Exhaust Restriction Further Update

[FreeBeeTony]

Re: Exhaust Restriction Further Update

The number on the upper is 6835410, can't read any number for the ratio. Will do the prop test tomorrow, don't want to get dirty again tonight. I don't think its a ratio problem, boat does ~22mph at 3200RPM with a 15" prop, boat weights 4000#.<br /><br />I haven't measured the cam yet......you guys think that's my next step? IN the manual it says I may need to remove manifolds to check cam. If that's the case I will probaly wait until I pull the engine.<br /><br />What about this spacer between the carb and manifold? I have the Weber/Edlebrock carb installed w/o a spacer. Should I install one and try that? What does the spacer do?<br /><br />If it is fuel.........how do I do a conclusive test? Should I start investigating different metering of the carb?

 

[FreeBeeTony]

Re: Exhaust Restriction Further Update

Any other ideas before I re-install the O/D tonight?<br /><br />This is really starting to get to me now!

 

[Buttanic]

Re: Exhaust Restriction Further Update

If you rev the engine up to 3500 and higher in neutral do you notice any different sound or anything different than it is below 3500. Where I am going with this is possibly a few bad lifters or weak valve springs causing premature valve float. This is a long shot but I read all your posts on the problem last night and other than fuel this is the only thing I can think of.

 

[Don S]

Re: Exhaust Restriction Further Update

Don't forget to do this:<br /><br /> Also put the drive in forward and turn the prop shaft till the dogs catch. Mark where the porp is, and where the ujoints are in relation to the drive, now turn the ujoint shaft in the direction of engine rotation till the prop turns 360°. How many turns of the ujoint shaft did it take...... be exact as possible.

 

[FreeBeeTony]

Re: Exhaust Restriction Further Update

I plan on doing that test tonight Don........<br /><br />Looks like I will be tearing this engine down in the fall, unless anyone else has any other ideas.<br /><br />I am going to put it back in the water for the rest of this season. If it is the valve train and I run it like this, will I cause any damage?

 

[Buttanic]

Re: Exhaust Restriction Further Update

I was looking at the Mercruiser parts break down on a 92 350 Alfa cylinder head and something doesn't look right. It showes valve rotators on the exhaust valves but the same spring for both intake and exhaust valves. To my knowledge all GM small blocks engines 1973 and later with exhaust valve rotators require a shorter valve spring (1.610 installed height) to compensate for the thickness of the rotator. Intake valve springs have a 1.78 installed height. You said the engine was rebuilt in 01.<br />Could it be the rebuilder put the shorter springs on all the valves which then would have insufficent spring pressure on the intake valves causing premature valve float.

 

[FreeBeeTony]

Re: Exhaust Restriction Further Update

Would it matter if the lifters were roller or not?

 

[KaGee]

Re: Exhaust Restriction Further Update

Tony, I think what Don is after, is to see if you have the right gear setup. Someone, I forget who, posted a similar problem in the spring and after a long time, finally figured out that a mechanic put the wrong gear set in his drive during a rebuild.

 

[rbezdon]

Re: Exhaust Restriction Further Update

FBTony, one thing I have been thinking about is did this boat EVER perform properly?? I know it is a newer boat for you which means you purchased it recently. Did you test ride it?? How did it perform then?? Seems that if the bog is so prevalent now it should have been at that time too if it is related to any of the things we have suggested/posted recently. Also, maybe you can contact the Prevf.Owner and findout how high the rpms would go right after the rebuild or possibly find out from him who the rebuilder was and find out what preformance testing was done after the rebuild. If the engine ever ran OK, even for a short time, it basically eliminates most of the issues related to the mechanical parts like cams, lifters, valve springs, gear ratios etc and really focuses you on fuel and timing/ignition. It just seems unlikely you would need a rebuild when it was just done in 01. I also assume if you bought this boat this year the Prev owner would have used it fo 4 years performing so poorly so it is most likely all of these mechanical issues are no the root cause but some other maintenance issue with the fuel or ignition systems.

 

[vipzach]

Re: Exhaust Restriction Further Update

KaGee, that was me; with the wrong ratio. Here is the link.<br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=24;t=012166#000010

 

[Buttanic]

Re: Exhaust Restriction Further Update

Type of lifter makes no difference unless a roller lifter was put on a flat tappet cam or flat tappet lifters on a roller cam.

 

[FreeBeeTony]

Re: Exhaust Restriction Further Update

I understand what Don is driving at and I will verify it tonight.<br /><br />As far as the boat ever performing right....not since I have owned it or test drove it. It was performing this way when I bought it, didn't think it was anything major. In fact the day before I picked it up I found a loose plug wire and I thought I fixed the problem but no such luck. I thought with a complete tune-up I would be on my way.<br /><br />I did speak to the previous owner and he told me he had some fuel problems last year (clogged pick-up tube/screen) but after that it ran fine. He said he never ran it over 4000RPM's. I really don't know what to believe or think at this point. I have never seen it go over 3500RPM WOT.<br /><br />Thanks for all the replys........keep 'em coming! I can use all the help I can get!

 

[FreeBeeTony]

Re: Exhaust Restriction Further Update

Just confirmed O/D ratio: 1.5 turns on the driveshaft yields 1 turn on the prop shaft.<br /><br />Now what?

 

[FreeBeeTony]

Re: Exhaust Restriction Further Update

No other ideas?