'72 65HP intermittant stalling-- dirty carbs?

[mike64]

I finally got the boat out for a shakedown cruise on saturday. When I tried to accelerate, the motor bogged down and died. I was able to start her up again, but she'd bog out again whenever I tried to go faster. I was giving up and heading back to the dock when I could hear a change in the motor. So I tried the throttle, and the motor performed like a champ, just like last year. I buzzed around the lake at WOT having a great time. thinking all I needed was to blow out the pipes and everything would be fine.

Then I stopped to do a little fishing. When I started up again, the motor did the same thing-- bogging down and ready to stall if I gave her a little more gas, but I could putt-putt ok. And once again, that passed after about 10 minutes and I was able to run her at WOT as fast as she goes.

So my guess is dirty carbs? Since the problem is intermittent i'm hoping it's not that serious. Would the first thing to try be cleaning out the system with seafoam, see if that helps...?

 

[jay_merrill]

Re: '72 65HP intermittant stalling-- dirty carbs?

Could be dirt in one or more carb, but my bet would be ignition. I would work from the plugs back. A quick check for spark with a spark tool and/or a timing light might reveal the offending plug(s).

 

[mike64]

Re: '72 65HP intermittant stalling-- dirty carbs?

Thanks, Jay. unfortunately my spark checker is broken and being Memorial Monday I couldn't pick up a new one. I'll check ignition this week.

Would a lack of spark be intermittent like that though? I thought you either had spark on all cylinders, or you had a problem.

 

[mike64]

Re: '72 65HP intermittant stalling-- dirty carbs?

Ignition tested fine. I took the boat out again today and I had the same problem, I could run at real low speed but trying to give her any throttle the motor would bog out and die. Then I'd hear a change in the motor and it would run like normal. One trick I figured out-- there's a a toggle switch choke right under the key on my throttle control, for starting the motor when it's cold. When the motor was running slow and bogging down, I could give the toggle a flick and the motor would "wake up" and run great again. So it's a fuel delivery problem, and I'm thinking either--

1. contamination in the carbs, crep on the floater

---or----

2. I replaced 2 low-speed needle valves this spring-- the splines on the old ones had worn out and the armature was just moving freely, not turning the needles when the lean/rich control knob was turned. So last year I was running super rich all season, to the point where black goop sometimes came out my prop exhaust. I tried to follow the service manual as best I could without a tach or timing light-- I went by sound to try to guess rpms. Yeah, I know that's not the best way to set the low speed adjustment, but on muffs I had the motor purring...it ran better than it ever had. But it's probably running too lean now. I found out a buddy has a timing light I can borrow, so I'll reset the low speed needles.

Anybody think it's 1 or 2, or a third problem I'm not thinking of?

 

[a70eliminator]

Re: '72 65HP intermittant stalling-- dirty carbs?

are you using a portable fuel with primer bulb? I have problems similar to what your experiencing with one of my 6 gal. portables, I haven't pinpointed it yet but i think something is not venting properly, I switch then back and forth and it;s just the one that gives me problems sometimes.

 

[mike64]

Re: '72 65HP intermittant stalling-- dirty carbs?

a70, yeah, I have a 6 gal. gas can that connects to the motor with a primer bulb. But I'm thinking, because the motor responds when I hit that choke switch, it's probably in my carbs. Don't want to rule out anything, though.

 

[jay_merrill]

Re: '72 65HP intermittant stalling-- dirty carbs?

There are a number of things that can cause the problem that you are experiencing. I was thinking ignition because of the "comes and goes" nature of what you have described. For example, my '72 J65 has been running like a dream ever since I rebuilt the ignition system, but last week I was getting about the same situation as you have had. When I got home, I noticed that the #1 spark plug wire was loose in the socket on the coil. I clipped about a quarter inch off the end of the wire, screwed it back into the socket and "re-siliconed" it. I ran the boat about 35 miles today and the motor never missed a beat. I guess my point with this, is that intermittant failure of a cylinder to develop power has been most often ignition related in my experience.

All of this said, you could have carb problems and timing problems. As you know, your high speed jets are fixed orifices, so barring debris in the carbs, they should be fine. That leaves questions about things like properly adjusted floats, properly adjusted low speed jets, etc.

The fact that the motor wants to run better when you choke it, suggests a low speed mixture that is too lean. Also, the fact that you did low speed adjustments on the muffs, instead of in the water is a tip off. You will never get the idle adjustments done correctly without having the backpressure on the exhaust that exists when the engine is immersed in water. I would reset the idle in the water, in gear, per the instructiions on page 3-11 of your service manual. If you don't have this info and need me to provide it here, let me know.

If this does not cure the problem, you might want to consider a fresh link & sync and timing check.

 

[mike64]

Re: '72 65HP intermittant stalling-- dirty carbs?

The fact that the motor wants to run better when you choke it, suggests a low speed mixture that is too lean. Also, the fact that you did low speed adjustments on the muffs, instead of in the water is a tip off. You will never get the idle adjustments done correctly without having the backpressure on the exhaust that exists when the engine is immersed in water. I would reset the idle in the water, in gear, per the instructiions on page 3-11 of your service manual. If you don't have this info and need me to provide it here, let me know.

Thanks a lot, Jay. I suspect it is my not doing the low speed adjustment correctly. I do have the manual, but I don't remember it saying to do it with the engine in water to have the exhaust backpressure, rather than on muffs (maybe they assumed that anyone using the manual would know that...but they didn't count on me )

I'll readjust my adjustments once I borrow the timing light. Thanks again!

 

[jay_merrill]

Re: '72 65HP intermittant stalling-- dirty carbs?

You're probably right about the manual not discussing the exhaust backpressure issue. The reason why, is simply that the primary audience for a factory service manual is made up of professional mechanics, who would already know this.

At any rate, you have to tune your motor with the amount of backpressure on the exhaust system that will exist in normal operation. Running a motor on the muffs allows to "breathe" much more easily, which affects a number of things, including idle ajustments to achieve a particular rpm.

Give the directions in the manual a try and see what happens.

 

[mike64]

Re: '72 65HP intermittant stalling-- dirty carbs?

At any rate, you have to tune your motor with the amount of backpressure on the exhaust system that will exist in normal operation. Running a motor on the muffs allows to "breathe" much more easily, which affects a number of things, including idle ajustments to achieve a particular rpm.

Would running the motor in a drum give the exhaust the proper backpressure and simulate running conditions well enough?

Eh, I don't have a 55 gallon drum anyway-- maybe I'll just pack my toolkit with me on my next trip to the lake and mix a little business with pleasure