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Mercury 500 High rpm random misfires

You might try this (since you're out of options): Back OFF the timing about 4 degrees (thanks to the crappy gas we're stuck with).

Here's why I say this: Just recently I torched my beloved triple that was timed at the "correct" setting of 23 degrees. Massive pre-ignition coated two pistons with aluminum--nasty.
Unlike previous runnings, it bogged lkike crazy on plane off since I was running a BIG prop for the first time. (Before, it cavitated like crazy, getting the rpms up into the power band and running 6,500 rpms atfull speed.)

With that big prop I had to sit on the bow to get it to plane off, as it bogged like crazy, and the rpms barely made 5,300 at WOT. (Befoe it screamed to 6,500 effortlessly with its smaller prop.) My point is, I GOT AWAY with runnign 23 degrees before because the motor never labored.)

Worth a try?

Jeff
 
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the diaphragm is good. like i said i just rebuilt it with a kit. and i just took it off to double check and its still great. the funny thing is that it is mounted on cylinder 2... which seems to have less oil on it

and this is my second set of plugs and i have switched them around
 
If i squeeze the bulb hard without the motor running at all and i look at the carbs i can see fuel coming out the idle tube? is that normal?
 
When you squeze the bulb hard, that CAN happen since the fuel pressure is roughly three times higher then. It should not leak when the motor is running (and not squeezing the bullb).

Jeff
 
guyjg said:
Jeff: Could it be related to an exhaust blockage?
Click to expand...

went down and bought a used block today after a slow slow day at the river. got my old one off and what do you know... exhaust hole was completely blocked off with pieces of charcoal like pieces.

pulled them out put it all back together. runs like a dream.

thanks you guys for all the help and ideas.
 
Well I'll be! Previous owner must have used a non-two stroke oil to have that happen.

Haven't heard of that sine the "old days" (the 50s) when it was a common occurrence.

Jeff
 
Wow I have been following this thread and was fascinated by all of the different directions and thoughts. How strange that the "Exhaust Blockage" thought was a one liner by guyjg, last post on the first page with no other comments on the matter..................
@ Burner67, I would love to see a video that motor running now, can you post something for us?
 
Wow what a feeling getting that screamer screaming again. Nice stuff, congrats and long may it last. The face said it all:D
 
haha yes it's a great feeling having a strong motor i can have confidence in!

on the sync i set the throttle engagements while in gear but i have yet to set max advance in gear with load. i can't do it at home in the barrel it will blow out all the water. i have it set to 34 degrees revving in neutral. when i have more help i will be checking it on the river
 
yeah i have used the sea foam spray a couple times before i got the exhaust fixed but i will definitely do it again and maybe start putting sea foam in a tank of gas once in a while.

what do you guys recommend for fuel? i have a hard time finding the fuel with no ethanol in it and when i do it has to be premium $4.25/gal
 
$4.25 a gallon for premium is a "super bargain" - regular is going for $4.91 a gallon on my side of the border. And agree, anything over 86 octane is more than fine.

And I will buck some of the "common wisdom" - running ethanol gas in your boat is not a bad thing - it actually keeps your fuel system "cleaner" than non-ethanol gas (you can use ethanol as a carb cleaner).

BUT - ethanol does attract and hold moisture so always run it with a fuel stablizer unless you go through a whole tank in the course of a weekend.

I ran E-15 for three seasons (had a "test" station in my area that was selling 89 octane E-15 cheaper than regular - coming soon to a station near you) and had zero issues. The test is over so I'm back to E-10 which I have been running for well over 15 years now - again, no fuel related issues.
 
...running ethanol gas in your boat is not a bad thing - it actually keeps your fuel system "cleaner" than non-ethanol gas (you can use ethanol as a carb cleaner).
Click to expand...
I agree w/you. Keeping it stabilzed is the key.
 
That's exactly what it means - the percentage of ethanol mixed in the gas.

Point to note - particularly for future reference (read that the EPA is pushing for higher percentage of ethanol levels on your side of the border).

While ethanol does burn "cleaner" than gasoline, it's octane is not up to snuff which is why the E15 we were testing up here was 89 octane. The gas itself was 89 octane but with 15% ethanol it reduced the "overall octane" to about 87, which is just regular gas.

So if the day comes where they are pushing 20-25% ethanol we will have to be running "premium" as the basic gas in our older outboards. And if you think it will never get there, E-85 (85% ethanol - the 15% real gas is needed for cold starts) is already widely available to certain fleet vehicles (that's what the "flex fuel" sticky means on vehicles already sold in North America - they can burn E85 without any retrofit)
 
E-85 is keeping the price of corn up in the corn belt here in the USA; Kansas, Nebraska, etc. Yes it's octane is not up to snuff but I expect the US GOVT. to force automaters to make all gas fueled vehicles "flex fueled" by 2020. One side effect from doing that will cause a reduction in demand for foreign oil unless the lobbyists get their way. I hope the E-85 and oil lobyists duke it out by having a price war.


Right now a 25 gal. tank of Shell gas for my boat costs $96. Cabela's synthetic blend 2 cycle oil is about $9 for 64 oz. (1/2 gal.) Since hot weather has arrived I only fish at night which cuts down the fuel comsumption w/a 10 mph speed limit after sunset.
 
We're burning our FOOD for FUEL! Am I the only one who sees this as bad policy? And when you consider that 4 THOUSAND items in a grocery store are corn based...

Furthermore--despite what you read--ethanol is an energy loser. It takes 8 units of energy to make ethanol that produces 10 units of energy, and guess where that energy comes from? (Coal.) Loser! It can't be piped to the refiners, so diesel trucks have to haul it all over the country--loser! And it takes more ethanol to create the same gas mileage--loser!

Finally, the USA is sitting on a MOUNTAIN of oil, both in the ground, in shale and just off shore. Despite this, we continue to pour trillions of dollars in middle east country's pockets for THEIR oil--does that make any sense?

Decades from now, serious historians will look back at this era and shake their collective heads. What thell were they thinklng? they will all wonder.

Jeff
 
Can't disagree with on that one Jeff (and have to watch my comments - after all I live in that country that not only burns, but tries to export that "dirty tar sands oil").

But as long as the Cappuccino drinking tree huggers have the ear of the people making the policy we'll be burning fluids that would be better served in a glass bottle from the liquor store :)

(hmmm, isn't bourbon just ethanol with a label on it?? )
 
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