hmmwv15

Well, I have this strange stumbling problem with the idle on my 250. (86 rebel 250) What it does is when you first crack the throttle open slowly, it will start sputtering/stumbling and sometimes die when you try to give it more gas. When you crack it open fast, no problems at all. When it warms up it will stop sputtering where it does when it's cold, but when you steadily crack the throttle it gets around 3-4k rpm's and does the same stumbling. When you are cruising along at higher rpms the bike runs great, but when the bike is turning low rpms it hesitates. (hopefully I explained it good enough)

So far I have cleaned out the gas tank, rebuilt and cleaned the ever loving crap out of the carburetor and ran it through several cycles in our ultrasonic cleaner, and added just a smidge of seafoam to the gas. I have also adjusted the valves. Brand new spark plugs and air filter. I checked the timing but I'm not sure if I understood which mark was supposed to line up. I'll re-read the clymer manual and try it again.

I believe it may be the carburetor (even though we really cleaned the crap out of it...) or possibly faulty timing components. Reason I say the carburetor is because of those tiny passages right near the butterfly valve, we weren't sure if they came completely clean or not. The fuel filter I installed looks clean. One thing I did is put regular gas in it, and I was told later that I should have put premium in it. Not sure exactly how critical that is.

I'm sure we can get it figured out at work sooner or later, after all I work with several guys over twice my age that have been building engines for a long time and they are very good at what they do. We just haven't had a slow day for me to bring in my junk to tinker with it. I was just curious to see if anyone else has had the same problem. Never hurts to ask! Thanks!

__________________

Guba

You don't need to put premium gas in a Rebel. You can if you want, but the cylinder diameter is too small to really need it. I've been running 87 octane just fine. In my opinion, using premium is just throwing your money away. My truck however, requires a minumum of 89 octane. I run the correct octane rating for the type of engine.

As for stumbling, my bike stumbles too when it's cold. It does sound like it's carb related. To clean those passages you need a small piece of soft copper/aluminum wire to push through there. You didn't say if you used the old seals/gaskets or put in brand new. If you reused the old ones I would spend the money to get them replaced.

__________________
Some days beer tastes good...other days beer tastes better!

'07 Rebel 250 26,000 miles

flitecontrol

Always a good idea when cleaning a carb to disassemble it as much as you can.Blowing it out with compressed air (wear eye protection!) is also good. Look in the FAQ and Wrenching sections of this forum for a carb diagram and carb cleaning pictorial on the 250. I'm assuming the choke is turned off once the motor warms up?

__________________
I'm keepin' all the left over parts. I'm gonna use 'em to build another bike!

2001 Rebel 250, 1989 Vulcan 750
Putting your bike info in your signature helps others help you!

GGrider

Hi Guys, I find my cmx450 sputters and stumbles ALL the time. It's very disconcerting so I tried higher octane gas.. seemed to help but could have just been the previous low octane fill was bad. She stalls when coming to a stop even after riding for over an hour. Have run carb cleaner once or twice and use Marvel Mystery oil in every tank fill. Brand new plugs and fresh oil change, have new tires ordered-went with CST's after all the hoorah- new cdi unit installed last Fall, and found the throttle cable was stuck causing the high revs from earlier post.. fixed that so no issue there.. If I keep the choke on just a titch..it runs better but really don't want to do this or think it's the best of plans for the long run! Seems like it just isn't getting clean delivery of fuel. Have an inline fuel filter, just haven't install it yet because I'm concerned it may contribute to fuel starvation issue. Have checked the tank and the petcock filter.. all clear. Takes a long time to warm up too but that is partly due to not running all winter and cool temps. (50's and low 60's shouldn't be causing an issue though...) That's all I can think of for now.. sure hope there's a fix for the issue because kinda scares me to be out on the highway going 55+ and feel a loss of power and as if I'm running out of gas when I have a full tank! any help is much appreciated!GG

__________________

Fridgitator

Is your tank vented, or does it have a vented cap? If the tank is not getting enough air, it will starve the engine of gas. Easy enough to check if you have two keys. Let it run until it sounds rough, then crack the cap and see if it sucks air and runs better.

__________________

hmmwv15

We didn't have a small enough wire to run through, but we used a helluva lot of carb cleaner and compressed air. We actually used several different cleaners. Also ran it through one of our machines like I said, basically it uses hot soapy water and ultrasonic pulses to break things loose. I believe it's close to what they use to break up kidney stones with, or it's what I have been told. I didn't get new gaskets, but those are next on my list. Choke is all the way off when I ride it. I believe the tank has a vented cap, when I am moving the bike around after a ride (engine off) I can hear the tank "venting". But I'm not sure if it's working the way it should while I'm riding. I don't think that's the problem though. It seems like if that were the problem the bike wouldn't want to run at all. It runs, but it's just got a strange miss/skip to the engine. It seems like if I had faulty ignition components it would skip all the time. I'm leaning towards fuel delivery.

As of now, I have been riding it around trying to wind it up to see if I can blow some crap out of the carb. I put a little more seafoam in the gas and filled it up with premium today. Since it's such a small tank and I'm used to a truck, spending a bit more on fuel doesn't bother me all that much. I'll see how it does. I've got the carburetor adjusted to where I think it runs the best at. (idle speed and mixture) I'll probably end up taking the carb back off and try to clean those passages better. I need to shop around for a tool that has those things, we have one but it wasn't long enough to really clean them out.

By the way; I read up on the carb before taking it off, just so I would have an idea about how far to disassemble it. I'm not afraid to take stuff apart! It's the getting it back together that gets me.

__________________

cagie

Have you checked to see that the choke cable is actually moving the plunger? Is it seating properly?

__________________
Comments contained in my posts are not intended to cause physical or psychological stress and are mearly my two cents worth, and in this economy, that's cheap!
87 CMX250C 'the Pygmy Pony'
87 CMX450C 'Black Lithium'

flitecontrol

If you haven't already done so, disassemble the carb completely, soak it in carb cleaner according to the instructions on the container, and blow out all the orifices with compressed air. Protect your eyes from cleaner when you do this.

Having to ride with the choke on is usually an indicator of a dirty carb, and no, it's not good to do it. Running higher octane gas is counter productive; don't do it.

It's possible there is crud in the tank that is making its way to the carb. If the tank is rusty, clean it. Install the inline filter after you do and [U]before[U] you clean the carb. Add a few ounces of Sea Foam to every third tank or so and you shoud never suffer from a dirty carb again!

__________________
I'm keepin' all the left over parts. I'm gonna use 'em to build another bike!

2001 Rebel 250, 1989 Vulcan 750
Putting your bike info in your signature helps others help you!

hmmwv15

I checked the choke cable when I had the carb off. When it was out the plunger seemed to move up and down with the cable the way it should. I assume it is seating properly, but I can't see through aluminum. (I don't know of a way to check that either)

__________________

cagie

You'd be checking the seat for any obstruction when you have the carb apart for cleaning. You'd also check to make sure the cable is not binding anywhere when you have it all back together, no sharp angles, etc.

__________________
Comments contained in my posts are not intended to cause physical or psychological stress and are mearly my two cents worth, and in this economy, that's cheap!
87 CMX250C 'the Pygmy Pony'
87 CMX450C 'Black Lithium'