Not GS but Suzuki tech question....

[vwbeatle1214]

1993 DR650 single cylinder dualsport. it runs out in 1st and 2nd till about 3/4 throttle then starts running rough. In third and fourth it will make it to 1/2 throttle before breaking up. In 5th it will make it to 1/4 throttle before doing it. Bike has new plugs, new coil, new battery. Its done this since i bought it and the longer i ride it gets worse till the point where it dies and won't restart till it sits awhile. it has a Cobra exhaust , i'm not sure if its jetted for it. any ideas where to go next? The bike should pull 100 mph but i'm lucky if it'll do 50. I've tried over at the DR specific forums but haven't gotten any response so i figured i'd check with the GSR gurus.

[focus frenzy]

gas tank vent is most likely semi clogged up and the bike is developing a vacume in the tank keeping the carb from getting enough gas to keep up with demand.

you can also check the fuel inlet screen on the petcock if it is clogged it will cause that problem.
looking at the diagrams for that bike, it shows that it has a automatic petcock, that could also be the problem, runnin with the lever set to prime would tell you if that is the problem.

my money is on the gas cap vent being clogged and or sticking.

[flyingace]

I'm a little leary of the fuel starvation hypothesis. Why can the bike build more RPMs in the lower gears? Seems like RPMs would be limited regardless of the gear you're in.

The question I would ask is if the bike revs OK when stationary. In other words does the engine need to be under a load to see the symptoms?

[vwbeatle1214]

It does do it in neutral but nowhere near as bad, also i tried riding with the gas cap off, no change, and i also dipped and sprayed my carbs, no change, and after about 15 minutes of riding it just shuts off. after 10 minutes of kicking with the gas on prime it starts and runs like crap. tommorrow it will start just fine and do the same routine.

[rphillips]

Because the more load there is on the engine, the more fuel (throttle) takes to get the same rpm. In neutral it may take only 5% throttle to get the tach to redline, 1st gear may take 20% 4th maybe 60 or 70% throttle & in 5th wide open throttle may not get to redline. If the same 20% throttle got the bike to redline in 5th as it did in first, wide open in 5th would be somewhere in the neighborhood of 672 mph.

[flyingace]

So if the throttle is wide open on a bike going uphill at only 2000 RPM, is it using more gas than a bike on a flat surface going 5000 RPM with 1/2 throttle? In other words, does more throttle always mean more gas is being consumed?

Anyway, I don't want to hijack this thread. I'm probably wrong anyway.

Fuel starvation is easy to fix - check the petcock, the fuel filter, junk in the tank. You should be able to open up the line to the carbs and get a good flow on prime. Then look at your air filter, a restricted flow of air will also cause higher RPM cut-out. Make sure there's plenty of air and gas.

After that, it could be lots of things.

[Billy Ricks]

Might try running valve clearances and do a compression check. The bike may have never been jetted right for the pipe either.

[vwbeatle1214]

The air filters clean the valve clearences are good and its got great compression, i'm thinking the jetting is off. I'm not really worried if it is the jetting, the part that really worries me is that it just shuts itself off like a kill switch every time i ride it. It makes me feel like theres an electrical problem.

[DaveDanger]

Definitely sounds to me like it's starving for fuel. And truly, the higher the gear you're in, the more relative throttle it takes to keep it rolling. It sounds like it's absolutely drying out the carb float bowls and shutting off, then s-l-o-w-l-y filling back up to the point that it'll crank and run again. Whether the fuel petcock is flowing freely or not, I'd bet there's some sort of restriction in the fuel delivery.

[SqDancerLynn1]

Try wrapping some ducktape around the air filter to choke it & see if it runs better. What does the plug look like ?

[KEITH KRAUSE]

So it never runs right but runs even worse as the motor heats up?
It also just "shuts off" when you ride it? Hot only I assume?
I assume you've checked for good spark as soon as it has shut off? Quick and easy to check that.
If the spark's good, then check for an intake leak.

[vwbeatle1214]

Plugs a good even gray/tan , I keep meaning to check for spark when it dies but everytime my mind goes straight to "survival mode" like i'm 5 miles from home get it started or your gonna be walking. I'll check it out tomorrow though. I't doesn't even have time to get real hot after 15 minutes i can still touch the head, its warm not hot.

[vwbeatle1214]

has spark when it dies, and i sprayed the intake boot, no change. I'm feeling a little frustrated.

[KEITH KRAUSE]

Well, if you see a good blue/white spark as soon as it shuts down, I'm going with the intake leak.
Spraying around the manifold doesn't always expose a leak. Only way to be sure is to inspect the manifold and any o-rings it may have. I'm not familiar with that model but all possible intake leaks need to be positively checked. On most models it's a pretty simple job.
You didn't mention any other symptoms but a classic intake leak symptom is a bike that idles around 1,000 rpm (approx) when cold/warming up, but then the idle increases significantly once hot. Since some owners have a higher than normal idle (because it's set incorrectly) this can disguise this symptom. To test yours, be sure the idle is set around 1,000 rpm's cold/start up and if it then rises significantly once warmed up, you for sure have an intake leak. An intake leak will lean out the mixture and cause fuel starvation.

[vwbeatle1214]

Mine idles at 800-1000 rpm cold and never changes . I'm going to do a full carb rebuild and rejet and see where that leaves me.