Petter M Set-up to Cure Back Firing

Discussion in 'Help Wanted' started by Kevbuts, Dec 18, 2011.

  1. petternut

    petternut Administrator

    The old taper seat US plugs I guess but I've no idea why.

  2. Kevbuts

    Kevbuts Member

    That's my good old colour blindness kicking in I guess Mark! I thought it looked white in the poor light of my shed last night!

    I will get hold of a few other old plugs and give them a try in the engine to see what works best.

    From posts in other threads / forums it seems that the governor linkage may be partly responsible for the misfiring (see this link: ... post201499). The next thing I am going to try is fitting a return spring to the trottle linkage to pull the butterfly towards the closed position. Hopefully this will reduce the jerkiness of the throttle linkage movement (resulting from worn linkage connections) when the engine is running. I will keep you posted on the results.
  3. jayeastanglia

    jayeastanglia Member

    fuel type makes a diffrent as petter m wouldnt run on unleaded fuel on a load as it got hot quickly but would run fine with no load on it..when mine was running on parrafin with a load it ran ok with no oil spots but off load it ran rough and would foul up ts plug after 2 hours running. mine had a 8com plug in it and as long as it ran on a load even a light one i never had to clean the plug....also make sure you got the right grade oil in the oil pot as seen a few on rally fields that are running with 2 stroke oil in them..
  4. petternut

    petternut Administrator

  5. lambe

    lambe Member

    Roland you say 18mm plugs weren't further developed after ww2, I would say they are now some of the most highly developed of all plugs now! All the large gas engines running all over the world use 18mm long reach, many flat seat, they are designed to run at full load 24/7 often to 3000hrs on very inhospitable conditions, ie refuse bio gas high in silicon, sulphur(sulfur) and other nasties and survive intact operationaly. I often carry some as they will start a stubburn engine though not run one as they are cool running., will put the number up when home.
  6. petternut

    petternut Administrator

    Interesting though not a lot of help to us :)

  7. Skankin_giant

    Skankin_giant Well-Known Member

    Been having a chat with the guys at Green Spark Plug as I would like to try a bit hotter plug in my Scott SE which is 1hp at 500 rpm to 5 1/2hp at 2000 rpm, I currently have a Lodge BBL fitted but its not 100%, he said a modern hotter alternative is the Bosch M12B, at £3.25 its got to be worth a shot!

    Cheers Steve
  8. Numpty1

    Numpty1 Member

    ....and have you read Green Spark Plugs advice on modern alternative plugs?

  9. Skankin_giant

    Skankin_giant Well-Known Member


    Cheers Steve
  10. highrange

    highrange Member ... on-vs-ngk/

    interesting...... but I don't recall having this sort of problem with older cars, my Landrover, or the motorbike, all of which have carbs, and have been flooded on occasion. Or is it just when modern plugs are used on very old engines with feeble magnetos ?
  11. Numpty1

    Numpty1 Member

    I think the best thing is to follow their advice, run the engine till hot then fit the new spark plug. As you say at £3.25 what have you got to loose? As for longevity....

  12. Skankin_giant

    Skankin_giant Well-Known Member

    See how it goes, i fit dosnt last 5 jumps out the back door I have 5 BBL's to choose from, in the mean time will keep a eye out for a 9-11COM.

    Cheers Steve
  13. Kevbuts

    Kevbuts Member

    Had the engine out today, and traced the source of the misfiring to a worn throttle linkage. As you can see in the video below (apologies for the poor quality, it was getting dark when i took it this afternoon), taking the play out of the linkage with my finger makes the engine run much better as it stops the butterfly moving back and forth of it's own free will on the worn linkage joints.

    Video Link:

    Next job is to make up some bushes to take the play out of the connections where
    the butterfly spindle connects to the throttle rod, and the governor arm and connects to the throttle rod. Alternatively I may re-fabricating the throttle rod in a slightly larger size rod to better fit the worn holes.

    Thanks to all that have offered advice to help me sort this problem out - it is much appreciated
  14. Victoria

    Victoria Member

    Best thing to do is make new bushes, its no use trying to fit a larger spindle to holes which could be worn oval. It will also maintain originality of the rods etc.
  15. AndyP

    AndyP Member

    You mentioned that the exhaust flange gasket is not very good, possibly air (oxygen) is getting in to the exhaust pot on over-run and causing any carbon monoxide to ignite?


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