Merc 260 high speed miss

[kush3406]

Hey,
I have a 2 year old 260 merc rebuilt from soup to nuts. Used all last season no probs. After a proper winterizing at the end of last year I pulled off the cover tuned her up with all merc parts new gas and dropped her in the water.
Runs great until around 3500 rpm then after a minute a miss starts and takes the rpms right back down then it goes away and starts again as soon as I bring it up in rpm's again. Its good for a minute and then it comes on????

Any Ideas???? Things ive eliminated as probs Cap, rotor, plugs, fuel, fuel pump. no water in any plugs.

Capt Kush

 

[Haut Medoc]

Re: Merc 260 high speed miss

Welcome to iboats.....
Plug wires?
At least a visual inspection to make sure none are chafed?......
What year?.........​

 

[ppagss]

Re: Merc 260 high speed miss

Hello. Capt. Does this happen at all temps? Depending on what year motor you have I would check for point floating. If it has points, check the contact ends, If there is build up of metal on one side you have a bad condensor. If you have the thunderbolt, I would start with the coil, eliminate that and than the module. Also, have you changed your water seperator? Another thing to look at is your charging voltage, batteries look normal(gauge) when RPM's drop? Hope this helps you eliminate some possibilities.
Pete

 

[kush3406]

Re: Merc 260 high speed miss

Thanks , nice place ya got here.
Went through wires swapped with my buddies boat all good.
I'm leaning towards a coil or that control box on the riser.

Thanks for the reply

Capt Kush

 

[Don S]

Re: Merc 260 high speed miss

While it could be either the coil or the ign. module on the riser. Disconnect the harness from the module and look at the pins and the connector. It doesn't take a whole lot of corrosion to cause a high speed miss or an advance problem.

 

[kush3406]

Re: Merc 260 high speed miss

Thanks Pete
No points, Thunderbolt ign its an 84. Water seperator Ok Fuel good.
Batteries good (got 2) Volts good. Temp so far does not seem to be a prob she runs cool 165. Im gonna swap my bud's coil tomorrow if that dont work i'll go to the control box.

Thanks man

Capt Kush

 

[kush3406]

Re: Merc 260 high speed miss

Thanks Will do Don.

Thanks
Capt Kush

 

[kush3406]

Re: Merc 260 high speed miss

OK

I changed the coil. The boat definitely runs better but the miss is STILL there.
Cleaned wiring harness connection as well. I'm thinking its the control
module (on the riser) I fixed a running hot prob a few weeks past The riser with the control module on it was quite hot until I repaired the prob. Used it for about an hour then realised it was hot and fixed. Maybe that hour fried the box??? it has insulation spacers but I dont know if they are enough to protect it when running that hot?

I'm sunburnt dirty and theres saltwater in my beer.

Capt Kush

 

[Reel Poor]

Re: Merc 260 high speed miss

It's possible it's the module but I didn't see where you changed any plug wires. May be a bad coil wire breaking down or arching to the top of the coil once the motor warms up a little.

 

[kush3406]

Re: Merc 260 high speed miss

After going through 2 sets of wires I have eliminated them as a prob.
Wires ran fine on my buds boat. I was very careful to make sure all wires are on tight and well seated I checked the firing order against the manual.
Its really getting to me. I cant work on it today weathers bad here in NYC.

I'll keep plugging away at it

Thanks for all of your advice it keeps me thinking.

Capt Kush

 

[kush3406]

Re: Merc 260 high speed miss

Well I Finally fixed it. I replaced the module and the amplifier box.
Runs like a raped ape its back 100 percent. Striper fishing N.Y. bay nothing better.

Capt Kush

 

[180shabah]

Re: Merc 260 high speed miss

Glad you got her running.