BTM GY125 Engine Modifications

Hello Fella , not a 200 but a BTS GY 125. Here is what I've done over the last year, I have concentrated solely on performance, my aim was for a top end of 80 and a cruisable speed of 70.

Base line. From stock the bike hit 60 (revving it’s guts out) up and down hills and with a pillion passenger. The bike was dyno’d at exactly 8 HP. 4 less than stated by the company which sold it to me.
Cold air mix= ¾ turns out. 92.5 main jet. Needle T3.
Dyno 8 BHP Road speed 60 mph

Mod 1) changed front and rear sprocket from 15 and 56 to 17 and 51. This lost me a tiny bit of acceleration, gave me the feel of a bigger bike, a total change, pulling longer through the gears and taking my bike up to 68 MPH with a following wind but struggling to hit 58 on the way back. At 6’2 and just under 14 stone aero dynamics and physics were always gona be a problem.
Road speed 68 MPH

Mod 2) hoping to get a bit more power back I removed the stock filter box and fitted a cone filter and new 1.15mm jet. This totally messed up the fuelling and put my bike off the road for a fortnight. After some adjustment to the cold air feed and moving the needle up a notch the bike had extra torque and pulled through the gears alot faster, but was topping out at 64 with a slight stalling at higher revs, also pre-ignition when engine run hard for too long. Liking the new low down power and the snarl and popping coming from the exhaust coupled with a dyno reading of 8.6 HP which is very good considering the gear change .
Cold air mix= 2 ¼ turns out. 1.15 main jet. Needle T4.
Dyno 8.9 BHP Road speed 64 MPH

Mod 3) Gutted the standard exhaust, what a difference, lost a tad more off top end, put that down to fuelling needing more adjustment, but now the bike wheelies, I wont lie, absolutely crapped myself and nearly fell off, was expecting 6 inches of lift and nearly got put on my back. BUT! it is a bit loud lol, get funny looks from old people and scares kids.
Cold air mix= 2 1/2 turns out. 1.15 main jet. Needle T2
Road speed 60 MPH

Mod 4) I fitted the AMR CDI and spent some time trying new Jets, I tried 140, 135, 115 and back to the original 92.5. Although I have lost some lower end grunt I've gone back to the 92.5, in testing it gave me the best top end and most evenly distributed power. It just seamed that I couldn't get enough air into the carb to match such big jets. The AMR CDI is fantastic! The engine doesn’t like the advanced timing, and only seams happy going flat out forward. Not so good for a commute, but perfect for shocking a few bigger bikes. This CDI really pulled all my mods together, the engine is very responsive and revs / sounds like a two stroke.
Cold air mix= 2 turns out. 92.5 main jet. Needle T2
Road speed 72 MPH

Mod 5) Fitted the 30mm Minuki carb ... cost £35
Over all it's a thumbs up. Top speed 74 MPH (was very windy though... bit blink.gif ) cruised at 60 but got there one hell of a lot faster. Pulled me nicely up the on ramp to the duals where normally wouldn't gain speed. It does seem to attack hills more now, definitely more torque.
The Minuki carb from the outside doesn't look all that different, but internally compared to the stock 26mm carb the design and build quality are far superior. Also bored out my inlet manifold from 26-30mm.
It came with a size 100 jet and I'm hoping that a 110 or 120 might sort out the top end. Not sure it'll get me to 80 but shouldn't be all that far off. Might need a sprocket change too, cause I don't think my ass can handle anymore 70 mph vibration.

Going to dyno the bike after I source a Honda coil and re-jet the carb, really wish I could’ve afforded to dyno every mod, but at £60 a pop it wasn’t possible. Over all I can’t say anyone of the mods were solely responsible for the gains, it was more a series of adjustments made together. Although the top end gains haven’t been massive the way that the power has moved up and down through the rev range has been impressive, and I expect the next dyno to show that. The bike is a totally different machine to the 8HP slug that landed on my doorstep and I’ve had a lot of fun (and tears) along the way.

Next mods: going for a full engine overhaul. Skim the head, port and polish, lighter push-rods and possibly a one off cam.
Will put up the new Dyno report soon (fingers crossed for 12 BHP) and if anyone wants any diagrams of the exhaust or CDI mod let me know.

Hope that helps… Shy:

Shy,

Sorry for the late reply but welcome to the board! That's an impressive list of mods and work done to your bike and it sounds like some has paid off.

I'm impressed you're taking the time to dyno the bike through these upgrades. How many runs have you done and do you have any charts you can post here? In China I know these engines almost always come heavily un-optimized and can find noticable gains by swapping parts.

Also, I'm not familiar with the BTS GY125. Would you happen to have any pics sitting around?

CC

It's been on the dyno twice now... getting another tomorrow :riding:
Really hoping for a 4 bhp gain... well more begging.

here is a pic of it now.... next week my beautiful and amazing mrs is paying for a full graphics kit and a carbon rear can. What sort of mods have you done fella?

http://a51.ac-images.myspacecdn.com/...625e8e6922.jpg

Since I try to ride these bikes and evaluate them, I usually stick as close to stock as possible. I have made some modifications but most of them are minor for convenience or comfort like higher bars or kickstand pegs.

I have changed the can on my Jialing JH150GY-2 and wanted to swap the carb with one equipped with an accelerator pump but the gas tank came down too closely on that model. There are no dyno facilites where I am in China so that makes it difficult to measure the effect of changes.

When I was in the US, my Magna and Bandit got the run around. Normal stuff like KN filters, jet kit, progressive springs, huggers, heated grips, higher fairings, waterproof fuse distribution blocks, GPS/aux power wiring, auxiliary driving lamps, Holeshot exhaust and luggage.

I did have the Bandit 1200 dynoed once but the dudes computer was all fugged up. The results said it only produced 100HP at the wheel and the power curves looked funny at high rpms. I had it looked at by a buddy who was an expert chart reader and he said the dyno set up was wrong and I should go back to get another free run or my money back. At the time I was getting ready to leave on a one month loop of North America so didn't get a second run although I probably should have.

I'm eager to see the results of your work! Do you prep for the dyno or just pull up and run the test? Also, are you still running the stock tires?

CC

I spent yesterday testing the mixture, new chain and going to put it back on the original gearing 15/56 so I know how far I have come and I have a direct comparison to the first dyno.

I still run the stock tyres, but only because road tyres are so expensive here, like $180. Off to the garage in a bit... Fingers crossed.... more nervous than a groom on the way to the alter. :scooter:

Sweet. How are the results from the run?

Also, is the WonJan 250GY available in England? I've ridden one here in China and they're quite strong. They use a Suzuki GN250 engine and pull real nicely.

I can't find enough pictures to compare the frames but do you know if a GN250 engine can drop in your frame? It looks like the plastics are much the same for the 125/150 and the 250 but I'm guessing the GN250 requires a larger frame.

- MyChinaMoto member "Tall Guy" on a Wonjan 250 in Chengdu -
http://photos.imageevent.com/comrade...e/Motobob4.jpg

:icon10:Inquiring minds want to know... :lol8:
CC

:( I didn't make it to the test centre on time. Well gutted!! I took my old chain off and my mate promised he'd be down my 12 for the run at one. He turned up 1:30 with the wrong chain. I was up till 2 in the morning like a nevous fool too :(

Will let you know when I get it done. Might be a week or so now though.

I haven't seen the above bike in the UK, the only 250's we have are cruisers. Because of the laws in the UK most either buy a 125 or when they get a full licenece go for a jap 600 0r 1000. But I'm strating my own company soon so I would like to stock the 250 motors for people to use as upgrades.

take care my friend.. chat soon.

Booked in for Wednesday 10am (British time), that's two days away... I'm hoping some new go faster stripes and graphics will see me clear of atleast 11bhp.. will report back with the results my freind.:deal:

Well fella the results are in....:deal: and I got a whole 9 BHP??? Think someone is pulling my leg. The guys in the test centre swear thats what it pulled?? I think it'w wrong seeing as I've gained 14mph top end. As you can imagine I ain't too happy. Gettin the paper work tomorrow so will post it to see what you think.

Gona have a sulk now :cryfiddle:

I wonder if the stock tires are screwing up the reading? You think that's possible. Also, I know some people let a few PSI of pressure out of the tire before testing to get more contact with the dyno roller. Ever tried this?

CC

No mate not tried different tyre presures. The bike was in the exact same condition as the first run except for the mods. I know it sounds bitter, but I really do think they didn't give the engine a proper thrashing. Will pick up the paper work today and compare. If it is right then the bikes going in the river and I'm off to the pub!:goodtime:

!!!!!!! UPDATE TO THE ABOVE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!

When I got the bike home I threw my toys out of the pram and decided it was going straight into the workshop for a complete internal overhaul.
As I took the chain off the back wheel fell to the side - Meaning after changing my chain two nights ago I forgot to tighten the wheel nuts! So some how I rode the bike there, they Dyno'd it and I rode it home with the back wheel only being held in by the chain and the wheel adjusters can't believe I or the engineer didn't notice it. Speaking to him he said he noticed the vibration but thought that was normal and that this would have had a huge impact on the reading, as every time the power was put on the wheel would've moved away and pulled against the engine slowing it down. Unfortunately the engine is already out, so I'll never know what it would have done. What a day, I don't drink but I really feel the need for a beer or seven :gun_bandana:

Man...that's fugged up! I guess life really is in the details yeah? :lol8:

Grab yourself a brew mate. Have another go. :deal:

CC