97 Johnson 150 looper vapor pump issue?

[RodDasher]

Hi everyone,
I am working on a Johnson 150 (J150NXEUC) that I re-built a couple of years ago and am still in break in. The problem I can't seem to fix is fuel spitting out of the #1 carb throat. I decided to pull the carbs and manifolds again and examine them for mistakes or defects and while it was apart, I decided to replace the manifolds, gaskets and the number 1 reed valve cluster (even though the existing one didn't seem bad). At this point i am just trying to eliminate possibilities and the troubleshooting section of my OEM service manual only mentions reed valves and associated parts as a possible cause for fuel spit-back. I just tried to run it on a flushing devcie and even though it didn't start yet, when I stopped cranking, fuel spit out of the #1 carb. Having read a little about vapor pump troubles I disconnected the hose from the pump to the #1 carb. Then when I cranked itno fuel spit from the carb OR the vapor hose. When I reconnected the vapor hose and cranked the engine, it spit back again! Am I looking at a possible vapor pump diaphram leak? Can anyone think of something else I should try? Thanks for any help you can give.

 

[faztbullet]

Vapor pump does not hook to carbs

 

[kevinj]

Johnson 150 (J150NXEUC) ...... fuel spitting out of the #1 carb throat. ....... OEM service manual only mentions reed valves and associated parts as a possible cause for fuel spit-back. .....even though it didn't start yet, when I stopped cranking, fuel spit out of the #1 carb. ..... vapor pump troubles I disconnected the hose from the pump to the #1 carb. ......no fuel spit from the carb

As Faztbullet said, the VST does not connect directly to the carb, so by disconnecting the VST outlet you cut off fuel supply from all 6 cylinders.

With a bad reed valve you'll see a chuff of air and atomized fuel blow out the carb throat on each down stroke of that cylinder. These engines came with stainless steel reed leaf petals which can go bad, but usually don't. It's possible when you had the engine apart you bent a leaf. Another possibility is some previous owner installed fiberglass/carbon fiber reeds like CCMS or Boyesen and maybe the leaf got chipped or broken. Removal and inspection of the reeds will tell that story very easily.

If you're getting liquid fuel spitting out the carb my best guess is you don't have the float level set properly on that carb and it's allowing a constant flow of fuel into the chamber. Or, if you worked on the carbs, you may have forgotten to re-install your main jet into the bottom of the float chamber and too much fuel is flowing into the carb. Whatever the cause, you can be certain the VST is not the culprit.

 

[RodDasher]

Thank you for your replies @kevinj and @faztbullet. I pulled the carb apart last week when I replaced the manifolds and the number 1 reed block. They are all factory stainless reeds and they all appeared to be in perfectly good condition, but I bought a new one for #1 just to rule it out. I also checked and re-adjusted the float, but it was already pretty much on spec and the carbs were all new when I rebuilt the engine.

To be sure it wasn't the float, I pressurized the system and filled the carbs by pumping the bulb and watching. No fuel came out of carb 1 or the others when they filled and pressurized. Also, unfortunately, I am certain that the main jet is installed. I will check my hose routing from the vapor pump. I am correct that the small diaphram style pump above the vapor separator chamber with 4 hose connections on it is the vapor pump, right?

I am including a few pictures to show how it's connected. I had photos of what it was before the rebuild and I connected the way it was. Although my hose routing diagrahm in the manual shows the hose from the upper main bearing to the air silencer with a tee leading to the vapor pump, My air silencer only has one inlet (and always did) at the bottom connected to the port side balance tube. The hose from the upper main with the tee is really only long enough to connect to the top of the #1 carb.
Thanks again for your insight and assist!

 

[RodDasher]

OMG @kevinj and @faztbullet! I just went out to the engine again and may have found my mistake! Feeling really dumb on this one. That hose I connected to the carb vent on #1 maybe was supposed to go into the hole on top of the air silencer that I didn't notice before?! Would make sense since all the other vent tubes just vent to the atmosphere. Not sure what I was thinking when I did it, but i am going to look for my old pics from before I started my re-build. Maybe I can blame it on the p.o.! Does this look right to you guys?