'94 Echelon mis-fire, 265hp carbed Merc Magnum Skier

[Michigan boarder]

There was a slight misfire in the boat last fall. So, when winterizing I put in new plugs, wires, cap and rotor. This spring I felt it again, and thought I'd get thru the current fuel. Well, I'm on the 3rd or 4th tank and it still does it. I have ran 3 small jugs of fuel treatment too. I changed out the fuel filter/water separator. I put a new coil in a month or so ago (the old one had oil leaking from the top where the wire to the distributor attached). Checked cap and rotor, and they were mostly clean. I scraped off some slight corrosion, so they are like new.

The misfire is very faint, but noticeable. The boat seems to run smooth, but I can hear slight pops out of the exhaust. If I am running thru any chop I can't hear it at all, but if I ask one of the rear seat occupants they will confirm "Yes, it's still doing it". RPM's and acceleration are strong even at WOT, 4600 to 4800. Misfire is more noticeable then, but still very hard to hear. Several times I thought it went away, as in last Saturday, but my wife said she still heard it occasionally. I never heard or felt it as the driver, nor as a rider.

What's left? What am I missing? I have not checked timing, but could that have changed? Time for a carb rebuild over the winter? I do have a new cap & rotor in the package, should I put them on?

[jk13]

Carb cleaning to start. You wouldn't believe the amount of corn syrup we washed out of mine. 6 straight hours in the parts washer with the hose on top. Also, there is a clear (well, probably yellow now) tube from the carb down to the fuel pump on the driver's side of the motor. Check that for clean as well, mine was completely plugged with syrup as well as the port on the pump itself. Throttle response and idle are much improved.

Other than that--and I hate to even mention--but it could be the Thunderbolt IV ignition/distributor. That's beyond my old-school troubleshooting, though.

I've also been meaning to update/upgrade all the power wires and grounds on mine to eliminate any future electrical issues, kinda like doing the "big 3" on a car for a big stereo. Just peventative maintenance on a 20 year old boat.

[martinarcher]

Could also be he fuel pump on the way out. I installed a fuel pressure gauge between my pump and the carb to help diagnose. When mine would act up the fuel pressure would drop 2-3psi when watching the gauge.

[Michigan boarder]

Thanks guys. This weekend I will go thru all of the electrical connections. If that doesn't do it I'm going to remove the carb over the winter, have it boiled and I'll rebuild it. I'll check that hose too JK, I know exactly which one you are talking about.

MA, how much is a fuel pump? Looks like an easy swap, right?

[Woodski]

Fuel pump is an easy swap, and not too expensive. I would strongly suggest a leak down test, this will tell you if there are any leaking valves, that is an area you would hear a miss, particularly through the carb, which is very audible in the cockpit. A carb rebuild is a maintenance item and needs to be done every few years particularly with the ethanol fuels now on the market.

[Michigan boarder]

Fuel pump is an easy swap, and not too expensive. I would strongly suggest a leak down test, this will tell you if there are any leaking valves, that is an area you would hear a miss, particularly through the carb, which is very audible in the cockpit. A carb rebuild is a maintenance item and needs to be done every few years particularly with the ethanol fuels now on the market.

Thank you, Woodski, I'll add that to the list. The boat is going in a heated building where I'll have lots of opportunities to wrench on it this year (unlike the last 2 years). But, the missfire is not easy to hear from the cockpit, even when I am leaning back towards the engine listening for it. But it is definitely heard thru the exhaust.

[Woodski]

Make sure when you go through the electrics you check all the ground connections, that is a source of electron trouble. Also, make sure all the terminals on things like the ignition switch are tight, battery terminals, etc.

You can check the plug wires by running the engine in the dark and looking for arcing, pretty easy to see. Boat engines are not hard on wires as they have water cooled exhaust.

Another thing to check, exhaust manifold gasket leaks, that is not uncommon and makes a noise much like a miss. Look for carbon traces around the ports. My boat eats manifold gaskets since I have both aluminum heads and exhaust manifolds, the expansion rate eventually wears out the gasket in a thinner section.

Sounds like potentially exhaust valve from the source of the noise being in or at the exhaust pipe, if the leak test shows something (over 20-25% leak rate IMO and a definite sound through the exhaust). Make sure you do it with the engine warmed up, not cold.

I have noticed these engines can miss a bit in colder weather or with a too cold thermostat. If you are totally lost, try a 160 degree stat and see what happens.

[Steve B.]

Make sure you have all the plug wires seated well at the distributor and the plug. I'd do that first. Look for any black spots on the wires to see if it's arc'ing somehwere.

Clean the umbelical connection at the engine too. Just electric contact cleaner.

Steve B.

[JasonK]

Could be the coil. We had one fail last week. It would only miss under load. Was sometimes hard to detect (hear).

[Michigan boarder]

Update:

So I checked the coil, the plugs, the wires, the cap, the rotor, the ignition connections, and the cannon plug last fall. All was good. No signs of arcs or anything. I stabilized the fuel and ran it in the driveway last Labor Day weekend, in Sept of 2012, and put her away for the season. Over the winter I never had a chance to service the carb. I finally got a building set up for me to work on it in April but had to take care of too many other problems.

I ran it in the driveway last week, and it started right up and idled very well, very smooth. I put it in the water last night (first time in the lake this year) and idled around. Seemed to be fine. Went for a slow, idle ride this morning with coffee. Gave it some throttle and it ran rough, like it was on 8 cyl, then 7 for a second, then back to 8 for 3 seconds, then down to 6, then up to 7, then 8, then 7, etc. Ran better at half throttle. Ran worse with more throttle.

Brought it back in and put it on the lift, and again checked all ignition components. All seemed good. But I do have a question on the distributor rotor - should I be able to move that by hand? It rotates like 1/16th of a turn if I try to turn it. It is solid on the shaft, but the shaft moves. Is that normal?

Next I got a can of carb & choke cleaner. While running I sprayed it pretty liberally (also with a towel next to me ready to throw it over the carb in the event of a back fire) into the carb (with safety glasses on too). I put my throttle switch in neutral and controlled the throttle at the carb, revving it so 3 or 4k RPM while spraying. It seemed to run really smooth while doing all of that. I thought I had it cleaned out. I shut it down and put the flame arrestor back on, and went for a ride. It ran horrible, losing power to the point of dying. It did start right back up, and I idled back in (a few hundred yards). To keep it running I had to feather the throttle around.

So....to me this is an obvious sign that I need a carb rebuild, correct? I took it off and brought it home. What carb kit do I need? Any suggestions or tips on rebuilding? I've rebuilt them in the past, but it's been like 20 years. I can post pics if necessary. We are going back to the lake on Wednesday, really hoping to have it ready by then.

[Michigan boarder]

So I figured out that I have a Weber carb, #9770S 0704, primary plate #291, with a manifold choke. I can get a brand new carb with a 1 year warranty for $471.07 to my door, minus a $128 core charge when I send my old one back (postage paid) from flying fish carbs. So I would net $343.07 for a new carb that I simply bolt on.

Thoughts?

[Michigan boarder]

Additional thoughts...should I have ran more carb cleaner through it? Like the whole can? I used maybe a sixth of it.

That yellow hose was only partially plugged by the entry point into the carburetor. Mostly clean. I'm going to replace that line regardless.

I already did the filter last year, but didn't this year. Wishing I would have maybe waited and done that first. Either way this carb looks dirty. When I tipped it upside down some nasty looking syrup came out. I took a pic. of it in a bucket. I know the fuel is not that old - from last fall but also stabilized.

Lastly, there is no filter/screen at the carb. I remove the metal gas line and expected to see some kind of screen, but found none.

[Woodski]

It does sound like the carb needs a good servicing. It will be key to clean out the small passages that really control the off idle mixture along with the accelerator pump nozzles. You shouldn't need a new carb unless the throttle shafts are loose in thier bores, that could happen if the throttle tried to pull on them and created a wear pattern. A thorough carb cleaning and rebuild can make a significant difference. If you order a unit you will want to verify the calibration (jets / needles / springs / accel pump) as there are numerous options to get the correct mixture for your application. That can make a big difference on how it will run.

There shouldn't be too much slop on the rotor, but there is the distributor gear to cam gear engagement where you might be feeling some slop. Exhaust popping, if not a mixture issue could be head gasket or valves, although your description points to the carb and debris buildup.

[Michigan boarder]

Thanks Woodski. I did call them to double check the settings and I was guaranteed that, with the application information I provided, it will be a bolt on replacement. The only possible adjustment would be the idle air screw. I paid the extra shipping so it would be here by Wednesday, in time for me to take it with me to the lake Wednesday night.

Some guys are probably like "Dude, just rebuild it! You don't need a whole new carb!" but I simply am out of time. Yesterday was supposed to be my first day behind the boat, and it didn't happen cuz it wouldn't run. I don't want to rebuild the carb, then bolt it on Wednesday when I get to the lake and have problems. Cuz then I'm back to work on Friday, then down to the lake Saturday with lots of company (no time for repairs) and then back to work again Sunday. Not sure if I'll be there the following weekend or not. Well, the summer is half over by then. I read some threads on here with Levi and others that rebuilt their carbs and there are small problems to work thru as they do that and I just don't have the time. So I'm going with a new one and at least I know that part is good to go. I have no intentions of selling the boat anytime soon either, so I'll recoup the carb investment over time.

This is what came out of the carb:

[Michigan boarder]

The carb itself:

[Woodski]

She is certainly looking for some love by the owner! The new carb should help, the molassis certainly is not doing you any justice:) I highly recommend one of David Vizards carb books, he covers the Weber / carter AFB style carbs in detail along with numerous performance tips (that work well by the way). Now that you will have 2 carbs, I would recommend rebuiding the original (to refresh it and to keep it from deteriorating more) and keeping it as a spare or experimental carb if you want to spend some time playing around (see earlier comment on Perf. tips) to improve your existing performance. Items that can be improved on via alternate jetting / accelerator pump size & setting / calibration needles & springs / secondary flapper include throttle response, initial acceleration response, smoothness. It does take some time and effort to get what you want in the end. It also will be needed if you plan some other mods such as exhaust / heads / cam ala MA and myself. Have fun.

[AdeL]

Hey Michigan Boarder. A couple of years ago my Echelon had starting problems when it was warm. So much so that I burned out my starter motor on one particular outing. One of the benefits of having an older carbed boat is that it is less involved than fuel injected or computer controlled boats. I decided that the problem was the low speed jets in the carb. I found a local car mechanic, who by luch specialized in carbs and starter motors. He acid bathed my carb, rebuilt it, which included new jets, seats and seals. I re installed it and I have not had any issues since. He charged me $120 and he did it overnight. Try and find a local muscle car mechanic. I'm sure there must be loads in Michigan due to it being home of old muscle cars.

[Michigan boarder]

Hey Michigan Boarder. A couple of years ago my Echelon had starting problems when it was warm. So much so that I burned out my starter motor on one particular outing. One of the benefits of having an older carbed boat is that it is less involved than fuel injected or computer controlled boats. I decided that the problem was the low speed jets in the carb. I found a local car mechanic, who by luch specialized in carbs and starter motors. He acid bathed my carb, rebuilt it, which included new jets, seats and seals. I re installed it and I have not had any issues since. He charged me $120 and he did it overnight. Try and find a local muscle car mechanic. I'm sure there must be loads in Michigan due to it being home of old muscle cars.

Thanks Adel, but with short notice and the holiday I just went with ordering a rebuilt and bolting it on. Figured with the time crunch everyone would be busy.

[Michigan boarder]

So I got the carb, looked great. Put it on, ran it for a minute at idle, then 20 seconds on plane. Same problem. Changed the fuel filter again and put gas drier in the tank. No improvement...got a little worse. No longer erratic, running a couple cylinders short. Started pulling spark plugs and found this with the second plug I pulled, #5 cylinder . The ground electrode is smashed down into the center electrode. Rough texture on all of it. Got out the compression guage and zero compression in #5 and 20 PSI in #3. All others 139 to 150.

Season over. Time for a new thread.