Bike cuts out after redlining

[darealestspigguh]

Well fellas, i'm starting to think I'm not gonna find much professional help on this forum, unlike most other auto motive forums.  But that doesnt mean i'm giving up.  I have yet another problem, it has to do with redlining.  I can tell that the engine is limited to 9000 RPM even though the tach clearly marks the red at 12000 RPM.  This could be dangerous if there were no limiter.  However, the limiter is unlike any other that i have experience with.  Rather than bounce off the redline, it seems to cut the fuel completely for a couple revs.  If anyone can tell me what kind of limiter this is and wether there's a way to remove it, i would appreciate it.  The reason this is important to me, is that i don't know what is causing my bike to shut off while dropping from high revs in 3rd and 4th. For instance if i redline it, it wont cut out , but when i let the throttle go, it wil drop all the way to 0 as if there is no gas.  i can start it back up if im still moving just by letting out the clutch, but tit seems like it is starved for fuel sometimes until i give it a little throttle.  I have tuned the carb to run just fine, but i'm slightly sceptical about my carb float height since i eyeballed it as opposed to using a caliper like i should. After about 10 minutes of running, the problem seems to stop completely but i'm curious as to whats causing it so i can be sure it wont get worse or become more frequent. 

[darealestspigguh]

hey, i'm starting to think i could have put a restrictive filter on my bike, but i don't see how it could be any more restrictive than the stock air filter. It is a K&N breather for amuch larger angine, but it fits right onto the end of the venturi (carb).  However, it is only about 3-4 inches long which i think could be too short, does anyone know a rule of thumb for engine to filter size ratios?  The mixture doesn't seem excessively lean or rich when i examine the plug either. Someone help, too many possibilities.

P.S. has anyone seen the youtube video where the guy is doin donuts on the 250?  That 250 must be on crack because the only way i can get my rear tire spinning like that is to push it up against a parking stone and let it rip HARD.

[kristifer]

Once I upgraded my spark plug to an iridium, it seemed to rev up higher without shutting off.  When I had it poorly gapped, it would cut out at lower rpms, but something similiar.  So I might try either regapping your existing plug or upgrading it to an iridum and having it gapped at .025" (thats what mine is at).  I don't know about how restrictive the filter/airbox is, I still have the stock intake system and have not changed any carb settings.

[Icey-ZS250GS]

Read somewhere in this forum its best not to change out the air filter.

[darealestspigguh]

Read wrong, however, as with any bike (any engine i know of) when you change the amount of air going into the engine, you must compensate by adjusting the fuek mixture, on a bike, this process is known as jetting.

[darealestspigguh]

btw guys still no confirmation on the redline, which im pretty damn sure aint no 12000 like the tach states. Mine gets to about 8500 and seems to bounce quite nicely off of something, rev limiter or otherwise.  In gear it's another story alltogether.

[kristifer]

I got mine up to 9k with no probs the other day.  Getting too cold to really go out riding, so it might have to wait until next spring.

BTW, Any new info with the SigmaSix rejet kit?

[darealestspigguh]

in gear i've been to about 9 pushing 10, but it didnt sound too good for my engine either. 
The jet kit is inching along like a snail.  Bright side of living in miami though is its 60 degrees right now in the middle of winter, i could ride with no sleeves if i wanted (and i dont). 
But they've sent me another two main jets, they do not replace your pilot jet because they say i isn't necessary and they give you instructions for about every DIY dirtbike mod you can think of.  It's up to you if thats worth the money or not. 
As far as knowledge about our bikes, i doubt they have any.  The printout they gave me of specs which they included in their Jetting Guide was from some chinese site i remember visiting when i first got my bike.  My original main jet was a 132, i am currently on a 150 and can't seem to get a smooth lower end without a popping mid-range and vice-versa.   
I generally get the best results with the needle clip on the middle notch (3rd) but i also find that putting the spacer on top of the clip as opposed to under it seems to yield better throttle response.
Again, this is my first time jetting, for all i know, i'm doing everything wrong. 

[z250gs]

That jet sizing sounds like you're getting way too big for the mods you've done so far. Those mods probably mean you only want to go up one or two jet sizes to get best fuel/air mix.  I think the Teikei jets go up in size from 132 to 135 to 138. In theory I think a 138 would be max to try. Though the 150 you used may not be a Teikei jet, in which case the sizing rule doesn't apply. The problem is that jets by other carb manufacturers don't correspond to our jet sizes exactly and the thread pitch can be slightly different,( but theywill fit at a pinch).  For example, MIkuni carbs jet #132 won't be the same as a Teikei #132. A TEikei #150 jet though is about 5 or 6 sizes up from the stock 132.

Anyway,  sigma should be the best ones to sort this out as I haven't tried rejetting yet. Hope you can get it all sorted soon.

[darealestspigguh]

That jet sizing sounds like you're getting way too big for the mods you've done so far. Those mods probably mean you only want to go up one or two jet sizes to get best fuel/air mix.  I think the Teikei jets go up in size from 132 to 135 to 138. In theory I think a 138 would be max to try. Though the 150 you used may not be a Teikei jet, in which case the sizing rule doesn't apply. The problem is that jets by other carb manufacturers don't correspond to our jet sizes exactly and the thread pitch can be slightly different,( but theywill fit at a pinch).  For example, MIkuni carbs jet #132 won't be the same as a Teikei #132. A TEikei #150 jet though is about 5 or 6 sizes up from the stock 132.

Anyway,  sigma should be the best ones to sort this out as I haven't tried rejetting yet. Hope you can get it all sorted soon.

 I see, well the jets deffinately dont resemble the factory jets, but they fit.  They could be some of those relpacements you mentioned.  The stamp has an AB on top and the size on bottom.  Why would the larger jet cause this leaner condition, i thought a larger main jet made your mixture richer? And if i deffinately felt an improvement overall using the 150, should i not then keep climbing?  As any jets i order should be free, i will order based on your advice, its far better than my own... I should probably also mention that the new jets seem to sit lower in the bowl.  however at Sigma's tech's sugestion i raised the floatbowl level.  I subsequently fouled an iridium plug, but other than that it seems to run better, when it's rich the ride seems much smoother, less jumy. What do you think???

[z250gs]

My guess is that the techy thinks you are going up too much with the jet sizes and has suggested u try raising the float level (did u write float bowl in error?) to get the mix a bit richer. If you fouled the plug up though you're already too big on the main jet (-if the floats level is now right-). Do you think you've got the floats right now? If so, you need to start the rejetting over again coz your floats were set too low prior to starting the rejet.
At this point it might be worth checking for small air leaks around the carby eg inlet and outlet clamps. Minor leaks may be causing extra air to be introduced into the system and leaning the mixture out. Can be checked by spraying a good layer of wd40 around the joints while the engine is running and listen out for any change in revs which would indicate a leak has been temporarily plugged by the wd40.   
Otherwise, keep going with the techs suggestions.

[darealestspigguh]

ok, but i've been there before, smaller jets and higher float levels, none of it worked.  I'm mainly trying to get my bike to redline without cutting off and to have a consistent redline.  I've asked what other people have gotten their bikes to and i've heard as high as 11,000.  I cant even get near that without it surging vary badly and very consistently at the same rev in each gear respectively. i'll try a new clamp around the intake flange to better seal the carb, but i have a small amount of oil that looks to be comming from the valve cover (exhaust).  It's prbably just a bad o-ring, i dont have my tools so i havent checked it out, but could that be causing the issue?   

[kristifer]

You should try these forums

http://chinariders.net/modules.php?name=Forums&file=viewtopic&t=9198

and

http://chinariders.net/modules.php?name=Forums&file=viewtopic&t=9165

It talks about the carbs off of the Dual sport Sierra 200GY2.  It has pretty much the same carb except for a bore difference (28mm sierra vs 30mm 250gs). 

Haven't tried putting in the new jets yet, but for less than 20 bucks for a few jets, I'm gonna try it.