Stutter on Highway; Intermediate - Honda Rebel Forum
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post #1 of 43 Old 03-01-2017, 10:23 PM Thread Starter
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Stutter on Highway; Intermittent

Hello all,
This is my first post here and I don't post in forums often. I've been having issues finding anyone talking about the specific problem I'm having. Maybe I don't know what to look for? Sorry if this is covered in another thread.

I ride a 2001 Rebel 250 with about 28,000 miles on it and I live in Orlando FL. I'd never been on a motorcycle until last September when I got my certification and bought this one. The bike operates fine at all times except for when I take it on the highway for more than 10-15 min. Once I've been sustaining 65-70MPH for 10 to 15 minutes the engine will begin to stutter and slow down. It seems like it starts to misfire as it stutters and lurches. I've tried both open and closed positions for the choke and switching to the reserve fuel (both of which function as they normally should when I need them) but there is no change in the issue. However, the issue goes away as soon as I let off the throttle no matter what speed I'm moving at (even in the 70's). If I immediately attempt to get back up to ~70MPH the bike will continue to stutter but if I drop to 60-65MPH it lessens or goes away completely. The issue will occur for no more than 1-2 minutes if I slow down and once gone, it will allow me to return to 65-70MPH for another 10-15min before coming back. This cycle of running smoothly, stuttering, then running smoothly, then stuttering with 15 min gaps in between has me completely stumped.


Any ideas on what might be causing this?
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post #2 of 43 Old 03-01-2017, 10:49 PM
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Welcome to the forum kylewt.

That does sound like an interesting problem, and one that may be hard to find because of the intermittent nature. I guess it could be a carb or fuel problem, but it seems too repeatable for that. More than likely something is heating up after running at WOT for 15 minutes. Spark could be breaking down, or timing fluctuating. It could be lots of things like the spark plugs, plug wires, coils, ignition pulse generator, exciter coil, or ICM, and probably some more that I have forgotten.

I will think about how I would go about troubleshooting this, and meanwhile maybe someone will chime in who has experienced similar problems.
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post #3 of 43 Old 03-02-2017, 07:30 AM
 
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Another possibility might be a pinched vent tube allowing a vacuum to develop in the fuel tank under heavy loads. You can test for this by removing the fuel cap and covering the opening with a couple of strips of duct tape with a small gap between them to allow air to enter. Take it for a run and see if the problem is still there.
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post #4 of 43 Old 03-02-2017, 09:44 AM
 
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I would strongly consider checking the fuel tank vent line as mentioned above. The way you describe the problem, it's as if the tank is creating a vacuum. At this point the fuel has been leaving the tank faster than air has been coming in. Once you slow down and give it a chance to catch up, it recovers and you go again. In a gravity feed design, sometimes this problem can be exacerbated by a low fuel level in the tank.
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post #5 of 43 Old 03-02-2017, 10:23 AM
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Good point guys. If you have a spare key, you can test it, while underway. Leave the spare key in the tank cap, and when the problem occurs, just reach up and pop the tank cap. The problem should disappear almost immediately while you are still under throttle.

You can also test the line by blowing air through it. I recommend adding air to the tank using your hand or a rag for a seal, and checking the end of the tube under the bike for airflow. If you do it the opposite direction you may end up with whatever is plugging it up in your fuel tank.

Dirt daubers are good at plugging the ends of open hoses.
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post #6 of 43 Old 03-02-2017, 10:52 PM
 
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I agree. The fuel tank vent seems like the most likely culprit. Try riding it with the tank about half full, without the fuel cap in place and see what happens. If that solves the problem, then you need to remove the tank and check/clean the vent. There are a couple of other possible issues, but that is by far the most likely. The vent is probably not completely plugged, and after the bike sits for awhile, air gets back into the tank. After riding for several miles at high speed, it creates a vacuum in the tank, which interrupts fuel flow to the carb.
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post #7 of 43 Old 03-03-2017, 07:13 PM
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Welcome to forum . Does sound like a vent problem



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post #8 of 43 Old 03-10-2017, 02:53 AM Thread Starter
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Thank you so much for the suggestions!

I have a spare key so I tried popping the gas cap and it did not resolve the issue.

The plot thickens though because today it happened much quicker than normal, the very first time I've had it happen so soon at WOT.
I sat in traffic generated by an accident in ~81 degree weather for about 20 min before making it to the highway (total running time about 30 min.) and when I got on the highway I immediately hit ~70 and stayed there for 2 min. at best before the stutter. I reduced to ~60 and road stutter free for another 20 min on the highway.


2001 CMX250C
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post #9 of 43 Old 03-11-2017, 09:09 AM
 
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If its not a venting issue, then I'd suspect temperature sensitive electronics. Your last post noted a connection between the air temperature and the length of time it took to see the problem. It may be either the ignition pulse generator or the ignition module itself (or possibly a poor connection in those circuits.

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post #10 of 43 Old 03-11-2017, 11:13 AM
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The idling while sitting in traffic for that long will overheat a bike, and probably explain why it happened so much quicker this time.

What confuses me is that it recovers as soon as you let off a little. If it is truly temperature dependent, then it doesn't seem that it would completely recover just by backing off slightly. It seems to also have an rpm component, or maybe it is vibration dependent. Does it happen only in 5th, or if you downshift to 4th is it still sputtering at high rpms?

These are the hardest problems to troubleshoot due to the intermittent nature, and this one is particularly difficult, because it seems that you can only troubleshoot it while going 70 mph at WOT.

Something is breaking down due to temperature and load or rpm or vibration. Figuring out what that is without just changing out parts is the difficult part. It can also get pretty expensive if you don't find it quickly. A buddy with a Rebel to swap parts with would be the best scenario for finding it without replacing good parts, but you don't list your location.

I would start with all electrical connections. A huge percentage of electrical problems are wiring and connection related. Service manuals for EFI systems often claim that 80% of EFI problems are wiring or connector related. Disconnect everything, clean with electrical contact cleaner, be sure connections are tight, or squeeze female connectors to make them tighter, coat with silicon dielectric compound, and reconnect tightly to insure good connections. Look for chafed wires, bare spots, broken wires, or any other bad spots in the wiring harness. Just wiggling, pulling, pushing, tugging, and moving things can sometimes either fix a mysterious gremlin, or make it fail completely so you know what to replace.

If that doesn't do it, hopefully someone has had some similar electrical gremlins who can at least point you toward which parts may be most likely to start with, or maybe have some more tests you can run. With no other info, I guess I would start with the cheapest things first, spark plugs, plug wires, etc.
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