I just installed a grubee skyhawk gt5 - interesting

[Street Ryderz]

The gt5 is a B type engine. 38mm stroke, B type piston, FM 80 rod. The A80 uses a ZL40mm rod, B type piston, and two base gaskets. They both use the 69.6mm jug.

Now to the exhaust height diff. I referred to It wasn't even a GT5 I was comparing with the A80. I misspoke. It was actually a PK80 jug at 70.5mm. that is probably where the 1mm diff. came from, well that and me not paying closer attention.

I have a tendency to get too many irons in the fire. Like to think I would have caught that before assembly. Still glad you called me on it.

I keep forgeting about gas bike having a gt5 B type engine usually when I think of the gt5 it' the grubee A type that comes to mind!

 

[gary55]

I remember when I was first getting into these things I thought 48cc and 66cc were all the variables. I had a guy replace a jug and piston, and my bike ran like s**t. When I figured out he put a b type piston in my a type motor I knew it was time to start doing things for myself again.

 

[KTOKTO]

Well I got the head gasket on and went for a spin today running 20:1 mix. Power is comparable to the ebay motor but it vibrates a lot less. The old motor started shaking my nuts around 22mph, the new motor doesn't feel like it is working until upper the upper 20s so that is a nice improvement. I can comfortably cruise about 5 mph higher with very little vibration. The clutch is also much quieter than the old machine.

One thing I noticed is when I started to open up the throttle, from time to time it would climb in rpm past 6000 and then would lose just a touch of power for a second, then climb in rpm again for a few seconds, then lose a few rpm again.

I also think the motor smells like it is running hot. It might be the two day old paint on the engine though.

Between the slight hot smell and the little loss of power up top I was thinking I might be running lean but I don't think so now after looking at the plug.

Everything ran perfect with the old motor with the exact same setup so there are definitely differences between the 2. It is going to get cold and wet again so I won't be able to get more miles on it for a couple of weeks but should be ready to troubleshoot after that.

 

[gary55]

Try one notch leaner. 4 stroking on the top end is rich. A lot of them do it at the very top end on flat ground, but straighten up when you hit a hill. If it is completely wound out before it starts 4 stroking you might be ok where you are.

 

[butre]

while you're at it, toss that 3 prong and get an NGK plug. it only sparks to one terminal anyway and gapping those abortions is a nightmare, plus you can't index them

 

[KTOKTO]

Try one notch leaner. 4 stroking on the top end is rich. A lot of them do it at the very top end on flat ground, but straighten up when you hit a hill. If it is completely wound out before it starts 4 stroking you might be ok where you are.

Thanks. Ya, I was only running about half throttle and it would lose power and yes, up hills it would straighten out. I will put 32:1 mix in it and a new plug in after break in and see how it runs. I have a set of jets for the carb, I'll go one smaller if it still 4 strokes after break in. Thanks for the info.

while you're at it, toss that 3 prong and get an NGK plug. it only sparks to one terminal anyway and gapping those abortions is a nightmare, plus you can't index them

Ya, I have a ngk iridium ready to put in when I get done running the break in mix.

 

[KTOKTO]

OK, so I got a set of jets and they are labeled ranging from #60 to #80. Any suggestions on which one to try first, what to look for and where to go from there?

 

[Street Ryderz]

What # is in it currently? Go with one size lower and see if the 4 stroking at wot is gone if not try again next size smaller.If you end up having to go down more than two you will most likely have to adjust needle height to maintain a good transition between the two!

 

[KTOKTO]

What # is in it currently? Go with one size lower and see if the 4 stroking at wot is gone if not try again next size smaller.If you end up having to go down more than two you will most likely have to adjust needle height to maintain a good transition between the two!

I'm not sure what size is in it now. I'm going to order a numbered drill index set and will figure it out. Thanks!

 

[gary55]

If it's a nt or speed it is probably a #70