Crankcase Venting

[PITBoat]

I checked/adjusted my timing on the lake Wednesday, and I noticed when I pulled the vent hoses away from the flame arrestor (to remove it and get at the dist. holddown clamp bolt) that the idle speed picked up a bit.

I think there is visible smoke coming out of those hoses, though the engine doesn't use oil to speak of. The arrestor gets dirty with it too, and the throttle plate(?) and top parts of the carb are a little oily.

I wonder how much power that is costing me? I know it's an emissions thing, and probably safety too to keep that kind of fumes from building up in the engine compartment. It was interesting though to see how the engine reacted to recirculating that vs. straight fresh air.

 

[Lou C]

These engines don’t have a PCV valve as they would in an automotive application. With the PCV those blow by vapors would get drawn into the intake manifold and burned. In this case the vapors are routed up to the flame arrestor. If it’s an older engine there can be considerable blow by and it can foul the flame arrestor in time. Best thing to do is to take off the arrestor and clean it in brake/carb cleaner. Should be done at the start of each season. Clean the choke plate and its linkage while you’re at it...

 

[PITBoat]

Yes, I prob. need to do that again. I noticed the RPM rise before I pulled the arrestor off though, just by pulling the vent hoses away. It lowered again after I got done with the timing and put them back in place. Not a lot, but enough to hear it.

 

[kenny nunez]

Try to set the timing where the engine is idling as slow as it will continue to run.

 

[PITBoat]

Try to set the timing where the engine is idling as slow as it will continue to run.

Advanced or retarded? That may be a dumb question; I don't know what happens when you advance it too far. I think the spec is 8 BTDC on 89 octane and I'm at about 9. I found it at about 10 last season if I remember.

 

[Bondo]

I don't know what happens when you advance it too far.

Ayuh,..... It causes detonation,..... the motor consumes itself, holes in pistons,.....

 

[Lou C]

I think what Kenny means is you want the idle as low as you can get it so that you are not getting any centrifugal advance. Then set the timing. BTW, for whatever reason the 4.3s don’t get as much advance as the V8s. In my OMC shop manual the spec is 6* BTDC and 12* of Centrifugal Advance at 3000 (from memory) rpm for a total timing advance of 18* at 3,000. And regardless of what the manufacturers say use at least mid range fuel to avoid pre ignition and detonation. The gas docks I use sell only 93 octane gas. When I took my engine apart 3 years ago there was no burning on valves or piston tops.

 

[Lou C]

BTDC=
before top dead center. TDC is zero on the timing tab.
so technically 6* BTDC is 6* advanced beyond zero or TDC.

 

[Lou C]

 

[Lou C]

OK looked up the spec...for your engine OMC says...
point gap: .019"
dwell: 37*-41* remember point gap and dwell are inversely proportional, small gap = large dwell angle and vice versa
timing: 6* BTDC
full centrifugal advance 12* for a total of 18* at 3200 rpm
idle speed 500-600 rpm in gear in the water

 

[Scott Danforth]

the reason your idle speed changed is the oil vapor is a fuel. so with the bit of blow-by you have, you have a bit of increased aerosols, so your motor is running a bit richer at idle on the oil vapor than it did......say 10 years ago.

you are not loosing any power

you simply have a motor that is getting a bit tired

 

[PITBoat]

I think what Kenny means is you want the idle as low as you can get it so that you are not getting any centrifugal advance. Then set the timing.

Yes, I realized that after I asked, but got busy with a new to me car, etc. and have only done lake once or twice since. I need to retard that a bit back to 6 and have it in gear when I check. I was idling at anchor. Is the 18 at (3,200) number something to look at too? Thanks.

 

[Lou C]

You can check that with an advance timing light but I’d do it with the boat in the water; I might not want to run it that high on the water hose. It will tell you if you are getting full advance. You set the dial on the advance timing light to total advance (base + advance) then point it at the timing pointer and it should read zero.

 

[PITBoat]

Ok. Advance timing light - never heard of that. I guess you'd do that check in neutral and not bumping along at 30mph+ ?