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Discussion Starter · #1 ·
Yesterday I was riding my Yzf750R at high speed WOT in top gear, when somewhere near top-speed the engine started acting funny. It felt and sounded like I had simply ran out of gas, but the tank was full. As I was slowing down the engine continued to sputter on and off until I pulled the bike over. The engine continued to sputter for another 15 seconds or so when I was stopped, but started running normally again after that. When I pulled away leaving, I gave it a good run through the gears, and the engine ran like nothing had happened. I have never had anything like this happen before, and haven't been able to recreate the problem.

Does anyone have and ideas what the problem could be? Bad gas maybe?

Thanks,
Devon
 

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Still defying gravity...
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Yesterday I was riding my Yzf750R at high speed WOT in top gear, when somewhere near top-speed the engine started acting funny. It felt and sounded like I had simply ran out of gas, but the tank was full. As I was slowing down the engine continued to sputter on and off until I pulled the bike over. The engine continued to sputter for another 15 seconds or so when I was stopped, but started running normally again after that. When I pulled away leaving, I gave it a good run through the gears, and the engine ran like nothing had happened. I have never had anything like this happen before, and haven't been able to recreate the problem.

Does anyone have and ideas what the problem could be? Bad gas maybe?

Thanks,
Devon
If you were near the redline (top speed as you say), you may have introduced yourself to your rev limiter. The rev limiter is your friend.

Do a search...
 
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my guess is water in the fuel had that same problem with my sled could be wrong though but its easy to drain the fuel which could be bad 2 then see if it happens again
 

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All the suggestions above are good possibilities. Also could be a rusty tank sending bits of crud into your carbs or clogging up your gas (line) filter. When you pull over the shit settles down and/or moves on and the thing starts up again. Had this problem with an older Yamaha. Thought it was bad gas till I found out the tank was shedding lots of rust particles.
 

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Discussion Starter · #6 ·
If you were near the redline (top speed as you say), you may have introduced yourself to your rev limiter. The rev limiter is your friend.

Do a search...
I am pretty sure I was a grand below the indicated red-line. I'll check out to see when that cuts in though.


All the suggestions above are good possibilities. Also could be a rusty tank sending bits of crud into your carbs or clogging up your gas (line) filter. When you pull over the shit settles down and/or moves on and the thing starts up again. Had this problem with an older Yamaha. Thought it was bad gas till I found out the tank was shedding lots of rust particles.

What is the best bet for dealing with a rusty tank if that is the case?
I had to go through another tank of gas before I got home so if it was
bad gas, then I should be done with the problem.

Check the vent on your fuel cap. The YZF was brutal for not breathing.
I suspect that this is the problem as running at WOT for more than a few seconds(which is what I was doing) is going to (attempt to) evacuate a substantial amount of fuel from the tank. Would make sense to me for a vaccuum to build up and cause the fuel flow to stop. It would also explain why that was the only time it has ever happened as during hard acceleration there isn't enough time to build the vaccuum. How do I check to make sure the vent is operating correctly?

Thanks for all the help guys
 

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What is the best bet for dealing with a rusty tank if that is the case? I had to go through another tank of gas before I got home so if it was bad gas, then I should be done with the problem.
Go to Canadian Tire and get some STP "Gas Treatment". It has methyl hydrate in it that gets the water out of your tank if you have any. Use about a 1/4 of the bottle. That is more than enough. Pour it into a full tank. If it isn't full measure accoordingly. Give you bike a good few shakes side to side to get the stuff mixed and ride out the tank. Next tank just to be anal pour in another 1/4 of a bottle. In theory you could have more water than the methyl hydrant can bond to but unlikely. This will knock water off your list of issues.

Willing to bet its rust. Even if you peer into the tank you may not see rust patches on the inside of the tank but the rust could well be there.

Assuming the issue is rust. Your first quick fix is an "inline" gas filter that you can check after a few tanks to see if rust has collected. Once installed you take apart the line and knock the filter against a container or white rag that you can see any rust particles. The filter will prevent it from getting into the carbs and fouling things up and save you a bunch of money in getting the carbs pulled apart and cleaned.

That should get you going.
 

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Fastronaut
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Do you still have an air box and filters? If it's not the vent like Mr 5 said I'd say it sounds like airflow at high speed is drawing away from the carbs instead of feeding them. Then there's all the other things too, dead bee in a float bowl and so on.
 

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Discussion Starter · #9 ·
The Rev Limiter idea doesn't explainthe poor running after pulling over.

Sounds to me like there was a starvation of some sort in the fuel air mixture when the flow rate at its peak flow/demand (WOT).

As suggested, inspect the tank for rust (this is an older bike). Also do a fuel system cleaner. Are the plugs old? Fouled due oil burning etc? How about the air filter, clean and breathing right? What about a carb synch, how long has that been?

(ps I had that Genesis engine in my '85 FZ750 - sweet motor BTW.)
I just put in new plugs a couple of weeks ago. Along with that I had the carbs cleaned and synched. That probably points even more so to a problem with the tank then I suppose.
 

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I suspect that this is the problem as running at WOT for more than a few seconds(which is what I was doing) is going to (attempt to) evacuate a substantial amount of fuel from the tank. Would make sense to me for a vaccuum to build up and cause the fuel flow to stop. It would also explain why that was the only time it has ever happened as during hard acceleration there isn't enough time to build the vaccuum.
Engines make zero in. of vacuum at WOT.
 
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