: Loosing power/dying above 5,000rpm
04-17-2002, 10:46 PM
Having problems running above 5k rpms and need some ideas...Heres a brief scenario of what occured.
Bike starts fine, idels fine runs fine even at high rpm but after about 1/4 to 1/2 mile at high rpm (call it about 6k to 8k)the bike starts to sputter like theres no fuel and dies. Pull over, choke it, starts right up and idels fine wait for five or ten minutes and repeat process all over again....Operating temp drops wickedly from 180 to 200 after warming up down to 120 or lower when running. Have Mikuni jet kit and Yosh RS3 full exhaust on it, carbs have been checked and are all good, fuel is good. There is a 35% leakdown in #3 cylinder which is not good but I'm trying to figure out why it runs like a rabbit on meth for a while then dies. The average temp lately has been about 28 to 40 degrees (F). I'm thinking fuel petcock (the rubber gasket) or filter but wanted to see if anyone else has any ideas
04-18-2002, 09:04 AM
Sounds sort of like what mine is doing. I would check your signal generator output. You are supposed to put out .4 Volts minimum and have between 50 - 200 ohms resistance across the generator. You can check it by pulling the plug off the CDI unit which is mounted under the front seat. With a multimeter connect the red wire of the meter to the black wire in the plug. Connect the black wire to the green wire in the plug. Set the meter to peak voltage and turn the engine over for a few seconds. You should see a peak voltage of .4 or greater. Next set the meter to Ohms keep the wores hooked up the same way and see what you get for a reading. SHould be between 50 - 200 Ohms. There is also a plug that is running along the frame between the rear seat lock and the main part of the frame you can unplug the connector there and double check your readings.
The only other thing I can think of would be the throttle position sensor. I am not sure how important this is on a carbed bike but on EFI cars it is very important. Hook the multimeter to the two outside pins on the sensor and take an ohm reading (with the throttle closed). Should be between 3.5 - 6.5k Ohms. Next check the two pins closest to the front of the bike. With the throttle wide open you should get a reading that is 76% of the first reading. If that is not the case than you need to adjust the throttle osition sensor until you get your 76%. It wouldn't hurt to slowly open and close the throttle while you have the meter hooked up to the two pins closest to the front of the bike. Watch the meter and see if you get a a smooth change in resistance as you open and close the throttle. All this is much easier if you have help. I got my girl to turn the bike over for me while I was checking readings. I can say if this will find your problem but, it will help to narrow things down. I have eliminated the TPS on mine and currently have a post about my signal generator findings. I hope this helps and is understandabe. Let me know how it turns out. Your fix may be mine as well.
04-19-2002, 12:18 PM
A loose coil wire perhaps? A friend of mines did something similar and all it turned out to be a loose coil wire.
04-20-2002, 09:17 PM
I checked my coils and my number 3 coid was wacked. I Checked spark and it fires ok from what I can see. I think I may be a coil going out under hing rpm demand. Ima going to put the bike back together ( I pulled the cam cover to check the timing) and run it till it dies and see if the coil goes bad again. I ill let you know if if it does. Good luck in your search of an answer.
04-24-2002, 10:37 PM
Ok, so far nothing short of heavy medication has worked....have found that electricals are good and no problems. One interesting thing, there are two lines from the tank to the engine, one runs straight to the carbs the second (smaller) runs to/from (depends on point of view)the engine. I can see the point of fuel draining from the one going to the carbs when you pull the tank off, but the second one (I'm assuming a pressure line) also has fuel draining from it as well when its pulled off? Sounds stupid to be asking the question but my expertise is mostly medical not mechanical, should this be happening? I pulled the fuel pump off and checked it and air flows through both ways, could this by part of my problem?....A tear in the gasket perhaps causing fuel to go back into the engine (explaining an initial fuel smell when the oil was drained) and then the bog down and death of the engine at higher RPM's as the engine uses all the fuel in the floats and isn't able to fill them because there is a reduced amount of fuel being pumped in? Other ideas???
04-24-2002, 11:01 PM
may not be, but I had this symptom on a cage once
It would run fine under no load, and at low revs, as soons as you accelerated hard, it would pull great, then stumble.
Turned out to be a semi-blocked fuel filter.
I wonder if this is the fuel pump ???/
the line running to the engin from the tank is a vacuume line. When the bike is started the vaccume in that line opens a valve to let the fuel flow to the carbs... If gas is comming out of this line when removed the valve at the tank is shot and needs to be replaced. Otherwise fuel will leak slowly into that cylinder making it run rich... And not letting the valve open all the way causing the bike to run out of gas...
04-24-2002, 11:10 PM
That's what I was thinking as well but after tearing the fuel pump out and cleaning it through found nothing blocking the filter. Just the gas in the vaccum line from the engine.
No it's not the filter it's the vaccume controled petcock valve not opening...
04-24-2002, 11:14 PM
JET, thank you much for that. Most everyone I've talked with locally has FI'd bikes and werent sure about the problem. Unfortunately that gasket couldn't be totally checked because I couldn't break it totally down to inspect the whole thing but that's where my suspicions laid as I contemplated drinking myself into a stupor in a vain attempt to obtain knowlege through the form of a vision....thanks again..
Lots of luck to you! Let us know if this resolves the problem!
04-25-2002, 12:03 PM
Yea I would check the petcock like jet was talking about.. I had a old gs1000 that did the same thing.. We took out the vacum control and I would just have to turn the fuel off when I shut the bike off... but never again had a problem with it.
05-21-2002, 03:28 AM
Just a little note to all that provided input. It was the petcock, after replacing it everything went smooth as silk. Thanks again to all who gave ideas on it.