Fresh rebuild - impossible to start suzuki ts125

[texasadv]

I just finished rebuilding a '71 suzuki TS125. Bore size was increased to 57.5mm and a wiseco piston installed. A stock suzuki head gasket "G" was used as well. Compression test shows around 110psi. I'm assuming thats good.
So when I tried to start it I could sometimes get the bike to turn over briefly but only with full throttle. It would die almost immediately. I could kick it all day long and not make any progress; it would start then die. I checked timing and it seems fine. I get spark. I must also mention that I dont have the airbox etc so I'm running a pod filter. I have cleaned the carb several times and feel pretty solid that it's clean. I tried a variety of pilot jet sizes from 25 (stock) to 32.5 and no difference. The plug seemed to be getting gas. But again, unless full throttle was applied there was no way it would ever start.
So is it a carb problem?
Does my stock cylinder head need to be reprofiled from 56mm to 57.5mm to match the cylinder?
Will the gasket I'm trying to use work or should it be enlarged?
Though it shows 110psi I am able to easily turn it over by hand via the flywheel. Is that ok?
I'm at a loss of how to address this problem.
Thanks for any help!

[darmst6829]

Originally Posted by texasadv

I just finished rebuilding a '71 suzuki TS125. Bore size was increased to 57.5mm and a wiseco piston installed. A stock suzuki head gasket "G" was used as well. Compression test shows around 110psi. I'm assuming thats good.
So when I tried to start it I could sometimes get the bike to turn over briefly but only with full throttle. It would die almost immediately. I could kick it all day long and not make any progress; it would start then die. I checked timing and it seems fine. I get spark. I must also mention that I dont have the airbox etc so I'm running a pod filter. I have cleaned the carb several times and feel pretty solid that it's clean. I tried a variety of pilot jet sizes from 25 (stock) to 32.5 and no difference. The plug seemed to be getting gas. But again, unless full throttle was applied there was no way it would ever start.
So is it a carb problem?
Does my stock cylinder head need to be reprofiled from 56mm to 57.5mm to match the cylinder?
Will the gasket I'm trying to use work or should it be enlarged?
Though it shows 110psi I am able to easily turn it over by hand via the flywheel. Is that ok?
I'm at a loss of how to address this problem.
Thanks for any help!

Check fuel flow at the petcock and consider non ethanol fuel. Sounds like a carb/fuel issue.

Dave

[texasadv]

Thanks Dave,

It has a new petcock. The carb bowl is full of gas. I have also checked the float height several times and its in spec.

[LasseNC]

Try putting on the stock filter, or limit airflow to the carburettor and try again.

I assume you checked for false air, and that your carburettor setup is standard.

[willis 2000]

Your crankcase seal on the left is leaking.

[Low Budget]

Check to make sure nothing restricting in the exhaust......mouse nest or somthing. Make certain its brand new fresh gas. Todays fuels can go bad very quickly.

[texasadv]

Thanks everyone -

Originally Posted by LasseNC

Try putting on the stock filter, or limit airflow to the carburettor and try again.

I assume you checked for false air, and that your carburettor setup is standard.

I dont have the stock filter setup - maybe I'll should just get one off ebay.

Originally Posted by willis 2000

Your crankcase seal on the left is leaking.

Interesting - the crank seals were replaced but I have reason to suspect the left one as I wasn't super happy with how it went in. I thought if it were leaking that it would at least run, but idle really high. What makes you think the left seal is acting up?

Originally Posted by Low Budget

Check to make sure nothing restricting in the exhaust......mouse nest or somthing. Make certain its brand new fresh gas. Todays fuels can go bad very quickly.

Exhaust is clear. Gas is fresh.

I did the compression test last night and it read 110psi. I left it like that and this morning it reads about 105psi. So I think compression is good. I'm still concerned that I can turn it over by hand by rotating the flywheel. Should my comp reading be higher?

[anonny]

Is it possible to get the ignition timing off 180 degrees?

I'd put a little fuel right down the plug hole and see if it flashes and yes 110 sounds low to me.

[Low Budget]

Compression sounds fine for not being run to seat the rings yet.

Once your ready to try again spritz a little premix direct into the carb and get a helper to do a good 2nd gear push start as fast as you can down a long stretch.

I doubt this is possible, but are both the piston and the carb slide in facing the right direction ? I think the piston would have caught the ring ends in a port possibly, and the only way the carb slide could be backwards is if it had pin grooves on both sides.

Again I gotta stress, you need to be absolutely certain your exhaust isnt plugged, even partially, have seen this same symptom dozens of times on sleds, only to find a mouse nest deep inside the pipe, out of sight.

[willis 2000]

Originally Posted by willis 2000

Your crankcase seal on the left is leaking.

Or you installed the carb slide backwards. The slide cutaway faces the intake, always.

[texasadv]

I removed the cylinder and found significant wear! This was freshly bored! The wear is only on the intake and exhaust port sides of the cylinder. The piston shows very very faint marks on the skirts. This leads me to think the rings are what are wearing on the cylinder walls. I checked the ring end gap and the seem in spec. It makes me wonder if the cylinder isnt really round. I cant tell with my digital caliper. The wear is only after a handful of starts (it doesnt idle) and the one time I did actually have it idling (with very minimal throttle). I cant feel the scratches with my fingernail so theyre not deep. Thoughts?

[Steamy Moose]

Valve clearances set ok mate?

[ADV8]

If it was rebored were the port edges chamfered . ?

[texasadv]

Originally Posted by ADV8

If it was rebored were the port edges chamfered . ?

Yes in a rather crappy way. I had to make the shop do it as their response was "We dont usually chamfer ports on small displacement motors." I decided to bite my tongue and just ask them to do it anyway. So yes they were chamfered but again, the shop didnt do them very nicely.

[3uba296]

Originally Posted by Steamy Moose

Valve clearances set ok mate?

This is a 2-stroke.