poor performance

[spetroff]

I have a 2003 3.0l Mercruiser Alpha One on a Silverline 1705, which is giving me nothing but grief. Over on the prop forum I describe my issues with not being able to get it above 3800 rpm with a 19" four blade aluminium prop. I took it in last weekend for a tune up and the performance is now worse than when I started. Assuming that the clowns who tuned it won't be able to help further, I'm looking for advice on where to look next, and most importantly what info I'm going to need up front. The boat 'lives' a couple hours away and I don't always get to it every weekend. It seems that there is only one engine at this vintage, a GM, so presumably the fact that I don't have a serial number handy won't matter. Right now the boat will barely get up on plane with one person in it and a half tank of gas. I did manage to pull my kids tubing last weekend, but it was pitiful. I think I can rule out the cap/rotor and plugs, since anyone can install these, even the people who did the work (that said, apparently the cap/rotor were fine, so they are not yet replaced). They also installed a carb kit, which is much more suspect, but the engine starts easily and runs well; it just has no power or high end rpm's. Apparently all 4 cylinders are at 175 PSI, so whatever is wrong must be fairly minor. I'm assuming that I will just change the fuel filter because it is easy and cheap to do. Haven't tested the fuel system, but I will try to follow the guide posted here. I'll try to get hold of a timing light to check that too (downloaded the service manual, so I should be able to look the spec up). I'm not really keen to mess around with the carb, since I've never tried before, but it could be a culprit. Not too sure how to look for vacuum leaks either. Any other likely culprits? Thanks

Shane

 

[wellcraft-classic210]

Re: poor performance

Have you seen the boat run better with that prop? If its running ok in general -- I am wondering if the prop is too much for your engine?

Carbs will usually give indications in the way of sputtering , stalling , black smoke etc.
If the timing is off by more than a small amount or you would notice symptoms other than just low power but It still a good idea to look.
I suppose partially clogged exhaust is a possiblity -- But I am not familiar with the specifics on your engine.

 

[bobhol]

Re: poor performance

I have a 3.0 with a 19 inch 3 blade prop that will hit 4500 rpm with me ,the dog and a half tank of gas ...I was thinking of a 4 blade but 17 inch to give me a better holeshot and keep my revs the same ...it is possible a 19 inch 4 blade is too much prop with a full load !! ....can you beg ,borrow or steal a 3 blade to compare ? regards,Bob

 

[spetroff]

Re: poor performance

The prop should be fine. The boat originally came with a 21" 3 blade, and I dropped it back for better holeshot. Before the 'tune up' it had more power; it wasn't great, but better than it is now. I don't really want to loose anything more off the top end than I already have with the 19". The 21" hit 42 mph and the 19" has brought that back to 37 mph. Those are speedo measurements, the gps measured 33.3mph on the 19". I didn't get a gps measurement on the 21", and I've now sold it. Taking another 5 mph off that would put me in the same speed category as our 9.9hp!
What I'm looking for now (besides a new mechanic) is advice on the engine tune. I want to at least get back to where I was.

 

[Bondo]

Re: poor performance

The prop should be fine. The boat originally came with a 21" 3 blade, and I dropped it back for better holeshot. Before the 'tune up' it had more power; it wasn't great, but better than it is now. I don't really want to loose anything more off the top end than I already have with the 19". The 21" hit 42 mph and the 19" has brought that back to 37 mph. Those are speedo measurements, the gps measured 33.3mph on the 19". I didn't get a gps measurement on the 21", and I've now sold it. Taking another 5 mph off that would put me in the same speed category as our 9.9hp!
What I'm looking for now (besides a new mechanic) is advice on the engine tune. I want to at least get back to where I was.

Ayuh,.... You answered yer own question,.... It ran Better, Before the tune up....

You don't do tune ups, so the Only answer is to find somebody else, who's actually capable of doin' a tune up,...

Properly....

 

[Failproof]

Re: poor performance

Sounds like what they did was not a tune up at all. They checked compression and rebuilt the carb. That is not a tune up! Get a real tune up, and a beter Technician, not just some part slinging joes.

 

[spetroff]

Re: poor performance

You don't do tune ups
Properly....

Says who?! No time like the present to learn! (That said, I think it is worth having the previous shop look at it again - provided I don't spend another dime on it)