Optimax 175 bogs down between 1700-2700 rpm

K

keithwp

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I have a 2007 175 Optimax that is new to me. Serial number 1B492347
(replaced Force 150)

Problem: Motor bogs down heavily from roughly 1700 to 2700 rpm. You have to be aggressive with the throttle to get it to go. If you creep up to those rpms it will go but only with full throttle and very noticeable hesitation. Similar feel to like it is flooding.

Once it starts to go, hang on. It runs fine and pulls strong from 2700 rpm to 5700. It can hit the rev limiter. I put a smaller 14 pitch prop (from 15) on to be able to more easily use rpm during break in mode.

Starts fine. It will die when starting when cold. Conditions at the lake: air. 40-45 F , water 60F An advance of the throttle for a minute or two to 1000-1200 rpm and it is fine after that. Once warm it idles just fine.

My altitude is 8500

Ethanol free gas. No issues with gas etc. with previous motor. Added more gas from another ethanol free station with no change in performance.

Motor history:
New rings and one new piston #6. New piston overbored .030. Other cylinders were honed.

2 new thermostats at that time.

Air and fuel pressure are per specs.

No warning alarms. No fault codes (not a factory Mercury tester but one a local mechanic uses)

New fuel filter. (no real change in performance)

New Gen II controls at time of motor swap. Local mechanic installed the controls and motor.

360 ish hours.

Motor was in break in mode. Plugs had heavy oil deposits after running for 2 hours. Cleaned plugs- used older Champion sand blaster and spark plug tester, no noticeable change in performance. Just completed 10 hours in break in mode.

Oil- Lucas Full Synthetic

used existing wiring on boat (1992 Bayliner Trophy 2002 Dual Console) to an adaptor to the Optimax harness

Battery shows 12-14v when running- from mechanics tester.

Moved motor to highest mounting position to eliminate motor position as a problem. If anything the motor is too high now as you can get it to cavitate in sharp turns.

I'm open to any ideas. Hopefully someone has had this issue in the past.

Thanks in advance!
 
Texasmark

Texasmark

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My thoughts are spark advance improper at that rpm. Not a 4 stroker but on 2 strokes, spark is real close to TDC and as you ramp up the rpms the spark advances on up to 20-22 BTDC at WOT. If there is anything to delay that spark advance a drop in performance would be noticable. Suggest you get a timing light and plot your timing as a function of rpm. You can figure out how to do that but I'd do it under load. If it's not linear, what does it do in the rpm range you mention.

Second, check your fuel injection linkage and see if it moves freely and evenly.

Just thinking about a mechanism and what I said above is all I can think of........ What's your rpm range from start of hole shot till boat is on the water? If it's in that range it says you may be lugging...you didn't say what boat, what kind of load.

Dying when starting is common on carbed engines. Just punch the choke till it recovers and let up; repeat as necessary. But the Optimax is fuel injected, right?

Cupping of the prop helps to reduce blowout in high speed tight turns at elevated transom heights.
 
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444

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Are you or your mechanic aware you are not supposed to use synthetic during break-in? Piston rings seat properly with conventional oil, not synthetic. If you're getting a lot of oil on the plugs, that could be why....
 
Texasmark

Texasmark

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444 said:
Are you or your mechanic aware you are not supposed to use synthetic during break-in? Piston rings seat properly with conventional oil, not synthetic. If you're getting a lot of oil on the plugs, that could be why....
Click to expand...

I bought a new farm tractor with a Cummins Diesel. I use syn. in most all my engines. So I called them and asked them. They said the engine would love for you to use full syn........after the 300 hr break in completion/first oil change comes due. Agree and that's all the more reason I use full syn. If you use dino to get rings to seat on new engines, must not be as good a lubricant as full syn. Makes sense to me.

I hadn't happened on to his high oil usage solution. However it may be as you say or it may just be normal 2 stroke oily plugs.
 
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keithwp

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Thanks for the tips.

The Optimax is computer controlled so no timing adjustments available. I'll check the other items as well such as throttle linkage etc.

The boat is a 1992 Bayliner Trophy dual console model 2002. Load on the boat is average. My previous Force 150 performed far better at low RPM than the 175 Optimax.

Motor heavily resists any load from roughly 1700-2700 rpm. If you hold the throttle in the WOT position it will eventually go past those rpm and then run fine above 2700 rpm..
If you go slowly through the rpm it could take a minute or more to get through the rpm or past 2200 or so. Sometimes it won't get through the rpm range.

If you put it in gear then go WOT once the gear is engaged then it will bog but catch the rpm around 2800 and run above that just fine.
 
Texasmark

Texasmark

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Texasmark

Texasmark

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keithwp said:
Yes I think we are talking about the same thing. Mercury calls them the Exhaust Extension.
Click to expand...
First time I heard of them falling off.

The horns are part of the loop charging scheme. 3 cylinder timing was the first looper designed by OMC back in 1960-69 time line. The Triumph was Evinrude's entry at 3 cyl and 55 hp. Their engineers found that by tuning the exhaust on that engine, they could use the exhaust to help in loading the next fuel charge such that more of the unburned fuel remained in the cylinder and didn't leak out as the engine was changing from the power to the load modes and vice versa. That and ported, flat topped pistons complemented the process. The difference in a looper design and comparable engines of the time was like 2:1 in fuel savings. I know. I was boating with one of those earlier model gas guzzling OMCs when it all happened. Like Rude said, it was a Triumph in fuel economy. Problem for me was that it was down at 55 hp and I was running the largest hp they made and 4 cylinders. These engines did benefit from absorbing some of the improvements, but being 4 cyl the timing wasn't quite right and didn't get the full effect and weren't therefore loopers. However, years later the technology improved and non 3 cyl. combinations could be effectively looped. Today that is/was the standard before the EPA basically edicted the 4 strokers.

The V6 uses a pair of 3 cylinder loop charged engines (essentially) cast together in one crankcase so 2 sets of tuning horns would be needed. Since the horn is part of the process, surely if one of them broke off it would affect the performance. However they are cast aluminum which work hardens easily and there is obviously vibration there from the exhaust pulses and just plain noise so yes they could crack and fall off. Interesting in that it only affected your mid range, but I was not part of the designing process so I don't know what all went into or came out of it.

Glad you got her fixed.

Mark
 
Faztbullet

Faztbullet

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The 2.5 Mercs fall off all the time and you wont notice that much of a performance issue but it wont cause a bogg. The Optimax bogg is a fuel /air issue so check compressor and tracker valve. You need to test the pressure under a load so back it in water and in gaer on a trailer to test..
 
K

keithwp

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May 1, 2013
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Thanks for all of the advice. I'm having the Exhaust Extension ( or Exhaust Tuner) repaired and then seeing if that corrects the problem. Currently waiting for gaskets to arrive.
 
K

keithwp

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Update. The problem is fixed. It was the exhaust tuner that caused the problem. Exhaust tuner had come off in the mid section. It was repaired and now the motor runs as it should. Smooth, no bogging etc.
 
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