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Discussion Starter #1 (Edited)
This is about a Silver series 2 stroke 6.5 hp Lawn-boy model # 10323. Like the title says I am having a no start when trying to restart hot. It will run great forever, but shut it off and try to do a restart, it will not.
Carb was just rebuilt and works great. Needle and seat not leaking when shut off
New correct spark plug
New coil. This was no help. No start hot with new coil, original coil and several other used coils from my used parts stock.
BTW it starts great cold
110 psi compression cold
No spark when hot

Did some searching on the interweb and I stumbled on a comment a poster made on a old thread on this site about this same problem and said Lawn-boy had a service bulletin that pertained to it. The link in the post was no longer working. Does anybody have any knowledge of this service bulletin?
Thanks for any help, Randy
 

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I know the 110 psi is good for the cylinder compression, but what about the crankcase compression? I think I would just get the engine hot and pull the spark plug and squirt some fuel mix directly into the cylinder to see if it pops. If it pops then I would lean toward faulty seals as the culprit. It might just be enough compression when cold to pull fuel into the cylinder, but when hot the compression is normally reduced 10 psi or so, and couple that with marginal seals, and that might explain the no start when hot condition. Just something to consider. It sounds like you have ruled everything else out.

I have experienced this scenario with the mower in my avatar. I cannibalized an extended crank crankcase, but used the original crank during the overhaul. Long story short; the crank sealing surface was now in a rough portion of the crank and would wear out seals rather quickly. The first indication that I would get would be that the mower was to hard start when hot. I could install a new seal and all would be well for a few months, then the same condition would creep in on me. After a few seals I decided I need to get the crank smoother and I think I did finally cure that problem.
 

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Discussion Starter #3
I know the 110 psi is good for the cylinder compression, but what about the crankcase compression? I think I would just get the engine hot and pull the spark plug and squirt some fuel mix directly into the cylinder to see if it pops.
Thanks man, but I already tried that.
As I said in the original post I am loosing spark when hot. That is why I put a new coil in it. No help. There is more to the story as Lawn-boy has a Service Bulletin about a no start when hot situation. I really need to know what is in that service bulletin.
 

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The Duraforce is an open to run coil system. Pulling back the bail to start the mower ungrounds the coil allowing spark to occur. Have you tried removing the wire from the coil that grounds it when the bail is released? If after removing the wire there is still no spark then the coil is bad. If there is spark, then you have a wiring problem. What type of new coil are you using? New Toro/Lawnboy or one of those aftermarket ones. Good luck and keep us posted. Bill
 

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Discussion Starter #5
Not sure why you are thinking the ground when it starts fine cold and runs as long as I hold the bail. I have clamped the bail and let it sit there and run for 10 minutes. Shut it off and it will not restart until it cools for about 20 minutes. Does this with 4 different coils.
Again LB is aware of this situation and has a Service Bulletin on how to fix it. Need to find a person who has access to this.
 

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Well hopefully someone will remember that service bulletin. To be clear you did state that there is no spark at all when trying to start it hot, correct? At that time did you remove the ground wire from the coil and re check for spark? No spark with the ground wire removed would indicate either the coil is bad or when hot something is grounding it. You said you had found some information on this site about a service bulletin. Can you provide the link to the thread? We'll get this figured out. Bill
 

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These two service bulletins may help.There may be another one. Be very careful when testing for spark with the plug wire disconnected. If you ground it or leave it hanging with no place for the spark to jump it can damage the C.D. pack. Sorry, I am unable to post the images at this time.
 

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Discussion Starter #9 (Edited)
Yard Nazi
Just to make sure I wasn't over looking something simple I took the cover off, disconnected the kill wire at the coil, put it back together and started it. After running it for about 7 minutes I pulled the plug wire to kill the engine. Put the plug wire back on, kill wire still removed from coil and got no start. After it cooled about a half hour it started right up. I also tested the the kill wire and it is working as it should

Mike72
So you have the bulletins I am looking for? Hope you can get the uploaded. I'm stuck.
 

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I don’t think I saw it mentioned but did you check compression when hot?


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Discussion Starter #11
I did see that, but compression is irrelevant if I am loosing spark, which is happening when hot.
 

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Not sure why you are thinking the ground when it starts fine cold and runs as long as I hold the bail. I have clamped the bail and let it sit there and run for 10 minutes. Shut it off and it will not restart until it cools for about 20 minutes. Does this with 4 different coils.
Again LB is aware of this situation and has a Service Bulletin on how to fix it. Need to find a person who has access to this.
Yard Nazi is correct. My bail wire has failed when it heats up before. I believe it has something to do with the wire shifting when it warms up, but I don't know how it does that. We are note suggesting these things to be rude or to joke around. It is just issues that we may have found when we had the same issue.

Like everyone else, the first thing that comes to mind is the coil. But the fact that you have been through several coils tells me that is not it. The only thing I can think of is perhaps either a defective spark plug, or the magnets on the flywheel are dirty, rusty, or otherwise impaired.
 

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Discussion Starter #14
Mike72
Bingo You da man
I'll read that a couple of times so I am sure what I am doing and give it a try.
I'll keep ya posted.
Many thanks
 

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That bulliten was for the early F engine coils. I am not sure why your mower is acting that way. The new coil should have solved that.
 

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Discussion Starter #17
That's what I thought. Kind of bummed when I put the new coil in and it did the same thing. Hate to give up on it. It runs great and looks like new. It just has this no start hot thing.
I refuse to sell it the way it is.
Back to the drawing board.
 

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Don't give up! You will probably find it is something simple and you will look back and wonder how you missed it. I had a mid 70's D series that intermittently would stop running. Couldn't find the problem. Turns out it was a loose connection where the coil ground wire plugged into the switch harness and was hidden by the protective sleeve. It's always the easy things that are the hardest. Bill
 

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Discussion Starter #19
ReedZ
Today I rechecked the compression cold at about 110 psi and checked it hot at 110 or just a hair over. So compression is solid.

I also rechecked for spark with a hot engine and no start situation and it seemed like there was a weak spark intermittently. To see it though I had to close all the garage doors and lights off to make it dark enough.

Checked fuel cap and it is venting properly. In and out.

And as I said before I would get a no restart with hot engine with kill wire removed from coil.

I also rechecked coil air gap with hot engine. Was a little more than .010 so I readjusted it to right on .010. No change

Choking and a shot of fuel from primer bulb is no help
Only thing that will get it started is a 20 minute cool down. Then it will start right up.
Pretty crazy
 

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I'm a retired electronic troubleshooter and would try crazy things with crazy problems.
Here's what I would do...
1) check coil resistance cold then hot. Very simple, plug wire to ground. Resistance should be the same.
2) since it's heat related...cool things off. Get a can of blow off spray, electronic section of Walmart. It blows air holding it upright...cold if you hold upside down. Freeze spray is better, but this is cheaper and it works.
When hot...verify it will not start. Now cool down one thing at a time. Cool coil...try it. Cool flywheel magnet...try it.
Logically if it's heat related, cooling down the culprit will make it run again.

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