97cc engine swap!

CrazyDan

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Jul 9, 2016
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1,661
Tha a

It gets going pretty quick, but I'm geared way to tall.
my buddie would pass me on his 40cc pocket bike! Untill he ran out of rpm and I chugged along past him, this was before I upgraded it so I was all stock, vs his somewhat modified 2 stroke, so I might be equal now, only time will tell ;)
I bet if you geared it for a lower speed, say at 50 mph at 7000 rpm, you would wreck your friend on acceleration and top speed.
 


mark20

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Sep 26, 2018
Messages
392
I bet if you geared it for a lower speed, say at 50 mph at 7000 rpm, you would wreck your friend on acceleration and top speed.
My next course of action is to remove all the restrictions this engine has (it has lots of them! Its like its breathing though a straw, even with the bigger carb!
I'm planning on buying me a 54-56t sprocket, but I dont want to just throw money at this thing yet (main reason for this project was to test out what I can do on a budget,which was 50$ and fix anything with skills
ie fabrication, trail and error, etc )
I'm going to gear it lower so this thing will fly! (I'll have to wait for April, as I get payed then)
Wish me luck!
 

CrazyDan

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Jul 9, 2016
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Nah you need to gear it higher (smaller driver gears or larger driven gears) to let it spool up to top rpm. You have It geared too low atm, if you can gain power, then you can gain speed while retaining low rpms. You've ungoverned the engine and barely got an rpm increase, which tells me you are already at too low of a reduction. If you can spin your engine to 7800 unloaded already, remove the internal governor parts and get a higher reduction to reach near top rpms. There are calculators here and elsewhere that can tell you what power is needed for certain speeds. Do maths and find the spot that doesn't hurt acceleration too much while still hitting your target top speed at a specific rpm. Might take a few tries trying different sprockets.
Edit: tldr: As it stands your gear reduction doesn't really let it go into ungoverned speeds, almost no point in bypassing the governor yet till you gear it to reach higher rpm.
 

mark20

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Sep 26, 2018
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392
Thats the plan! I think a 56t would work great! (As a I have a 44t already, that would lower my gearing dramatically! I would hit 35mph around 5600)
And that would get my acceleration faster as well!
I'll do that when I get the $ (agian, in April)
So far this build is going great!
 

The_Aleman

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May 2, 2007
Messages
785
Use both of these tools together: gear calculation utility and power calculator. Both available on this forum, made by @loquin. Wish he was still a part of the forum, he has done much to pioneer these new custom motorized bike setups (go away trolls, thousands have studied his posts and downloaded his calcs, they are very accurate).
Yeah, he did a lot of work so that you can fake post about your theoretical speed freely! You're not fooling me tho, you're still pretty slow.
 

mark20

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Sep 26, 2018
Messages
392
Yeah, he did a lot of work so that you can fake post about your theoretical speed freely! You're not fooling me tho, you're still pretty slow.
I never said I was speed demon
I gotten up to 35mph on the gearing I have right now.
Also, weren't you arguing about people going too fast on there "under engineered maxi wannabe scooters" on the other thread lol. It seems people that are going faster than you are dumb and people going slower than you are dumb, pick and choose man! You cant have both!
 

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The_Aleman

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May 2, 2007
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785
I never said I was speed demon
I gotten up to 35mph on the gearing I have right now.
Also, weren't you arguing about people going too fast on there "under engineered maxi wannabe scooters" on the other thread lol. It seems people that are going faster than you are dumb and people going slower than you are dumb, pick and choose man! You cant have both!
Never said you were a speed demon, either, I wasn't even talking to you. Looks like reading comprehension isn't your strong suit.

A lot of people on this forum are either missing the point or butthurt because I think putting huge engines on these and going fast is dumb :rolleyes:
 

JerboaJohn

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Jul 29, 2018
Messages
900
I bet if you geared it for a lower speed, say at 50 mph at 7000 rpm, you would wreck your friend on acceleration and top speed.
yup and there's another source for speed other than the engine. weight reduction and lowering friction. like better chain, maybe #35 instead of 415, bearings in hubs/stem can be upgraded, etc
keep us posted!
 

mark20

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Joined
Sep 26, 2018
Messages
392
yup and there's another source for speed other than the engine. weight reduction and lowering friction. like better chain, maybe #35 instead of 415, bearings in hubs/stem can be upgraded, etc
keep us posted!
yea but im cheap lol.
its getting up there now as the clutch is wearing in.
chain alignment is my main problem. the chain is #40 chain so its pretty beefie (and heavy)
im just going to ride it and enjoy my one of a kind build!
ill keep you posted if i do anything (or if it blows up)
 
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