Need advice / suggestions before I call in the pros :-(

[KnotConnected]

1994 7.4L Merc BravoIII . Starts with some priming & coaxing when cold. Starts right up with a tad throttle when warm. Will run if i give it throttle at ~1,000 RPM, but if I back it down to 800 it runs rough, and if I back it down any below that it'll die quickly.

I just replaced all plugs with new AC Delco MR043T @ 0.035 gap, added 2x 16oz bottles of SeaFoam to about 80 gallons of gas (gas that was added last Fall before putting her into heated storage. No additives or stabilizers were added to the gas), and sprayed half a (large) bottle of carb cleaner through it. Now it seems to run smoother at ~850-1,000 RPM, but still dies below 800. ALSO, since doing this, it doesn't die instantly, but sputters and fires sporadically until it finally quits (I swear it was firing on 1 or 2 plugs for a good few seconds before it actually died) .

Didn't have this issue last fall, and i DID have it out once this spring for an hour or so, running well (up until the end, when it died out in idle twice, then I decided to bring her in)

any suggestions of what to check / do next before I call in the pros?!


thanks!

 

[Don S]

Re: Need advice / suggestions before I call in the pros :-(

When was the last time the fuel filters were checked and replaced (old one emptied to check for water)
Spraying carb cleaner does nothing, the inside of the carb having water or dirt in it may be the problem.
How about the cap and rotor, plug wires?
When was the last compression test done?
Are you sure all the plug wires are on the correct plugs?

 

[KnotConnected]

Re: Need advice / suggestions before I call in the pros :-(

Hey Don,

Fist of all, thanks for the quick reply. You've helped me and, as I've read, many others, many times. Your knowledge, advice, and willingness to help others is greatly appreciated!

*Don't know about the fuel filter, but if that was it, wouldn't it run poorly at higher RPMs (as it needs more fuel?). None the less, I can replace it anyway for good measure (won't hurt, I assume)

*Damn on the carb cleaner. My next step is going to be pulling it off and having someone rebuild. Even if it's not the root cause idk when it was last done and figured it wouldn't hurt.

*Don't know about the distributor either. Is there a teltale sign or test I can do, or is this something I should just replace for good measure too?

*I had a compression test done last august when I purchased the boat. I don't recall what the c ompression was, but it was consistent around all cylinders.
**EDIT: I just checked the survey documentation from when I purchased the boat. "All cylinders are within 5 psi at 130-135 dry. "

*I'm 99% sure the plug wires are correct. I didn't have any issues last fall, and did the plugs one-at-a-time to ensure the wires were consistent.

Worth Mentioning? I had an issue with the outdrive shifting into gear. They replaced the shift cable and the back plate on the upper. Also, I put a new rem'd lower unit on this spring before launch, as the old one was corroded. Not sure if anything done in the process would have effected the current issue? Both procedures were done by certified qualified mechanics.

I've included two links below to the engine starting / dieing from this afternoon.

VIDEO0004_zps5f99173e.mp4 Video by n915aa | Photobucket
VIDEO0005_zps71ae8b67.mp4 Video by n915aa | Photobucket

 

[KnotConnected]

Re: Need advice / suggestions before I call in the pros :-(

Update: Got it working!

Things done: *Checked timing (fine)
*Replaced Plugs. (Was using Autolite plugs, gapped anywhere between .030 and .045. Replaced with ACDelco M043T @ .035)
*Replcced Fuel Filter
*Added 48 ounces of seafoam to gas tank (~80 galons)
*Sprayed 1/2 bottle carb cleaner into carb

End resolution: Adjusted idle speed screw to hold RPMs at 800, which is where I was able to get the engine to run at with throttle. Then slowly backed idle speed screw down to 550 RPM with throttle in neutral position. With the throttle at Neutrual and the speed screw determining the baseline idle speed, the engine sat at 550 and is running no problem.

Hope this helps someone in the future! Thanks for the assistance everyone!

 

[brnschoneck]

Re: Need advice / suggestions before I call in the pros :-(

ayou still may wanna do carbs soon ??? maybe this winter if u get through the summer ..Id make sure you put some kind of stabalizer in fuel for winter,especially with the ethanol gas !!!

 

[KnotConnected]

Re: Need advice / suggestions before I call in the pros :-(

Yeup, I'll have the carb pulled and rebuilt this winter. The fuel dock has primum gas with no ethenol (or so they tell me), but what do you add for winter? Just Sta-bil?

Also, if I pull the carb off and have a shop rebuild it, what will I need to tune when I re-install it? Just idle speed and mixture?