Motoscrubs.com

Hey Guys,

happy new year...

So I just "mostly" finished a 250 Monza re-build, and I'm having an "issue."

The bike starts and idles fine, but when I start to take off on it, it bogs down the more I release the clutch.
I have to constantly feather the clutch in to keep it running, If I ever give it full clutch it shuts off.

I've tried to check over everything, but nothing jumps out at me.

The UBS24 carb is freshly rebuilt. It seems to have good flow when I drain into a jar.
It does it with/without the fuel tank lid open when trying to ride, so I don't think it's a vacuum problem.

any thoughts?

stu

" but when I start to take off on it, it bogs down the more I release the clutch.
I have to constantly feather the clutch in to keep it running, If I ever give it full clutch it shuts off. "

____ I'm afraid your wording fails to make me understand what you mean exactly, cuz it seems that you mean to say that the engine runs as it should but after engaging into gear, the motor will make your Monza go & head-down the road but only if you don't let the clutch fully engage, and if you do let the clutch fully engage, the engine then dies or locks-up.
Please straighten-out my interpretation, if I got it wrong.


Hopeful-Cheers,
-Bob

it seems that you mean to say that the engine runs as it should but after engaging into gear, the motor will make your Monza go & head-down the road but only if you don't let the clutch fully engage, and if you do let the clutch fully engage, the engine then dies or locks-up.

Yes that's exactly right Bob.

I should be more clear in my descriptions.

The bike starts 1st kick, idles fine, rev's fine, while in neutral. After engaging the gears and releasing the clutch slowly, the bike starts to move off. However, if I let the clutch fully engage, the bike sputters, and dies out, even with lots of throttle. If I dis-engage or feather the clutch before it dies, I can keep the engine from stalling. Using this technique can get the bike up to 20-30mph, but it's not pretty. Never even tried to shift into 2nd.

hope this is a little clearer.

stu

" Yes that's exactly right Bob.
I should be more clear in my descriptions. "

____ Well I guess you were clear enough after-all Stu, cuz I did get it right, as it turns-out. _ I had thought I must have misunderstood because I've never ran-into such a strange issue.
__ You didn't follow-up with whether the engine simply dies (but still turns-over), or if the motor actually 'locks-up'... And if it does lock-up (only when the clutch is fully engaged), does the rear-wheel then also wish to lock-up along-with, as well ? ...
Have you tried pushing the bike up to speed in neutral (with the spark-plug removed), and then drop the trans into gear,, so as to note whether the rear-wheel is able to rotate the engine (in a normal manor) while the clutch is then fully engaged, without any similar problem occurring ?


Tillater,
-Bob

Using first gear?

It doesn't lock up.
The rear wheel does turn the engine over just fine.
And it spins it while on the center stand, rev'ing just a bit. But when on the ground it stalls.

I'll try the run up with the plug removed to see if I notice anything strange.

I'm starting to think it may be a fuel delivery problem of some sort.

stu

may try to get some video tomorrow to illustrate.

As DCT-Bob says, check that wheels turn freely, no transmission problems, however my guess is that it could be a weak spark that dies under load, try a new hotter plug and close the gap down (testing only] ,if things improve you will know to look closer at points, coil, lead,condenser. Also fuel starvation, needle clip broke?,needle on top notch?,water in carb?float not free?,main jet blocked?.Twist the carb to raise the chamber level.What does the plug look like? shiney black?,fluffy mat black? clean and dry?,wet?.

" I'm starting to think it may be a fuel delivery problem of some sort. "

____ Could it be that your clutch-cable is in some way interfering with the throttle-cable ?


Tillater,
-Bob