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1985 cmx250
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Discussion Starter #1
Was looking at the single and duel carbs and was curious if there are any pros and cons to have having either. Is the hp/performance the same or different.
 

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The Aussie and Asian rebels have twin carbs standard and have a bit more HP and torque and with a cam upgrade will make a lot more HP . How do I know I have done it to my 250 rebel
 

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A wide lobe cam re grind not a high lift cam
 

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1985 cmx250
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Discussion Starter #5
Sorry but not sure what that means. Would be a different can or altering the existing one
 

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The cam sharft has to be removed from engine and is reground by a cam sharft specialist
 

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Was looking at the single and duel carbs and was curious if there are any pros and cons to have having either. Is the hp/performance the same or different.
I'm curious as to what you're trying to achieve. If you're simply going for more power, I wouldn't bother with twin carbs. I don't think you'd get ENOUGH additional power to feel satisfied with the money you spent to get there (I may be wrong).

I have my doubts that the power increase is due to the twin carbs in and of themselves. My guess is that along with the twin carbs comes a different intake. I don't know that, but it's either that or a fancy rubber 2-into-1 boot, to the stock intake. If it does come with a different intake, that intake likely has better flow performance than the stock single carb intake, and would be the root cause of the increased hp. The stock carb is plenty capable of providing enough fuel, and then some. But the stock intake, and the design of only 2 valves per cylinder, well the cute little 233 cc engine can only gulp & puff so much air with those limitations. This is what I think, but I'm wrong almost all the time. I guess I would fit in nice at any dealership.


7milesout
 

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1985 cmx250
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Discussion Starter #8
Nah.. makes sense. And really I was just afraid the carbs wasnt acting right.. but ended up being the bent valve. But still went and ahead and took the carb apart, soaked in chem dip and replaced some internals. Only pilot(assuming pilot) jet was replaceable. Weird cause my main jet didn't look like what I got in the rebuild kit. And couldn't really find a kit with that same jet. But the chem dip did a great job on cleaning the carb, so just looking forward to seeing how it preforms. Head gasket to reinstall the head was supposed to be here today but just got notification is was gonna be late. But almost there.
 

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Only pilot(assuming pilot) jet was replaceable. Weird cause my main jet didn't look like what I got in the rebuild kit. And couldn't really find a kit with that same jet.
Here's a diagram showing how the main jet fits into the jet holder and the slow/pilot jet. If you don't know the main jet unscrews, it's easy to assume the whole thing (jet + holder) is the jet. The slow jet is replaced as a unit. 1986 Honda CMX250C A CARBURETOR | Cheap Cycle Parts
 

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1985 cmx250
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Discussion Starter #10
You was so right.. just took back apart and yes they did separate. Very thankful. Quick question though. How do I get #2 out. Or is it ok not to change.
 

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1985 cmx250
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Discussion Starter #11
Also what's the difference in these jets and which would be better to use.. sorry my camera not so Good
109087
109088
 

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1985 cmx250
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Discussion Starter #12
I just looked up where I got the kit and pretty positive the new jet is a 135. Is that ok or should I just use the old one. Factory air box and pipes
 

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If it hasn't come out, leave number 2 in place. If it comes out, put the concave end into the tube first. Stock jet sizes are 128 main and 35 slow for first generation carbs. Those tend to work best in 1st gen carbs if they haven't been damaged. FYI, the slow jet has a very fine honeycomb structure at the bottom of the jet. It's there to atomize the fuel as it passes through it. If that has been punched through in the mistaken assumption it was blocked, it needs to be replaced. Ditto if someone enlarged the main jet holes. Stock jet sizes for 2nd generation carbs are 108/38. If the old jets have been cleaned, they should function fine.
 

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128 main? Wow! Flite as you know, I'm running a 105. And it works great. I wonder what all is different about the 1st gens that they had to run such a big main. Are they able to get more air than the 2nd gen? If so, they should be making more power, or running rich as all get out. 128 is like a fire hose compared to my 105.
 

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On 2 wheels: 1998 - Rebel 250, 1980 - CB125, 1982 - CM125, 1980 - CM200, 1987 - Yamaha FZ750
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I do not understand the "resistance" against dual-carbs. And most among those that never tried it.
Also the negative tones that exist here, when tuning is mentioned/asked for.
(While tuning a Briggs & Stratton is ok)
OK, more CID is always the easy answer. But it is NOT always practical, wanted, possible, or what members ask about.
AND, it is possible to get more power (and speed) from the 250cc. It may cost, it may reduce the lifetime of the engine...so what?
 

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I stand corrected. The Honda parts fiche says the 1985 model jet sizes are 135/35, and the 1986 and 1987 models are 128/35. Wondering if the 135/35 is a typo?
 

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On 2 wheels: 1998 - Rebel 250, 1980 - CB125, 1982 - CM125, 1980 - CM200, 1987 - Yamaha FZ750
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Keihin or Mikuni?
 

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I do not understand the "resistance" against dual-carbs. And most among those that never tried it.
Also the negative tones that exist here, when tuning is mentioned/asked for.
(While tuning a Briggs & Stratton is ok)
OK, more CID is always the easy answer. But it is NOT always practical, wanted, possible, or what members ask about.
AND, it is possible to get more power (and speed) from the 250cc. It may cost, it may reduce the lifetime of the engine...so what?
I'm not sure resistance is the correct term. For the non-Aussie/Asian bikes, going with dual carbs involves sourcing the correct intake and buying the dual carbs, which isn't cheap. Ditto for the internal engine mods, especially if you have to pay someone else to do them. Wjmrty is an accomplished mechanic/machinist with the skills and equipment needed to do those modifications. If someone wants to modify their engine for more power, I say go for it. But for the average rider, it's just easier and cheaper to get a bike with more power from the factory than try to boost the CMX250 engine to its potential maximum. Possible and practical mean different things to different folks. Can't find the link, but Honda made a one off 250 that made ungodly amounts of power on the track. Think it still holds the records in its class. But they had the engineers and resources to make that happen, and cost wasn't a consideration.
 

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1985 cmx250
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Discussion Starter #20
Just still not sure which hey to use. The kit says 135 but it looks totally different than the factory jet just wish I could get a better pic of the jets.
 
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