80 Sportfire center crank o-rings?

[Ethan6171]

I have a 1980 Sportfire that is very hard to start in the cold. About 20 seconds of laying on the electric start with choke and it will finally come to life. It won't idle cold. I have to give it throttle a bit until it warms up. When cold it also seems to have quite an inconsistent idle. Once it warms up though, it runs near perfectly. It'll also start warm with no problem.
I've taken the motor apart and replaced the two crank seals on each end. The PTO side had a big chunk ripped out of it.
I made sure the choke plunger was adjusted to spec, and taken the carb completely apart twice now and run it through my ultrasonic cleaner. I've also replaced the ignition coil. It used to have weak and intermittent spark, and a new coil seemed to fix that.
I've come down to thinking that the two o-rings on the centre of the crankshaft are leaking, causing the gas to go from side-to-side in the case instead of up in the pistons... and as it warms up, the o-rings expand, creating a better seal thus fixing the cold idle and starting problem.
When I split the case open to replace the outer seals, I lifted the crank out of place a bit to make it easier and when I set it back in, the centre o-rings got a bit of a 'nick' in them from the upper case halve, creating a little cut in both rings that wouldn't go away. It's almost like those o-rings are 40 years old and dry-rotted or something, and I should've replaced them but due to my inexperience especially at the time I didn't want to take the whole thing completely apart. At the time I figured what's those two stupid little o-rings gonna do? Well, now I suffer...
That's what I'm thinking at least. I'm curious if anybody else on here had a similar problem, and was it something else, or was it the centre o-rings? I'm not taking this thing apart again if I don't have to.
Thanks

Edit: I did check the compression. It's getting 150 PSI in both cylinders.

[Charliev65]

Was it like this before you took apart?

[Charliev65]

How is fuel pump, lines? Does carb have factory jetting and is it the correct powerjet carb?

[Ethan6171]

Was it like this before you took apart?

It's impossible to tell. Due to the bad outer seals, pickup line, and coil, it barely ran at all before. It almost always ran on one cylinder, and it would only have a bit of power for 5-10 mins before the bad seal leaked more, leaving it with almost no power at full choke. Miraculously, the motor seemed to survive... It has been in the family for years, and my father has no problem admitting to how badly they treated it

It does have the factory powerjet carb, but I haven't checked to make sure all the jets are correct. The air screw being 1 1/2 turns out is as far as I've gone. Runs great when warm, so I had a feeling it wasn't jetting but I'm no genius

I've replaced all the fuel lines, and I've put a new fuel pump in too.

[Charliev65]

Did you pressure test needle and seat? Is it flooded, maybe when shutting off the needle and seat leak fuel past and flood engine.
I would think if you have lots of smoke when starting that would be excessive amounts of fuel burning out. Correct spark plugs?

[Ethan6171]

Did you pressure test needle and seat? Is it flooded, maybe when shutting off the needle and seat leak fuel past and flood engine.
I would think if you have lots of smoke when starting that would be excessive amounts of fuel burning out. Correct spark plugs?

I did test it and adjust it. Doesn't seem to be that much smoke when I start it. No more than the Liquifire, which starts and runs perfectly. I have brand-new NGK BR9ES plugs in it. I believe those are the correct equivalent to the Champ N2's?

[Charliev65]

I always use a small screwdriver and my finger to measure depth of choke bore and adjust choke cable to match. Then when installed and tightened and gauge pod down the lever should have a little free play. Are you using full choke or just first or half on position?

[Ethan6171]

I always use a small screwdriver and my finger to measure depth of choke bore and adjust choke cable to match. Then when installed and tightened and gauge pod down the lever should have a little free play. Are you using full choke or just first or half on position?

Waaaaiiit... I forgot full choke existed on these. I was using half choke. I just tried with it cold just now using full choke, and it started quite easily.
Still won't idle cold though, no matter what choke setting. After starting, it seems to like no choke the best.
The liquifire starts 2 pulls on half choke so that's my bechmark.
I adjusted the choke so the plunger comes out 32mm, like the service manual says. But I noticed there's no gap or play between the lever and the dash. Maybe I need to adjust it lower yet?

[Charliev65]

Well when it’s warmed up and idling with airbox on adjust idle air screw slowly and pay close attention to when engine runs best or the fastest. Then find out how many turns it goes in. I think if it’s 1 1/2 open you can get a fatter pilot jet

[Ethan6171]

Well when it’s warmed up and idling with airbox on adjust idle air screw slowly and pay close attention to when engine runs best or the fastest. Then find out how many turns it goes in. I think if it’s 1 1/2 open you can get a fatter pilot jet

1 1/2 is what the service manual says to back it out to when resembling. I'll see what works tomorrow

[snowmoer]

When I had my 1980 Sport Fire back in the day it would start cold like yours. I would start it on full choke and it would fire up on the second or third pull. I would then have to flip it to half choke right away and start riding it at a slow speed. I would then flip the choke off after maybe a 1/10 of a mile and it would run great. After it warmed up a little, it would idle without any problems. If I did not start it like this, it would die and be a bear to start. It was like this from the day I got it brand new. Warm starts, one pull and it idled without any problems. I just chalked it up to how that sled ran. All carb settings were spot on.

[Ethan6171]

When I had my 1980 Sport Fire back in the day it would start cold like yours. I would start it on full choke and it would fire up on the second or third pull. I would then have to flip it to half choke right away and start riding it at a slow speed. I would then flip the choke off after maybe a 1/10 of a mile and it would run great. After it warmed up a little, it would idle without any problems. If I did not start it like this, it would die and be a bear to start. It was like this from the day I got it brand new. Warm starts, one pull and it idled without any problems. I just chalked it up to how that sled ran. All carb settings were spot on.

Well, I went out today and re-adjusted the choke plunger to be just a little further out to make sure it was seating. While putting it back together, I realized I put the small metal shim between the carb and the 12mm nut on the plunger on upside down. I was trying to get it to line up right on the carb like that, before I realized I was putting the damn thing upside down this whole time! Well, I flipped it right side up and everything went together perfect. I'm guessing the shim snagged on a higher part on the carb, causing the whole choke to not seat properly and leaking air in from time to time. Still starts cold with full choke only, but with what I hear from you I suppose this is normal for this sled... the idle is now consistent, and it'll idle all day even when cold. Great!
It won't quite rev up like it should when you accelerate, but I think this is a clutching issue. The weights and rollers seem really worn out. I've tried replaced the spring already. It's got lots of power.
Thanks for the info everybody