Mini Road Racers Forum

When at practice today with Jeff, Jordan, Aaron, Marc, and Brian, my bike started having some power problems.
It was starting with a little bit of power lacking when really leaning the bike over. Particulary on turn 5-6 running counterclockwise.
I would roll on the throttle and the power wouldn't pick up. It was pretty subtle at this point.
It stayed like this for probably 30 laps or so until I took a 5 minute break (didn't change anything) and when I went back out there was some serious power issues. It would come on the pipe strong, when it built a few more rpms, the bike would feel like it went off the pipe (same noise and feel).

I pulled the head and jug, everything looks good, no scoring, plug looks good, no play in bearings.
Any ideas?

Unless the bike is starting to seize, and you said the cylinder looks good, it is hard to imagine a 65cc two-smoker having serious power problems and the plug still looking good. Regardless of whether the problem was due to spark or fuel, the plug should give some indication......take a picture of the plug and post it.

Could the head gasket or base gasket be bad and leaking when the engine gets hot? Any indication of that on the mating surfaces?

Have you ever ridden it on the track in these temperatures before? Sounds like with the rise in ambient temp, your jetting may have been a bit fat. Just a guess, and im no expert, but that would be my guess.

Sounds like case seals...........

I never ever had any problems with my KX65 other than it was getting slower due to 3 years without any engine work. Complete rebuild and its back on track with some better performance due to porting etc...

We run 30:1 KLOTZ with techniplate....... same great smell with better suspension additives........ On race days we usually run a mixture of 110 and 93 pump gas at 50:50. Otherwise we run 93 all the time........... had to bump up the jet size due to V-Force reed block, FMF Gold series pipe..........

Well it was the hottest day I've ever run it, and it was worse after it sat for a couple minutes maybe heat soaked....

Dude!

You need a top end............ Millenium is the best for cylinder work! Stock piston and rings........ get new crank bearings, rod as it looks like it is smoked, seals, have your ports smoothed out........

That motor looks TIRED

Mine was clearly in better shape than the pictures you have posted and it only had minimal power loss.

Ron rebuilt his motor in his RM65 (same bike as KX65) he had problems like what you are experiencing... when first started ran decent then the hotter it got the power fell flat........... and now his bike rips like better than new

We both spent less than $500, niether of our bikes needed a new rod or crank!

After reading your post on SMJ I still think you have a Seal issue, and it looks like that motor is tired.... Just from the 2S motors I have seen apart.............. You could try checking out those Carb theories but Carbs don't act up because the motor is at operating temps.........

Seals can be tight enough at cold temps and then when you have material expansion with normal operating temps the seals leak.......

I have brutalized my KX65, sure I keep it tuned and maintained but its rode hard.........

Just saying.........

Your cylinder looks like it has some scoring and when you look at the piston, there seems to be an area that is freshly worn (the section where there is some brown but has new shiny). With the fresh wear on the piston, marks on the cylinder wall, and dry plug......I wonder if the engine was starting to seize?
But......how much time is on that piston and cylinder? Have you done a top end on the bike before and if so, does the cylinder look appreciably different than it did before? What jets were you running and can you check with people who have run the KX65 before and get some feedback from them? I have no idea how sensitive they are to jetting or what range of jets would be appropriate.
Teddy is talking about the same thing as I mentioned previous to seeing the pics......if all else looks good, you would want to check for leaks in the base or head. But having seen the pics, if the cylinder and piston are pretty new I think I'd look there first.

Alex,
Your top end is done. Your photo's show excessive wear and I would say one race from seizing and doing more damage to the motor and you. Like Teddy, I like millenium for repair and replating and I would run the overbore stock pistons. If you are feeling lucky, just do a complete top end rebuild and roll the dice. It is always safer to rebuild the bottom at the same time but that will at least double the cost and may not be necessary at this time. Do you know the motor's history? Ideally you should be able to get a OYL season out of a top end rebuild, three seasons out of a new cylinder, crank, bearings and seals. Of course there are alot of variables, your results may vary.
Smallwood can probably do the rebuild for you if you want.
Good Luck

I agree 100% with Matt & Bill. That top end is TOASTED

Mine was looking very clean other than one little area about the size of a quarter that had some scratches starting...... It was very tidy. It had three hard seasons on it! Tight enough I did not replace the crank or rod......

I know the history of my bike from the first day it was bought new. No hidden issues etc...

Jetting is a snap, get it dialed in and RACE, there is no fiddling with these bikes in fact stock they were designed to be RACED for 100 plus hours before any rebuild (according to Kawasaki). Mine has waaaaaaaaay more hours than that.

Slap on a pipe, V-force block, Porting, jet up 1 or 2 sizes and BLAMMO game on So simple even a caveman could do it Oh you already have all that stuff

But really dude those photos say it all.

teddy wrote: BLAMMO game on

Hey, if there's a reliable "place to send yer 2-smokes for rebuilding" in central Ohio, please, someone spill the beans. For reference purposes, at least.

Hey BLAMMO.......the rebuilding part is easy. It is the machining part that you want done right and that's easy......

http://bore-tech.com/

....you have a iron cylinder so there are no plating issues to be concerned about like with the KX65. If you had a plated cylinder, machining it takes away the plating so you need to send it to someone who can cut it and then replate it and that's definitely Millenium - they do cool airplane $#!@ too. With your iron cylinder it is simple.....measure the piston and then cut and hone the cylinder to the right diameter (piston diameter plus correct clearance) and BLAMMO!, you're done.

Sorry if you know all this stuff already.....I'm just in the mood to hear myself talk.

lucky13 wrote:I'm just in the mood to hear myself talk.

HA! I can relate, check this out.

That couldn't possibly be a better story and it is TOTALLY SELF-INDULGENT which makes it all the better. I had trouble following it but that probably is just more - but unnecessary - confirmation of my severely impaired ability to attend to tasks.
I can only imagine how mesmerized I'd be if I had recently treated myself to one of nature's herbs and got to hear the story told in person. Reminds me of the time a guy was explaining to me the difference between how lasers operate in the vacuum of space compared to how they operate in an atmosphere, particularly what would happen as the beam bounced off objects and what it would be like to observe the differences from the various environments......I've never been so confused, enamored, and happy to be alive!

Do you know Rockmastermike? That dude seriously looks like someone I'd like to hang out with.......that hat thing he's wearing is SO PERFECT!

Do you read Andrei Codrescu or The Exquisite Corpse stuff? If not, check him/it out.....

Well nuts!

I don't know the motor's history and this is the first time I've taken it apart.
It's running a weisco "racers edge" piston and hotrods crank, squish has been reduced, a lot of porting and it runs on c12 gas.
I have no idea on the jetting,
Guess I'll be sending it out for replating and order a new top end kit. I figure a stock piston should be good, I wonder if I'll be able to run regular gas if I do that.

If they are going to cut the cylinder and replate it then a stock piston won't work.....at least not the original piston. But, a standard overbore will.

Whether you can use high-test pump gas is going to be more dependent on that modified head IMHO. I think the best chance you have of running lower octane fuel is to have the work done we mentioned and put a standard overbore piston in it and put a stock head back on the bike.

You also might want to measure the cylinder, and go ahead and get the piston, then send it to get it plated. That way they can set the clearance to the piston you are actually going to use.

Steve-o wrote:You also might want to measure the cylinder, and go ahead and get the piston, then send it to get it plated. That way they can set the clearance to the piston you are actually going to use.

Right-on Steve....or just send them the piston, right?

yeap measure that stuff up, call Millenium personally!!! you'd be surprised at the growth from the plating, they should be able to make it stock A unless its been really bored up to 72cc.

Get a stock piston, A is stock, B is over sized I do believe, the wiseco pistons are not that good but really great for people that tear their motors apart all the time (you wanna race and have fun right? not work on your finicky bike all the time right?)............ PlusThe Kawasaki pistons have 2 rings.......

You should still be able to run 93/4 pump gas, you can set the squish back to stock if need be........ I would just get yer top end done, and call it good.

This is all about having fun and honing skills. It is not about trying to become some mini bike builder guru with bikes that are so odd you have more hours with your wrenches than seat time on the track!

Yeah, thats what I mean matt... just didn't get all the right words in there and in the right order. Thanks for the help :)