305 down on power (a little long)

[wolf396]

ok guys, here's the deal-
My boat is an '80 glastron cvx18 with a mercruiser 228 (305 chevy 4bbl). When i bought the boat about 3 years ago, it would run around 4800 rpm w/ a 21 pitch going about 55-60 mph. at some point it lost power and i am now down to 4500 rpm w/ a 19 pitch going about 45-50 mph. Here's what i've tried and found:
I rebuilt the quadrajet carb- very little effect
Checked timing, discovered a bad balancer, replaced balancer, set timing to 10 degrees at idle- no difference
new plugs, wires, ignition module, and coil- no difference
cleaned out the fuel line and replaced filters- no change
checked compression and found most cylinders at 160 psi range, but one was 125 and one was 135; both the rear cyls, #7& #8. - is that enough for this kind of power loss? maybe a flat cam? fuel pump?
i'm at the end of my rope here, im thinking about pulling the motor and rebuilding, but i dont want to if i dont have to. i'd really appreciate anybody's advice/opinions!
Thanks in advance. -Wolf

 

[lilmandavis]

Re: 305 down on power (a little long)

sounds like its time for a leakdown test to figure out where the compression is goin. thats gonna drop performance a bit. if the valves are sealing then its probably the head gaskets. is it the origanal engine?

 

[wolf396]

Re: 305 down on power (a little long)

yes it is the original engine. however, the boat was not used for a number of years, stored inside, before I got it. I hadn't considered the head gaskets, definitely a possibility. I was thinking rings or valves.

 

[AlanR]

Re: 305 down on power (a little long)

the 305s had a soft cam That could be a problem... Id do a leak down test first.

 

[wolf396]

Re: 305 down on power (a little long)

I had heard the car 305s had cam issues. was that a problem in mercruiser engines also? I'll try to get ahold of a leakdown gauge and test that. I'll let you know what happens. thanks.

 

[wolf396]

Re: 305 down on power (a little long)

an aquaintance had me convinced the exhaust was clogged. he described my boat's symptoms to a 't. so i pulled off one of my risers, and it looked very clean. I've read that mercruiser put one way shutters in the y pipe. does anyone think that could be the problem? maybe either hung partially shut or broken and stuck in the pipe sideways? how could i check for this? has anyone ever heard of this happening? Thanks
-wolf

 

[Bondo]

Re: 305 down on power (a little long)

"so i pulled off one of my risers,"

You Should have been staring at 1 of the Flapper Valves, Right There..............

Here's Where it Probably Is,...................

 

[wolf396]

Re: 305 down on power (a little long)

I thought the pre alpha had the shutter in the y pipe, lower down, am i wrong?

 

[wolf396]

Re: 305 down on power (a little long)

does anyone know where the shutters are on a 228 setup? how can I check them?

 

[b00tstrap]

Re: 305 down on power (a little long)

Hey Bondo..I found the same thing in my 88' Citation when I took the drive unit off to do a shift cable replacement. Funny in a way... half my exhaust shutter was wedged against the shift shaft just like that picture!