sudden loss of power

[SimonP]

as I was saying...
there we were motoring in after sweet presidents day sail and I was thinking that all was right with the world and all the work I'd put in to the boat was actually worth it ...
when the motor faltered a couple of times and lost power. Running at low revs <1000, it barely pushed us along, in no wind. Revving up caused it to starve, and makes a throatier than usual sound. Motor will rev happily in neutral and runs smoothly, but in gear, it has no power, starves when revved and stalls if I don't ease back quite quickly.

I had a bad feeling that the problem is valve related, but that is just a hunch.

I've been all over the outside of the engine in recent years : carb, fuel filters and pump, water pump, starter, etc. I've got a cannister water/particle filter, a priming bulb, a polishing filter, and an old facet pump - though I think the motor would run gravity feed if it died- bottom of tank is above carb.

Please make suggestions on troubleshooting procedure and guesses at what my problem is.

[ArtJ]

The first thing to check is the spark plugs and wires. Check for a healthy
spark from the coil center wire to the block.
Disconnect a plug wire at a time and see if engine slows down, if not
then that cylinder is a suspect

then check for stuck valves
. You can sometime unfreeze a stuck valve using a allen wrench in the
spark plug hole. Only one cylinder not firing can cause a problem.

Once having done all the above you could follow up with a compression
test. Anything less than 80 psi would be a possible problem. Squirt
some mystery oil in the cylinders may help. Especially direct towards the
manifold side as that is where the valves are.

Good luck

Art

[baileyem]

Simon,
While the items Art mentioned are all very valid checks to make, I believe that you have either a timing problem or a carburetion problem.
First, check to see that your distributor hold-down is tight and has not allowed the timing to change. Second, begin checking your carburetion system: is the choke working properly? ; is the float stuck? ; are there any air leaks?
There are many threads in this forum that will tell you how to check these things.
Good luck.

Mike

[msmith10]

I agree with Mike. I have had similar results a couple of times when I accidentally left the choke closed and forgot to open it after the engine started. The plugs fouled badly but everything was fine after a plug cleaning.
I've also had similar symptoms with a fuel starvation problem. In that case it may help diagnostically to squeeze the primer bulb while the engine is bogging. That may force enough fuel through to help.

[Marian Claire]

More ideas: The squeeze bulb, as mentioned, can help if you have an air leak or crud in the jets. If the choke is set correctly try choking it a little as you rev it up. If it runs better than you may have a fuel flow problem. Do you have the adjustable main jet? If so back it out a turn or two and see if it helps. Dan S/V Marian Claire

[marthur]

I agree with Mike. This really sounds like a fuel problem to me. I had exactly the same symptoms and it turned out to be a dirty carburetor. Not massively dirty either, just few little specks.

I would definitely inspect the fuel system from tank to carb. Clogged screen in tank, obstruction in carb (my own personal favorite), failed fuel pump, clogged filter. Your symptoms are also consistent with an air leak in the fuel system, though it seems unlikely that this would occur suddenly. Might as well check the hoses and connections though.

Next I would inspect the ignition and timing.

I would also check for an obstruction in your exhaust system. How old are the rubber hoses? Could the inner wall have collapsed?

As for valves, I strongly suspect that most of our A-4's would run pretty well on three cylinders. Not saying that isn't the problem, just that it wouldn't be the first thing I checked.

[SimonP]

I just composed a long reply, and tried to post it, then I got a not logged in and lost my mail (I _was_ logged in) Has this happened to anyone else?

as I was saying ... thanks all for tips and suggestions.

After sleeping on it I think its a fuel problem. The 'starving' sound suggests it. The couple of falters before the power-drop suggest that too - don't they? I will try the run-with-choke and squeeze bulb suggestions. The carb is newish, and I run it dry every time. I've suspected the thing runs quite rich - I open choke immediately after starting with no ill effect, even on coldest days - well it is socal No adjustable main jet, regretably.

I have had fuel problems before -crud from the monel tank, etc. But I've got a good filtration system in place. Last time I looked, my old facet pump was losing bits of old rubber seal down the fuel line downstream of the polishing filter - I guess its about time to replace that baby. (As I said, it think it would run without a pump

After I do the fuel system - again - I'll look at electrics. Check dizzy, wires and sparks. Pull plugs, check for fouling and gap. What is the gap BTW? And how often should I replace plugs- its been a while I realise. What is the suggested brand/number?

I have had a sticky valve, I could hear it come unstuck after a minute or two running. MMO and running weekly fixed that. So I don't think this is the problem. But I'll squirt some MMO just to be safe. But its time to do a compression test - last time, a couple of years ago, it was at the low end, 70s as I recall. The A4 is an oldie, installed mid sixties.

[ArtJ]

Not to counter anything said above, but I have had engine performance
decrease to the level you describe merely from having a bad wire or plug
on one cylinder. pulling the wires one at a time is a quick sanity check.
and worth checking first.

[Marian Claire]

Is your pump down stream from the filters? I think the polishing filter should be just before the carb. Dan S/V Marian Claire

[charles@pricefarrington.c]

Just my two.... I seemed to have had the same problem over the summer, it turned out to be a fishing net wrapped around the prop. Worth checking.

[SimonP]

[QUOTE=Marian Claire;19482]Is your pump down stream from the filters?

no, there's a short copper line from facet to carb.

> I think the polishing filter should be just before the carb.

so do I

[SimonP]

Not to counter anything said above, but I have had engine performance
decrease to the level you describe merely from having a bad wire or plug
on one cylinder. pulling the wires one at a time is a quick sanity check.
and worth checking first.

will do, thanks

[Baltimore Sailor]

[QUOTE=SimonP;19486]

Is your pump down stream from the filters?

no, there's a short copper line from facet to carb.

> I think the polishing filter should be just before the carb.

so do I

Most. Definitely.

[captain kenny]

Simon hi Kenny from the marina sorry to hear about the problem you should try what i am doing and running fresh fuel from an outboard tank. Lets face it in socal we have "boutique blended fuel that fouls easily. Nothing beats fresh fuel. Stop by the coffee is on me next time

[marthur]

Small bits of rubber!! That is exactly what I cleaned from my carburetor when I had your symptoms.

Your symptoms are not symptoms I would expect from a too rich mainjet, just the opposite in fact. If you have a fuel problem I would expect that it is starving of fuel when you open the throttle

Good luck!