Acceleration issues.

Your constipation hypothesis carries a lot of weight.  All kidding aside, it does make a lot of sense with the known history of this boat. I know the previous owner did replace one of the exhaust tubes from the manifold back to the transom due to failure. I would suspect an overheating issue at some point as you described. I know the previous owner also experienced an impeller that came apart as well and was replaced. 

After I took on the boat years later and got it running, I took it out for a test on the water and made it about 50 yards out from the no wake zone and the engine began to run hot quickly and I shut it down. Which takes us back to me and my GF pushing it back to the dock. Still haven't lived that one down.

In any event, it was another impeller that came apart. I then proceeded to remove all of the impeller pieces I could find from the inlet on the raw water pump (where a lot were smashed into), the thermostat housing and the hoses from the thermostat housing to the exhaust manifolds. This is where I stopped. I recall looking into the manifolds from the inlet side (which was pretty small) and really couldn't see much. 

So I am assuming I need to remove the exhaust tubes from the ends of the manifolds and check the exhaust tubes for any obstructions and see what I find inside the manifolds from the exhaust end? I can only image how fun removing the exhaust tubes from the manifolds will be, but I will be careful with the manifolds. This may take a bit for me to get done but I will update as I move along. 

If this is the solution, I might have a new name for this boat.

The collapsible exhaust tube explanation makes a lot of sense, especially with the known issues of the two failed impellers and one failed exhaust tube. Pretty ingenious safety feature for an exhaust hose and great information to know and share. I told myself I wasn't going to work on the boat today but I couldn't resist inspecting the exhaust tubes from the exhaust flap forward. Both exhaust tubes are clear all the way up to the point where they bend up to connect to the manifolds. After the bend to the connection at the manifold is not visible. 

Also, when the impeller came apart on me and I spent the time to try and find all the pieces I was concerned that perhaps some of it made it to the manifolds. After reconnecting everything, I recall using an infrared temp gauge to check both manifolds to see if either one was running hotter than the other. Both were running at equal temps +/- a few degrees, so I assumed they were good. However, the flip side is they could be equally clogged. I'm not looking forward to removing the exhaust tubes and inspecting the manifolds but that will be next unless this information is helpful enough. 

My novice experience leads me to suspect that is time to return to the carburetor again after two previous shop rebuilds. The good news is we have checked a lot off the list (at least in my opinion) and I have learned a ton. We have to be getting close to a solution. Any other suggestions, advice or homework assignments? Thanks again for all the help, I really appreciate it.

I have had 2 quick fuels (2 different boats) and they have be hassle free.

 

Thank you as well KENO for pointing me in the right direction regarding the fuel line and providing the part number. A new carburetor without a fuel line that fits wouldn't do me much good. Ha. I will get that Sierra fuel line ordered as well. 

I also thought I read an earlier post about a spacer that was available for the QF conversion. If I find it I will post that part number again here as well. Hopefully I wont need it if my arrestor is small enough, but inevitably I'm sure I will.

Thanks again for all the guidance in getting this far!  I will get the orders in this weekend and update soon with the new QF installed. For those of you with smooth running boats, enjoy the weekend!

Something on the advance mechanism didn't look quite right, so I removed the nylon screws and did a quick inspection of the dizzy.  After poking around a bit, I was able to get the advance mechanism to freely rotate without issues.   Then I re-installed the nylon screws...not too tight.  Everything worked as it should.  Cap back on and the engine fired up and the advance curve was spot on.

At the time, my assumption was that the nylon screws had somehow impeded the advance mechanism from rotating.  Perhaps my poking around a bit somehow freed-up whatever was binding-up the advance mechanism.  As the dizzy worked as advertised, we buttoned-up everything up and I didn't give much more thought to the nylon screws.  Go figure...

JQ

 

I did want to share a few things in getting it installed that may help others in the future who decide to go the QF route. If you are using the Holley 12 degree wedge under your QF, the 3.50" carburetor studs in the rear worked perfect for me. The mechanic had used bolts (not sure why) in the rear with the 4160 which will not work with the QF as there is not enough clearance to insert a bolt on one side. 

The spark arrestor just barely hit the float adjustment hardware on the top of the QF so I decided to go the spacer route. JQ has a previous post with a B&B Air Cleaner Sure Seal 1.50" spacer and another one from K&N which got me looking and I found a few others. Sorry, I need to review how to post a link or quote some ones previous post. In any event, I also found a Stef's Fabrication 72255 B&B Performance Air Cleaner Sure Seal 1" spacer that should be here today. I know its only a 1/2" shorter but it looked like the clearance was going to be close. After I ordered it I also found a 1/2" spacer on the Holley/QF site made by Mr. Gasket. So just a few options if clearance may be a concern.

I just want to thank everyone again for all the help. I hope to get the boat on the lake in the next week or so and give it run under load and see how it does. I am very optimistic and I will update as soon as I do. Thanks again. 

New carb ran great on the trailer. Easy starts and restarts so I was hoping for the same at the lake. Backed the boat down the ramp into the water and it would not start. The look from the GF was not one of confidence. It acted like it was starving for fuel. After about ten minutes of breaks and multiple attempts with multiple throttle pumps each time it finally started and idled great.

The Good: Once launched, it shifted into gear with no hesitation or stumble at all which was one of the previous issues. It was extremely smooth and it was great! Throttled up past the no wake zone which was smooth all the way to WOT. The Ahhhh sound on the high end had disappeared. However, when I looked down, the RPMs still remained at 2700 and the speedometer showed about 30. The Ahhhh was gone but the top end speed remained about the same. So we were content with that for the day. Cruised around awhile and the low end issues were gone and found a spot to anchor for a bit. Started back up after awhile and low end issues were ok but not as quite as good as it was before shutting down for a bit. 

The Bad: After starting back up and idling out we cruised for a bit at maybe half throttle and then I opened it up to WOT, there was a pop which sounded like it came from the carb and it died. GF look number 2. After multiple attempts to restart, it sounded like it wasn't getting any fuel. A passing boat was nice enough to tow us to a cove away from the rocks so we could anchor up and call in for a tow. Which of course took two hours to arrive. GF long two hour look number 3. While waiting I could see that there was no fuel in the primary float window. 

The Ugly:

 

The long tow back to the dock. I told her it runs great as long as we are being towed.  Yup, you guessed it...GF look number 4.

After contemplating this from yesterday until now my thoughts are it has to be the fuel pump. The pump is definitely older if not original. It is also about the only thing that hasn't been replaced in the fuel system. So I decided to go out this am and turn the engine over a few times and see if I could get/see fuel in the primary window. There was none. I adjusted the float level on the primary float to raise the float and no change so I returned it to the original position. I disconnect the fuel line from the carb and turned the engine over a few times to see if fuel was being delivered and fuel pumped out into the can at the same rate when the fuel pressure and fuel flow was tested earlier in this post. I am so confused.

 

I am going to order a new fuel pump no matter what based on its age but I am confused.  Why is there no fuel in the primary bowl on a brand new carburetor that was running fine (other than full top end), then dies, and the fuel pump seems to be delivering fuel? Am I lucky enough to get the one QF carb with issues? I also don't want to be tinkering around inside a brand new carb with no experience of rebuilding carburetors especially with what the new QF cost. Thoughts?

Additionally, any recommendations on a new fuel pump for this 351W. The one that is on it is a Carter with the internal filter. The new Carter pumps didn't have the best reviews. Is a pump with the internal filter necessary since it also has the fuel/water separator filter as well? 

Thanks

I was able to get the fuel pressure check done this am as well. Initially there was none while cranking and then it jumped to 6 psi. I tried it again and about the same. So I re-attached the fuel line and cranked it (I didn't crank it last time I raised and returned the float after I got home) a bit and it looked like some fuel in the primary bowl. I adjusted the float bowl up a bit and fuel level is back right in the middle of the window. When I tried this exact same thing at the lake after it died it did not produce the same result as it did today. In my novice opinion, it has to be a failing fuel pump. If we are correct it may also explain the hard start at the dock and loss of power at the top end (the only issue left after the fuel pump). Keeping in mind that I was the one stranded on the water for two hours so my opinion doesn't carry a lot of weight. 

This seems like really good news to me since I was really hoping to rule out the new carb. Any thoughts while I wait for the new fuel pump?