Engine issue

[DP70]

Thank you to those whom helped me narrow down my selection on a potential new to me boat. It was very helpful as I’ve not owned a direct drive boat prior.

I test drove the boat (93 Sanger DX2) this evening. It has a newer engine in it - a Mercruiser 5.7L w/70 hrs.

The boat handled well & has been well maintained, but there was an issue with the engine.

I have no expectations that the issue will be solved from what limited info I have, I’m simply hopeful to narrow down where to look.

If it’s a simple issue with the engine that can be fixed easily, I’d rather not discard this boat as an option out of ignorance.

 

The boat didn’t have the pick-up / hole shot I expected - based on riding / driving other direct drives.

It ran really smooth through 3000 rpm - but above that there were issues.

The highest rpm I could get it to was 4000, but only briefly, then it fell off to 3800 or so. Everything I’ve read indicates WOT rpm should be 4400-4800 - typically 4500-400.

As soon as it was in the upper rpm range the engine got a lot louder - disproportionately. It sounded like it had a kind of rattle & minor squeal a bit & began to run pretty rough with a bit of a stutter / surge.

When I backed off the rpms it kept these symptoms until 3200 or so and then back to smooth at 3000.

 

I’ve been driving diesels for 25 years, my memory is pretty foggy regarding gasoline power plants. My instinct is to start at the carb? Possibly the fuel / air mixture is out of whack. Not clear on why the threshold at 3000 rpm.

 

I’d appreciate any suggestions that would help point me in the right direction.

The guy that owns the boat now has maintained it really well, but he’s not a skier and not someone who you’d expect to be a boat owner. I believe he inherited it from family. If I can figure out what the issue is, it may help favourably with the purchase price.

 

Thank-you in advance.

[LK_skier]

Possibly it has the wrong prop?? But I doubt it’s that simple… good luck

[BraceMaker]

What does it do in neutral when revved up?

 

Can be timing carb fuel supply propping stuff wrapped on prop.

 

Squeal can be a bad vacuum leak belts etc.

[EricE]

Agree with @bracemaker on potential causes, I would start with the carb, specifically looking at the secondary barrel and jets. May want to try and verify the secondary choke plate and linkage are not binding up and free to move with the engine off and the throttle wide open.

[EricE]

As for the lack of hole shot, could also be carb related if the accelerator pump in the carb is bad. In neutral, engine should react quickly and rev with throttle, not be sluggish to increase rpms. When the engine was replaced, was the carb replaced?

 

[Wish]

How long ago was it replaced? Who did the job? Sounds like it was not the owner? You could bring it back to the shop that did the work and have them look into the issues. Or hire a machanic to come to the boats location and trouble shoot. All answers lead to negotiation on price.

[ReallyGottaSki]

I concur, suggests of fuel supply issue.

 

Tank pickup, sometimes there is a conical screen in the dip tube/elbow union that clogs first.

then there is hose collapsing/deteriorated

water/fuel separator

 

We do not yet know if it is throttle body injected or carb?

 

Yes prop pitch needs to be verified. as well as timing.

 

Twiddling with idle mix wont correct this, its something more fundamental.

 

A bud on his 92 twiddled with the quadrabog for a good long many seasons before just getting the spreadbore Holley, and didn't regret it. but always go upstream first and correct fuel filtration before going into carb else do the carb twice.

[DW]

A sudden increase in exhaust noise can be a loss of water flow in water cooled exhaust systems. We’re you monitoring water temps and oil pressure on your test run? Another culprit based on your description could be ignition timing (advance) is off.

[DP70]

Thank-you all - very helpful. A bit more info.

Current owner has had the boat since 2014. Some water got trapped in the block over winter 2015 & cracked the block.

He replaced the block in 2016 - a number of the original peripheral parts were re-installed - including the original carb.

Boat has been stored indoors since then & winterizing process each year has been thorough.

Boat has not been serviced professionally since the new motor installed in 2016. Apparently it's only seen the water 1-2 times per year since the motor replacement so he didn't feel it was necessary.

 

Original carb

No service or tuning for 5 years

That's a solid recipe for having running issues

 

Sound like it could all be resolved with a service appt & worst case a new carb.

Any recommendations on a new carb? There was a vote above for the Holley Spreadbore over the Quadrajet.

[DW]

@DP70 - are you concluding that since the carb is original that is the problem? From your commentary, I would consider that a risky conclusion. More times than not problems result from the last item touched by human hands. You could be spot on but are you comfortable if that is not the root cause?

 

Don’t let the shiny object and first time buyer red mist cloud rational judgement. Your last post leads to many questions, there is a reason the boat didn’t get used just after a new short or long block was installed?

[jpwhit]

The opinion of my grandfather, who owned a garage his whole life and personally specialized in carbs, was that the Rochester Quadrajet was a much better carb than the Holley.

 

I've rebuilt both myself and I will say the Quadrajet is a much more complicated carb, so you better bring your A game if you're rebuilding one....

[Fastguy888]

I would try and ensure that the reason why the original block required replacing has been resolved; beyond that I would guess fuel and a lean condition at higher RPM's. A good place to start would be replacing all fuel filters, inline and water separator as well as ensuring you have good fuel. A little 5 year old fuel in the lines will surely gum up your filters and possibly the carb. New plugs wouldnt hurt either.

[Dano]

Does he have receipts for the engine replacement? If not who knows for sure what was installed? Providing the engine is the correct block with the correct heads, and the correct ignition system. It's likely something relatively simple, like fuel supply (carb), timing, or weak spark. Carb's can be troublesome especially if you have a vacuum leak at the base of the carb (most likely spot on a boat). If he's installed an automotive distributor rather than original equipment your timing will be all messed up since cars generally use vacuum advance, boats do not. faulty spark plugs or a weak ignition, can cause most of the issues you mention in your post. Because your problem seems to worsen at 3000rpm it seems to point towards a weak or failing ignition. Check the ignition components are the correct ones, check timing both at idle and insure it's advancing as it should, by 2500 RPM you should see roughly 28 degees of advance give or take. If that all passes then install new spark plugs. If no change your likely looking at a fuel issue.

 

[Rednucleus]

Ask the owner to make it right and call you when fixed for another test run. That motor should go 44-4600 rpm; it's supposed to be a new motor, it should run like one!

[MDB1056]

@jpwhit - would agree Qjet is a great carb, but disagree it's more complicated to rebuild. I did the one on my 92 GM 5.7 and found it surprisingly simple. Had not done one before. Took just a few hours, and I was going SLOW as a rookie . Would encourage anyone to tackle that needs to.

[UWSkier]

What octane gas is in the tank? :D