GN250 running too rich?

**Ginge09** · 11th February 2018, 17:40

So that should tell you that your new exhaust is going to be fussier on carb settings than the original. Dirty carb didn't matter on the old pipe but does on the new one.

Suggest your old pipe was clogged or leaking so back pressure or flow was not optimal. Now with the new pipe you have some tuning to do.

Go through the procedure in my previous post now the carb is clean.

**globe** · 21st February 2018, 19:05

Looks like i spoke too soon....*sad face*

Finally got chance to take it for a spin today, was bogging a low revs and low gears (sub 4-5k revs, in first second and third, didnt get into 4th or above). Thought it mightve been the inline fuel filter, came home took it out, no difference. Opened the air/fuel mix screw half a turn, didnt seem to get much better. Tried winding the idle screw in and i noticed it didnt stall as one would expect.

Will check for air leak following reinstall of carb (the back hose - air filter side - was a bit tricky to get on).

Other than that any other thoughts, suggestions? Cheers

**Ginge09** · 22nd February 2018, 07:43

Doubt that's an air leak. Air leaks tend to induce a lean condition.

Blocked air filter? Try running it without one, although if it didn't stall when you wound the idle down then it's not running on the pilot circuit. Is the slide hanging in the throttle body ( check by sticking your finger into the throat of the carb).

Is the throttle cable adjustment too tight ( if you have one)

What sort of carb is it, Mikuni round slide?

**globe** · 22nd February 2018, 08:26

Originally Posted by Ginge09

Doubt that's an air leak. Air leaks tend to induce a lean condition.

Blocked air filter? Try running it without one, although if it didn't stall when you wound the idle down then it's not running on the pilot circuit. Is the slide hanging in the throttle body ( check by sticking your finger into the throat of the carb).

Is the throttle cable adjustment too tight ( if you have one)

What sort of carb is it, Mikuni round slide?

I don't think its a mikuni, I think the previous owner must've out an aftermarket on it - no ID that I can see from anywhere.
By bogging, I mean it slows down has not guts even with the throttle out - presuming this is the international definition of bogging, then is this an indication of running to rich still?
The odd thing is when it is up on it stand and idling away nothing appears too untoward, still get it stalling every now and again when I twist the throttle but nothing like it was before the clean.

The throttle cable adjustment feels OK but I can loosen it off a bit to see if that makes any difference (why do you think that would affect this, or is it one of those odd things that can't be explained but sometimes do).

Will have a look at the throttle slide over the weekend.

Cheers

**Akzle** · 22nd February 2018, 08:59

Originally Posted by globe

is this an indication of ...

plug chop .

**globe** · 22nd February 2018, 10:13

Originally Posted by Akzle

plug chop .

Not sure what this means, are you recommending I check the plug to see if this looks lean, rich etc? If this is the case I has hardly done any kms since I cleaned the carb (and replaced the plug) maybe 5-10kms, would this be enough to show the running condition you think? Cheers

**Akzle** · 22nd February 2018, 11:51

http://www.lmgtfy.com/?q=plug+chop

**Honest Andy** · 22nd February 2018, 11:55

Originally Posted by Akzle

plug chop .

+1
You don't have to cut it but at least look at it, it's a quick and easy rough guide. You've changed a bit of stuff now so maybe it's running lean, it'll bog down with fuel starvation too, especially under power.
And don't forget that it's really easy to introduce a second problem while trying to fix the first one.
So put the filters back in after you've done the test so you don't block up the jets...

**globe** · 22nd February 2018, 13:14

Thanks for the suggestions thus far chaps much appreciated. Quick question, if i have the idle screw out too far so it is idling high (say 1500rpm upwards) would it still cut out once the air/fuel screw is adjusted to try and lean it up? Wondering whether that might be an issue that is one of the reasons that it wont stall on the a/f screw? Hope that makes sense ?

The other thing that may or may not be of relevance is that I don't need the choke to start it most times, its just fires up first time.

Even though it is frustrating its great fun learning

Cheers

**globe** · 22nd February 2018, 14:02

Originally Posted by Akzle

http://www.lmgtfy.com/?q=plug+chop

Good one, you couldn't tell me the weather forecast for Auckland for Sunday too while you're googling stuff for me could you?

**Ginge09** · 22nd February 2018, 18:01

Quick question, if i have the idle screw out too far so it is idling high (say 1500rpm upwards) would it still cut out once the air/fuel screw is adjusted to try and lean it up?

Yes. If you wound the air/fuel screw far enough. Enough to either completely open or completely close whatever orifice it is designed to meter.

But if it doesn't do much then your not running on that orifice. Your running on the next metering device in the chain which is probably the slide. Air/fuel screw only adjusts idle and transition to slide or needle jet normally. Hard to know without knowing your carb.

This is why you check your throttle cable adjustment. If it is too tight the slide is not closed at idle and is active (hanging off the cable) and passing air into the throat of the carb. You are using the slide as your idle circuit. The pilot should be your idle circuit, the slide is secondary circuit then the needle and then the main jet. Roughly speaking.

So stick your finger into the throat of the carb and make sure it is bottoming out when on zero throttle. It should snap closed when you let go of the twist grip. No gaps.

I don't need the choke to start it most times, its just fires up first time.

It's summer. If you live North of the 45th parallel that would be normal. In winter up your way may also be normal.

Take a photo of your carb and post it. Be a good lad.

Stick with it!

**globe** · 22nd February 2018, 19:31

Here you go. I’ll post up some more when I take it off again this weekend

**Akzle** · 22nd February 2018, 21:37

ah yes. it's all clear from the pictures. your hooferdacky is misaligned with the whoserwhatsit, you need to kerfluffle the thingamabob widdershins

**Honest Andy** · 23rd February 2018, 07:25

Ahh. Vacuum slides. Pictures help

As Ginge says, check the action of the throttle, which is the butterfly, make sure it returns fully and without hesitation.
Disassemble and clean. Really thoroughly. Especially the jets but also make sure the piston slide is really free with no hesitations. Reassemble making sure there are no air leaks through bad seals.
Return all adjustments back to factory settings...