carb size
- Thread starter ravenfan
- Start date
2strokerfun
Member
- May 19, 2006
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You have good taste in bikes
Thank god for ebay when we need something for these old bikes
Thank god for ebay when we need something for these old bikes
2strokerfun
Member
- May 19, 2006
- 1,500
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Keihin was stock. The 250 came with a 34mm stock. However, a whole lot of the 125s were converted to 34mm Mikuni VM roundslide. And a lot of the 250s (mine included) went to the 36mm Mikuni.
2strokerfun
Member
- May 19, 2006
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I like both, but you can still buy parts for the older Mikunis. Hard to get replacement needle, needle jet and chock plunger for the old 73-76 Keihins. And the used parts I find on fbay are usually as worn as the ones I want to replace!!
So, like so many people, I gave up and switched to Mikuni. Lot faster to change needle clip setting on--but it does seem I have to change it a little more often for weather conditions than on the old Keihins.
So, like so many people, I gave up and switched to Mikuni. Lot faster to change needle clip setting on--but it does seem I have to change it a little more often for weather conditions than on the old Keihins.
2strokerfun
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- May 19, 2006
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Yep. That's the only real beef I hear about the Mikunis. And I learned to be real gentle when changing the main jet because you can accidentally push the needle jet up where you can't catch the threads without taking the top off the carb and pushing it back down.
- Thread starter
- #8
i found the carb to be a 28mm, if i measured right. i guess they make them in this size but ive never heard of one this small on a 125, could this be right? also, what is the affect of a different size carb have on the performance of a bike, whether it be bigger or smaller?
Bigger causes less velocity to the intake charge and will cause the bike to run lean with the same jets because of less vacuum acting on the orifices. Larger than necessary will reduce throttle response and cause a loss in toque.
Gains would be noticed if you have a modified engine that needs the extra flow. A smaller than necessary carb would restrict RPM on the big end when used on a modified engine but give very good low end response.
An engine that is modified with a ported cylinder, proper pipe and compression combination will appreciate a carb size increase of 2mm.
Gains would be noticed if you have a modified engine that needs the extra flow. A smaller than necessary carb would restrict RPM on the big end when used on a modified engine but give very good low end response.
An engine that is modified with a ported cylinder, proper pipe and compression combination will appreciate a carb size increase of 2mm.
2strokerfun
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- May 19, 2006
- 1,500
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ravenfan said:
That is the stock carb. Also, it was the 32mm mikuni the serious racers switched to on that bike, not the 34mm. A regular rider on a stock engine is not going to appreciate a 32mm carb on that bike.
You've got to remember the 250 elsinore came stock with a 34mm Keihin in 73-77. And they still got 33 hp + out of them.
OHIOMOTOXER
Member
- May 9, 2002
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Changing carb size depends on allot of things.
Porting, cranking psi, pipe and your ability to keep it pinned WFO.
I have a wicked 125 that I use a 34 mikuni on for "slow tight" tracks and a 36 for "fast" tracks.
I also run grenade class cranking pressure and a GEM or DH reed valve, so I can get away with it.
On a basic piston port stock engine with a good aftermarket pipe you should run a 30 or 32 mm Mikuni.
Here is my Elsie.
Porting, cranking psi, pipe and your ability to keep it pinned WFO.
I have a wicked 125 that I use a 34 mikuni on for "slow tight" tracks and a 36 for "fast" tracks.
I also run grenade class cranking pressure and a GEM or DH reed valve, so I can get away with it.
On a basic piston port stock engine with a good aftermarket pipe you should run a 30 or 32 mm Mikuni.
Here is my Elsie.
