Introduction: My Bike, PICS, Thoughts, Findings, and Questions

Grlzzly

New Member
May 9, 2020
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Hello,

Great to finally be a part of the community. This is my third MB. Cumulative experience so far working on these things has also made it my best in terms of reliability and smoothness of operation. Wanna share my findings and learn anything I can to increase performance.

I'm no speed demon. I like to coast. But having power when you need it makes your bike more safe on the road (helping you to merge and deal with traffic). My bike is on the slow side. Tops out at a pathetic 47km/h (29mph). Can't keep up with traffic here in Montreal. People drive at 60km/h (37mph) on main roads. For starters, my Fenders rattle like **** when I get the RPMs up (any fixes for that?). My brother and his friend ride motorcycles and want me to ride with them (off the highway, of course). So unless I get this thing to move and cruise faster, I can't ride with them. Now on to the nitty gritty!


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Grubee GT5A Skyhawk 66cc slant head on a Hyper Easy Rider. NT carb, standard CDI, 44T sprocket. Everything else is custom or modified.

Motor mount. Upgraded mounting studs using grade-8 M6 threaded rod. Kept stock rear mounting block, but front mounting hardware I always found to be rickety, so I made a front mounting block from a hockey puck. Super solid. Fits like a glove. Might adjust to lower the motor a bit. Should improve handling.


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Learned the hockey puck trick on a forum back in 2015. Also learned (the hard way) that motors tend to pull and bend out to the left from all that torque. So I reinforced it with another hockey puck, a 5" mending plate, aluminum flat bar, and some nuts and bolts. This motor aint going nowhere! Not without the bike frame attached to it!


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The second (but perhaps most interesting) subject would be the exhaust; I used the stock one, cut it at the muffler, then clamped on some 3/4" automotive heater hose and ran it to the back of the bike. I used a lawn mower muffler (for a 4-8HP Briggs or Tecumseh motor). It is 3/4" threaded, so I fitted a 3/4" copper threaded plumbing adapter to it. The non-threaded side of the adapter fits snugly into the heater hose. Sounds much better than stock but doesn't provide enough back pressure. So I sandwiched a metal washer inside the threaded part of the connection, allowing me to try different size washers between the muffler and adapter; a 5/16" washer offers a decent compromise between noise and power.

The muffler was spitting gunk all over my back rim and tire. I picked up a 3/4" 45-degree Male/Female copper elbow to re-direct exhaust gases away from the bike. To secure it to the end of the muffler, I pressed the male side into a 2" piece of heater hose, then pressed the heater hose into the end of the muffler. The only place it leaks now is on the seam of the muffler (because of the way it is designed). [email protected]% me right? But the heater hose fits on tight enough to seal itself with no leaks whatsoever. And with hose clamps it isn't ever coming off unless I want it to. Some day I might cut away a small section of hose and throw on an expansion chamber. I would really love to hear suggestions as to what expansion chamber I should get. Banana pipe? Dirt bike exhaust? Whatever it is, I would like the heater hose to fit on both sides of it.

Disclaimer: I heard about the heater hose trick on a forum so I take no credit for it. We ought to spread the word about EPDM rubber heater hose (for MB exhaust pipes). It certainly doesn't get enough mentions on the MB forums. People seem to talk incessantly about welding exhausts together as if there are no other alternatives. Had me pulling my hair out until I learned this trick. I don't mean to start any kind of polemic, I'm just saying, yes, welding/brazing is way cool, but not everyone can do it. My hose is holding up great and if it starts to degrade in a few years, so what. It's cheap and easy enough to replace. I've even read of a heater hose outlasting a china-girl engine. So yeah. Moving on...


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Now the tank. Wanted something to fit inside my frame with decent capacity. A small fire extinguisher would look nice and but only give me 1L. A 1.89L rectangular bottle of Ocean Spray Cranberry Juice was the perfect size and shape to fit in the frame but was only a plastic juice bottle, so not at all safe, although the idea for a transparent gas tank seems totally impressive to me. Any way I can strenghten and seal the plastic bottle so I can use it as a gas tank? Maybe coat it with multiple layers of fiberglass resin? That might obviously take away the transparent aspect but give me a decent shape and capacity to work with. Anyway, for the time being, I opted for a 90-degree 4" ABS plastic elbow, sided with matching 4" ABS threaded end plugs. The end plugs only fit loosely into the elbow, so I had to build up some thickness on them using hockey tape, then covered that with yellow teflon tape, so the end plugs press firmly into the elbow. No leaks, although one started to push back out from the pressure. I took it apart and put more tape on, tightening the fit. No more problems as of yet, and never a leak. Might just JB-weld it for good measure. The filler neck is a 90-degree 1" steel street elbow and the filler cap is a 1" PVC threaded cap. Used the stock petcock at the bottom. Tank holds ~ 1.3L and looks better to me than the dorky stock tank (no offence to those who use it). I would like a higher-capacity, more form-fitting tank but can't weld or make one from styrofoam and fiberglass as seen on the forums somewhere. Way too difficult but the results sure are amazing. Any other ideas? Would love to hear your thoughts.


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Chain tensioner uses stock roller mounted on a 6" mending plate, bent to alignment. Oversized washer with a small hole on the other side of the roller to attach a spring on each side of the chain, avoiding rotational pressure on the arm. Oh, also doubles tension.


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A trick that enduro racers use to stiffen up their wheels; put zip-ties around where the spokes intersect. Get them on tight. Wheels feel much more rigid after the procedure and lord knows we could use the extra reinforcement if we're using rag-joints. This mod should be higher on my list with the heater hose. Takes about an hour to do, costs only a couple of dollars, but results are so worth it. Highly recommended and absolutely essential mod to anyone who rides a motorized bike without a clam-shell hub adapter. Now if I upgrade to 12-gauge spokes with zip-ties, these wheels will actually become bomb-proof. They might even make pedal-starts on rag-joints a thing of the past (assuming the clutch can take it). Thoughts?

Another absolutely essential mod is the "stop-chain-lock-up" bracket that I made from aluminium flat bar. Doesn't require any permament modification of the engine case and completely eliminates the problem of the chain bunching or locking up on the front sprocket, under the cover. Simple, highly effective fix.


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We all hate the stock plastic toy-throttle assembly. I made a killswitch and brake-lever-throttle. Was thinking of wax-potting the switch for weather resistance like they do with guitar pickups, but don't know if the switch mech would still work after that. They're cheap enough to try and replace anyway. The brake-lever-throttle gets mad uncomfotable after riding for extended periods of time. Napa Canada apparently doesnt stock a single twist-grip throttle in all of Canada (the metal one, # SME 703921). Might just order from ebay or get an ATV thumb-actuated one. Just hate waiting months for things to come in from China. Wishing for a local vendor in Montreal that sells MB upgrade parts. Only vendor I know sells stock parts only. Already ordered a cone air filter for my NT carb and I might have to wait until July to get it. *sigh*

Corrugated electrical wire housing to keep things neat around the bars. I love the look of it, especially with hose-clamps holding it in place.

Kenda Kinetics 26x2.35" tires. Montreal roads are notoriously bad. The stock cruiser tires were 26x2.125" and the difference might not seem like a lot but the Kinetics really do cushion those handle-bar-loosening blows a lot more. Tried a pair of Kenda 26x2.5" Nevegals which looked rad but were too wide to clear the chain... mostly because the tire knobs stick out past the wall of the tire. If I could find cruiser tires or slicks that are 26x2.5", they might fit. My first motorized bike was a Felt "Tip" cruiser, which had jumbo tires on it. I loved them for their old school linear tread pattern. Also really like the schwinn-style tires, sort of like the ones on Huffy Cranbrooks, but they only come in 26x2.125" width. I would really love that tire in 26x2.35" or even 26x2.5". Any leads or pointers for tires would be greatly appreciated. Note: I really don't like Maxxis Hookworms. Thick Bricks and Thick Slicks are not bad though.

Cooling fin silencer mod.

E3.10 spark plug.

Atlas universal small engine fuel filter.

So how would you go about modding it for a higher cruising/top speed? It's well broken in and I love how it pulls after slowing down at stops. Would hate to lose torque, but there's no escaping the trade-off. Only a compromise. As mentioned earlier, running a 44T on 26x2.35" tires. Weight 160lbs. Montreal is moderately hilly. Should I go 40T, 36T, or 32T? What other performance mods, if any?

Cheers!
 
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PeteMcP

Well-Known Member
Jun 27, 2017
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Time for a survey.
We asked 100 forum members....
Your call. 'Dorky stock tank' supplied in bicycle engine kits? or the U-bend tank pictured above?
Our survey sez....
 

Grlzzly

New Member
May 9, 2020
3
1
3
28
Time for a survey.
We asked 100 forum members....
Your call. 'Dorky stock tank' supplied in bicycle engine kits? or the U-bend tank pictured above?
Our survey sez....
Hey man, that's just my opinion.

Can you help me with the more important stuff like sprocket size and getting more HPs??

please sir
 
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PeteMcP

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Jun 27, 2017
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Important stuff: Right. You mean, like, the importance of having a sealed gas tank that isn't about to pop like a champagne cork? That tank set up on your ride is out and out dangerous. No joke.
You gave us chapter and verse on how you built your plastic 'tank' using unsealed, interference-fit end caps, secured in place using hockey tape to prevent the end caps blowing off due to gas fume build-up. No mention of a vent in the cap, so I'm guessing there isn't one. Dude, that set up is only marginally safer than riding round with a Starbucks styrofoam cup-full of gas in your bike's cup holder. Think about how safe your tank set-up is if you and your bike take a spill. Your bike, your opinion. I'm just giving you mine.
Less important stuff: Yeah, like, Squeeky fenders can be annoying - but maybe the Hockey Store has something you can jerry-rig up a fix with.
 
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