Piranha 140cc how to tame motor

kirkallen143 · 10-26-2018, 05:55 PM

Howdy, see if y'all could give me a couple of pointers. Got a piranha 140cc, 4 speed manual, with VM26 genuine Mikuni and exhaust is from a CT70 that I have cut out the last section of baffles and welded back together. The engine is so peppy once the throttle is cracked, in fact too peppy for trail riding. Almost feels like the old MX 2 strokes from the 80's with a backwards/opposite powerband (all up front and then hardly nothing at the end).

What I have done so far is retard timing to 28 degrees total (best thing for kick back at kick starter) and installed the heaviest flywheel that Tbolt sells. This motor is in a CT90 with full sized (18"/21") wheels, and it is geared with 15/51 sprockets. Some have told me a full sized oil slinger from a Lifan would also help, but I can not find one for the life of me. I have thought about steel clutch plates, and again have no clue about that either. I also thought about putting a washer in the header pipe to limit exhaust flow (seen that done on a small 80cc Yamaha). Would the smaller 22VM Mikuni nock-off carburetor that came with the motor make a difference? Hell, I even thought of also converting it to a semi-auto clutch, though haven't seen anyone attempt it yet (that would actually be the best for trails). Any and all suggestions are welcome, Thanks.

Kirk

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Mudflap · 10-26-2018, 06:09 PM

Sounds just like my Lifan 140 powered Trail 90. Megatorque little engine. I tamed it somewhat by restricting the exhaust which also made it quieter. Other things that helped were new hub rubbers and an aftermarket throttle with a small pulley so it takes more of a turn to lift the throttle slide. Big fat handgrips also helped a bit with fine throttle control.

Bruces · 10-26-2018, 09:24 PM

You already have a huge restriction on your exhaust with the little ct70 pipe ,I would not bother restricting it any further .I would think the best bet for you might be playing with the gearing at this point ,those are my favourite engines because of how nice they work in terms of power per dollar and engine life , but in this case you probably would of been happier with a 110 or 125 version of it .I will be building a zongshen 125 trail 90 or two this winter for my camp rig ,actually have a Honda 125m engine I could go with as well if I feel like that as well .

pete · 10-27-2018, 10:32 PM

put a spacer plate between the cyclinder and crank case to
drop the compression..
or see if there is a less aggressive cam that will fit it..

..

wheelbender6 · 10-28-2018, 09:08 AM

Adding an extra head gasket is an easy way to lower the compression ratio. That's how Detroit tamed the muscle cars in the 1970s: Lower compression and catalytic converters.

kirkallen143 · 10-28-2018, 09:15 AM

Thanks everyone. Pete, I thought about adding another gasket under the cylinder, but being a new motor kind of hate to tear into it. They do have some cam profiles that pull this engine up into the upper rpm range, because this engine goes flat once in that zone. Appreciate it, though.
Been reading up on this "lessening the hit" and a lot suggested gearing like Bruces has said. Ordered a 17 tooth counter sprocket, some 714 GP grips and we'll start there.
Mudflap, I also looked into the throttle tamer, but not for what they want price-wise. Seems like one could fab their own from a stock piece with a little time and a dremel, might try that next.

Kirk

kirkallen143 · 11-01-2018, 05:51 PM

Still at it, the parts I ordered have not come in yet. I was thinking to myself maybe I could jet the carb to tame the hit? Isn't a lean engine kind of jerky and acts like it need more? First tried lowering the needle to fatten up the mid to lessen the hit, but no luck engine just bogs in the mid. Richened up the pilot and all I got was bog off idle, even tried both needle and pilot together and engine wouldn't run clean at all.

I even tried to make my own throttle tamer from the throttle tube, no dice so far. I made the first part of the pull smaller (about 3/4" long and 3/16" deep) and then ramped it back up to the initial diameter of the cam. Might have to take more of the first pull diameter of the cam off?

One thing I did determine is if you ride the engine hard, you don't even notice the initial hit at all...go figure.

Now I got a bad vibe right about mid throttle like something is loose inside the engine. Flywheel or oil slinger, it is almost like the engine shakes side to side at mid throttle. Once past mid throttle it smooths itself out. Looks like the side covers are coming off...

Best thing I did get out of this is, if you act like you want the best gas mileage possible out of the engine and ride like your scared (barely twist the throttle), no initial hit what so ever.

Kirk

10-26-2018, 05:55 PM	#1
kirkallen143 Join Date: May 2015 Posts: 84	Piranha 140cc how to tame motor Howdy, see if y'all could give me a couple of pointers. Got a piranha 140cc, 4 speed manual, with VM26 genuine Mikuni and exhaust is from a CT70 that I have cut out the last section of baffles and welded back together. The engine is so peppy once the throttle is cracked, in fact too peppy for trail riding. Almost feels like the old MX 2 strokes from the 80's with a backwards/opposite powerband (all up front and then hardly nothing at the end). What I have done so far is retard timing to 28 degrees total (best thing for kick back at kick starter) and installed the heaviest flywheel that Tbolt sells. This motor is in a CT90 with full sized (18"/21") wheels, and it is geared with 15/51 sprockets. Some have told me a full sized oil slinger from a Lifan would also help, but I can not find one for the life of me. I have thought about steel clutch plates, and again have no clue about that either. I also thought about putting a washer in the header pipe to limit exhaust flow (seen that done on a small 80cc Yamaha). Would the smaller 22VM Mikuni nock-off carburetor that came with the motor make a difference? Hell, I even thought of also converting it to a semi-auto clutch, though haven't seen anyone attempt it yet (that would actually be the best for trails). Any and all suggestions are welcome, Thanks. Kirk
	2

10-27-2018, 10:32 PM	#4
pete Join Date: Jan 2012 Location: ChCh , NZ Posts: 2,262	put a spacer plate between the cyclinder and crank case to drop the compression.. or see if there is a less aggressive cam that will fit it.. .. __________________ 09 XT660R ... 06 TTR250 ... 80 Montesa H6 125 Enduro... 77 Montesa Cota 348 MRR "Malcom Rathnell Replica"... Current resto projects.. 81 Honda CT110... 80 Kawasaki KL250A1... 11 Husaburg TE125 enduro... "sold" along with another 31... Lifan 125 Pitbike.. "stolen" ... KIWI BIKER FORUM...... http://www.kiwibiker.co.nz/forums/content.php All the best offroad rides in NZ... http://www.remotemoto.com/ E-mail... xtpete1@gmail.com
	1

10-28-2018, 09:08 AM	#5
wheelbender6 Join Date: May 2015 Location: Houston area Posts: 1,902	Adding an extra head gasket is an easy way to lower the compression ratio. That's how Detroit tamed the muscle cars in the 1970s: Lower compression and catalytic converters. __________________ "Its not WHAT you ride; its THAT you ride"
	0

10-26-2018, 06:09 PM	#2
Mudflap Join Date: Sep 2014 Posts: 1,887	Sounds just like my Lifan 140 powered Trail 90. Megatorque little engine. I tamed it somewhat by restricting the exhaust which also made it quieter. Other things that helped were new hub rubbers and an aftermarket throttle with a small pulley so it takes more of a turn to lift the throttle slide. Big fat handgrips also helped a bit with fine throttle control.
	1

10-26-2018, 09:24 PM	#3
Bruces Join Date: May 2018 Posts: 1,588	You already have a huge restriction on your exhaust with the little ct70 pipe ,I would not bother restricting it any further .I would think the best bet for you might be playing with the gearing at this point ,those are my favourite engines because of how nice they work in terms of power per dollar and engine life , but in this case you probably would of been happier with a 110 or 125 version of it .I will be building a zongshen 125 trail 90 or two this winter for my camp rig ,actually have a Honda 125m engine I could go with as well if I feel like that as well .
	0

10-28-2018, 09:15 AM	#6
kirkallen143 Join Date: May 2015 Posts: 84	Thanks everyone. Pete, I thought about adding another gasket under the cylinder, but being a new motor kind of hate to tear into it. They do have some cam profiles that pull this engine up into the upper rpm range, because this engine goes flat once in that zone. Appreciate it, though. Been reading up on this "lessening the hit" and a lot suggested gearing like Bruces has said. Ordered a 17 tooth counter sprocket, some 714 GP grips and we'll start there. Mudflap, I also looked into the throttle tamer, but not for what they want price-wise. Seems like one could fab their own from a stock piece with a little time and a dremel, might try that next. Kirk
	0

11-01-2018, 05:51 PM	#7
kirkallen143 Join Date: May 2015 Posts: 84	Still at it, the parts I ordered have not come in yet. I was thinking to myself maybe I could jet the carb to tame the hit? Isn't a lean engine kind of jerky and acts like it need more? First tried lowering the needle to fatten up the mid to lessen the hit, but no luck engine just bogs in the mid. Richened up the pilot and all I got was bog off idle, even tried both needle and pilot together and engine wouldn't run clean at all. I even tried to make my own throttle tamer from the throttle tube, no dice so far. I made the first part of the pull smaller (about 3/4" long and 3/16" deep) and then ramped it back up to the initial diameter of the cam. Might have to take more of the first pull diameter of the cam off? One thing I did determine is if you ride the engine hard, you don't even notice the initial hit at all...go figure. Now I got a bad vibe right about mid throttle like something is loose inside the engine. Flywheel or oil slinger, it is almost like the engine shakes side to side at mid throttle. Once past mid throttle it smooths itself out. Looks like the side covers are coming off... Best thing I did get out of this is, if you act like you want the best gas mileage possible out of the engine and ride like your scared (barely twist the throttle), no initial hit what so ever. Kirk
	0