Losing RPMs at WOT

[terankinjr]

Hey Guys... got a question, and I hope this is a simple fix but here goes..

My Boat stats:
Year: 1977
Make: Classic Industries
Model: ??
Boat Type: Cuddy Cabin
Size: 21ft
Engine: 188HP Mercruiser 8cyl
Cooling Type: Raw Water
Drive style: I/O
Drive Make: Appears to be Mercruiser as well
Owned the boat > 1 year

The problem: Took the boat out about 1 week ago and I noticed that I wasn't getting to normal speed... I didn't think too much about it because I recently (the day before) found the anode on the cavitation plate was angled in the wrong direction, I replaced it and corrected the angle (it was also terribly corroded) and I assumed I was getting inaccurate readings from the speedo because of the hard pull to port... that day I almost got stuck in some muck in a VERY shallow area so I had to "power" my way though it. All seemed fine bringing it back to my slip... so fast forward to today....

I get out on the boat... idle's fine... slow speed fine... I throttle up, planes ok... and once I get to WOT, I find I lost even more speed off my top end and the RPMs seem unstable... engine sounds like its intermittently chugging... so I bring it it in and start talking to the guys at the Marina... they give me some ideas and I get to working on the problem... I pulled the prop, looks ok, not bent, and seems to be same since I dropped the boat in earlier this season. I try a new prop to test and add some dry gass and fill the tank (I was low and figured this might be a "bad gas" situation.... I take the boat back out... it chugs once... then seems ok, I get some speed back (not all of it) but the boat just doesn't sound right... I keep on going, then I turn the boat around at speed to head back... the engine begins to intermittently chug again (but only when I turn it seems)... I check the RPMs and I am around 3500 to 3700.... I back the throttle down to neutral and check the engine to see if it is making any odd sounds at idle, sounds normal to me... I throttle back up... I now get 4100 to 4300 RPMs... throttle down again to neutral then back up... I'm at 3500 to 3700... and I notice kind of a "wooshing" noise coming from the engine, I never noticed it before but before today I was not listening to the engine for problems. I get back in to my slip and put the original prop back on and talk to the guys at the Marina. They start talking about doing a tune up, I am not sure when the last one was done on the boat I have only owned it for about 9 months, (also my first boat) I did all the winterization stuff except for the tune up items...(I was under the assumption that the tune up was done last year and that one only needs to be done every 2 years) which I know to be; cap, rotor, condenser, points, plugs, fuel/water separator and to replace/clean the flame arrestor, but I will probably have someone else do this because, I have no clue what points are or where the condenser is...

Any Ideas on what might be causing this problem? or do you think a tune up would cure this issue? ( I will do one anyway just so I know when it was done). I hope this will be a cheap/easy fix cuz they cut hours at work and I am a little low on cash and the Boat is what I use to get away from it all...

Well I'm rambling... its late and Im exhausted....

Thank you for your continued expertise and assistance...

Regards,

Tom

 

[Bondo]

Re: Losing RPMs at WOT

Ayuh,... A Tune Up is a Good Idea,... I think the Fuel Filter are at the root of your Problem...

 

[terankinjr]

Re: Losing RPMs at WOT

Fuel filter or fuel/water separator? I know what al filter looks like but I dunno if I ever seen one on the boat... I will check... I really hope it is something this simple...

-Tom

 

[Wet Wonder]

Re: Losing RPMs at WOT

I'd check two things.

First, the fuel/water separater. It's an old boat and ethanol may be causing debris to get into that fileter.

If you find the filter OK, pull the plate out of the distributor and see whether the spring weights are sticking, which would stop the timing from advancing - if this is happening you'd have trouble getting up to high rpm and at WOT the motor will sound like it's missing.

 

[terankinjr]

Re: Losing RPMs at WOT

What exactly do you mean Plate out of the distributor? You mean the bottom plate under the cap, are those parts serviceable or cleanable?... oH and Im dumb, the fuel filter IS the separator as well... I went and bought all the parts needed for the tune up, Just need some time to get it done... buying the parts was a hassle because that year Merc put out 4 different ignition styles using 2 different spark plugs... yeah, awesome....

-Tom

 

[Wet Wonder]

Re: Losing RPMs at WOT

I mention the timing advance as a possible cause b/c it happened to me. I learn as I go. Pull off the distributor cap, and the plate is there under the points or the elec ign module, whichever you have. You remove the plate and will see the spring weights.

When I had this problem, one of the springs was broken and the other rusted frozen, so timing wasn't advancing and if I tried to get above 3200 rpm the motor would become erratic. I replaced the entire distributor w/ a Pertronix electronic setup. You can also get it rebuilt, or get a spring kit to rebuild that part of it yourself.

The above is one possible cause. When you do figure it out, please post the solution onto this thread.

 

[terankinjr]

Re: Losing RPMs at WOT

Ok... how would I know if they are frozen or would it be as obvious if one was broken? Also, how do I gap the point and correct timing if need be?

I know point gap is .16


-Tom

 

[Wet Wonder]

Re: Losing RPMs at WOT

Go onto youtube and search on how to set timing and how to gap plugs and you'll get numerous video clips on how to do either.

 

[terankinjr]

Re: Losing RPMs at WOT

Ok I think i got that Down pretty good at this point as far as watching how its done... looks like tomorrow morning should be nice enough for me get out there and do it all up...

Ill let ya know.


-Tom

 

[terankinjr]

Re: Losing RPMs at WOT

soo i lied... i went out yesterday evening... i got the plugs and wires in, as well as the fuel filter and ran out of daylight.... ill be going back out today to do the distributor, rotor, points and condensor.... get this though... the old plugs were gapped .040 to .045, they are supposed to be .030....

 

[terankinjr]

Re: Losing RPMs at WOT

Ok so I got it all done... cap router points condenser, the points were just about 50% off center on the old ones... engines fires right up and i tested the ride... no stuttering... all runs good, rpms are right about 4200 where they should be... HOWEVER... my speed doesnt read right.. saays in running 27 to 30 when last i checked I was around 35... Ill be going back out tomorrow with my GPS to get a better Idea what my speed is.... Never gapped points before.. interesting stuff.. next time though, Im gonna get an electronic ignition pertronix "Flame thrower" coil with the "Ignitor" electronic ignition, my father-in-law, a mechanic for about 40 years, swears by em..

http://www.pertronix.com/

http://www.pertronix.com/prod/ig/ignitor/default.aspx

http://www.pertronix.com/prod/ig/flame/coils/40000_volt.aspx

Thank you guys again for all your help... Ill let you know how the GPS reads (last year it was about 35mph)

-Tom

 

[terankinjr]

Re: Losing RPMs at WOT

sooo i get back out on the boat with the GPS... i am getting about 30... so i mess with the trim anode again... i get about 32 to 33 mph now but I have all these weird steering problems... before i messed with the anode the boat used to pull hard to port... after i messed with the anode the pull to port is minimal but at WOT I get odd steering issues, the the boat tipping on its side... and it feels like the boat is "walking" all over the place, i have bennett trim tabs and they dont seem to correct the issue... im going to set the anode back to where it was before, with the hard pull to port and see if i still have any funkyness... any ideas??

 

[carlfarey]

Re: Losing RPMs at WOT

Mine does that if my trim is to far down or the trim tabs are set wrong.

Carl.