhausts and stock jets.  I initially toyed around with replacing the jets with a larger size but finally decided against it.  The problem was that the bike really didn't have a lot of power below 3500 rpm but past that it really picked up.  I then played with the discs in the Supertrapps (they control the flow) and that helped a bit, I guess because of the back pressure difference.  
In short, a larger jet size might have helped the low end but since I love how it runs at higher revs, why change?
This led me to believe that a free flowing exhaust will lose you some power, probably throughout the power range.

[tvrla]

From all I've read, and heard, the intake and exhaust tract are tuned parts of the engine. Much like a two stroke engine requires a specially shaped pipe, a four stroke depends on pressure waves back and forth within the pipe returning to the exhaust valve to prevent the outflow of fuel when both valves are open at the beginning of the compression stroke.

It's probably true that the bmw engineers have to compromise horsepower for quieter exhaust, but don't believe they give up much.

Frankly, I prefer the stealth approach. I'd rather not attract attention to myself and appear to be going slower than I really am.

[Barry]

I like the sound of the original Zuena silencers. The sito ones I have now are a touch too loud.  

On the induction tuning and noise, does any know, why the early R45/65's have the drilled clam shell airbox. It wasn't introduced until the R90's on the type 247 airheads so it can't be that our bikes need the extra volume of air flow. Perhaps it's to provide cool air or maybe it was just picked from a common parts bin. I know for sure that it adds induction noise.

[tvrla]

Yeah, it doesn't make sense, does it Barry? Both of my R65s had the newer style airbox, so haven't ever seen one with the holes, but I'll sure be watching for them.