1998 200hp Ocean Runner Questions

[Richman]

Hey Folks,

I have been wrestling with an RPM issue for months (years). I had been able to only get about 4300 rpms's at WOT on a 23 ft. Sea Fox walkaround with the stock 14.5X19 aluminum prop. I went to a 15X17 prop and only gained about 200-400 rpm's but lost top end so I went back. I raised the engine so the Cavitation Plate was just skimming the surface on plane and got it up to 4600 rpm's and am doing about 39mph on GPS, an improvement Some of you long ago suggested compression and spark so with the warm weather in the east this weekend and the boys away at merit badge camp here's my next set of questions.......

Each plug was firing, there was a notcieable drop in rpm's when each plug was pulled although some pulled plugs dropped rpm's more than others. But spark was audible and visible on all plugs.

I ran a compression test first by warming the engine fully, pulling all plug wires and turning the engine with the starter. Readings were taken after the needle stopped moving upward. Results were all 82 to 88 lbs. Seemed low but all within 10%. So then I decided to run the compression test while the engine was running. The results were 125 to 128 lbs.

I guess my questions are....is it normal for there to be such a difference between the first method and second? Are the initial readings in the 80's OK for this engine?

And finally what else can I do to get my rpm's up? The hull is clean and unpainted, I have spark, even compression, I assume fuel delivery is OK, the bulb does not get compressed at WOT. It purrs like a kitten, gets decent fuel mileage (how the heck would I know, I've never owner a fuel injected or 4-stroke) and never fails to start. The tach is set to "6" and seems to read correctly at idle, there's no water in the bilge, the boat is all glass so there's no saturated wood. I only weigh 170 lbs...... I am out of thoughts. What else can I look for? Is it time to replace the cheapo tach that Sea Fox (Sea Era) put in these boats? Any help appreciated?

Richman

 

[Dhadley]

Re: 1998 200hp Ocean Runner Questions

We'll assume the linkage and timing is all set correctly and all 6 carb butterflies are opening correctly. I would check the tach with a known good one. You're at about 13% slip so the tach may be OK. Most dealers have a shop tach they can hook up and run the boat.

It seems the hull responded to the pitch and X dimension change. If you can still use all / most the trim range without venting you might try going a little higher.

I'd check the tach first though. It may be off on the high end.

 

[Richman]

Re: 1998 200hp Ocean Runner Questions

Thank you Dhadley,

Yes, the linkage opens the butterflys all the way, I forgot to tell you that. I will have a mechanic with a good tach check mine out. Any idea if my compression readings are good/bad/ugly?

Richman

 

[Dhadley]

Re: 1998 200hp Ocean Runner Questions

Normally we see them a tad higher but that can be your gauge vs. ours. It can't hurt to do a decarb. Especially if the motor really is less than 5000.

Do you know what the timing is? What spark plugs are you using?

And 87 octane, right?

 

[Dhadley]

Re: 1998 200hp Ocean Runner Questions

Been thinking about this and when you get the tech to verify the tach have him put the test prop on and see if the motor comes up to full rpm (the service manual will tell what # wheel and what rpm it should come up to). That's a good way to seperate motor issues from boat issues.

 

[jonesg]

Re: 1998 200hp Ocean Runner Questions

My compression is the same as yours and I get at least 5K rpm.

You said you checked the spark, did you use a proper gap tester?
using one of the spark plugs is not a test as you need to set the gap to around 1/2" ....... not the typical spark plug gap.

If you don't have a gap tester get one for $10 , the adjustable type, from any auto store.

 

[Richman]

Re: 1998 200hp Ocean Runner Questions

Thanks for getting back to me. I replaced the plugs with what was cross referenced in my manual. Champions if I recall. I use 89 octane because that is what my marina sells. And, I have no idea of what the timing is, something for the tech to check.

I am not familiar with what a "test prop" is but I appreciate the extra thoughts Dhadley.

Jonesg, I gapped the plugs but you are also talking of something I've never heard, a "gap tester". Clue me in, I am pretty competent once I learn.

Thanks guys, we've got plenty of winter left to get her running right.

Richman

 

[roger777]

Re: 1998 200hp Ocean Runner Questions

I cant weigh in on the rpm issue but as far as your compression goes it sounds fine.. Most of the time I compression test on a motor not running and i always get low readings.. I beileve 20% is the maximum difference in readings so under 10% sounds good..good luck with the rpms and post your results..

 

[jonesg]

Re: 1998 200hp Ocean Runner Questions

Jonesg, I gapped the plugs but you are also talking of something I've never heard, a "gap tester". Clue me in, I am pretty competent once I learn.


Richman

http://www.toolfetch.com/Category/Automotive/Spark_Testers/LIS50850.htm

you need something like this, an adjustable gap tester. Less than $7.

A spark plug will spark but when its re-installed the compression prevents the spark from jumping, so you might think you have spark but actually have none or intermittent spark. This tester will help discern how healthy your coils are and ignition in general. I guess you don't have the service manual.?

 

[Richman]

Re: 1998 200hp Ocean Runner Questions

The coil could be weak hence the fact that pulling the plug wire on the bottom left cylinder ALMOST made no difference in rpm's and that spark plug was noticably more black and oily than the other five. I could get the spark to jump when I held it up to the block but was not seeing or hearing much spark when held away from the block. Might we be on to something here?

I do have a manual.

 

[KLINDWW]

Re: 1998 200hp Ocean Runner Questions

Might also try swapping that plug to a different hole. I have had a couple of plugs over the years go bad and would not work under compression.