Grubee shyhawk 66 cc carb tuning question

[AussieSteve]

it mostly runs bad idle-3/4 throttle

That sounds like the slide needle is too high, but you adjusted correctly - when the needle is at it's lowest, the mixture is leanest.
The main jet still has a fair effect on mid-throttle as well as WOT.
Do a plug chop at WOT and if it's rich, change the main jet and that will also lean out the mid-throttle mixture.

I was thinking about checking the float level but not sure if that would make a difference anyway

Yep, that could make a difference - the float level should be 21mm from memory. See NT Carb Tuning Basics for a bit more info on that.
There's also a link to a good illustrative video of 'four-stroking' that might help.

Worst case scenario is I buy an aftermarket carb that allows mixture setting.

I'm considering that myself for better performance, but it's possible to get the NT carb pretty well tuned with a bit of f'ing around.

Did I have it right adjusting the clip like I did??

Yes, see above.
Moving the clip up lowers the needle into it's seat, reducing the amount of fuel in the mix and vice versa.

 

[AussieSteve]

Ensure that there is no fuel in the float and that the float needle and seat are clean, too.

 

[butch100]

Ensure that there is no fuel in the float and that the float needle and seat are clean, too.

OK, Thanks again Steve, I will mess around with it this afternoon, I ran the first 1/2 tank without a filter (have one now) so it's possible some bits might have gotten in there, I see SBP has jets at a reasonable price, gonna order some as I really don't want to run it rich like this for too long, afraid I might carbon up the head badly if I do..

 

[skipS]

OK, Thanks again Steve, I will mess around with it this afternoon, I ran the first 1/2 tank without a filter (have one now) so it's possible some bits might have gotten in there, I see SBP has jets at a reasonable price, gonna order some as I really don't want to run it rich like this for too long, afraid I might carbon up the head badly if I do..

Butch do you also have the new "speed" carb"?

 

[butch100]

Butch do you also have the new "speed" carb"?

Don't know, it just says "NT" on the side..

 

[AussieSteve]

butch100, your's is a standard NT carb, by the sound of it. I'm pretty sure that the Speed carb has 'SPEED' on the side.

 

[skipS]

butch100, your's is a standard NT carb, by the sound of it. I'm pretty sure that the Speed carb has 'SPEED' on the side.

yes Steve the Speed carb does say "Speed" on the side of it.

I ordered four jets in a range from 72 to 82 . hopefully that will fiinish the fine tuning process.

 

[skipS]

yes Steve the Speed carb does say "Speed" on the side of it.

I ordered four jets in a range from 72 to 82 . hopefully that will fiinish the fine tuning process.

We have success jets came in today and I installed a 72 as the main jet.. it four stroked a little from 1/2 throttle to wide open but very sporadic . I then raised the needle to the top clip and its pretty darn good. I can get to wide open with no bog and it only four strokes now at low rpm under no load . As soon as i turn the throttle on a little any where in the rpm range it stops four stroking and runs smooth. I know its still a little rich on the top end but the 72 is the smallest jet I ordered. I think ill add a few holes to the air box to lean it out just a tad. What plug gap would give it the least opportunity to four stroke...Smaller or wider ?

 

[AussieSteve]

Excellent. And about the same as mine, by the sound.
I considered a thicker slide needle to lean it out a touch more, but didn't worry in the end.
I fitted a low-profile air filter from Sick Bike Parts. That helped a little more.

Not sure that the plug gap would make much, or in fact any, difference.
If I were you I'd gap it for 0.6mm, (0.024").

The 4-stroking at idle is possibly an indication that the float level is a bit too high. Should be 21mm, measured as described in NT Carb Tuning Basics.

 

[skipS]

Excellent. And about the same as mine, by the sound.
I considered a thicker slide needle to lean it out a touch more, but didn't worry in the end.
I fitted a low-profile air filter from Sick Bike Parts. That helped a little more.

Not sure that the plug gap would make much, or in fact any, difference.
If I were you I'd gap it for 0.6mm, (0.024").

The 4-stroking at idle is possibly an indication that the float level is a bit too high. Should be 21mm, measured as described in NT Carb Tuning Basics.

I checked the float level earlier and set it at 82 thousands of an inch( I think thats the conversion to 21 MM) but it may be off again, ill check it next time its apart .