Mercury OptiMax Runs Poorly at High Engine Speeds

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
Bigwylie
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Joined: Mon Sep 20, 2021 4:18 pm

Mercury OptiMax Runs Poorly at High Engine Speeds

Postby Bigwylie » Thu Nov 17, 2022 9:34 am

In August 2022 problems began with Mercury OptiMax 200 engine on my 2001 VENTURA 21. The engine is sluggish and chugging running over 4,300 to 4,500-RPM.

Below is a list of repairs made or planned to be done:
    Engine run time 483 hours
    Fault codes: none
    Peak cylinder pressure tested: good
    Spark plugs: new
    Coils: test as good
    Fuel hose: found slice in hose due to use of improper clamp; replaced hose section
    Primer bulb: replaced clamps
    Fuel hose downstream of primer: suspected problem with gray hose. The fuel being used now is pure gasoline treated with Mercury Quickleen,
    Air compressor: rated by mechanic as good. I have found a local rebuild service available; new seals were installed
    Water pump: impeller replaced replaced. Good water flow
    Vapor Separator Tank: needs to be cleaned. A needle valve is often a problem
    Fuel lift pump; dIaphragm kit needs to be installed
    Injectors: may need cleaning.

BACKSTORY
I bought a 2001 Ventura 21 with a Mercury OptiMax 200 XL. The boat and engine was previously used in Connecticut. The boat is very clean. The survey of the boat was very positive. The boat is amazing. The boat will now be used in Canada, in the Lake Ontario and in the Muskoka Lakes. Our first outings with the 2001 VENTURA 21 with the OptiMax 200 were fine.

jimh
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Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
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Re: Mercury OptiMax Runs Poorly at High Engine Speeds

Postby jimh » Thu Nov 17, 2022 9:40 am

A restriction in fuel flow at high fuel flow rates will often cause the engine to be unable to accelerate to full engine speed.

I am unclear about the resolution of the problem of the engine running poorly at high engine speeds.

Q1: did the repairs to the fuel hose and related fuel components provide a remedy to the problem of the engine running poorly at higher engine speeds?

The use of a gray fuel hose with a somewhat metallic appearance could be a problem. There are many prior discussions about the tendency of these gray fuel hoses having a separation between the inner liner and the out jacket, causing the fuel passage through the hose to be obstructed. Considering the modest cost of a new rubber hose, you should remove the gray hose from the fuel system.

Bigwylie
Posts: 5
Joined: Mon Sep 20, 2021 4:18 pm

Re: Mercury OptiMax Runs Poorly at High Engine Speeds

Postby Bigwylie » Thu Dec 08, 2022 8:49 pm

November 2022 Update on the Poor Running Optimax Engine

The fix to fuel hose on the fuel tank produced immediate improvement. [The old fuel hose] must have been allowing air into the fuel system.

The [OptiMax 200-HP engine] was run at an engine speed of 4,800 to 5,000-RPM for over 30-minutes. The sea state in this run was rough chop.

I thought the solution had been found, but only at the very end of the ride to the ramp did [the OptiMax 200-HP engine] again begin to run poorly. This was most frustrating. This outing was the last time I was able to run the boat [in 2022] prior to putting it into winter storage.

In Spring 2023 I plan to accomplish the following
  • install a new diaphragm kit on the fuel lift pump
  • open and clean the vapor separator tank [VST]
  • test the pumps
  • clean filters on pumps
  • replace the needle valve in the VST (which was mentioned elsewhere as causing problems)
  • replace the section of gray fuel hose from the primer bulb to the engine

Replacement of the gray fuel hose should be done in case there is any varnish or debris buildup in that portion of hose.

Completing these remaining small items should culminate any do-it-yourself-overhaul of this Mercury OptiMax 200-HP engine since I bought it [as a used] engine in 2021.

I will feel more confident with this Mercury Optimax engine after these maintenance tasks are completed

More options to cure the problem of poor running on the Mercury OptiMax 200-HP engine:
  • [service or repair or replace] the air compressor
  • clean the injectors
  • clean the fuel rails
  • replace the trim relay.
I am trying to avoid those repairs due to their cost

[The problems with the Mercury OptiMax engine running poorling at high engine speeds have been] really frustrating. The 2001 VENTURA 21 boat is dry and in great condition. At full throttle the boat is a ton of fun.

I expected to [need to perform] most of these 300-hour-type hour maintenance services when I bought this boat in September 2021.

I really don't feel like the Mercury OptiMax engine is failing. On the report from the engine control module there are no faults and 480-hours of run time. [Maintenance on this] Mercury OptiMax engine was a bit neglected. The simple upkeep should resolve these running problems.

In 2021 when I purchased the boat, I did plan to re-power in the future, but not so soon as 2022.

In Spring 2023 I will give more updates after I have completed the maintenance of the fuel system.

[Problems with engines running poorly at high engine speeds are] part of the fun of buying a 20-year-old engine. To tinker with the engine is fun.

jimh
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Location: Michigan, Lower Peninsula
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Re: Mercury OptiMax Runs Poorly at High Engine Speeds

Postby jimh » Fri Dec 09, 2022 8:31 am

Bigwylie wrote:The fix to fuel hose on the fuel tank produced immediate improvement.
What was changed in the fuel hose? Your narrative did not explain what was done.

Jefecinco
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Joined: Fri Oct 09, 2015 6:35 pm
Location: Gulf Shores, AL

Re: Mercury OptiMax Runs Poorly at High Engine Speeds

Postby Jefecinco » Fri Dec 09, 2022 9:12 am

You may find installing a fuel system filter to be useful. The filter would be primary to any filters installed in the engine and would eliminate any need to service them. Another step you could take would be to flush the fuel tank to ensure any sand, water or other debris is not present. Finally, examine the fuel tank vent to ensure it is fully open and clean.

The intermittent nature of your engine's high speed misfires indicates fuel starvation possibly caused by dirty fuel entering the tank pickup tube as fuel sloshes around as speed and planing attitude changes.
Butch