Merc Promax Issue og

Jus bought a 1991 Bullet 21VEE that’s Got a 2000 Mercury 225 Promax on it. Boat was running fine and out of the blue it cut back to only about 4600 Rpm max. Won’t get on plane unless you run someone to the front of the boat. Once on plane max 4600 rpm then all of a sudden run perfect for a half mile or so then cut back to low power. When it is running right you can stop and get back on plane normal and run good then all of sudden back to low power. Run good then bog run good then bog. Only thing I did before the issue was change plugs. Went from BUHW to BR9HS gapped on 40. Figured Plugs should b changed for jus to know they were fresh. In neutral engine will rev up fine coughs a lil as it is decelerating but revs fine. Just under load the issue of not accelerating is happening. Any help is appreciated. I know Jay Smith and Chris Carson are a Promax guru well any outboard guru I should say hopefully them or someone like them sees this post. Thanks in advance

they are most likely too cold

try BR8HS

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Originally Posted by TEXAS20225

try BR8HS

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Had the BU8H in it not sure if they are hotter or colder but did it with them too. Wanted the BR8HS but local shop didn’t have em

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Originally Posted by TEXAS20225

try BR8HS

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Had the BU8H in it not sure if they are hotter or closer but did it with them too

its NOT plugs... tha bu8h's or buhw's should run jus as good as any.. what it does in neutral and/or ona hose will never be same as under a load.... sounds more like a switch box?.. maybe droppin' a cly. or two for whatever reason?...... but we're settin' here ona computer so..........................................................................

Check your plug wires for good tight connections or damage.

Think you answered your own question stating the issue started after plug change. Never know box could have been dropped during shipping making the plugs an issue. As Bobby said try a set of BR8HS and see what happens. Also as Tux stated the steel connector that clips on the top of the plug inside the boot can get loose. You should feel a positive snap as they clip on the top of the plug, if they are loose you can get strange things going on at different rpm.

Dave

Have seen some chat about amazon plugs are counterfeit china knock offs. If purchased there?

Did it with the old plugs too tried changing back

Run it in the dark, mist the wires with a spray bottle of water if you have a spark leak it will show up.

Dave

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Originally Posted by Euroski

Have seen some chat about amazon plugs are counterfeit china knock offs. If purchased there?

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Bought the plugs from Advance Auto Parts they had them in stock

weird it started when you changed plugs

Still chasing the issue waiting on a DVA adaptor to come in the check the issue further