Boy go fast/engine


Active Member
Local time
12:37 AM
Nov 17, 2007
Note: After posting this, I went online and noticed that this vendor now sells engines with the locking clutch lever, roller wrist pin bearing, and bearing wheel tensioner. If clutch and paint issues are improved then my review may no longer be applicable. Please submit your experience with these engines!

I've had the opportunity to purchase two of his engines over the last 3 months.

Here are my general observations:

1. Quick shipping is a plus.
2. First engine was not properly packed and the plastic throttle assembly was (crushed) damaged. Vendor replaced it reluctantly but said he normally requires buyers to file a claim with the shipping company. Shipping company would not have honored the claim if I had. The box was not damaged on the outside.
3. Cheap older style clutch assembly. Yuk! These types NEVER work on amy of my bikes. They can't be depressed sufficiently to lock on my Skyliners or Searcher bikes.
4. Both engines start easily and are VERY smooth. Much less vibration than my older Dax engines. My only comment regarding the engine is that the engine is very sensitive to the choke setting and requires some fiddling with the choke while starting to get it to fire up. I drilled out the hole on the choke plate and opened up the airflow going into the engine. This solved the problem and engine now starts easily on full choke.

5. Clutch: BAD. Unlike Dax engines, the clutch cannot be adjusted properly. To this day, I cannot find an appropriate setting on the cable that allows me to have the clutch engage completely when released and NOT spin the wheel when it is locked into place. I have never had this issue with Dax or Kings motorbike engines. Also, the clutch setting seems to be tempermental and dependent on temperature. On colder days, releasing the clutch lever does not allow 100% positive engagement and clutch slips when starting. On warmer days the opposite is true and locking clutch does not completely allow disengagement. This is a deal breaker for me and the 75 bucks I saved in buying these engines is not worth it in my opinion.

6. Power: First engine power came on quickly with my normal break in procedure and was pulling 25 up hill on a 50 tooth sprocket. Second engine can only muster 17 mph. I'll let you know if things change.

7. Paint: Probably the worst paint quality I have seen in the almost 50 Happy time kits I've purchased over the past several years. If you value a decent paint job on your tank and chain guard, look elsewhere.

Overall comments: Value is offset by the clutch issue, need to buy locking clutch and a true roller bearing chain tensioner and lousy paint job. You get what you pay for.
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I'm sure they were already here in the country before the ban. Containers, warehouses, barns, etc. Vendors wouldnt knowingly import illegal items into the country just to make a buck........
OR WOULD THEY??????????????
You wont be able to turn the sprocket by hand. Use the socket that came with your kit.....

Thanks, that worked. I didn't even know what that socket was for. I assumed it was for the spark plug. Now I need to get a chain tool since the chain is much to long.
Well I got my boygofast motor the other day. My original plain to mount it on my chopper was a bust, go to order the wheel spacer. I decided to go high end on the chopper build, pretty much keeping the frame and scrapping the rest. I'm going to take the time and build that one right. Anyway...

I went to the wall mart and bought a cruiser for $150. Took it home and took the thing apart, used locktight and better bolts on almost everything.

Boygofast kit looked good in the box, it was not packed all that well but not completely just thrown in and shipped. The install went well, I'll skip the details for now.

One thing that really ****ed me off, the clasp for the connecting link for the chain was broken, looked to be old and the chain was not the best so I scrapped it and got a #41, near impossible to find 415 in so cail. @41 is a bit larger but not enough for me to care. When I build the chopper I will use #41 and change the sprockets to match.

Another bad point, The **** brass end piece for the clutch wire was MIA, I had to tighten the screw down so much that it broke. I'll mill a new clutch arm at work tomorrow night but the clutch is working fine. Good thing I got it right the first time other wise I would be ^&*$%.

The best flaw, I guess they didn't think to use high temp paint on the pipe. Lots of smoke.... I'll fix that later.

So after that was the spark plug, BoyGoFast was nice enough to send a new plug with the kit, it's just too bad I can't use the **** thing. not till I get a new plug wire to fit. O'well...

I am having some problems with the engine running rough at low speed, it smooths as RPM rise, my guess is the cheep plug. Other then that boygofast motor runs fine and started up right away. The gas tank had no rust and free of shavings.

The throttle just sucks, does anyone know of an upgrade? The clutch is ****, going to have to get an upgrade for that as well.

So this is my first build, I cant compare BoyGoFast with another HT but I will say, for my next HT I'm going with someone diff.
I have the BGF motor, too, and with some tinkering, you can get it to run just like any of the others, I think.

But first off - you'll blow up the motor trying to even hit 30mph with the 44t sprocket. I just upgraded to a 40t, and WOW - what a difference! I cruise very pleasantly at 25mph, and also at 30...but not any faster. I think it would do 35+ if I let it, but I think that's over-revving the motor. I weigh 220lbs., btw.

The best thing I've done so far was my latest change last night: I replaced the head gasket with one from Dax. Like a new motor.

I'm also running AMSOil 3oz/gallon - about 38:1 or so...I had it richer, but I don't think that's necessary with this quality synthetic stuff. I've played with the mixture on the carb...tried all slots, and I think it's happiest at the STOCK break-in setting (2nd ring from the top - blunt end).

I've also ported the intake and exhaust to match the motor, and also trimmed up NEW gaskets as well...finally, an o-ring in the carb/manifold connection to seal it.

My bike is running GREAT now!

I think most of us can agree that the stats on these engines are also very decpetive { simliar to many other things that overate their performance }

for example...on boygo fast engines...

they arent 80 cc...they are 69 cc

they are rated for 38 mph top speed and I think thats with a 170lb rider......well I have now ran 3 tanks of gas thru my engine and theres no way in **** it is gonna hit 38 mph on flat guess is 20- 25 mph tops....with my 230 lb bodyweight and my wife weighs 170 lbs...and it isnt pulling her 38 mph either....the rpms on the engine just dont seem to allow it

this engine is also rated to get 150 mpg.....which seems to be another lie......

with that said, at least my engine runs, starts up easily and does pull me around my backroads/ neighborhood. I purchased mine more as a novelty item and may build a go cart with it soon.
What's wrong with the twist throttle? Mine works perfectly, although I did change to a gel type grip...other than that, it works fine....well, unless you think turning it past the "stop" will make your bike go faster...then you'll just break it. It's plastic inside, but if you can be somewhat gentle, it should be fine.
I like the break lever idea, reminds me of my 3wheel motorcycle's thumb throttle, what a dangerous toy for a 12 year old.. but the 3 wheeler was fun, :)
I got a BGF 70cc about 2 weeks ago and in that time I've learned more about engines and motorized mechanics than I ever would have otherwise. I have already come to understand... THATS THE POINT! If it had just snaped on in 20 minutes, fired up and broken the sound barrier with all stock stuff, it would have just been a traditional buy-an-go transaction like so many Americans have been spoiled by. This isn't just transportation, or just joyriding. This is an experience. I love looking at all the cool things people have come up with to take up the slack from the poor production tollerances of these things. If they ran perfectly, only die-hard moders would be on this forum. As it is, a HUGE variety of people are here sharing their experiences. I have had a few bumps in my build process but nothing that's put me out much. The 9-hole sprockets that all these kits include are made to fit wheels with a certain number of spokes. If you've got a couple more or less, like I did, it's going to take a few tries and a little ingenuity. (part of what I've loved!) I did get it on and it fits perfect now. I also noticed that every time I took it off and put it back on, I did it faster, more precicly and more perfectly centered. All the stock items worked out of the box. Mind you, they didn't all work exactly right on the first try but they did work eventually. Right now I'm trying to solve my extreme vibration problem. I've gotten the feeling talking to others that it's probably due to something on my bike more than the engine. I'm not sure how the other kits are, but this sucker is a no-frills 2-stroke. It's filthy! And I love every minute of it. For me the cheap price got me in the market so to speak. There's no way in the world that I would have payed $300 ($140 more) just to be told that someone will answer my questions. How am I supposed to learn? In e-mails with BGF I've come to realize... He's a punk! But to be fair, he pretty much sayes as much in the eBay add. All that said, I'd buy another kit from BGF no problem.