YZ250 Blaster Build Log
- Thread starter Tbrock77
- Start date
Changed my mind on the radiator mount, I think this works a lot better and keeps it safer. View attachment 30498View attachment 30499
It crossed my mind
maybe a Banshee hood will fit
It crossed my mind
Now I remember why I traded my banshee for a 450, I passionately hate jetting 2 strokes
Doesn't want to start, pull the plug and it's soaked, put a new one in and adjust the air screw, still doesn't start and the plug is bone dry...
Doesn't want to start, pull the plug and it's soaked, put a new one in and adjust the air screw, still doesn't start and the plug is bone dry...
Best has a point about the fuel mix; 50/50 is probably a little overboard. I'm not far from the same altitude but have more compression and only ran 25/75. This sounds a lot like something that happened to me (first a wet plug, then dry as a bone and wouldn't start for anything). Being such a low specific gravity, race fuel has a nasty way of seeping past petcocks, float valves, etc. and is harder to ignite. When going to a lighter fuel you have to adjust the float valve to compensate. There's a good chance your bottom end is just loaded up. After eliminating all the obvious stuff you could try pulling it around the yard a bit in 3rd with everything shut off to clean out the case. Good luck!
Did you decide to go with the PWK? If so do you have something like the Duncan Racing Keihin guide?
I'm using the mikuni TM38
It keeps backfiring, which I've seen online could be timing but I checked the flywheel, woodruff key and stator and they're all where they should be and not damaged.
I have a blaster leak down tester but it's definitely too small, I'll have to see if I can rig it up. The carb is brand new so there shouldn't be anything wrong with it.
Yup, need to leak down. All the carb fiddling in the world won't get you where you need to be if your low side is not pumping fuel the right direction.
Not saying there's anything wrong with the carb, just older mills are in a pretty low state of tune compared to newer YZ engines. A newer style carb might be a jetted rich for your engine in stock trim
Not saying there's anything wrong with the carb, just older mills are in a pretty low state of tune compared to newer YZ engines. A newer style carb might be a jetted rich for your engine in stock trim
Now I remember why I traded my banshee for a 450, I passionately hate jetting 2 strokes
Doesn't want to start, pull the plug and it's soaked, put a new one in and adjust the air screw, still doesn't start and the plug is bone dry...
Hmmm, a 450 is great until anything goes wrong, then it is a nightmare!
A single cylinder 2 stroke is a joy in comparison.
I didn't like 2 strokes either, until I grew to understand them.
Leak test is simple, just get a different size plumbing plug for the carb boot:
Air screw is fine tuning. I don't normally mess with it until I've got them running.
2 turns out and give it 2 kicks with choke then 2 kicks with a crack of throttle to start.
Some makes of MX motors have leaky powervalves during a leak test.
I'm lucky that the KTM is generally pretty good.
Hmmm, a 450 is great until anything goes wrong, then it is a nightmare!
A single cylinder 2 stroke is a joy in comparison.
I didn't like 2 strokes either, until I grew to understand them.
Leak test is simple, just get a different size plumbing plug for the carb boot:
Air screw is fine tuning. I don't normally mess with it until I've got them running.
2 turns out and give it 2 kicks with choke then 2 kicks with a crack of throttle to start.
Some makes of MX motors have leaky powervalves during a leak test.
I'm lucky that the KTM is generally pretty good.
The power valve gasket cover is leaking oil, would that contribute to the problem? I was going to pull it off and seal it up either way. I'll leakdown test it tomorrow, I checked the crank seal on the stator side and it looked fairly new (doesn't mean it's sealing correctly, but it looked new)
I remember finding a 2 stroke tuning guide but I can't recall what it was. It mentioned something about messing with the air screw. As I turned it out (leaned it out) the RPMs increased but I was about 3.5-4 turns out, can't remember which way I need to go with the jetting with that information.
Max RPM should be 1-2 turns out. Below 1, it's lean. Go with a bigger pilot. Above 2, rich. Smaler pilot. Two Strokes have air screws and 4 strokes have fuel screws. The more you unscrew the air screw the more air you allow into the pilot circuit to compensate for too much fuel. You'll need at least one and possibly 2 sizes smaller pilot.
A little leak from the PV cover doesn't really effect jetting.
I have one of awk08's leak down testers, the hand pump one, I've pumped and pumped and it's not building any pressure in the cylinder... do I have to pump this thing forever? It seems like it's sealed around the exhaust and intake
Made a new leakdown tester so I could just use my air compressor, I've found out that it leaks around the intake boot, around the driven side of the power valve and there is a tiny leak underneath the intake port. I used an OEM base gasket and its torqued to spec so I'm not sure what to do about that one. Any suggestions for how to handle each leak?
congratulation on the last 2 years of your progress.
i'm tuned in keep it coming
i'm tuned in keep it coming
Ahh! Do not ever pump to more than 7psi or you risk blowing out your crank seals.
Even a quick shot of air from an air compressor can blow out the seals.
If you use an air compressor, make sure to have a 7psi max regulator. 5psi is enough.
5psi held for 5 minutes is enough.
The square flange of the intake boot and reed valves is a common place to leak. They are often bent from overtightening (why we need torque wrenches). Many have a gasket sealing bead which you will destroy if you file them flat, so which is the worse evil? The warp or losing the bead? I usually first try a bit of Permatex Gasket Maker or RTV to fill in the low spots.
Same story on the base gasket. I prefer to install them without sealer but sometimes due to imperfections they leak a bit. Sealer on the cylinder side only is my first resort, and if that doesn't work, both sides.
Powervalves vary greatly from make to make. Some are very leaky as they are designed and make it almost impossible to leak test. Small exhaust leaks have very little effect on engine performance. I have sealed up powervalve leaks (such as push rod holes) with RTV in some cases and removed it later.
Find where the leaks are one by one and repair them.
I cranked the regulator all the way down, there was at most 7psi flowing through it. That 0-160psi air pressure gauge was the lowest range I could find, I ordered a 0-30psi though so I'll be able to get a more accurate reading in the future
I Permatexed the intake boot, no more leaks there. I don't think there is anything I can do about the power valve leak. I guess I'll pull the cylinder up and put a light coat of permatex on that, it's a tiny leak so I bet that'll do the trick.
I checked everywhere with soapy waters the cases definitely are not leaking so I think once I seal up the cylinder it's safe to say it doesn't have any air leaks.
Okay, sealed up the base gasket, there's definitely no other air leaks besides the power valve.
It keeps backfiring, I'm really at a loss, if it's not timing and not jetting could it possibly be the CDI?
Any suggestions?
It keeps backfiring, I'm really at a loss, if it's not timing and not jetting could it possibly be the CDI?
Any suggestions?
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