what limits RPM?

**da buckwheat** · 03-02-2003, 11:36 PM

What was the first year that Mercury began rev-limiting 2.5L 150 and 200 carb engines?

My 2003 model XR6 is limited at somewhere between 5700 and 5800 rpm.

Also, can anyone tell me what the rev limit is on the 2003 model 200 EFI Merc?

**us1** · 03-03-2003, 09:15 AM

Originally posted by us1
Merc carb motors don’t have rev limiters. The port timming is what keeps the RPM down.

**Greg Moss** · 03-03-2003, 10:17 AM

If you keep posting it sooner or latter they will believe you

**tmerc25** · 03-03-2003, 10:20 AM

Guys, this post all started with the man wanting to build a MERCURY 200, not a johnrude or OMC but a MERCURY, yea the johnrude and OMC power packs might be RPM limited I don't know but the MERCURY switchboxes (3 cylinder/6 cylinder) do not have any RPM limiting capabilities.

Sorry I did not make my self clear.

**sasbenson** · 03-03-2003, 11:59 AM

Originally posted by us1

John, without seeming to be argumentative, Mercury Marine really does install rev limiters on all of the sportjet and jet model V6 powerheads. And I can assure you that the exhaust port height,(as low as it is), in a stock 150 or 175 will not keep the engine from reaching a very self destructing rpm level when the jet pump "sees" air instead of water.

The downside to the limiter is if the operator lets the motor run against the limiter we see a lot of reed breaking. We have a big box full the rubber coated cages with split and fractured reeds taken from engines with rev limiters. IMHO the guy with the throttle in his hand is the best "rev" module.
Regards,
sasbenson

**ShorePounder** · 03-03-2003, 12:29 PM

I love it!! 3 or 4 people who KNOW for FACT WTF they're talking about give you the answer and it either gets ignored or picked apart.

Thanks for putting up with us guys.

**Capt.Insane-o** · 03-03-2003, 01:12 PM

Is a sportjet a 200 merc, no. Let's keep it apples to apples here. My 2.4's have stock switch boxes and both of them turn better than 7500. Omc are rev limited because they are so damn heavy inside.

**us1** · 03-03-2003, 03:34 PM

I believe we are talking about outboards here. I will go back and read the first post again but I didn’t think he was talking about a Sportjet.

**Capt.Insane-o** · 03-03-2003, 03:46 PM

"John, without seeming to be argumentative, Mercury Marine really does install rev limiters on all of the sportjunk and jetjunk model V6 powerheads. And I can assure you that the exhaust port height,(as low as it is), in a stock 150 or 175 will not keep the engine from reaching a very self destructing rpm level when the jet pump "sees" air instead of water."

.
"I am thinking about starting w/ a Merc 200 and building a motor, I know the ecu controls the rev limiter on an efi motor, but on a carb motor what limits the rpm? i'm thinking of buying an old motor and just seeing what I can build and this was my first question. thanks."

Like I said let's keep the Apples to apples and omc's in the dumpster.

If someone brings me a limited 1980's switchbox from a 200 MERC OUTBOARD I have a nice bridge I need to get rid of...................................................granted the Hi perf ones last a lot longer above 7000 rpm. I've burnt holes in quite a few stockers, but I have boxes of them.

**Dave S** · 03-03-2003, 08:54 PM

The switch boxs that limit reves are the ones that only fire two or less plugs.

I have seen 2.5 fissin 150 HP blown up because the prop was too small, the small ports did not keep it alive

The fissin man did'nt slow down until the motor slowed him, Dam no good Merc,s.

**us1** · 03-03-2003, 09:28 PM

I see a little confusion here. The port timing is not a form of revlimiter. The limit in RPM is a byproduct and a lesser aggressive port timing for the purpose of gas economy and smooth reliable motor characteristics. The height of the ports was never intended to control the motors ability to rev over a safe limit.

**Jay R.** · 03-03-2003, 09:36 PM

I was only commentng on the blaket statement made that NO POWER PACKS hanve limiters. i don't know much about merc's and said my peice on OMC. i am an OMC tech so i just added my two cents. my friend has a 2.4 and is a tech who knows a ton about merc's. he has complained about some props bounceing his moter on the rev limiter and also telling people that they are bouncing on their limiter. i don't nkow where it is in a merc but i would think there has to be some sort of over speed protection in a merc.

Also i saw somwone post that 3-4 people have posted the right answer to this.... well which is it? i have a hard time beleaving it's the port timing alone, but stranger things happin, which is the real answer???

who ever started the thread, sorry i know this all can not be helpful to you, but it does get more info for the masses!

**us1** · 03-03-2003, 10:09 PM

I think most of the statements here are related to the first post about what limits the RPM on a Merc 200-carb motor.

**da buckwheat** · 03-03-2003, 10:55 PM

I'm reposting this from another board. This is one of several I found concerning late model 150, 175, and 200 Merc carb motors. The hesitation that the guy describes is really a surging condition. The smaller the prop (under proping) the more pronounced it is. A larger prop that eats all the hp up right at 5800 can make the condition very subtle.

All of you guys are on target more often than not, but my money is on the guy with the wooden shoes on this one.

[Hesitation at WOT]

Sherm, first of all let me say thanks a lot for all of the info. With your help I installed my own hot foot and pro-trim with few problems. My question now is that my 2001 150XR6 (23 tempest) at WOT is hesitating a bit but only at WOT. Im runnin it at 5800 RPM this winter, and this is when its doing it, when i back off to 5700 it runs fine. Does this motor have a rev limiter and is the limiter causing this to happen? Should I be concerned about this?
Thanks again!

[Re: hesitation at WOT]

Hey TX,..Yes it has a Rev. limiter and it is set at 5900 +/- 100
So I would say your right your hitting the limiter..Your motor is rated for 5500 max. WOT........ Sherm

**Raceman** · 03-03-2003, 11:15 PM

Surely you're not quoting Sherm to contradict what John Marles and a couple of others have posted here. That would be roughly equivalent to walking in the Mayo Clinic and argueing with them based on what Dr's Larry, Moe & Joe said on TV.