79cc Predator 4-stroke with Q-maitc on 29" Macargi Fatal Love

This build was originally going to be a 212cc Predator with GTC TC1002P torque converter but when all the parts were here it looked to be way to big so I exchanged the 212 for 79cc.

I went with Quentons special Q-matic for the 79cc Pred from E-Z Motoribikes.
The engine shaft is a bit too long for the thin profile cover (which is good) so I just cut a hole for it but you could cut 1/2" off the end of the shaft.

79ccPredL.jpg


79ccPredR.jpg


The bike is a 29" Macargi Fatal Love I put a pair of caliper brakes on to help the coaster brake and of course HD tubes and liners in each wheel.

The engine mount base and wide cranks were left over from a 49cc HS jackshaft shift kit build. By leaving the engines mounting plate off the engine it mounted to the plates front slots but we had to drill rear mount holes.
Note we tack welded the plate joints on the underside of the plate as we didn't any adjustment after it was fit.

The exhaust was removed and we fabed a new pipe using the flange on the stock exhaust welded to a spare section of SBP expansion chamber pipe and then a 2-stroke Cat muffler with spiffy heat shield.

If that pipe proves to be too restrictive I'll pop the end cap, pull out the Cat Plenum and make the end covers hole a little bigger.

79ccPredLB.jpg


We redrilled a 56T Maniac Maniac #41 chain sprocket for a 9 hole rag joint fit.

The gas tank was removed and the linkage from the manual throttle/governor, then we fashioned an adjustable throttle cable end to the engine.
The normal pull for a throttle is ~ 1.5" and 1/3 throttle turn, the throw of the carbs throttle tab would have made the throttle about 1/8 turn from idle to wide open so we extended the throw by adding an 1.5" tab to the carb top.
This worked out great! It gives the full 1/3 throttle twist response and lined it up perfectly with the cable stay.

Then we just used an old NT carb spring for a very nice 'snap back' throttle action.

79ccPredRF.jpg


The gas tank is 1.2 gallon Whizzer tank that was mounted with a combination of 1.5" muffler clamp stays, frame tube brackets, long bolts and spacers.

It has a drive side chain tensioner for future adjustment but with use of a #41 chain 1/2 link it is darn near direct drive.

Last but not least the hard rubber grip was removed from the throttle barrel and BMX foam grips with spiffy end caps installed as well as nice new brake handles from a bike that got a dual pull for the front and rear calipers.

We still have some odds and ends to do today like put the pedal chain guard on then get some test riding to decide about the exhaust but that's easy stuff.

If you are an experienced builder with welding skills and lots of spare parts around this project isn't too bad (~60 man hours).

BUT, if you are an MB rookie or just don't have the tools, skills, and misc parts I highly recommend you just start with a 49cc HS with 4G tranny complete MB kit for ~$360 as just the 79cc Pred and Q-matic were $400 and you still need a mount plate, rear sprocket, wide pedal crank set, gas tank, custom exhaust and throttle to make it go.
 
I opened up the main jet on my 79 a couple of thousandths and it runs better.
All these motors are too lean - govt interference again.

By the way, I do not know the limits of the stock flywheel.
With the governor intact, it will never explode. On mine, I loosened the stock lever pivot nut (that attaches a throttle cable to) tweaked the gov a little higher and went with it.

One of the nice benefits of a gov is under increased load- it automatically compensates and gives it more umph.
 
Nice build KCvale ... Any problems running the stock carb? Mine took 3-4 pulls with the choke on to start initially.
That was a customer build I did in summer so no problems starting it, here it is the end of January with mid 60 lows and mid 70's for a high ;-}

I don't recall what I did with the governor but it it wasn't just 'flopping around'.

Thanks for the Kudos guys.
 
I opened up the main jet on my 79 a couple of thousandths and it runs better.
All these motors are too lean - govt interference again.

By the way, I do not know the limits of the stock flywheel.
With the governor intact, it will never explode. On mine, I loosened the stock lever pivot nut (that attaches a throttle cable to) tweaked the gov a little higher and went with it.

One of the nice benefits of a gov is under increased load- it automatically compensates and gives it more umph.

Ya you should be fine, and a flywheel explosion is pretty rare. It's just if it does happen it could easily kill you

The rod's more of a problem, I'll take a wild guess and say that anything under 4000rpm is totally safe for continuous use
 
Looks nice! How fast does it go? And what's the MPG like?
This bike was like 30 or 40 builds ago and it didn't have a speedometer but well over 30 MPH with those big 29" wheels.
The MPG wouldn't be as good as a 49cc shifter but over 60 MPG I would think.
 
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