Does anyone know what is the compression ratio on a 30 d yamaha outboard as I can not find it

50 to one if its a newer one

Re: 40hp Yamaha oil mix?

50 :1
Yamaha recommends ringfree

have a look at you owners manual http://www.yamaha-motor.com/outboard...px?ls=outboard

It means your engine's cylinder volume from the piston being at bottom dead center to top dead center divided by it's compression volume (the volume in just the cylinder head with the piston at TDC) equals 6.8,
which is a very low compression ratio.
It is not a measure of PSI. It's the ratio of how much the gas/air mixture is compressed before ignition.
The engine is taking 6.8 units and compressing it into 1 unit before ignition - a ratio of 6.8 to 1.

talk with a yamaha outboard service center as generally the oil injection is set to the fuel usage to maintain the correct ratio in the mix

50:1 since the late 60's
Too much oil will gum up the rings, smoke too much and foul plugs. Use ONLY major outboard manufacturers oil, Mercury, Yamaha, Johnson/Evinrude TCW-3. They work the best, and no alcohol fuel.

2 stroke ?? choking up do you mean ? what oil make and mixture ratio ?

100 - 1

is you propeller bent? a dent the size of a quarter will cause a shake. If not that means your engine is misfiring. here are the troubleshooting test and tool list you need to find out. Tools(1) A compression gauge (2) a spark gap tester.(3) A Clymer service manual for your engine. (you can purchase from your local outboard dealer. I know all these are expensive but if your going to be a outboard tech you will always need them. Troubleshooting (1) check compression. without the year model I'm giving you a average numbers. Look at your Clymer manual. all cylinders need to be over 100 lbs and equal each other within 5 lbs.(2) check spark. use a spark gap tester all cylinders should jump a half inch gap. if you have good compression and good spark, fuel is the problem nine times out of ten.Ethanol gas is proven to stay stable in fuel systems for 30 days in 90 + degree heat. Drain gas tank,clean fuel lines replace primer bulb and replace all fuel filters. Yamaha has a gravity filter under engine coul clean it. Finally replace spark plugs, I know spark plugs probably don't look bad but this is a outboard. Fresh spark plugs means less resistance for the ignition system. The ignition system is week compared to automotive. Test drive boat, if the problem is still there then there is further steps to take. Again I don't know the year model so I guessing its fuel injected. Pull out your clymer manual. what is great about the Clymer Manual for Novice techs is it gives detailed info on your outboard. Troubleshooting tips and teaches you how your outboard works.