Pressure Drop All Cylinders?

[Jo Ross]

I asked this in a facebook forum and got some interesting answers but want your input:

Any ideas why all four cylinders would drop in pressure when tested cold? Previously had a solid 120 but now all cylinders read right around 60.
I brought the boat out of winter with great success but the other day on a long sail coming out of an inlet it started dying as the boat pitched with the waves. I suspected back pressure since the exhaust was plunged under the water with those waves. Had a few runs where the engine died with little indication of why. Dying when at idle was particularly repeatable. The next morning, the engine had a lot of difficulty starting. Cleaned off some very sooty spark plugs when it sounded like I had a misfire. Compression test of all cylinders and spark test sat but the pressure in all four was about 60psi.
Fuel level was almost full.
Eventually I got her running and got out of the marina confidently on flat water with throttle.
Thoughts?

[indigo]

Dirty Fuel

Pitching in big waves brings to mind stirring up muck lying in the bottom of your fuel tank. Take a look at your in line fuel filter and also drain the carb bowl and see what comes out. If there is a lot of foreign debris, a thorough carb cleaning is in order.

Tom

[Jo Ross]

Pitching in big waves brings to mind stirring up muck lying in the bottom of your fuel tank. Take a look at your in line fuel filter and also drain the carb bowl and see what comes out. If there is a lot of foreign debris, a thorough carb cleaning is in order.

Tom

Will do.
Is there a way to check the polishing filter?

[roadnsky]

What kind of fuel filtering do you have inline? (Tank to Carb)
What kind of fuel pump? (Manual or Electric)
Do you have a fuel pressure gauge by chance?
Agree it could easily be stirred up crud.
As Tom said a quick look at what comes out of the carb would help tell you.

Lastly, might be worth taking a look at your oil and see if it's milky or the level has gotten higher.

Is the engine running well now or still hard starting/running?

[Al Schober]

I take it you're talking about cylinder compression. Before you get excited, try it with a different gauge.

[Jo Ross]

What kind of fuel filtering do you have inline? (Tank to Carb)
What kind of fuel pump? (Manual or Electric)
Do you have a fuel pressure gauge by chance?
Agree it could easily be stirred up crud.
As Tom said a quick look at what comes out of the carb would help tell you.

Lastly, might be worth taking a look at your oil and see if it's milky or the level has gotten higher.

Is the engine running well now or still hard starting/running?

Ah sorry. Electric fuel pump, no fuel pressure gauge. I have the Racor fuel water separator and the in line polishing filter from Moyer.
I haven't been able to troubleshoot further because it's been hauled out and the marina isn't big on running the engine. I can disconnect the fuel pump and dry start to get the pressure at some point so I'll try and do the alternate pressure gauge.

[JOHN COOKSON]

Is there a way to check the polishing filter?

Yes, it would be great if the polishing filter stopped the (alleged) crud from entering the carb.
The only way to "check" the polishing filter if you don't have a fuel pressure gauge after it before the carb is to remove it.

ex TRUE GRIT

[Dave Neptune]

How did you conduct the 2 compression tests?

The test should be done first dry and then with some oil sprayed into the cylinder the wet test.

When conducting the tests the throttle and choke should be set at wide open, all plugs removed and the batteries topped off. Use the same gage and you are looking for how close the values are to each other from cylinder to cylinder.

Did you adjust the valves and double check for "crank position" to be sure you were on the heel of the cam?

Dave Neptune

[ArtJ]

I asked this in a facebook forum and got some interesting answers but want your input:

Any ideas why all four cylinders would drop in pressure when tested cold? Previously had a solid 120 but now all cylinders read right around 60.
I brought the boat out of winter with great success but the other day on a long sail coming out of an inlet it started dying as the boat pitched with the waves. I suspected back pressure since the exhaust was plunged under the water with those waves. Had a few runs where the engine died with little indication of why. Dying when at idle was particularly repeatable. The next morning, the engine had a lot of difficulty starting. Cleaned off some very sooty spark plugs when it sounded like I had a misfire. Compression test of all cylinders and spark test sat but the pressure in all four was about 60psi.
Fuel level was almost full.
Eventually I got her running and got out of the marina confidently on flat water with throttle.
Thoughts?

I have a Tartan 34 with side exhaust. The exhaust is often underwater and
presents little problem with back pressure. Of course it has the Tartan standpipe exhaust which prevents waves enterng the exhaust.

best Art

[Al Schober]

The standpipe with the side exhaust works so well on the T30 and T34 that I'm surprised other boats aren't converting to it.

[ndutton]

I have a Tartan 34 with side exhaust. The exhaust is often underwater and presents little problem with back pressure.

From a discussion 12 years ago:

https://www.moyermarineforum.com/forums/showpost.php?p=17517&postcount=8

[Jo Ross]

I think it's the head gasket

After a few more surveys I'm thinking it's a blown head gasket where there's opening between the cylinders. That would make sense for the common 60 psi pressure between the cylinders. If I remember right, I checked the pressure with a single spark plug removed at a time which would prevent it from going to zero. I'll try and verify that the next time I'm out there but I have a feeling it's going to be a long hard battle of getting that thing replaced.
Ugh...
Thoughts?

[joe_db]

I always do compression tests with all 4 plugs out.

[Jo Ross]

New Head Studs?

I just noticed Moyer's been sold out for a while. Any thoughts on buying replacements for the studs when I pull the head off?

[Jo Ross]

Alright, here she is.

So, I'm all good with the head. Came off no problems.

Going to start scraping off the old head and cleaning everything. The manual says wood chisel? Is that a good idea? Currently soaking in PB Blaster and I'm going to get a scraper.

Moyer Marine is out of head studs and I would like to replace them since the stud puller does a number on the threads.
Can someone either point me to a comparable source or give me the specifications to simply have them made?

Any other pointers welcome. Thanks, ya'll.