Differing max rpms

[jobu2k]

Hello all.

I have searched a good bit and found a hint or two to try but haven't been able to nail down what I perceive as a problem. I was hoping someone could shed some light for me.

I got my boat this spring (2012 AR240). I've used the boat all summer without an issue on the mechanics. A couple weeks ago I was pulling a tube with one of my heavier friends on it so I was hitting the throttles a little harder than usual on the launch. I looked down and noted that the starboard engine was up close to 8k while my port engine was much lower - approx 7k. When running the two engines at the same RPM (below 7k) everything seems to be fine - no strange sounds or odd tones coming from the engine compartment. She still jumps up on plane quickly even when fully loaded.

I tried running the engines down and up again later and the port engine was still capping at 7k.

I pulled the spark plugs last week and none of them looked particularly fouled. But to be certain, I replaced the plugs and verified the gap. This past weekend I went out and checked again - same result.

I did read that the throttle can sometimes be off a little bit and I did check it this week. At WOT position, both cables were at the stops.

I also noted, when flushing the engines Saturday evening, as I finished the flush on the port engine and burped the RPM's a couple times to blow out the remaining water, there seemed to be a slight shimmy in the boat as the rpms settled back to normal. The same was not present on the starboard engine. I don't know if this is me being overly sensitive or indicative or something wrong.

Does anyone have anything else I might check for myself before I bite the bullet and take it to a dealer?

Thanks for any help you can provide.

Steve

P.S. This is my first post on this board and I just created the profile. I apologize for the stock pic - didn't have any personal ones available to me at work

 

[swatski]

Something is not right. It has nothing to do with your heavy friend in general or driving the boat hard in particular. These engines are designed to ride wide-open throttle as long as you want.

 

[Bill D]

Do both engines accelerate similarly when you push the throttles forward? Then the port engine just stops gaining revs at 7k?

I agree with @swatski, your heavy friend won't have any effect. (A lot of heavy friends may, but it would be different than this) Also, don't worry too much about what it sounds like when you're flushing. Mine sounds like bolts in a coffee can on a paint shaker...

 

[jobu2k]

Thank you both for your responses.

I agree that the heavy friend shouldn't have an impact here. I only mentioned it as I went to WOT to yank him out (while when I have my kids on the tube I increase thrust much more carefully) and that is when I noticed the difference in RPM.

With regard to the acceleration, they seem to accelerate evenly up to 7k and then the port engine just stops gaining RPM. Maybe an ECU issue?

The flushing is less about the sound - both of mine sound similar to what you describe - and more about a slight shake you can feel in the boat as the rpms drop after you burp the water out. My mind started making up scenarios like something is out of balance and is causing the problem. However, I don't know if there's anything that can even get out of balance in an inline 4 cylinder. In addition, if something was out of balance, I would assume it would get worse and be more noticeable at higher RPMs.

Steve

 

[Bill D]

I'm wondering if there is an electrical issue in the throttle control system. I have attached that portion of the service manual below. If you are a technical guy, you may be able / willing to check some of this, and if you have access to a YDS, that could be very helpful.

 

[jobu2k]

Bill,

Thank you for the response and the service manual section.

I'm reminded of a line from Magnum Force where Callahan utters the statement "A man's gotta know his limitations" and I think trying to wiggle through some of what's described in the service manual would stretch my limits to the breaking point. I will look at it again when I get home and see if I can make more sense of it then.

Unfortunately, I do not have access to a YDS which many of the tests call for. I have been debating grabbing a set (ebay seems to be the place?) just to have it available.

 

[Bill D]

If you check the user map, you may find someone near you with a YDS that is willing to help out. Also, if you add your location to your profile, you will show up on the map.

I completely understand the quote. After checking the obvious things and ruling out everything we can, sometimes we still have to punt. At least you can start ruling out what it's not.

Hopefully more members will jump in with ideas.

 

[Billtex2000]

I've been dealing with something very similar for years jobu2k. My tachometers are in sync up until about 5500rpm, then my port rpms start to drop off slightly until that engines tach is about 500rpm slower than the starboard engine at WOT (7700/8200). I've tried everything you mentioned as well, plugs, cables etc., and then I started to believe my ears! When I pull back on the starboard throttle a little to even out the rpms on the tachs at 7700 (WOT is 7700 on the port tach) the engines don't SOUND in sync and the boat pushes to the right (lower rpms from the starboard engine?)! If I move the throttles forward together through the range the engines always sound in sync and the boat tracks straight. I've resigned myself to the fact that my left tach starts to lag for some reason when it gets above 5500rpm. I don't think there is a way to adjust the tachs and I don't understand why the port only starts to drop off above 5500. With the throttles together the engines always accelerate and run smooth, and sound perfectly in sync. I've learned to ignore the tachs.

 

[jobu2k]

Wow. I hadn't even considered the failure might be in the tach and that there's nothing really wrong... well, now I want to go drop the boat and test this idea

This weekend is going to be a bust due to the hurricane throwing up a lot of wind all up the east coast, but now I'm going to be itching to see if this is all due to a mis-calibration in the tachometer.

Thanks for the response, and the hope that my port engine isn't about to die!

 

[jobu2k]

Sadly, this wasn't the issue. I still don't know what the issue is. Was able to tell a noticeable difference in the two engines with the throttles both all the way forward.

The port engine is still only hitting 6900-ish rpm while the starboard goes to 8. May be nearing the point that a professional will be required.

 

[itsdgm]

Welcome @jobu2k. Sorry to hear about your issue. One thing that would be simple to try would be to swap all of the coils from one engine to the other and see if the problem follows tithe other engine. Another thing to check would be for oil in the air filters (especially the affected engine). Anyway, hopefully it's a simple fix. Keep us posted.

 

[jobu2k]

Thank you @itsdgm for the welcome. The coils swap is an interesting idea. Maybe I can get out this week sometime and try that. With the oil in the air filter - I'll certainly check that. What would that indicate has gone wrong if it is present?

 

[itsdgm]

Oil the air filter is an indication that the oil level is too high in the engine. The oil on the filter can reduce the engines performance due to the reduction of air flow. Usually it's caused by simply overfilling the oil level. But it's also possible that a stuck fuel injector can dump fuel in the oil and cause it to thin out and send some back into the air filter. It's not that common. But worth checking the oil level and smell to see if it's thinned and smells like fuel.

 

[jobu2k]

Thanks for the explanation. I realized almost as soon as I hit the "post reply" button, I could have googled that my damn self (which I did) so thanks for taking the time to reply when you could have easily told me to quit being lazy

I'll check it tonight.

 

[jobu2k]

Ok, so, pulling out the air filter on the port engine, there was oil at the bottom of filter housing (no gas smell). The paper of the filter doesn't feel particularly oily but I'm assuming that doesn't mean there isn't enough oil in the filter to affect performance.

After reading around it would seem like I could run the boat this weekend without a filter on that engine and see if I notice an improvement.

**Before asking my next question, I understand that any action I take is my own and no one bears any responsibility but me.

Is there a compelling reason that I couldn't run without a filter on my port engine for a day to test the theory that it's been contaminated with oil and causing my lower RPM?

Thanks for any thoughts.

 

[jobu2k]

the follow-on question, of course, is: if the filter is causing problems is it worth the $115-120 to replace it? Can I run without the filter or is it just smarter to pony up the cash and make sure I don't over fill again?

 

[swatski]

There is no reason to worry about running without an air filter for a day. Many of us have done that. Boats used to not have air filters.

 

[jobu2k]

And the winner is.... oil in the filter! ran without the filter this afternoon. Starboard 7900-ish, Port 7800-ish. Much better! And then one of my plugs blew... awesome

Anyway, thanks all for your help with getting this sorted out. I appreciate the advice and things to look for.

Steve

 

[itsdgm]

That's awesome @jobu2k glad that you figured it out. Out of curiousity how do the oil levels look?

 

[Billtex2000]

And then one of my plugs blew... awesome

Whoa! What happened with the plug?!?!?