Lousy mileage - fuel issues???

Sign Guy · #1 03-17-2010, 09:27 AM

Ok the bike has been sluggish since I pulled the air cleaner off and cleaned it out probably 30 or so miles ago. I also decided to change from 32:1 to 50:1 using synthetic oil. My clip on the needle setting was at the middle (3) so yesterday I got it running (when I first got it, it fired up right away about about 20-30' now I ride for a couple blocks before it starts to fire grrr....) Anyway, I got it running with the air cleaner off and it was spewing fuel out the carb onto my bike seat tube post area and rear fender - Hmmmm....???? (spark plug had a nice light layer of black on it - no oily, cakey residue)

I moved the clip up a notch to the #2 position and ran it around the neighborhood and still the same thing. The spark plug didn't change. When I rev'd it a little it still spewed fuel all over the back of the bike.

I moved the clip to the top notch and it sounded even better and this time only when I rev'd it really high did fuel start spraying out of the carb. The plug was now a tad cleaner and starting to look like it could be a browish color.

On the way to work this morning it crapped out on me, I think I ran out of gas and I'd only gone 27 miles on about 3/4 of a gallon - this sux! So....... What do you think it could be for fuel to be spraying out of the back of the carb and lousy mileage??? I wonder if the float is not working properly in the bowl? Anyone got any ideas??? Bueller? Bueller?

**BarelyAWake** · #2 03-17-2010, 09:40 AM

Alla these HT kits run on the rich end of things to begin with, by switching to 50:1 you made it that much richer (less oil = more fuel). By moving your clip up it sounds like you compensated for that (it's all mine required when I switched to 50:1), I'd guess your float decided to start messing with you just for the fun of it... from the spray - it does sound like that might be it (it may even be filled w/fuel & sinking).

It's easy 'nuff to pull the bowl off and bend the tabs down a touch, there's a limited range of operation tho - too low and you'll starve at prolonged high RPM & WOT, too high and it'll do what yer describing. It sometimes takes a coupla runs to dial it in.

The carbs really outa be rejetted, some do this by soldering & drilling the jet to make it smaller, even sanding a taper into the pin to allow more fuel at WOT after they've done that... I fortunately didn't need to bother with mine

Sign Guy · #3 03-17-2010, 10:53 AM

I'll mess with the float first and test it out. I can't believe that it is shooting fuel out the back end, no wonder the air filter is soaked and why it's getting so hard to start, gotta be something going on in the carb.

**BarelyAWake** · #4 03-17-2010, 11:06 AM

Any 2 stroke will backblow to a certain extent as it doesn't have an intake valve - tis why reed valves were invented for them

I wants one teh naow kthx o.o

AussieSteve · #5 03-17-2010, 11:39 AM

If it helps, the correct float level for an NT carb is 21mm. (Measured with the carb upside down and gasket removed, from the gasket seating face to the top of the float.)
As BarelyAwake mentioned, double-check that your float isn't punctured. (Shake it and see if there's any fuel in it.)
If everything is OK, rejetting is the answer. Mine had an 0.79mm main jet stock, but it didn't run properly until I worked down to an 0.72. Even then, I still needed the slide needle at it's lowest setting.

Sign Guy · #6 03-17-2010, 03:37 PM

Thanks Steve, I'll check it out either this afternoon or tomorrow and give an update!

Sign Guy · #7 03-20-2010, 09:04 PM

OK I finally got to it today and the float did not have a hole in it but it didn't look like there was any room for it to really float. I flipped the carb upside down and took a measurement and it was ~18.5 so I moved the tabs up so the reading is now 21. I also put the clip on the needle on the 2nd from the end instead of the first and we'll see how that does.

When I ran out of gas the other day I had the clip at the top of the needle and the plug looked like I just cleaned it. No black at all but a bit of brown around the electrode, I'm not sure thats how a 2 stroke should look thats why I moved it down 1 notch and will ride around like that with the new float settings and then check. I'll keep you posted.

fm2200 · #8 03-20-2010, 10:48 PM

I have never had gas mileage like the 150 they refer to, at best I probably get 50-60mpg. I have a 40T sprocket on the rear, and rarely run the engine in the higher rpms (too much vibration) but the plug is clean and it runs fairly well. All in all I would say that if your not getting the best of mileage is probably because the lack of a balanced engine would counteract any real performance in terms of mileage. The kind of terrain you ride in, hills really require way more throttle and riders weight is another consideration.

stv1jzgte · #9 03-22-2010, 08:08 AM

Sounds like your float needle is stuck open resulting in fuel spewing out the air cleaner this would be where your fuel milage is going. would be the most common fault i have had with the NT and cns carb

Cabinfever1977 · #10 03-24-2010, 01:12 AM

I weigh 115lbs and have a 44t on a 26 wheels and i get around 180mpg+ @ 32mph.
I ride on mainly flat roads at WOT. So it would depend on your weight and if you have hills.

If you can stop the gas from coming out of your carb your fuel milage will increase.