ec300 chokes and goes flat Help!

C

clerky clerk

New member
I am in need of some technical help, My ec300 has a bad flat spot on full throttle and sometimes (rarely) doesn't accelerate as it should. But some times it while out burning up the mountains it rips right through the revs once in a while and I can see how it should perform.
I have had a complete top end rebuild; piston, rings, bearings, gudgeon pin, gaskets etc (done by a motox team mechanic), my pv is working correctly and opens fully when it should, I have a N1EF needle now on the third slot (previously on the second) air screw turned out 2.5 times, I have 178 main jet, carbon reeds, removed reed spacer, 13:42 gearing and standard gas gas exhaust, I run 40:1 castrol mx oil. (even when on stop in neutral the throttle can be opened to full but will not rev high enough to sound painful) Please please what do i do?
 
What elevation and temperature are you riding?

Start with the simple stuff.

Check the condition of the plug. While you are at it, put in a new spark plug.

Try changing the main jet - your jetting may be off at full throttle.
 
I have the exact same problem have tried everything. changed both crank case seals, new boysten pro series reeds, new rubber inlet manifold, reconditioned stator, repacked silencer with new baffles new air filter correctly oiled and loads of other things .runs like dream when in the power valve but at the transition when coming into powervalve it stutters. i rn a b8eg plug and is alot better without a transistor. but i am running the bike in UK wih colder Temps
 
I ride between sea level and 500 feet but with the same problem at both altitudes. I changed the plug as my first point from the standard ngk b8eg to ngk Iridium but with no benefit (both burn at a nice sold brown), I then put back in a new Ngk b8eg, de coked and re-packed the silencer. Yet I remained with the problem. I to am in the UK on the south coast of Wales.
 
the temp is from 0c up to 10c at the moment and I run 178 main which is fairly large as I believe. I have stripped down the carb, blown out all the jets for blockages yet nothing seems to make a difference. Where do I find the transistor, I'll try removing it.
 
13:42 gearing:eek: Typo?

Does this happen when the engine is cold or just when it's fully warmed up or after a certain period of time?

Have you examined your float needle assy. Could that be hanging up somehow and starving the motor for fuel? Have you checked the petcock assy for blockage? The gas caps have been known to cause an issue you describe when they don't vent properly. Check all grounds carefully/clean/tighten. If the main was super rich it would blubber or 4 stroke and possibly foul plugs. Slide is moving easliy through it's full range?

You did not mention the year of the bike which might be good to know?
 
Put the N1EF needle on clip 1.

The bogging you are describing is a rich bog just before pv is fully open. Lean it out by putting needle on clip 1. It will work. Trust me.
PS gearing should be 13:48.
 
I am looking at changing the rear sprocket from 42 to 48, I have stripped down the carb completely "twice" including taking out the float needle and cleaning everything up but it is all in good clean condition. The slide moves freely its a 2000 model ec300. I'll try putting the needle in clip 1.
When the bike is cold approx for the first 30 secs I get the usual pull away splutter until the choke is not required. I have good low and mid range power but then flat on the top, on full throttle it bogs out and on occasion clears and takes of like a jet giving me a taste of how it should perform but by the time the flat has cleared everyone else has pulled away. I have on rare occasion had a back fire on the over-run or when I have cut the bike off after a blast. Prehaps something to do with it?:o
 
sorry I forgot to mention: I dont think its fuel starvation, the reason being I ride with several friends on various bikes (ktm exc 300, yam wr250f, honda cr250, husky 400f and suz rm 250) we often compare fuel usage at the end of the day and my bike has always used the most. By quite a bit.
 
From the description it really sounds like the PV is sticking or the PV governor mechanism is messed up. Have you removed the cover and watched the mechanism move properly with no jerkyness? It also sounds like your float level could be adjusted lower (may help the mileage). When you tip the bike to the side how far over can you go before gas starts coming out? If it's only a little way lower the float height until the bike can lean over about 45 degrees without leaking out the overflow. When's the last time you had a look inside the ignition cover? Those things fill with crap if not attended to and should really be removed to dry after every wash IMO. Again, different gas cap maybe? And you really did have a 42T sprocket on it? How could you even ride it that way off road?
 
About 6 months ago I did have a problem with the float level and needle, I took out the needle and there was a bit of crap in there causing the needle to seat to high. I removed this and lowered the float, you are totally correct the bike can now basically lay on its side before overflow.
I have never removed the ignition cover, thats sounds like a good avenue to persue. As for the gas cap; I have a vented gasg cap. Yes, it is runnng 42T, very small I know. But not really a problem, Im used to it, just want the bike to work correctly, I have had the power valve cover off to watch it operate and it all seems ok.
 
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