Loud "clicking" at higher RPMs

[kevin d]

Hey All,

Last year I swapped out my old Atomic 4 for a rebuilt one. I got it from a reputable mechanic in Northern California....

I'm fairly familiar with these engines (have done a lot of tinkering and I taking on most repairs with help from Moyer Marine and the internet over the past 10 years)...I was hoping to get some feedback about my current symptoms before going down the rabbit hole of running thru every possibility I find on Google.

Currently, she starts like a champ every time (requires little choke), the idle RPM adjust is set to standard, the plugs/wires/coil are like new, the electronic ignition is fairly new, the timing (not 100% sure...I set it for the first time) is good, gas is fresh, carb is new, exhaust and raw water seem normal.

Well...when I run her at higher RPMs (i.e. wind dies and we motor a few miles back to our marina), she'll at some point sputter, lose power and a LOUD clacking (electrical spark sounding) noise then will almost die and then I need to back her down to a low RPM and she is fine again. But I feel like she's limping a little. This is hard to replicate because it seems to only happen after awhile under load at higher RPMs.

The most suspect aspect of the boat is the DC wiring. Before I rewire the DC circuit, I'd like to have a really good reason as this seems very time consuming.

Any thoughts?

Thanks in advance...

[hanleyclifford]

Mixture may be getting lean after hard running. Look at fuel tank vent for possible blockage. Check fuel pressure at carb while at cruise rpm. I have had similar experience. Also, pcv can lean out mixture at high rpm.

[Marian Claire]

Do you have an electric fuel pump? Dan S/V Marian Claire

[jbsoukup]

ignition coil?

[kevin d]

Mixture may be getting lean after hard running. Look at fuel tank vent for possible blockage. Check fuel pressure at carb while at cruise rpm. I have had similar experience. Also, pcv can lean out mixture at high rpm.

Looks like I'm about to learn some new stuff...I've never checked my fuel tank vent. Is it as easy as a visual or is there something else to consider?

How does one normally check the fuel pressure at carb while at cruise rpm?

Also, can you expand on "pcv can lean out mixture at high rpm"? I have no experience with the pcv.

thanks!

[kevin d]

Do you have an electric fuel pump? Dan S/V Marian Claire

nope, the original pump.

[kevin d]

ignition coil?

the ignition coil is about a year old.

the issue would seem to be electrical. there is a loud misfiring racket when it happens. sound like throwing some screws into a fan..then it loses power until i power down and then it runs fine at low RPMs.

[Marian Claire]

Good deal. That eliminates the electric pump stuck ball "clacking" noise possibility. Another long shot but it ties in with the lean condition Hanley mentions. http://www.moyermarine.com//forums/s...ead.php?t=3369 So maybe try closing the choke some when it starts to stall. If that does not help at what RPM does this happen? Advance weights sticking?
Dan S/V Marian Claire

[hanleyclifford]

Fuel pressure can be monitored right at the carb using one of these. http://www.mcmaster.com/#atmospheric...gauges/=lfs4fa This can save a lot of diagnostic grief in the long run.

[Sony2000]

It sounds like fuel starvation, brought about by vapor lock, or a restriction to the flow, prior to the fuel/water separator.

[ndutton]

Reading the description my first thought was as Dan mentioned at the end of his post, faulty timing advance mechanism:

• It's affected by RPM.
• Malfunction affects performance.
• Depending on the nature of the malfunction, it could be the source of the noise.
• Mix them all together and it fits the symptoms.

[JOHN COOKSON]

It Could Be This

Electricity jumping between the spark plug wires. After the engine is run for a while the insulation could be breaking down and electricity is jumping between plug wires and a plug(s) are firing at the wrong time which results in a knock or a hellish engine sound.
Are you running graphite core or solid core wires? In my experience graphite core spark plug wires aren't worth a crap on a boat.
Also have you checked for tracking or arcing between the terminals inside the distributor cap?

TRUE GRIT

Edit: Kevin: When I read about arcing, sparking, and "loud clacking, electrical spark sounding", as reported in your post #1, I think of something after the coil not the 12 volt circut.

[edwardc]

My first two thoughts were :

- Sticking valve
- Distributor advance weights

[tartansailboat]

fuel pressure gauge

Hanley, there are so many pressure gauges listed in the McMaster link, could you be more specific and tell me which one you used? Also, is this gauge plumbed into the fuel line with a tee as would be for a gas pressure gauge? Or in line, like a flow meter gauge? Did you mount your gauge on the output of the fuel pump, or on the input to the carb or in the middle of the fuel line (rubber or copper line)?

Thanks, Herb

[kevin d]

Electricity jumping between the spark plug wires. After the engine is run for a while the insulation could be breaking down and electricity is jumping between plug wires and a plug(s) are firing at the wrong time which results in a knock or a hellish engine sound.
Are you running graphite core or solid core wires? In my experience graphite core spark plug wires aren't worth a crap on a boat.
Also have you checked for tracking or arcing between the terminals inside the distributor cap?

TRUE GRIT

Edit: Kevin: When I read about arcing, sparking, and "loud clacking, electrical spark sounding", as reported in your post #1, I think of something after the coil not the 12 volt circut.

Thanks....I've got a spare coil/set of wires. I'll swap them out and take a look at the distributor cap (and timing) and see if the problem goes away.