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 Post subject: 45mph max?
PostPosted: Sat Apr 14, 2018 2:38 pm 
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Joined: Aug 30, 2016
Motorcycle: 2009 Rebel 250
Rebel: 250
Country: United States
State/Province: DC
City: Washington
Upfront, I am sorry for the long post, but I am quite desperate. I have a 2009 CM250X that I bought used a year ago and have been struggling to find out why it maxes out at about 45mph ever since. According to many posts, the bike should go much faster. I weigh about 150 pounds, so weight should not be an issue. Everything on the bike is stock and when I bought it it had always been kept in a garage by the previous owner and was in fantastic condition with about 1500 miles on it.

It starts and idles like a charm, accelerates nicely, but screams when it maxes out at about 45mph. In winter, I seem to have to keep the enricher pulled out for quite some time though, like more than 15-20 minutes. Even with the enricher pulled put to its sweet spot, the thing only does 50 max. Also, there seems to be a dead spot when I turn the enricher in that the bike revs up at about a third turn, then dies at about half and rev up beyond that again. I changed the oil every season and do about 2000 miles a year. The screaming I heard is just a common feature of the Rebels so I am not too worried about that:). What I can’t get over though is the top speed of 45mph.

I checked the valves and the clearance is exactly where it should be. Today, I pulled the carb and checked the jets, because I thought that they may be too small, but with 38S and 108 they seem to be stock as well. The little star on the jet suggests that they are original Keihin too, but what does the S after 38 mean? The air filter looks like new as does everything else. The reason why I thought the jets are too small is that the pipes coming out of the cylinder are blueish, so I thought the engine is running too lean and therefore hot. Should I go for a larger main jet or change both jets? If so, how much larger?

I live in Washington DC, so altitude should not be a problem either. I have a crappy Chinese 125CC scooter which easily does 55mph. I cannot believe that 45mph is all my Rebel can deliver. Any suggestions would be more than welcome!


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 Post subject: Re: 45mph max?
PostPosted: Sat Apr 14, 2018 6:04 pm 
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Joined: Feb 23, 2009
Motorcycle: Rebel 250 plus a few others
Rebel: 250
Country: Canada
State/Province: NB
City: Fredericton
The screaming at 45 mph suggests a slipping clutch. at max speed when you roll off the throttle and then back on does the engine change speed quickly? If so that confirms its time to fix the clutch. At 45 mph in 5th gear, the Rebel should be purring , not screaming.
The enrichener should be turned off completely after a couple of minutes of running on the road even in cooler weather. If it won't run without some enrichener on all the time, the carb is probably partially clogged and needs cleaning.

_________________
2004 Honda Rebel 250
2003 BMW K1200GT
2004 BMW R1200GS
1996 Ducati 900SS
1973 Norton 850 Interstate
1968 Triumph Bonneville


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 Post subject: Re: 45mph max?
PostPosted: Sun Apr 15, 2018 9:01 am 
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Joined: Aug 30, 2016
Motorcycle: 2009 Rebel 250
Rebel: 250
Country: United States
State/Province: DC
City: Washington
Screaming may be a bit exaggerated I guess. Everything seems to behave normally when I roll off and re-accelerate at top speed.


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 Post subject: Re: 45mph max?
PostPosted: Sun Apr 15, 2018 3:13 pm 
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Joined: Feb 23, 2009
Motorcycle: Rebel 250 plus a few others
Rebel: 250
Country: Canada
State/Province: NB
City: Fredericton
IF your clutch is not slipping at 45 mph, I can't imagine describing the engine noise as "screaming" IT would be roughly 4500 RPM which is just past a fast idle for most Japanese bikes. So you are sure that the clutch isn't slipping.
If the engine seems to be running OK but just not making much power, and you are sure it is firing on both cylinders, I would start to suspect a loss of compression or some other mechanical condition issue. If it was ignition or carburetion, it should obviously be running rough.
It is entirely possible that it is running on one cylinder too. It may sound quite smooth but very sluggish on the pickup and have no top end power.

_________________
2004 Honda Rebel 250
2003 BMW K1200GT
2004 BMW R1200GS
1996 Ducati 900SS
1973 Norton 850 Interstate
1968 Triumph Bonneville


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 Post subject: Re: 45mph max?
PostPosted: Sun Apr 15, 2018 4:12 pm 
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Joined: Aug 30, 2016
Motorcycle: 2009 Rebel 250
Rebel: 250
Country: United States
State/Province: DC
City: Washington
I actually pulled the plugs and took a look and some pictures:

https://ibb.co/fmQyZ7
https://ibb.co/cqi7SS
https://ibb.co/m7p31n

It looks like both cylinders are firing, but I have no experience with interpreting the color of the plugs and comparing them to example pictures does not help either. Maybe the engine is running on the hot side judging by the yellowish color?

I actually do have a tachometer on the bike. I will check for signs of clutch slippage again. Since the bike has only been used very little, I thought a bad clutch would be unlikely, but who knows.

Would anybody know whether the 38S jet is any different from the "regular" 38 jet. Maybe the S indicates a smaller size? I know the previous owner cleaned the carg and replaced one or both jets. Maybe the 38S is different from the stock one? I was looking at this, but the list states two part numbers for the 38 jet 99104-MAZ-0380 and 99103-MA1-0380. I will email them to find out which one I should be using or if they are the same:

https://www.cheapcycleparts.com/oempart ... carburetor


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 Post subject: Re: 45mph max?
PostPosted: Sun Apr 15, 2018 8:59 pm 
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Joined: Oct 16, 2005
Motorcycle: 2014 CB500XA
Rebel: None
Country: USA
State/Province: AZ
City: Green Valley
Here are the listings for your 2009 Rebel:

Image

I would bet that the carb needs cleaning and/or that the main jet is slightly plugged. Your slow jet doesn't have much effect on high engine speeds.

_________________
John, 2014 CB500XA (Daily Rider), 2009 CRF230L (L'il Red Piglet), 1989 NX250 - sold, 2001 Rebel - sold; first bike was a gently used 1958 Matchless G2 (250 thumper)
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