1983 GS750E BS32 carbs jetting questions

[Guest]

I just picked up a 1983 GS750E a couple of weeks ago. It was in pieces after being broken down by the PO for a cafe build that he gave up on after picking up a different project bike. He has had the bike for several years and road it regularly before braking down for a build, so I know it ran.

I tore into the carbs and found some strange stuff. I texted the PO and he told me that he didn't do any of the carb mods but that his PO had some race/drag bikes and had probably done some tuning.

The bike has a 4 into 1 exhaust with aftermarket slip on muffler and was running pods.

The pilot jets are 37.5 mikuni's. They don't have cross holes like jets R us shows for this model. Are cross holes stock or non cross holes?
The main jets are what appear to be nylon with no makers mark sized 145. From what I've read 117.5 is stock mikuni for this bike, so I have no idea if this jet is similar in size to what maybe a 125 would be for mikuni or what. I know that keihin sizing has a 145 about equal to a 125, but again these nylon jets don't have any marks on them except the size.
I haven't looked at needles yet, but I'll check those soon.

Does anyone know anything about these 145 mains? or if these pilots are actually stock? My plan is to go ahead and assemble as is and run the bike. the PO said it ran ok, not perfect. I suppose that will have to be a starting point for me before I start sinking money into additional jet sizes...

[chef1366]

If you plan on running the pods and pipe then I'd install a Dynojet kit. I'd also go up to 40s on the pilot jet.

[dilbone]

If you plan on running the pods and pipe then I'd install a Dynojet kit. I'd also go up to 40s on the pilot jet.

I was planning on going up to 40 on the pilot and 122.5 on the mains, then shimming the needles a bit....but I'm curious to see how it runs as is to have a base line to check. My main hope though is that I can find something out about these nylon mains. I did take the cap off a carb and saw that the needles haven't been changed, nor have the air mix screws covers been removed. I'm not sure who replaced the stock mains with out having done anything to the pilots or even air mix screws with pods on this thing, but I'm not convinced they knew what they're doing.

[chef1366]

I'd start with a 130 main fearing the 122.5 will be too lean.
Remove the stock spacer on the needle and add two radio shack washers.
Of course I'd clean the carbs and replace the O-rings including the idle mixture screws.

[tkent02]

Nylon main jets? Who makes them, and how do the numbers compare with Mikuni jets?

[dilbone]

I'd start with a 130 main fearing the 122.5 will be too lean.
Remove the stock spacer on the needle and add two radio shack washers.
Of course I'd clean the carbs and replace the O-rings including the idle mixture screws.

I was thinking two steps(half steps) up would be a good start because that's what I did on my xs650 BS38's which are running pods and open exhaust. Also, the DJ kit includes a 130 main, which from what I've read so far, is actually about a 122ish in Mikuni sizes. Someone please correct me if I'm wrong on that!!! The thing I don't like is that the DJ kit doesn't include a new pilot jet...maybe not necessary, but every time a carb goes to pods I've always heard to take the pilot up one or you're likely to run out of air screw adjustment.
Definitely planning on bringing up the needle a hair.

Nylon main jets? Who makes them, and how do the numbers compare with Mikuni jets?

That's exactly what I'm trying to find out!!! Anyone?

[chef1366]

I've seen those jets before.
The DJ kit changes the main air jet so don't go on the jet sizes alone.
I have jetted many bikes and am giving you solid info.

[dilbone]

I've seen those jets before.
The DJ kit changes the main air jet so don't go on the jet sizes alone.
I have jetted many bikes and am giving you solid info.

Thanks chef1366,

I don't doubt your info, I'm just looking to go as cheap as I can on this bike since it may just be a flip for me. The DJ kit vs. just picking up jets and shimming needles is my debate right now which is why I'm hoping to find something out about these 145 nylon mains. If you're saying a 130 main the DJ kit doesn't even come close at 122ish(Mikuni size). If those nylon mains turn out to be a mikuni size 125ish(which is what a keihin 145 should be) then I'd feel even more comfortable just shimming the needles to see if I can get this thing tuned at least close.

Do you know the manufacturer of those nylon jets or a size comparison from your experiences? Thanks for your input so far.

[bikemtn]

I read somewhere that in the late 70's that nylon jets were somewhat common. I would not be surprised if the owner that had race bikes tried something funky and slapped some nylon 145's that he had sitting around.

[dilbone]

I read somewhere that in the late 70's that nylon jets were somewhat common. I would not be surprised if the owner that had race bikes tried something funky and slapped some nylon 145's that he had sitting around.

I've heard that they were popular with the racing crowd and the threads could be altered enough to use them in virtually any carb body.

[dilbone]

I got the carbs apart and they are the worst I've ever seen...gunk upon gunk upon gunk...


The air mix screws were 2.25turns out under the stock caps which had never been removed.


The needles are 5D12 and they were shimmed as seen in the pic. I've read that to shim these needles that you need to thin the upper plastic spacer...no mention was made of washers under the c clip. Any thoughts on that?