Jetting ?

[rootsnrocks]

Need some quick advice. I am pretty sure my main jet is too small. The bike runs great down low and mid-range is fine, but it just does not want to get on the bike and open up. I can sometimes get it to do it if I really try, i.e. today I held it WOT in a sand pit and after about 5 seconds it finally came alive... It's an 09 EC 250 and currently has a 180 main. I read the jetting post and I see other people with 180+ mains in the same elevation (sea level-1000ft) 80-95 F... I guess I will try to go leaner. How low can I go safely? I guess I am wondering if I should try a 175 or is that too big of a jump maybe I should try 178? Thanks for the help, really the first time I've had to play with jetting on a bike. It also has a ton of spooge out the exhaust prob from all the low speed riding in the tight stuff?

[noobi]

Originally Posted by rootsnrocks

Need some quick advice. I am pretty sure my main jet is too small. The bike runs great down low and mid-range is fine, but it just does not want to get on the bike and open up. I can sometimes get it to do it if I really try, i.e. today I held it WOT in a sand pit and after about 5 seconds it finally came alive... It's an 09 EC 250 and currently has a 180 main. I read the jetting post and I see other people with 180+ mains in the same elevation (sea level-1000ft) 80-95 F... I guess I will try to go leaner. How low can I go safely? I guess I am wondering if I should try a 175 or is that too big of a jump maybe I should try 178? Thanks for the help, really the first time I've had to play with jetting on a bike. It also has a ton of spooge out the exhaust prob from all the low speed riding in the tight stuff?

Depends on the needle, and its position. You can run a rich needle with a small main and achieve similar results as a lean needle with a large main.
Although, it does sound like being rich.

[Jakobi]

Like Noobi said. The needle plays a large part as it overlaps with the main circuit. If its a rich needle providing extra fuel towards WOT then you can run a leaner main. If its a lean needle you may need a larger main.

Also you start your post also by saying you think your main jet is too small, but then state you want to go leaner. I'll assume you meant you think your main is too big.

I'm also going to take a stab here and suggest that its not all your main jet and quite possibly the needle involved too. If it was just the main that is rich, then no amount of open throttle at WOT will improve it. It will simply burble more. It sounds to me like you are too rich somewhere lower in the revs which is then loading the bike up and inhibiting its ability to rev out cleanly on demand.

As for making changes, I'd suggest 1 step at a time whichever way you do it. If its the stock needle (N1EF) then you should safely be able to run a 175/172 at those temps. If its a JD needle/yamaha you'd expect 178/180. Possibly 175 on a humid day or with some elevation.

[rootsnrocks]

Sorry, yes I meant to write I think it is too large.

[GMP]

Where are you located, and what are your complete jetting specs? '09 should have older PWK AS I carb with screw top, correct?

[rootsnrocks]

Located in MA (sea level, it's hot as hell here and humid 90F 90% RH). Yes the cap screws onto the top of the carb. I am going to try a 178 main, and I guess I would agree that perhaps it is loading up in the mid-range, would explain all of the spooge, and also why it is taking a very long time to clean it out when I am WOT on the main. I will try the CCK needle and maybe also the NEDW needle at some point. It has never ran right since I got it which I find very strange, got it from a "AA" rider, figured the jetting would be spot on... What is the exact model of my carb? Bike is 09EC250Race.

[Jakobi]

Stock carb should be a 38mm PWK AS1. I'd still suggest pulling the carb to double check the needle you have in there currently too.

[wasp4banger]

Originally Posted by rootsnrocks

Located in MA (sea level, it's hot as hell here and humid 90F 90% RH). Yes the cap screws onto the top of the carb. I am going to try a 178 main, and I guess I would agree that perhaps it is loading up in the mid-range, would explain all of the spooge, and also why it is taking a very long time to clean it out when I am WOT on the main. I will try the CCK needle and maybe also the NEDW needle at some point. It has never ran right since I got it which I find very strange, got it from a "AA" rider, figured the jetting would be spot on... What is the exact model of my carb? Bike is 09EC250Race.

Fuel to oil mix also affects the fuel to air mixture, so if the AA rider was running more oil than you it would have been leaner

[rootsnrocks]

Good point but I doubt he ran more oil than 40:1 which is what I'm running...

[Jakobi]

Originally Posted by rootsnrocks

Good point but I doubt he ran more oil than 40:1 which is what I'm running...

Yeah jetting depends on a lot of variables. Its possible he ran at 32:1, but more likely would be that it was jetted for winter. You'll also find people who are harder on the throttle will also require a richer mix than someone who puts around mostly putting little load on the engine for any period of time.

The best approach is to do as you are. Have a look and see what you have in there to start with. Make one change at a time and see how you go towards making it better. Down the track you can experiment with different needles if you want to improve economy/change the power delivery.