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H99 starts great idles great stops after 5 mins hard to restart

sailorickm

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"Three days in a row, my 9.9a

"Three days in a row, my 9.9a starts instantly, idles smooth as can be for about 5 minutes and then stops. It won't restart for about 15 minutes then runs fine (stops and restart) all day long.

The 5 minutes or so is suspiciously about how long it runs with the fuel in the bowl when I disconnect the fuel line (for winter storage, for example).

I found a similar post here from a year ago, but the poster never came back to say what it was. The suggestions were to check the plugs, check the fuel O-ring (where the tank hose attaches to the engine, I assume?) and possible exhaust leak starving air (run with cowling off to test).

The only test I've done so far was to put it into gear and run it a bit faster than an idle. Same thing.

I change the oil and spark plugs every spring. I had a carb job done a year ago. This last winter was the first time that I didn't drain the bowl for the winter. The mechanic who did the carb job told me to leave it fuel. I'm in Canada, so it sits in an unheated attached garage for 7 months or more. It gets to 0 deg F in the garage.

Last year I had the fuel filter in backwards for quite some time after the carb job. I don't recall if I put in another new one when I discovered it was backwards. I hope I did; it seems obvious now that I should have thrown it away. (I have a bag full of filters).

The odd thing of course is that once I get it restarted, it runs great all day, even with stops and restarts (it's on a sailboat)."
 
"It sounds like your fuel is i

"It sounds like your fuel is iniitially back-flowing into your tank. At initial start up, there is a big gap of air in the fuel line that the fuel pump can't handle, thus the stall. You likely have a small air leak between the fuel filter and the tank. Also, the check valve on your pump up bulb is probably not functioning properly. To test that, pump up the bulb tight, run the engine until it stalls, and see if the pump up bulb is still tight. If there is an air leak, I would first suspect the O ring at the fuel filter housing."
 
"I would install some clear pl

"I would install some clear plastic fuel line between the fuel line connector (which on a sail boat I would remove and connect directly to the tank) and the fuel pump. That way you can see where the fuel is at all times. AND if you get bubbles, will help find the air leak."
 
"Thanks for the replies.

On


"Thanks for the replies.

One thing I've never noticed or tested, when things were working normally: should the bulb stay hard after running the engine (say at 3/4 throttle for 20 minutes)? It's always soft the next time I go to start it (after being off for a couple of hours or more).

I didn't check the bulb after it stopped. I did notice that the fuel filter has very little fuel in it after it dies. I don't know what's normal for that either. Should it always be full?

It seems like fuel starvation to me, but...

I called the shop where I had the carb job done a year ago. I didn't think the mechanic would be in on the weekend but he was. He thought the opposite: that it was running too rich and it would slowly flood and then die.

He suggested I back off the screw with the spring on it that's found on the carb. "Counter-clockwise?". "Yes", he said.

I tried that and it would not start or even fire at all. So I went clockwise 1/4 turn back to the original position and then 1/4 turn clockwise more. It started and ran for over 20 minutes, so it seems the problem is solved.

I can't explain what the screw does. It regulates air I think, but I'm not sure if it's only during idle where it has an effect?"
 
"Your primer bulb would not re

"Your primer bulb would not remain hard during operation, but it should not collapse either.

Your fuel pump draws fuel through the primer bulb and a blockage between the bulb and fuel source (or a blocked vent) would cause it to be sucked flat by your starving fuel pump.

If you are referring to the filter between pump and carb, mine is usually half or so full.

There are Two screws with springs, first is close throttle stop screw and second is idle (only) fuel mixture adjustment. Sounds like you were adjusting second and it should be set with a warm engine idling at the clockwise side of max RPM and smooth idle. If it hesitates on acceleration, then back it out slightly CCW (richer).

"...the first time that I didn't drain the bowl for the winter.
The mechanic who did the carb job told me to leave it fuel. ..." he must like doing carbs, have plenty of stabilizor in the fuel.
"
 
Seems to me those had a small

Seems to me those had a small filter on the fuel pump under a slot headed screw. You might check that.

Pull a spark plug and tell us what color it is?
 
"Hi, I'm back. I see that

"Hi, I'm back. I see that my last post a while back isn't here. I had just said (in response to questions about the color of the spark plugs) that I can't work on the engine without dropping tools to the bottom of the lake! (BTW, what are the different colors one might see and what do they mean?)

The engine has been running much better, but it will still stall some days.

I've been bothered by the fact that I could only find one screw. Also, the original instruction from the mechanic was to "back out 1/4 turn the _brass_ screw with a spring under it". The screw I was turning was not brass. It sticks up about 1/2" or so. I keep looking for the other screw and I finally found it yesterday. It's brass, but I don't see a spring and it turns _very_ easily. (The other is very tight).

It was hard to find as it's recessed about 1/4" in a cylinder (tube) that is horizontal, facing sideways. I guess I hadn't ever looked from that angle.

As for the silver screw with the spring, as I turn it clockwise the engine just idles faster and faster, so this does indeed seem to be the close throttle stop screw. I tried to set it at a slow but smooth setting.

I turned the new-found brass screw a full turn in both directions and didn't notice any change in RPM. I was afraid to turn it too far, mostly out of fear it would fall out and go to the bottom of 21 feet of lake water. What now?"
 
"Although turning the brass sc

"Although turning the brass screw in both directions didn't seem the change the RPM, I left it 1/4 turn counter-clockwise as instructed and it has been fine ever since."
 
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