Jackshaft Not maintaining enough to get up hills

Sitherus

Active Member
Joined
Apr 4, 2016
Messages
252
So it goes, I lose 10% power from the jackshaft because of gearing.
Im having trouble maintaining my speed. I live in roanoke va, an you'd have a hard time finding a flat spot to ride. plus im using my bike for work.

When im going fast down a hill and come to an uphill, I lose all power and have to pedal like crazy to keep the engine running. If the engine stalls, Ill have a hard time getting it running until im on a down hill.

Im running a 66cc engine with delarto-sha clone carb with what ever jet came on it.
a sbp shift kit that runs to a high gear of 28 teeth and a low of 14 teeth.
a 6 speed thumb shifter on the left side below the clutch.
A YZ700 style Expansion Chamber made for these two stoke engines with no muffler.
(I didnt order it from this guy but its the same) http://ebay.to/2wlkiM7
no fuel filter because i cant fit one. Ill get an internal one day.
e3 High performance spark plug
A high comperssion head, (Jakes Head)
the bike weighs 100 ++ pounds although theres no way to be sure an i weigh 250.

What can i do about the power?

 


FurryOnTheInside

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Joined
Sep 23, 2013
Messages
3,686
I think you're saying that you can't keep the engine RPM up due to insufficient gear range.
10% less RPM is 10% less power; but actually it's a lot worse if you're no longer "on the pipe" (if the pipe was ever working, that is).
So extend the gear range. Time for a new rear hub.. A freehub with a mountain bike cassette of 8 speeds or more and a *real derailleur. :)





*not Tourney PoS. Goggle: "Shimano hierarchy"
 

crassius

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Jul 23, 2012
Messages
4,575
I'm wondering what speed is on flat ground in a high gear - should be somewhere near 30-35mph if motor if running right.

Otherwise I'd suspect muffler or carb problems.
 
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6blueoval9

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Aug 28, 2017
Messages
1,120
Looks like a nice torque pipe but who knows...for the price id go with a tried and true zeda mz65 which is actually an MZMiami pipe.

As far as the carb...rather its jetted properly out of the box we cant tell..your elevation and how it runs would help determine that.

I lived in west virginia for a few years and some of those hills can get rather steep.

Does it want to stall out even in first gear?

Shimano has a super range cassette that would help but lack of power doesnt help much.

How much power determins how much you can invest really.

You can get a longer intake that will help with torque but it will hurt your max speed.

You really want to be sure the carb is tuned/jetted properly..if its too rich you lose a bunch of power..if its too lean you can also loose power AND damage your motor.

I can recommend some changes but you have to handle the carburetor end of things.
 

Sitherus

Active Member
Joined
Apr 4, 2016
Messages
252
I'm wondering what speed is on flat ground in a high gear - should be somewhere near 30-35mph is motor if running right.

Otherwise I'd suspect muffler or carb problems.
I don't have a speedometer but i keep up with traffic in 25mph zones
 

Sitherus

Active Member
Joined
Apr 4, 2016
Messages
252
Looks like a nice torque pipe but who knows...for the price id go with a tried and true zeda mz65 which is actually an MZMiami pipe.

As far as the carb...rather its jetted properly out of the box we cant tell..your elevation and how it runs would help determine that.

I lived in west virginia for a few years and some of those hills can get rather steep.

Does it want to stall out even in first gear?

Shimano has a super range cassette that would help but lack of power doesnt help much.

How much power determins how much you can invest really.

You can get a longer intake that will help with torque but it will hurt your max speed.

You really want to be sure the carb is tuned/jetted properly..if its too rich you lose a bunch of power..if its too lean you can also loose power AND damage your motor.

I can recommend some changes but you have to handle the carburetor end of things.
Actually i paid 60 for my exhaust.

I cant get it go up hills in anything but 6th, and in first which i assume is the smallest is fast on the flats (walmart parking lot)

I modified my bike frame to take fat wheels which limits how many gears i can get, I think i might be able to fit 7 but thats it unless there is a way to a more to the other side.

longer intake? im thinking about getting a reed valve with a boost bottle, what are your opinions on that?

I guess ill do some research on what my altitude is and how to check rich/lean.
 

panmines

Active Member
Joined
May 28, 2015
Messages
113
I am curious to know what your gear ratios are. Did you use just the stock sprockets that came with the SBP kit?, or did you buy the ones for low gearing? With the stock kit you have a 17t left jack shaft sprocket, 10t right jack shaft sprocket, 44t outer chaining and a 36t inner (pedal) chainring. If you are using the stock sprockets, you have a 23.9:1 engine to rear wheel gear ratio in your lowest cog (28t) on your freewheel, which is no where near low enough to climb moderate hills without peddling. You should have at least a 35:1 ratio for good hill climbing. I personally use a larger 21t left jack shaft sprocket and a smaller 24t inner chaining, which gives me a 53.7:1 ratio in my lowest (34t) gear. In my highest gear (14t) its a 24.5:1 ratio which gives me about 17mph at 5000 rpm. I know that's slow, but that is my ideal cruising speed.
 

Frankenstein

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Joined
Jun 24, 2016
Messages
5,078
Actually i paid 60 for my exhaust.

I cant get it go up hills in anything but 6th, and in first which i assume is the smallest is fast on the flats (walmart parking lot)

I modified my bike frame to take fat wheels which limits how many gears i can get, I think i might be able to fit 7 but thats it unless there is a way to a more to the other side.

longer intake? im thinking about getting a reed valve with a boost bottle, what are your opinions on that?

I guess ill do some research on what my altitude is and how to check rich/lean.
Somethings wrong with your bike. If you are getting your top speed in a Walmart parking lot then you aren't going fast enough to have a reasonable top speed.

Put a fuel filter on that fuel line please. You should still have a stock muffler, put it on, if no change check for an air leak.

Your carb has a gasket on the top where the spring and weird click lever plastic top part gets screwed on, it's a small red gasket, very easy to put the top on without it being in place right, some don't even come with a gasket which is a big source of a leak. You'll want to make sure the plastic insert is completely seating in the carb over the intake.

I have lots of starting fluid usually, that tends to choke the engine if introduced, but sometimes makes it Rev faster depending where the leak is. I would spritz it around along gaskets and mating parts, if it changes the idle (just hit the filter lightly with it to see exactly how it would respond) then you have a leak.

That carb also tends to spit oil and clog the cheap filter, it really slows down the motor when it does that.

What head are you using? Did you do a compression reading at all? Do you actually know if it's appropriate or just off the wall and giving you bad results?
 
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