2006 Gas Gas 300 Top rpm/Open throttle range problem

[joppiesch]

Good day guys

I have Three Gas Gas 300s. I have sorted out the jetting on the other 2 and they are running 110% with loads of crispy power through the entire rpm range.

However the last one I'm having difficulty with the top rpm range. From closed to 3/4 throttle range it has loads of power and torque and runs perfectly, but as you fully open the throttle it still accelerates, but I can feel its low on power, especially compared to the others. Its like it runs better on 3/4 throttle.

Now I have the stock gold needle in a brand new Keihin pwk 38 mm carb, with a 42 pilot jet. I have played with numerous bigger main jets as I thought with the top rpm range being the problem that the main jet might be to small. However there is no difference even if the main jet is 20 sizes bigger up to 200. I have numerous sizes slides (5-9), Main jets (145-200) and Pilot Jets (38-48).

I did notice if you lower (richer) the needle clip the bike has more power at open throttle, which i don't understand, cause thats the main jets function. So the clip is at the lowest slot of the needle at this stage.

Is there anything else I could do maybe with an exhaust, silencer, new spark plug, carb slide ??? Maybe any recommendations for a thinner/other needle?

Cheers
Joppie

[Zman]

What is the main jet size and needle number?

It sounds to me like you are running out of fuel.

1. You may have a fuel restriction. I would check to see if your petcock filter or secondary filter is partially plugged with debris. Also verify there is no debris stuck between the needle and seat and the carb inlet port.

2. Low float could run out of fuel. Even though it is a new carb, I would double check the float setting is set properly for the GG bike. Start here http://www.gasgasrider.org/forum/showthread.php?t=1427

3. Carb Angle - The carb in a GG is positioned on a complex angle that is difficult to eye properly. After you set the float height put the bike on a stand and put a bubble level on the carb top to verify it is not twisted. You may be surprised how far off the bubble level measurement is from eyeing level.

[RudolfHucker]

Also check that the tank vent is not blocked and stopping air replacing the used fuel. This may be enough to stop the carb refilling properly.

Is the float valve opening all the way or sticking as the fuel level drops?

[Zman]

Originally Posted by RudolfHucker

Also check that the tank vent is not blocked and stopping air replacing the used fuel. This may be enough to stop the carb refilling properly.

Is the float valve opening all the way or sticking as the fuel level drops?

Excellent Point!

[Jakobi]

All of the above.

Intake restrictions will munt top end power. Exhaust restrictions will too. Timing/spark/lack of advance will do the same (stator, cdi, coil, plug and/or cap). Fuel starvation can show up under increased demand of extended throttle.

Powervalve actuation? Is it opening fully?
You've changed the carb so unlikely that.

Given you have 2 other bikes to borrow parts from, I would be working down that path. Start simple..

Confirm that the intake and exhaust is clear. Repack the muff. Double check earth/grounding points. Trim back some of the spark plug lead where it joins the cap (should be able to find resistance specs for this if you'd rather just probe first). Then swap out bits to check off list.

[(F5)]

I was thinking of power valve opening and muffler collapse. Swap ign coil over complete, and muffler for ease of test.