A couple of small (?) issues w/4.3L Mercruiser

[v1_0]

So, I finally got the boat to the water. Being a newbie at it, I did the obligitory "back/forward back/forward it's finally in the water, what do I do now... etc." I did happen to choose a slow time to do this so as not to have anyone waiting on me.

It's a used boat (circa 1989), so I did expect some additional issues. [I tested it at home with the outdrive in a large bucket, didn't rev it - but did put it into gear to make sure things worked.] So, I have three issues:

First the specs: Mercruiser 4.3L Alpha, counter rotating.

(1) When I put it in reverse I can only move backwards at a slow speed. If I try to give it any throttle (slowly or quickly) the engine dies. I'm suspecting that the gear shift / throttle need to be synchronized and that I'm going into 'full' gear too soon.

(2) After running at almost full throttle (4000 rpm, <WOT seems to be about 4500>) for a few minutes, when I bring her back down to about 3000 rpm the engine will loose power and backfire - until I drop it to about 1000 rpm or so. It will then chug along with no backfiring. Prior to this I ran at about 3000 rpm for a while just fine. After stopping (see next issue), I could again run at 3000 rpm with no problems.
I suspect that I am running a bit rich and need to adjust the carb.

(3) When I run at a low rpm the engine seems to overheat (gauge goes into the red). This occured when I brought it down to 1000 rpm after the above incident - so I found a nice place and dropped anchor. After about 45 minutes, started it back up and ran at about 1000 rpm: the gage again started to creep back up into the red. I increased speed and the temp dropped back to normal.
I'm not sure about this one. There's always the obvious "don't run at 1000" but I don't think that the engine was designed that way.

Thank you,
-V

 

[thrasher]

Re: A couple of small (?) issues w/4.3L Mercruiser

If the engine overheats at low revs it's usually a sign that the impellor in the lifter pump is dead (this is the water pump that is located in the outdrive). It's a relatively cheap thing to do, but takes an hour or two to do right (mainly refilloing the outdrive!!).

I would check your ignition timing and advance in the distributer and try cleaning the carb.

Gary

 

[alaska_av8r]

Re: A couple of small (?) issues w/4.3L Mercruiser

On number 3...

I had similar results when I changed out a lower unit. The higher rpm the engine cooled down....I mistakenly thought that the lower unit had a new impeller.....after some research I found out that was not the case so I changed it.......that cured my problem

I assume the old impeller could not pump enough water at low rpms since it was pretty stiff but once the rpms increased it was a bit more efficient...

anyway just a guess as to the why but it did solve my problem.... they recommend changing them yearly and that seems like a good idea to me....not very hard to do either.