Rebuilt Johnson WOT issues

[chevy76]

Engine -1998 johnson 130 hp v4 90 deg. looper

History - Rebuilt powerhead had a bad piston, 3 hours on engine at 1500 -2000 RPM with 32:1 oil mix, disconnected the VRO. Idles great at 1500 - 2000 rpm

Problem - Above 3000 rpm engine will surge and rpm's will surge, At WOT rpm's surge from 4500 to 5500, top two plugs after inspection look normal, bottom two plugs are wet.

Any ideas?

 

[tashasdaddy]

Re: Rebuilt Johnson WOT issues

check spark and compression on all 4, you have 2 carbs, top carb for top cylinders, bottom carb for bottom cylinders, sounds as if bottom carb is over fueling, possibly, float needle not closing all the way.

 

[chevy76]

Re: Rebuilt Johnson WOT issues

The mechanic I bought the engine from, just called me back and thinks that the fuel mixture has to much oil. He wants me to go to 50:1. I was advised by others to run 25:1 during my 10 hour break in, but I was also told that would foul plugs, so I went to 33:1 as advised by a shop that does rebuilds and said that it would not foul plugs, but give sufficient oil for break in.

My question is why are the bottom plugs the only ones that are wet, I would reason that all 4 plugs would be wet if I had too much oil in gas?

 

[chevy76]

Re: Rebuilt Johnson WOT issues

compression is 140 psi on all four. spark is good on all four.

 

[northwoodslivin]

Re: Rebuilt Johnson WOT issues

I would listen to Tashasdaddy. Sounds like sound advice to me, obviously it is bottom carb related, hopefully.

 

[ezeke]

Re: Rebuilt Johnson WOT issues

Surging is very often because of air leaks; check from fuel pump through the intake manifold.

 

[emdsapmgr]

Re: Rebuilt Johnson WOT issues

Wet plugs could be a sign they are not firing. Put an inductive timing light on the bottom two cyls when it starts to surge and check for good spark. Weak ignition components tend to fail as the engine gets up to normal operating temps. It's easy to do and once you eliminate spark as an issue, you can get back the the fuel system.