Help, Spit and sputter at top end

Tripnosis02

New Member
Feb 2, 2009
3
0
0
Pennsylvania
if i give my bike full throttle it spitts and sputters, i'm guessing there is too much gas, and not enough air, but i dont understand why my motor would just be like that when my buddy's engine runs fine and everything is the same between them. can anyone help, also my clutch slips and i have the flower nut on the the disk as tight as i can get it, i feeel like buying a new engine and just starting over.
 

ibcnya

New Member
Oct 29, 2008
220
0
0
Concord NC
1.Heavy mixture
2.Intake leak
3.Wrong plug gap
4.Bubbles in the float bowl
5.Running outta fuel up top, need to drill the jet
6.Petcock not flowiing quick enough

These are all common problems, good luck
 

jasonh

New Member
Jun 23, 2008
1,590
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37
Longmont, CO
What makes you think it's too much fuel? Have you checked the color of your spark plug? Do this before making any changes to the mixture.

What oil/fuel ratio are you using? Is it a fresh mix, or has it been sitting a while since you mixed it? (a month or two?)

Check for air leaks by spraying carb cleaner or WD-40 around the intake while the motor is idling. Any change in idle will suggest you have a leak.

Check the gap of your spark plug. People use a wide range of gaps here. Anywhere from .018 to .040 I've heard. Would be wise to replace the plug with a good NGK plug (B5HS or B6HS) and a good 7mm automotive spark plug wire.

As for the clutch, try pulling the lever in and locking it before adjusting the flower nut.

Your buddy's motor is not actually identical to yours. Quality control on these motors varies wildly from motor to motor.
 

Norman

LORD VADER Moderator
Jan 16, 2008
2,605
2
38
68
pampa texas
the main jet controls wide open throttle, most are around 0.026 dia. and not all throttle slide needles are the same most measure about .070 dia. at the fat end where the c-clip is, and 0.068 dia. at the sharp end.
Measure yours and your buddies and see how they compare to get it a little richer at w.o.t. drill it 0.027 and then try it these are very sentive to the changes and if you mess it up solder it shut and redrill.
I kind of cover this in the classic post on the carb teardown.
When I tell you to drill it find out what dia it is to start with and deside if you need it richer or leaner don't use a power drill get a pin vice drill that is used by hand, I have a picture of it in the post. The pin vice can be bought at a hobby shop the drills can be bought at some better auto parts shopes or speed shops. Some of the main jets are drilled very sloppy if you find it that way solder it shut and start with the 0.026 dia bit and go from there. My measurement here were in thousands of an inch and not metric.
Norman
 
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Goat Herder

Gutter Rider
Apr 28, 2008
6,248
12
38
N.M.
Check for good flow of fuel the screen clogs in the tank easily. last if the screen fell apart the fuel cock will always be clogged These ch gotta breath too a restrictive air filter will hold it back. Mabey run for a quick jont without it . Just guising gotta try some simple stuff first? Keep us posted.
 
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glacknoid

New Member
Oct 22, 2008
184
0
0
robbinsdale MN
I've had a similar problem. My four stroke honda rev's up in neutral fine but when in gear with a load on a.k.a, me, in the process of accelorating it will hesitate like it's running out of gas so I have to accelerate slow to avoid that. I did Kreem the inside of the tank. Could too much epoxy like Kreem sollution have gotten into where the fuel comes out and restricted the flow. How fast should gas flow out with proper flow. BY the way stupid me Kreemed the tank with the gas cap on and plugged the venting holes which caused other problems I fixed by getting a new cap. When I kreemed it, where the fuel valve screws on, I put a mini condom meant for covering the ends of open calking tubes to keep the kreem from flowing out the hole.

Thanks
Glacknoid
 

Tripnosis02

New Member
Feb 2, 2009
3
0
0
Pennsylvania
i moved the clip to the top and its runing a little better, but at top speed it still like sounds terrible, it's deffintaly not enough air for the filter right? what about tuning the carburator? my friend is arguing with me saying that the idle screw controls the topend which is ridiculous right? when you have it full throttle the idle screw isnt even touching anything anymore. right?
 

Norman

LORD VADER Moderator
Jan 16, 2008
2,605
2
38
68
pampa texas
the idle screw controls idle speed only and it is done by the idle screw raising the throttle slide take it apart and look inside and you will see how it works at wide open throttle the main jet is what controls the fuel flow bigger hole in the jet allows in more fuel( rich) smaller hole(leaner) in the main jet allows less fuel. if it sounds like a 4 stroke at wot my guess is you need to solder the main jet shut and go to a smaller size hole. You will need to find out what Dia. the hole is now in the main jet and then decide if you need to go bigger or smaller in size.
Some of my carbs had sloppy drilled holes so I soldered them shut and re drilled them. Look at the classic posts for more info on how to drill and size the main jet.
The throttle slides metering needle will control the fuel flow at low to almost wot and the taper will determine the fuel mix. Most needles measure 0.070 dia up at the clip end of the needle and 0.68 dia at the tip not much of a change but when you start messing with it it can and will change the fuel from way lean to way too rich and if you mess with it and mess it up the best bet is to replace it with a needle with the right measurements, standard setting on the needle is the e-clip in the #2 slot from the fat end of the needle.
Norman
 

Prasinos

New Member
Dec 1, 2008
257
0
0
CT
Make sure all of your wires are well insulated. try disconnecting your kill switch wire. If any of your wires are close to touching, running the engine at higher rpms might be producing enough voltage to short out your engine intermittently causing sputtering. This happened to me after fastening an upgrade to my bike using a hose clamp, the clamp cut away just enough insulation from the kill switch wire that at high rpms a spark could jump through the bike's paint to ground. It would only sputter at high rpms and ran great otherwise.

hope you figure it out soon
 

Norman

LORD VADER Moderator
Jan 16, 2008
2,605
2
38
68
pampa texas
spit and sputter sounds like too rich/too big of a main jet. air filter (what little there is) I don't think will cause it( unless it soaked in oil) but if your choke lever vibrates to the choke position it will cause it to spit and sputter.
with it wide open put on the choke it should almost or will kill the engine if it don't and runs better then you need to open up(drill it bigger) the main jet.
swap out carbs and see how your will run and put yours on your buddies if it works better run like h3ll
with it and don't be friends anymore. Just kidding.laff
Norman
 

ibcnya

New Member
Oct 29, 2008
220
0
0
Concord NC
the idle screw controls idle speed only and it is done by the idle screw raising the throttle slide take it apart and look inside and you will see how it works at wide open throttle the main jet is what controls the fuel flow bigger hole in the jet allows in more fuel( rich) smaller hole(leaner) in the main jet allows less fuel. if it sounds like a 4 stroke at wot my guess is you need to solder the main jet shut and go to a smaller size hole. You will need to find out what Dia. the hole is now in the main jet and then decide if you need to go bigger or smaller in size.
Some of my carbs had sloppy drilled holes so I soldered them shut and re drilled them. Look at the classic posts for more info on how to drill and size the main jet.
The throttle slides metering needle will control the fuel flow at low to almost wot and the taper will determine the fuel mix. Most needles measure 0.070 dia up at the clip end of the needle and 0.68 dia at the tip not much of a change but when you start messing with it it can and will change the fuel from way lean to way too rich and if you mess with it and mess it up the best bet is to replace it with a needle with the right measurements, standard setting on the needle is the e-clip in the #2 slot from the fat end of the needle.
Norman

Jet was my problem too, the Dellorto #68 worked good, but the Dellorto #65 works great. Check with Treatland.com for parts and service. 2 day shipping cross country.