Black Carbon Plugs
 

My Hp500 started up this season with no problems. The motor has 132hours on it since new. After 1/10 of an our it started running rough and missing, it stalled a few times. I got it back to the dock and on the trailer. I pulled the plugs and they were carbon filled. I changed them out and put in ne AC DELCO Mr43T plugs. The boat ran great for the rest of the day. The boat sat a week. I started the boat and it ran a little rough, skipped a few times. Then was ok, ran it for another 15 minutes or so and decided to pull a plug. The plugs were all the same as before, dry carbon, solid black., the plugs are the correct ones, the wires are new, cap and rotor are also. Could the choke be causing this, or is the carb out of adjustment?? Any help would be greatly apreciated. I know the motors are better running a little rich but I should fol plugs after 15 minutes.

Re: Black Carbon Plugs
 

Could it be the choke heater, if so how can I easily check it? Or doesn't this sound like a choke issue

Re: Black Carbon Plugs
 

I Don't Use Mr43t In My Hp's Use Ngk-ur5(v-power)
Much Better Plug And Once The Motor Warms Up
Take The Air Cleaner Off And See If The Choke
Is All The Way Open. I Took My Choke Off.

Re: Black Carbon Plugs
 

I do use MR43's in mine and have never fouled a plug. I would also start looking at the choke.

Re: Black Carbon Plugs
 

Could the choke just be gumed up, should I spray some choke cleaner.on it.

Re: Black Carbon Plugs
 

let the motor warm up and take the air cleaner off and the choke should be open. if it's not then thats you'r problem.

Re: Black Carbon Plugs
 

Idle mixture is too rich causing your plugs to fowl. Turn in your idle mixture screws and back out 1 1/2 turns to start. Use a vacuum gage to obtain maximum pressure. Make sure that you set all of the idle screws and don't forget to count number of turns in.

Re: Black Carbon Plugs
 

How many idle mixture screws are there

Re: Black Carbon Plugs
 

Just get a small wire tie and wire the choke open. See if it solves the problem and go from there.

Re: Black Carbon Plugs
 

Do you have fuel pressure guages? If it's a mechanical fuel pump soemtimes they make to much pressure as they get old and will push fuel passed the needles and seats in the carb. Just had one do it changed the fuel pump and all is better.
Oh ya the fuel pump was a Holley only 1 year old.

Mark

Re: Black Carbon Plugs
 

How about going up a couple notches in the heat range of the plug. Also, gas stabilizer of some types leave soot. Good luck!

Re: Black Carbon Plugs
 

My carb has (4) One for (each) Primary and One for (each) Secondary. You can also remove them and spray carb cleaner in each hole. Then spray carb cleaner into the air bleed valves. Make sure when removing idle mixture screws not to loose them cork o-rings which prevent the screws from vibrating loose. I'd check that you didn't blow your power valve also.

Re: Black Carbon Plugs
 

Odds are, if the boat was running fine when you put it away, you probably don't have to start screwing with the carb (yet). Before you do anything else, as was said before, make sure your choke is opening fully by taking off the air cleaner, and observing the choke valve. Then, run that old gas out of there. Especially BEFORE you start turning screws! New gas sucks, and even with stabilizer, I've had engines act tempermental until I got some fresh gas in there. Yes it is possible that something got gummed up or stuck over the winter. I had this happen to me last year. My boat was running real rich, and when I removed the air cleaner, and took a look down the carb, I saw raw gas pouring out of the boosters (Rochester). Turns out the float got stuck. A simple fix, and 15 minutes later I was good for the season. If all else fails, then you might have to start adjusting. My point is..Keep It Simple!:)

Re: Black Carbon Plugs
 

Yea its real hard to count the number of turns on those idle screws. Speaking of getting gummed up. I never heard of those air bleeds getting gummed up either. NOT!

Re: Black Carbon Plugs
 

I Will start with the choke and go from there tomorrow. I will also spray choke and carb cleaner. Also a good time to blow through a tank of gas, maybe that is the culprit too. Is there anything I can do to tell if the float is working properly without tearing into the carb??

Re: Black Carbon Plugs
 

Get yourself some clear float level sight plugs to check float and fuel levels.

Re: Black Carbon Plugs
 

I'm not saying that it's difficult to turn the idle screws, I'm saying if they were ok last year, why would they be out of adjustment this year? Gremlins???
I agree with checking the float levels. They can stick. If a float is stuck, and dumping gas, you might see gas coming out of the "J" tubes or the boosters. If you look in the carb while the engine is running, and see raw gas dumping in from anywhere, something is wrong. There are other things that can cause a rich condition, like a ruptured power valve (Holley), dirt lodged in the float seat, etc. If it's dumping enough gas to foul the plugs, I can't beleive an idle mixture adjustment alone would cause that. Especially if no one touched it while it was in storage. I'm just telling you what I would do before making any major adjustments. I've been working on cars, boats, motorcycles, and electronic equipment for almost 30 years.
Some professionally, some as a hobby, and anyone who has any troubleshooting experience will tell you, Work systematically starting with the easy stuff, then work towards the more difficult things. It's always worked for me.:)

Re: Black Carbon Plugs
 

Idle mixture screw if turn out too far will cause a rich mixture and dump fuel into the carb causing the plugs to fowl during long idling or traveling through no wake areas. A stuck choke or improperly adjusted float level will cause a similar result. Power valves can easliy be ruptured from a backfire. There isn't just one answer it could be any of the above. I'd rather have as many options as possible instead of trying one thing one day and then another the next day. Beside getting "CHECKROCKET" back on the water and everyone learning from the technical board is what forums are all about.

Re: Black Carbon Plugs
 

I am heading to the lake today and see what I can do. I am hoping for success. If its not the choke and I clean everything out. I am going to run the boat for a while and burn off some of the gas from last year, then I guess I will try the mixture screws and some new plugs so I can get a reading, does this sound like a good order.

Re: Black Carbon Plugs
 

The power valve was bad on my motor. However I need to get the air and idle mixture correct. I see that I should start at 1.5 turns after seating out. Does closing off the mixture screws to lets say 1.25 make it richer or leaner?? I just want to be on the correct page. Also, I believe before this problem started my HP500 idled at 750rpm, is this what I should shoot for??? Any help would be appreciated, Also where should the large adjustment screw on the throttle side be at. What exactly is this adjusting??

Re: Black Carbon Plugs
 

I don't have a Merc manual near me but I think you may have to ground out the purple/white timming wire from the module. I'm thinking the V module will fight to keep the idle at 750rpm's. You should be able to use a tach and vacuum gauge to set your idle mix adjustment screws then use the main throttle adjustment to touch it up or down to your 750 rpm's.

I hope someone else can confirm this but I'm pretty sure this is the procedure for that set up.

Re: Black Carbon Plugs
 

When I put the carb on it idled high. It was idleing at 1000-1100 rpm, So i turned the large screw on the carb near the throttle till it idled at about 800. I think I did the wrong move. The boat ran good but the plugs were still rich, should I turn it back to 1000rpm-1100rpm and then adjust the idle adjustment screws to lean it out till it makes 750rpm at idle. Please help its almost there, I did a plug reading they are still black carbon, but it ran, i think it just needs a little adjustment.

If I need to get a vacuum gauge, where would I attatch it to get the proper reading, and where can I get one and what should the reading be.?

Re: Black Carbon Plugs
 

When I put the carb on it idled high. It was idleing at 1000-1100 rpm, So i turned the large screw on the carb near the throttle till it idled at about 800. I think I did the wrong move. The boat ran good but the plugs were still rich, should I turn it back to 1000rpm-1100rpm and then adjust the idle adjustment screws to lean it out till it makes 750rpm at idle. Please help its almost there, I did a plug reading they are still black carbon, but it ran, i think it just needs a little adjustment.

If I need to get a vacuum gauge, where would I attatch it to get the proper reading, and where can I get one and what should the reading be.?

Re: Black Carbon Plugs
 

When you put the carb back on and it was idleing high you more than likely had a vacuum leak at the gasket. Here is the info for adjustment.

Holly Tech

Re: Black Carbon Plugs
 

Check,
I'm glad you were able to find the problem. I wasn't too far off, I did mention in a previous post that a bad power valve could be one of the causes of such a rich condition. The important thing is you found the problem, and now with a few adjustments, you'll be back on the water.