Johnson FD-12 Won’t Run

[crosbyman]

There is a utube of a guy repairing a similar pump and it does not have a push spring inside  like the omc square pumps     just  2  rubber check valves leading me to think it works with both  pressure and vacum   to suck fuel  in to the pump  and  then a pressure pulse to  push fuel OUT to the carb ….

(44) Ferris mower Mikuni fuel pump repair – YouTube

 

in other words it needs both.. push and pull to flex the large inside plastic diaphragm  .

Your pump  may not like   the absence  of a  strong vacum pulse  from the  side air  nipple …. it giving out just a pressure pulse since  it’s  vacum   is cancelled out by the reeds openning up on the upstrokes to draw fuel in the crankcase .

 

anyhow you are  on the road to  happiness 🙂

Joining AOMCI has priviledges 🙂

[Bob Wight]

OK, so I found a bypass cover with a fuel pump port off a 1960 18hp and installed that along with a Sierra square fuel pump.   Motor will now stay running but sneezes and coughs at mid-range speed and no amount of fiddling with carb adjustments seems to make a difference.   I think the problem now might be the fact I re-used the old ignition coils.   They tested good on the meter and initially seemed to put out a good spark with the plugs in free air, but I think I may be losing good spark under full compression load while running.   Here’s a Youtube video:

https://www.youtube.com/watch?v=SFCkzKldlhM

I did manage to get one pretty good run after this one where the motor ran pretty smooth but then died out at the very end.     I pulled the plugs after testing today and you can see in the attached pic a big difference in the plugs with the bottom cylinder heavily oil fouled, so that makes me think I’m losing spark.   I tested the plugs in free air again after removing them and although they put out a spark, it’s not a hot blue spark, more yellowish-light blue.   And FWIW, these are brand new NGK plugs.

Comments welcome.

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1955 Johnson QD-16
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."

[Steve D]

New condensers?

[fleetwin]

I dunno, that sneezing/coughing doesn’t sound like a spark issue.  Have you tried the engine on a boat?  You can’t judge to much by revving it in neutral in a test tank.  The engine idles well, correct?   Where is the idle needle set now?  The only other thing to check is the sync adjustments.  The engine will cough and fart off idle if the carb is opening too soon.  Any possibility that the choke linkage is messed up holding that throttle plate open?  Perhaps the carb linkage is binding causing it to hang up.

Again, I wouldn’t go crazy looking for problems until you run the engine on a boat and dial in the needle adjustments properly.

[Bob Wight]

Steve D – yes, it has new condensers.    I re-used the original OMC points as they were in good condition.   Just filed and cleaned real good.

Don – haven’t tried it on a boat yet, but I’ve never had one that wouldn’t run smooth in the test barrel.   It seems to idle well, although it did sneeze a few times and it took some adjustment to get it to smooth out.   Idle needle is a little over 1-1/2 turns open, high speed at 1/2 turn.   I’ve looked at the sync adjustments and they seem spot on but I’ll look at that again tomorrow along with the carb and choke linkages.

I’m just puzzled about the big difference in the spark plug appearance.

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1955 Johnson QD-16
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."

[crosbyman]

hopefully the crankcase purge valve is working ok otherwise oily vapours may pools down the the  crankcase.

Joining AOMCI has priviledges 🙂

[Bob Wight]

As noted in the Service Manual, I cleaned out the bleeder valve passages when I had the powerhead torn down.    I’m getting a good oil slick in the test barrel at slow speed, so it seems like it’s working correctly.   Something else to look at I suppose.

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1955 Johnson QD-16
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."

[fleetwin]

I remember you mentioning that you altered the reed plate, perhaps this has something to do with it.

[Bob Wight]

With the original air pulse pump fed from the air nipple on the manifold, I had removed the reed plate check valves and plugged one of the two ports to get pressure and vacuum off one cylinder (I’ve used this approach on several other motors when I used an air pulse pump).  See pic of reed plate plug.

 

In the 2nd test run with the new pump fed from the bypass cover, I left the reed plate plug in place and capped off the air nipple on the manifold.   Not sure if it will make a difference, but today I pulled the manifold and reed plate and re-installed the check valves on the reed plate.   In pulling the manifold and reed plate off, I also opened up the carburetor again just to make sure nothing was amiss there – it all seems OK.

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1955 Johnson QD-16
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."

[billw]

To me, if I looked at those two plugs, I would be thinking I had poor spark on the one that is NOT fouled, as it doesn’t even look like it fired much at all. If you don’t have true, open-air spark testers, you can just rip the ground electrodes off regular plugs, creating a bigger gap. A good OMC ignition will jump that gap in open air.

Long live American manufacturing!

[Author]

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