Petter M Set-up to Cure Back Firing

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

  1. Skankin_giant

    Skankin_giant Well-Known Member

    I havnt plaid with a Petter M in about 10 years, I can't remember what plug I had in it, but I have had positive results running a 7com in a WX11, though it more of 8 stroked rather then 2 stroked.

    Cheers Steve
  2. petternut

    petternut Administrator

    Its the grade of the plug that matters.What is the grade of your pink plug?
    Easy Martin. If Kev wants to chase his tail that's fine by me.

  3. campingstoveman

    campingstoveman Active Member


    As you are undoubtedly aware we have spent many hours looking for something that doesn't exist, I just dont want poor Kevin falling into that trap and it is turning a little bit into a Petter Fest :twisted:


    Martin P
  4. Numpty1

    Numpty1 Member


    It can be a fact that no 2 engines will run the same, even if they are identical models. It also seems true that engines with lower compression run better off load than those like new. Perhaps Roland or Eric can better explain the maths behind that one? I am reminded of comments made by a well known Engine Restorer about his extensively rebuilt Ruston Hornsby open crank and the fact that it knocked, rattled and banged more than the completely worn out and bodged example further down the line that ran like a clock!
    As far as fuel comsumption is concerned, ISTR a chart quoted by Listers for the D type which showed light loads consumed more fuel than medium loads with only heavy loads needing more.
    If you can get access to a genny, or can make a brake up, I'd give it some load to help bed the rings in. I'm in the process of re ringing an engine that didnt bed in, beautiful compression but burnt oil BAD!

    Tea is ready must dash.

  5. Skankin_giant

    Skankin_giant Well-Known Member

    Im have noticed this when running my Scott SE, it will mop fuel running no load (up to 2 gallon in a day!) but with a dynamo on it, it seems to drink closer to the 0.8 of a pint a hour quoted in the manual, have not been able to give it a good run on load as I blew the bulb and its a £25 replacement!

    Cheers Steve
  6. petternut

    petternut Administrator

    Its an engine related thread in the right place. I don't see your problem and I'd still like to know the ID of the pink Lodge.

    Happy New Year
  7. Victoria

    Victoria Member

    If I might join the "Petter Fest", I think Mark and Roland are both correct. It defies all known science but certain engines run best on certain makes of plugs. In the 60s when I ran Sprites and Midgets, undoubtedly they were best on Champion plugs, VWs and derivatives run best on Bosch and they last longer. I have never found anything that runs best on NGK!! With stationary engines its generally a case of 'suck it and see' - but by and large most are best on Champion, maybe its the low compression that's a factor and the grade of electrode material. Getting off the Petter theme - Victorias are best on Champion 11-Comm and I suspect that like Petters, though not two strokes, they burn a significant amount of oil.
  8. highrange

    highrange Member

    In the late 60s NGK were a new breed, catering mainly to the Japanese bikes that were startng to arrive. They certainly knew how to tame 2-strokes.... I changed to NGK in my (even then) old Lambretta (aka "The Heap") and said goodbye to whiskering and the other ills 2-strokes fell prey to.
    My current Honda uses NGK plugs as OE..... I recently fitted their iridium-tipped version, and the bike never misses a beat: it has 2 plugs per cylinder which probably helps, although I suspect it's really to help combustion in a slightly odd shaped (with 3 valves) combustion chamber.
    Back to Petters ..... does the oil used have any bearing on running? I understand it's not a "petroil" system, but I imagine some oil enters the crankcase and mixes with induction air/mixture and is burnt.
  9. Skankin_giant

    Skankin_giant Well-Known Member

    My Norman SC will only run in a NGK A6, put a Champion D16 in and it wouldn’t look at starting!

    Cheers Steve
  10. Numpty1

    Numpty1 Member

    Before we wander too far into 'plug wars' I think it is fair to say that the first thing Kevin needs to do is bed those new rings in, and my advice is a few hours running with a moderate load, do we all agree?
    After that look for a selection of plugs and try a few both modern and old equivalents to see which gives best performance.
    If you dont have a tin of plugs handy get down to your local autojumble and have a rummage. Look for 'two piece' plugs, Lodge C3, Champion 8 Com to start with and then look for similar plugs in other brands and different heat ranges. Dont worry about them being dirty/rusty. So long as the electrodes aren't worn away and the insulator looks good buy em, at 50p - £5 you cant go wrong and if the odd one is duff.... well so what its a darn sight cheaper than paying the ridiculous prices on the internet.


  11. petternut

    petternut Administrator

    Yes but.....bedding in the rings will actually make it run worse off load as it will hunt faster and over a wider range. Yes some oil does get burnt when an M is working and should be seen as a very slight haze in the exhaust. Off load the oil emerges in unburnt fuel as the dreaded Petterspots (TM PT-E).

    I stand by my plug recommendations which do not include the Lodge C3 or the D16 or the 7Com all of which are too cold.
    When you find an old plug please do not use any metal brush as this will leave traces of metal on the insulator. Grit blasters damage the ceramic. I suggest petrol or carb-cleaner only and this is a must on the mica insulated plugs. Use only unleaded with mica plugs as any additive pollutes the mica. It was the addition of lead to fuel that caused the mica to be replaced by ceramic.

    I'd like to avoid plug wars too :roll:

    PS Thanks for the 11COM tip for the Victoria Eric. I have one and will try it. I suspect the lack of an oil ring may explain the oil burning !
  12. ArthurG

    ArthurG New Member

    A most interesting thread!

    Keep going chaps. :)
  13. Numpty1

    Numpty1 Member

    Silly me, of course I'm in 4 stroke mode!

    Interesting you think the C3 is too cold, I was under the impression it was a similar heat range to the 8 Com, I will agree with you on the fact that the older C3 with Mica or white insulator is a much better plug than the later redesigned Pink ones. My suggestions were for a general 'come in handy' box (I should have pointed that out). Personally I think the older plugs are better suited to equivalent age engines but I know others have had great success with new ones so I wouldn't rule them out entirely.

  14. Numpty1

    Numpty1 Member

  15. Kevbuts

    Kevbuts Member

    Thanks for all the tips guys. I must confess to having very little 'plug knowledge' so all your responses and advice are much appreciated. I am learning fast!

    I checked the Lodge plug Roland - I was mistaken, it wasn't a 'pink' Lodge, but a white Lodge C3 with the triple electrode. The engine started and ran ok on it (well, as well as it has run to date!), but I note your recent comment about the C3 not being suited to Petter M's.

    Following the earlier comments I got the engine out again yesterday morning and tried a Champion 8 COM plug in it. With this fitted the engine started even easier than normal and ran well, but the misfiring was still there. With a substantial load applied to the flywheel the engine will run evenly, firing on every stroke with no misfiring at all. On light load there is ocassional misfiring, and with no load it is still misfiring regularly on the first firing stroke after a few missed beats on the over-run.

    I have just got myself a copy of the Petter M wall chart (from Kelsey Publishing). This chart suggests adjustments that can be made to help cure misfiring on light load, most of which have already been mentioned in this thread (plug, reducing gap in reed valve stop, retarding ignition). However, one thing that is mentioned on the chart is the introduction of a 1" diameter pipe 8" long into the silencer below the outlet neck! I guess this is to increase back pressure? Has anyone tried this? My silencer is the version where the outlet has a male thread on the outlet casting, and a female threaded sleeve to receive the main outlet extension pipe (see photograph below):

    My outlet pipe is 1 1/2" BSP and is currently 2' long. As can be see from the photo below, the actual diameter of the outlet in the neck of the silencer casting is actually very small (I am guessing it's approximately 3/4" diameter), so this must increase the back pressure notably anyway. I would welcome your thoughts on this.

    With this restriction in the silencer casting, I don't see how I could ever introduce a 1" diameter pipe into the silencer below the outlet as recommended on the Petter M wallchart!

    I think a load is the only think that is going to make my engine run without misfiring. So the next job is to find a nice centrifugal pump or something to put a decent load on the engine! I don't fancy a generator / dynamo as electronics are not my thing, and I would probably end up firing myself across the rallyfield if I had one!!

    Thanks again for all the helpful comments, and Happy New Year to you all.

  16. Kevbuts

    Kevbuts Member

    Thanks for this Mark - that's a really handy link. Interesting that the Lodge C3 is claimed on that webpage to be the hottest 18mm plug that Lodge produced, and hotter than the Champion 8 COM! How do you know what temperature plug an engine requires? Is it just a cast of experimenting to see which plug your engine runs best on? Am i right in thinking that an engine working on light or no load will be happy using a 'colder' plug than if it were running on heavy load?
  17. marshall-man

    marshall-man New Member

  18. Numpty1

    Numpty1 Member

    Kevin, that is a pink Lodge C3 The white C3 has a plain cylindrical insulator. As you have found a different plug makes a change in characteristics.
    Load will only completely cure the problem, but changing plugs may improve things. I wonder if an 11 COM would be any better? but stick with Rolands advice, he knows best.

    Happy New Year

  19. petternut

    petternut Administrator

    No reason you shouldn't try a 9COM or 10 or 11. Its all grist to the mill.

    I only offer opinions which in the end are worth what you paid for them :)

    Having spent many hours with such comparison charts, and a stack of old plug catalogues, I'll make two observations: they claim equivalence when only a partial overlap exists, they cannot be made to work in both directions. That one looks to be based on a late Champion book when most of the plugs were long gone. The D16 claims to be the equivalent of an 8COM which it plainly isn't!!
    At best they are a suggestive guide only.

    A 1938 Lodge cat shows the 18mm 1/2" reach plugs from cold to hot as (then Champion equivalent in brackets); H3 (16), CV (7COM), C1 (7), C3 (7COM), sc (15A, 15), BBL (8COM), 3BL (9, C15).
    At that time the recommended plug for the Petter M was the BBL and the same plug for most Lister petrol models. The 3BL was recomended for the petrol/parrafin Listers.
    For me an old mica C3 will work for an on load M but not off-load. The later pink C3 won't do for either.
    I offer the thought that each WW drove vast strides in plug develpoment so that the mica plug was at its best from c1918 until the adoption of lead in the late 1920s. That drove the development of ceramics like Lodge's Syntox and they reached a peak during WW2. I doubt that 18mm plugs were much developed post WW2.

  20. highrange

    highrange Member

    Apart from the taper-seated abberations used in Ford's Pinto engine. Where did that come from?? :?

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