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Discussion Starter #1
My 816 has been displaying wierd symptoms.

When cold, it starts right up, in this weather just a touch of choke, or none at all. But if I've been running it, and manage to run it out of fuel, it really doesn't want to start again until it's cooled off.

It's not just empty fuel line; I've tried pulling the fuel pump lever by hand until I see the filter fill with fuel. Doesn't make any difference. I need to let it cool down again, then it starts immediately.

The carb's on top of the engine: Could it be that it gets so hot that the fuel is just evaporating out before it has a chance to get going? Maybe if I swap it for an electric fuel pump and let that run for a while before cranking?

It's wierd. The thing starts perfectly, hot weather or cold, unless I've run it out of fuel.

Yes, yes, the fix is to not run it out of fuel. Got it :)

Other ideas?
 

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Coils as they get older will do strange things like this when they get hot. Cool them down and they're good for a while again. Not sure that is the issue here though.
 

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Discussion Starter #3
Coils as they get older will do strange things like this when they get hot. Cool them down and they're good for a while again. Not sure that is the issue here though.
Yeah . . . I don't think so. If I've been mowing for an hour, don't run out of fuel, shut it off, and come back 5 minutes later, it starts right up. The issue correlates strongly with running out of fuel. That's why I'm grasping at the straw of vapor lock.
 

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Try a little gas in the carb directly when it's not starting to see if it starts. That will definitely rule out a coil issue. Wonder if your fuel filter has a small air leak that when it gets cold and contracts closes. To check run a hose directly to carb bypassing filter for a little bit.
 

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Do you have the stock muffler that runs right next to the carb? I've always hated that. My brother's 816 has had similar issues in the past and I've suspected the same. Didn't correlate with running out of fuel but still seemed like vapor lock nonetheless.
 

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Discussion Starter #6
Yes. It gets awfully hot in there.

I ran the 816 out of fuel again monday. It did the same thing to me. Couldn't get it started for anything until it cooled down.

Next time, I'm bringing a tool kit with me. I'll at least eliminate stupid stuff like spark etc. I don't think that's the problem, but I aim to prove it. I think my next step after that is to open/clean the carb and fuel pump, on the off chance that something in there is marginal.

It's wierd. When cold, it starts within 1-2 seconds, with a touch of choke. When hot and I haven't run it out of fuel, it starts right up with no choke.

One thing that might be a clue: This last time, after I put fuel in it, I tried for several minutes to start it, different throttle settings, different choke settings, twiddle the fuel pump by hand to ensure fuel was getting to the carb. Nothing. But I didn't let it cool all the way down. I got impatient after about an hour, and went back out to try it again. It was still warm, but not super hot. When I cranked it, I still got nothing for about 10 seconds. But I was seeing some pale smoke out the exhaust, similar to trying to start a flooded engine. So I went to wide-open-throttle, no choke, and cranked. After a few seconds, I got a couple of puffs. Several more cranks like that, and it caught. Ran perfectly after that.

So maybe I have multiple things going on. Something causing the spark to fail, leading to a flooded engine? Dunno. This one's bugging me.
 

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Discussion Starter #8
Is it the old 6 volt coil? Maybe it's going bad when it heats up?
Don't know. I should check it. But I only have a problem when it's been run out of fuel. If it was running a while and I shut it off, it will start right back up again.
 

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Fuel pump issue?

Remember (I know I sound like a broken record here) today's ethanol laced pump gas is terrible stuff. It has lower fuel value per pound so engines run hotter and leaner than the old gas and it boils in the float bowels easier too.

I only have the older T-head engines in my stuff and since they tend to be thirsty I do use pump gas due to the cost of race gas around here. I do tune the carbs to be a little richer than I would normally like and I always run the carb dry on shutdown so the evil ethanol does not stay in the fuel bowel any longer than necessary.
 

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Discussion Starter #10
Fuel pump issue?
Maybe. It's hard for me to rule anything out at this point, but it doesn't really make sense to me.

When trying to get the thing started again, I sometimes hook a wire to the lever on the fuel pump and run it manually until I see fuel flowing through the fuel filter. That never helps. I sometimes try squirting a little fuel down the throat of the carb. That never helps either.
Remember (I know I sound like a broken record here) today's ethanol laced pump gas is terrible stuff. It has lower fuel value per pound so engines run hotter and leaner than the old gas and it boils in the float bowels easier too.
Yep. But I mostly run avgas :(
 

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Discussion Starter #12
Well, ok, I did some more mowing, and experimenting.

When I run it for 5-10 minutes, don't run it out of fuel, and shut it down, it starts immediately. Tried that multiple times, and it worked perfectly.

Then I mowed some medium-heavy grass for 45 minutes. Shut it down, tried to restart. Cranked for about 5 seconds, and gave me a really healthy backfire. Tried a couple more times, got some more backfires, then it finally caught. It sounded loaded up for the first few seconds, then settled and ran fine. Shut down, tried another restart, but couldn't get anything but backfires.

I tried that a few more times, but it didn't want to restart.

I think I have a carb problem. I haven't cleaned out the carb and reset everything in a couple of years. Maybe it's running so rich that the plugs are getting borderline fouled, and they don't want to cooperate when hot. I don't think I have a coil problem, because it wouldn't be giving me backfires if I wasn't getting a spark.

I can't really explain how all this fits with problems after running out; that should have run lean before it quit, and left it cleaner then when I started. But who knows, I can only debug the thing I have a clear indication on.

Any more wisdom from the assembled multitudes?
 

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Discussion Starter #13
. . . and after letting it cool for about 30 minutes, it started right back up.
 

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Well it could be lighting off unburnt gas in the hot muffler couldn't it? Do you have a spark tester? I'd still be curious what it would do if you sprayed a little ether in there when it was doing this.
 

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Discussion Starter #15
Fair

I don't have a real spark tester. Usually I just pull the plugs and lay them on the head.

And I agree, there's still something not adding up about what it does when I run it dry.

So I think my plan is this:

1. Clean the carb, and reset the mixture controls. Make sure it's running well after that.
2. Get it hot, and run it dry. If I try to restart and it fails:
3. Pull the plugs and confirm that I still have spark
4. Button it up and try it with a squirt of ether.

If I still have spark when hot, it's awfully hard to see how I wouldn't get at least a few pops with some ether. If the spark is really weak or intermittent, I go after that.
 

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Discussion Starter #18
Pretty sure yes. It looks like I may be diving deeper into this thing . . .
 
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