89 merc 100 4500rpms @full throttle

[joeb]

I HAVE A 17' SEA RAY SKI BOAT WITH A 100 HP MERC(89). THE BOAT HAS A 21 PICH PROP . I JUST HAD THE CARBS REBIULT AND MOTOR DOESN'T RUN OVER 4500 RPMS. I TOOK THIS MOTOR IN THE SHOP BECAUSE IT TOOK A LONG TIME TO PLAIN. BOAT NEVER RAN MORE THEN 4500RPMS EVEN WITH SMALLER PROP. SHOULD THIS MOTOR RUN MORE RPMS THEN THIS. MOTOR HAS GREAT COMPRESSION ACCORDING TO SEA RAY. MOTOR NOW DOES NOT WANT TO IDLE AFTER ABOUT 5 SECONDS WHAT MIGHT MY PROBLEM BE. HELP PLEASE.

 

[MURX]

Re: 89 merc 100 4500rpms @full throttle

I had an 18' center console with a 89 100 2+2 merc I'm pretty sure I was turning a 13.5 X 17 prop it came with a 13.5 X 15 I feel that you're way over pitched, that little motor is stugling to turn that much prop IMHO 17 is ideal 19 is pushing it 21 out the question

 

[ODDD1]

Re: 89 merc 100 4500rpms @full throttle

Murx is right.. if you came to me with the boat and nothing on the propshaft, my first guess would be a 17pitch....

 

[hondon]

Re: 89 merc 100 4500rpms @full throttle

I would agree that you are well overproped at a 21 ,but you state that things were no better propped not quite as tall. When that dealer did the comp. check ,did they also do a timing and sync observation?

 

[joeb]

Re: 89 merc 100 4500rpms @full throttle

hey guys thanks the input. the dealer went threw the motor $1754.00 worth. the boat had a 19 pich prop., sea ray told me that the 21 pich is what should be on this boat. I also live in south carolina about 50 miles from ashville north carolina does this change things? boat comes out of the water good but then again i'm not pulling any skiers or anthing . i'll check on another prop. thanks

 

[joeb1300]

Re: 89 merc 100 4500rpms @full throttle

Hey guys 7 years later and motor still runs but sucks. I believe that chrysler, force made a better motor then these. Why did they make suck a crappy motor ?(2 +2) I'm down to a 16 pitch prop and turning 4900 rpms. boat will not plain out with more then one person in boat. How can i get rid of this "2+2 "?If i put new plugs in boat runs better. Then go to putting around plugs foul . Back to struggling. Help..

 

[jsturkie]

Re: 89 merc 100 4500rpms @full throttle

Hey guys 7 years later and motor still runs but sucks. I believe that chrysler, force made a better motor then these. Why did they make suck a crappy motor ?(2 +2) I'm down to a 16 pitch prop and turning 4900 rpms. boat will not plain out with more then one person in boat. How can i get rid of this "2+2 "?If i put new plugs in boat runs better. Then go to putting around plugs foul . Back to struggling. Help..

This isn't a bad motor. It sounds like the bottom 2 cylinders are not firing/kicking in @ 1800 due to fuel mix. Get a manual. Do a compression check. link and sync the carbs. Adjust the accerator pump clearance. It would be a good idea to rebuild all carbs with new gaskets but atleast remove the bowl plug/main jet cover and catch the gas in a glass. Look for junk. Set fuel mix per manual, I think its 1.5 turns out from seated. The bottom two carbs don't have fuel mix screws. Check/replace main inline fuel filter on right side of motor. Check/replace small inline filter behind the oil tank. I had to remove my tank for this but you may get lucky. Run a remote tank with a can of Sea foam threw it. Change all plugs. The 2 + 2 is a funny animal.

I have A '95 125 on a very heavy 18' SeaRay w/20p SS prop. Sometimes it is quick out of the hole and other times it drags a bit then shoots off. All cylinders must be getting fuel at WOT or you will be rebuilding it soon unless it dropped a cylinder already. I can only tell you what I have done and my motor is running much better. Good luck.

 

[joeb1300]

Re: 89 merc 100 4500rpms @full throttle

Thanks js, I have had a guy just change fuel pump and accelerator pump. I think the filters too. I will call him and ask. The primer bulb doesn't stay hard. Come to think never changed bulb, maybe this could be my problem. The compression is good. I have a manual and it is set to spec. The only thing i could think if it's a fuel issue is a added a filter on the gas line before the motor. Sea foam how do I use that?

 

[verado7]

Re: 89 merc 100 4500rpms @full throttle

change the bulb anyway it's shot.

 

[joeb1300]

Re: 89 merc 100 4500rpms @full throttle

Hey guys changed the primer bulb. After two minutes boat ran out off gas due to new primer bulb flat like a pancake . Yes the flow arrow was correct what is this all about?

 

[CharlieB]

Re: 89 merc 100 4500rpms @full throttle

Sounds like you have a couple of different problems.

First, a flat primer bulb is often caused by a restriction in the fuel line in the fuel tank dip tube or check valve in the fitting on the tank, clean them both. Not reaching full RPM could also have been caused by this and you may be fortunate NOT to have fried the engine by running lean at WOT.

Second, sickening and dying after idling a while plus blackened spark plugs are a sign that one or more carbs may be flooding OR the enrichener valve is leaking additional fuel into the engine.

Remove the air inlet cover from the carbs AND remove one of the enrichener fuel lines from the intake. Make sure the engine is trimmed to level.

Pump the primer bulb and look for any fuel leaking either into the carb throats or from the enrichener. Repair any fuel leak.