Yanmar 3gm30, one cylinder runs hard

[SY_ELIN]

Hi,

Just found this forum, seems great, so my first contribution before I start asking my question is to show you this site where you can find most workshop manuals for Yamnar engines..
Albin Motor

Ok, now to the more important stuff:
When starting my 3gm30, cyl nbr 3 needs about 15 seconds before it runs smoothly, and when it starts, it runs "harder" then the other two. It like it is knocking harder. I found out that it was cylinder nr 3 by lifting the decompression lever when the engine ran.
For every cylinder the hard sound was still present, but when lifted it for cyl 3, it got more quitet and the engine ran on 1 & 2 but more smootly.

Is this fault mechanical, or can it be so "simple" that it is the fuel pump that delivers wrong amout of fuel to it compared to the other two cylinders? Or something else.
All tips are really welcome..

Best regards
Kalle (sweden)

[Chief Engineer]

Probably a bad injector

Any smoke?

[roverhi]

Mine does the same thing ifI start it with the throttle all the way closed. I ust crack the throttle a little and it starts up smoothly. Haven't specifically tested it but the engine seems to run fine if I retard the throttle to the stops after it starts. It's been doing it for a couple of years and still seems to run strong. Maybe for as long a I've owned the boat as I almost always crack the throttle before starting it. My son discovered the problem when he took the boat out on his own and cranked it over with the throttle against the stops. It did it to me the last time I started it when I didn't advance the throttle before starting.

[SY_ELIN]

No smoke, maybe just when I give full throttle.. but not otherwise.

It doesn't matter how I have the throttle when it starts, idle or max.
It always starts, and it has been like this for 10-13 years accordingly to the previous owner, I just wanted to fix it since Im going on a longer trip in two years from now so.. I want to have it top condition..

[ColdFusion]

Originally Posted by SY_ELIN

When starting my 3gm30, cyl nbr 3 needs about 15 seconds before it runs smoothly

Smoothly or quietly? If smoothly then I'd suspect the fuel side of things. If quietly then maybe lubrication, or lack of.

Originally Posted by SY_ELIN

No smoke, maybe just when I give full throttle.. but not otherwise.

It doesn't matter how I have the throttle when it starts, idle or max.
It always starts, and it has been like this for 10-13 years accordingly to the previous owner

No smoke rules out piston rings, etc. If it always starts and it's been the same for that long then to be honest I wouldn't worry.

[FloridaWriter]

Is your idle rpm set at 900? If it is set lower it will run very rough.

[Sailmonkey]

Pull the injectors, you can have a shop test the pressure and check the spray pattern eaisly enough. The most common problem will be a clogged tip caused by running with too little of a load on the engine. When the tips clog the fuel isn't atomized properly, leading to knocking.

[shakey doug]

Kalle,
Possible one of three things -- check. 1. noisey cyl. -injector 2.fuel pump delivery valve 3. leaky valve guide. if fitted with manifold cold start vapour system check element valve.