I would like to start out by stating that even though this is my first post and I haven't been a member very long, I have search all through the forums looking for ideas to my problem. First off, I found Mr. Don's list and started from there. Then searched through the forums looking for some ideas. Anyways here goes:
I have a 1996 Mercruiser 4.3L balanced shaft w/ thunderbolt IV ignition and alpha drive. I hate to make this post really long, but I'm trying to explain my whole story in detail so I can get more answers. I bought the boat 5 years ago and havent had many problems until now. Only thing I have done to it is a basic tuneup...ie plugs,wires,cap, rotor and starter. All in the first year I owned the boat. Until I started taking it out this year. The first time I took the boat out this year, it ran excellent. The second time is when everything went downhill. The only difference between all the WOT problems that I have found is that the motor runs excellent for the first mile to the next no wake zone(ridin on the river). After that no wake zone, I put it in WOT and it doesnt want to hit above 3500-3800 rpm and surges. I figured it is 16 yrs old now so the carb was needing a rebuild. I took it out last weekend after the rebuild and was tuning the carb how the manual tells you to. Got it in tune and engine still does the same thing after the no wake zone.
Now to Don's List:
1. Always put Stabil when I winterize. Also at the beginning of the season i put a bottle of SeaFoam in tank. After reading the list, I put some isopropyl alcohol in the tank just so I could make sure I had no water in the tank and filled with 91 octane.
2. Haven't changed props between years and haven't hit anything to damage prop.
3. Pulled pick up tube and is clean. A couple small pieces in the screen, but easily sprayed out. I don't think that I have an antisiphon tube because I shoved a garden hose down through the fill hose and sucked fuel out of the tank with a bulb primer.
4. Oil is at normal level. Maybe a tiny bit low.
5. I run in fresh water river and clean/wax hull regularly.
6. Same gear ratio as last year when it ran fine.
7. Sprayed flame arrestor out with brake clean and then with compressed air. Of course inside to out.
8. For this one, I am not sure where the flapper is at the transom or drive. Pulled the risers off and the flappers in the exhaust "up pipes" are working fine.
9. I have not done a compression check yet, but will certainly have one done tomorrow afternoon.
10. Just rebuilt carb. Have good vacuum and secondaries are opening on time and everything. Have accel pump on richest setting. I have a Weber 4 barrel model 9600.
11. I only got the first test done, looking for bubbles in the clear hose, but haven't done the tests on the water. (Funny how you can always have friends that will come out and party when boat runs good but when you need help fixing it, everybody is too busy!!) Also when I was on the water, I found out that I fuel pump hasn't ever been wired in since I have owned the boat at least. The purple wire was just zip tied next to the distributor cap. I wired that in and it still did the surging.
12. Last time I took it out, it was just me and my wife. not overloaded at all. Trim is unchanged from last year.
13. Not running hot at all. This year I changed out impellar, but old impellar looked good and no missing fins. Positive I did it correctly. Not loosing any outdrive oil or anything. Engine runs at about 175, never above that I have seen, using IR temp gauge.
14. I haven't checked the timing but all the threads I have read, nobody has had a problem with 4.3's w/ carb having timing issues. Looked at spark plugs, but they don't look very bad. I figure that I will try changing the plugs tomorrow. When at WOT it kind of sounds like it is only running 4 or 5 cylinders to justify my changing the plugs.
15. Linkage is good. It opens everything when running and on the water.
Ok....That is it and what I have done so far. If I had a guess, I would say that it is something to do with my timing, but am unsure. Again, I am sorry for such a long post, but I want to be detailed enough to help yall help me. Thank you in advance for any help that you can give me.
I have a 1996 Mercruiser 4.3L balanced shaft w/ thunderbolt IV ignition and alpha drive. I hate to make this post really long, but I'm trying to explain my whole story in detail so I can get more answers. I bought the boat 5 years ago and havent had many problems until now. Only thing I have done to it is a basic tuneup...ie plugs,wires,cap, rotor and starter. All in the first year I owned the boat. Until I started taking it out this year. The first time I took the boat out this year, it ran excellent. The second time is when everything went downhill. The only difference between all the WOT problems that I have found is that the motor runs excellent for the first mile to the next no wake zone(ridin on the river). After that no wake zone, I put it in WOT and it doesnt want to hit above 3500-3800 rpm and surges. I figured it is 16 yrs old now so the carb was needing a rebuild. I took it out last weekend after the rebuild and was tuning the carb how the manual tells you to. Got it in tune and engine still does the same thing after the no wake zone.
Now to Don's List:
1. Always put Stabil when I winterize. Also at the beginning of the season i put a bottle of SeaFoam in tank. After reading the list, I put some isopropyl alcohol in the tank just so I could make sure I had no water in the tank and filled with 91 octane.
2. Haven't changed props between years and haven't hit anything to damage prop.
3. Pulled pick up tube and is clean. A couple small pieces in the screen, but easily sprayed out. I don't think that I have an antisiphon tube because I shoved a garden hose down through the fill hose and sucked fuel out of the tank with a bulb primer.
4. Oil is at normal level. Maybe a tiny bit low.
5. I run in fresh water river and clean/wax hull regularly.
6. Same gear ratio as last year when it ran fine.
7. Sprayed flame arrestor out with brake clean and then with compressed air. Of course inside to out.
8. For this one, I am not sure where the flapper is at the transom or drive. Pulled the risers off and the flappers in the exhaust "up pipes" are working fine.
9. I have not done a compression check yet, but will certainly have one done tomorrow afternoon.
10. Just rebuilt carb. Have good vacuum and secondaries are opening on time and everything. Have accel pump on richest setting. I have a Weber 4 barrel model 9600.
11. I only got the first test done, looking for bubbles in the clear hose, but haven't done the tests on the water. (Funny how you can always have friends that will come out and party when boat runs good but when you need help fixing it, everybody is too busy!!) Also when I was on the water, I found out that I fuel pump hasn't ever been wired in since I have owned the boat at least. The purple wire was just zip tied next to the distributor cap. I wired that in and it still did the surging.
12. Last time I took it out, it was just me and my wife. not overloaded at all. Trim is unchanged from last year.
13. Not running hot at all. This year I changed out impellar, but old impellar looked good and no missing fins. Positive I did it correctly. Not loosing any outdrive oil or anything. Engine runs at about 175, never above that I have seen, using IR temp gauge.
14. I haven't checked the timing but all the threads I have read, nobody has had a problem with 4.3's w/ carb having timing issues. Looked at spark plugs, but they don't look very bad. I figure that I will try changing the plugs tomorrow. When at WOT it kind of sounds like it is only running 4 or 5 cylinders to justify my changing the plugs.
15. Linkage is good. It opens everything when running and on the water.
Ok....That is it and what I have done so far. If I had a guess, I would say that it is something to do with my timing, but am unsure. Again, I am sorry for such a long post, but I want to be detailed enough to help yall help me. Thank you in advance for any help that you can give me.
