1983 GS750E BS32 carbs jetting and needles questions

[crazypj]

If you know it has stock cams (remove cam cover and look for any markings saying they are Yoshimura or something)
Then do a compression test. You should be getting around 170~185psi if everything is in good condition.
Pull out one of the end spark plugs and see if pistons are high dome, if stock,(low dome)
If you have stock cams and pistons, the setting I suggested will work better than the 145 plastic jet (in fact, I have a set of 150 nylon jets here that I removed from a GS750 around 1980 ;D )
The nylon jets were often used as a testing point, plus, you could distort the thread to use them in Kei-Hin, Mikuni, AMAL or Hitachi carbs (personally I always thought they were junk)
Use genuine Mikuni or aftermarket from JetsR-Us, Sirus consolidated, etc

 

[dilbone]

If you know it has stock cams (remove cam cover and look for any markings saying they are Yoshimura or something)
Then do a compression test. You should be getting around 170~185psi if everything is in good condition.
Pull out one of the end spark plugs and see if pistons are high dome, if stock,(low dome)
If you have stock cams and pistons, the setting I suggested will work better than the 145 plastic jet (in fact, I have a set of 150 nylon jets here that I removed from a GS750 around 1980 ;D )
The nylon jets were often used as a testing point, plus, you could distort the thread to use them in Kei-Hin, Mikuni, AMAL or Hitachi carbs (personally I always thought they were junk)
Use genuine Mikuni or aftermarket from JetsR-Us, Sirus consolidated, etc

Awesome, Thanks a ton crazypj

I just layed out the glass for my seat pan yesterday, so the attention will now turn toward the motor. I'm curious as to what I'm going to find.

 

[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?

 

[crazypj]

There should be a 'thick' nylon spacer and a 'thin' nylon spacer, unusual to use washers as it's much easier to swap spacer positions or use the 'thin' spacer with washers
looks like the thin one is missing so washers are probably close to same height as original?.
Only real difference is the extra weight can delay slide opening.
You need to find parts pictures to check (at least they should be available online somewhere)

 

[hillsy]

I dont recall there being 2 nylon spacers in those carbs PJ, but it's been many years since I've had a set of them apart.


Either way, they haven't been set up by someone who knows what they're doing if the idle screws are still capped.

 

[hillsy]

Here you go:

http://www.cmsnl.com/suzuki-gsx750es-1983-d_model13699/partslist/FIG12.html#results

Only one nylon spacer according to that (#7)

 

[dilbone]

Here you go:

http://www.cmsnl.com/suzuki-gsx750es-1983-d_model13699/partslist/FIG12.html#results

Only one nylon spacer according to that (#7)

Thanks hillsy, much appreciated. You guys are quick.

Either way, they haven't been set up by someone who knows what they're doing if the idle screws are still capped.

Exactly what I've been saying...I couldn't believe that mains had been changed, needles had been shimmed and yet no air screw adjustment...makes no sense.

So...

1. would you say that these 3 washers are 1, 1.5, or 2 clip position increase? what would actually be suggested as a starting point for pods and open exhaust?

2. why have I read that thinning the plastic spacer is how to raise the needles? does the spacer need thinned as well as keeping these washers below the c clip?

At this point, knowing the needles have at least been raised to some degree, mains changed out, and that now I'll have the ability to alter the air mix screws I'm even more inclined to re-assemble as is and see how it runs before I do anything else to them...although the nylon main jets are making me want to at least start with some sized as pj mentioned earlier.

 

[teazer]

Nylon jets were popular for Mikuni carbs way back in the seventies I think. I probably have some that came with different bikes or carbs over the years but the sizing tended to be a bit random at best.

I agree that you need a starting point but DOHC does have a valid point that until it's running, there's not a lot of need to spend too much time worrying about it.

On BS series carbs there were quite a few changes over the years from BS90 series jets to regular cross drilled VM22 jets and to jets with no cross drilling. For your year/model of carbs it is important to find out which jets were used. Using non drilled jets in carbs made for drilled jets will potentially make it run much richer at low throttle settings. That is possibly what a PO did.

Assuming that the motor is reasonably stock inside and that you have decent air filters you could start with stock jets or go up a couple of sizes just to get a safe starting point and then head to the dyno

 

[dilbone]

Nylon jets were popular for Mikuni carbs way back in the seventies I think. I probably have some that came with different bikes or carbs over the years but the sizing tended to be a bit random at best.

I agree that you need a starting point but DOHC does have a valid point that until it's running, there's not a lot of need to spend too much time worrying about it.

On BS series carbs there were quite a few changes over the years from BS90 series jets to regular cross drilled VM22 jets and to jets with no cross drilling. For your year/model of carbs it is important to find out which jets were used. Using non drilled jets in carbs made for drilled jets will potentially make it run much richer at low throttle settings. That is possibly what a PO did.

Assuming that the motor is reasonably stock inside and that you have decent air filters you could start with stock jets or go up a couple of sizes just to get a safe starting point and then head to the dyno

Thanks teazer, that's part of my problem...I don't know what stock is in terms of the pilots(cross drilling or no) and the needle configuration(how many and thickness of shims). I don't think stock is the place to start, but knowing what stock is/was will help knowing where to go.

 

[downeaster]

I think you can answer some of your questions here http://zeus.mtsac.edu/~cliff/storage/gs/GS750E-ES_Shop_Manual_1983.pdf

 

[teazer]

That confirms the 37.5 pilots and 117.5 mains and teh cross sectional diagram shows NO HOLES in the pilot jets, so those appear to be stock as long as the diagram is accurate.

 

[dilbone]

That confirms the 37.5 pilots and 117.5 mains and teh cross sectional diagram shows NO HOLES in the pilot jets, so those appear to be stock as long as the diagram is accurate.

Yep...I'm thinking about ordering some 125 and/or 130 mains as a starting point instead using of these nylon 145's

I still need to figure out exactly what is going on with the needles and shimming. With the way the spring and clip are installed it does look like I need to thin the top spacer to get the needle to go up some. It looks like all the washers on the bottom are doing is increasing the tension in the spring but can't push the needle higher until the top spacer is thinned.

Am I correct in what I'm seeing/thinking?

 

[danejurrous]

Not to throw a wrench in the mix but I am pretty sure the BS32 carbs on my 81 gs750 do have cross drilled holes on the jet. I can double check tonight if my memory doesn't bomb out on me.

From what I understand tuning these carbs with pods are an absolute mess, so hopefully you get it right and I can just follow suit afterward ;D

 

[teazer]

I think that the carbs changed over the years, the same way they did on the Yamaha XS650 twin. I can't tell you what changed and when but I'm sure that someone over at GSresources has the answers.

My GT750 two stroke uses a set of BS40 carbs which were an earlier incarnation and I ran with pods on the street and now race it with stacks and it runs cleanly.

Fortunately, pilot jets are cheap and easy to swap out.

The carbs that are basically impossible to set up are Keihin CVs used on DOHC bikes and the 400/450s. They do not track well between circuits and require extensive knowledge (see PJ for details) to modify.

Edit: I checked a few years of carbs over at CMSNL and they show the change occurring on 84 model GS(x)750ES. Earlier had bleed holes in the pilot jets and had the older BS40 style needle jets. Later carbs has no bleed holes but had a "normal looking" needle jet.

So the question is what do the needle jets look like - that will help to determine which style of pilot jets are needed. The two types of carb look the same but the float bowls and needle jets etc are very different.

 

[dilbone]

Not to throw a wrench in the mix but I am pretty sure the BS32 carbs on my 81 gs750 do have cross drilled holes on the jet. I can double check tonight if my memory doesn't bomb out on me.

From what I understand tuning these carbs with pods are an absolute mess, so hopefully you get it right and I can just follow suit afterward ;D

great...

I'll have to keep you posted...I sure hope I can get it running well...doesn't have to be perfect to me, but drivable

 

[dilbone]

I think that the carbs changed over the years, the same way they did on the Yamaha XS650 twin. I can't tell you what changed and when but I'm sure that someone over at GSresources has the answers.

My GT750 two stroke uses a set of BS40 carbs which were an earlier incarnation and I ran with pods on the street and now race it with stacks and it runs cleanly.

Fortunately, pilot jets are cheap and easy to swap out.

The carbs that are basically impossible to set up are Keihin CVs used on DOHC bikes and the 400/450s. They do not track well between circuits and require extensive knowledge (see PJ for details) to modify.

Edit: I checked a few years of carbs over at CMSNL and they show the change occurring on 84 model GS(x)750ES. Earlier had bleed holes in the pilot jets and had the older BS40 style needle jets. Later carbs has no bleed holes but had a "normal looking" needle jet.

So the question is what do the needle jets look like - that will help to determine which style of pilot jets are needed. The two types of carb look the same but the float bowls and needle jets etc are very different.

Here are the needle jets

 

[teazer]

As far as I can determine, that is teh later style needle jet and goes with the holeless pilot jets. You have the right type in there.

 

[dilbone]

As far as I can determine, that is teh later style needle jet and goes with the holeless pilot jets. You have the right type in there.

Awesome, thanks a ton teazer...I guess I'll finish the clean up and reassemble these.

 

[teazer]

Take time to be 110% sure that ALL of the tiny drillings through the jets and carb bodies are clean.

One trick I learned is to spray carb cleaner through one drilling and repeat on all the carbs to compare flow. Repeat on each hole. The tiny bypass holes are the ones to take time over., They are a bit tricky but must be clean.

 

[dilbone]

I was finishing cleaning up the carbs and was assembling them tonight when one of those friggin nylon jets twisted off. I tightened it by hand only then grabbed a flat head to just snug it literally just a hair to make sure it wouldn't back out like I had already done to the first 2....

I guess it was an excuse to not have to see if these 145's would work. I ordered a set of 125's, so I'll feel a bit more comfortable knowing I'm at least in the ballpark with those.

Also, I checked the spacer on top of the needle and it measured .100" while the 3 washers on the bottom of the clip measured .063"

I'm thinking I might just switch the two, putting the spacer below and the washers above effectively raising the needle .037" I just don't know how much needle shimming would be a good starting place. I've also read to basically cut the spacer in half, which would be raising the needle .050"