Boat running bad!!!!... Won't hit full rpms!!!!...

[zildjian29]

OK here is the deal! The boat is a 1985 stingray 175ss with 3.0 140hp mercruiser. Outdrive is pre alpha. I haven't had it long! Took the boat out for the first time and every time I would throttle up it would die unless I slammed to full throttle then it would go but only about 20mph and would over rev super easy. So come to find out it had a 13 pitch prop on it. I put a 14 1/2x19pitch prop on it and it will only go about 30mph at 4000rpms. Sounds kinda sluggish! Still has the dead spot while accelerating. Half the time the rpm gauge doesn't work. I know the prop is correct now so something is holding the boat back. Tested compression and got 130,130,130, and 135 so that is good. I changed plugs and wires! The points look brand new! Can a carburetor cause my problems? What else should I look at. Please help(-:

 

[achris]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

OK here is the deal! The boat is a 1985 stingray 175ss with 3.0 140hp mercruiser. Outdrive is pre alpha.

It's not... read this -> http://forums.iboats.com/mercruiser...ve-needs-help-go-down-597987.html#post4160821

Serial numbers please. Engine serial number for engine problems, drive serial number for drive problems. If you're not sure, provide both...

I haven't had it long! Took the boat out for the first time and every time I would throttle up it would die unless I slammed to full throttle then it would go but only about 20mph and would over rev super easy. So come to find out it had a 13 pitch prop on it. I put a 14 1/2x19pitch prop on it and it will only go about 30mph at 4000rpms. Sounds kinda sluggish! Still has the dead spot while accelerating. Half the time the rpm gauge doesn't work. I know the prop is correct now so something is holding the boat back. Tested compression and got 130,130,130, and 135 so that is good. I changed plugs and wires! The points look brand new! Can a carburetor cause my problems? What else should I look at. Please help(-:

How do you know you have the correct prop? Has this engine/boat combination been running with that prop, and getting the right revs?

The 'correct' prop is the one that allows the engine to achieve the manufacturer's recommended maximum revs at wide open throttle. You also need to verify the engine speed with a calibrated tacho. The one in the dash is not accurate enough, especially since you're saying it's not working half the time... You need to find a prop that will allow the engine to achieve 4200-4600 rpm at WOT.... Unless this prop has in the past been running at the right revs, now you have to find out why it has lost those revs...

Chris......

 

[zildjian29]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

4443146 is the drive i think it has the preloaded pin on the tip of it believe the one before alpha had that. The engine # is 6920324. from the people i have talked to around here that have mercruisers with the 3.0 and about the same type of boat get about 45mph out of there boats. some use 19p some use 21p. I had a friend with almost the same boat 3.0 140hp 17.5ft boat thats what he used and it was great. couple guys on the water today with similar boats that is about what they said they get. I don't im at a loss.

 

[zildjian29]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

preloaded pin on the driveshaft is what i meant. i think the one before alpha had that.

 

[achris]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

The drive is from 1975, an earlier MC-1, the engine is a 1985. Since that drive is clearly not from that engine, which one was changed? Given that you said the boat is 1985, then someone has changed the drive at some stage in the past (NOW you see the importance of serial numbers?)..... The very first thing I would be doing is checking the drive ratio. The ratio with the 3 litre engine should be 1.98:1. Being a different drive you need to confirm that. If the ratio is different, then that would explain why you're not getting the revs you think you should with that boat/engine/prop combination....

Easiest way the determine ration (you're going to need the help of a friend who can count to 10).... Remove all the spark plugs. Put a paint mark on the propeller and put the engine in forward gear. Now have your friend watch the prop while you turn the engine. as you turn it, count the number of times it goes round to get the prop to go round 10 times. The number of times the engine turned (hopefully almost 20) divided by 10 is the drive ratio.... (No you can't just turn it once and look at it, the ratios are too close for that to be accurate)....

Chris......

 

[zildjian29]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

How do I turn the engine? Won't turn with key unless in neutral. So I imagine by hand?

 

[zildjian29]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

If the engine ratio is 1.98 and the drive is say 1.84 or 1.65 shouldn't I be able to off set it with the correct prop? But then am I losing speed?

 

[zildjian29]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

OK I did what you said and the engine turned 20 times and the prop 10 times! Now what should I look at next?

 

[zildjian29]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

I'm sry it was almost 20 like u said

 

[achris]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

Now we need to find out why you have lost engine power.

Have you checked the ignition timing, and the advance?

 

[zildjian29]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

No I haven't! It does run fine in neutral don't know if thats important or not. Can I check the timing and advance or does a pro have to?

 

[Howard Sterndrive]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

the points look new, but I would have a look at the advance weights and springs underneath the plate the points mount to - rusty springs, and gummed up sticking advance weights are a common issue.

you could also check fuel pressure at the inlet of the carb when running it under load in the lake... the fuel pump should deliver enough gas to maintain 4 to 7 psi there. weak fuel pump or anti-siphon valve issue could be the cause if flow insufficient

revving up in neutral doesn't mean much.. any motor will do that with half the pistons removed

 

[achris]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

Running in neutral is nothing like running under load. Fine for checking idle and timing, but that's about all...

If you have a timing light and a service manual, and a bit of nous... It's not too difficult...

Chris......

 

[achris]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

If the engine ratio is 1.98 and the drive is say 1.84 or 1.65 shouldn't I be able to off set it with the correct prop? But then am I losing speed?

Lower reduction + lower pitch prop will equal X mph.... High reduction + higher pitch prop will equal the same X mph.....

Like putting bigger tyres on your car, then driving in a lower gear...

Chris.....

 

[zildjian29]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

I will get a timing light and get ahold of you then! Thank you.

 

[zildjian29]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

The timing is at 12? at 2000rpms while just in regular idle you can't see the mark at all!

 

[zildjian29]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

If you could write down the timing procedure for me that would be great the manual is a little vague. Thank you

 

[Bondo]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

If you could write down the timing procedure for me that would be great the manual is a little vague. Thank you

Ayuh,... At Idle, point the light at the mark, 'n rotate the distributor til the marks line up, 'n tighten down the lock nut,...

 

[zildjian29]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

What should it be at? My marks are kinda hard to see! Think it reads 12 10 8 beffore then after and the same. Its very worn so hard to see! Right now it lines up with 12 at 2000rpms otherwise you can't see it. The thing that confused me the most is the jumper wire and interrupter switch. I don't see that. Anyways I'm sure I will get it.

 

[slothman]

Re: Boat running bad!!!!... Won't hit full rpms!!!!...

dead spots while accelerating is more than likely the carb, or a plugged up filter. A plugged jet or other orifice inside the carb can cause random bogging, especially on take off. if it hasn't been cleaned or rebuilt, it wouldn't hurt to do it .