engine not reaching WOT

[jfl1959]

Hello and thanks for any help.
1979 AMF crestliner 2450 Mercruiser 228(I think) Jasper rebuild sometime in 1996? (GM 305) Full FWC system.

Put boat in water and she sounded real good. Got up on plane RPM at about 3800 looked down and temp indicator was buried. Shut it down waited about 2 hours and she started right up, temp at about 170. Ran great at trolling speed but everytime I gave it gas she started to overheat.
Checked flow, and determined that Exhaust risers were bad. Replaced them and now boat runs at right temp when at idle, as well as when I give it full throttle, but RPM s only get to about 3500 and she is struggling and running poorly.

I am about to go through the whole flowchart to find the problem (gas, plugs, carb, etc...) but was wondering if my new problem was some way related to the overheating.

What do you think?

 

[jfl1959]

Re: engine not reaching WOT

Also, while not in gear she sounds great as well as when I give it gas. RPMS go up nice, engine sounds great. If anything bad like a blown head gasket was the problem would I be able to start it up easy and run it while not in gear like this? It is only under way that she runs bad.

 

[Bondo]

Re: engine not reaching WOT

When you Replaced the Risers,.......
Were the Flapper Valves still in the Y-Pipe,..??..??.....

Is sounds like they may have Burnt Up,+ fallen into the bottom of the Y-Pipe, causing an Exhaust Blockage...........

It is only under way that she runs bad.

Or the Fuel Filters are Dirty,+ need replacing.........

'course,...... That's Justa Guess.................

 

[FreeBeeTony]

Re: engine not reaching WOT

Is the a 305 in a 24' boat?
Did it ever reach the correct WOT RPM's?

 

[jfl1959]

Re: engine not reaching WOT

thanks for the help

yes it reached WOT of 4200 before the overheating. boat ran very nice.

would the overheat cause these problems only under way? it seems to sound and run fine at the dock at idle and while I give it gas.

It sounds like two seperate problems, I fixed the overheating with new risers, but before I start to test fuel etc... I was thinking that the overheating could have caused a problem.

I need to check the flappers, do I need to pull the boat out to do this?

The original set up let the exhaust go through the transom. Can I connect the risers back through the transom and run her to see if the flappers are stuck in the Y pipe? I assume (again bad choice of words) I would not hurt anything if I did this correct?

 

[Bondo]

Re: engine not reaching WOT

The original set up let the exhaust go through the transom. Can I connect the risers back through the transom and run her to see if the flappers are stuck in the Y pipe?

That maybe your Best Option............

I Think that in 1979 the Flappers were at the Bottom of the Y-pipe,......
Not at the Top like later models.........

You'll want to Cap Off the Y-pipe during your Tests,+ until you get to the Repair, if necessary.....
The top of the Y-pipe is Just above waterlevel outside the boat...... Usually.................