250cc flat spotting

[Woodsy]

GSX250S - I'm in afew different minds with this problem, If i ride the bike at a higher speed for a little while it will start to flat spot, initially i thought the engine was going to seize so i grabbed the clutch, the engine died straight away and i pulled over, it was hard to start but was turning over freely.

It happened again today after i hit a bump in the road, The plugs are a good colour i was thinking maybe it was running out of fuel with the higher load? After i manage to get the bike started again the problem goes away. I thought it may be clutch related as the clutch will slip with higher revs but that just needs adjustment but the revs drop dramatically they dont rise so i'm thinking fuel prob.

The carbs have been cleaned out twice.

Its really bugging me and i'm at my wits end with this bike, i just want to fix it, sell it and buy something else.

 

[tkent02]

If i ride the bike at a higher speed for a little while it will start to flat spot, initially i thought the engine was going to seize so i grabbed the clutch, the engine died straight away and i pulled over, it was hard to start but was turning over freely.

The problem occurring as you ride at higher speed for as while would indicate a clogged gas cap vent. Test it by riding with the cap loose to see if it runs correctly. Not sure about your gas cap, the vent on the larger bikes is the keyhole.

 

[Woodsy]

Ok i'll check that today and get back to you.

 

[Woodsy]

Checked the cap and all the vent holes looked clean, took it for a ride this afternoon and it was fine, although i will take it up the same road i had the problems and see what happens, its weird that both times the bike acted up after i hit a bump in the road.

 

[Woodsy]

Ok problem is still there, Could the prob be to low float level?

 

[2Wheel_Kungfu]

Possible damaged or bent float? Fuel petcock or hosing gummed up or clogged on rust?

 

[bobthebiker88]

if you have a vacuum petcock, check the vac line, if its cracked or failing, it can cause similar symptoms through fuel starvation.

there are many issues that may be culprits.

 

[Woodsy]

I'll double check the fuel hoses, it has an erratic idle now too. I'm abit over these carbs!!! Why doesnt someone make a kit for the Mikuni BS30SS carbs!?!??!

The next bike i get i'm making sure they do carb kits for lol

 

[SqDancerLynn1]

Idle could be carb sync ? Try running it on prime to see if it still does it

 

[Woodsy]

hmm i'll see if i can borrow a carb sync gauge..

 

[Woodsy]

Ok, pulled the carbs down today and found some brass stuck in the pilot jet, just a little fleck of it but enough to half block the jet on one carb.

Also the O-ring on the float needle housing is completely hard and was not sealing at all, when i drained that carb it had alot more fuel in it than the other one.

So i'm going to find an O ring for it and see if that fixes the problem.

 

[Guest]

Aaaaaah now that sounds promising! I haven't chipped into your thread yet because I had no idea.

However, I thought I recalled you redoing your carbs already, but maybe I'm wrong and you hadn't done it yet?

 

[Woodsy]

Hi Pete,

I did pull them down and clean them out, i didnt put any new parts in because they are way to overpriced from Suzuki and you cant buy kits for these carbs, But when i pulled them down last time the o-ring was sealing, this time the seat just fell out. So i dont know what has made it harden that quickly.

Going to put it all back together today and take it up the same road i had problems with, going to double check the float heights as well, HOWEVER.....

I have 2 workshop manuals here for this bike, one is a genuine Suzuki manual and the other is a Haynes? Its the same one thats on bikecliffs website and they both give the same float height BUT where they measure them from is different, the Suzuki one measures to the very top of the float where the arm and the float join, The Haynes one measures to the top of the float itself, which is 2-3mm difference.....

 

[Woodsy]

Ok i put everything back together and its worse! I have a clear fuel hose from the tank to the carb and when i rev the bike the fuel level in the hose drops alot, maybe 2 inches or more could this maybe be the cause? Long straight doing 60kph and accelerating the vac just cant keep supply up to it?

If so what controls the vac?

To make things worse, the clutch is slipping now but hopefully thats just an adjustment.

 

[landshark]

Does your fuel tap have a prime setting? If so try using it on prime and see what happens. Also is the vacuum hose and nozzle all clean?
I havent read this whole thread yet, but is it a new fuel tap?

 

[Woodsy]

The tap doesn't have a prime on it, the vac hose and nozzle are spotless, i checked them when i had the carbs out... its really bugging me.. lol

 

[landshark]

OK, Make a temporary fuel "tank" from a bottle straight into the carbs, rev the sh1t out of it and see what happens, if nothing is wrong its probably your fuel tap.

 

[Woodsy]

will have to keep it at a constant rpm for a while as the bike revs fine at stand still, i'm trying to borrow a petcock so i can test it on the road as a new one is outta budget at the moment... something for me to do tomorrow i spose

 

[Guest]

Quick one... which manual did you set the float height from? I will never ever trust a Haynes spec again after stripping a thread in my crankcase because they put the torque spec as twice what is should be.

Go by the Suzuki manual or a Clymer if you can find one.

I hope you get it sorted soon so you can enjoy the ride!

 

[Woodsy]

This time i took it from the Suzuki one, But it is extremely close to just having the floats rest on the body of the carb.

I have to take it for a 40min ride this morning so i'm going to check afew things before i head out to see if i can isolate the problem... coz its ****ting me now.. lol

I missed a ride 2 weeks ago with a Suzuki Katana group because of this prob, I JUST WANNA RIDE!!! lol