Hole in Upper exhaust boot MCM260 drowning the motor?

[maxum_man]

Been a while for me as I have been without a boat for a few years (bought a dang camper). Anyhow, I bought a 1981 Wellcraft 255 Suncruiser with a MCM 260 5.7 (sn 5953535). I have replaced all the normal tune up parts, and even went as far as replacing carb with reman Qjet from a place in Florida I have used before with great success. Replaced anti siphon valve as well and cleaned p/u tube. Fuel is a little old and not shiny clean like it should be, but after all this that I have done, i took it out to run it. I eased the throttle up and she almost got on plane, but kinda stumbled, ran real rough (not a missing feel, but rather a “choked out” feel) and died when I went to neutral. Opened the “hood” and water was all over the top of the engine. After further review, i found that the port side upper exhaust boot (between elbow and y pipe I’m assuming) has a small crack in it and it is pointed right directly toward carb and dizzy. Now...dizzy cap is new with fresh gasket under it but not ruling it out. But does it sound like to yous guys that she was spraying like a sprinkler head under the hood when I throttled up and just drowned the motor through the carb??

Reason I did the tune up was due to the stumbling/rough running problem. After test drive, acted the same. Swapped carb and did the anti siphon valve swap and cleaned the tube...then the water spraying issue started.

 

[Rick Stephens]

So, you gotta replace the rubbers. Until you do that any other guesses are just that. Replace the rubber, dry everything and test away. If you want to test before the rubber gets there, tape it up and work on it in the driveway with muffs attached. The lower back pressure probably keep most of the water out.

 

[maxum_man]

No trailer my friend! Stays on the marina unfortunately in this case. The water spraying didn’t happen until I got everything else freshened up so I fully believe it split on the last test drive. Fingers crossed anyways. Got new boots today to swap in the AM. Will post results.

 

[Rick Stephens]

Better you than I. Wrenching in the water is not always much fun. Never bring all the tools the first time. Best of luck.

Rick

I'd rather be wenching.

 

[maxum_man]

Does the riser have to come off or can I wiggle the old one out and new one in there?

 

[Rick Stephens]

I would think you need to pull the riser. Get gaskets for riser to manifold - only use the proper OEM ones with the metal. The after market paper ones fail.

 

[GA_Boater]

While the rubber tube is off, check the shutters on top of the Y pipe. An overheat in the past may have melted the shutters and weakened the tube.

I hope you are doing both sides.

 

[maxum_man]

Ok...so I hope I won’t get kicked out of Fight Club for this one, but I pulled the riser and got the old boot off pretty easily. As easy as it is for a 6’3” 230lb dude to sit on a battery and cram himself into the engine compartment! Anyhow, I had a tube of hi temp RTV that I used between riser and manifold when I put it back together. After reading the comment about using only OEM gaskets, I am ordering 2 new gaskets from my local dealer and gonna pull er back off. It was a pretty easy job though. I ran it for about a minute or so after ward to make sure the boot wasn’t leaking but didn’t test drive. I’ll post back when I do it right! . Thanks thus far guys.

 

[Rick Stephens]

The issue with failing that gasket is hydrolocking your motor when water gets into the exhaust. Can get mighty spendy.

 

[chs marine service]

yeah. i second that comment from rick. gasket sealer is not the way to do it. if you don't have the gaskets, let it sit until you do, that anxiousness can cost you bigly

 

[maxum_man]

Any idea on a part number for the gaskets for a 1981 mcm 260 riser? I have looked at the manual I have without any luck. I also noticed there is a one piece metal gasket that replaces the plate and 2 gaskets. Worth getting or do the 3 piece set?

 

[Rick Stephens]

I’m guessing on Model, but you might look here for part numbers.

 

[maxum_man]

Thanks for that link. Mine’s an ‘81 model and apparently a different manifold and riser. I’ll look on that site though for the proper one.

 

[maxum_man]

Ok...So I got the gaskets from the local marine shop and replaced the upper rubber boot and put the correct gasket on there. Still running terrible. Here's what I have done so far:
-New anti siphon valve and P/U tube cleaned out
-new fuel filter
-new plugs
-new dizzy cap
-new (reman) q-jet from Guaranteed Carbs in Florida
-base timing is at 8* and will advance in neutral when throttled up. Have not put the timing "tape" on the balancer to see where its at in relation to the timing chart, but I don't think this is the issue.
-new coil from same marine shop
-has mallory distributor with electronic magnetic unit inside in place of the old breaker plate. According to previous owner, that was put in 9 or 10 years ago.

Here's where I'm thinking at now...when I wrap my hand around the distributor, touching the wires as well where they connect to the cap, I get a slight shock in my fingertip that is touching the hold down clamp for the cap. I have no clue how old the wires are, but they do not appear to be dry rotted on the outside but there's no telling what they are on the inside. Not sure how old they are either. Think a old/bad set of wires would keep it from idling properly and falling on its face when throttled up in gear but rev just fine in neutral?

Also, I haven't checked fuel pressure or compression yet. plan to do it next trip.