Reaching 50mph on 66/80cc

Next mods to push over 45mph

  • Mz65 pipe

    Votes: 0 0.0%
  • Stuffed crank case

    Votes: 0 0.0%
  • Advanced timing

    Votes: 0 0.0%

  • Total voters
    3

Warphones

New Member
Mar 23, 2020
10
8
3
30
Albuquerque
1584409278694.jpg
1584409199466.jpg
1584409259484.jpg
1584409240044.jpg
Hello family and friends! I have been trying to obtain 50mph on my pk80 and am getting closer with every mod. Right now I'm hitting 41mph(gps) and know it will go faster.
  • Pk80
  • High compression head
  • Copper head gasket
  • Ported/matched intake/exhaust
  • Ported/matched knifed transfers
  • SKS bearings crank/clutch
  • G2 Reed w/19mm intake
  • Dellorto SHA/HP 15.15 with .68 jet
  • Windowed/ramped piston
  • Fatbelly expansion chamber (cheesy but cheap, temporary till mz Miami restocks the mz65 pipes)
  • 36 Tooth Sprocket
  • NGK B6HS Plug
  • Stock CDI
  • Stock timing
  • Stock magneto
  • .6 gallon tank
  • 20:1 fuel
  • Spring chain tensioner with sprocket roller
  • Custom tank mounts
Right now I have a wicked power band that takes me up some pretty good hills. 20-30mph is super quick. 30-40mph pretty quick too. At 40mph it totally feels like it wants to go faster, but runs out of fuel. I might try upjetting a little more to .70-.72 and see if I get more mph. I have not stuffed the crank case. Or advanced the timing.
I have also read that the dellorto clones you can drill out the top hole of the jet tube to allow more high rpm fuel delivery. And also modify the slide. I am reluctant to get a mikuni carb or anything else as I've read the dellorto should be able to get to 50mph. Maybe......

Does anyone have advice or has anyone reached 50mph on similar setups? What did you do to get to 50mph?
 

indian22

Well-Known Member
Dec 31, 2014
3,648
3,939
113
Oklahoma
I've run several engines that use the actual Dellorto carb or the SHA clone and similar mods to those you've made, not exact, but similar. So I'm on the same page if not the same sentence as you. Here's my observations on the 66cc reed setups and with the China girl motors in general. The SHA carb can be quite good but in my experience the Dellorto is much better...both can flow enough to reach 50mph when jetted properly. The carbs design limits tuning and a larger Mikuni makes more sense than trying to get a little more from the SHA carb.

I'd suggest mounting an inexpensive inductance tach/hour meter to the spark wire lead just to see where your motor is struggling. I'm guessing with the 36 tooth sprocket it's not getting much past 7,500 rpm, if that. When these engines run well they can pull over 10K and some 12K plus. Now they won't last long at these revs but they can pull to these numbers.

I normally use 44 to 48 tooth sprockets for tuning my motors, even the modified ones and at times I've found that they also hit the wall at around 7k & they shouldn't, but felt good getting there, and running 38tooth or higher ratio the motors struggled to reach even that many rpms; though I was running faster mph with the smaller sprocket I lost rpm.

Without gaining engine speed, actual speed is pretty much stuck where you are. Tuning makes the difference, but what kind and in what combination will vary. You don't mention plug chop, but if the plug looks good both fuel flow and compression can't be too far out of line. You're pleased with the way it performs all around, save reaching that elusive 50mph mark so I'd say the motor is functioning fine as also, but the performance tune isn't working...your mods are not working in combination to build power at high mid-range rpm, let alone high speed power, of which you have none at this point.

I've spent a lot of time trying to get some of my motors past this "sticking point" and each one has been trial and error, a lot of error, and no two responded to exactly the same changes made. Some wanted less or more compression, others a different x-pipe, one responded to an aftermarket CDI, jetting, carb change etc. None exactly alike. I run a third port cylinder and a window piston in two of my reed (2 petal) engines & one runs super the other not so well and both are tuned alike in every way.

On a positive note when you break through the bottleneck you won't need a tach to realize it. It's a dramatic difference when you come on pipe.

Rick C.
 
Last edited:
  • Like
Reactions: Tony01 and fasteddy

Warphones

New Member
Mar 23, 2020
10
8
3
30
Albuquerque
I've run several engines that use the actual Dellorto carb or the SHA clone and similar mods to those you've made, not exact, but similar. So I'm on the same page if not the same sentence as you. Here's my observations on the 66cc reed setups and with the China girl motors in general. The SHA carb can be quite good but in my experience the Dellorto is much better...both can flow enough to reach 50mph when jetted properly. The carbs design limits tuning and a larger Mikuni makes more sense than trying to get a little more from the SHA carb.

I'd suggest mounting an inexpensive inductance tach/hour meter to the spark wire lead just to see where your motor is struggling. I'm guessing with the 36 tooth sprocket it's not getting much past 7,500 rpm, if that. When these engines run well they can pull over 10K and some 12K plus. Now they won't last long at these revs but they can pull to these numbers.

I normally use 44 to 48 tooth sprockets for tuning my motors, even the modified ones and at times I've found that they also hit the wall at around 7k & they shouldn't, but felt good getting there, and running 38tooth or higher ratio the motors struggled to reach even that many rpms; though I was running faster mph with the smaller sprocket I lost rpm.

Without gaining engine speed, actual speed is pretty much stuck where you are. Tuning makes the difference, but what kind and in what combination will vary. I see you've thinned the mix so you must feel confident the motor is broken in. I'd not think the motor will last very long at that mix ratio, but it will be faster. You don't mention plug chop, but if the plug looks good both fuel flow and compression can't be too far out of line. You're pleased with the way it performs all around, save reaching that elusive 50mph mark so I'd say the motor is functioning fine as also, but the performance tune isn't working...your mods are not working in combination to build power at high mid-range rpm, let alone high speed power, of which you have none at this point.

I've spent a lot of time trying to get some of my motors past this "sticking point" and each one has been trial and error, a lot of error, and no two responded to exactly the same changes made. Some wanted less or more compression, others a different x-pipe, one responded to an aftermarket CDI, jetting, carb change etc. None exactly alike. I run a third port cylinder and a window piston in two of my reed (2 petal) engines & one runs super the other not so well and both are tuned alike in every way.

On a positive note when you break through the bottleneck you won't need a tach to realize it. It's a dramatic difference when you come on pipe.

Rick C.
Awesome information I appreciate the reply! My plug chop is pretty much golden brown. I've got maybe 1200 miles on this motor and feel it is pretty broken in. And do allot of 40mph wot runs for up to 20 minutes at a time. If it blows it blows, I got spare jugs and bottom ends, pistons gaskets ready to go at it!
 

indian22

Well-Known Member
Dec 31, 2014
3,648
3,939
113
Oklahoma
No problems. Sounds you've got determination and some skills , just persistence, time and $$ with some study of what experienced builders have done. If you spend time at forty keep a close watch on bike hubs, that kinda' speed and heat generated ...eats grease and bearings quick and tires too. Real are useful and I know your not going to be cautious so...

Rick C.
 
  • Like
Reactions: fasteddy

Tyler6357

Well-Known Member
Mar 15, 2012
1,115
162
63
Santa Barbara, CA
Wow! I almost have that exact set up, except I have a Mikuni VM18 carb and the MZ65 pipe. If I wind it up, I can hit 46 mph on a good day, but I seriously don't like going that fast, the bike is so light, not like a motorcycle, I feel like a big gust of wind from the side and I won't be able to hold it.
 
  • Like
Reactions: Greg58

indian22

Well-Known Member
Dec 31, 2014
3,648
3,939
113
Oklahoma
Tyler you've got a nice setup & it's running well, but your motor is a case inducted reed & that makes it a really different motor from the cylinder reed port design Warphones is working on. Neither one of you has yet reached the power that these two designs can produce when tuned to the max. There are guys that build "port timed" motors that fly by fifty mph. It's all in getting your tune on with the components you choose to run and the basic motor design. Here's the order of design that I find it easier to make power with using a 66cc China girl #1 case inducted reed, #2 Cylinder reed port with window piston and #3 port cylinder. port timed engine. Note I said easier & not easy because getting any of the three to really make impressive power takes work and money, maybe your own work but there's the option to pay a pro to build it, and that gets pricy. Going fast is dangerous on a typical bike frame

I like both you guys motors to this point and see no real reason to do a lot more as they seem to run well right up to the point they're at, but either one can make more power.

Tyler p.m. me about that feeling you get at high speed 'cause I run the same style frame and know they can get real flaky going fast.

Rick C.
 
  • Like
Reactions: Tyler6357

indian22

Well-Known Member
Dec 31, 2014
3,648
3,939
113
Oklahoma
Warphones I read the list of things you have done again, this time I read carefully. If you are running 20 to 1 mix that's break in mix and you should switch to 36 :1 or 38:1 mix for daily running. I'm certain you will find the motor runs much stronger with less oil in it. Engine life will be fine on this mix too. I'm sorry I miss spoke in the earlier post and I've edited it so others won't use the bad information on fuel mix that I gave you.

I would hold off on up jetting until you try the new mix and chop the plug.

Rick C.
 

Warphones

New Member
Mar 23, 2020
10
8
3
30
Albuquerque
Wow! I almost have that exact set up, except I have a Mikuni VM18 carb and the MZ65 pipe. If I wind it up, I can hit 46 mph on a good day, but I seriously don't like going that fast, the bike is so light, not like a motorcycle, I feel like a big gust of wind from the side and I won't be able to hold it.
I'm jealous on the mz65 and carb. Good looking bike! Sweet fmf silencer! I love tinkering on these and pushing the limits!
 

Warphones

New Member
Mar 23, 2020
10
8
3
30
Albuquerque
Tyler you've got a nice setup & it's running well, but your motor is a case inducted reed & that makes it a really different motor from the cylinder reed port design Warphones is working on. Neither one of you has yet reached the power that these two designs can produce when tuned to the max. There are guys that build "port timed" motors that fly by fifty mph. It's all in getting your tune on with the components you choose to run and the basic motor design. Here's the order of design that I find it easier to make power with using a 66cc China girl #1 case inducted reed, #2 Cylinder reed port with window piston and #3 port cylinder. port timed engine. Note I said easier & not easy because getting any of the three to really make impressive power takes work and money, maybe your own work but there's the option to pay a pro to build it, and that gets pricy. Going fast is dangerous on a typical bike frame

I like both you guys motors to this point and see no real reason to do a lot more as they seem to run well right up to the point they're at, but either one can make more power.

Tyler p.m. me about that feeling you get at high speed 'cause I run the same style frame and know they can get real flaky going fast.

Rick C.
When we get the formula down. I want to spread the word to anyone and everyone. I'm so used to searching forum after forum and finding literal crap on allot of them. I just want people to have better aim than what I started with
 
  • Like
Reactions: indian22

Warphones

New Member
Mar 23, 2020
10
8
3
30
Albuquerque
Warphones I read the list of things you have done again, this time I read carefully. If you are running 20 to 1 mix that's break in mix and you should switch to 36 :1 or 38:1 mix for daily running. I'm certain you will find the motor runs much stronger with less oil in it. Engine life will be fine on this mix too. I'm sorry I miss spoke in the earlier post and I've edited it so others won't use the bad information on fuel mix that I gave you.

I would hold off on up jetting until you try the new mix and chop the plug.

Rick C.
Even with the Reed I still get oil building up in my carb and filter. My petals I think aren't sealing. They are junk. Trying to find replacements but not easy. I hope to contact boyesen and see if they have something that will fit. But yes here soon I'll try 36:1
 
  • Like
Reactions: indian22

Tyler6357

Well-Known Member
Mar 15, 2012
1,115
162
63
Santa Barbara, CA
Thank you both for your kind complements on my bike. It means so much coming from guys who are such excellent bike builders and who know what they are talking about! I've seen the case reed design, I'm certain the more direct fuel dynamics would make a pretty big difference over the type I have. But I'm happy with the power of my bike, I'm not particularly that interested in hitting 50 mph on this thing, I'm no longer a young man, it is what it is.
 
Last edited:
  • Like
Reactions: FOG and indian22

Tyler6357

Well-Known Member
Mar 15, 2012
1,115
162
63
Santa Barbara, CA
I'm jealous on the mz65 and carb. Good looking bike! Sweet fmf silencer! I love tinkering on these and pushing the limits!
Yeah, that's a FMF Powercore 2 silencer. I would have never put it on the bike but I got such an unbelievable deal on it that I couldn't resist. They have a shorter one they call "the shorty" that might have been better but there was no deal on that one. One thing is for sure, it's very quiet with that thing on there.
 
Last edited:
  • Like
Reactions: indian22

indian22

Well-Known Member
Dec 31, 2014
3,648
3,939
113
Oklahoma
Tyler sorry I was thinking of an entirely different engine build, which is case inducted and yes I'd think you would be quite pleased with your bikes and these mods. The handling you described at higher speeds however is troubling and I'd caution to not approach these speeds without addressing some frame issues first. This style frame is a nice one, but wasn't intended to be ridden this fast.

Rick C.
 
Last edited:
  • Like
Reactions: Tyler6357

Tyler6357

Well-Known Member
Mar 15, 2012
1,115
162
63
Santa Barbara, CA
Tyler sorry I was thinking of an entirely different engine build, which is case inducted and yes I'd think you would be quite pleased with your bikes and these mods. The handling you described at higher speeds however is troubling and I'd caution to not approach these speeds without addressing some frame issues first. This style frame is a nice one, but wasn't intended to be ridden this fast.

Rick C.
No worries, no need to apologize. Anyhow, I think the frame would do better at high speeds if it was a bit longer but weight must be a factor too, a heavy motorcycle cuts right through wind gusts but this thing feels like it can't stay on the road at really fast speeds, like it's almost hydroplaning down the road, haha. It's not really even noticeable until I get up to about 42 mph and there is some wind.
 

indian22

Well-Known Member
Dec 31, 2014
3,648
3,939
113
Oklahoma
I increased my hybrid Grubee to 53" wheel base with axle drop extension plates and run a bit more than 2" plus of trail. on the forks. And yes loaded weight has some advantage if not overdone and that includes the rider as well. My hybrid is about 150 lbs wet and 320 loaded. Speed does create the need for bike modifications. No one should build power to the point that frame and brakes are out run!

Rick C.
 
  • Like
Reactions: Tyler6357

Tyler6357

Well-Known Member
Mar 15, 2012
1,115
162
63
Santa Barbara, CA
I increased my hybrid Grubee to 53" wheel base with axle drop extension plates and run a bit more than 2" plus of trail. on the forks. And yes loaded weight has some advantage if not overdone and that includes the rider as well. My hybrid is about 150 lbs wet and 320 loaded. Speed does create the need for bike modifications. No one should build power to the point that frame and brakes are out run!

Rick C.
Wise words for sure.
 

Tyler6357

Well-Known Member
Mar 15, 2012
1,115
162
63
Santa Barbara, CA
I increased my hybrid Grubee to 53" wheel base with axle drop extension plates and run a bit more than 2" plus of trail. on the forks. And yes loaded weight has some advantage if not overdone and that includes the rider as well. My hybrid is about 150 lbs wet and 320 loaded. Speed does create the need for bike modifications. No one should build power to the point that frame and brakes are out run!

Rick C.
You know, when I look at warphones frame I don't see a much longer wheel base than what I got. I don't know how heavy his bike is, maybe it's a steel frame, mine has an aluminum frame and my entire bike weighs only 68 lbs. Do you think his frame would create the same phenomenon at high speeds or heavy winds as my GT2-A frame?