Hey guys, I did a search on this and couldnt find what I am looking for. I have a spare set of MC28 carbs I want to overbore to complement my larger displacement engine, and have no idea if this has been tried, and how far it can go. I have a very competent machinist here who is willing to do it, but if anyone has any specs or experience with this, could you help me out?

Matt, didnt you do this once? If so, any problems fitting or rejetting?

Thanks!!
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Paul Herr
'88 FZR4/GSXR/YZF Frankenbike
MY BIKE PICS

FUEL INJECT IT !!!!!!!
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These aren't the droids you're looking for.

Yeah, right!

If I had the ability to do that and keep a proper powerband, than the manufacturers would have done that long ago. This would have made them smog legal world-wide and they would still be making NSRs...
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Paul Herr
'88 FZR4/GSXR/YZF Frankenbike
MY BIKE PICS

Bimota's 2 stroke 500 was injected, met all the regs and went like hell.

Unfortunately it cost a lot and the autolube was so dire they blew up lots.

I know a guy who is working on getting injection to work on his RG500 - after a reliable 158bhp (at the wheel), carbs become too restrictive so - injection it is.

It just takes mucho time and money. The guy concerned makes dynos and happens to own an engineering company so I guess he has everything he needs - git
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These aren't the droids you're looking for.

Binka wrote:
Bimota's 2 stroke 500 was injected, met all the regs and went like hell.

I thought it was only the carb'd ones that worked? StephenRC45 will tell us; he's worked on a few.

I know a guy who is working on getting injection to work on his RG500 - after a reliable 158bhp (at the wheel)...

...The guy concerned makes dynos and happens to own an engineering company...

Would that "reliable" 158 be on his own dyno? I wish him the best of luck, but personally, I think 158hp in an RG500 is going to be somewhat less than reliable! 158hp is only about 20hp short of a bike that went on to win 5 World Championships!

Can anyone else hear that?... tick, tick, tick, tick...
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Andy.
NSR-WORLD.COM

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You were invited to come and see that bike Andy, but couldn't make the date.

The problem isn't reliability of the engine, it's the chassis, they keep snapping apparently.
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These aren't the droids you're looking for.

Bimota's 2 stroke 500 was injected, met all the regs and went like hell.

Well, from what I heard, it was the poor fuel injection/engine performance that actually caused all the recalls, making the company go under. If their R&D couldnt make it work right, there is no possible way I ever will either!

And for God's sake, why cant we stick with the question here?? I really dont care to hear your fuel injection "stories", I want to know about overbored MC28 carbs!!
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Paul Herr
'88 FZR4/GSXR/YZF Frankenbike
MY BIKE PICS

The Bimotas had 3 problems, the first being they were a Bimota! The injection was the second, it worked most of the time but was abit hit and miss with the throttle responce, the third was they had some probs with the barrels, this was sorted and once coupled with a set of carbs the bikes werent too bad, they did sell some "SP's and Corsa's" like this but not many. All the ones we sold ended up going back and everyone got a 6 or a 6R for free, i can't remember which. They never made much power though.

As for 28 carbs, Ive not seen a set myself but most flat slide type carbs lend them self to being bored alittle so im sure there is some scope in there. Try talking to some on the MX guys as 125 lads are always having carbs bored.
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If I have to take the carbs off once more...

Yeah, we've bored 21 and 28 carbs to...well...about that big. But you have to make sure that you don't go over about that size and it has to be offset bored by about this much.

Clear?

Oh, and on the 21 you have to get ready to epoxy it up here and there. Eh Andy?

Matt@TYGA wrote:
Oh, and on the 21 you have to get ready to epoxy it up here and there. Eh Andy?

That's what I heard!
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Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.

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Sorry for the silliness.

MC28 carbs can be safely bored to 33.5mm, but you have to make sure that it is bored with a vertical offset of 0.75mm.

What this means is that you don't want the bottom of the bore to be cut as the slide won't seal properly.

You can go over 33.5mm but you'll then cut into the choke orifice.

I've gone to 34mm on a set of 28 carbs for Paul, but I've had to modify the choke system to prevent airleaks.

Thanks Matt, that is exactly what I was looking for!
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Paul Herr
'88 FZR4/GSXR/YZF Frankenbike
MY BIKE PICS