I have the same engine ace and I love it.

From what you are saying I think the problem is your injectors. I would pull them both out and have the tips reconditioned or replaced. It should cost about $200. New tips are a bit over $100 each. You should take the injectors to a marine injection specialist and preferably one that is "old school". Your engine is about 40 years old, first came out around 1975.

There is a copper sealing ring that goes under the injector and you need to make sure you get the old ones out and replace with new. You could anneal the old ones and reuse but not recommended.

Unless you are very handy with a spanner you should get a good marine mechanic to do the job of removing and refitting.

Couple of links:-

http://www.yanmar.com.au/marine.htm

www.yanmarmarine.com/

If you PM me with your email address I can email you about 10 pdf docs of the complete engine manual and parts lists and others.
Cheers.

theace said..
thanks cisco you have confirmed what I was thinking, I will pull them out next week and report back. I have the full manual for this motor but it does not have a fault finding section.
While I was up on the slip I had a marine engineers inspection done for insurance $450 for 2 hrs work, not a bad living if you can get it.

Before you do that, check the heater on the reluctant cylinder. The fact that they both start first up when warm might indicate a faulty heater or heater connection on one cylinder.

Since your taking out injectors, you may as well do a compression test as well.

So if you can hand crank it, it's time for a rebuild? Sounds easy

I have been using the "snake oil" that Ramona recommended, FTC Decarbonizer from Cost Effective Maintenance which seem to be doing the job. About $120 for a 1 liter bottle but the %age ratio to mix in the fuel is small so a liter should be enough for years on a sail boat.

costeffective.com.au/product/ftc-decarbonizer/

Yeah mate.
The solvent is just the carrier of the active ingredients.
The Octanol Phenol acts like an anesthetic and puts the carbon to sleep, softens it up and lifts it off the metal surfaces.
Then along comes the Trinitro Phenol which blows it up into microscopic particles.
The Trinitro - iron is like the dust pan and brush that throws it all into the exhaust and says, we wont see you later.

It is quite a simple process really.

Already got a stainless exhaust elbow for the 3GM30F, and just ordered the decarboniser. Thanks for posting this info

Crusoe said..

cisco said..

Krusty said..
Since your taking out injectors, you may as well do a compression test as well.

The compression test for one of these engines is that if you can't hand crank it past the first compression stroke, the compression is OK. It takes a silver back gorilla to hand start one of those engines.

And aint that the truth. Had the 3 cylinder version with a hand crank and there was no way I could hand crank it even using the decompression lever. As soon as I reset the decompression lever there was no more cranking.

I did hear of a solo round the world sailor who rigged a sheet rope on the engine V-Pulley with the other end led back to the boom via some blocks. He then jibed the main to get the required force to start the engine.

Regards Don

brilliant!

theace said..
hi cisco
I pulled the injectors and had them tested on thursday,one was shot and the other one ok.
I had a small pinhole leak in the top of the exhaust wet box so while i was at it I thought i would remove it and do some repairs .Imagine my surprise when I tried to pull the exhaust hose off and the whole end of the fitting came away from the water inlet down.The only thing holding it on was the lagging tape. "I have a raised exhaust pipe where it comes out off the exhaust manifold". I will get some pics tomorrow .
catch you later .

Yeah it definitely sounded like injector problem from your description.

If you get all these side issues sorted, like cooling system, manifold, wet elbow etc, these little 660 cc engines will out last the lot of us.

Having determined that my engine problem is a "small" problem I've ordered the FTC decarboniser too.
Thanks for the info on this thread.