Warm engine won't restart...compression issue?

[Mr. Close Reach]

Hello,
My rebuilt A4 runs like a top in all circumstances except the following: if she has been running for more than 20-30 minutes and I shut her down (at a fuel dock, for example) she will not restart for at least another 25 minutes or so.

I've posted about this here and also gotten some excellent support from Ken that has ruled out most of the simple stuff (fuel pump, no spark etc). The local "A4 guy" (Tony at Watanabe Marine) said that it is probably a compression issue and I should test the compression on the engine after running it.

This sounds plausible to me, interested in hearing anyone elses take on this.

[Mo]

Could very well be. If she has spark and fuel and is getting air it should go. The only thing left really is compression. So I would get a gauge and check the compression. I would think, however, that if it starts cold it should start warm as well. Others may have more to add.

Do you have lots of power when driving the boat? Will she do hull speed or do you notice the engine revs just don't come up?? Typically, if she has lots of power under load she has the ability to put out some horse power...that would suggest that she does have some compression. Certainly worth a check and then you know.

All that said, I be making sure there's a nice blue spark from the wire when checking fire...if not, it could be coil or something else in the ignition system.

[Dave Neptune]

?

Mr, are you using the choke when trying to restart warm? How is the idle, smooth, rough surging etc? What temp does the engine run at?
From your post I asume you did check for spark(??).

Dave Neptune

[Mr. Close Reach]

Thanks guys. Yes the power seems fine, no problem to get the engine to hull speed assuming a clean bottom/prop.

I will check the spark again today, it was strong last season (I've had this problem for years) but probably worth another look. Yes I do re-start with full choke, to no avail. The engine seems to run cool - plenty of cooling water (that comes out hot). Can't remember the temp I usually see but will take another look at that as well.

[JOHN COOKSON]

2 Questions

Does the engine ever shut down while it is running perhaps longer than 20-30 minutes?
Or does it just not start when you turn it off after running when it is well warmed up?

TRUE GRIT

[67c&ccorv]

Sounding a lot like the overheating coil problem.

[Mr. Close Reach]

John - no, except yes. The previous three seasons it never shut down on me, whether I was running it 20 minutes or 4 hours. However, this seaon it has shut down on me twice. Once after running for just a few minutes (in that case I was able to start it right back up) and one after running for ~25 minutes, woud not restart that time.

67, that occured to me but wouldn't that cause a shut-down, rather than just a restart issue?

[Dave Neptune]

Checks

Mr, time to possibly look at the ign switch itself. Next time it occurs check spark immediatly and then run a "hot wire" to the + side of the coil and check again or do a voltage reading at that terminal. Coils are usually a bit consistant time wise regardoing intermitant failure if comporimised but the switch can screw up anytime and even supply a weak voltage.

Dave Neptune

[ndutton]

This caught my attention:

Yes I do re-start with full choke, to no avail.

I don't need any choke restarting a warm engine. In fact, every engine I've ever had in my life didn't need choke when restarting warm. That covers any manual choke gasoline engine you can imagine - inboards, outboards, lawn mowers, generators, motorcycles, chain saws, weed whackers, you name it.

Using choke in these cases virtually guaranteed a [fuel] flooded condition.

[sastanley]

Mr. CR..I am with Neil...and I've had trouble here too...with a warm A-4, choke does not help it start...if the engine is off for 20 mins (fuel dock/pumpout etc.) if I apply choke (out of habit) it will not start.

I find that leaving the throttle at idle and no choke and just spinning the starter, and she magically fires.

[Bingy]

I also agree,as my engine starts without choke after an initial warm up and will continue to do so for up to 2 hours or so unless air/water temp is very cold .

[Ball Racing]

Sometimes when my motor is warm it takes some throttle to get it to fire.
Seems like the warm manifold maybe warms the carb body and causes it to spill some fuel or vapor and makes a rich condition that needs some extra air to fire.
(This is not always needed, but noticed it on the hot days of this past July)

[Mr. Close Reach]

Thanks; I have tried every permutation of choke/no choke/throttle/no throttle.

Hoping to check the compression this weekend.

[JOHN COOKSON]

A Momentary Digression

Sometimes when my motor is warm it takes some throttle to get it to fire.
Seems like the warm manifold maybe warms the carb body and causes it to spill some fuel or vapor and makes a rich condition that needs some extra air to fire.
(This is not always needed, but noticed it on the hot days of this past July)

+1 on this.
I've noticed the same thing - the warmer the weather the less choke I need to start the engine. This is true when the engine is warm or cold. Maybe this is because gasoline is more volatile at warmer temperatures???

Side note to Mr.CR R\E post #7 last sentence:
A heat damaged coil will cause both shutdown and restart issues. A heat damaged coil will cause a shutdown when it warms up and the engine will not start until it cools down. This will usually occur in cycles. The shutdown cycle will become shorter as the damage progresses.

TRUE GRIT

[Sony2000]

Another option is to close the valve on the gas tank when you think you might have difficulty restarting the engine. Then reopen it, just after the engine restarts.