bs38 jetting for hotrod engine?

[malloym]

anyone have any " ballpark" jetting info for a set of 79 BS38's. i'm doing a complete rebuild and I just wanna get it close so I can get it running, i'll fine tune once running..

motor is rephased, weisco 80mm pistons with higher compression, pod filters, open exhaust...

i have some 155 and 160 main jets... ( is this overkill??)

 

[5twins]

Yes, that's overkill. No matter what you do to these 650s, mains in the mid 140s are usually about all they need. But there's more to re-jetting these stock 650 carbs than just swapping mains. You need to change pilots and adjust needle settings as well.

 

[malloym]

thanks 5twins, after doing a search I found that pretty much stock settings are where I need to be.. i'm just glad I got a set of 79 carbs and I hear they are the best of the 38's.. i'll put them at stock settings and go from there.

 

[5twins]

You will want some re-jetting, just not the large steps you were contemplating. I would recommend getting 30 and 32.5 pilots (stock is 27.5 for your carbs) and maybe 142.5 and 145 mains to start. I would also lean the needles a step right from the start. Going up 3 to 4 sizes on the mains is going to make that necessary.

One of the secrets to successfully re-jetting carbs is not to jump all over the place with the jet sizes but rather to try a few successive sizes. If none of the sizes you've chosen is correct, they will at least point you in the direction you need to move (richer or leaner).