Engine cuts out in high RPM?

As my bike reaches 9.5 to 10k rpm under 3/4 to full throttle, the engine seems to cut out for a moment. It abruptly stops producing power for a second which has made me back it off and take it easy. It started doing it this week and I'm curious what this could mean? I't is a 27 year old bike though, so I probably shouldnt wind it up that much anyway...but I cant help it

 

rev limiter going weird?

 

Interesting, mine does too. I just thought it was characteristic of the power band drop off cause it's allways been that way. Now Imma have to camp out and wait for possible answers, maybe I need to look at something too..................

 

Them Brighton boys know how to party and drink, plus how to brawl and bar-fight...i worked on a project with a team of them and had a great time. Of course i might have been listening to metallica too, so you know the rest...


Is this something new? Was it running higher revs last week, month, year,... but now this week it won't?

What's the rev limit on that V4? What does it do when you hit it? (cuts the spark off). Warm it up good and go for a ride in 2nd or 3rd gear to find out. Hold the throttle steady when it cuts and see if it comes back on when the revs drop below the redline, and cuts off again as the revs hit the limit--that would be normal rev limiter response.

If this is a new problem and it were a real electrical issue then it wouldn't heal itself, but it could be that the ignition pulse counter gap has opened up due to loosening of the adjuster screws or some other reason such that it works okay at low revs but can't generate the necessary voltage at the higher revs.

The coils might be leaking at the higher revs (old insulation breakdown and high-voltage punch-thru). Run it on centerstand at night in a dark place with the tank off and look for sparks and arcs around the coils to the frame. Or better yet borrow a megger and ohm out the coils for insulation resistance to chassis. but this would manifest as a progressively getting worse sort of issue that will eventually fail completely such that it won't run.

 

Im not sure if this is "new" but its the first time I've noticed it happening. I have revved it higher in the past. At first I thought my clutch was slipping but the tach dosnt shoot up when it happens, it stays stationary or wiggles. The rev limit is 12k and thats also where the redline starts. I'm not reving it that high so I dont think I'm hitting the limiter. like I said I've only seen it happen when under hard acceleration, in which case feeling it cut out is startling. The last instance of this I went hard shifting 2-4 and experienced it consistently in each gear.

I will take it for a ride on the next sunny day and run it to the 9.5 - 10.5 range gently and see if it behaves odd. Thanks guys.

 

Alright so I tried running up to 10k slowly at about 1/4-1/2 throttle. The engine hesitated exactly at 10k but I kept on it and it smoothed out and the needle pushed past to 11.
I did this a few more times and it stopped hesitating completly... however, it still breaks up if I really get on it. at 3/4-full throttle it still breaks up at 10k rpm very consistently.

I'm not really worried about it anymore. I'd like to know why this is happening, but there really is no reason for me run it past 10,000 rpm anyway. I'm just going to leave it alone. kennybobby I will look for sparks and such soon. I'm going to be replacing the plugs and air filter and will have the tank off for that task.

 

it seems more like a carburetor issue than an electrical problem. Of course you also need to try it at wide-open throttle. the 1/4 throttle test would be running on the transition ports, but the 3/4 test would be on the main jet and the fat part of the needle. The WOT would be main jet plus the needle taper toward the tip.

So from my magic crystal ball point of view, i predict that your main AIR jet is clogged and it is running too rich on the main circuit causing a bog down in the power. When you ran it up on the transition circuit several times you said the problem went away because it was getting a good mixture from the pilot circuit, but when you went wider throttle onto the main circuit the problem was worse. At WOT it might be even more apparent.

If you were running too lean there would be backfiring and popping in the exhaust, and you haven't mentioned that was occurring, so that is why i think it is a rich condition power bog.

You might be able to do a plug chop from 9500 rpm to determine if you are running too rich or too lean, or better yet get some dyno time with exhaust gas analyzer. If it doesn't bother you then not to worry, but a good carb cleaning would fix it.

Here's some porn that might help show you wher it's located:
http://vfrworld.com/forums/1st-2nd-...r-circuit-identification-porn.html?highlight=

 

It's essential to clean/probe/poke wire through the side holes on the main jet holder tube when doing a carb clean.

 

Thanks guys maybe that is the problem. It certainly gets worse at wot. If I have the carbs off in the future I will take a look at it. Last spring I cleaned out the jets but maybe didnt do a proper job. It is running lean though and does pop when the throttle is shut off. It's been that way as long as I've owned it.

 

So I replaced my clutch plates and springs today. Refilled the oil and went to buy gas. I put half a bottle of injector cleaner in the tank and then rode it for awhile. I did not encounter the engine issue. Full throttle, half throttle, 10,000rpm whatever I threw at it, nothing odd happened. It ran smoothly and of course the clutch feels fantastic :redface:. No Idea what "solved" the problem though.