more power from 86/87 125m

[HarrisoN*]

is it me or are these bikes lacking the power of its brothers the 185/200s?

ive ridden various and yes i know theres a distinctive lack of cc but overall engine design is very similar, they just appear so gutless and top out very quick. i know this can be changed by sprockets but i feel theres plenty more power to be gained from the motor.

havnt stripped one down to see the potential but id imagine opening the ports,maybe high comp piston or bigger piston and a few other adjustments and they'd be just as quick as the 185s.


but there seems to be a distinctive lack of motor upgrades for this model being produced for only 86/87 in 3 wheeler and upto 88/89 in 4wheeler i believe.

has anyone had experience with these motors or seen any big bores, profiled cams?

these really are a great trike just lack the front suspension but soon to have a 200x front end rigged up i felt the need to investigate the possibility of finding more power.

opinions welcomed, il strip down a spare motor and post my progress on finding these extra horses...

[shortline10]

200x head , cam , carb will wake it up . Never seen a HP piston for that model . Possibly use a big bore 56mm piston from a 110 model ?

[HarrisoN*]

is that head a straight fit, i noticed the stroke is funny size and not shared by any other atc.

if the 200x head is a direct swap that would mean the stud pattern is the same so maybe a 200x con rod could be fitted to the 125m crank, hmmm...

[shortline10]

I believe the stud spacing is the same . I did the 200x cam swap and it def woke it up .




is that head a straight fit, i noticed the stroke is funny size and not shared by any other atc.

if the 200x head is a direct swap that would mean the stud pattern is the same so maybe a 200x con rod could be fitted to the 125m crank, hmmm...

[HarrisoN*]

the 200x cam in stock 125m head? that sounds the easiest think, i have a feeling the stud pattern is different just by looking at the 2 engines side by side.

if i cant find a high compression piston il look into the 110 set up, do these jugs need to be lined or coated after theyve been bored over size?

[shortline10]

You will have to cut the end off the cam to look just like the stock 125m cam and you also need to use the 200x cam sprocket but otherwise its a direct swap .
Cylinder can be bored with no issues . I had to move the carb slide needle up 2 notches to get it tuned also .
I have both heads lying around so I will measure them up but I did read somwere that it can be done .




the 200x cam in stock 125m head? that sounds the easiest think, i have a feeling the stud pattern is different just by looking at the 2 engines side by side.

if i cant find a high compression piston il look into the 110 set up, do these jugs need to be lined or coated after theyve been bored over size?

[oscarmayer]

hrmm, what about using a 200x jug, deckign it down (top and bottom) to thwe heigth of the 125 one and using the 200x head setup? maybe a mini 165ish cc engine? Then he can run a wiseco 10.25:1 or even the 12:1 (but recommend you get the 200S head with the decompression lever on it if you use the 12:1 piston). jsut a though. We did that on a prototype racing engine we run for the series... oops cat's outta the bag. Dangit!!!! no I'm not tellin the details.. :p let's jsut say 18-19 hp from a 125cc 4-srtoker and about 16 troque is VERY nice!!! ;)

[HarrisoN*]

there was a series for this model? would love to see some pics/more info on that...

i have the facility to turn down a jug, and i think i know of someone local with a complete 200s engine for parts. the jug and head from a s with the decomp and then a performance camshaft set up? coupled with the 200s carb? any other suggestions on carbs?

other than uprated camshaft what else can be done to get more performance from the 200s head? much room for porting, slot the cam sprocket for abit of advance on timing?

[HarrisoN*]

according to a online CC calculator a 65mm piston from 200s in the 54.5mm barrel thats 181cc.

i have faith in the honda rod taking the extra pressure.

trying to do this build on a budget due to just picking up a 85 R which needs a fair amount of work. whats a cheap good aftermarket cam for the 200s?

[oscarmayer]

well you can get a mikuni 24mm carb from ebay for $40 shipped. i run them all the time for my son's racing ATVs.
yea the stock rod shoudl be fine in my books.
don't port the stock head just "port match" it the intake and exhaust. If you want more then a web cam is good. but remember if you go more than the stage1 i beleive you have to harden your rockers after that, so the stage1 is fine. it's mroe agressive than a xr200 cam and will drop into the 200s head. i woudl repalce the vavles with aftermarket ones and haev a valve job done on the head for best sealing and job. My son's race motors have about $1400 in the top ends due to all the custom machinging work, so how fast you go depends on how much you got. we go through 3-4 motors a season.

if your on a budget, just do the jug and use a xr200 piston. it's slightly higher comp than the 200x and the xr200 cam and you'll be fine.
you will need to use a bigger exhaust too, so you'll need to look at taking the pipe from a 200x and then modifying the bends and muffler angle to fit.

Biggest thing, MEASURE and document and confirm everythign before you start ANY work or machinging. if the head bolts on, chances are the piston and jug will work, but again double check everything FIRST..... if all else fails, you spend $50 on 200s engine parts and pust them for sale here. someone will by them.