How big is too big??

Tom T. · Joined: 31 Jan 2005 Posts: 3 Location: Bermuda

Hey guys!

Time to put in my 2 cents worth: I have a 2003 RT125 which has some 7000+ miles on it. It is the U.S. edition, black, and has had a 150cc kit most of its life.

I have been fortunate enough to have had some close connections with what MZNA did on these kits. They originally experimented with both 150 AND 200cc kits. The 200 was never produced, but I did see it, in the company of a friend who was an experienced power boat racer. His first comment was that in his opinion, to make the 200cc kit work (stop blowing head gaskets), it should be 'Decked' as in 2 stroke motors: i.e. Give the top of the cylinder more support.

Most people are not aware, there were TWO iterations of the 150cc kit made: The first one (of which I suspect there are still a few on shelves) was a head gasket blower. I know 'cause I had one, and blew gaskets about every 300 miles. One time it blew so bad that the entire contents of the radiator migrated into the crank case.

The second iteration of the kit used the same Wisco piston & rings, but the cylinder was lined with a Nikosil liner. Not only was this a better liner, but the method of fitting it was much more accurate, and tighter. We had established that the cause of blown head gaskets was due to the liner 'Rocking' back and forth at the top. THis was confirmed by a British machine shop that one of our group sent his Mk1 cylinder to.

I have probably done in the region of 5000 miles on the Mk 11 kit, with NO PROBLEMS whatsoever! I regularly flog the hell out of the little bike because it is so much fun! The 150cc kit gives it the performance that you would wish for in a 125, but is not over the top.

My bike has the kit, a Mikuni 28mm 'Flatslide' carb (from that EXPENSIVE German company), and a Ninja pipe (manufacturer unknown to me). There are no other motor mods except a 15T front sprocket. This allows me to use 6th gear at our lower speeds in Bermuda without lugging too badly, and doesen't make 1st too racy at starts.

The bike performs so well in the stop & go mode that the chassis faults become apparent: Mostly suspension and damping (the chassis itself is very rigid).

Before anybody starts thinking that my opinions are 'Bermuda-Centric', I must add that I've owned 3 Harleys which I have kept U.S. based for the last 10 years. The present bike is an '05 FLTRI Road Glide which has covered 18600 miles through the U.S. and Canada in the last 18 months. A short ride for me is from N.E. Florida to New Hampshire!

I hope this information is helpful to several of you, and I can be reached by PM if anyone has further questions.

Regards all, and Merry Christmas.

Ride safe,

Tom T.
Bermuda

jbthumper · Joined: 23 Mar 2004 Posts: 311 Location: Malaysia

Welcome and thanks for sharing Tom.

Do you think that a 32mm carb would do a better job over the 28 with the 150 kit on??

Because looking at the Honda CRF150R specs,it has almost the same spec as the 150 kit(bore & stroke wise) but the crf is utilising a 32mm pumper carb.I'm not sure about valve sizing and port flow for the crf,though.

Cheers.

Merry Christmas!

mxsteven · Posted: Mon Dec 25, 2006 8:31 pm Post subject:

oh!! i really need a bigger carb... i can feel that my carb is insufficent. 32mm carb? if it can fit why not! but i do really need some carb setup guide for my bike. now mine is 147cc, everytime i ride i felt my bike lag of air after 7000rpm!

Tom, what type of carb are you using now? can you share with us what is your carb configuration? and also thanks for your very infomative info on above reply!

regards
MXsteven

DAVID THOMPSON · Posted: Mon Dec 25, 2006 8:49 pm Post subject: piston

tom do you know if anyone has a supply of the wisco pistons
or the wisco part number
as i can make a do it my self job of it if i can get the piston and rings
and the piston fitting sizes

mx steven what piston did you use
ar dave

mxsteven · Posted: Mon Dec 25, 2006 9:08 pm Post subject:

im using the local bike aftermarket piston here or you can refer to the same piston kawasaki 175 (if not mistakken) Hmmmm JBthumper knows the best coz he was spying way much on my bike!!!

regards
MXsteven

jbthumper · Joined: 23 Mar 2004 Posts: 311 Location: Malaysia

actually Steven, I only saw your bike's internals before the upgrade...I think only Jan saw the big bore and all... = i don't know jack s*!t

all i do is "assuming" Razz

Dave, the piston that Steven is using is from a local manufacturer(Modenas) from a model named Jaguh(refer www.modenas.com.my )...
it had a longer stroke, so what they did (i assume Very Happy

)was decked the piston's top to match the stock stroke while keeping the same piston bore...

a few lines of my assumptions

Regards.

mxsteven · Posted: Tue Dec 26, 2006 2:41 am Post subject:

The stroke remains the same but the bore is diffrent (i can't recall how many mm). Total is 147cc as per caculated, the water jacket cylinder wall had been reconstruct. Well have to get back my book to see what had been mod! i have forgotten most of them!

regards
MXsteven

Tom T. · Joined: 31 Jan 2005 Posts: 3 Location: Bermuda

I trust you all had a good holiday season, and that all are safe and well. To answer jbthumper regarding carb size, in my case the 28mm flatslide was 'Plug & Play' on my bike as it came from that expensive German company. To be fair, it was quite a comprehensive kit, with a bored manifold etc., etc..

I have not taken it to a larger size as at 28mm it works so much better than the stock carb (which is a terrible carb), and so well with the other mods, that it is not worth messing with it any further. I had had a flatslide on one of my previous Harleys and it was a crisp performer just like its 28mm little brother.

Incidentally, fitting this carb into place is not easy, and requires some patience. There is barely enough space to fit it in.

All the best for the new year!

mxsteven · Posted: Wed Jan 03, 2007 9:26 am Post subject:

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