oldfartracer
07-29-2006, 07:18 AM
Please can someone give some ideas!
I just built up the engine in my sons 300ex
it ran good stock but we are racing MX and needed more power
build up
.040 over 11:1 Wiseco piston
ported head by Janssen Motorsport +1 intakes
Curtis Sparks X5 exhaust
400ex carb with choke plate removed
Megacycle 166-20 cam .370 lift/272 duration/107 lobe center
The problem is this:
The engine starts and idles fine, when I first put it together it seemed to run fine, not as fast as i thought it should be, but faster than stock.
It had a little miss at the top rpm's but figured it was jetting
We were at a race so after practice tried rejetting but no luck the miss got worse with everything I did.
My son took it out for the first moto and about half way through it started missing as soon as you tried to give it any gas.
I changed the CDI, the spark plug, closed the gap on the plug, jetting changes, back to the 300ex carb, but nothing helped.
This last week I took the top end back apart, no leak down past the valves, cam was in right as per the service manual, check the bore looked good, .002 piston to wall within 1/10th.
I re-honed for ring breakin, put it back together and it is still doing the same thing.
It starts fine, idles good, if you give it very little gas it will rev OK very slowly. If you try to accelerate at all it starts to miss real bad.
Does anyone have amy ideas??????????
Thank's in advance for any "HELP"
I just built up the engine in my sons 300ex
it ran good stock but we are racing MX and needed more power
build up
.040 over 11:1 Wiseco piston
ported head by Janssen Motorsport +1 intakes
Curtis Sparks X5 exhaust
400ex carb with choke plate removed
Megacycle 166-20 cam .370 lift/272 duration/107 lobe center
The problem is this:
The engine starts and idles fine, when I first put it together it seemed to run fine, not as fast as i thought it should be, but faster than stock.
It had a little miss at the top rpm's but figured it was jetting
We were at a race so after practice tried rejetting but no luck the miss got worse with everything I did.
My son took it out for the first moto and about half way through it started missing as soon as you tried to give it any gas.
I changed the CDI, the spark plug, closed the gap on the plug, jetting changes, back to the 300ex carb, but nothing helped.
This last week I took the top end back apart, no leak down past the valves, cam was in right as per the service manual, check the bore looked good, .002 piston to wall within 1/10th.
I re-honed for ring breakin, put it back together and it is still doing the same thing.
It starts fine, idles good, if you give it very little gas it will rev OK very slowly. If you try to accelerate at all it starts to miss real bad.
Does anyone have amy ideas??????????
Thank's in advance for any "HELP"