Float height doesn't make sense??

[Jakobi]

Is it only going from closed to WOT? Does it still do it when rolling to WOT?

 

[Davehuge]

Hi Jakobi, it still won't pull WOT when rolling the throttle open steadily.

185 Main Jet arrived in the post today, so will fit it tomorrow and see what happens. Will also do a couple of plug chops.

I'm beginning to suspect I have an air leak, making preparations to replace the left side crank seal, will have to order a flywheel puller.

Thanks, Dave.

 

[swazi_matt]

Or borrow one from a ktm friend who has one

This is a smart way to remove the seal as well
https://m.youtube.com/watch?v=iQwulUnPxew

 

[Davehuge]

Fixed!

I'm happy to say I've now fixed my carburettor setup.

Just to recap... after adjusting the airscrew and needle position, it was running really nice from ZERO to 80% throttle position, but it just wouldn't pull or rev cleanly at Wide Open Throttle.

When I bought the bike, the float height was set at 20mm. I reset it to 16mm which seems to be the recommended height, but the carb overflowed at the slightest movement of the bike. I've now set it to 18mm and it's working well.

Originally the carb was fitted with 175 main jet, I thought it was running lean at WOT so I tried a 180 and then a 185 but it was clear the problem at WOT was worse. Clearly I had misread the plug after the plug chop and it was actually rich.

I fitted a 170 main jet and that solved the problem, it now pulls and revs cleanly at WOT, the bike's a missile!

All the best, Dave.

 

[Joginen]

I got the same problem as u had. I tried also 175-182 mj, and always bogging on WOT area, absolutely poor. Now on 170mj is clear and powerfull. Don't know why my bike also likes so small mj, but only thing what matters is that it runs fine.

 

[Davehuge]

Hi Joginen

Yes, I also have to run with my needle on the top clip position (leanest) but it does run really nice like that!

All the best, Dave.

 

[Jakobi]

Sometimes on the older bikes the needle seat actually flogs out and then allows a bit more fuel to come up past the needle at any given position.

 

[Davehuge]

Sometimes on the older bikes the needle seat actually flogs out and then allows a bit more fuel to come up past the needle at any given position.

Yes, a good point, that sounds feasible.

Cheers, Dave.

 

[Jakobi]

When I say needle seat, I mean the actual orifice that the needle runs through (emulsion tube?).. not the seat that the float needle seals against.

Another possibility is that the choke circuit is allowing fuel to pass.

 

[Davehuge]

Hi Jakobi

Yes, I understood that's what you mean't, I call it the needle jet.

Yes, when I stripped the carb I checked that the choke closes fully and seals nicely.

Thanks, Dave.

 

[Jakobi]

That's the one Dave!

 

[BlackScreener]

Glad to hear that Davehuge. But my bike still run like crap in WOT area. I changed float height back to 16 mm but it does not make any difference. It won't rev at 178 jet, only on 176 when engine is very hot but it isn't arm stretcher (still flat on top). I will try to fit a new plug. When I bought that bike with 250 cylinder it had similar problems with high revs, but N3EG and 178 jet helped a little. With 300 cylinder it's even worse.
Jakobi, can CDI cause that kind of problems?

 

[Jakobi]

I'm sure something electrical could cause such issues. Either coil breaking down at higher revs and missing, or something with the ignition curve in the cdi.

But you'd be at a point where I imagine you'd need access to someone elses bike to start swapping bits to determine what it is.

 

[BlackScreener]

I checked stator, it seems OK. Ignition coil also gave good readings according to others users. I fit new NGK BR8EG plug, now after playing with float height (16mm) 176 jet gave me max 8700 rpm on stand and when I ride. After hard ride plug seems to be white. I have no idea what is going on with this carb.

 

[Davehuge]

If you've run the spark plug long enough to get a colour on it and it's white, then it's sounds like you're dangerously lean.

I suspect you may have an air leak somewhere on the engine, sucking in air and making the mixture lean. Only way to really tell is by pressure testing the engine, but you need some simple kit to do that.

Could be left side crank seal, if it was right it would suck in gearbox oil and smoke a lot. Leak on reed valve housing? Perished/split carb rubber? Damaged cylinder base gasket?

Good luck, Dave.

 

[BlackScreener]

Thank you very much. I forgot to check air leaks... Seals are new. Also reed valve rubber and carb rubber are new. But when I move piston at TDC I hear strange air leak. I thought it was normal. I think I have got loosened cylinder nuts.

 

[Davehuge]

When you move the piston at TDC maybe it's just air leaking past the piston rings that you hear, which of course is normal.

But of course it could be air being sucked in somewhere?

Good luck! Dave.

 

[BlackScreener]

I tightened cylinder nuts to 35 Nm and changed jet to 178. Now max RPM is lower, on stand 8700 and 7800-8000 on WOT.

 

[Davehuge]

Hi BlackScreener

If you have an air leak, that's 'if' because we are not sure, tightening the bolts may not fix it. You need to remove the cylinder head and barrel to inspect it.

From my experience, revving the bike on the stand doesn't tell you much, it's how it reacts riding it under load that gives you feedback on what's really happening.

From what you're explaining it sounds like some over problem rather than your carburetor, so you need to start from basics.

All the best, Dave.

 

[BlackScreener]

Mayby new s3 2013/14 cylinder don't work very well with ignition curve in the old 2001 cdi. I will try to change timing on stator.

EDIT:
I changed timing at the stator, when advanced (1,5 -1,8mm) bike gains low and middle power but top and max RPM stays the same. When retarded (2 mm), bike lost idle and max RPM to 7200.