How to set the idle (& Crankcase vent. sys.)

[Paul_NY]

Good afternoon, Don:

Saturday I installed on our late model Atomic 4 the Indigo Electronics AT-4CVS Crankcase Ventilation System. Thanks to many of the postings on the Moyer Marine site, installation went quite smoothly. (I also installed 4 new spark plugs.) However... on our first time out post-installation, the idle was running quite a bit higher than pre-installation. In fact, so much so that when returning to our dock I had to keep taking the motor out of gear to slow down (instead of leaving it in gear and just with no throttle advancement, as I used to). Also while under our normal cruising speed the temperature hovered around 180. Pre-installation our typical temperature was closer to 160.

Back in the slip I adjusted the throttle cable linkage assembly on the carburator and the throttle assembly stop screw, which lowered the RPM somewhat. The AT-4 CVS installation instructions suggested turning the idle screw in a quarter turn once the system was installed, though I do not know why. In the slip, I also tried to adjust the idle by turing the idle screw, but even with the screw fully in, the RPM did not drop to the pre-installation level.

So here are my questions:

1A. Do you know whether installing the ventilation system somehow increases RPM given the new ventilation flow direction?

1B. Would the vent. system cause a higher running temperature of 180? (Is 180 okay or should I look to lower it?)

2A. What steps do you recommend for resetting the idle? (I do not have a tach but could get one.)

2B. How many full counter-clockwise turns does it take before the idle screw falls out of the carburetor and into the bildge?

Thanks in advance for your insights.

Paul

PS. Sorry to hear about the Moyer Marine family loss.

[Don Moyer]

Paul,

I'm reluctant to offer too much advice on someone else's system, but in my experience, the only thing your engine should notice from installation of the Indigo Electronics crankcase venting system is a slight leaning of the fuel air mixture at idle. This change is usually easily compensated for by turning the idle mixture on top of the carburetor in (clockwise) approximately a quarter turn (hence the instructions that came with the kit).

I am not able to relate any of your other indications to installation of the Indigo kit. I suggest you call Tom Stevens at 1 (800) 428-8569 for more information.

For whatever it's worth, the idle mixture screw in the carburetor that happens to be sitting on my desk fell out after 7 complete turns.

Regards,

Don

[wlevin]

Idle adjust after vent kit install

I installed Indigo Electronics' crankcase ventilation kit yesterday, and found that the idle went up significantly (from 800 to 1300) after install even though I followed Tom Stevens' directions to start with the idle adjustment screw backed out 3/4 of a turn. Turning the screw in (even to stop) did not lower the idle. Turning it back out three full turns did, but the idle never smoothed out at sub-1,000 rpm levels.
I found this old thread (2004) on the subject, so it looks like this has not been a problem for the group, but I thought I'd try posting this question in case folks had dealt with it since then.
Bill and Jeanne
T34C #453
Otter

[wlevin]

Never mind

OK, then. Two minutes after posting my question on this site I got the answer from Tom Stevens over the phone. I should have called him first.
Turns out there is a stop adjustment for the throttle cable arm which I didn't notice, so if I simply let the throttle arm extend further the rpms should drop with the idle adjustment screw at a reasonable setting.
Thanks anyway.
Bill and Jeanne
T34C #453
Otter

[hanleyclifford]

yes, do mind

What we need to get out of this is that the Indigo PCV modification does indeed constitute a vacuum leak downstream of the carburetor. That is why it leans out the mixture. I have the system myself and I love it. Make sure the hose is tight and well clamped all the way to the chamber. The carb will always have to be completely readjusted to compensate for the new system.

[Dave Neptune]

Pcv

The PCV system is just what it implies, that's a Positive Crankcase Ventilation system. It works by allowoing a small amount of air to be drawn from the crankcase and routes it into the intake manifold. This is in carb-talk what is refered to as un-metered air or air that the carb hasn't added a bit of fuel to. The PCV valve allows a tiny bit of air to be drawn in while at a "hi-vacuum (idle)" and as the demand is put on the engine for power the valve actually opens a bit to allow in more air, this is why you need to have a PCV valve that matches the size and demands of a particular engine. I have the Indigo on my A-4 and have installed and worked with the MMI system as well, they both work fine.
When installed you will notice a few more RPM's and it will vary a bit from motor to motor that is why you need to slow the engine back down to your idle RPM, at this point the air being allowed "around the carb" needs more fuel as it is just smokey air from the cranckase so a bit of fuel needs to be added to the idle circuit via the mixture screw. On my A-4 of which I keep the idle adjusted to 700 rpm and as lean as I can make it for a smoothe idle it took very little adjustment ( a bit less than a 1/4 turn) however if your idle is a bit off when you add the kit (either one) the added air can make a much bigger differance, don't worry just re-adjust for the kit and all will be good.
Check the connections of the PCV system to be sure they don't leak and all should be well. I used clamps on mine and have had no problems with anything coming loose. The PCV will also make a drastic differance in keeping the engine clean on the inside of the crankcase, not to mention how much less smoke (blow-by) will no longer be in the cabin, yes the boat will even smell better.

Dave Neptune

[wlevin]

Worked

Dave was spot on. I had to put hose clamps on the hose connecting the pcv valve and the carbspacer plate, then setting the idle was easy. In fact, I found that mine was very forgiving. 3/4 turn one way or the other was just fine. All normal now.
Bill and Jeanne
T34C #453
Otter