Surging Engine. RPM'S Up and down. In Idle and under load.

[Cap'n Fiend]

Hello All,


I am the new owner of a 1977 Catalina 30 and have been doing a massive amount of work restoring this boat to its proper conditions as well as fine tuning what I can and eliminating all the gremlins I find hiding.

One problem that still eludes me is this atrocious RPM surging issue. The gremlin boss so to speak. I have seen it plague many other posters on here and I am joining the ranks of those who wish to find all the reasons for such a thing and attack it head on. Milkus Bilkus!!

I had the motor running perfectly without a skipped beat for a solid 13 hours yesterday motoring up the coast of Vancouver. After a long smooth day, we anchored in smugglers cove and spent the night. The next day when I went to start the engine, it sounded a little different and then when it fired up I'm now surging all over the place with my RPMS.

I am currently motoring and it sounds weak and wobbly and then occaisionaly suddenly I can hear the performance getting to where it wants to be, a nice solid strong steady rpm. It holds that steady for a few seconds and sounds great, then falls back into the surging problem. It sounds like shes trying to find that sweet spot constantly and once shes got it cant hold onto it.

I have read many threads about this but I am wondering if anyone out there has any quick Ideas. I am not in a position to take the carb apart right now and as I'm typing this it just did another cycle of strong for a few seconds and now its backing to wobbling.

I have installed new spark plugs, new cap & rotar, new water separator fuel filter (previously cleaned out the tank so I know it was a clean tank.) New fuel pump (4-5.5 PSI Facet)

Anybody got some good Ideas. I am not a mechanic but I do have some tools on board and am close to a marina. But would obviously like to figure this out with the help of other A4 owners. I am not electrically inclined at all so I don't have any testing equipment.

Thanks!!

P.S

I have been diligent with my oil changes, I use the boat alot so it has not been sitting.

[JOHN COOKSON]

Sure sounds like one cylinder is cutting in and out. Sticky valve or a weak spark plug that is cutting in and out. Or maybe a spark plug wire that is cutting out.
Do you have MMO on board? Do you use MMO in your gasoline? Do you have a points based ignition? Did you install the plugs, cap and rotor before or after the problem started?
Hang in there. Others will be along with more ideas and possible causes.


ex TRUE GRIT

Edit: Feel the spark plugs as the engine warms up. Is one plug cooler than the other three?

[Cap'n Fiend]

Hi there! Thanks for your ideas. I will check the plug temp. tomorrow and get back to you.

We are at Anchor right now in Codfish bay Jedidiah Island Marine park.

After I posted initially we motored for about 2.5 hours.

Power loss and surging rpms throughout, but she finds the groove occasionally.

I am unfamiliar with "mmo"


I was having a surging issue prior, and so in response to that I removed the old plugs and replaced them with new ones. I used this forum to find the ideal plugs, they were not available so I went with a "less hot" plug. Is there a chance this could lead to fouling?

The old distributor cap looked pretty bad with chunks of plastic missing from around the contacts.

I still have the old coil, and old spark plug wires on. The wires looked pretty new when I got the boat as well as all the contacts on the wires looked nice and gold. But they ARE the originals that came with the boat purchased in may 2019.

After replacing the plugs, cap, and rotar the engine ran perfectly. I have put about 30 hours on the engine with the new gear and it didn't even skip a single beat. It was beautiful albeit short lived. It took me a long time to get it running that way so I am disappointed, but the lesson continues. I find it very strange that it suddenly returned to non optimal running conditions.

I'll check back on this before I head out tomorrow. Thanks again!

[Peter]

MMO is Marvel Mystery Oil. It is a fuel additive that many on the forum use to keep the valves from sticking. Available in Canada at Costco.

Does applying the choke have any impact on the surging?

Peter

[edwardc]

One possible cause of random RPM changes is dirt or sediment in the float bowl of the carburetor. As it gets stirred up, it will randomly obstruct the main jet, causing variations in the fuel flow.

The A4 is tolerant of a lot of things, but it really wants clean fuel to run well.

Don't be intimidated by the carb. It's really a pretty simple disassembly and reassembly. The only part I find the least bit tricky is getting the choke linkage reattached properly.

You'll be amazed at the crud you can find in the float bowl. The first time I did mine, the bowl was almost completely filled with a tan gel, about the consistency of butterscotch pudding! I have no idea what it was, but assume it was one of the many problems resulting from alcohol laced fuel.

[roadnsky]

Hmmm, the 30 hours steady running before this started seems telling.
As Ed says it may be dirt in the carb "recycling" and clogging/unclogging the jet.

You could easily do a "quick clean" on it in an hour or less.
To give you an idea, take a look at Don's video... HERE

It might also tell you something by taking out the plugs and checking their appearance.

[capnward]

I suspect your problem is fuel-oriented. In my experience, fuel problems are more likely than electrical ones. You may have gotten some bad gas since you cleaned the tank. Check your water separator filter; it may have water in the bowl at the bottom, indicating water may be getting into the carb. If you have a fuel pressure gauge, it would be interesting to see if it changes with the surges. I had a similar problem with rpm surges. It happened after motoring for hours in smooth but not always flat conditions. You don't need to motor through much chop to dislodge crud in the tank, sending it into and maybe past the filters. Cleaning the carb, including removing, inspecting, and running a thin wire around in the jets, and replacing filters, solved the problem. Jedediah Island is a better place than most to take a few hours to do that. You should be prepared to clean the carb anywhere. It seems to take me three hours, but I work slow. I'm sure others can do it much quicker. Anyone who owns an A4 for very long will get used to that procedure. I have been known to clean the carb in the spring as a preventative measure, along with new filters. Keep all the parts and tools on hand. Definitely see Don's video.
I used to get the butterscotch pudding in the filters and carb until I stopped using ethanol fuel. IMO, ethanol binds the water in the fuel with the dirt in the fuel and sends it into your engine. This is a good way to clean your tank if you don't mind shutdowns, carb cleanings and filter replacements.
MMO may be hard to find in Canada, but it was considered helpful, if not essential, by the Universal engineers who worked testing A4s. It not only prevents sticky valves, but lubricates the rubber in the fuel system; the hoses, pump diaphragms, and the float valve needle tip. I believe it delays the degradation of the rubber by the ethanol.

[JOHN COOKSON]

. IMO, ethanol binds the water in the fuel with the dirt in the fuel and sends it into your engine. This is a good way to clean your tank if you don't mind shutdowns, carb cleanings and filter replacements.
.

After the ethanol binds water it phase separates and sinks to the bottom of the tank - right where the pick up tube is. Ugh.

ex TRUE GRIT

[ndutton]

Something to think about

If the consensus of fuel contamination is correct, a thorough cleaning of the carburetor and filter cartridge replacement is of course indicated. The bigger question is where did the contamination come from? Unless that is found and resolved you'll be doomed to a repeat performance.

Here is my one and only (so far) fuel contamination story from last year. It discusses my contamination source in detail:

http://www.moyermarineforum.com/forums/showthread.php?t=11084

edit: Which reminds me, it's time for the annual fill plate O ring replacement. This Sunday for sure.

[Sam]

I had this "surging" problem about 4 seasons ago. My early model w/points A4 would run fine for a while then start surging on way to winter layup. RPMs would momentarily drop to then return to cruise repeatedly - playing with throttle/choke just complicated things. I put the word out on the forum and much help arrived, especially from N Dutton. Problem was solved during spring commissioning by:
- set up a battery operated pump and flushed the tank a couple of times to clean it. Bottom couple gallons were pretty much off color and did not smell like gas.
- cleaned carb
- changed fuel lines to lined A1 low perm to offset ethanol issues disintegrating the innards of the old lines.
- changed electric fuel pump [there is a filter in there]
-changed filters
-added a 0 to 15 psi fuel pressure gauge between carb and pump.
Engine still runs fine. If I had to name one thing for you to do now I would drain the tank, dump the current gas and replace with new.

[W2ET]

Is there a more beneficial, cost-effective add-on to an A4 than a fuel pressure gauge installed between the fuel pump and the carb?

Bill