Merc 4.3 6cyl RPM's jumping? not started 2 years

[dolemite_1]

Hello guys,

Thx for your help so far. I am looking at buying a '93' boat from friends father that has not been started for 2 years. He's original owner and boat engine was running fine beforehand. Recently just changed oil in engine, alpha1 outdrive, and drained all the gas from the tank. filled it back up with 5 gallons of 87 octane and ran it today. The rpm's were jumping with a range of about 300-400 throughout the entire rpm range through 3000.

The plugs have not been changed in a few years, wires never, distributor cap, air filter needs replacing and water fuel seperator as well. I also don't know condition of carburator.

I like the boat and want to buy it since he is giving it to me for a good price but don't want to start changing plugs, wires, cap, filters and find out the engine or something major is shot. My sense says problem with fuel delivery or air fuel mixture ratio.

What should I do first? My knowledge of car engines is ok but not knowledgeable with boats (first boat)

Thank You

 

[Don S]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

Tune it up and do a compression test. Just like what was suggested in your previous question.
http://forums.iboats.com/showthread.php?t=247840
You no doubt need the OEM Mercruiser manual since you are unfamiliar with boats.

 

[dolemite_1]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

Thanks don for the quick reply. I actually downloaded that 1 gig file of the "service manual 1." Unfortunately due to work I am not in the same state as the boat right now and will have a limited window of opportunity to check things out when I get back. Do you have any suggestions on the order of things to change or check with the tune up first.... being in line with the problems? Although I plan on performing all of them as I go, time is my biggest restraint right now.

I don't have a compression guage so will have to buy that, but my first thought is a gunked up carb since the boat ran smoothe before hibernating. Maybe some carb cleaner? The boat also seems to have spats of running a little less jumpy at times as well. What do ya think?

Thanks

 

[Bondo]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

but my first thought is a gunked up carb since the boat ran smoothe before hibernating. Maybe some carb cleaner?

Ayuh,...... I tend to Agree,...

But,....
Spray Carb Cleaner is NO Substitute for a Carb Rebuild Kit..........

 

[dolemite_1]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

Will the carb cleaner spray help me narrow down the problem--- letting me know I need to rebuild or replace. Or do the gunked up places tend to be to hard to get to with spray?

thx

 

[bomar76]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

as you have already been told, the aerosol cleaner will do NOTHING for you

 

[dolemite_1]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

Did I say soemthing to annoy you? Bond-o said it is not a substitute for a rebuild, it may still help me narrow down my problem; if it even lies with the carb. Or maybe other suggestion that would lead me to conclude that I need to change the carb.
I'm still in an investigating stage and trying to figure out whats best to try first.

 

[ziggy]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

service manual #1 don't cover your 93 4.3 engine. sorry i don't know which one ya need, but that ain't it.
you've answered your own question in yer first post.

The plugs have not been changed in a few years, wires never, distributor cap, air filter needs replacing and water fuel separator as well. I also don't know condition of carburetor.

i don't see how ya can auto assume that it's the carb. w/o doing a minor tuneup on it so ya know the spark part of the equation is right on. you will need the compression tester too. that'll tell ya the if basically the engine is sound. I'd do that first after priming it too (from the other thread). no point in tune up parts if it has bad compression. then the tune up parts. as for the carb cleaner. spraying it around in the carb from the outside just cleans off the outside. granted, the outside is what makes the air flow, (venturi) that's about it. everything else is from the inside. all the little air passages that work off pressure difference that could be plugged up from the bum fuel that sat in it, that's where the carb. cleaning and rebuild come in. cleaning the outside really aint gonna do much for it. can't remember if it was mentioned in the other thread. but fuel filters would be a good idea to check out too... simple check prior to assuming carb. or fuel delivery issues....

 

[Limited-Time]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

The cost of a compression gage coupled with a complete tune up is a small price to pay (cheep insurance) to rule out any major issues.

 

[Coors]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

Did I say soemthing to annoy you? Bond-o said it is not a substitute for a rebuild, it may still help me narrow down my problem; if it even lies with the carb. Or maybe other suggestion that would lead me to conclude that I need to change the carb.
I'm still in an investigating stage and trying to figure out whats best to try first.

The spray only cleans the outside of the carb, which has nothing to do with operation.

 

[dolemite_1]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

Guys Thx for all the help so far, it's been great.

So I have changed the plugs, wires, dist cap and rotor and the engine is idling a lot better but still a bit high around 1000rpm's.

Still need to change water/fuel seperator, carb filter( couldn't seem to find it tonight- thought was in-line heading into carburater). clean air filter (Water?)

New things to fix:
Blower light comes on but not blower( critical I know)
Trim guage not working
Outdrive only comes up,with trailer switch
Back Light doesn't come on with post insertion
Belt - pully noise (consistent chirp-- not squeel)


Fun stuff to figure out:

Two wires with no connections 1 purpleish i think behind carb -- other teal I think behind and starboard to carb.

Another black (ground looking wire) portside to carb.

Clip with no wire coming off of it sitting on what seems to be a ground of something.


Any suggestions are greatly appreciated. Will also be working on getting a manual

Thx

 

[watermellonI]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

Hi dolemite
your idle will seem a little high on muffs, when ya get in the water it tends to drop a little.

the air filter on a boat is metal, it is also a flame arrestor in case the boat backfires thru the carb, take it off and let it soak in soapy water and blow it out real good with compressed air check to make sure the vents aren t damaged and make sure its nice and dry before ya put it back on


the purple wire sounds like it could go the automatic choke, you really need a manual to be sure it ll have a wiring diagram in it if you get the proper one, its well worth the money.

You need to be very careful going without a manual it can get real expensive
real quick if you make a mistake.

Tilt and Trim problem sounds like your trim limit /sender on the outdrive plenty of posts on that here. PIA to fix.

Go slow and take one problem at a time.

 

[dolemite_1]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

Thx. I downloaded one of the manuals from the links here but think it is the wrong one (1Gig).

Got the boat in the water, unfortunately still idling at 1000 rpm, might try finding the idle adjustment screws. When I'm searching for the spot for the carb inline filter.

Thx

 

[ziggy]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

ya really need to get the right service manual for yer boat....

pick and choose yer poison here......http://forums.iboats.com/showthread.php?t=251571
dons was even nice enough to put what is covered up so we can see which one to get..... very nice....
for yer elec. gremlins. have ya gone thru every connection ya can find, disconnected it, cleaned the terminals shiny and reinstalled? especially the grounds..... for yer multiple failures, ya might see if some of these failures are on the same circuit.... a wiring dia. might help there... it's in the proper sever ice manual for yer of engine and drive... or this might help too. it's a sticky from the electric, electronics forum....http://forums.iboats.com/showthread.php?t=186986


after ya get the service manual ya think is correct. ya can double check yer s/n against the service manual application guide at the very beginning of the book and see that the manual ya got covers, what ya got....

 

[Don S]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

You are going to need a SN to determine exactly which engine you have. 93 was a changeover year for the 4.3 with Mercruser. Some had the balance shaft (would take manual 18) and some didn't (takes manual #7).
Downloading the wrong one only confuses things.

 

[ziggy]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

and some didn't (takes manual #7).

, that'd be a bummer. if that turns out to be yer case, ya still need the right one. spend the hundie if thats what it takes.... or there's ebay too (got me some service manuals there myself), and get the proper one....

 

[dolemite_1]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

Thx for the help, am going to get the serial number now. I checked mercurys website but didnt see a place to look numbers up. Any suggestions?

thx

 

[ziggy]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

Any suggestions?

post yer s/n here. someone might know.... or dons put the general application next to the manuals available. ya could download the one ya think ya need and look at the beginning of the book and see if yers is covered. only 1 and 2 are huge files. the others are smaller files and faster downloads......

 

[Don S]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

only 1 and 2 are huge files. the others are smaller files and faster downloads......

Haven't downloaded #3 yet have you ziggy

As I said earlier, he needs to post his SN to find out which manual he actually needs.

 

[ziggy]

Re: Merc 4.3 6cyl RPM's jumping? not started 2 years

Haven't downloaded #3 yet have you ziggy

i stand corrected......... again....... 1.36gb......