New 4 stroke, revs up, but just won't move

zhono

New Member
Feb 2, 2012
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MA
So I recently decided to sell my scooter and build a new bike. All the previous bikes I built were with cheap 2 stroke kits. Mixing gas sucks, as does pedaling up to speed to start the engine. So I got a 4 stroke kit. Grabbed a cheap Walmart beach cruiser to mount it on, and a bunch of small extras(mirrors, lights, rack and trunk, etc).

The mounting plate came broken, of course. And the seller was no help. I wasn't about to pay $50 that I don't really have for another one, so one trip to Home Depot and $4 in nuts and bolts later, and that issue was solved. Got the engine mounted, then everything else. Put in some 10w30, pushed it to the gas station, gassed up. Engine started in 2 pulls. Walked it home. Started up and ran the engine a few times, 10-15 minutes each time.

With the bike up on the stand, hitting the throttle gets that back wheel moving like crazy. But the problem is, if I sit on the bike, no amount of throttle can get the bike moving, unless I am facing downhill a bit, or a push off with my feet(I have no crank/pedals. And if I do move, it's gotta be like 5 mph. The engine will rev up to what seems like about all the RPMs in the world, but it just won't go more than that 5 mph. And if the bike if facing a slight incline(not even a hill, just the tiniest of inclines), you can forget it. It will just sit there, and I'll hit the throttle for a few seconds before I'm afraid of destroying the engine or something.

Anyone have any advice here? What would the most likely things to check be? This is my first 4 stroke, so I'm used to the 2 strokes, where either the engine runs and you go, or it doesn't and you don't. The 4 stroke kit WAS just the cheapest one I could afford from Amazon, so it's entirely possible that I just got a piece of junk. Unfortunately though, it doesn't look like the seller is going to be of any help with returns or replacements or anything, so I'm stuck with what I have.
 

MotorBicycleRacing

Well-Known Member
Jul 28, 2010
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SoCal Baby!!!
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How much did you pay for your kit?
There are different transmissions on 4 stroke kits.
Yours is probably the crappy pocket bike gearbox.

Is the centrifugal clutch slipping?
Do you have the choke on?

Post some pics.
Are you planning on installing functioning pedals?
 

zhono

New Member
Feb 2, 2012
13
0
1
MA
How much did you pay for your kit?
There are different transmissions on 4 stroke kits.
Yours is probably the crappy pocket bike gearbox.

Is the centrifugal clutch slipping?
Do you have the choke on?

Post some pics.
Are you planning on installing functioning pedals?
Choke is not on. No idea how to check the clutch on these. The specific kit I got is https://www.amazon.com/gp/product/B06WRQRTH4
I didn't really expect it to be great or last very long, but I did expect it to at least work for a little while until I had money to upgrade. All the 2 stroke kits I've ever had were less than $100 on ebay, and they all ran pretty damn well, even when I beat the **** out of them. I'm guessing the 2 strokes are just more sturdy/forgiving than the 4 stroke setups. Or maybe I was just lucky.

As for pedals, I hadn't planned on it. I bought some pegs and bolted them in place of the crank.
 

Going2Hell

Member
Nov 22, 2013
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Victor, Colorado
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Yes, that is exactly what my bike will do... if the choke is on! I was sort of disappointed you figured it out; luckily I read the thread before I suggested it. Once you get the gist of the 4-cycle - check your valve-lash when you get the motor, set accordingly - Break-in is everything - Oil changes are your best friend...
PS: That mount is crap, same with the Throttle and method of attaching the sprocket to the spokes. I switched the tension-wheel/bracket over to the pedal side to reduce torque on a flimsy product; after I sized the 'engine chain' to be adjustable in a standard rear-fork 'slide distance'. Checking the clutch is not hard, remove the transmission; make sure the dark gray 'pads' are wearing evenly and don't appear damaged... just like brake pads! ~ DO NOT OVERTIGHTEN THE BOLTS - LOCTITE IS GOD! ~

I've gotten 6,000+ Miles on my 'Huasheng' and 6-years of quality mountain riding! Build journal is in my signature...
 
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zhono

New Member
Feb 2, 2012
13
0
1
MA
Yes, that is exactly what my bike will do... if the choke is on! I was sort of disappointed you figured it out; luckily I read the thread before I suggested it. Once you get the gist of the 4-cycle - check your valve-lash when you get the motor, set accordingly - Break-in is everything - Oil changes are your best friend...

I've gotten 6,000+ Miles on my 'Huasheng' and 6-years of quality mountain riding!
I don't really understand your post. I haven't figured anything out, and I haven't solved my problem. Setting the choke one way or the other made no difference to my problem. I tried running the engine with the choke open, closed(kills the engine), and half way in between. All the same.
 

Chippa

New Member
Nov 5, 2015
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0
1
Round Rock, Texas
Maybe it's the carburetor. Try cleaning it out, in particular check the bowl for debris.

I was going to upgrade my 49cc to the predator 79cc, but then I decided to clean out the carburetor on the 49CC 4 stroke. Wow what a difference in acceleration. I have been running this 49cc for two years, and never realized that the carburetor had debris in the bowl. It didn't make much difference in top end speed, only in acceleration. But I no longer want the 79CC predator. The max RPM doesn't seem to much different.

So this is something you might check. It sounds like it is just your acceleration.
 

zhono

New Member
Feb 2, 2012
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0
1
MA
Definitely not a carb problem. The engine runs great.

I just found the problem, actually. And thankfully. I decided to pull off the transmission and have a look at the clutch, as per MBR's suggestion. Immediately upon loosening the first bolt, the smell was terrible. The entire area was filled with black powder, obviously the pads, ground up to nothing. Reading some info on another forum, seems these springs are too hard. I used a screwdriver to spead a small gap in the middle of each spring, put everything back together, and now the bike actually goes. Quite a huge difference. Still not as well as it should, but once I replace the clutch flyweight with new pads and use softer springs, I should be golden. Might have to bite the bullet and replace the mounting plate, as I really don't trust the one I have, but that's much better than shelling out for a new kit like I was worried I might have to.

*EDIT* What do you guys think about replacing the flyweight with a 2 spring flyweight? Bad idea? Also, looking through Amazon and ebay, and not sure how to find the correct parts for this engine.

*EDIT 2* Also realizing, the pads are completely gone, so probably a bad idea to keep running the thing as it is.
 
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waynesdata

Active Member
Jul 10, 2017
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How much did you pay for your kit?
There are different transmissions on 4 stroke kits.
Yours is probably the crappy pocket bike gearbox.

Is the centrifugal clutch slipping?
Do you have the choke on?

Post some pics.
Are you planning on installing functioning pedals?
What transmission / gear box would you use. Wish we had a 79cc how to. This stuff keeps getting asked. Serching all over the site is time consuming.