Mercruiser 4.3 maxes out at 2200 RPMs at WOT - Please Help.

acevedor2

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So I picked up a new anti-symphony valve, new fuel separator, gasket kit for the outdrive since I'll be removing it, impeller kit, and new flappers for the exhaust. I'll also be doing a compression test and checking the cylinders to confirm there is no water, etc in there.

Since I'll have it broken down this far, is there anything else - maintenance wise - that I should take the time to do now? I need to replace the trim sender/limit switches so I am assuming now is a good time for that. Anything else?
 

Scott Danforth

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Maybe touch up the paint you ding as you separate the lower
 

acevedor2

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Thanks guys. Quick question on the anti-siphon valve. Do the threads need any kind of sealant?or do I just unscrew one and screw in another? If sealant is retired, what should I use? I still have to pick up bellows glue for the rubber seals.
 

Scott Danforth

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I use loctite hydraulic thread sealant or Teflon pipe sealant depending on that I gave handy
 

acevedor2

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Found almost the entire exhaust blocked. I'll still check cylinders, etc. but there is no way this thing was exhausting well...
 

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Scott Danforth

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that is good news. sucks that you have to take most of the drive apart.
 

acevedor2

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Ok - been a pretty productive morning/afternoon but still a bit more to go:
- Pulled stern drive and conducted inspection. All boots are good, gimbal bearing is good.
- Re-greased gimbal bearing
- Replaced exhaust shutters and re-installed exhaust elbows
- Replaced anti-siphon valve
- Replaced fuel-filter/separator. Fuel that came out of old one was perfectly clean.
- Conducted compression test - all cylinders at 180psi
- Re-installed plugs and wires

Now I am getting ready to do the impeller and then I'll probably be spent for the evening and do the re-install tomorrow and optest on Sunday. I really do appreciate all of the help!
 

acevedor2

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Another productive day:
- Outdrive Installed and optested - SAT
- Shift cables adjusted - both were pretty good from the get go
- Trim limit and trailer switch verified SAT, trim adjustment switch adjusted - now perfect

Runs and idles strong - though I did not take it up higher than about 1400 RPMs. I will be putting her in the water tomorrow to verify all is well. Idle is a little low at about 625 or so - but no stalling or rough running so I decided to leave it as is. I'll report results tomorrow after I get back. Thanks again for all of the help everyone! I really appreciate it!
 

acevedor2

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Still not fixed. "@&&! Actually out on her as we speak. Throttled down and she got to 2200 quickly and then crawled to 3k. As soon as I throttled down, she will now only go to 2200. Frustrated does not seem to cover it! Any thoughts?
 

alldodge

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Since your on the boat, look on the side of the engine block behind the starter for something that looks like the pic below. If not found look on the other side just to make sure one is not installed

1knock.jpg
 

acevedor2

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Didn't see anything like that. I have the blue drain plugs, but nothing connected to them. That I can see anyway. Why? What is that?
 

alldodge

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Didn't see anything like that. I have the blue drain plugs, but nothing connected to them. That I can see anyway. Why? What is that?

That is a knock sensor, and never heard if you had one or not from post 21. Just wanted to make sure timing was not being retarded before I left it alone and tried looking into other things. Right now I'm stumped, along with you
 

acevedor2

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Thanks dodge. I'll look in the Manual for that when I get home. That said, I noticed one of the things on the list of things (sticky) that could cause this problem is too much oil in the crankcase. I've checked the oil several times and didn't notice it being too full. Probably because it was on an angle on the trailer in my driveway. Well I just checked it and it is definitely too full. Could that be my issue? Here is a pic of the oil level. I checked it in he water so it should be accurate. I am going to motor in and pull her out, drain some oil, and launch and optest again. Thoughts?
 

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Fun Times

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I noticed one of the things on the list of things (sticky) that could cause this problem is too much oil in the crankcase. I've checked the oil several times and didn't notice it being too full. Probably because it was on an angle on the trailer in my driveway. Well I just checked it and it is definitely too full. Could that be my issue? Here is a pic of the oil level. I checked it in he water so it should be accurate. I am going to motor in and pull her out, drain some oil, and launch and optest again. Thoughts?
Yes being over full on engine oil could have an affect on the running performance and it looks like you are roughly 3 quarts over the full line.

Hope that's it, good luck.
 

acevedor2

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Ok - frustrating day. She's not fixed but I have additional symptoms. As mentioned, I took her out, tried to open it up, not very responsive, went up fairly quickly to 2200k, and then crawled to 3k. Once I throttled down and tried again, she would not go past 2200. We anchoring for about an hour and a half to take a break and then started back in. Same thing, she went up to 2200k and then not any further. After about 20min of putting back in at 2200 rpms, she all of sudden started to surge and pick up rpms. She made it to 4100k. She would be steady for a bit and then fall back down to 35-3600, then climb back up. All the while I was NOT touching the throttle. When I stopped it, and then gave it full throttle, she climbed quickly to 2200k, though in my opinion labored - and not hauling butt like she should, and then after about 4-5 seconds she would pick up quickly and start climbing back up to about 4100k.

I am thinking the problem is either fuel or timing related. When we got back to shore, I emptied some oil out of her (about 1 1/2 qts because that's all I had containers for). She is still about a quart or so too full, but nothing major. We headed back out and ran some more tests. Same as above. The only difference here is that it did backfire a few times as she was running up to higher rpms (3600-4100). Also - my guess/hope is completely unreleated, but now my speedo doesn't work. It was working when we were out most of the time, and then stopped on the last run. Again - probably not related, but it isn't working. I checked and the fitting at the stern drive is still on tight as it should be. I am definitely feeling a bit frustrated.
 

alldodge

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Some times a day on the water and some beer, lots of beer in some cases causes an epiphany or some damage to some brain cells, then again sometimes both. So here I go with some thoughts, I believe we need to start from scratch because we are missing something:

For a carb engine to run well we need:
Air fuel mix of sufficient ratio.
Good Spark
Timing advance of 22 degrees for TB-V

Timing is set at base timing to 10 degrees BTDC
Fuel pressure of 4 to 7 psi from idle to WOT

What I have not seen in this thread is (correct me if I missed it)
What timing is actually set at,
what max advance timing is seen,
and what the fuel pressure is through the rpm range

What did I miss?

Also while I agree to much oil will reduce rpm, it will not IMO keep it to 2200. It usually causes foaming and then damages the engine from that
 

acevedor2

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I agree, I don't think the oil is a culprit. The one thing that keeps crossing my mind is "What changed from last year to this year?" It was running great when I put it away last year. The first time out this year is when I had issues. That's why i am leaning to a fuel issue. Could be bad fuel,fuel pump could also have gone bad. In truth, I don't know how/where to test the fuel pressures. Do you have a link tot he procedure?

The timing is certainly suspect - particularly given the backfiring. But why would timing have changed from the end of last year to this year? The distributor is on tight, wires look good. Plugs looked like the system has been running rich. I'll post pics later. I can definitely check the timing, I have a timing gun, but how do you read it on these engines? The engine is stock, but I don't see any pointer or indicator to line up with the mark on the harmonic balancer.
 

acevedor2

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Found he timing line. No scale - just a single line. I'll have to pull the procedure to see what it says.
 

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