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Discussion Starter · #1 ·
Hello all,

I'm working on a rebel that acts like it has a rev limiter but feels more like a bog at full throttle. If I keep it at full throttle it, will continue slightly bogging but never die out. I recently cleaned the carb and it still does this (made sure all passages were clear, and they all were). The bike only has 800 miles on it. I checked a forum yesterday mentioning a full-throttle bog could be an ignition or bent valve issue. I adjusted the valves to .003 and that didn't work. I checked timing, and the left cylinder was perfect, idle firing at the F mark, and when revving, firing in between the "I I" mark. But the right cylinder was firing very slightly to the right of the F and the "I I" marks. I did a compression check and that checked out. The tester I used only read 125 psi each cylinder but I think it's just one of those badly designed testers because the last rebel I worked on also was around 125 psi (same tester) and that bike worked like a charm. So if this bike gets the same compression as the good working rebel then I'm assuming there are no bad cylinder leakages. I also drained out the bad gas and put in new gas, as this bike has been sitting for more than 8 years.

But I just remembered there should be a gasket in between the intake manifold and the carburetor. This bike didn't have one there so the carb got real hot. I don't know if carb should be getting hot so I'm assuming that gasket is like an insulator. So I'm wondering if that is why I'm bogging at full throttle? hot air and fuel maybe isn't good? Or if firing so very slightly to the right of the marks is causing the issue.

Thanks in advance
 

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Assume your Rebel 250 is a 1996-2016 model, correct? If the paper gasket is missing (number 5 in this diagram 2009 Honda CMX250C A CYLINDER HEAD | Cheap Cycle Parts), you can make one from gasket material the same thickness (it's pretty thin material), cut one from a cereal or similar box, or order one. Per the description, it does serve as an insulator.

Suggest you fix that first, and install an inline fuel filter if that hasn't been done. How To Install a Fuel Filter | Honda Rebel Forum

If it still bogs after that, the carb may not be clean. Many of the internal passages cannot be seen, and they must be spotless for the carb to function properly. If carb spray was used to clean the carb, I would bet money it isn't clean.
 

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Discussion Starter · #3 ·
Assume your Rebel 250 is a 1996-2016 model, correct? If the paper gasket is missing (number 5 in this diagram 2009 Honda CMX250C A CYLINDER HEAD | Cheap Cycle Parts), you can make one from gasket material the same thickness (it's pretty thin material), cut one from a cereal or similar box, or order one. Per the description, it does serve as an insulator.

Suggest you fix that first, and install an inline fuel filter if that hasn't been done. How To Install a Fuel Filter | Honda Rebel Forum

If it still bogs after that, the carb may not be clean. Many of the internal passages cannot be seen, and they must be spotless for the carb to function properly. If carb spray was used to clean the carb, I would bet money it isn't clean.
Darn. I did use carb cleaner. I'll just reclean and install a filter and that gasket. And yes it's an '07 Rebel
 

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1987 CMX250C AC
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Back in the day waxed cardboard milk cartons were the go to diy gasket material, cheerios box should work nearly as well..
Napa or any good auto parts store should carry sheet gasket material..
 
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Dirty carbs are the number one issue with the engine not running properly. Soak only the metal parts of the disassembled carb in Berryman Chem Dip for 2-7 days (the longer the better). There are O-rings on the pilot/air fuel screw and carb drain screw, a rubber gasket on the bowl, and the float valve has a rubber tip. Chem Dip will destroy rubber and plastic. After soaking, rinse well with water and blow out every opening with high pressure compressed air. Canned air isn't strong enough.
 
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05 Honda CMX250C | 93 Kawi VN750
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If you've got good compression, check your spark plugs for fouling and being gapped to spec. This would also show if you're burning oil (outside of checking your oil level after a ride), which would point to either piston rings, worn valves, or valve seals.

Another easy check is your carb's piston and needle. If it's not opening fully or smoothly, that'd cause poor acceleration on top end. Make sure the diaphragm isn't cracked, torn, and is fully seated. When you push it up, it should move smoothly and give good suction.

I'd lean towards your spark plugs being dirty, though. I had been burning oil from worn valve seals when I had similar acceleration issues. Cleaning and gapping my spark plugs solved it after I replaced the seals.
 

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On 2 wheels: 1998 - Rebel 250, 1980 - CB125, 1982 - CM125, 1980 - CM200, 1987 - Yamaha FZ750
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Chem Dip may not affect rubber or plastic for the 30 minute period the guy soaked the carb in the first video, but it definitely will if left for an extended period. Experience by myself and others here has shown that really dirty carbs need a much longer soak period. I recommend 2-7 days. I do not recommend carb spray as it just isn't good are removing stubborn deposits, Compared to many of the Rebel carbs I've seen, that first one looked pretty clean to begin with. The second video showed what a moderately dirty carb looks like, and spray isn't effective on carbs that dirty.
 
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