Motor will not restart after running WOT. Any Ideas?

[svenr]

The motor will start easily (1-3 pulls) and runs good at low RPM and high RPM. When I run at WOT for 5-10 minutes though, and shut the engine down for a few minutes, I can't get it restarted. No matter how many pulls. If I wait a few hours though, then I can restart it no problem.

Any Ideas what the problem may be? I am completely stumped!!!

HISTORY OF THE MOTOR:
1992 - Johnson 9.9 Long Shaft

I just installed a higher capacity fuel pump kit (standard after 1993 on this motor), new fuel hoses, rebuilt the carb, new spark plugs, adjusted the throttle linkage and cam adjustment, and am using a brand new OEM fuel hose & bulb. Also last year I did the water pump.

The engine runs pretty cool (i.e. block never gets hot enough to burn you). The water tell-tale pees a solid stream.

One of my questions is generally how many turns is typical to adjust the mixture adjustment knob on the carb (needle valve)? After seating gently I have tried adjustments between 3.75 turns out, and 6.25 turns out. Any suggestions here? I have seen minimal impact on engine performance.

 

[57feathercraft]

Re: Motor will not restart after running WOT. Any Ideas?

could be a coil. when you put a big load on it, it whould fail. but there are other things that could cause it to do that. is the gas tank ventalated?

 

[tashasdaddy]

Re: Motor will not restart after running WOT. Any Ideas?

carb controls http://www.iboats.com/bbboard/bbBoard.cgi?a=viewthread;fid=28;gtid=818798;gpid=818802

 

[svenr]

Re: Motor will not restart after running WOT. Any Ideas?

>> Tashasdaddy - thank you for the link, that will definitely help me adjust it. I think I am probably off pretty far right now. By the way, could a BAD mixture adjustment cause the problem I am having? Not being able to restart after running (in this case the engine is warm, and running through the slow speed needle valve). What do you think?

Second question, I was thinking the heat could be changing the expansion of the metal in the block and either affecting the leaf valves or piston skirts which would cause poor suction / no fuel delivery, therefore no starting. Is that possible? Have you ever seen leaf valves go bad on these engines?

>> Feathercraft - the tank is vented, and the vent is open. The engine runs fine for a long time, it is only when I shut it down that I can't restrart it. Do you think a bad coil would cause that?

 

[jimmbo]

Re: Motor will not restart after running WOT. Any Ideas?

It might be heat related. how bout if you idle for 10 -15 minutes after the high speed run, does it run ok? If shut down after idling for long periods, does it do the same? The ignition system can get funky when heated up, especially the parts under the flywheel. another thing 3 1/2 turns out for the low speed needle sounds excessive, maybe so rich it's flooding the engine making it hard to start when warm. Cold engine like/need more gas so it would be fine until you slow down when warm.

 

[Texasmark]

Re: Motor will not restart after running WOT. Any Ideas?

You got some good answers. Here's some of my experiences.

1. Had a thermostat stuck closed in an engine and it acted like that.

2. Had an ignition coil go bad and acted like that.

3. When it doesn't want to start pop a plug and see if it's wet or dry. Wet means flooding or no spark. Dry means no fuel... Gonna bet yours is wet.

The new fuel pump may be flooding the engine....more fuel available than you can use. A carb overhaul may be in order paying particular attention to the needle valve that shuts off incoming fuel to the bowl and the float level adjustment.

Mark

 

[svenr]

Re: Motor will not restart after running WOT. Any Ideas?

>> Jimmbo - thanks for the ideas. I will have to try the different test scenarios mentioned. I did run it WOT for a while, then idled around for 5 minutes, then WOT again. Only when I shut it off did I have the problem restarting. It ran OK at low speed. I did not try long periods of idling in neutral though. I will try that.

Also, from responses so far (yours included) I am getting a sense that I am running rich and may be flooding out when warm and not starting. Also, running rich would explain why the engine runs cooler (rich = cooler engine, lean = hotter engine). I will adjust that and then reply with what happened.

>> Texasmark - Would a closed thermostat mean the water is circulating or not circulating through the block? The thermostat appears to be original. I was wondering if I should change it out just to be safe, but I'm not sure if that it is the problem.

I rebuilt the entire carb when I added the new fuel pump. The engine has been running much better overall since I did that, only thing is the current problem I am having.

Thank you for all the suggestions so far!!

 

[Texasmark]

Re: Motor will not restart after running WOT. Any Ideas?

On thermostats. I had a Chev wagon once and was always working on it. Once I decided that I should change the thermostat as the old one had been in there forever. I put in a new one and it broke (literally) the first time I used the wagon going to the lake (of all places). The bracket holding the end of the valve came loose and it couldn't open....obviously I was stranded on the side of the road.

Course never had that problem before with any stat.
--------------------
Had I even known about a stat in my OB I would have probably changed it, or at least checked it. This was my first engine with one.....didn't know it existed and that was a lotta years ago ('75 70 hp looper).

Looks can be deceiving and as stated, new ones can fail too.

Your call but I'd put in a new one just in case.
-------------------

The exhaust of the OB has to be water cooled always to keep from burning up the block and exhaust manifold. Therefore there is (has to be) a separate water system (passages) for this function. You wouldn't expect this to be interrupted, ever.

The stat controls cylinder environment and since the head gets hottest, a great place to put it is in the cooling loop that cools the cylinders and in particular the head. So, that's where it is on all the engines I've seen. I don't know where it is located in the OMC V4 engines. I don't know the exact arrangement of the water around the cylinders and the head as to how they are interconnected. I would however, figure that they were both on the stat loop so as to keep the cylinder walls and the head at reasonably the same temp.

Probably a certified mechanic will pick up on this and give you the particulars.

Mark

 

[svenr]

Re: Motor will not restart after running WOT. Any Ideas?

I am still having problems, although the problem is a little bit different now.

I adjusted the carbs per the instructions from J. Reeves (link above). Final adjustment of 1.75 turns out (but I may have seated more than i was supposed to). If I adjust the needle value more rich or lean the engine sounds like it will stall, so I think I found a fairly happy medium.

THREE PROBLEMS THOUGH.

1) The engine will only idle in fast idle (max throttle in neutral). If I slow it down at all the engine will stall unless I bring the idle speed back up.

2) Even at fast idle, the engine sounds like it wants to stall sometimes, but if I apply the choke for a second, the engine will recover. So I find myself playing with the choke a little bit to keep the engine running for a long time at idle speed (10-15 mins). This seems to happen in Neutral, and is less of a problem when the engine is in gear.

3) Every time I start the engine (warm or cold) I have to use the choke. In the past it would start with one pull if warm (and about 5-7 if cold). Now it starts with 1-3 pulls cold, and 1-3 pulls warm (with choke).

Not sure what to do next. Any ideas?

 

[Texasmark]

Re: Motor will not restart after running WOT. Any Ideas?

Unscrew your needles and look at them. They should be perfect cones. If any rings are present you did as you said and put them in too tight. You cannot control flow if a ring is present.

The ring, if present could explain a rich condition. Usually an engine sneezes when lean and not under load (in the water in gear). However. If rich, being under load will require more fuel so a rich condition may be your problem.

Other thing could be floats. If the float needle isn't seating properly including a maladjusted float level, you could have flooding problems. A quick check of that would be to drop the bowl and with one hand on the squeeze bulb and the other on the float (very gingerly) with the float down and fuel coming out of the carb (you're keeping the bulb full of fuel with the other hand), carefully lift the float till fuel stops flowing.....usually parallel to the upper carb casting. If fuel doesn't stop or it takes a fair amount of pressure from your finger to stop it, or the float is above parallel when it stops, you have your problem identified.

Do that and come back,

Mark

 

[svenr]

Re: Motor will not restart after running WOT. Any Ideas?

Unscrewed the needle value. Cone looks perfectly straight, with no rings. In fact it almost looks like brand new.

I made a bit of a mess with the bowl and fuel, but I determinted it is seating correctly. I adjusted the float according to the instructions in the manual when I rebuilt the carb in February.

I'm not exactly sure where to turn next. I have to admit it is running better overall since I rebuilt the carb and did the fuel pump & hoses, but it is still not 100% reliable. I feel comfortable getting it started when cold (1-3 pulls), now I just need to get it to restart easily and idle better at low speed and we are set.

Any other ideas to get it running better?

 

[jimmbo]

Re: Motor will not restart after running WOT. Any Ideas?

Have you done a compression test on it?

 

[Texasmark]

Re: Motor will not restart after running WOT. Any Ideas?

After your compression test you might try some Sea Foam in a decarb. Has worked wonders for me in numerous engines of all types.

Mark