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mikeracha

Is a 24 big enough for an RT225 with Big Bore Exhaust

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I have a Mikuni TM24 on my RT225 with a big bore exhaust (Evergreen/Ancilloti). I like the carb a lot and ran it for years on my iron barreled stage-4 GP200 motor. I may have another use for the TM24, and was wondering if it is a big enough carb for this set up. Would it be better with a Delly 28 or 30? Something else?

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24 is a fairly good match for a big bore exhaust. You could go larger to try to get a bit more revs...

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You'll be happier with a Dellorto carburetor. A 24/26/28 will do well. As TR said, you'll need to go bigger to get higher. But with piston ported I would stay smaller.

Put the Mikuni on a V3$p@.

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28mm sounds about right.... then once you throw on a true expansion pipe you won't have to do a carb swap except a bit of jetting.

I have a 35mm Airstriker on my RT230... but I still have to modify the reed block clearance issue before I get around to jetting it

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I have been running jetex 24's by Al on both my bikes for a while now and no issues.(pod filter)

 

But...........i also believe i am at the limit. 

 

One is a bgm195 and the other a Solepower iron225.

 

Both run a gp pipe. So i think if you are going to go with a bigger down tube  than i bet you'll have to introduce more air. 

 

I cant say for certain because i have not tried anything bigger than 24.

 

I did try a bigger down tube pipe on the 225 for about a week and didnt like it at all. 

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I have been running jetex 24's by Al on both my bikes for a while now and no issues.(pod filter)

 

 

Those seizes you had were not issues?

 

 

 

I've run everything from stock 20's to Keihin/Mikuni/Dellorto from 22 up to 30. If you run a small/choked exhaust the feeling you get at the end of your engine's output is almost like trying to fight somebody with your friends holding you back; you want to but can't. Nothing really bad happens. With a small carburetor matched to an expansion chamber the heat goes up at sustained high RPMs. In other words, bad things start to happen. Pretty sure it has something to do with the amount of air and pressure at the carburetor and how much fuel can be pulled into it given those conditions. 

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Those seizes you had were not issues?

 

 

 

 

Those were horrible jetting skills........ I was running sh20's at that time .... I also post about failures alot more than other folks. I think people are scared to post failures because theyre afraid of what people will think......i dont give a fuk what people think.

 

 

.......Yea, since i have had these Al carbs its been great. Probably wont change for a long while.......and i run the piss out of these bikes. Freeways and canyons. Town and country biatch.

 

Staying with the post, if i were to go with a bigger pipe i would probably need a bigger carb. , I think my 24's are maxed out.......but i dont know for sure cause i havnt tried.

 

Theres always another day.

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Carb seemed to be giving you no trouble on Sunday's ride... :D

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Carb seemed to be giving you no trouble on Sunday's ride... :D

 

 

Hee hee.....thanks Erik. Yea, thats the bgm195 rivvy 47/18 with the Al jetex24 and a  gp pipe. 

 

The 3rd gear is a blast in the twisties..........and keeping up with Skinner is no easy task.

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I got myself a PHBH28 and am dialing it in. Pod filter on the air hose. According to my butt dyno, the low end torque is a lot better and it revs higher.

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Here is some great info on the effects of carb size from Darrell Taylor on the scooterotica forum:

 

http://scooterotica.co/forum/viewtopic.php?f=7&t=30470&sid=9b747a0c681f6b6c644e8270493ef664&start=10

 

To which I might add that in your specific case a 28mm is probably the upper limit for usefulness and going bigger than that won't buy you much improvement, if any, unless you do additional porting or a reed conversion to that RT225 and pair it with a higher revving pipe.  A stock RT and big bore is still a fairly low revving setup optimized for torque so it matches well with smaller carbs.

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