Carb jet size

[Murf]

Thanks Ted I have now downloaded the data sheet,  I saw your post but  I missed the link you had put.

Thanks Bryanj, I had looked at the parts book in Ash’s stash but wasn’t sure which one was correct for my bike and used the 500 550F one, thanks for pointing out the correct one.

At least I have 2 100 jets so only need to source another 2 .

[K2-K6]

Yep, we got a bit high on altitude there, pun intended 

As noted in here though, the std settings are remarkable in their accuracy considering they were made so long ago.

Usually, any problem will derive from impairment (particularly idle circuit hardware) and possibly wear as experienced by some on forum,

If it didn't run properly when put back together, likely the standard jet sizes wouldn't be the culprit.

Adjustment for modern fuel etc, probably an lucid test of idle mixture settings (this is within fuel injection system as short term trim) or perhaps  moving the needle position if there's definitely a better compromise to be had (long term trim in fuel injection nomenclature) to hone them slightly.

The idle jets size would be the first consideration if there's a confirmed need to change fuelling in reality, rather than main.

I doubt you'd find it much out on those jets you've identified though. The 100 may give you reason to start with the needle moved down one position to mitigate,  then assess from there .

[deltarider]

My advice: first have it standard (see chart below) and start from there. The chart is open for corrections, be it that it runs via me. So far there have been none.

[Sesman]

I’m with Delta: start with 100/38,  assuming you are running standard exhausts and air box?

[McCabe-Thiele (Ted)]

I agree with Sesman & Delta on the starting point.

Lastly for completeness I ought to mention you need needles & jets that are not badly worn ideally orignal brassware.
The needles need to have the circlip fitted in the correct groove with a needle has the appropriate number of grooves.

I believe there are some needles with only 4 circlip positions instead of the usual 5.

[deltarider]

I’m with Delta: start with 100/38,  assuming you are running standard exhausts and air box?

The air intake can indeed make a difference, the exhaust... mwah... on these relatively tame engines, not so much. Therefore all suppliers of aftermarket exhausts back then advertised that no rejetting was required: Marshall, Dunstall, Jamo, all. I remember just one exception: the Austrian brand Sebring had two options: a popular standard one and a racing version that did need rejetting.

[Sesman]

I agree delta, but the question hasn’t been answered.

I tend to agree aftermarket exhausts sourced from reputable companies will probably produce reasonably acceptable results. As mentioned previously my Dekelvic 4:1 works fine, but whether its comparable to standard I really couldn’t say.

[Murf]

My plan is to have the bike in standard trim, it was standard when I bought it with filter and air box plus a very good set of original 4 into 4  exhausts and silencers. The exhausts could be copies  of course as  I have no idea how to tell the difference.

After strip down and  a spell in the ultrasonic cleaner the carbs and all the parts have come up very well and are in surprisingly good condition. There appears to be very little wear on any of the moving parts. Is it still possible to get genuine Keihin jets for these carbs, DS has the 100 jets but I am guessing they are copies.

[Nurse Julie]

If your exhausts are original, they will be stamped HM323, if they are aftermarket, they should still have the 323 but no HM in front of the numbers. That's assuming you have the original style system fitted.

[Murf]

Thanks I will have a look, they are stored in the garage roof so might take a while to get around to it.