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Discussion Starter · #1 · (Edited)
Hey guys!

First post here. I bought a 2009 Rebel 250 about 2 months ago and she's been absolutely great. However I've run into a couple issues since I've gotten her:

1. Mainly, I'm concerned with the lower-than-usual top speed. She used to be topping out at 77-80mph on WOT on flat ground. Now it seems that the limit is 67-70mph. Interestingly enough, I reach the same top speed in 4th gear as I do in 5th. Switching up to the final gear just results in lowered RPMs with no additional power. I recently cleaned the carb but that didn't solve the issue. I read a post about a shrunken CV diaphragm being a problem, I'll check that next but it's my only hypothesis so far. She was running perfect the first month, then one day on the highway I was maxed out, felt a drop in power as my speed dropped from 80 to 65mph. It came back after a few minutes, but after that day it's been gone.

2. (Resolved) There's a noticeable grinding sound when I downshift to first. To clarify, this is when I'm coasting with clutch to a stop. I can feel it in the shifter as well as hear it. This only happens from 2nd to 1st gear. It almost always "catches" on neutral because it doesn't want to go to 1st. My only guess is that the clutch isn't fully disengaging, but that doesn't explain why it doesn't occur for other gears. Also the sound is the same whether I pull the clutch halfway in, which clears the friction zone easily, or if I yank the lever all the way. This is also a problem that only started about a month ago. I think it's unrelated to the first issue, but possibly not.

3. (Resolved) A torn rubber boot between the air filter and carburetor. I noticed this when I cleaned the carbs, there's a rather large gash. I'm sure a replacement part isn't too expensive, but my friend said it wouldn't affect anything that much and wouldn't bother. Just wanted another opinion.

4. The exhaust pipes are pretty rusty. This was the case when I bought it. It doesn't bother me much but I was just wondering the best way to remove it and prevent it in the future.

Sorry to dump a bunch on you guys! I've been a lurker in the community for a bit and learned a ton from previous posts. Just figured it was time to make my own.

Thanks
 

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1986 Honda CMX 450 Rebel
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Welcome aboard.

To make it short. Point 3. is where your "power" has gone.
Additional air causes your Motor to run lean. That is very bad for the engine because what is running lean, is running hot ! Valves, pistons and cylinder can be destroyed and will be, if the situation prolonges.
I guess that your friend has few expereance with engine and carburator mechanics/physics

To Point 2. The rider is not supposed to shift to first...while coasting to a stop. Coast to a stop shifting slowly from 5`th to second and neutral. Then, to launch again from stop, to first.
Adjust the clutch cable to fully engage the clutch with a little slack.(a little less than a 1/4 inch at the lever.). Adjust the clutch with the engine at it´s working temperature. (ride for 15 to 30 min before. adjusting.)
I hope your Motor isn`t damaged already seriously.
 

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Discussion Starter · #3 ·
Welcome aboard.

To make it short. Point 3. is where your "power" has gone.
Additional air causes your Motor to run lean. That is very bad for the engine because what is running lean, is running hot ! Valves, pistons and cylinder can be destroyed and will be, if the situation prolonges.
I guess that your friend has few expereance with engine and carburator mechanics/physics

To Point 2. The rider is not supposed to shift to first...while coasting to a stop. Coast to a stop shifting slowly from 5`th to second and neutral. Then, to launch again from stop, to first.
Adjust the clutch cable to fully engage the clutch with a little slack.(a little less than a 1/4 inch at the lever.). Adjust the clutch with the engine at it´s working
Welcome aboard.

To make it short. Point 3. is where your "power" has gone.
Additional air causes your Motor to run lean. That is very bad for the engine because what is running lean, is running hot ! Valves, pistons and cylinder can be destroyed and will be, if the situation prolonges.
I guess that your friend has few expereance with engine and carburator mechanics/physics

To Point 2. The rider is not supposed to shift to first...while coasting to a stop. Coast to a stop shifting slowly from 5`th to second and neutral. Then, to launch again from stop, to first.
Adjust the clutch cable to fully engage the clutch with a little slack.(a little less than a 1/4 inch at the lever.). Adjust the clutch with the engine at it´s working temperature. (ride for 15 to 30 min before. adjusting.)
I hope your Motor isn`t damaged already seriously.
Hey Pete, thanks for getting back to me so quickly!! You definitely seem to know what's going on. A few quick questions:

My understanding was that the carburetor and butterfly valve within had almost exclusive control of the amount of air going to the engine. Since the gash is before the air reaches the carb, it doesn't seem like it would affect the AFR, instead just providing a route for unfiltered air to get in (which probably isn't the best either haha). Help me to understand how a break in the air line before the carb causes it to run lean.

Is there a way to know if my engine has been permanently damaged? What should I be on the lookout for?
 

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The original Intake-tract creates an environment which lets through a certain amount of Air. A relative underpressure is created. Only a certain amount of Air can enter. For this amount the carburator is designed.
For more air intake it needs to be rejetted to not run lean.

For better understanding you can try a experiment. use a straw and try to breath through it. then remove the straw and open your mouth to breath. you can tell yourself in which way you can breath better, or in other words can take in more air.
The carburator needs a certain underpressure to work correctly.

Yes, it´s more dangerous having an air leak, between cylinder and carburator, never the less, with additional air on the airfilter side it still runs lean.

The slider-valve in the venturi tube opens up by trying to equal the suction-pressure in it. That it does acccording to the amount of air that passes the venturi tube. The pressure above the diaphragm is always a little lower to open up the slider.

In short: repair the air leak...and your Motor will run normal. (if not already damaged beyond immediate repair.).

Please understand that i´m trying to help,not to belittle you.
However, I´m into two things:
Working with motorcycles (Motors, carburators, Ignition systems and more.) and photography.

I´m better with Motorcycles. :)
 
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Welcome! I am a relative newbie but i have had 3 rebels in the last year- all bought non-running for $400 or less- and issues all were with the carb. You mentioned carbs as in plural- do you have 2? I will respectfully disagree that the problem lies in the air filter, seems unlikely that your issue is there. I will defer to the sages on the forum though😀 if it was my bike i would do a compression check, check for air leaks around the carb intake by starting the bike and spraying carb cleaner around the intake boot, then trying another carb if you can find one cheap on eBay or craigslist. Again though, i will bow to the superior knowledge of the forum gurus. As far as the grinding noise- i would have no clue but can’t you just change your shift habits and not go into first until stopped? reminds me of the old joke- “doc, it hurts when i do this” doc says “don’t do that”🙃
 

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Mahonri clearly stated that there is a leak/gash in the rubberboot between carb and airfilterhousing Definitely and obviously a defect. Before doing anything else... he should repair that !
 

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The Motorcycle Safety Foundation basic rider course teaches that the bike should always be in the gear appropriate for the speed the bike is moving. That way, the rider could accelerate immediately if the situation called for it. At a stop, the rider should be in the "ready" position; bike in first gear, left hand pulling clutch lever, right hand on throttle, left foot down, right foot on brake, eyes checking mirrors for approaching vehicles that may or may not stop, ready to accelerate into the pre-planned escape route.

Shifting into first at speeds above about 20 mph will result in a loud "clunk" from the transmission, and should be avoided.

The service manual calls for 3/8" - 3/4" of free play at the end of the clutch lever. See post number 7 here: Bike feels like its slipping gears. HELP! | Honda Rebel Forum
 

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That´s what i wanted to say.

Shifting into first at speeds above about 20 mph will result in a loud "clunk" from the transmission, and should be avoided.
 

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ok, i am all kinds of wrong and you should disregard my non- educated advice. my recency of experience may be suspect since i got my cycle license 50 years ago…and most of my wrenching has been on cars….so i will keep my opinions to myself…anyway, sorry and good luck!!
 

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I misread and mis-diagnose problems frequently. Not a problem, others are going to correct me and make sure the poster gets good info.
 

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@mark.

You are not all wrong. But diagnosis goes step by step. Alas, if something is obvious it should be taken care of first.
However, if the problem persists, what you have written is "Gold".
 
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Discussion Starter · #13 ·
Alright here's the update. I replaced the boot but to no noticeable effect :((. I now understand I'm not supposed to be downshifting to first until I'm close to a stop, thanks guys.

Any other ideas of what the problem could be? I'm just baffled because I'm getting full power in gears 1-4, getting to the full redline on each one. Then I shift to 5th, the RPMs drop, and it feels like the accelerator pump or something else in the carb is releasing less fuel than before. Why could that be? If power is fine in the other gears, why would shifting into 5th change anything?
 

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85 CMX 250C, 82 GW Remember that you are invisible, treat all others accordingly. Avoids Road RAGE!
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I'm wondering if your clutch is not adjusted correctly. How much play do you have on your clutch lever between when it is disengaged until you feel it starting to engage?
 

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Discussion Starter · #15 ·
I'm wondering if your clutch is not adjusted correctly. How much play do you have on your clutch lever between when it is disengaged until you feel it starting to engage?
I'm definitely new to riding, but I feel like the clutch is fine as is. I usually pull the clutch with 2 fingers and it fully disengages easily with a bit of free play on the end. In the same way, when it's closed there's a bit of free play before it starts disengaging.
 

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Sounds ok, but 5th is usually the 1st one to start slipping. Just my two cents.
 

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I'm with Emil, and would think the clutch is slipping, except that you say the rpms go down in fifth, even with throttle. When the clutch slips, speed goes down but rpms remain high. I don't have a clue other than it might be a carb or electrical issue.
 

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Getting to the point #4, rust on the exhaust pipes.
I've found that using 00, then 000, then 0000 steel wool cleans it without scratching. The 0000 polishes the chrome very well too. Afterwards there are a few different types of protective polishes that are more resistant to heat. The main manifold pipes I only clean, I don't use polish on them.
 

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Discussion Starter · #19 ·
Alright, update time again. I've pulled apart the carb again to see if I've missed anything. The diaphragm on the top and accelerator pump look good, as does everything else. The only thing I can't get my head around is the accelerator pump nozzle. To be clear, the brass piece that juts up into the air side of the venturi. I can't blow through it, nor shoot carb cleaner. I've stuck a wire through, but obviously it can't go all the way because the outlet is through the side. What's the best way to unclog this?

Side-note: despite this, it seems like the accelerator pump is still working. I know this because I didn't hook it up right the last time I cleaned the carb, and when I fixed it there was a noticeable change in acceleration.
 

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Soaked Karma had a pic showing how to test the accelerator pump with the carb off the engine, but I can't find it.
 
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