RPM at Idle Question

[jwilson1515]

Okay, another dumb question from me to the intellect of the board. How steady should my RPMs at idle be? Quick history to my question.

I had a vacuum leak where the carb attaches to the intake manifold. Rather than get just a new gasket, I ordered the indigo PCV kit (as my slash tube was missing and I was blowing whatever was in my crankcase into my cabin ). I thought this would fix two problems at once.

After installing everything, my idle would vary about 200 – 300 rpm. Even after adjusting the idle screw on the carb, I could not get a consistent idle. I was around 600 – 850 rpm. Not rough, but not consistent.

After reading some posts about the PCV kit causing some air/gas mixture problems, I removed it and just replaced my gasket. My idle is much more consistent now, but it will hold at around 600 rpms but occasionally drop every 10 seconds or so to about 450 – 500 rps for just a quick second, then go back up to about 600 RPMs. When I give it gas, no problem.

So I said all that to go back to my original question, should the RPMs at idle be spot on the same…say at 600 RPMs, or is a little fluctuation in the RPMs normal.

Thanks.

[ndutton]

Although it's difficult to do so with such a beautiful set up I'll resist commenting on your PCV experience. When I do it seems to get the hair up on everybody's neck.

My idle has no such fluctuations with a factory original configuration.

Can you tell if your alternator is putting out a charge at idle, 13+ volts on the voltmeter or positive amps on the amp gauge? If yes, I wonder if alternator load is causing the RPM dip. The cyclical nature of your symptom doesn't fit the alternator theory but then again, who knows? Maybe test run at the slip with the alternator belt removed, see if that makes a difference.

[Marian Claire]

Does it run smoothly at say 800 RPM? 600 seems low. I think 700 to 800 RPM would be fine. Just stay below 1000 when placing in gear.
Neil: What control you have. Dan S/V Marian Claire

[ndutton]

Neil: What control you have. Dan S/V Marian Claire

Ha! When I first read that I thought, "Huh? Control for what, choke, throttle, alternator?" Then I read it again and the fog cleared.

I still got a veiled zinger in there, that'll have to do this time around.

[jwilson1515]

Thanks for the replies. I will up the idle to around 800 and see what happens.

Ndutton – you may be on to something with my alternator. It does make a muffled clacking noise (obviously hard to explain) which seems to correlate with varying RPMs. How do I test it without the alternator belt as you mentioned? Do I just keep the boat plugged into shore power and take off the belt?

[ndutton]

How do I test it without the alternator belt as you mentioned? Do I just keep the boat plugged into shore power and take off the belt?

Nah, no need for shore power. Just remove the belt and start normally. The electrical requirement to run the engine is small and your battery can supply sufficient power for quite a while.

[Dave Neptune]

Idle

My suspicion is your idle adjustment and or a vac leak not associated with the PCV valve. I have the PCV and idle rock solid at 600 in gear and 700 in neutral with the J-8's. I can do this for hours and no RPM fluctuations.
I do find that getting the idle right requires a bit more than one adjusting session. After adjusting every time I restart cold I give the idle screw a tiny twist out until I have an occasional stumble then close the idle screw back around 1/8 turn max. Then I run til I need to remove the carb for it's next bi-nual inspection.

Dave Neptune

[ndutton]

Ooh, that caught my attention.

After adjusting every time I restart cold I give the idle screw a tiny twist out until I have an occasional stumble then close the idle screw back around 1/8 turn max.

To confirm, you adjust the idle screw every time you start cold? I seem to recall Hanley saying he also makes adjustment a routine part of normal engine operation.

These are the only two such reports I remember and as they come from forum regulars I'm wondering if this is more commonplace than reported.

Anybody else??

[ILikeRust]

I have the Indigo PCV valve kit installed, but I haven't yet put significant time on the rebuild. When I did run it, though, I ran it for probably about 20 minutes, and there was no fluctuating or pulsing of any kind. I will say, though, that the idle seemed a bit high, so I'm thinking at some point I'm going to have to fiddle with the idle adjustment and see what's what.

[jwilson1515]

Thanks for all of the help with this. Another question and forgive me if I should have started with a new post.

Rarely, but sometimes, when I hit the button to start my engine, I get nothing. The lights will dim, but nothing happens. This happened last weekend, I taped the solenoid a few times, and it stopped.

I suspect I need a new solenoid. Is this an easy job? Do I have to remove the starter to replace the solenoid? What all is really involved.

Thanks again everyone.

Cheers

[Dave Neptune]

No No no

Niel, only until I have leaned a tick at a time and it idles rough then 1/8 closed and it will sit until I have the carb off again. I got good at this whiloe trying different jets and float settings a few years back. The last I touched it was probably march of 2010.

Dave Neptune

[ndutton]

No, I don't think it's a solenoid issue. The dimming lights are the giveaway.

It sounds like the starter has an intermittent issue resulting in a locked rotor or short to ground. The dimming lights tell me the solenoid is conducting electricity fine and plenty of it. A failed solenoid doesn't conduct, your symptom is the opposite.

Dave,
It looks like I misunderstood. That's why I asked.

[Dave Neptune]

Starter

jw, you can replace the solenoid however unless you are good at it I wouldn't bother. Just pull the starter and take it to a rebuilder. They can do the whole thing including replace the solenoid, brushes and bearings for about half what a starter would cost and not much more than just the solenoid. In my humble opin just have it done, unless you're good at rebuilding a starter or just want to learn how. Personally I have the skills and tools and I take it to a rebuilder they're a bit of a PIA but not bad if you know the trix!

Dave Neptune

[jwilson1515]

Thanks for all the replys and help. If you guys are ever in the Clear Lake area of TX I will buy you a beer!

[TomG]

Thanks for all the replys and help. If you guys are ever in the Clear Lake area of TX I will buy you a beer!

Wish I had known that two weeks ago.... Spent the weekend on a friend's boat slipped at Watergate. Maybe next time!

You might also check for corrosion at the heavy wire from the battery at starter terminal. Mine was acting the same way and cleaning that connection really seemed to help.