GY6 150cc Scooter Cutting out above 37MPH

gmcjetpilot · 12-02-2017, 09:17 PM

Well my scooter was running OK but the plug said LEAN. I up'ed the main jet and the plug now has a little color, but TOP SPEED was still about 52 MPH (hoping it would help). It is like the ignition is cutting off. It continues to accelerate to 42 mph. Any TIPS to trouble shoot. I had the plug back out and checked the gap an color.

The scooter starts easy, idles nice. has good low speed acceleration, but right at 37 mph like clock work it misses.

I have done some work that was unrelated to fixing this issue, but just FYI:

Removed the emission system
Removed the vacuum fuel petcock and put a manual one on.
(The above work was after the problem and the bike is running great at low speed)

gmcjetpilot · 07-13-2018, 11:08 PM

Thanks for all the GREAT replies...

Well after lots of trouble shooting I found it was my main jet was too big. The scooter was running way lean and went up two sizes from what I thought was in there (which had no markings). I should have measured the orifice with a drill bit and compared to the jet kit I bought. Well the original was likely 108 (not 110 or 115 as I thought). I went up two sizes up from 110, to 120. That was way too much.

Well I took the 120 out and put in 110... after verifying the original was 108.

Now before you say OF COURSE... Right after the jet change to RAN FINE, with the 120. The high speed miss came later and got progressively worse (bike missing at lower and lower speeds). I may have also had a spark plug issue crop up (bad luck and confusing). It was clear the plug was getting fouled. However unrelated and may be bad luck the plug may have developed a defect (meaning a crack in porcelain not visible or internal conductor break). I measured the plug and got zero continuity.

New 110 jet installed (one size up from original) and replaced plug and it runs perfect.

tortoise · 07-14-2018, 11:20 AM

Similar preference for a 110 jet in a 150cc.

Weldangrind · 07-14-2018, 06:31 PM

Glad to hear you got it sorted; I missed your original post.
You indicated that you removed the emissions device; have you removed the cat? They're crazy restrictive.
Please show us the new petcock you installed.

gmcjetpilot · 07-15-2018, 02:49 AM

Quote:

Originally Posted by Weldangrind

Glad to hear you got it sorted; I missed your original post. You indicated that you removed the emissions device; have you removed the cat? They're crazy restrictive. Please show us the new petcock you installed.

Thanks appreciate it. I don't see a CAT in the system. I think it was all EGR and gas tank vapor trap. It did not make the bike faster, but I took out a box of parts.

The vacuum petcock was replaced with a regular motorcycle petcock. It is under the seat right now, but with a little bracket it came out nice. I have to reach up under the plastic body work and feel for it. I consider this a great theft prevention aid. However it goes many blocks before running out of fuel. The down side is you can't see it, you have to feel for it. Fwd is GO and down is OFF. The one I went for was on ebay... like this one title:

"1/4'' Inline Fuel Shut Off Valve Petcock Dirt Bike Go Kart ATV"

https://www.ebay.com/itm/1-4-Inline-...Xpetcock+.TRS0

or

"Inline Fuel Shut Off Valve Petcock Dirt Bike Go Kart ATV"

https://www.ebay.com/itm/Inline-Fuel....c100005.m1851

Weldangrind · 07-15-2018, 12:25 PM

I figured that was the style of petcock you used; I'm just struggling to wrap my mind around how you accommodated the bodywork.
There is likely to be a cat in the muffler. This is a thread that deals with my adventures on a 50cc with a cat: http://www.chinariders.net/showthread.php?t=9421
If you read both pages, you'll see where I was thinking about how to incorporate a motorcycle petcock back then.

Nyccooldude · 07-18-2018, 01:52 AM

Quote:

Originally Posted by Weldangrind

I figured that was the style of petcock you used; I'm just struggling to wrap my mind around how you accommodated the bodywork.
There is likely to be a cat in the muffler. This is a thread that deals with my adventures on a 50cc with a cat: http://www.chinariders.net/showthread.php?t=9421
If you read both pages, you'll see where I was thinking about how to incorporate a motorcycle petcock back then.

So I didn't know my scooter had a cat in the muffler!!! I read this post and just for giggles I cracked open the original cast and ''boom'' I have a kitten in there!!!. I'd always wondered why it was so heavy.

12-02-2017, 09:17 PM	#1
gmcjetpilot Join Date: May 2017 Posts: 37	GY6 150cc Scooter Cutting out above 37MPH Well my scooter was running OK but the plug said LEAN. I up'ed the main jet and the plug now has a little color, but TOP SPEED was still about 52 MPH (hoping it would help). It is like the ignition is cutting off. It continues to accelerate to 42 mph. Any TIPS to trouble shoot. I had the plug back out and checked the gap an color. The scooter starts easy, idles nice. has good low speed acceleration, but right at 37 mph like clock work it misses. I have done some work that was unrelated to fixing this issue, but just FYI: Removed the emission system Removed the vacuum fuel petcock and put a manual one on. (The above work was after the problem and the bike is running great at low speed)
	0

07-13-2018, 11:08 PM	#2
gmcjetpilot Join Date: May 2017 Posts: 37	Thanks for all the GREAT replies... Well after lots of trouble shooting I found it was my main jet was too big. The scooter was running way lean and went up two sizes from what I thought was in there (which had no markings). I should have measured the orifice with a drill bit and compared to the jet kit I bought. Well the original was likely 108 (not 110 or 115 as I thought). I went up two sizes up from 110, to 120. That was way too much. Well I took the 120 out and put in 110... after verifying the original was 108. Now before you say OF COURSE... Right after the jet change to RAN FINE, with the 120. The high speed miss came later and got progressively worse (bike missing at lower and lower speeds). I may have also had a spark plug issue crop up (bad luck and confusing). It was clear the plug was getting fouled. However unrelated and may be bad luck the plug may have developed a defect (meaning a crack in porcelain not visible or internal conductor break). I measured the plug and got zero continuity. New 110 jet installed (one size up from original) and replaced plug and it runs perfect. Last edited by gmcjetpilot; 07-15-2018 at 02:51 AM.
	1

07-14-2018, 06:31 PM	#4
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	Glad to hear you got it sorted; I missed your original post. You indicated that you removed the emissions device; have you removed the cat? They're crazy restrictive. Please show us the new petcock you installed. __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
	0

07-15-2018, 12:25 PM	#6
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	I figured that was the style of petcock you used; I'm just struggling to wrap my mind around how you accommodated the bodywork. There is likely to be a cat in the muffler. This is a thread that deals with my adventures on a 50cc with a cat: http://www.chinariders.net/showthread.php?t=9421 If you read both pages, you'll see where I was thinking about how to incorporate a motorcycle petcock back then. __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
	1

07-14-2018, 11:20 AM	#3
tortoise Join Date: Jan 2008 Posts: 221	Similar preference for a 110 jet in a 150cc.
	0