Mikuni RS Series vs. Mikuni VM33s on a GS1150ES

[Guyver]

Well, my bike came in last night, several days earlier than expected. It is in wonderful shape and fires right up and purrs. Things were all good and then I went for a ride. The bike either needs a major tune-up or the carbs gone through or something.

The Vance & Hines exhaust sounds like crap, something like a Harley in a sense. The exhaust note is not steady; however, the bike is not missing or backfiring at all. There is also a definite lack of power. I can feel it being held back when I give it throttle.

The bike has 14k on it, Vance & Hines four into one and Mikuni VM33 Smoothbores along with K & N Pods. I was given the original carb bank and the air box as well. I'm going to tune the bike up and clean out the carbs as I don't know how long it has been sitting.

My question is what carbs are best on this bike, the Mikuni VM33s or Mikuni RS36, even RS38 Flat Slides? I need to unleash the power; at as reasonable a cost as possible right now. As it is running right now my '82 GS1100E would have walked all over it.

 

[80gs1100]

maybe you have an ignition problem of some sort?? Are the carbs clean? If it sounds like a harley, you might have a misfire...check out the plugs, that's the most simple thing to do.

 

[Commodus]

Well, my bike came in last night, several days earlier than expected. It is in wonderful shape and fires right up and purrs. Things were all good and then I went for a ride. The bike either needs a major tune-up or the carbs gone through or something.

The Vance & Hines exhaust sounds like crap, something like a Harley in a sense. The exhaust note is not steady; however, the bike is not missing or backfiring at all. There is also a definite lack of power. I can feel it being held back when I give it throttle.

The bike has 14k on it, Vance & Hines four into one and Mikuni VM33 Smoothbores along with K & N Pods. I was given the original carb bank and the air box as well. I'm going to tune the bike up and clean out the carbs as I don't know how long it has been sitting.

My question is what carbs are best on this bike, the Mikuni VM33s or Mikuni RS36, even RS38 Flat Slides? I need to unleash the power; at as reasonable a cost as possible right now. As it is running right now my '82 GS1100E would have walked all over it.

I would think the VM33s should work OK. Certainly the RS carbs will work better, but that's a thousand bucks and I wouldn't call that a reasonable cost. I think you are better off finding out why it doesn't run properly before buying parts. Perhaps 33s are too small, it sounds big to me but probably one of our resident drag racers can tell us.

 

[Frankenzuki]

misfire

misfire

If the exhaust note is crappy, you have at least one dead cylinder. A squirt bottle with some water sprayed on each header tube with the motor running would tell you quickly which cylinder is not firing. Water will vaporize instantly on a cylinder that is firing, it will bead up or run off a cylinder that is not firing. You can diagnose it from there.

VM33's on a stock 1150 should work well, and better than the stock 36mm CV's

 

[rosco15]

I ran both 36 and 38 mikuni flatslides on my dragbike with stock pistons, head, and cams. The 38's seemed way too big. I would get a horrible bog. If I yanked the throttle open nothing woud happen for a second or two. The 36's were better, but would still do it sometimes. I always thought 34's would be best with a totally stock motor, but I never tried them. For racing the 36's amy give you more power on top.

I'm a fan of the flatslides. I've seen guys running nearly identical motors except for the carbs and I've always made more HP.

I'm not sure what 33's you have. I know there area alot of guys that are big fans of the 33 round slide carbs. Guys swear by them and I've heard of them making alot of HP with them.

 

[Guyver]

The carbs on the bike are the Mikuni VM33 Smoothbores with round slides. I was looking at possibly going with a set of RS38 Flat Slides as I ran RS36 Flat Slides on my '82 GS1100E and my Katana 1000m and they ran great. There was a slight hesitation when I first started from a stop; however, that could have been due to running pods or something else. I guess I might have to pass on the RS38 carbs then and clean up these VM33s and see how they run. I've heard good things about them.

 

[Guyver]

If the exhaust note is crappy, you have at least one dead cylinder. A squirt bottle with some water sprayed on each header tube with the motor running would tell you quickly which cylinder is not firing. Water will vaporize instantly on a cylinder that is firing, it will bead up or run off a cylinder that is not firing. You can diagnose it from there.

VM33's on a stock 1150 should work well, and better than the stock 36mm CV's

Thanks Zuki

 

[rosco15]

In an attempt to fix the problem I increased the spring pressure on the accelerator pump lever. I was trying to get it to dump in as much gas as possible when the throttle is yanked open. It did help. The best fix for the 38's was a 1260 kit

 

[RobGS850L]

In an attempt to fix the problem I increased the spring pressure on the accelerator pump lever. I was trying to get it to dump in as much gas as possible when the throttle is yanked open. It did help. The best fix for the 38's was a 1260 kit

I wonder what would've been cheaper? New carbs or the 1260cc kit? I'd say the fun factor rides on the 1260cc's.:twisted:
One other thing. There's no sound like a set of RS's at idle.

 

[rapidray]

Guyver, clean up the 33s & run them. They will work AWESOMELY on a stock 1150! Call me again if you need help. I did a 1229 motor for KatanaGreg with GSXR cams & that bike runs GREAT with the 33s! Ray.

 

[Guyver]

Ray,

Thanks for your offer to help again. According to the owner of the local shop it sounded to him like at least one of the secondaries are clogged. He asked if the bike ran better with the choke on, and it does, and he arrived at this conclusion. I'm going to pull the carbs again because I overlooked the secondaries, which are apparently in a recessed area to the side of the mains, and clean them out as well as check the mixture screws. Then I will throw it back together and see how things run.

~Gene

 

[Guyver]

Ray,

Is running the GSXR cams a drop in deal or do you need to replace and rework the head from a GSXR?

 

[rapidray]

Drop in with a couple of things to check. Call me at 714-356-7845 when you are ready to do it. Ray.

 

[Guyver]

Will do Ray. The bike reportedly already has racing cams in it. I don't know what they are or anything else about them so I will have to pull the valve cover to get a peek.

 

[rapidray]

If it has aftermarket cams they will have #s stamped somewhere either on one end or near the cam sprocket flange. When you find out call me with the #s you find & I should be able to tell you exactly what they are. Ray.

 

[Hap Call]

I'm with Ray on this one. I've been running VM33 carbs on my 1166 GS1100 for over 20 years and have never had a problem - when set up right they make plenty of power and are smooth across the entire powerband.

Hap

 

[Strangelove9000]

Bumping and RENEW this thread

Bumping and RENEW this thread

Greetings,

Why start a new thread when this one discusses exactly what I was searching for??

This is my first post here!! (after several months of lurking) First, I must say there is an abundant wealth of old-school GS knowledge here, which I think is just Awesome!

Anyway... I am once again building out the engine of what must be one of the finest motorcycles ever created by mere mortal beings. I must stress that this is NOT a "dragbike" project. I am not going to make any compromises that would sacrifice the all-around drivabilty of this machine. I like everything this bike gives in such a (perfect?) balance of performance, handling, comfort, and style.

I just want 25-30% more of everything? And some people call me crazy...

So.. I have begun with a red 1983 GS1100ED with about 20k miles. It's not bad but needs help in a few areas. Cold starts puff a little too much smoke for me to be happy with, so it was off with the cylinders. Rings and a hone would probably keep things happy for another 20k miles but why tear all the way down and not go with some nice Wiseco 78mm (1261cc) units @ 10.25:1. To keep valve lift somewhat in balance with the increase in CC, I think the Web Cam grind #223 would be adequate?

The stock carbs are junk for all practical applications. Even with this planned increase in displacement and compression, from what I have heard here and elsewhere, the Mikuni 40mm RS flat-slides are too much. Open throttle at low RPM's results in the engine "falling on it's face". 38's may be on the fringe too.

Many (many) moons ago, I built out another GS engine to similar specs and used the round slide VM33 "smoothbores" with tremendous success. However they are getting hard to find in decent condition. Are there even many parts available for these (discontinued) units these days?? I have seen gaskets and a few jets for the 33mm's but thats about it. What do you do with a worn slider or linkage?

Age/condition and parts shortages for the 33's have forced me to consider a set of flat slides. As I have heard in other discussions, 36mm seems to be a happy medium for displacements in this range. I have also heard people say that the round slide carbs can flow more air than a flat slide with the same throat diameter? Anyone believe or experienced that?

Off on the total bleeding edge of reasoning, I have seen several set's of GXSR throttle bodies on Ebay for pretty cheap along with programmable control modules. I have been wondering if am I barking up the wrong tree with carburettors? Anyone here have any experience with a fuel injection mod on a GS1100E? How tuff could it be?

What are your thoughts?

Peter