Mtx125 Power valve upgrade

Lynxx · Scooby Slapper Joined: 19 Nov 2010 Karma :

Anyhow, my 200cc is screwed, the right case had to be welded, and that didnt work + the flywheel key ate a hole in the crank.

So i got a guy that will do me a trade, 200cc parts for a really good 125cc engine.

So my plan is too pull the power valve clutch bearing from the 200cc and put it in the 125cc case (hole for bearing is there), Then use te 200cc clutch & clutch cover (with power valve linkage), fit the 200 power valve gear too the 125 crank, also use the 200's power valve actuator.

Now the hard part, drilling a hole into te 125cc cylinder for the power valve, valve. after that i will thread it and fit the valve, If all works, i will have a 200cc power valve & 200cc clutch in a 125cc engine. Also i am planning on using a 200cc gianelli exhaust, and posibly the carb. Also porting the cylinder, and using a carbide burr to open the exhust up (not the port but the alloy from the port too the manifold) where it has a 5mm step, i plan on removing the step then polishing with a bluestone and 1000gritt sand paper. With any luck the 125cc wont be short from the 200's power.

If anyone has any ideas or i working somthing similar, please share !

Ill also add pictures when i get the 125cc engine and start work on it!

Tom
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Current: 1992 Suzuki GSF400V - 1984 Honda MTX200 (SOLD) - 1975 Honda Xl350 (SOLD) - 1993 Honda CB250 (SOLD)

Damon · World Chat Champion Joined: 24 Aug 2007 Karma :

Sounds interesting...

make sure you keep us posted and upload loads of pictures as you make progress. Thumbs Up

gwernybwch · Nova Slayer Joined: 30 Jul 2008 Karma :

I can't really help you apart from wishing you good luck on the project.
One thing that you might what to check is that the 125 clutch cover does has a hole (that can be easily be drilled out) for the ATAC power valve to be fitted in, but I'm not sure if it has the threading in the cover for the power valve to screw in?

Regards.

Lynxx · Scooby Slapper Joined: 19 Nov 2010 Karma :

tbad93 · Two Stroke Sniffer Joined: 30 Apr 2010 Karma :

keep us posted mate ive got a honda mtx r125 and i am intreseted to see if it works Smile

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T:BAD Razz

Lynxx · Scooby Slapper Joined: 19 Nov 2010 Karma :

Havnt got a photo yet but all the clutch, + mechinism works i just need too fit the valve into the cylinder now. i used the 200 clutch cover, crank gears/spacer, clutch & power valve parts/bearings.

will get a photo later on today maybe.
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Current: 1992 Suzuki GSF400V - 1984 Honda MTX200 (SOLD) - 1975 Honda Xl350 (SOLD) - 1993 Honda CB250 (SOLD)

Damon · World Chat Champion Joined: 24 Aug 2007 Karma :

Sounds great but...

https://farm1.static.flickr.com/129/321421416_778e4cda62.jpg

Lynxx · Scooby Slapper Joined: 19 Nov 2010 Karma :

Been a bit slow recently, as water pump has been giving me issues, that's fixed now. But now i have a new project (1975 Kh250). I did get the mechanism fitted in the clutch cover , now i just need to take the cylinder into college 1 day and fit it on a milling machine and drill out the 'plug' on the exhaust valve port. For now i machined a piece of steel to fit down the valve port, thus giving more higher Rpm power (after i fit the valve, i will give out this port blocker if anyone wants it).

Also have to pull her apart this Friday as 2nd gear is hopping in and out. And my friend Richard is bringing over a few 2nd gears and shift forks. I will probably keep the cylinder off and bring it into college on Tuesday.

Then i shall take some photos once its all together.
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Current: 1992 Suzuki GSF400V - 1984 Honda MTX200 (SOLD) - 1975 Honda Xl350 (SOLD) - 1993 Honda CB250 (SOLD)

Lynxx · Scooby Slapper Joined: 19 Nov 2010 Karma :

Ok so yesterday i had the valve fitted in the cylinder, And i had a problem with it hesitating when the valve closed. So after porting the exhaust out, i fitted a Mtx200 carb and it goes like stink now.. no flat spots in it like the other times i put a 200cc carb on it.

Defiantly worth doing though, when in 1st,2nd,3,4,5 gear it will go right past the red line with no problem.. Not quite like a RM, Kx, Cr or any other motocross but has a smooth power band to it. Will not be 100% sure if it made a huge difference until i put the Gianelli pipe and 14t front sprocket on, it has a 8tooth now which makes the top speed 70mph and 1st, and 2nd gear useless.

Will post pics and specs up later on this weekend after i borrow an SD card reader.. mines broken Sad

And a vid maybe this Monday or Tuesday after i get a new Vesrah top end gasket kit (my head gasket is blowing a bit & base gasket is silicone).
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Current: 1992 Suzuki GSF400V - 1984 Honda MTX200 (SOLD) - 1975 Honda Xl350 (SOLD) - 1993 Honda CB250 (SOLD)

badas · Scooby Slapper Joined: 22 Mar 2010 Karma :

70mph down hill / flat? Razz

My old stock 20 year old 125 (MTX) would do 65 on flat if not nearly 70 on a nice day.

mad4it028 · World Chat Champion Joined: 04 Jul 2006 Karma :

badas · Scooby Slapper Joined: 22 Mar 2010 Karma :

God knows what the sprocket was :/

It was close to revving its ballocks off though at 65 but was below the red.

Wish i didn't get rid of it but ah well Sad

Will get another in the future

Lynxx · Scooby Slapper Joined: 19 Nov 2010 Karma :

45t rear sprocket, and 8t front
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Current: 1992 Suzuki GSF400V - 1984 Honda MTX200 (SOLD) - 1975 Honda Xl350 (SOLD) - 1993 Honda CB250 (SOLD)

stevo as b4 · World Chat Champion Joined: 17 Jul 2003 Karma :

Don't fit the exhaust std or aftermarket from a 200cc version, as it will have too much volume and reduce power instead. Id look out for a Gianelli MTX125 exhaust instead. A full power MTX with a bigger carb, performance exhaust and a bit of tuning, would probably easily make use of a +1tooth front sprocket over std, to give a bit more top end but not totally ruin the acceleration. It should get close to 75mph with a good set up!

Welshd1k · World Chat Champion Joined: 03 Oct 2006 Karma :

75 ? .... umm try more like 80
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Current >Cb600fx hornet, ns125rk90 21.7bhp@wheel<
Sold >,zxr400 h2 (33bhp kit) rd350 n1 rd350 lc2<

Lynxx · Scooby Slapper Joined: 19 Nov 2010 Karma :

its a 125 gianelli but it has the manifold modified out of 1 1/2 inch pipe. i thought it was a 200, because it came off my 200, but it turns out its a modified 125 gianelli, Anyway i got 95mph down hill out of it with a 15t front and 46t rear. but is bogging in 6th gear, so i will reduce it to a 13t front. at the moment 5th gear does 80mph redlining, but 6th gear is useless, unless you go down a hill. that's with a standard pipe. and standard carb.
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Current: 1992 Suzuki GSF400V - 1984 Honda MTX200 (SOLD) - 1975 Honda Xl350 (SOLD) - 1993 Honda CB250 (SOLD)

bradh511 · Scooby Slapper Joined: 30 Apr 2009 Karma :

when i picked my mtx 125 rwf it was like 6 gear was dead but now shes cleared up she will pull in 6 on the flat to about 75 spedo indicated and 80 down a hill reving it past the red line something i dont tend to do as i want the bike to last ... mines not fited with the atac and running standard exhasust alought the restrictions have been removed and carb has been played with by previous owner i dont know what has been done to the engine but in two weeks ive done 1500 miles and she seems to run better since she had been sat in the lads garage for 2 months and i also recon befor he got it all moted it was sat since 99 mines an 88 e reg model