Some help with Trek 720, 80cc BGF ebay engine

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jdubbya

New Member
Jul 15, 2011
10
0
0
Port Angeles, WA
Hi guys, im trying to build a Trek road bike with a 80cc boygofast engine from ebay. Ive got it in there, and can start it with an air ratchet on the magneto bolt, but i just cant get it running at all with pedal power. Im wondering if its partly a clutch not engaging hard enough problem? I can have somebody hold the bike down with clutch engaged, and it turns the motor with an air wratchet on the magneto while the clutch slips and the back wheel stays stationary, should it be holding tighter on the clutch?

Seems like if i installed the pullstart that he sells, id have a chance of the bike firing up if it died on the road, right now i can only get it going with air power on magneto bolt. It has good compression, checked that, 120 lbs. I think the magneto is flakey though, white wire is reading dead short to ground, I ordered a new one, so i took the old one and cut some windings on the inner white wire coil, so if its still shorting out, it wouldnt be as bad. Im hoping hotter spark will help when the magneto comes this next week.

Anything else i should try? Im wondering if a bike with 27" tires can get the motor spinning fast enough on flat ground to start? It seems geared really high on these big ol tires.

Looking for moral support here :)
 
R

Ratman9366

New Member
Apr 2, 2012
5
0
0
Northern Illinois
I just joined the website, waiting for delivery of my first kit. I also am planning on using a Trek 720. Hope to get the project goinf this week, I will post how it goes. Did you have any clearance problems mounting the motor?
 
rustycase

rustycase

Gutter Rider
May 26, 2011
2,746
5
0
Left coast
Oh Boy!

...probably should not have went in there cutting windings, JW..

anyhow, the white wire is for a lighting circuit, and should just be clipped and capped off, for most of us who are not interested in electronic experiments.

<< I >> would not use a power tool on the crank, and you should not have to.
Also, IMO, pedaling is far more efficient than pulling a string, for starting.

Yes, you could have a slippy clutch.
Clutch pressure can NOT be adjusted via the RH cover plate, so review the threads on that subject.

May I suggest you review the threads on troubleshooting in the repair section?
You'll read about defective kill switches and funky plug wires... all kinds of stuff!

There's a good possibility you have a defective part, new from the factory, but a strong probability you can resolve the problem by going through step by step diagnosis.

Good luck
rc
 
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happycheapskate

happycheapskate

New Member
Nov 26, 2009
1,989
3
0
Rockwall TX
Are they 27" (old American standard) or 700c (modern road standard)? Either one should work just fine with the stock 44tooth cog, as long as your wheels can take the punishment. The rag joint is a bad idea, esp on road wheels. But it's been done! A guy on youtube put a HT on a Walmart hipster bike (cheap steel fixie with flip flop hub)

PS, I use the white wire for the kill switch, leaving the CDI circuit alone.

If your clutch is not slipping, you should be able to pedal to around 10-15mph, release the clutch and pedal, till it fires. Being "high geared" actually gives you mechanical advantage over the motor to start it.

jdubbya said:
Hi guys, im trying to build a Trek road bike with a 80cc boygofast engine from ebay. Ive got it in there, and can start it with an air ratchet on the magneto bolt, but i just cant get it running at all with pedal power. Im wondering if its partly a clutch not engaging hard enough problem? I can have somebody hold the bike down with clutch engaged, and it turns the motor with an air wratchet on the magneto while the clutch slips and the back wheel stays stationary, should it be holding tighter on the clutch?

Seems like if i installed the pullstart that he sells, id have a chance of the bike firing up if it died on the road, right now i can only get it going with air power on magneto bolt. It has good compression, checked that, 120 lbs. I think the magneto is flakey though, white wire is reading dead short to ground, I ordered a new one, so i took the old one and cut some windings on the inner white wire coil, so if its still shorting out, it wouldnt be as bad. Im hoping hotter spark will help when the magneto comes this next week.

Anything else i should try? Im wondering if a bike with 27" tires can get the motor spinning fast enough on flat ground to start? It seems geared really high on these big ol tires.

Looking for moral support here :)
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