4.3L WOT Help!!

[emmettfire45]

:huh:Hello all I have a 87 21' Searay Seville. I have the 4.3 with 175hp. It has trim tabs and a hydrofoil. At wot I only hit 3600 rpms and 31mph on gps. I know I am supposed to get 4400-4600 rpm. It has a 14x19p prop in good condition. It runs like a top idles great and gets up to speed well. But its not hitting the right rpm range. Please help I am praying it is not a motor issue.

PS I am going to replace plugs next time.

Thanks in advance

 

[wileecoyote]

How do you know what the rpm is? Are you sure the tach is correct if thats the only reading you are getting? I would make SURE what my RPM is before I check other things. Since you are not describing other issues like not planing, maybe thats your only issue.

 

[emmettfire45]

What can I do to check the tach? That is the only reading I am gettin. It gets up and planes out very nicely. Maybe 7-10 seconds ish. Plus the trim tabs help it seems. Is there A tool I can get to check the rpms other than the tach? Thanks

 

[wileecoyote]

What can I do to check the tach? That is the only reading I am gettin. It gets up and planes out very nicely. Maybe 7-10 seconds ish. Plus the trim tabs help it seems. Is there A tool I can get to check the rpms other than the tach? Thanks

Lots of DVOM's have plug wire inductive pickup which clips on the plug wire and is the best way to check the RPM's. It's generally how I set the idle speed. If you don't have one, maybe you can borrow one. You'll want to keep a steady RPM and check your tach reading. If your speed on GPS is the same as it was before I would think you have a tach issue. This is much cheaper than some of the other options. While you have it check idle speed, timing, etc. to be sure all is tuned properly. This is where I would start to look, it's the cheapest and if thats all it is the easiest to fix.

 

[SCORPIO]

What wiley said. Also, most timing lights have a tach feature and are simple inductive pickup, just clip onto plug #1. Tune up is a good idea. Is this your first year with the boat? Has it ever made 4400rpm or better? If this is your first year, you could be over propped, also once on plane, retract your tabs as they add drag and can slow you down or increase load on the engine. Are you trimming your drive out after getting on plane? That will also remove stress on the u-joints and decrease drag there by increasing rpm.

 

[emmettfire45]

Thank you for the advice. This is my first year with the boat. Never got over 3600. I will try retracting the tabs nextime I go out. I dont think I did last time. I did trim out the drive also I knew how to do that from a past boat but never had trim tabs. I am still pretty new to boating. With about 40hrs on the water in my life.

 

[SCORPIO]

Since this is your first year with the boat, check on the Sea Ray website for the recommended prop for your boat. If the prop doesn't match, it could be that somebody wanted a larger prop to get a quicker holeshot to pull up a skier etc.. Dropping two inches of pitch will increase your wot by about 400 rpm if I remember correctly. My '89 300 DA with twin 5.7s and Alphas is turning a pair of 14x19 aluminum props and I turn about 4400 rpm with them. Not that this matters, load, boat size, amount of fuel etc all affect wot and pitch requirements. Start with the prop specd by Sea Ray. If you have the specified prop and your tachis accurate, you may have more gear or the boat may have gained weight from water absorption and you may still be over propped. The engine could be a bit tired but don't sweat that till you have her tuned, and double check you tach and prop.

 

[SCORPIO]

Does your boat have a Merc engine and outdrive or an OMC outdrive? I'm looking at the '87 prop chart and the only 175hp I see listed are OMC drives. If it is an OMC, Sea Ray recommends a 15.5x15 prop. Thats a common OMC prop. It would also mean you are over propped. But we need to know what drive the boat has and its specific model to be sure. There is a 185hp Merc listed and it DOES spec a 14x19. We need to know what you have.