Low compression symptoms

[Steve509926]

I've just finished servicing my 9.8 Tohatsu and came to fire it up to test it.
After quite a few pulls it fired up and died. Managed to get it started again, but it died after 30 secs. Third time lucky, started and ran for approx 10 mins on a slightly open throttle, then died again. After that I couldn't get it started at all.
Striped down the carb thinking it must be something I've done, clean and no obvious problem, put it back together and refitted it. Again tried to start the OB, slight inclination to fire up but just wouldn't.
I don't think it's a fuel problem and I've checked the spark (good and strong)
I've noticed the black carbon oil drip again that I saw when I first got the ob, pic in #24

https://www.rib.net/forum/f36/tohatsu-9-8-2s-newbie-91068-2.html

Could it be possible that a ring has broken/cracked hence the carbon oil drip and the reluctance to start?

[Fenlander]

Steve triple check everything related to fuel as it’s likely the number one issue from what you describe. The oily drip is probably a red herring.

[beamishken]

You can buy a compression tester from a tenner so not expensive to rule out the compression being low but I agree with fenlander double check everything on the fuel side, the oily drip could just be unburned 2 stroke

[willk]

Originally Posted by Steve509926

Could it be possible that a ring has broken/cracked hence the carbon oil drip and the reluctance to start?

I did 2 laps round a marina with one of these engines wondering why I had no power. After I connected the second HT lead it ran a lot better. My point is that they run pretty well on one cylinder. Fuel side is my bet too.

[Steve509926]

Compression tester ordered, just to completely rule it out.

I'll go down the fuel route tomorrow. The only thing I can think of is the fuel pump (not checked) and/or fuel pipes.
Couple of questions, what drives the fuel pump? How do I check the fuel pump operation?
To check the fuel pipes, is it just as simple as taking off and making sure they are clear and not fractured on the inside?

[beamishken]

Fuel pump is driven by crankcase pulses, the diaphragm can fail & pour raw fuel into the crankcase , relatively easy to check, if you unbolt it from the crankcase ( or pull the hose from the crankcase) if the diaphragm has failed you will find fuel leaking into the pulse port when you try to prime the fuel.

[Fenlander]

As Ken says re the fuel pump.

In truth given the outboard has such low hours, ran so well this year and you've done nothing very intrusive during this service I'm thinking something really daft so you're going to kick yourself when it's known.

[Fenlander]

>>>did 2 laps round a marina with one of these engines wondering why I had no power. After I connected the second HT lead it ran a lot better. My point is that they run pretty well on one cylinder.

That was rather my thinking having managed to start a 4-stroke 9.8 on one cylinder with a plug lead off the other year. Yes it took loads of pulls, needed some extra throttle and bogged down under load... but it ran.

You can always prove a fuel issue vs anything else by spraying a fuel mix mist into the air intake while pulling over.

[Steve509926]

Originally Posted by Fenlander

As Ken says re the fuel pump.

In truth given the outboard has such low hours, ran so well this year and you've done nothing very intrusive during this service I'm thinking something really daft so you're going to kick yourself when it's known.

I really hope so, and I don't mind looking daft if it is something stupid/simple that I've overlooked, the simpler (is that a word?) the better.
When I get around to posting "service video 2" I hope I'll l be reporting such a simple mistake. If I learn from it and others learn from it as well, then that's not a bad outcome.

[Peter_C]

Originally Posted by Fenlander

You can always prove a fuel issue vs anything else by spraying a fuel mix mist into the air intake while pulling over.

^That is always the down and dirty test for lack of fuel. Use a carb cleaner or starting fluid. If it runs and dies after a couple seconds rebuild the carb again. This time though make sure to take the emulsion tube, the jet(s) and the low speed mixture screw out. Clean thoroughly which includes using high pressure air and carb cleaner. Ultrasonic machines are great, along with high pressure air. Sometimes it can take a jet cleaner to poke and prod, for which I use my oxy torch cleaners.

[Steve509926]

Carb fully stripped and cleaned, now running beautifully

Thank you all for the advice.

I'll be posting video 2 & 3 re: service later today

Not sure if it was cleaning the jets or I may not have tightened the two carb bolts enough, allowing air in the manifold.