My bike has started 'choking' at around 8-10k RPM usually in either 2nd,3rd or 4th gear more often in 3rd. It doesn't happen all the time but is almost guaranteed to happen once on every ride. It tends to happen earlier on in a ride although not always.
The feeling is hard to explain as I am a relatively inexperienced rider and haven't had any problems on any other bike that I have ridden. It is the same feeling as when your bike runs out of fuel and you have to switch over to reserve although it is a drop in power and then it picks back up immediately. Sometimes it is a 'double stutter'.
Does anybody have any idea what the problem is? I have had my carbs flushed/cleaned, synced/setup again to check whether that was a problem but that hasn't fixed the problem. One person told me that it is just typical of carburettors that high in the rev range, but I'm not sure.
Any thoughts? Cheers.
Three easy-fix possibilities...
1.) Carb hose routing. Carb hose must be routed between the airbox and the battery, out of any wind. If wind catches that hose, you'll have symptoms of fuel starvation.
2.) Vapor lock. Caused by clogged gas cap vent. Diagnose by pulling over when problem occurs, open gas cap, and listen for a whoosh sound. If you hear a whoosh, clean your gas cap vent.
3.) Fuel starvation from the frame Petcock. Diagnose by turning the Petcock to prime when issue occurs. Prime bypasses the vacuum, which had been known on occasion to cause some fuel starvation at WOT on some model years.
- Bboy
Quote from: BockinBboy on March 03, 2013, 07:18:33 PM
Three easy-fix possibilities...
1.) Carb hose routing. Carb hose must be routed between the airbox and the battery, out of any wind. If wind catches that hose, you'll have symptoms of fuel starvation.
2.) Vapor lock. Caused by clogged gas cap vent. Diagnose by pulling over when problem occurs, open gas cap, and listen for a whoosh sound. If you hear a whoosh, clean your gas cap vent.
3.) Fuel starvation from the frame Petcock. Diagnose by turning the Petcock to prime when issue occurs. Prime bypasses the vacuum, which had been known on occasion to cause some fuel starvation at WOT on some model years.
- Bboy
This was my issue at one time. I just left it in PRI and forget about ut
This would happen to me on the freeway with my '93. After trying many things, I changed the spark plugs. Pretty sure the ones installed were the ones it rolled off the line with.. Bike runs like a champ now.
I wonder why 8-10k rpm so much - and in 3rd gear?
That seems excessively high RPMs considering 11k is red line.
Peak power is around 4-7k RPM (can vary depending on how your bike is set up).
6k rpm in 6th is 60 mph. I can't think of being above 8k rpm except a few times passing cars on a highway and going 70 with acceleration to 90.
Just wondering?????
More info would be good here. Does it only do it under hard acceleration, or only when on the highway for long periods of time?
You mentioned it happening mostly early in your ride... early as in when the bike is still cold? May be a jetting issue.
8k in 3rd gear wow, mines around 4k.
Side question, does it hurt to run Petcock in prime for long runs? Just wondering on this encase i need it down the road.
Remember that PRIME only bypasses the vacuum valve thingy. When the vacuum opens up the petcock, it is the same as prime. Gas is flowing. The floats in the carbs control the fuel flow when the bike is running.
The only difference between prime and ON or RES is prime lets fuel flow with no vacuum (i.e. bike is off).
As long as the carbs are working, prime is perfectly OK.
remember: when the bike is running, the vacuum, opens up the fuel flow same as if in prime.
Quote from: adidasguy on March 04, 2013, 11:21:05 PM
Remember that PRIME only bypasses the vacuum valve thingy. When the vacuum opens up the petcock, it is the same as prime. Gas is flowing. The floats in the carbs control the fuel flow when the bike is running.
The only difference between prime and ON or RES is prime lets fuel flow with no vacuum (i.e. bike is off).
As long as the carbs are working, prime is perfectly OK.
remember: when the bike is running, the vacuum, opens up the fuel flow same as if in prime.
Great info there, learn something new every day.
The diagram in the link below talks about how a vacuum petcock works:
http://wiki.gstwins.com/index.php?n=Upgrades.Petcock
I would leave the stock petcock alone. Keeping in PRIme is OK AS LONG AS your float needle and needle seat are in good condition. If they leak, then you will get fuel in the oil sump and that is no good. :nono: Had an old 1982 with this problem. Gas went every which where when I left it on PRIme with the bike not running. Replaced float needles, everything A-OK!
Fuel starvation at 8-10k sounds like a pinched fuel hose or house routing issue. It could remotely be ignition related since that's a lot of juice being generated to power your bike at that RPM, but I tend to think that it's fuel starvation. IF you have a fuel filter installed, remove it.
Had this same thing happen on my 1982 once. EVERYTHING pointed to Fuel Starvation. When all fuel parts were replaced, the CDI Ignition box went out. Turns out it was the ignition all along when run to its limits.
Start with fuel first. It's the most likely culprit.
Just to chime in with an update, the issue seems to have become less prevalent rarely happens at all. Not sure if it is the warmer starts or what.
Also the main reason for high revs in 3rd/4th is getting onto motorways (done twice daily) and to be honest my revs were more likely 7-9k. The power on my bike seems to stay until about 8-8.5k
Quote from: stuart576 on June 09, 2013, 09:10:50 AM
Just to chime in with an update, the issue seems to have become less prevalent rarely happens at all. Not sure if it is the warmer starts or what.
Also the main reason for high revs in 3rd/4th is getting onto motorways (done twice daily) and to be honest my revs were more likely 7-9k. The power on my bike seems to stay until about 8-8.5k
That "getting onto motorways statement" makes me think, does it always seem to happen when you are getting on the motorway in the same ramps? I know my bike will starve out if I am lower on fuel on this particular ramp on my way to work that has a right handed curve, it always happens in the same spot about 1/2 mile from the ramp. I assume it is because all the fuel sloshes to the other side of the tank.
I'd have to check that, no bends on any of the motorway ramps I use, they are downhill though, will check soon as bike is currently out of action: http://gstwins.com/gsboard/index.php?topic=64560.0 (http://gstwins.com/gsboard/index.php?topic=64560.0)