A-4 problem

[Mike Thomas]

All

I ordered a carb rebuild kit this morning. Almost everything points to the needle valve except the stall when using starter fluid.

I guess if that fails the next look goes towards the exhaust.

Mike T

 

[Mike Thomas]

Well folks,

I rebuilt the carburetor and no luck. It fires but will not run.

New distributor, rotor, wires, plugs and checked the wiring harness. Checked the fuel pump, replaced the filters and rebuilt the carburetor.

There is a distinctive hissing sound coming from the exhaust after the engine stops cranking. It's lasts about 5 seconds and definitely sounds like pressure being released.

I guess it's time to focus on the heat riser. Does anyone know exactly what these things are? What they do and how they do it. Is it just a couple of pipes welded together? If so, in what configuration?

Mike T

 

[timday5]

Here's a link to a thread with lots of collected information on wet exhaust components:

http://www.moyermarine.com/forums/showthread.php?t=1591

I'm collecting information in prep for commencing this project this weekend, so I have no personal insights yet...

 

[raleighm]

Check exhaust manifold

I would also recommend pressure testing your exhaust manifold. If you have a leak in the water jacket, it could be letting water enter the cylinders, which would definitely cause some of the symptoms you have described. It is very easy to test without removing the manifold from the engine. Simply plug one of the water hose outlets on top of the manifold and insert a automotive valve stem into the hose on the other end (cut off the rounded bulb at the opposite end from the valve and it will fit perfectly into the 1/2" hose). Clamp the valve stem into the hose and pump it up to 25-30 psi with a bicycle pump. If it holds the pressure, your manifold is probably fine. Mine wouldn't hold pressure at all and I found a 1/8" hole in the water jacket when I removed the manifold. Bought a new manifold and the engine runs perfectly now! Water in the manifold could also explain the hissing sound after cranking the motor.

My other guess would be a contriction/partial plugging in the exhaust system. If you can remove the two bolts holding the exhaust riser to the back of the manifold, you might ask Don Moyer if you can borrow a spacer with a threaded connection for a pressure gauge (I did this once). Bolt the spacer between the riser and manifold and run the engine with the gauge in place. If you have more than a couple of lbs. of pressure, there's a blockage somewhere in your exhaust system. Atomic 4's are quite sensitive to excessive exhaust back pressure. More than a couple of lbs. tends to cause problems.

 

[wurzner]

Mike,

Don't despair, the A4 is a very easy engine to troubleshoot and extremely reliable due to its simplicity. With all the things you have done, I would guess it is the heat riser as well. The guy who bought my boat purchased a new one from www.go2marine.com for a really good price if I'm not mistaken, but it may have been old stock they were trying to move. Either way, you will be able to get her going. The issues I had with my A4 were 2 failed coils and 2 failed fuel pumps over about 200~400 hours of motoring with it. Verify good spark, check plugs for pressence of gas/no water, and fix the exhaust and I would be surprised if your not good to go. I also rebuilt my carb and it was REALLY easy.

Hang in there and I'm sure you'll be putting around real soon.

shaun

 

[wanderer]

i'd bet more than a few bux that it's your exhaust system as others have mentioned.

just got finished rebuilding my motor and another boat here in our marina.

my recommendation is to forget the OEM type riser and get a good water lift muffler and build your own dry section from galvanized pipe. yes, iron will last longer but are you planning on owning the boat another 30 years? there will be considerable weight savings in galvanized pipe and i pieced it all together for around 40 bux. i triple wrapped the pipe with fiberglass header tape.

if your exhaust system is fried, i'd also recommend pulling your manifold and giving it a once over. it's much easier than you'd think and WELL worth your time

the A4 is bulletproof. simplest motor i've ever rebuilt and WAY overbuilt. that's why they're still around. best little flathead 4 ever made

quickest, not the cleanest, way to check if your exhaust is plugged is to drop your exhuast outlet away from the manifold, turn off your water inlet and fire that thing up. yes, it'll smoke like hell in the cabin but for a quick check it'll air out quickly and your results will be immediate and it won't hurt to run it dry for a few seconds

 

[Mike Thomas]

Thanks for the recent answers all.

Actually, my original post was on 5-24-06 and I have since fixed the problem. It was the exhaust and over this winter I installed a water lift. Now she's quiet as a kitten, putts slow like a Harley and I have 30% more power. I actually like the way the water lift sounds. Attached are some pics of the project. I cleaned up the locker and wiring while I was in there.
See attached

Mike T