Heres one for the pros......or anyone??

Ballin on a Budget

Ballin on a Budget

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Acceleration problems.....need advice

So now im startin to pull my hair out! Im not a complete newb with two-strokes or anything and im very mechanically inclined, but im having an odd problem with tuning my carb that I cant for the life of me figure out......

It all started when I put on my FMF exhaust. Basically its a straight pipe back to an FMF powercoreII silencer. My carb has never been perfect, but always manageable untill this.

HERES THE ISSUE - If I ride it normally it will start to bog out at about 1/2 throttle. This problem is fixed by putting the choke half on, and then it runs PERFECT (I know just need to richen the mix as its getting to much air in the mix right?) However with the choke on, it will completely stop accellerating at 46 KM/H (26ish MPH). Now if I take the choke OFF when it dies out at this speed, it runs perfect again and pulls all the way up to 32 MPH like it used to.

I just cant be taking my hand off the bars every few mins to turn the choke on and off when im riding to keep this thing riding good. I figured these symptoms mean that I just need to richen up the mix up to 3/4 throttle, so I dropped the needle to the lowest setting.....still does it. And because at high speed it runs great with the choke off, my main jet is fine.......(I have tried the carb needle on all settings to no avail)

HELP!!!! Any suggestions would be appreciated. Only mods are an NGK plug, the exhaust and a free flow intake
 
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every 2 stroke i have messed with seemed to be quite sensitive to tuning , and never seemed to stay that way through out their life span, constant fiddling was required , use a bigger jet , it sounds lean...
 
The slide needle controls the fuel delivery from 1/8 throttle to 3/4 throttle.
The fuel jet controls the fuel delivery from 3/4 throttle to full throttle.
If you dropped the needle by raising the c clip to the next higher groove that reduced the volume of fuel delivered.
You need to raise the needle by installing the c clip to the next lower groove. That will increase the volume of fuel delivered.

It sounds to me like you have a mid throttle lean condition. Messing with the clip position may work out well, but you might also to need to use some fine (300 grit or thereabouts) sandpaper to make the needle skinnier too. I would remove the c clip and put the needle in a drill motor and spin it while pinching the sandpaper over the needle. Sand the needle evenly and do not keep the sandpaper in one spot too long or you will sand a step into the taper of the needle. That said, sometimes a step placed carefully in the right spot on the needle is necessary too. Skinnier needle = more fuel delivered and still allows for adjustment by changing the c clip position. Also it is better to sneak up onto the best diameter of the needle by sanding then testing again and again rather than sand it alot skinnier right from the start. If you mess it up, new needles are cheap enough to order another one, no big deal.
 
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Thanks....I actually have had the best results with the clip in the lower most position (richest setting) because it runs best up to half or 3/4 only with the choke half on which kinda led me to believe it needed more fuel, (like you said a lean condition). I think the main jet is fine cuz at WOT it runs great with the choke off.

Basically what it seems like is that up to 3/4 throttle it needs more fuel but the clip is at the lowest setting so what if.....

before I attempt to file the needle, (as i have never done that before and am a lil leary to ruin the needle) could I try filing another notch slightly lower on the needle to add more fuel that way. Can this be done?

My needle is the older NT style that only has 4 notches vs. the newer ones which i think have 5.

Finally....instead of all this trying to add more and more fuel to richen the mix, what about decreasing the amount of air going into the carb instead to get the same effect? I dont have an airbox or anything on the carb, just an open setup with a thin nylon filter with very little resistance. Maybe this is causing the issue too....i dunno im gonna play around some more tomo.
Thanks for any suggestions guys...much appreciated.
-Dan
 
Installing the factory air filter may very well be all it needs.
Running with no air filter or a piece of nylon pantyhose as a filter will indeed increase the air flow, but at the cost of accelerated engine wear as all the fine dust and dirt in the air will get ingested inside the engine.

I did not mean to literally file on the slide needle, in fact I recommend not doing that.
It really should be done with the use of a drill motor and fine sand paper.

As for cutting a new notch in the needle, if you can do it accurately and cleanly, go for it. Sanding the needle would be easier though.

Try re-installing the air cleaner first though, you may be surprised.
 
Hahaha sorry I meant sand the needle, not file. Ha ha i was thinkin about filing a notch while I was typing that. Ok well im gonna try the factory air filter today and hopefully that will richen up the mix enough. I also found that my sparkplug connection in the boot had broken off when I took it off, so im guessing that it was cracked which would seriously hurt the spark energy too so I picked up a new NGK plug boot.

If the filter doesnt work, im really startin to think that maybe because this all started when I added the exhaust, that maybe its as simple as there just isnt enough back pressure in the system ( you can see in the pic that its just a straight pipe w/ a silencer) so I may try adding a plug/stringer to the FMF pipe. I have a feeling that the airbox might be the cure tho.

I cant thank you enough for takin the time to help me out with your suggestions. Ill keep you posted!
-Dan
 

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Alright heres an update just so maybe someone can benifet from my tinkering if they have a similar issue in the future, I solved the poor running problems and my bike is runnin the best it prob ever has!

Heres what fixed it for me.... Since it was still running rich with the needle on the bottom notch, I tackled the problem from the other direction and put my factory airbox and filter back on. This actually caused it to 4-stroke a little tellin me itr was actuall a bit TOO rich now, so I raised the needle a notch to lean out the mix at 1/2 throttle....and....TA-DA! Runs good and more importantly CONSISTANTLY all the way from a stop up to 34 MPH.

Just for good measure I drilled a small hole in the top of my fuel cap as I felt that it wasnt venting proporly, and I also replaced the spark plug connection with an NGK one with a much better connection. I know these motors are finiky especially when they are modded, but with a bit of time and tuning, the first ride running good is a great feeling!
-Dan
 
Good to hear it, Dan.
I've experimented with different air filter designs and modifications to the stock one but I've found that it is the best option for me @6K above sea level. With the stock, undrilled filter housing all I've ever really had to do is play with jet size and 'C' clip setting to get the most from my engines.
Some will say to drill holes in the filter housing. I disagree. Opening it up too much caused problems much like you were having. My engines run strong and consistant through all RPM ranges and I use the stock filter on all my bikes.
Tom
 
Ya thats what im finding as well, Tom. The velocity stack, and other styles of high flow intake systems ive tried have difinately shown some improvements in power, but it always seems to be a boost in only a narrow RPM range, and the rest of the RPM range suffers and is difficult to tune. The factory airbox/filter combo it very consistant all the way from idle to 30+MPH. I guess with more signifigant mods like porting and such, then it would warrant a free flow system, but for now with just a few mods I have done, I think im gonna leave the factory stuff on. Speed is great but theres somethin to be said for reliability as well!

I do have to say tho, even with the frustration of tuning a motor that isnt runnin right, every time I finally solve a problem, its one more thing I have learned and can now pass that knowledge on to help others that may have a similar prob in the future, and thats what the forums all about!
-Dan
 
Other then changing the studs, all of my bikes are stock (other then a boost bottle and the clutch roller). Nothing extra and all run great from idle to WOT. I really can't complain on a $125.00 engine. You all say what you want, these Chinese junky engines are doing me right.
 
Al.Fisherman said:
Other then changing the studs, all of my bikes are stock (other then a boost bottle and the clutch roller). Nothing extra and all run great from idle to WOT. I really can't complain on a $125.00 engine. You all say what you want, these Chinese junky engines are doing me right.
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Amen, Ron.
Anyone who has ever had dealings with high performance engine knows the limitations of drivability. I always get a kick out of the guys with high lift, long duration cams, extremely low rear gears, tunnel ram intake manifolds and massive carburation then wonder why they get 4MPG and the engine is screaming it's innards out at 55MPH. :)
You don't have to stay dead stock but over modification and drivability through all ranges just don't mix well.
Tom
 
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