RS38 Jetting, Standard bore 1157

[Roger P.]

Fitting the DOT head to an 1157. Using K&N RU-2922 duplex filters. Yoshimura RS3 can and midpipe, Black Widow headers on the way.

Considering the displacement is not enlarged, and  the carbs are setup generally for a pipe and filters + some headwork, does anyone have an edjumicated guess as to what the likely jetting would be required for this setup? I'll fuss with it for awhile, but there is a dyno and setup guy near enough that I'm willing to chuck some money at it if it gets too infuriating.

 

 

Edited August 30, 2016 by Roger P.

[Quist]

135.

[busa ash]

i have rs 36 mikuni s , std bore and sb filters and open pipe no baffle ,i have 135s in  not had it on dyno yet but seams fine on road 

[Quist]

1127, sidewinder exhaust, dyna 4000 ignition.

 

Tried and tested several jet sizes 125 - 145 on the dyno. Mikuni recommend jet 135 in the datasheet and they were right in my case. Don't look at fuel consumption or a "correct" AF ratio. In my case running a bit rich result in good Numbers on the dyno and on the track.

[Roger P.]

Thanks fellas. Hoping for as little drama as possible, as the riding season is getting short and I'd like to have a few runs on it before I have to tune up the snowblower.

I got 38's as they were actually $100 cheaper to buy than the 36's on Am*z*n, even if they are a bit much for such a mild upgrade. Call it future-proofing I guess.

Took forever for them to arrive, and The Man took another $200 tax bite when they showed up at the door. Came the same day as the Black Widow head pipes. They weigh a hell of a lot more than the pipes do!

 

[Roger P.]

Well, drama.....

Finally fired this thing up after finding a fuel tap to fit. Started up fine, but what a racket. Are RS carbs that noisy? It sounded like detonation. I was concerned I was getting valve to piston interference with the 750K cams, but I checked and triple checked my cam timing according to the Bandit manual, and swapped out each cam sprocket one at a time to ensure I didn't mix them up. Got it to idle on choke and went to fill it up but it just ran rougher and rougher until it died. Pushed it to the gas station, put in some high test and cranked but would not fire. Also sounds like the starter motor was working hard. Pissed off good. 2km push to home. Flooding? Got the odd backfire from the pipe. Sounded like it was trying to fire but couldn't catch, kinda like starting a stored bike after the winter with old gas in it.

Dumb question, does the RS carbs come with jets installed already? If not, that would explain a lot...

Plugs were black but not wet. Got some smoke on start up which I put down to the new head pipes burning off oil. Idle screws were lightly snugged by finger and backed out 1/4 turn.

Individual pod filters. The K&N RU2922 were far too wide to clamp down properly on the RS38 bellmouths, and they only went onto them by about 1/4".

Also a loud buzzing sound. This is my first time with RS carbs so I don't know what they are supposed to sound like.

Pretty poor result for the time I put into this, I was careful not to rush it. Haven't had time to sort it out, but it will come right, hopefully before the snow.

 

[Roger P.]

Starts a lot easier with straight exhaust valves...

Exhaust cam was retarded just enough to burnish the piston reliefs. Couldn't see any damage by eye, but filling the chambers with gas revealed leak through to the exhaust ports. I swapped in my Bandit valves and the chambers stayed full of solvent overnight so I'm satisfied they are sealing well. Finally buttoned it up  and started it, and was immediately rewarded with a cloud of smoke from a pinched valve cover gasket leak. That was after the last headpipe bolt refused to thread in and I had to disassemble it again to chase the thread. Hoping to hit around 130bhp at the wheel, which the RS38s should help with. What a cunt of a job getting them into the inlet rubbers in cold weather. Finally had to run an extension cord out the back and hit it with the heat stripper, whereupon they popped into place almost silently, which was both a relief and a pisser considering the effort expended in the previous hour with ratchet straps and cursing. Must be the most prolonged dot head swap in the history of this goddamned motor, but it's finally in and working. It better go like a streak of shit through a tin whistle!

[Foz]

Found my rs38's were killing plugs initially and traced it back to rich pilot jets , I had 20's fitted,standard is 17.5 I fitted 15's which now means it starts easier and runs much cleaner , main jets are 135's . These jets may get altered when it goes on the dyno, however my bikes 1216 with a lot of headwork and cams but it seems that 135's work regardless of state of tune