Wants to be lean?
 

Just picked up an 03 ec300, and I'm having a tough time getting it to run right.
The guy I got it from had it jetted 170 main, 40 pilot, and an unmarked needle with a #6 slide.
It would run well at low rpm/throttle but would fall flat on its face if you went past about 1/3 throttle.
I read up on here and ordered a N3EG needle, and put in a 175 main and #7 slide as that seems to be a successful combo. Not the case for me.
The only way I can get it to run halfway decent is to put in a 160 main with the needle on the highest clip. Spark plug is a dry light-medium gray.
It also has a hanging idle issue, that will eventually come down, to a very low idle with the idle screw turned almost all the way in. The idle mixture screw does almost nothing.
I know very little about the history of the bike, seems to have quite a few hours on it based on the wear on the frame. A new top end was put on before I got it.
Fuel is pump 91 with amsoil saber at 100:1. Sea level, 75 degrees.
Anybody have any ideas what is going on?

Kinda sounds like an air leak. Spray some brake cleaner or starter around the reedblock. And see if it races. Try not to set yourself on fire.
Check for oil leaks behind flywheel.

Welcome to the forum, you've come to the right place, a lot of knowledgeable people on here who are happy to share information and help. They've helped me a lot. :)

1. As F5 suggests, could be an air leak, sucking in air will really mess up the running. Places to check are reed block housing, main bearing seals especially the left side behind the flywheel as this runs dry on the outside, also cylinder base gasket, remember you said it's just had a new top end fitted.

2. Fuel starvation? Is the carb getting plenty of fuel? There's a gauze filter on the petrol tap inside the tank, remove/inspect/clean. Also check the fuel tank breather in the filler cap is working and isn't blocked, if no air's getting into the tank, petrol won't flow out easily.

3. Is the tail pipe clear? I've seen tail pipes blocked with wadding that's come loose. Bikes start but won't rev.

4. Check operation of float valve, is it flowing fuel freely? You don't mention fuel overflowing from the carb, so I assume the float valve is closing/sealing properly. Check float height before adjusting any jetting.

5. You didn't mention it but I assume you have a freshly cleaned air filter.

6. Choke not closing properly? Is the choke cable operated or just a pull knob on the carb? Cable operated chokes can stick open a bit, check. Also remove the choke plunger and inspect the rubber seal on the end of it.

I haven't listed these in any particular order, just as they came into my head, best to check the easiest/simple things first.

Once you fix or improve things, be careful running the bike on a 160 main jet, could be pretty lean.

I don't think this is related to your problem... but premix oil at 100:1 Are you sure that's correct? I think most people mix 100% synthetic oil at 50:1.

Ahhhh, I've just looked up Amsoil Saber, it's designed for garden power tools such as chainsaws, that's what I read. I think you should be using Amsoil Interceptor or Amsoil Dominator at 50:1 or another brand of 100% synthetic oil designed for competition 2 stroke engines.

Good luck, hope you get it sorted. Please let us know how you get on. :)

Thanks for your suggestions.

I confirmed there are no air leaks, exhaust and fuel are free flowing and float is set properly. The choke is just the lever on the side of the carb, I pulled it and cleaned it for good measure.

The air filter appears to be a new UNI, however removing it seemed to help quite a bit. It will now rev with a 170 jet much higher than before but lacks power and is pretty flat at higher rpm. It now also has a flat spot just above idle, where it was nice and crisp before. I have not tried the 175 jet yet, but I will next time I get a chance to play with it. Pulled the plug after a higher rpm run, and it's a nice tan color.

The idle issue still remains. Idles real low with the idle speed screw all the way in, and little to no response from the mixture screw.

Also, the bike may in fact be an EC250, not a 300. The vin and engine number say 250. The registration and old owner say 300. At some point I'll have to pull the head and measure.

The amsoil saber at 100:1 is what my buddies have been running for years in their bikes with good results, so I figured I'd run the same for consistency.

Good to hear you're making some progress.

I'm surprised to hear what you say about the Amsoil Sabre at 100:1 but if it's proved to be OK over time, then why not!

So from what you've said it sounds like you need to persevere with the jetting experiments to get it where you want it.

There's plenty of information on here to help you understand exactly how the jetting works and which settings effect which particular throttle positions.

Something that really surprised me is how sensitive my carb is to clip position on the needle, although I guess this could be down to the needle I'm using. Well worth spending some time on this.

I found it important to only change one setting at a time, then test ride, then make notes on how the bike felt at different throttle positions. If you don't follow this method you can end up going round in circles!

It can take a bit of time to get it right, but don't give up, it's well worth it!

Good luck and all the best, Dave.

Won't turn this into the dreaded oil thread, but consider this. Every other manufacturer, and we are talking the big players with actual r&d budgets, specifies much richer oil mixtures. Only Amsoil have cracked the technology to run 100:1 without unacceptable wear.
Really?

Hi Supernovabjt

Once you're getting closer with your jetting, it would be worth checking the operation and adjustment of the exhaust power valve. Again, there's plenty of information on this forum to help you with this.

All the best, Dave.

Jeff Slavens of Slavens Racing is maniacal about testing and maintenance and he recommends Amsoil Saber at 80:1 for convenience.. an 8oz bottle treats 5 gallons @ 80:1.. He does however say 100:1 is fine as well. He has videos on youtube where he pulls engines apart and analyzes everything.. seems legit to me!

Oh God. Run away! Oil thread.

Sorrrryyyy

double check the power valve is actually operating. Pull the PV cover off the left side and rev the bike to make sure it is actually opening.