Question about Pre-mix.

[Upallnight]

I'm running premix in my 95 Sportster 40:1 and still have the oil tube to from the oil tank to the rotary valve at the bottom of the crankcase. The engine appears to smoke quite a bit. I'm wondering if the oil for the rotary valve is also being burned since the crankcase is used to feed the cylinder with gas and air. Could I get by with just the oil in the premix?

 

[Sportster-2001-951C-Stock]

You have to keep oil in the RV chamber and you need to have oil in the tank to accomplish that, it lubricates the driven gear.

 

[Dr Honda]

Yep... what he said.

..... The engine appears to smoke quite a bit. I'm wondering if the oil for the rotary valve is also being burned since the crankcase is used to feed the cylinder with gas and air. Could I get by with just the oil in the premix?

The RV cavity is not in the intake track... where the air and fuel pass into the cyls. So no... you can't remove the oil lines to the gears.

The reason it smokes is.... you are running premix. When you are on the pump... at idle, it will go to about 75:1, and at full throttle it runs 40:1.

if you want minimal smoke... put the oil pump back on. The Seadoo/Mikuni pumps are super reliable. The only time we hear about failures is because people NEVER service the system, and give it a bad wrap when the hoses rot, or the filter gets plugged up.



With that all said... what oil are you running?

 

[Upallnight]

I'm running Quicksilver Personal Watercraft PWC 2 Cycle Oil. Replaced the carrier bearing and took it out on the river. Don't have water in the hull anymore, however the engine seems to be running really rich. Took the plugs out after about 10 minutes on the river at WOT and the plugs were wet and Black. Rebuilt the carbs earlier in the summer and when we went out last time the engine would rev and we could get the boat on plane. This time the boat bearly got on plane and when it did it would lose power.

Took a compression test when I got the boat home and both cylinders read 120 PSI.

Any thoughts on what could be the problem?

 

[LouDoo]

Well, that's your problem, low compression, I'm afraid you're ready for a rebuild.

Lou

 

[Sportster-2001-951C-Stock]

Well, that's your problem, low compression, I'm afraid you're ready for a rebuild.

Lou

So on an RV motor, low compression will cause the plugs to become wet and black?

 

[Dr Honda]

So on an RV motor, low compression will cause the plugs to become wet and black?

On any engine... the plugs will look "Rich" when the compression drops. You don't have enough cyl pressure to properly burn the mix. Not to mention... seadoo's run a little on the dark side anyway.

 

[Upallnight]

With the compression at 120 in both cylinders, should I do a complete top end with new pistons and cylinders or just replace the rings and have the cylinders honed. Can I use an over size ring of .5mm to make up for any wear in the cylinders?

 

[Sportster-2001-951C-Stock]

On any engine... the plugs will look "Rich" when the compression drops. You don't have enough cyl pressure to properly burn the mix. Not to mention... seadoo's run a little on the dark side anyway.

Granted his compression results are sub-par. However, if this was my watercraft, I'd throw a hotter plug in there. I believe the OP should try a BR7 for grins and giggles.