RPM issues

[Diebroke1]

I have a '98 DA w/8.2's No MAS but fuel injected. I am having a problem obtaining max rpms with starboard engine. I replaced all sensors I could find on the plenum, gaskets idle position sensor to no avail. boat runs great, gets up on plane with no problem but engine will not rev above 3800 rpms in gear. In neutral it revs. Filters changed twice.I really don't need the rpms per say, but in case I need to outrun some bad weather would like it to perform as designed.

 

[Strecker25]

starting simple...unlikely it would affect one side but is the bottom clean? any chance that side's prop is out of spec, any "odd" vibrations while up on plane?

If you haven't done plugs and wires recently it might worth a try as well

 

[searay30]

Hey, just a quick question? How much would a bad bottom affect the rpms? Top end?

 

[Strecker25]

Hey, just a quick question? How much would a bad bottom affect the rpms? Top end?

Depends on how bad and the how the hull is designed, the guys in south have it way worse with warm water growth, barnacles, etc. Last year because of the high water in Lake Ontario a few guys only went out once or twice until august and the bottom was bad enough where they could not get on plane. This was in some small bowriders and even a few cruisers, one of them being a 350 powered 268 sundancer. Growth can really kill performance, especially on the running surfaces.

 

[searay30]

Depends on how bad and the how the hull is designed, the guys in south have it way worse with warm water growth, barnacles, etc. Last year because of the high water in Lake Ontario a few guys only went out once or twice until august and the bottom was bad enough where they could not get on plane. This was in some small bowriders and even a few cruisers, one of them being a 350 powered 268 sundancer. Growth can really kill performance, especially on the running surfaces.

 

[searay30]

Darn, thanks. I'm boating in Western lake Erie. We do have an algea issue in the latter part of the summer. My boat gets scummy. But I do paint it every year. we

 

[Strecker25]

Darn, thanks. I'm boating in Western lake Erie. We do have an algea issue in the latter part of the summer. My boat gets scummy. But I do paint it every year. we

Best thing you can do is run it. We put 60-100 hours a year on ours in Lake Ontario (slipped in Irondequoit bay) and all I need is a half hour with an electric pressure washer to clean it in the fall. We use hydrocoat eco for paint.

 

[sbw1]

As pointed out, condition of bottom can effect rpms. Also, in no particular order....spark plug wires, spark plugs, and points if you have them, cleanliness of spark arrester, condition of props.

 

[joeyleggz]

If your boat is running up on plane at 3800 RPM if you can push the port motor higher than 3800 RPM then clearly you have a problem with that particular motor on the starboard side I would verify this first before looking any further

 

[searay30]

I don't have a rpm problem with my engines. But I heard this issue rage on and on. Just wanted to get both point of views.
I know when I had a boat in Florida had a diver under the boat monthly.
Running the boat does solve a lot of issues, just like with most mechanical devices.

 

[northern]

A very slight growth on our boat costs us 3 knots in speed. It just fuzz on the bottom.

 

[Jaybeaux]

A very slight growth on our boat costs us 3 knots in speed. It just fuzz on the bottom.

Work with me here, I'm agreeing with you.....So your engines don't know if there is growth on the bottom or not....they still spin their WOT RPM's, but the props won't push the boat at the proper speed, due to "growth" on the bottom....right? In other words, a fouled bottom has nothing to do with an engine that won't get up to RPM....or am I missing something?

Jaybeaux

 

[Korkie]

Experienced same problem , stbd motor would not go over 3300 rpms. Changed plugs, swapped plug wires from port motor, checked spark, nothing on smartcraft and nothing on computer when running diagnostics, no change. Took it merc mechanic, he showed me how the motor was idling a little rough, sprayed some starting fluid or something in the air intake and motor smoothed out, it was obvious. His diagnoses was clogged fuel injectors. Removed and sent out to be cleaned, re installed and now get WOT at 4400 and a ton more power getting up on plane. Did Port motor in the off season and OMG, what a difference.

 

[Diebroke]

thanks to all that responded. The boat was just placed back in the water. I experienced this problem last season, and thought some of the replies were causing the issue[ scum on bottom, prop, plugs wires etc.] same this year as last, so eliminated them.
Never thought about fuel injectors, but will definitely check them out. I did notice some soot on the starboard side of the boat, not on the port.
Thanks again.

 

[searay30]

Here another general question, if an engine has a compression issue, how long will it tunnel until other issues creep up.

 

[Korkie]

To clean the injectors they must come out. The fuel additive just don't cut it. I sent mine away and had them done. Turnaround was really fast and they did spray patterns before and after cleaning. With no faults on your smartcraft, poor injector flow certainly in the mix of what it could be.

 

[Diebroke]

All indications point to the injectors as everything else ruled out. thanks all.

 

[SeadawgVB]

To clean the injectors they must come out. The fuel additive just don't cut it. I sent mine away and had them done. Turnaround was really fast and they did spray patterns before and after cleaning. With no faults on your smartcraft, poor injector flow certainly in the mix of what it could be.

May I ask who you sent them to? My port engine is running rather rich and I suspect injectors (8.1)