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Old 10-22-2009, 11:34 AM
Evanewk Evanewk is offline
Motorized Bicycle Newbie
Join Date: Oct 2009
Location: Denver Metro
Posts: 4
Default Please confirm jet size Grubee Sky-Hawk

Hello all,

I am up at altitude (5280 baby) and I am attempting to tune my motor appropriately.

I am experimenting with a few things and I would like confirmation of the following:

1. I read here somewhere (can't find it again of course) that the jet on the new style HT "performance" carburetor sold in the kit with the Grubee Sky-Hawk engine could be replaced with any of the Dellorto 5mm Jets. Is this correct? they also have 6mm jets (the rest of the engine is all #6 and 6mm pitch equipment in general, I'm pretty sure) so I wanted to be sure before I purchase a few for testing.

Here's the search page:

Search Results : Dellorto Carburetors, And parts for you.

2. Someone wrote somewhere what the tolerances on the carburetor pin were (pin set with the e-Clip and manipulated by throttle adjustment). By tolerances I mean the measurements from the beginning of the taper of the pin head to the size the head should be. I would like to check to see if mine came from the factory tapered correctly but i cant find that information again.

I am looking to go to a smaller jet size as it seems my engine is "4 Stroking" at about 21 MPH and there seems to still be some throttle left. I've also momentarily revved the engine at idle when warm to hear what higher range rpm's should sound like on this engine, and I am decent in the mid range (some times some 4 stroking there too...) but at the top end, like I said, power cuts and it will not accelerate any more.

The fuel lines and flow are fine and I have regularly checked the air filter for cleanliness.

Right now I am experimenting with first(top, pin set farthest down) and second from the top. Factory setting in the middle was ehh compared to what people report here in the forum. I ran a bit on the second from top setting of the e-clip and performance mid range did improve, but again top end of 21-22 and 4-stroking sound.

I will post how my first race and comparison goes with my roommate and his bike with my pin set all the way up and my jet unmeasured but factory (no mod).

What do ya say ladies and gents?
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Old 10-22-2009, 11:54 AM
Evanewk Evanewk is offline
Motorized Bicycle Newbie
Join Date: Oct 2009
Location: Denver Metro
Posts: 4
Default Re: Please confirm jet size Grubee Sky-Hawk

Here's another thought:

I've had about 3/4 of a gallon of about 25-28:1 on the gas to oil mix.

Do I need to break it in even further at this point before I start working on dialing in the carb?

I've replaced the spark plug once, and the new one is still running dark dark tan with the e-clip set at second notch down. Better than factory, but not by much. Still running the factory plug will switch to NGK soon.
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