#1
IP: 142.68.205.144
|
|||
|
|||
Idles great, no power in midrange, then revs freely
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: https://picasaweb.google.com/Paul.Mo...eat=directlink 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! |
#2
IP: 71.118.13.238
|
|||
|
|||
Hmmm
moir, I'll take a shot perhaps 2. Have you checked the exhaust? What you described is pretty much one or both of 2 things. And my first choice will be the exhaust because of the ssoty plugs and no power. How old is the exhaust primarily the "watrer injecdtion" spot?
The other could be a plugged jet or inadequate fuel supply. You said you have been through the carb so I would have my doubts as to it being fuel. Dave Neptune |
#3
IP: 71.118.13.238
|
|||
|
|||
oops
Now that I have read the whole post I'll now say the reving is probably the trans slipping. This is a simple adjustment if you have easy access to the trans cover plate. When shifting into forward do you feel it "CLICK" into gear? If not this is where to look after double checking the cable for full travel first.
Dave Neptune |
#4
IP: 142.68.205.144
|
|||
|
|||
Hi Dave,
Somehow I've got a double post going. The more active one is here: http://www.moyermarine.com/forums/showthread.php?t=5727 Looks like it was "Barnacles on the prop" mostly, causing the prop to cavitate. I think the sooty plugs were either from all the misfiring on the old ignition or the fact that they were somewhat cold. The RJ12C that are in it now look perfect. (NGK 6 is ~ 7ish on Champions numbers. They cross it to 8 and 6 Champion plugs. Never trust a cross-reference!) |
#5
IP: 207.38.208.13
|
|||
|
|||
I had a weird experience with my Atomic 4 that I would like to share. For many years the motor would “get tired” late in the day. Things finally got so bad that the engine would slow up to an idle before catching its breath. Figuring the problem might be in the fuel supply i.e. the alcohol in the fuel might have turned the 30+ year-old supply hose into chewing gum, I replaced the hose and also the fuel filter cartridge. No improvement. The hose was a little stiff but looked fine.
Well it must be electrical. When I put the voltmeter on the ignition coil, with the motor turning, the voltage was jumping all over the place. I thought the problem might be caused by a bad ignition switch, but voltage at the switch was the normal. There was only one other place the problem could arise. The 10+ foot wire harness between the instrument panel (3 gauges, two switches and a starter button) and the engine. This harness consisted of seven wires spiral-wrapped with black electrical tape. I peeled off the tape and got a really big surprise. Each of these wires consisted of five 2-foot sections of wire spliced together with butt connectors. The “hot” lead from the battery consisted of one piece of red wire (the correct color), two pieces of yellow and two pieces of white. The lead to the ignition coil was four pieces of brown and one black. On hindsight, the ignition wire was the only wire that was not “self-diagnostic”. If the wires to the temperature or oil pressure gauges were intermittent it would be reflected in the gauges. There would have been similar cause/effect for the other wires. Counting each butt connecter as two crimp joints, there were ten crimps per wire, including the end terminals. There was plenty of room for a bad connection. My Ranger 33 was built in the summer of 1978. Did the factory produce this lemon or was it done by a boatyard mechanic? I doubt we will find out. Last edited by Joel Hutzler; 09-22-2011 at 04:22 PM. |
#6
IP: 75.68.130.228
|
|||
|
|||
Good find, The temperature "indicators" show that there was resistance in the joint and enough amp flow to create the heat. What happens is that as it heats up the metal expands losing contact surface.
This is typical of a hand crimper and not a racket crimper. Steve |
#7
IP: 64.20.183.217
|
||||
|
||||
Quote:
Way more likely one of the previous owners. I found this mess left to me by a PO when replacing my running lights. I was just "fine threads" away from shorting out.
__________________
-Jerry 'Lone Ranger' 1978 RANGER 30 |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Idles great, no power in midrange, then revs freely | moir | Troubleshooting | 12 | 09-20-2011 11:18 AM |
Just Another Power Loss Issue | Bruce A | Troubleshooting | 33 | 06-16-2010 02:21 PM |
Idle's great with full choke | j bridges | Troubleshooting | 1 | 07-19-2008 06:38 AM |