1988 kx500 engine rebuild

[scottysg]

Too many projects! Back to the KX500 for now...so the swap seems to be a success, I have 15 hours on the yzx500 and I thought it would be time to tear it all down, double check all consumables, and put it back together. I found all part numbers either on this forum (thank you) or directly on the parts upon disassembly. PM me if you need any #'s and I can check my receipt list. These are the key points:

-all new bearings. every bearing in the case has been replaced with a new japanese bearing
-Crank rebuild (worn out on bearing pins)- repair bearing pins, vesrah rod, wiseco piston, balanced, trued
-40mm shorty lectron
-fresh reeds
-billet water pump impeller
-all new clips in transmission (between each gear)
-weld crack in clutch cover (caused by brake from crashing)
-weld crack rt side in engine case (caused by swingarm clearance issues)
-clean all casting imperfections in cylinder
-mityvac for testing

Overall this rebuild is going well. The removable shift dog pins make disassembly\case splitting very easy compared to my previous yz250.

Crank, piston, and rod back from crank works


rtv to fill space in carb boot (is this a terrible idea, it is momentive high temp RTV) I'm not sure if i want to run this or not. i don't know how well the rtv will stick to the rubber, but i wanted a smooth transition from the carb boot to the reed cage


parts


Progress:
Old bearings out
cylinder casting flash cleaned up
clean all parts
new bearings in

to do:
complete assembly. I've set aside some time this weekend so hopefully it will be enough.
leak down test. this is certainly not my first 2 stroke build, but it is my first correct build, as I will be using a vac\press tester this time. i usually have a steep, beer-influenced learning curve so we'll see how it goes.

[Foxx4Beaver]

lookin good...
I myself would not run that RTV in the intake....even RTV that's resistant to fuels I wouldn't, as it will eventually break down, and you know where it goes from there....
try to get a new one, or a good used one at the least.

[scottysg]

Im sorry to blue ball y'all but my laptop got stolen. d**n crackheads. should be getting high on premix like the rest of us. Ill figure out a way to post pics from my phone or ipad.

I just have to say thank you to everyone who posts here. I have hit so many roadblocks in this build that have been solved more or less by cruising the pages here and learning from someone elses...issues. Surely i have saved money and time because of your input!

pressure tested the motor to 6 psi and it dropped 2psi over 15 minutes. had almost identical vacuum loss(in hg). Success! In the bike it goes.

used that fancy dial gauge and set my timing. or so i thought. I will definitely have to play with timing to get it right. I would love to use a timing light on this and just set up a potentiometer inline with the cdi somehow to adjust my timing like that. put a sweet little window in the ignition cover with an LED lighting with every spark. so checking/changing timing could be a pit stop speed procedure. and at night youd have a bitchen strobe effect coming out of the left side of the bike :p but we all have dreams...

Rode Gorman last weekend with the brand new motor. Unfortunately it just didnt run perfectly and i somehow forgot my d**n lectron needle turning tool, so I really couldnt make adjustments. between the 500 and the desert tank in this 250 frame, carb adjustments are time consuming so i would like to minimize them.

it is pokey off idle and revs slow. then gets to a point and literally sounds like a 4 stroke bouncing off a rev limiter, wapopopopopopopa. like those anoyying quad guys on raptors that just sit next to each other at camp having rev/fart battles. just wont turn any faster and im yankin but the front wheel is still on the ground. on slow, steep climbs, it does tractor up so i can tell it wants to make power, its just not there up on top. The bike also heated up on me climbing east frazier trail, despite the oversized billet impeller. fyi i run my radiator overflow routed so it starts steaming my nads when it starts to heat up. trick i learned from running a 2 stroke wide open for hours at a time in 120+ weather 3 weekends a month. Im running the parallel radiators from the yz so that is also an area i may need to change. During this climb, i was really walking away from my buddy on his yz250, who is usually much quicker than i am aka better rider(when both our yz250s had 250's). But i didnt feel fast and it wasnt exciting. but it really felt like it wanted to go faster so im maintaining optimism that the 500 will make me crap my pants once set up right. all i want is loaded britches is that too much to ask!! I sold my 450 cuz it was fast but not fun

My plan is to again go through the "troubleshoot your kx500 electrical system" article this week after work to just make sure the rest of the electrical components that i haven't tested yet are good.  Fuel level seems to be fine in the clear bowl. David at Lectron suggested I start with leaning the metering rod 1/2 turn, so I will do that this week as well. Then after the next ride, If playing with the carb more doesnt seem to work Ill move on to playing with timing. then with myself if that fails.

I am wondering if the air boot/box/filter that I am using (2002 yz250) is more restrictive than that of the oem kx500. I doubt it because the 250 was designed to turn more rpm but its something i need to look into eventually if i cant sort it out other ways. come on scott, fuel air spark! you can do it!

Ill post with results of these changes once tested. Please let me know if you see me doing something the back asswards way!