Carbon deposits on plugs

[Moby]

This may have been discussed before but I couldn't find anything here or on the Catalina 30 site.

I bought a Catalina 30 with an A4 back in December and motored up to Maine in April. The A4 ran like a top.

Now, back at the ranch, I mean marina, I have been out about 16 time since the delivery and last time out the engine ran really rough. Pulled the plugs and lots of carbon deposits. Changed the plugs and it runs smooth again.

If I just use the engine to get in and out of the marina so that it never reaches the 160-165 degrees nominal temperature, how do I prevent the fouling? With the price of gas is it cheaper to replace the plugs or run the engine longer and harder to burn the carbon off?

Points and distributor cap looked great. Idles smooth with new plugs. Just little white puffs in the exhaust.

Thanks for your help! Some day mine will go from rust bucket to pinup!

Moby

[David Masury]

The next time this fouling happens... replace the Champion plugs with Autolite 437's... same gap as the Champions. The problem will go away.

David

[Don Moyer]

Moby,

Your plugs shouldn't need replacing every 16 hours, even given your operating conditions. I suggest you check your compression. Any compression values over 85 should be OK. I'd also check for the strength of the secondary discharge from your coil by removing the coil lead from the distributor cap and hold it close to the head while cranking the engine. You should be able to stretch the arc to at least 1/2". If those items are OK, I'd recheck for proper ignition advance by loosening the distributor hold-down bracket and slowly rotating the distributor a small amount in each direction to see if you can gain a bit of RPM. If you can, retighten the hold-down bracket in the location of max RPM.

Being relatively new to the Catalina 30, you might not have seen the attached technical notes which you might find useful.

Don

[Moby]

David,

Are the Autolite 437's a hotter plug? Someone else suggested I switch to a hotter plug.

Don,

Thanks for the suggestions. I will check each one and read the notes as well.

Great website and forum! Thanks for sharing your knowledge!

Moby

[High Hopes]

Moby,

I installed plugs without checking the gap. The gap was woefully to small and I got lots of carbon build up.

I'm not sure if this willl help, but in order to get my A4 running smoothly, I had to set the timing (17 degrees at 1600 rpm), gap the plugs, lean out the fuel mixture with Don's needle valve kit, and set the idle for 800 rpm and fiddle lots with the carb idle mixture valve. I also added a strong spring to the carburetor throttle to hold it shut. The throttle seemed to have two idle speeds when the shaft was wiggled. Oh yea, I pulled out 2 quarts of oil. (I now do oil changes with with three quarts. I was using 5). Plugs run clean now.

Steve

[Moby]

Thanks Steve. All good things to check. The plugs I pulled were the ones in the boat when I bought it and I did not check the gap but I did gap the new ones I put in to 0.035 in. I have not played with the mixture or timing yet. I really want to get through the summer without too much work on the engine and then pull it in the fall. I am not sure if I need a rebuild yet (haven't checked compression) but it certainly needs paint and a good going over (replace all hoses, add some upgrades...). Should keep me busy over the winter (that's our built-in maintenance period up here in Maine).

I have also decided it would be a good thing to zoom around the harbor once to get the engine warmed up and burn off any carbon before heading in. I think my problem is just like a car that drives 2 miles to work and back in the winter, it never gets warm. I also might want to check the choke to see if it is sticking.

This is my first boat with an inboard engine so I have lots to learn! This forum is a great resource!

Moby

[High Hopes]

Moby,

I puirchased a 1975 Sabre 28 in November last year. It is my first inboard and my first boat. Quite an experience! Maybe someday, I'll actually sail her.

Steve

[Moby]

One question that may be of interest:

Do you think that the carbon deposits could be the result of going from E10 (ethanol) gas to gas with MTBE? I moved the boat up from Connecticut to Maine this spring and am pretty sure E10 was used on the way up. Once I reached Maine I continued with the gas in the tank till I was about 1/4 full. I then filled with MTBE gas and had the problem shortly thereafter. After changing the plugs I have motored enough to use half a tank with out any problems. Of course, due to the amount of motoring, the engine has been run up to temp for good period of time so I am running differently than just going in and out of the slip.

Moby

[Moby]

OK, this is beginning to bug me. I put new plug in, checked the timing by warming the engine up, putting it in gear (tied to dock) and giving it some gas. I rotated the distributor one way until it started to run rough, went the other way until it started to run rough, then put it in the middle of those two spots. I checked the spark by pulling a plug and checking the gap to the engine block, got good spark.

Ran the engine for about 5 minutes, pulled a plug and it was loaded with carbon.

Oh, BTW, before I did all this I also pulled out some oil because I think I was over full. Now reads between add and fill. Didn't seem to make a difference.

That leaves me with the carborator. The choke seems to operate OK. Could it be the mixture?

[Moby]

Well, compression is OK. 100-105 psi in all the cylinders. We checked the choke again by removing the whole flame arrestor assembly and it looked like it was not opening all the way so we adjusted the cable so that it will. Ran the engine under no load, mostly idle for 5 min and plugs had carbon deposits. Running out of things to try!

[Moby]

Tried running the Champion RJ12C plugs. No difference. Ran around the harbor for about 20 min. at 5 knots and let the temp get up to about 180F. Still carbon fouled. Check the spark going to each plug and it was good. I normally operate at about 160F but ran it up to 180 to see if I could burn off the carbon. I usually flush the block with fresh water after running that hot.

At idle we pulled the spark wire on each plug, one at a time, and the idle speed/sound did not change. I even pulled 1&3, 2&4 and it starts right up and idles fine. Sounds a little different but not lugging or sputtering.

[Don Moyer]

How fouled do your plugs get? Do they foul to the point of the engine missing or running poorly? If there are no performance issues with your fouling, you may simply have a slightly rich fuel mixture. I would try to give the idle mixture adjustment an arbitrary 1/4 turn in a clockwise direction. If the engine still idles OK try another 1/4 turn. If you get to a point where the engine idles poorly, go back to the previous setting.

You can also install an adjustable main jet and lean your mixture. There are some carburetors from the mid-seventies (prior to the advent of the so-called five-bolt carburetors) that tended to run rich due to poor internal pressure regulation.


Don

[Moby]

Don,

Thanks for the reply. Yes, the plugs will get to the point where the engine will run rough and not have power. Usually after about 1-2hrs of operation.

I just found the "5 bolt carburetor" article and will check mine. The thing that baffles me is that the engine ran great for 5 days motoring up from CT. If it was a high speed mixture issue I would have fouled plugs on that trip. Why all of the sudden is it running rich now?

How many cylinders can an A4 run on? As I mentioned I pulled 1&3, 2&4 alternatively and the engine started and sounded pretty good. Maybe I'll try pulling 1,2,3 or 1,2,4.

Moby

[High Hopes]

Moby,

I read your postings and I'm not sure I understand everything.

Is it only when idling that you have soot showing up on the plugs?

Was it only after you changed the gas type that you had the problem?

Do you have a tachometer? (Are you really idling at 800 rpm?)

Did you drain all the oil out and only add 3 quarts back in? (I would ignore what the dip stick indicates.)

Do you have a timing light? I think it is best to set the timing to spec and make sure the distributor is following the advance curve spec (available on this site). I picked a midpoint and set it (while not under load). This was critical to a good idle.

Can you stall the engine at idle if you open or close the idle adjustment all the way? You be able to do this.

Did you rebuild the carb? The upper housing on mine didn't mate properly with the bottom housing. It was warped and leaked (air and gas). My main carburetor was a #24 which was too large. Do you know what yours is?

[Moby]

Steve,

Thanks for having an interest in my problem. After searching this forum I found several messages wrt carbon fouling and some did not post the final answer to their problem.

1. Idle or at full speed at 180F I still get carbon fouling very quickly, anywhere from 5 min to 1hr depending on when I pulled the plugs.

2. As far as I can tell the engine ran fine until I filled up in Maine the first time with MTBE. I'm pretty sure I was getting ethanol on the way up from Connecticut.

3. I don't have a tach installed yet but will put one in tomorrow to adjust the idle mixture and rpm. I seem to get fouling when I idle or go at top speed.

4. I pulled a little over a quart out to get it between the full and add marks on the dipstick. The oil is black after only a few hours but my friend who has an A4 says that is normal. He think the engine sounds OK, just a ticking which he hears on his too. My idle speed is a little low according to him so I will check it tomorrow with a tach.

5. I don't have a timing light and my flywheel is covered. I don't have access to remove the cover. That is a sweet setup you show in the picture. Looks like the engine is off the boat though. If not, you have great access!

6. I will try tightening the idle mixture screw to see if it will stall when it is too tight.

7. I just bought the boat and I don't think the carb was rebuilt although it is not painted so it might not be original. I just found out about the 4 bolt vs. 5 bolt carb so I will check for gaps between the body sections. I will take copious pictures of the carb tomorrow.

Thanks for your help!!