YZSKY.. (Husky CR125/Yamaha YZ125 crossbreed) won't rev past 3/4 throttle

[Synyster06Gates]

wow looks good. sorry I cant help you with your problem though

[Jethro]

Originally Posted by 91YAMAHA91

Thats a Rowdy bike man. good project. I have a 440 snowmobile engine I wanna stick into something maybe Ill find a golf cart or a go cart carcass laying around somewhere some day. Or a lawnmower thatd be kool.

There's a vaccum cleaner lying in my shed you could try it in...

[91YAMAHA91]

Originally Posted by Jethro

There's a vaccum cleaner lying in my shed you could try it in...

That would be quite the shop cleaner wouldnt it hahah.

[Jethro]

...guarantee the girlfriend wouldn't put it down, if nothing else the vibrations would beat the washing machine anyday!

[ossagp1]

It will be interesting to see what is actually wrong. Have you ridden a similar yz125? I am curious about any changes you made to the air box. Did you have to make any?

[91YAMAHA91]

Originally Posted by Jethro

...guarantee the girlfriend wouldn't put it down, if nothing else the vibrations would beat the washing machine anyday!

All I can say is LMAO

[Jethro]

Well, it's the original Husky box and filter. Both carb venturi's are identical in diameter, and I'm kinda banking on the fact that even though they're completely different engines, they should both still displace roughly 125cc's with every stroke of the piston. I'm hoping that some fine jetting work will flatten out any minor issues raised by the transplant, I'm concerned though that generally jetting and reeds affect the lower rev range and not so much the top. I have no history with either of carbs, or the engine for that matter so I'm feeling around in the dark a little, I have no idea if either carb has standard jets or if they've already been changed (bearing in mind the YZ already had a set of Boyesens+cage fitted. Suppose this could even be a CDI issue or a crank case air leak, hope not though...

[ossagp1]

Go with what Higs suggested for a minute. remove the cover off of the power valves and see if they are moving freely. I was hoping that you airbox was the culprit as I have had similar experieces, but it seems to be something else.

[Jethro]

... good suggestion, haven't checked the valves yet. I'm expecting the new reed cage etc either today or tomorrow so will wait until that's installed then check that the power valve's moving freely. Will update shortly.

[HiG4s]

Originally Posted by Jethro

Which was faster, the YZ or the Husky? I've kept the original mounts for the Husky engine in place, so basically the engine's are interchangeable (if I can get the Husky running). Plan was to repair the Husky engine and re-install it, but if the YZ's a better engine I might not bother... probably good to have a spare though. Just wondering if I could stick on a third set of mounts for a four stroke... might be nice to have the option to change!

The Husky had more low end and better accelleration (until we had the YZ off to Eric Gorr and had it bored 133 and ported), both had screaming top ends. The YZ had better suspension. Both were great, I liked the Husky better, the YZ always seemed a little small to me ergonomically.



By the way, I like the black plastic on the Husky,, mine was all yellow and white, everyone thought it was a Suzuki.

[Jethro]

Cheers HiG4s...

Update:

Got the new Boyesen RAD cage and reeds today, fitted them.... and it's still the same, sounded a bit more 'relaxed' when it's idling though. Checked the power valve and it's definitely opening freely at the correct point (had the cover off when I was reving it). Decided to remove the main jet and check the gauge, it was a 400. Dropped the jet size by four and stuck a 360 main in there, issue is definitely still there after having dropped the main jet size (won't rev past a certain point) but the throttle reponse is now very crisp, and it does seem to rev a little higher. Still think there's another underlying issue though... then suddenly it cut out and wouldn't start. Checked for a spark and there wasn't one. managed to get a regular spark from the side of the plug though so it looks like the plug core's toast. Is this starting to sound like a CDI issue to anyone else, or is it just me?

Will pick up another plug tomorrow and take the bike out for a field trial to see if it's improved any, failing that it'lll be ebay for a CDI unit methinks.

Thoughts anyone???

[Jethro]

SOLVED IT!!!

If you ever feel inclined to wac a YZ engine into a Husky, here's how to get it to run like a beast...

Brand new Boyesen RAD cage and reeds, BR8EG plug, original Husky Mikuni carb with 400 gauge main jet and the needle clip set to second rung from the bottom.

Yep, popped in the new plug, went back to the 400 main jet and raised the needle a notch. Took it out for a field run and the front wheel didn't touch the ground for the first three gears. As soon as the powerband hits, the front wheel won't stay on the ground. Revs out too, spluttered a little initially but then it cleared and stayed clear.

Thanks for the input and suggestions chaps, much appreciated.

Cheers...

[OLDMXRACER 393]

Sounds like you've really enjoyed this project. Congrats on getting it sorted out!