1995 Carver 355 Vacuum in Crankcase

[Triwing]

Hello, new Carver owner. Just bought a 95 355 aft cabin. Starboard engine want running after previous owner did a "tune up". Found firing order wrong. Fixed that, now it starts and runs, but not very well. Found huge vacuum draw on breather tubes going to the flame arrestor. Lots of smoke coming from exhaust. I seem to have a huge vacuum leak into the crankcase. Suspeting the intake. Any other suggestions?

[tomschauer]

I believe I would start with a compression test on all cylinders.

[Viper]

Welcome aboard. A little vacuum can be normal, especially at idle. Excessive vacuum can be due to a few things. You may have an intake gasket failure, excessive oil in the combustion chamber which would also explain the smoke in the exhaust, and if your application utilizes a PVC valve, it may not be working properly or is the wrong one for the application.

A compression test is a good idea but you should also consider doing a vacuum test, it'll tell you a lot about what's going on if you know how to read it.

[Triwing]

Thanks for the quick replies. What exactly is a vacuum test. Vacuum gauge on the throttle body? Manifold? What should I be looking for?

[Viper]

Vacuum gauge on the manifold is best. I'm sure by now there's a lot of YouTube videos on how to interpret the readings.

[bud37]

Source of the post Hello, new Carver owner. Just bought a 95 355 aft cabin. Starboard engine want running after previous owner did a "tune up". Found firing order wrong. Fixed that, now it starts and runs, but not very well. Found huge vacuum draw on breather tubes going to the flame arrestor. Lots of smoke coming from exhaust. I seem to have a huge vacuum leak into the crankcase. Suspeting the intake. Any other suggestions?

Considering this is a new boat to you. ...Any tune up or basic engine troubleshoot should start with the very least a proper compression test to make sure the engine is mechanically sound, the cadillac of tests is a leak down, that will require good gages and an air supply with someone that knows how to set the engine for a correct test, but that test will reveal lots more info if done right.
Remember you can't tune a bad engine no matter what. Once the compression is tested and verified ok, you can move on to the possible pcv / vacuum leak/ tuning issue.....imo.

Welcome to the forum..

[Viper]

Gotta disagree with ya on that one bud. I'd consider a vacuum test way better (Cadillac) than a leak down. It'll tell you way more about how the engine is operating than a leak down will as you perform the test with the engine running. It'll actually point you to the problem as the runability issue will be evident while the engine is running more than it will static. Unfortunately it's not used as often as it should be, guys just get too used to just swapping parts instead. Don't get me wrong, a leak down has it's place but really I only go there if there's a red flag in a compression test reading and I want to determine how bad the leak is and where it is.

[bud37]

In this case he has no history on the engine other that the previous owner tried to tune it....it still runs badly. There is no telling what the reason for the tune up was but, the firing order was wrong ( starboard side ), and the engine is smoking ??
Like Tom alluded to the First test in any tune up is a proper compression test, that will give the basic health of the engine. Now like I said and you did, a leak down done on a bad or marginal cylinder by someone that knows what they are doing can show ring condition, valve condition, gaskets, and leakage into the cooling side.
Like I said, this test has to be done right, my guess this is why a lot of guys don't use it. Fairly comprehensive for a static test. Once that passes then you will know whether you have a good base for tuning or not. All of these tests go hand in hand and have a specific order in my experience.
Vacuum gage testing is ok for tuning lean best idle and getting some ideas, but you need to have experience to interpret the findings properly ( or there will be guessing) after all the static testing is done properly .Myself I have always liked to go forward from a base engine I know is good. Methinks we may be a bit off here.

It could simply be a bad or missing PCV valve, who knows as there are many things to cross off the list.

[km1125]

Whether you're doing a compression test, a leakdown test or using a vacuum gage, most only give cursory data unless you're doing them right and know how to interpret the info. Using a vacuum gage correctly is being able to interpret the movement of the needle as much (or more) than just getting an accurate reading. It's the difference between just getting a spark on a sparkplug or actually seeing/measuring the voltage and seeing the voltage on a scope which tells you infinitely more than just whether or not the spark is working and if everything in that circuit is functioning correctly.

A lot more needs to be known about the OP's engine before you could really start troubleshooting the problem. Knowing the firing order was wrong after a "tuneup" would really make me question everything that was done in the "tuneup" and I'd have to start from scratch. I'd use whatever tools I'd have available to give me data and all the above would contribute some amount of knowledge or confidence in what I was starting with.

[Triwing]

Thanks for all the help. I will pull the plugs and do a compression test. it will be a couple of weeks before I can do that. I am still open to other suggestions. Again, thanks for the help.