Missing and loss of power after about 15 min

[lubberdink]

Hello everyone-
This is probably addressed previously as this being the home of experts on the A4 for many years, I"m sure it's come around the pike a time or two but here goes;
We usually warm up our 1970 A4 at the slip for a bit then head out. Normally 10-15 minutes and we're out where we can set sail and shut 'er off. Same thing coming back. However this weekend in 100 degree weather we had to motor over 15 minutes and experienced missing and a slow down of rpms. It never died but slowed down so slow at times I thought it was going to. As someone else noted, a praying, white knuckle ride back

Fuel tank over half full and never any trouble starting or running and engine not overheated (I don't have a gauge but I could touch the motor (carefully-not my first rodeo) and it wasn't hot. Plenty of water coming out the exhaust.

I suspect a coil or points getting hot and degrading in the high temps after good and warmed up. But I'm open to other ideas as well. I plan to upgrade to electronic ignition and a new coil when pulled out this fall.

You think I'm on the right track or something else obvious I'm missing.

As always, you taking time to comment is much appreciated.

Best regards

[romantic comedy]

Good that you got home. Then what happened. Does it start. How does it run now? Did you run it in gear at the slip? Did you check the ignition? How is the spark? Yellow? blue?

First guess is that you were starving for fuel. How is the gas? Is it old?

Remember that the stock ignition will run the engine just fine. So it is fine to upgrade to electronic, but trouble shoot what you have.

Remember the basics:

Getting fuel?
spark?
air?
compression?

[lubberdink]

Thanks for the reply RC-

I don't think it's a fuel problem (but been wrong before). Put in two fresh gallons about two weeks ago. Do you supposed the fuel pump might degrade after run for awhile? I also dug some mud dauber goo out of the fuel tank vent and I think it's open but could that be it?

I honestly didn't check the spark but it starts easily with a little choke whether first thing or on startup when heading back.

It started missing on the way out and we shut it off to anchor and swim. On the way back it started right up and ran almost all the way back (about 15-20 minutes) before it suddenly missed and from then on it was rpm drop then catch and run back up to speed then degraded as we got further in until it was just running above idle at the slip. However when I had it out of gear at the dock I could run up the rpms but with some miss.

This is the first time we've actually run the motor for that long of time. Up until now we've had no problems but maybe always shut it off before it got to this point. I suspected the high ambient temp was part of the problem but maybe not.

Anyway, thanks for listening and helping out another hapless sailor buddy.
Regards from HOT Kansas.

[ndutton]

I'd like to see you pursue a possible tank vent issue to discovery or elimination. The standard test is to run with the gas fill cap open. Problem goes away - the vent is the issue.

[lubberdink]

Excellent idea Neil. I will do it first thing if it happens again. Could very well be it.
Kindest regards

[tenders]

The cause of the symptoms I had exactly like yours about five years ago was a degraded electric fuel pump. Engine would run fine at pretty much any speed for 10 minutes, and at low speed pretty much indefinitely, but once some amount of reserve fuel was taken out of the carb float chamber, the engine started sputtering.

If slowing the engine helps reduce the symptoms, I'd pursue that angle.

This season I added an inexpensive fuel pressure gauge between the pump and the carb to help flag problems like this going forward.

[keithems]

if it were i, and i suspected the coil [not unreasonable, given the time sequence], i'd go to the local auto parts place and get a new one [$25-50] --

make sure you get one with internal resistance if that's what you have now, or get and install a resistor if you don't have one and the coil requires one.

installing the coil is one of the easier things to do.

then if it was the coil, good. if not, you can carry a spare, which is a good idea anyway.

i'll be curious as to the outcome.

[keithems]

also

examine the black wire which runs from the neg coil pole to inside the distributor.

the insulation can wear and it can ground against the distributor.

i cannot tell you how much grief that wire has given me in the past. -- does anyone know where you get one with the grommet to protect it where it goes thru the distributor body?

for now, without the grommet, i use a thicker gauge [8 or 10], which seems to be working ok so far.

btw -- the cross reference on the coil is standard / blue streak uc 12 or uc 15, i think. they are easy to find, at least around here.

[Dave Neptune]

Checks

lubberdink, souns like fuel to me. Most of the time there is an ignition issue it is off or on not sputtering, although it still can be.
I suspect fuel as you say it's starts easy cold. Have you checked the plugs for color. If their black your rich and fi their whitish you could be starving for fuel. Both can have similar symptoms.
And mechanical or electric fuel pump? And do you use a polishing filter in front of the carb?

Dave Neptune

[JOHN COOKSON]

Side Note To Keithems

You can use a couple of layers of heat shrink tubing over the wire to protect it where it enters the distributor.

TRUE GRIT

[lubberdink]

Thanks all for the great suggestions. I did pull the cap off the distributor and see where the wire goes through. It appears to be ok. I'm seriously thinking it's either a coil getting hot or a fuel problem (including the vent which might be plugged). It has a mechanical fuel pump so would think this would be more in line with an electrical pump though.

It does have a newer filter up by the fuel tank put on by the PO. Not sure what a "polishing filter" is. I would be delighted to be illuminated on that.

Might be a bit before I get back to try some of your suggestions but I"ll be sure and post the result for everyone's information.

Again-thanks all. Some great ideas.

[roadnsky]

...Not sure what a "polishing filter" is. I would be delighted to be illuminated on that.

It's a "secondary filter" downstream of the water separator usually for catching smaller particles (7-10 micron)
Ergo the name... polishing.

You can get one here from MMI...

Product No. - FPMP_07.1_473

http://www.moyermarine.com/cgi-bin/shopper.cgi?search=action&category=FPMP&keywords=all&template=Templates/B000_storebuilder.html

[roadnsky]

Maybe a little better representation of the filter...

http://www.moyermarine.com/360/index.html

[lubberdink]

Wow Jerry. Great pictures and information. I'm adding these item to my "gotta have" list. Thanks again for taking the time to reply.

[sastanley]

lubber,

We all think Jerry's A-4 is a museum piece...I've never seen one speck of dirt in any of his pictures.

Be sure to report back with your findings..lots of good suggestions, but I am gonna guess fuel starvation as well. Make sure you try out each test separately so we will know which thing was actually causing the issue.