I just got my boat back after basically having it rebuilt, and first of all the boat runs awesome. It is a PD with PVT's Pistons, Rockers and Rods, and BPS Cam, IM heads, Hig Rev Coils and a Mikuni. Block has 17 hours on it, so everything is basically brand new.

Running it for the first time today was impressive. It jumps up on plane immediately and then runs straight to about 29.5-29.8...and I stopped there at about 4350 RPM's(this was with a fairly light load with two people). I didn't want to run it too hard before she gets broken in a little bit. But at around 4300-4350 I started to hear a "pinging" noise inside the engine, it almost sounded like something was jumping around inside the block, but as soon as I backed off to around 4200, the noise went away.

I am hoping this is just bad gas, as it has been sitting since duck season, but not sure what to think. Thoughts?

Detonation.

Sounds like a BB in an empty beer can.

What type of gasoline were you using? Replace with fresh high octane gasoline and try again.

My last engine build did that....but only when using the BPS intake. I had to run a 50/50 mixture of super unleaded and AV gas.

Be careful with it....It'll cause internal cylinder damage pretty quick.

You mentioned that you have iron mountain heads...are they decked?

Depending on what pistons Al put in the engine, running decked heads may be too extreme.

I ran the flat top billet pistons with stock heads and my engine continued to detonate...

Considering your build...fresh gasoline should fix your problem.

Stock or CDI coils?

What main jet do you have in the Mikuni?

If you are running a 165 main at sea level with those mods you are going to be lean. I run a 170 with everything but pistons and rods. Always start with fresh gas, and def with a high compession motor that is prob going to have a hard time not det at sea level in the first place. I know of guys with those mods at sealevel running 180 mains

Sounds like you need to find a place that sells AV gas, or high octane race gas

IM heads are decked .030, I do believe, not .020

you prob. wouldn't have any issues trading them up with somebody for a stock set. Only thing to remember is the stock valves are a crap grade 2 piece. You may wanna think about replacing those with the stainless valves that come with the IM, SE TX, and Performance V-twin heads.

The engine recipe Al uses is the same as MB.

Pistons are shaved .110 and the connecting rods are .120 over stock.

When I called MB years ago questioning an engine build, I was told by Micah that there heads were decked .020 and is what the use on the MB 7000.

Again, that was quite a while ago so I'm not sure if they've increased the decking on their heads or not.

There are MANY of people running that same setup with no problems. Hopefully, your issue can be resolved by using fresh fuel.

Did you check your carb. jet sizes?

You should have at minimum a 167.5 main jet..I'd go 170.

As an update...the Carb had a 160 main still installed, and the spark plugs were not gapped correctly, they were still at around .045. I switched plugs, and gapped them to .030 and swapped the main jet for a 175.

All problems went away. I haven't played with the needle yet.... The boat runs really well. All deep water but runs 29MPH at around 1/2 throttle at around 4050 RPM's. Full throttle and trimmed appropriately it hits the governor at 4700 and is running 31-32. I only did this once b/c i am still seating the rings on the new piston, and breaking in the new cam. At about 3/4 throttle and prop buried a little it runs 30 MPH at around 4250-4350. This is with one person and fairly light load for me, but I did have a winch on the bow, a pull pal, two anchors, tool chest, two deep cycle batteries, 9 gallons of gas and my 100 pound lab and cooler.

It was a good thing I had the winch and pull pal also! We need some rain badly around here. This is on a back side of an island, that is normally around 6 feet deep!

Stuck.jpg

Good day though...it was nice to be back out! Thx to all of the guys who helped out on the site!