Lousy mileage - fuel issues???

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Sign Guy

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Jan 19, 2010
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Everett, WA
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

BarelyAWake

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Jul 21, 2009
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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 :D
 
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Sign Guy

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Jan 19, 2010
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Everett, WA
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

BarelyAWake

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Jul 21, 2009
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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

AussieSteve

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Nov 26, 2009
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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.
 
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Sign Guy

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Jan 19, 2010
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Everett, WA
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.
 
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fm2200

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Nov 16, 2008
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new york city
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.
 
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stv1jzgte

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Feb 11, 2009
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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

Cabinfever1977

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Mar 23, 2009
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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.
 
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Sign Guy

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Jan 19, 2010
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Everett, WA
OK this morning I get out to ride it to work and it takes 3/4ths of a mile of peddling just to get it started grrr... The darn engine just wont rev up to 58-5900 anymore which I think would pull me up to the 28 mph I had 40 miles ago. I am topping out at 25 and there was some serious vibration during part of the ride then it smoothed out again. I'll pay more attention on the way home this afternoon and pull the air filter, plug to check color, and maybe the carb to see if I'm shooting fuel out the back, if so I'll look at the float needle.

Can we just buy different jets at the local motorcycle shop? I think it would be easier to get a jet than to find a drill bit to drill it out after dropping a bit of solder in to fill the hole.

CabinFever - awesome stats! I realize the weight and hills are a mph & mpg killer and feel that 100-120 should be easily attainable with both my weight and terrain.

So to recap, I pulled the carb changed the float from ~18 to 21 mm and have the needle clip set at the #2 position from the end. I'm running a 50:1 synthetic fuel ratio. Everything on the engine, carb, airfilter, chain, whatever the sprocket is all bone stock.
 
BarelyAWake

BarelyAWake

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Jul 21, 2009
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Before ya delve too deep in the rejetting, ya said it was fine till ya "decided to change from 32:1 to 50:1" - out of curiosity, have you tried a tank of yer old mix just to see how she likes it?
 
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Sign Guy

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Jan 19, 2010
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Everett, WA
Barely - I haven't switched back but thought that would be a good thing to do/try. Shoot, I might just go back to 24:1 which I had for the first 110 miles (or so) on the engine.

This afternoon I'll try that when I get home, first I'll squeeze out the fuel in the air filter then drain my tank and change back to 24:1 mix and ride that around to see if it'll get those rpm's back. I must say this is a learning experience :)
 
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Sign Guy

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Jan 19, 2010
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Everett, WA
I've been reviewing how to test the CDI and there are 3 basic checks. zpt

1) + lead is on black wire & - on blue wires (supposed to be 130-150K ohms) I have No reading...
2) + lead on spark plug w/- on blue (135-155k oms) I have NO reading again...
3) + lead on spark plug and - on black should read 2.5-2.7 and I have 4.5

The bike starts really hard I ride about a mile before it fires and the spark is weak but once running it does fairly well. I think I need a new coil. Anyone try one from a high end weed eater or chain saw that might have a better quality than one from these Chinese engine companies? Or any other suggestions? I hate to purchase a part that might go out quickly if I can spend a little bit more for a better quality unit.

I'm sure this is the cause of the lousy fuel mileage and starting issues.
 
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stv1jzgte

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Feb 11, 2009
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I would focus on the carb, if the bike does eventually start the coil (cdi) is fine.

Have you cleaned out the carb and made sure there is nothing keeping the float needle open,
when i used the NT carb whenever it started running out the airfilter 100% of the time it was the float needle.

What plug you runnin not stock i hope, iether way replace it and check the colour of it.

Did you go back to your old fuel mix settings? any better
 
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Sign Guy

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Jan 19, 2010
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Everett, WA
Just and update - I finally got my speed back - woohoo! Out on the flats I hit 28+ and maybe a 29 and I feel it has to do with the fuel/oil ratio. As you remember I bumped up the ratio to 50:1 and my mileage went into the dumps ~30 mpg or something horrendous. I changed back to 24 or 32:1 and my speed came back up and I'm sure my mileage has too I was going to test it this morning but couldn't get it started.

I don't have spark which I feel is the main issue on getting it started (like taking a mile of pedaling to get it finally going). I do have a coil on order and hope to have it soon! More later when I get my new coil.
 
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stv1jzgte

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Feb 11, 2009
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Sign Guy said:
Just and update - I finally got my speed back - woohoo! Out on the flats I hit 28+ and maybe a 29 and I feel it has to do with the fuel/oil ratio. As you remember I bumped up the ratio to 50:1 and my mileage went into the dumps ~30 mpg or something horrendous. I changed back to 24 or 32:1 and my speed came back up and I'm sure my mileage has too I was going to test it this morning but couldn't get it started.

I don't have spark which I feel is the main issue on getting it started (like taking a mile of pedaling to get it finally going). I do have a coil on order and hope to have it soon! More later when I get my new coil.
Click to expand...
If you got it going 28mph you have spark, when you got your new plug did you gap it? if not try closing the gap
 
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Sign Guy

New Member
Jan 19, 2010
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Everett, WA
It is hit and miss with the spark. I've had enough and ordered a new CDI. Yesterday morning (after I riding around the neighborhood for 20 min trying to get it to fire) I pushed it around the driveway for 20 min with the plug out and grounding it and no spark at all. I just pushed it to the side and will wait for a new CDI. When I can get it started it sounds like it's dieseling and I have to pedal for another 100 yards before it really catches. It used to fire up in 30'.

I got a new plug NGK B6 gapped at 0.027 which I just tossed in. I'd been using a B7, I'm not wasting more time on it until I get the new CDI and see spark when I push it around.
 
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freewheeling frank

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Mar 10, 2009
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ridgway colorado
if yer throwing fuel like you describe you have a peice of crap in the needle valve or it has come apart more than likely something is stuck in it clean it out, and beware of 50;1 stick with 32:1 after a good break in. frank
 
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