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Hello. Different Moir here, but one who knows how to spell. And certainly no expert with the A4! 
I'm trying to help out an old friend with his A4. My background is in outboards so I'm a little out of my depth. CDI I can handle, but what's this distributor thing? And 4 strokes; isn't that two too many?
My friend has been laid up half the summer with engine troubles. Mostly his problem has been with lack of power and the engine suddenly dying on him. Dockside, I went though the carb and didn't find much. Later we conclusively determined that there was a problem with the electronic ignition system as the ignition module's output to the coil disappeared the moment trouble struck. After obtaining new parts, we found that the particular problem was the optical pickup in the distributor.
After we replaced both the pickup and the module, the engine started, ran and idled very well. It revved in neutral, holding reasonable RPMs, as you would expect. It seemed to reverse under load fine (we were on a mooring), but this was the extend of the load testing we did.
Today he tried to take the boat out. In forward he had very little power, no matter how far forward he put the throttle. I went down and had a look, thinking that it probably needed a timing adjustment since we had made that out-of-gear, but no adjusting the timing helped. Essentially the engine would bog after getting off idle with a hollow sound coming from the carb like it was lugging.
After some experimentation, I pulled the plugs. They were NGK B6S which is about a 6 or a 7 on the Champion heat range, and minus the resistor. They were all sooty. We brushed them off and tried again, but the symptoms didn't change. I've seen cases where an abused spark plug - such as from the over rich from all the missfiring on the old ignition - will fail under load so I was a bit suspicious of them. I located an old set of Champion RJ12 (C or M?) and tried them. These are the only things that changed the symptoms. I seemed to get more power, but after about 2000 rpm the engine would suddenly rev up high. Again, no timing adjustment seemed to help the problem. All the plugs checked dead white on the insulator and slightly crusty on the sleeve.
I took off the carb again and went through it properly at home. I found a couple small things (float was off, main jet wasn't tight) but nothing big. Tonight I went back down and put in the carb and some fresh plugs, but the problem persists. The bogging might be a bit better but it still refs out.
Here are a couple videos of what it's doing:
One is me goosing the throttle in neutral. (~1 sec hollow sound from carb, but takes off pretty quick. I need an opinion if this is "explosive"), the other is in gear while tied to the dock. You can hear the in gear test suddenly take off and I have to back off.
I'm starting to think that perhaps the prop has gotten fouled up, and is cavitating at higher RPMs. I say this because when it revs up high, the thrust drops off as felt in the spring lines at the dock.
Further info: Fresh rebuild (not mine, but done by a very competent mechanic). Compression 100-98 on all 4 (my compression tester tends to read a little low at lower values, pumps up in 2 or 3 revs). Timing not quite right but close: ~0-5 degrees at idle and it advances smoothly to about 15-20 BTDC at somewhere near 2000 (no tach). Firing order checked, double checked and triple checked, 1-2-4-3. Spark good on all 4 (jumps at least 9/16", good hot SNAP). No backfires or lean pops. Bumping the choke has no effect.
So what do you think? I need help: they're talking about taking my wizard cap away!
I'm trying to help out an old friend with his A4. My background is in outboards so I'm a little out of my depth. CDI I can handle, but what's this distributor thing? And 4 strokes; isn't that two too many?
My friend has been laid up half the summer with engine troubles. Mostly his problem has been with lack of power and the engine suddenly dying on him. Dockside, I went though the carb and didn't find much. Later we conclusively determined that there was a problem with the electronic ignition system as the ignition module's output to the coil disappeared the moment trouble struck. After obtaining new parts, we found that the particular problem was the optical pickup in the distributor.
After we replaced both the pickup and the module, the engine started, ran and idled very well. It revved in neutral, holding reasonable RPMs, as you would expect. It seemed to reverse under load fine (we were on a mooring), but this was the extend of the load testing we did.
Today he tried to take the boat out. In forward he had very little power, no matter how far forward he put the throttle. I went down and had a look, thinking that it probably needed a timing adjustment since we had made that out-of-gear, but no adjusting the timing helped. Essentially the engine would bog after getting off idle with a hollow sound coming from the carb like it was lugging.
After some experimentation, I pulled the plugs. They were NGK B6S which is about a 6 or a 7 on the Champion heat range, and minus the resistor. They were all sooty. We brushed them off and tried again, but the symptoms didn't change. I've seen cases where an abused spark plug - such as from the over rich from all the missfiring on the old ignition - will fail under load so I was a bit suspicious of them. I located an old set of Champion RJ12 (C or M?) and tried them. These are the only things that changed the symptoms. I seemed to get more power, but after about 2000 rpm the engine would suddenly rev up high. Again, no timing adjustment seemed to help the problem. All the plugs checked dead white on the insulator and slightly crusty on the sleeve.
I took off the carb again and went through it properly at home. I found a couple small things (float was off, main jet wasn't tight) but nothing big. Tonight I went back down and put in the carb and some fresh plugs, but the problem persists. The bogging might be a bit better but it still refs out.
Here are a couple videos of what it's doing:
One is me goosing the throttle in neutral. (~1 sec hollow sound from carb, but takes off pretty quick. I need an opinion if this is "explosive"), the other is in gear while tied to the dock. You can hear the in gear test suddenly take off and I have to back off.
I'm starting to think that perhaps the prop has gotten fouled up, and is cavitating at higher RPMs. I say this because when it revs up high, the thrust drops off as felt in the spring lines at the dock.
Further info: Fresh rebuild (not mine, but done by a very competent mechanic). Compression 100-98 on all 4 (my compression tester tends to read a little low at lower values, pumps up in 2 or 3 revs). Timing not quite right but close: ~0-5 degrees at idle and it advances smoothly to about 15-20 BTDC at somewhere near 2000 (no tach). Firing order checked, double checked and triple checked, 1-2-4-3. Spark good on all 4 (jumps at least 9/16", good hot SNAP). No backfires or lean pops. Bumping the choke has no effect.
So what do you think? I need help: they're talking about taking my wizard cap away!
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