You guys were a huge help on my '79 SN 351w rebuild a few years ago.....so I'm hoping you won't be too biased to help with my new-to-me '82 Mastercraft S&S with a 351w.

The boat came with a property we purchased earlier this year.   Hour meter says 1,100 hrs but stopped working a long time ago.  Original 351w, original Holley carb.   The boat was running really well, except for a little smoke and stumble right at startup.  The problem is - it was leaking fuel from the supply connection and from somewhere around the accelerator pump gasket.   I figured I would try my first ever carb rebuild - so I ordered the correct kit from Holley and tore the thing apart.  

I was pretty meticulous with the disassembly and reassembly but must have screwed something up, because the boat will barely run.  I can get it to start with almost full throttle and then back it down to about 15% throttle and it stumbles and smokes - white/blue at lower RPM's, slightly black if I rev it.   It will not idle.   I started with the idle mix screws 2-turns out and have tried playing with them but with it running so poorly, and needing so much throttle just to run it is hard to say.  Closing them to 1-turn out seemed to make it worse so I backed them out to 1.5 turns. 

In the rebuild, there were a couple things that I wasn't 100% on:

-Choke - I forgot to make an index mark on the choke during disassembly.   I also replaced the plastic choke cap and threw the old one out.  This seems like it could be a choke issue.  I tried playing with the choke index a little and didn't notice a change.

-Gasket - The replacement cork gasket on the back of the thing (I think it is a secondary vacuum??) next to the choke, where the vacuum port goes to the main body - this replacement gasket didn't fit great, but I think I got it sealed up.

-I used the gaskets that came with the kit for spacer to manifold, and carb to spacer.  I'm reading that I should have ordered the felpro that I used on my nautique build.

I can't think of anything else I could have screwed up.   Note that the boat was running really well - other than a very light smoke and stumble for about 10 seconds after cold start - 2 days ago when I pulled the carb.

I debated just getting a new QF m600 like I did on the SN, but it looks like they are backordered for quite a while.   So I need to try to figure this guy out!

Any ideas on where to start would be appreciated.   I have a vacuum gauge and a timing light, but feel like I need to get it closer to running before either of those will be much help.

Possible problem.....

Here's a link to a fairly recent thread with spacer and gasket info  There are pictures and gasket part numbers in the thread.

http://www.correctcraftfan.com/forum/forum_posts.asp?TID=49395&title=carb-gasket" rel="nofollow - link

Being an 82 MC you should have a PCM engine with the aluminum intake spacer and an excellent path for a big vacuum leak if your gasket between the engine and spacer isn't big enough 

I'd take the spacer off and see if the gasket is big enough to form a seal before doing anything else

If you're suspecting the choke, just block it open, give the engine some warmup time at 1200 or so RPM and it should idle good after that with it blocked open. If it does then you can figure out what you did to it.

Correct PCM gasket ordered.  I'll inspect the one that's in there in the daylight tomorrow.  I could hear a strong hissing/sucking sound around/over the carb when it was running, but that would be normal with the spark arrestor off and 1/4 throttle, right?

I'll play with the choke tomorrow, but can say that I moved it back and forth during my attempts earlier today and nothing let it run anywhere near smooth.

Thanks!

The choke does seem to be operating normally.

As long as the valve is good and you didn't mess up it's gasket, you should have no issues 

Okay, another update after more messing around.  The choke is definitely operating normally, though I turned it so it opens earlier.

The motor continues to run very rough and only with about 15%+ throttle.  Still black smoke and stumbling.

I closed the idle mix screws all the way and it does not change how the motor runs.  It still keeps running at 15% throttle and dies at idle.   I turned them in (from 1 1/2 turns out to closed) while it was running and nothing changed.

Also - and this is probably the important one - after I shut the engine off the passenger side primary venturi continues to drip pretty rapidly for 30 seconds to 1 min.   From my prior reading I believe this is a sign of a different issue but I can't find that thread now.  Note that I did not do anything with the fuel pump or filter, so I don't see any reason I would have a sudden fuel pressure issue.   The possible issues I can think of:

1)  Faulty power valve - I installed a brand new Holley 6.5 so this seems unlikely

2)  Some problem with my little check-ball modification?

3)  I'm having paranoia that I installed the primary metering block backwards.   Is this even possible?  Not sure why/how I could have done this because I reinstalled the jets as I was doing it....but you never know...

The new gasket is on its way but won't be here until Monday.   I looked at the spacer>manifold gasket and it seals all the way around the outside of this connection.  I did not pull the carb to see what it is doing on the inside.   Is the potential vacuum leak usually on the inside?

Keno - I used the new gasket that came with the new valve.  I only hand-tightened the power valve because it looked like the ports needed to be at 3 o'clock and 9 o'clock to function properly.  Maybe I left it too loose and it is leaking?   Is the orientation of the power valve important?   It looked like the hole has openings at 3 o'clock and 9 o'clock, as does the power valve.  It was nearly hand-tight at this orientation so I left it there.

The power valve should be tight, otherwise any leakage past that gasket is going directly to the intake cleverly bypassing all metering systems making for a really rich running engine especially at idle.(it's different than having a power valve that's open too early, it's like having a ruptured power valve diaphragm.

I'd take the metering block off and tighten the valve and you may get lucky 

The orientation isn't important, but being tight is.

PS .......It's impossible to put the metering block on backwards

If you have the tube there's an O ring on each end. One end pushes into the carburetor body and the other end into the metering block. A missing O ring will wreak havoc with your fuel mixture.

If you don't have the tube, but have a small hole instead, you need to make sure you use the right metering block to carburetor gasket or you'll have the same rich issue.

Post a picture of your metering block's backside if in doubt .

The picture shows the gasket used with the hole/orifice on top and the one for the tube on the bottom.

If you have the hole and you use the gasket for the tube, you have a big unmetered leak

If you have the tube, only one gasket fits 

I have a feeling you've nailed it here.   I don't believe I have the tube (think I'd remember seeing that) but I'm pretty sure I used a gasket that looks like the bottom.   The kit had a blue one like the bottom and a black one like the top.  I thought 'well, since all the other gaskets I'm using are blue, I should use that one".... And since that wasn't dumb enough....I'm pretty sure I threw the other gasket away and the garbage man came yesterday.  Doh.

Carb disassembly round two will ensue tomorrow.

First one is a metering block with just the hole to line up with the corresponding hole in the main body and uses the top gasket with the small hole in the previous pictures 

Second one is a metering block with the transfer tube that has an O ring on each end and pushes into a corresponding hole in the main body and uses the bottom gasket in the previous pictures.

Thanks.  Definitely no transfer tube on mine - I would remember that and would have done the o-rings that came in my kit.

Fingers crossed that between that gasket and tightening the power valve we've got it licked.

Ken, does this suggest he also has the floats set too high?  Or you think the wrong gasket and lose power valve might cause this dripping too?

Numerous things will give it the drips

Keno - You nailed it.....gasket was the culprit.   Ran into town for a replacement, installed that and put a light twist on the power valve, put it back together and she started up with no throttle.   Running like a rebuilt carb!

I'm not sure how long it would have taken me to pin down the gasket myself, but it would have been after a lot of other screwing around.  Thank you!

It's one of those things you only screw up once  

And your first Holley carb rebuild is in the books