Keihin CR carbs 31s or 33s?

[wyly]

i tried 34RS on an 1150 and wasn't as happy as i was with the 36mmRS carbs.
these carbs are easy to tune(at least at my altitude..1000' or less/more depending on conditions).
do not try and use an air box...use either APE or K&N offset ovals.
what is 3 tenths in the 1/4 mile equal in horsepower gain?
i wish some of the other GS 1100/1150 tuners would post so i could see there opinions.

I've been convinced too many smart people all saying the same thing, Mikuni RS36 it is.
Airbox is definetly going if I'm going to spend 1k on carbs I want them to be seen, the entire point of the project was visual modification with improved performance thrown in, all done on small budget. Not sure how the finished project will end up at this point I expect to do modifications every winter for three or four years riding in summers.

I ride at 3,500-4000ft so I suppose I'll need to pass that info on to the supplier when does his set up the carbs. If I get 15% increase of torque and hp I'll be very pleased.

What exactly am I changing in the clutch assembly that will prevent it imploding?

 

[blowerbike]

IMO the basket modification is best left to professionals.
there is drilling and grinding and welding plus making sure the assembly is bottomed out and clamped tight before tacking the rivets plus a really good tig welder(person) is needed.
i always did my own then took it to pearson or mcintosh to tack then weld fully.

 

[wyly]

IMO the basket modification is best left to professionals.
there is drilling and grinding and welding plus making sure the assembly is bottomed out and clamped tight before tacking the rivets plus a really good tig welder(person) is needed.
i always did my own then took it to pearson or mcintosh to tack then weld fully.

I normally do most of my own work, if it's out of my skill set or if I don't have the specialized tools I'll take it to a pro.

Once I have it taken apart I'll get an estimate for the modification, I suspect the labour costs for modification and my personal investment of time and fuel it maybe less expensive to purchase an improved aftermarket basket.

 

[blowerbike]

or find a good used 1150 basket with the HD backing plate kit already installed.
a new billet basket ready to bolt in will be near as much as the carbs cost....very pricey!

 

[wyly]

or find a good used 1150 basket with the HD backing plate kit already installed.
a new billet basket ready to bolt in will be near as much as the carbs cost....very pricey!

I'll keep my eyes open for a rebuilt one. I found a rebuilt kit for $190, a rebuild of my clutch $299 USD, plus shipping my parts for rebuild. Billet basket $469...kit plus welding fee seems at this point to be the winning formula. Early days yet so lots of time to research the most cost effective method.

 

[wyly]

i tried 34RS on an 1150 and wasn't as happy as i was with the 36mmRS carbs.
these carbs are easy to tune(at least at my altitude..1000' or less/more depending on conditions).
do not try and use an air box...use either APE or K&N offset ovals.
what is 3 tenths in the 1/4 mile equal in horsepower gain?
i wish some of the other GS 1100/1150 tuners would post so i could see there opinions.

RS36 seems to be the consensus but what about 38's? The supplier recommends both for the 1150, would a RS38 be more for modified engines(overbore, cams, valve work)? I'd hate to buy the RS36 and find later 38s would've been a better choice.

And why no airbox? I had this discussion with my mechanic he's wrenched on the world super bike circuit and recommends the airbox. He says pods will work but contribute to premature wear of the engine, are susceptible to crosswind interference, moisture/rain issues and are a pain in the butt to tune the carbs properly. He says if I leave all the fairings on I may reduce the crosswinds effecting the carbs. What's the reasoning behind your viewpoint?

I see in another thread Rapidray whose experience I don't doubt says RS36 will reliably add 10hp. Combined with new 4-2-1 headers maybe another 3-5hp. So I'm hoping for a final 15hp gain.

I did some power to weight ratio calculations including planned the weight reductions, it will have feel like I've gained an equivalent of 15hp.

A HD clutch basket is in the plans but I read elsewhere on the forum of cranks being welded as well, how important is this? I don't drag race so I'm never doing any hard launches. Ok I did do one in the last few years, I couldn't resist spanking a kid in his ricer. Very anticlimactic I spanked him so badly, from all the evident cash he dropped on his mazdaspeed I expected much more.

 

[GregT]

RS36 seems to be the consensus but what about 38's? The supplier recommends both for the 1150, would a RS38 be more for modified engines(overbore, cams, valve work)? I'd hate to buy the RS36 and find later 38s would've been a better choice.

And why no airbox? I had this discussion with my mechanic he's wrenched on the world super bike circuit and recommends the airbox. He says pods will work but contribute to premature wear of the engine, are susceptible to crosswind interference, moisture/rain issues and are a pain in the butt to tune the carbs properly. He says if I leave all the fairings on I may reduce the crosswinds effecting the carbs. What's the reasoning behind your viewpoint?

I see in another thread Rapidray whose experience I don't doubt says RS36 will reliably add 10hp. Combined with new 4-2-1 headers maybe another 3-5hp. So I'm hoping for a final 15hp gain.

I did some power to weight ratio calculations including planned the weight reductions, it will have feel like I've gained an equivalent of 15hp.

A HD clutch basket is in the plans but I read elsewhere on the forum of cranks being welded as well, how important is this? I don't drag race so I'm never doing any hard launches. Ok I did do one in the last few years, I couldn't resist spanking a kid in his ricer. Very anticlimactic I spanked him so badly, from all the evident cash he dropped on his mazdaspeed I expected much more.

36's will give a higher airflow velocity over 38's. This will result in better response and midrange without noticeable top end loss. They'll also be easier to tune.
Whatever you do to the head and engine, you won't exceed the 36's flow capacity.

Tell your mechanic friend that airboxes from this period vs airboxes from WSB bikes are night and day...Been there, built engines across most formulas from the 1970's to current. The airbox on your 1150 is there to provide a convenient way of using a single air filter on four carbs. It certainly was not developed to generate HP. As has been suggested, oval K&N's or similar are your best choice IMO.

If you're not dragracing and avoid radical downshifing no need to weld the crank. It's extreme load reversals that twist them or break the alternator ends off.

In my experience, the cheapest way to wake your 1150 up, once the carbs and pipe are on, is to dial the cams to 106 inlet. 108 exhaust lobe centers. This will give you a huge midrange - which is very usable on the street.

 

[TeamDar]

1150’s already have welded cranks. The clutch basket modification is a good idea. Dar

 

[wyly]

1150’s already have welded cranks. The clutch basket modification is a good idea. Dar

thanks for that confirmation, I've read elsewhere that may have welded crank but I couldn't find any verification.

 

[wyly]

36's will give a higher airflow velocity over 38's. This will result in better response and midrange without noticeable top end loss. They'll also be easier to tune.
Whatever you do to the head and engine, you won't exceed the 36's flow capacity.

Tell your mechanic friend that airboxes from this period vs airboxes from WSB bikes are night and day...Been there, built engines across most formulas from the 1970's to current. The airbox on your 1150 is there to provide a convenient way of using a single air filter on four carbs. It certainly was not developed to generate HP. As has been suggested, oval K&N's or similar are your best choice IMO.

If you're not dragracing and avoid radical downshifing no need to weld the crank. It's extreme load reversals that twist them or break the alternator ends off.

In my experience, the cheapest way to wake your 1150 up, once the carbs and pipe are on, is to dial the cams to 106 inlet. 108 exhaust lobe centers. This will give you a huge midrange - which is very usable on the street.

Great info thanks.

I refrain from telling my mechanic anything he's not a young guy, he's been building, racing and wrenching since the 70's as well. I'm aware of my limited knowledge and stay humble, I ask and I listen and try make the best decision based on what I'm told. Not any easy thing to do when so many smart people don't always agree with each other. It's an easy decision for me when everyone agrees on the correct carb size, the carb supplier, yourself and my mechanic all agree for the exact same reasons. It's when the moto smarties don't agree that has me in predicament.

I'll need to figure out how to "dial the cams", doing anything different than following my factory manual's instructions is a new challenge.

 

[Guest]

What about a 2V GS1000 engine with a 1085 or 1100 cc overbore and hot aftermarket cams? Would RS34 or RS36 be the better choice for street and roadrace style trackday duty?

 

[GregT]

What about a 2V GS1000 engine with a 1085 or 1100 cc overbore and hot aftermarket cams? Would RS34 or RS36 be the better choice for street and roadrace style trackday duty?

Here the bike would be built to our pre '82 regs which specify period carbs.,..So my experience has been with Keihin CR's.
31's produce a very sweet running GS1000. 33's and above generally produce a curve with a huge bump at about 5500RPM.
Our race GS1000 is a wheelie monster at 5500...

 

[wyly]

What about a 2V GS1000 engine with a 1085 or 1100 cc overbore and hot aftermarket cams? Would RS34 or RS36 be the better choice for street and roadrace style trackday duty?

The supplier for my carbs recommends the RS36 for the GS1000-1150, I'm no expert but that appears to be the consensus with every GS expert I've asked. The 36 is ideal for street/road performance and offering greater usable midrange.

A RS38 is for people who live in the upper end of RPM range, racers and those with a wish to lose their license.

 

[wyly]

Looking at a photo of the Mikuni RS36 I see each of the carbs has an atmospheric pressure vent to the float bowl. Do those atmospheric vents eliminate the need for a vacuum line from the petcock for fuel flow?

If that's true I'd like to replace my oem petcock with a Pingel for better fuel flow.

 

[Guest]

Looking at a photo of the Mikuni RS36 I see each of the carbs has an atmospheric pressure vent to the float bowl. Do those atmospheric vents eliminate the need for a vacuum line from the petcock for fuel flow?

If that's true I'd like to replace my oem petcock with a Pingel for better fuel flow.

I use a Pingel fuel valve with my RS34s. No vacuum line is required. If I could do it again I'd go with the RS36.