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!
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.
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.
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.
Thanks everyone - I dont have the stock filter setup - maybe I'll should just get one off ebay. 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? 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?
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.
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.
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?
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.
It's probable the cylinder was hogged out with a fixed, commonly called Sunnen, hone. A true boring bar is required to get the bore straight. That's not the reason your bike won't run. Let's see, you have compression, evidently plenty of fuel, so you need only a few more variables put out of the way. Does it have spark? I mean, with a clean, preferably new, spark plug stuck into the cap and laid on the cylinder head, kick it over. Blue sparks with a nice arcing sound? CDI or points? If you have the spark I described, you can go further down the road. If not, fix this first. Oh, yeah, you should have the top end reassembled before you go to kicking it over. Use the parts you already have, unless the cylinder base gasket is torn, it'll be alright. Post your results here, we'll get this figured out. Oh yeah, chamfer your own ports. Get some heavy-duty 80-grit emery paper, it comes on a roll, and sand the edges of the ports until they're slightly rounded, as in, not sharp. The chamfer is to prevent the rings from snagging. Bum 3-4 inches from a bud for now. Clean the sandpaper grit out of the cylinder, for sure. Hot, soapy water works the best. Respond to the posts on your thread frequently.
Before my last round of attempts to get this thing running I replaced the points with a new set. I have spark. I checked compression again and it's 110psi. Can anyone recommend a good shop to send my cylinder to? It needs to be somewhere that is proven to be knowledgeable in boring cylinders. Back to the hard-start issue: I have cleaned the carb probably 8 times now. I confirmed the float setting etc. The pilot jet is the stock size and clean/clear. So my thoughts turn to float height again only because it would only idle with the idle screw all the way in, the air screw removed, and the air filter housing door removed. It seemed to start easier (compared to not at all) with a little throttle as well. So it acted like it was running rich on the pilot. So that's why I'm wondering if the float height is affecting the fuel pressure. Thoughts?
I know next to nothing about two strokes, but when I checked the compression on both the M31 and the K11p they were over 130psi. I'm assumming then yours is running a little low? Also judging by the bore wear, seems you do not have enough oil injection going. Like another said, run a little premix.
