GT250 - crank seals bad?

[jabcb]

73 GT250 was running good. Started 1 or 2 kicks cold & 1 kick hot. Made good power (for a 73 GT250).

Then one day I couldn't kick start it.
Fully charged battery made no difference.
Checked spark -- when manually operating points have good spark on both cylinders & timing is spot on.
Checked compression with squirt of oil in spark plug holes -- both good & about the same at around 130.

Have inline fuel filters & Pingel vacuum petcock.
Noticed that fuel filters were empty & kick start attempts didn't cause any gas to flow.

Installed new vacuum line & new fuel line that emptied onto the ground.
Kick start attempts didn't cause any fuel flow.

Switched out tanks with another that has stock petcock.
Used prime to fill carbs & still no luck starting the bike.

Am thinking the crank seals for left cylinder are shot resulting in lack of vacuum for petcock & choke.
Only the left carb has a choke. Choke on left carb feeds both carbs, so its not starting on just the right cylinder.

Any thoughts or suggestions?
Could something else be the problem?

[Flywheel]

How long did it sit not running? Were the carb bowls drained during that time? Reason I'm asking, when I bought the Seca, the carb bowls were filled with this jelly like substance that was clogging the jets.

[jabcb]

Was sitting for maybe a week or two at most.

Also, bike has stock intake (boot + air box + filter).

[Flywheel]

Well it definately didn't sit long enough for the gas to gel. Is the bike trying to run? A sputter? Or just nothing?

[Vintageman]

did you put petcock on prime? This skips vacuum line and flows fuel direct

Are the plugs wet with fuel? If you kicked it several times and did not start they should have signs of (soaked) fuel.

If dry put a little fuel down each plug hole and try again. If it starts maybe float needles stuck closed?

Did you get plug wires swapped?

I don't think a leaky seal would stop it from starting. Unless it was really wasted. And still the other side should do something and at least here it attempt to run.

How did you check timing. If marks on flywheel it may have spun the keyway ( a stretch but have seen this happen)

If you think your seals leak remove are box and Y boot. hold throttle wide open and compare suction each carb. You should feel suction and if very bad seal you'll note one does not suck as much.

Again I have had some wasted seals in my day and bike would still start.

Also worn rings will make it hard to start, but still should, push start it.

[pearljam724]

A bad seal shouldn't prevent starting. A bad seal, would cause a lean condition on that cylinder. But, at least one cylinder should fire just fine. Is it getting spark, firing at all ? I had a similar problem on an RZ. Found a ground wire had pulled of it's soder inside the ignition housing. Try unhooking the vacuum line from the carbs, suck on the line by mouth to see if the vacuum petcock draws fuel with the petcock in run position when you suck on the line. If not, you have a petcock problem. If you had a vacuum issue, the bike would still start with the bowls being filled by priming them. But, would stall after that fuel in the bowls is consumed. Just because the petcock is on prime. Doesn't mean the bowls are getting filled. You have to confirm it by taking the tank off and turning the prime on and putting the petcock on run and sucking on the vacuum line to verify it's getting fuel in both positions. If you verify it's getting fuel. All pilot and starter jets are clean, than it's an electrical or ignition problem. Test your coils and leads for ohm resistance. If both cylinders share a single coil. It doesn't matter if the leads are switched. Sometimes, the boots have a bad connection with plug terminals and the boots need replaced. Or you have a dead cell in the battery, regardless of it being fully charged. I'd be positive of the condition of the battery before I start anywhere. I've painfully learned that lesson on 2 separate bikes in a short time period. Thinking the battery was fine. Even when I knew they were fully charged by testing them. A dead cell will give you head aches and can easily fool anyone.

[jabcb]

Thanks for the tips.

When I switched gas tanks, I used a tank from a bike that runs good.
Used prime & I could see that gas flowed through the inline fuel filters for a while, so there definitely was gas in the carbs.

I checked the timing. One side was correct & the other side needed only a minor adjustment.
If the flywheel had spun, then the timing would have been noticeably off.

Manually operating the left points produces a good spark for the left plug. Same for the right side.
So HT leads aren't switched.

Will try a different battery. (An upside of having too many bikes.)
Will remove air box + intake boot & do the hand suction test.
Will try to bump start it with new plugs.

[Vintageman]

Plugs wet with fuel?

So you checked timing with gauge in plug hole... not by using marks on rotor. If so did the marks on rotor agree with your setting.

I suppose also the saprk could be week... you should be able to draw at least a 1/2 inch arc. thin bluish sharp snap to it

130 psi with oil added is not very high... but my gauge versus yours who knows. I had an engine with realyl worn rings and still gave numbers like you said. I notice when i moved the kicker by hand it just did not have the nice springy pop feeling... tore it down and ring gap way large... not saying rings is prob. just and experience i have had with compression testing versus reality.

Seams like fuel, air and spark it should start... even if it does not run as well as it should.

Once I pulled plugs out and accidently crossed wires.... All with in a few minutes so I knew what to recheck... this will surely stop an running engine from starting... plugs wet too and good sharp spark. why I thought of that one


Good luck

[jabcb]

So you checked timing with gauge in plug hole... not by using marks on rotor. If so did the marks on rotor agree with your setting.

Oops. My 5:30AM waiting-for-coffee response was a bit short on logic. I had used the marks on the rotor.

130 psi with oil added is not very high... but my gauge versus yours who knows. I had an engine with realyl worn rings and still gave numbers like you said. I notice when i moved the kicker by hand it just did not have the nice springy pop feeling... tore it down and ring gap way large... not saying rings is prob. just and experience i have had with compression testing versus reality.

Am inclined to think you are right about the rings.

[Vintageman]

If you used the rotor mark the keyway could have sheared making the marks alignment a lie

I have only seen this myself a few times in my life. And, not always does it move far so far it won't start (run like poop though... seams like it usually ends up advancing too?).

Knew a person that a dirt bike, would not start no matter how hard we tried proved to be the problem for spun quite a ways in his case . I am not saying it is it, but one of those things when you checked everything more than once and all looks OK. Make sure that mark is 24 degrees (or whatever it means) from piston TDC

If a 130 PSI does seem if you get it too spin fast (bump) should start. I went through this on my 76 GT250 and it would not kick over to start. It did bump start with a couple guys pushing me.

Pulled head and saw a ridge in cylinder top where the ring stops at TDC.... if cyl wall worn so you have a metal ridge so aren't the thin little rings on the piston.

Fuel on plugs? Better be or no chance of starting.

good luck

[jabcb]

Pulled the cylinders.

Rings were beyond the wear limit. Cylinders look good.

[Flywheel]

Pulled the cylinders.

Rings were beyond the wear limit. Cylinders look good.

Time for a top end rebuild. Still wouldn't be a bad idea to get the cylinders mic'ed.

[jabcb]

Pulled the cylinders.

Rings were beyond the wear limit. Cylinders look good.

Time for a top end rebuild. Still wouldn't be a bad idea to get the cylinders mic'ed.

Am going to check the ring end gaps for NOS rings.

[Vintageman]

Thanks for feedback,

yes let us know how much new rings close up gap. I am sure it will and since such a low cost thing to do worth a try as is versus all new top end. can always save up and do later.

I wouldn't hone the shite out of it, just a little to deglaze. a few scratches is better than large piston to cyl clearance in my opinion

Did a chain saw for a friend recently, he just wanted new rings due to cost to my surprise it ran real strong and starts real easy

[jabcb]

Have an update…. Rats.

Installed the new rings today.
Its obvious from kick starting it that the compression is much improved.

The Pingel vacuum petcock doesn't have a prime position.
Kickstarting didn't activate the petcock.

Hooked a vacuum gauge up to the carb vacuum tap for the petcock.
Kickstarting resulted in pretty much no vacuum.

So it looks like the crank seals are likely shot.