LT 80 lacking vacuum
 

Hey gang,

so I was trying to improve my (and my kids) lt80 ....ha.!

I did brake cables, air filter, new intake boot, straight flo petcock and carb rebuild kit from moose.

It was running ok before but wanted to finish up the job i started. I bought it dead this summer , It was lightly seized because the oil injector had failed.
I disconnected the oil injector put in a new starter and battery, cleaned the carb and lubed the top of the piston it ran. And quite well I thought
( slightly rich I thought) but fine on 32:1 premix. It pulled me and my two kids on it at a good clip and would wheelie with just me on command.
but... I had to mess with it... I am very good at breaking things that are not broke. :)


anywhoo, a while back I ordered the parts I mentioned erlier for the fixes and installed them all yesterday.

after everything was put back together last night one slight touch of the starter and it purred like a kitten making popcorn.
thats good in my mind :) . I was super pumped that it all went schmooth.

I let it warm up, drove 10 feet and it bogged.
could not get it started again. tried for 10 min.

Pulled the carb and went to the place I thought was the most suspicious.
that little rubber o ring that came with the carb rebuild kit under the main jet.
it seemed too big and somehow not right. so after the second time i pulled carb last night , I found it restricting the size of the jet, I took it out and put a smaller o ring in its place.
I also noted that the vacuum line wasnt blocked properly so I made a good seal. checked float level with a clear tube also. seems good.
it seemed to me that the gas was not getting into the engine.

a squirt of quickstart and the engine fired right up but only for a sec.

today I learned that if I put my hand over the intake of the carb the bike will fire right up. and stay idling,
I can put the boot back on and go for a ride. So I thought I fixed it by reducing the size of the o ring and tightening up the vacuum port
. Once its warm, I can fire it up no prob. again and again

BUT If I leave it for an hour or two, it wont start unless remove the boot and I cover the intake at the carb.
Its not quite as powerful as before the rebuild but runs well once its started.
mind you its also -2 and snowing

the choke seems to work but its not enough choke to start it . I have to completely restrict airflow to build initial vacuum,
or atleast thats what I have deduced.

could leaky crank seals do this? I would have thought it wouldnt run well with leaky seals ? but it does run well, just wont start well.
should I completely remove the rubber o ring under the main jet? is that making it harder for fuel to get moving untill there is vacuum built from
a running engine? I mean its strong enough to wheelie with me on it so I would assume the compression is ok?

what are your thoughts ?

thanks in advance for taking the time to read this. '
let me know if you have any q's

cheers
Tarik

It's a compression issue. Do a compression test to make sure (90 min).
You were lucky to have it run so well after seizing. You need a new bore/piston.

Ok Thanks man, I will get a tester and check.
maybe build a leak down tester.
by new bore you mean honing the cylinder?
thanks for your time
cheers
T

I guess the whole top end is pretty reasonably priced, was just looking on Ebay,
any brands, or sellers you recommend for a bore and piston kit?

They are all the same china junk kits. $13 bucks in bulk.
I recommend getting the next size up Suzuki piston and have the cylinder bored. Any reputable shop can do it. FYI: It'll cost you a lot more than the china kit but it'll last a lot longer IMO.

Until a gauge proves me wrong, yes I feel it's compression.
Cold= too much distance between piston and cylinder causing a lack of vacuum. Now comes the choke thing and it runs. The motor heats up and expands the piston enough to let it run OK.
That's my version. :)

ok, you make a lot of sense.
comp tester on the way.
will let you know when I get results next week.

thanks for talking this through with me.
I really appreciate it.
cheers
T

do you know off hand the size of plugs i need for intake and exhaust to build a leak down tester for the lt80?
thanks
T

i read that the exhaust is 28.5 mm , is that inside DI?
and the intake is possibly 21mm? is that inside diameter?
just looking to get some plumbing parts tmr and wont have a chance to measure before hand