Engine Builds What Carbs 38/40CV or 41CR Keihin - Suzuki GSX-R Motorcycle Forums Gixxer.com
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post #1 of 3 (permalink) Old 05-28-2019, 11:24 AM Thread Starter
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Join Date: Oct 2004
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Engine Builds What Carbs 38/40CV or 41CR Keihin

Hey Guys,

While sourcing parts for a build that was going slow (and in another direction) I happened upon an awesome streetfighter build for sale here in Mtl. Having part of the GSXR scene 20yrs ago I kinda knew the seller and was easily persuaded to pick up this bike. Eventually I also returned to bad habits and picked up a load of spares. As much as I have wanted to build an 815 with the several 750's I have lying around the big cc vs price and ease was too tempting (and it goes back to my earlier 7/11 days).

So now I have one built 7/1216 bike that has 38mm carbs attached. A few threads down you'll notice they were gunked and I lost a part while dismantling them. I have not run the bike now but up and down the street. Blows some blue smoke in start up, black in acceleration, running 147.5 jets.

Now I have also picked up 40mm CV's and a set of 41 Keihin CR's (not FCR, older set I gather). Both seem clean, I don't think rebuilds are in order.

What carbs would you recommend I fettle with to get this running great. Do flatslides induce more chance of stalling or flooding. Always heard CV's as friendlier options and the 38mm or 40mm as great options on the 1100 series engines, especially big bore. And I'll throw a curve into the mix.

I have an 1127 and Bandit 1200 engine as back-ups, DOT heads and enough stuff around in case something were to go down with the 1216. So what combo's should maybe be set aside for use if I ever go down to one of these alternate engines?

How would you build your bike(s)? I should mention I have a Stage 3 Dale Walker Bandit 1250 for sport touring or daily use, so consider this a head to the bar, cruise the local countryside type bike. No long distance or heavy traffic plans.

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post #2 of 3 (permalink) Old 05-30-2019, 06:56 AM
Join Date: Jun 2013
Location: south of England
Motorcycle: GSXR1186N mainly, plus a few others I've bought over the years
Posts: 1,012
Re: Engine Builds What Carbs 38/40CV or 41CR Keihin

Just wondering about the smoke issue, could a ring or two be upside down ? - it'll make an engine smoke.

I have 40mm cv carbs on my big bore 1992 1100, they only work well with the airbox, the delivery without the a.box was full of dips in the torque delivery. On any head bar the 1991/92 1100r you'll need to blend in the port entry to the larger inlet rubber/match them up.
I like the smoothness of cv's on a torquey motor, it helps a lot in slower corners and tricky conditions.
Be careful when using high compression pistons with the dot head, the piston to valve clearance can get very close if you go down that route.
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post #3 of 3 (permalink) Old 06-04-2019, 12:04 AM Thread Starter
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Join Date: Oct 2004
Posts: 37
Re: Engine Builds What Carbs 38/40CV or 41CR Keihin

Funny the answer comes in from England. I was looking through all my old Perf Bikes and Superbike mags for builds and recognized that some of the best builds and dyno graphs were success stories of CV carbs. And I'll add that 36 (which I also have in stock) and expecially the 38mm were highly recommended and used in these builds.

The head is indeed a 91 head, but again I have all the manifolds for all the sizes.

So I am going to dig a little further into the 38 vs 40, and your 40mm without airbox experience makes me hesitant to try those. It is in a 750 frame, and I have to admit I hated fitting the box back in the day when things were stock, even less so now.

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