1987 Yamha Pro v 150 crank case check valve

[th365thli]

I have an issue where the motor runs a little rough on idle, but at higher rpms/throttle it runs fine. It also smokes a lot. Also, I see slight oil bleed from the carb main jet gaskets and drain screw gaskets. This makes me wonder if I have a crank case check valve issue.

The motor sometimes is hard to start when warm, especially if it's been sitting for an hour ish. I have to throttle it alittle to get it to start. The oil leak tells me there's a pressure situation causing the oil to be forced out. All signs point to excess oil, it smokes a lot in idle, even after warming up, and even after warm starts.

So it's either an oil pump sync issue or the crank case check valves. How hard is it to replace the check valves?

[99yam40]

not hard if you can get to them without taking a lot of stuff apart.
have you checked to make sure the oil pump linkage is set properly?
have you checked to make sure the check valves in oil lines are good?

[th365thli]

So I think I can access them, do I just use pliers or a vice and pull them out? And is installing them as simple as sticking them in?

The oil linkage is set a little rich, as in it's farther than normal from the stopper. The mechanic did that on purpose, said he'd likes to keep older motors running rich than lean. The check valves in the oil lines should be good, I just changed out the oil pump to a mikuni this a few months ago.

I'm not sure why oil is bleeding from the carb gaskets either. It also bled through the bottom of the air silencer gasket, where it collects to be returned to the crank case. I sealed it with gasket maker, but there's some positive pressure going on. I wonder if my oil vent is blocked. The motor will run, and it will start with throttle, this issue has just been bugging me, hoping someone has insight.

[99yam40]

yes just pull and twist.
a little sealer and tap back in.

did this start right after you changed the oil pump?

[erniefish]

I had a problem with several of the recirc valves on my 04 150 , rough idle , cheap and easy fix , quick test , take a syringe with alcohol and small tubing push through valve , through then pull back syringe handle , check valve should prevent any pull back , you can tell if they are working or not quickly , it stops you pulling back instantly . Recirc valves are cheap , shipping is as much as valves ,

[panasonic]

Are you oil fouling the plugs from running the oil/fuel mix to high? Pull the plugs and look.

I would set up the oil pump as per the manual and test it to make sure it is pumping the correct amount of oil. You said you replaced the pump with new so why not set it up to work as it should??


When this is done perhaps the excess smoking will stop.

Right now you are guessing at the right adjustment on the oil pump and maybe putting way to much oil through the engine.

[th365thli]

yes just pull and twist.
a little sealer and tap back in.

did this start right after you changed the oil pump?

Would something like permatex work?

No I don't think so, don't think the pump is the issue.

[th365thli]

Are you oil fouling the plugs from running the oil/fuel mix to high? Pull the plugs and look.

I would set up the oil pump as per the manual and test it to make sure it is pumping the correct amount of oil. You said you replaced the pump with new so why not set it up to work as it should??


When this is done perhaps the excess smoking will stop.

Right now you are guessing at the right adjustment on the oil pump and maybe putting way to much oil through the engine.

Like I said, the mechanic set it up a little rich, he says he set it up rich to greatly prevent a lean condition and a blown motor. He told me he could adjust it back for me if I want but there's no harm running rich.

You're right, having it adjusted that way can cause a rough idle. Perplexing factor for me is the oil leaks past the carb main jet and drain gaskets, as if there's positive pressure forcing the oil past the gaskets. Also, the fact that it smokes at idle even during warm starts. Don't see how that's an oil synchronization issue. Something doesn't add up for me, but maybe I'm thinking about it wrong. For whatever reason, it seems like the engine is slightly flooded with extra oil, and it's either bad recirc valves, or oil sync, or both.

I guess I should adjust the oil synchronization first? I realize 2 stroke carb motors have "personalities" and have margin for errors, but this issue has been tickling my brain. Back to the carb gaskets, yes replacing the carb gaskets seems like the obvious solution, but if there is a positive pressure situation, then the oil will just be forced out somewhere else. I don't even think there should be oil in the carbs in the first place.

[zenoahphobic]

Remember oil's purpose, it is very good at getting everywhere. Even a tiny amount can saturate whatever it gets to.
The oil is injected just behind the carbys, and when the engine is tilted small amount of oil can run back out through the carb.
Now I think you oil pump has been set too high, you said so yourself. I would get that adjusted correctly, as you have been already advised.
As far as smoking, if you have excess oil in the crankcase it will take a while to burn out. Not at all in sync , just takes whatever time.
Your running issue confirms you have too much oil, just tell your mechanic to adjust it properly.

[99yam40]

Would something like permatex work?

No I don't think so, don't think the pump is the issue.

service manual for my C40TLRX calls for Locktite 242(Blue) on the check valves

I would be testing the check valves before pulling them to make sure they have problems

[th365thli]

Remember oil's purpose, it is very good at getting everywhere. Even a tiny amount can saturate whatever it gets to.
The oil is injected just behind the carbys, and when the engine is tilted small amount of oil can run back out through the carb.
Now I think you oil pump has been set too high, you said so yourself. I would get that adjusted correctly, as you have been already advised.
As far as smoking, if you have excess oil in the crankcase it will take a while to burn out. Not at all in sync , just takes whatever time.
Your running issue confirms you have too much oil, just tell your mechanic to adjust it properly.

Ahh okay, then I can probably replace the carb gaskets if I really wanted to. It's such a small amount of oil i can probably just wipe it off every now and then. I will get the mechanic to adjust the oil sync first and see if that fixes anything. I guess it makes sense, when the motor is shut off, the gas will evaporate but the oil will stay, especially since there's excess oil at idle because of oil sync. I don't think the carb gaskets are meant to keep out oil, just gas.