Fouling All 4 PLugs

[Vermonstah]

All,

Glad to hear from Mo that the overall fleet of A4s seems to be doing well of late. Unfortunately, I cannot claim that my A4 is thriving of late.

All summer, I have been fouling plugs. All four of them, and quickly. As in, less than an hour of motoring under load with new plugs will yield four carbon-encrusted plugs. When I can get her started with a new set of plugs, she idles well and runs strong under load and will do so for several hours.

I have tried both the Champion RJ12C and the Autolites from MMI - same result.

Some background:
1. Late model engine on a C&C 27 Mk I. Original engine from what I can tell. New to me two years ago. RWC, running in cool Lake Champlain.
2. Season 1 chasing cause of overheating issues. Resolved by extensive flushing. Engine now does not get above 150 degrees under load so Holley t-stat never opens.
3. Season 2 chasing cause of sticking valves. Resolved by replacing faulty (paper) head gasket.

Here is what I know:
I. Compression was good in all four cylinders to start the season (90 +)
II. I started the season with a clean fuel tank, and re-fueled with ethanol free 91 octane.
III. I started the season with a new MMI coil which produces a good spark.
IV. I have a modest fuel leak somewhere in the vicinity of the lower bushing of my carb. Carb does not leak while engine is running.
V. I have significant amounts of soot accumulating across my transom in line with the "tailpipe" thru-hull.

Here is what I don't know (among many other things about my A4):
1. Where do I begin the diagnostic testing to determine cause of fouling plugs?
2. Do I begin with checking for excessive back pressure?
3. Do I begin with adjusting the carb for the mixture?
4. Do I begin with re-checking timing?

I don't yet have the MMI back pressure gauge, so I have not done #2 above. I have done #3 and #4 repeatedly.

I am not very bright, so the "idiot proof" sequential, diagnostic tests that this forum is famous for providing, I think that is what I need.

Thanks in advance.
Brian

[JOHN COOKSON]

Brian
A quick and easy one. Is the choke all the way open when you think it is?

TRUE GRIT

[Dave Neptune]

If the choke is fully open the first thing to do is fix the leak in #IV. An abundance of fuel will foul the plugs in short order.

Dave Neptune

[edwardc]

Excessively rapid plug fouling, and carbon soot on the transom, both suggest an over-rich fuel mixture to me.

Since you have a late model, it doen not have an adjustable main jet on the carb (unless you installed one). The "mixture" screw is actually an air-bleed adjustment (more open == more air) that only affects the idle mixture.

As mentioned, an incompletely opening choke plate can result in an over-rich condition. Similarly, dirt in the carb float needle valve can result in the same thing.

Since you report a fuel leak at the lower bushing, this would support the theory that the float valve is not shutting completely, allowing it to dump too much fuel into the throat, where is sucked up by the scavenge tube, but not before some leaks out thru the bushing.

The cure for all this is to disassemble the carb, and clean it, and replace the float needle valve.

[Vermonstah]

Confirmed the functionality of choke

Thank you for the timely feedback.

We have confirmed the choke is performing as it should.

So, I will turn my attention to the innards of the carb which does not have the mod for the adjustable main jet (far as I can tell).

I have previously messed with the float so that might explain the cause for an abundance of fuel / over-rich mixture.

Thanks again!

[sastanley]

have spares on hand

Vermonstah...if it has been a while since you removed the carb, be sure to have spare gaskets (flange & carb bowl) on hand. The carb bowl gasket is delicate, and the way the carb comes apart often damages it. I usually get pretty lucky with the flange gasket, and it stays intact, but I never count on the bowl gasket surviving a disassembly..additionally, my thought process is, if I am having troubles, why not replace it with a nice fresh gasket anyway?

Every time I prepare to place an MMI order, I go thru my spares and update my gasket inventory..I like to have two of everything that I might change in the field in my box...like all carb gaskets, water pump, impeller, etc. I like to carry one spare set of major things like head gaskets (2), valve cover, water jacket side plate, etc. This way, if I have a repair to make at the dock, I should be able to get the engine back up and running without waiting for parts, and can replenish my spare supply at me convenience.

[Vermonstah]

Order placed with MMI

Thanks Shawn for the advice to have good collection of spares on hand. In addition to the associated gaskets, I ordered a new float and float valve. I am not entirely confident that I can restore the existing carb to good working order, but if I can, it will become the jewel of my spares kit since I also ordered a new carb. Parts due late Thursday so I will update the thread with my progress.

Thanks again for the good counsel from throughout the forum.

[sastanley]

vermonstah..I was chasing what I thought was a chronic issue with my carb, so I ordered a new one last year too..turns out it was totally unrelated, but it is nice to have a shiny new carb and a good spare on hand. Taking the carb apart in the cockpit in the middle of an anchorage is not really my idea of fun.

[wlevin]

fouling plugs

We had the same problem with fouling plugs this season and for a week messed with the carb (which I had rebuilt last winter) to lean out the mixture for before finding that the points setting (should be .025) had slipped to .010. Weakened spark and inefficient combustion, it seems. Fixed!
Bill and Jeanne
Tartan 34C #453
Otter

[sastanley]

Bill..good point. I had a '78 Civic and I had to periodically pull over and re-adjust the points as the set screw was stripping, and they would close up on me after prolonged highway runs. A streetlight usually worked well enough to do the job at night and get rolling again.

[Mo]

EI...I always said either / or.

Electronic ignition, new coil and resistor is not a bad option. My spare engine sitting in the garage had EI on it and Dave Neptune talked me into installing it. Changed over the coil and external resistor on it as well and I've run the engine for 6 hrs straight at times without an issue. I didn't have an issue with the points and condenser, but the EI is still more efficient and trouble free. It took me about an hour to do the switch and that was taking if off in the garage, driving to the boat and installing it.

For those wondering if EI is a decent option?? Sure is, but also put a new coil and external resistor as well ...works perfect.

[67c&ccorv]

Thank you for the timely feedback.

We have confirmed the choke is performing as it should.

So, I will turn my attention to the innards of the carb which does not have the mod for the adjustable main jet (far as I can tell).

I have previously messed with the float so that might explain the cause for an abundance of fuel / over-rich mixture.

Thanks again!

What...exactly did you do to the floats?

[Vermonstah]

Clean plugs!


I am very pleased to report progress.

Last weekend, I installed the new carb from MMI. And has been addressed many times on other threads in this forum, removing and replacing the carb is straightforward. So much so, even I can do it....

I knew right away that I had resolved the fuel leak, but I did not have the opportunity to get the engine up to temp for any period to test the plugs.

We have had some steady winds at 20 knots this weekend, so I took her out today and made a point to motor the final 3 miles to the pin. And when I pulled the plugs, they were clean! All four of them! The photo might not do it justice, trust me, that is the cleanest plug I have ever removed from my engine. Note: I am running the Autolite 86 plug that MMI recommends as a slightly hotter plug.

I have a new float and float valve for my previous carb, and I hope to get that back to decent working order so that it can serve as a reliable spare.

As suggested, I also got the the Electronic Ignition from MMI. I have not yet installed it, as I wanted to deal with only one thing at a time. And now that it appears that I have the carb dialed in, then I will move on to the EI. I will be VERY happy to be done with points. Points are no big deal for many on this forum, but been too much for me....

Again, cannot thank the members of this forum enough. Don and Ken too - tops in my book.

[marthur]

That is a nice looking plug. The picture shows it very well. Good job!

[joe_db]

I think you did the best thing. I have discovered that the carbs have a finite life span before cleaning them does not fix all their ills. A new carb from MM did wonders for my engine.