Dual spark plugs?

[sawfun]

Well I know a Briggs won't even with the engine warm.

I doubt like hell you would even get a "normal" saw to fire and run on that fuel... Nowhere near the compression required, let alone the timing.[/QUOTE

 

[Skeans]

Based on what I have learned about Honda's 250r's over the years, and building up my own shown in my avatar pic that is running the same 350 big bore that Spencerpaving is running on his saw but with slightly less carb and not being drag ported.. I would say that 55hp is very realistic, if not a conservative estimate of what his saw is putting out.

Just as a for instance and not intending to jack the thread, but I own another '85 ATC250r just like the one in my pic.. It is a stock engine with just the usual bolt-on mods, ie better carb, exhaust, and reedblock. In bone stock config, a 250r was stated to be right around 36hp. You could reasonably expect to be close to 40 with descent bolt-ons, and a bolt-on modded 250r is nothing to scoff at, but the modded 350 big bore R makes the other feel slow! And I am not exaggerating one bit. I have seen dyno sheets from an ESR 310 (which is 295cc actual on it's first bore) with similar add-ons as my 350, except a smaller carb and different brand of pipe, Paul Turner if I recall... That motor peaked out at 49 hp. So yes, I would say 55-60 hp pretty easy on his drag ported 350cc saw.

That thing RIPS Spencerpaving!!! Thanks for sharing the vid!

Just throw this up as well I run big bore 250r's my last motor was a 363 and in the 70's with no issues, a 431 it's possible to hit 100.

Sent from my SAMSUNG-SM-G890A using Tapatalk

 

[RIDE-RED 350r]

Absolutely right Skeans... Your 363 a CPI Sphynx by any chance??

 

[Skeans]

Absolutely right Skeans... Your 363 a CPI Sphynx by any chance??

Yes it was 4 mill hybrid engineering motor and one off pipe bigger body then that out of frame drag pipe.

From left to right a 431 puma 250r based motor, and the right is a 363 sphinx with its inframe "torque" Shearer pipe.

Sent from my SAMSUNG-SM-G890A using Tapatalk

 

[RIDE-RED 350r]

Badass mills right there! Some of the nastiest 250r's going are running CPI's built by Pete at Hybrid Engineering with pipes by Shearer! Nice!

 

[Backyard Lumberjack]

Based on what I have learned about Honda's 250r's over the years, and building up my own shown in my avatar pic that is running the same 350 big bore that Spencerpaving is running on his saw but with slightly less carb and not being drag ported.. I would say that 55hp is very realistic, if not a conservative estimate of what his saw is putting out.

Just as a for instance and not intending to jack the thread, but I own another '85 ATC250r just like the one in my pic.. It is a stock engine with just the usual bolt-on mods, ie better carb, exhaust, and reedblock. In bone stock config, a 250r was stated to be right around 36hp. You could reasonably expect to be close to 40 with descent bolt-ons, and a bolt-on modded 250r is nothing to scoff at, but the modded 350 big bore R makes the other feel slow! And I am not exaggerating one bit. I have seen dyno sheets from an ESR 310 (which is 295cc actual on it's first bore) with similar add-ons as my 350, except a smaller carb and different brand of pipe, Paul Turner if I recall... That motor peaked out at 49 hp. So yes, I would say 55-60 hp pretty easy on his drag ported 350cc saw.

That thing RIPS Spencerpaving!!! Thanks for sharing the vid!

well, my initial thots were maybe easily 50--60 hp... but then I thot if I was wrong... lol... everyone would laff at me. Backyard Lumberjack: so I came in a bit conservative, with an out as needed if needed... " maybe more." interesting to hear what the bolt ons do... and as such the comp saw prob is quite a bit more... cuts timber like it was paper mache... I like the abbreviated topside handle... right above the L & R spark plugs...to be honest... that saw scares me... just looking at it!! lol... good case: pix worth a thousand words!

enjoyed the vid! I assume it is on gasoline... maybe avgas? definitely quite a 'Bench Project!"...

 

[Backyard Lumberjack]

Looking back, it's a good thing that as we grow older and mature, we learn from our life lessons of the past.

If we didn't, most of us wouldn't be alive today.

I remember the TM 400s when I had my TM 250... and thought.... OMG! 400!! and the 250 nearly kills me every time I take it out... course I had changed rear sprocket...

 

[Backyard Lumberjack]

I doubt like hell you would even get a "normal" saw to fire and run on that fuel... Nowhere near the compression required, let alone the timing.

I agree with you - no normal saw... lol but...

history tells us - mechanical ingenuity knows no limits... is only limited by the imagination of man. if built right, could start on gasoline, switch to alcohol, then the nitro... or gasoline, a gasoline/nitro mixture - then nitro. mite work in the example... turbo charged... T/F blown motors CR about 6.5:1!... I have seen engines that start on gasoline and switch over to a more exotic fuel once heat soaked...

and I think dual plugs may be a good starting point.

 

[Little Al]

I'm curious if anyone has ever ran a saw that way.
Hers a pic of a stock 046 cylinder with a second spark plug in the decomp.
View attachment 483972
I imagine one could solder a pigtail on the end of a spark plug wire for a second boot.

Back in the days of single cylinder road racing motor cycles in the UK( thinking Norton, AJS etc.,) a couple of tuners of these R Jackson, F Beart, developed twin plug head variants The Jackson motor ran a modified magneto producing 2 separate sparks, the additional plug sparking a tiny amount timing wise after the original plug, how this was done I have no idea, the standard single spark 500cc Manx Norton dependent on state of tune produced 52/54BHP at 7,800Revs. the twin plug variant from Jackson was quoted at 53/55BHP at 8,000RPM but from what I remember back in the mid 1950's the reliability was not as good as standard.

 

[Skeans]

well, my initial thots were maybe easily 50--60 hp... but then I thot if I was wrong... lol... everyone would laff at me. Backyard Lumberjack: so I came in a bit conservative, with an out as needed if needed... " maybe more." interesting to hear what the bolt ons do... and as such the comp saw prob is quite a bit more... cuts timber like it was paper mache... I like the abbreviated topside handle... right above the L & R spark plugs...to be honest... that saw scares me... just looking at it!! lol... good case: pix worth a thousand words!

enjoyed the vid! I assume it is on gasoline... maybe avgas? definitely quite a 'Bench Project!"...

You can tell by the sound it's on Alky minimum, now going to nitro or nitro/menthol mix I've seen and of the guys doing in drag bikes but they don't gain like you'd think and end going back to straight alky. Where do see it is in 4 strokes though with a single plug head roto start application with nutty compression. My 431 and 363 I had both ran up at 15.5 to 1 on 110, for M1 alky I'd be in the 17 to 19 to 1 range on compression for nitro I'd throw out maybe 22 or 25 to 1 range and that'd be full roto start application because there's no way in heck my little butt is kicking that. The original point of those dual plug heads was to thread a decompression in for someone that couldn't kick over a big bore R or for a guy's wife could kick her bike.

Sent from my SAMSUNG-SM-G890A using Tapatalk

 

[Backyard Lumberjack]

You can tell by the sound it's on Alky minimum, now going to nitro or nitro/menthol mix I've seen and of the guys doing in drag bikes but they don't gain like you'd think and end going back to straight alky. Where do see it is in 4 strokes though with a single plug head roto start application with nutty compression. My 431 and 363 I had both ran up at 15.5 to 1 on 110, for M1 alky I'd be in the 17 to 19 to 1 range on compression for nitro I'd throw out maybe 22 or 25 to 1 range and that'd be full roto start application because there's no way in heck my little butt is kicking that. The original point of those dual plug heads was to thread a decompression in for someone that couldn't kick over a big bore R or for a guy's wife could kick her bike.

Sent from my SAMSUNG-SM-G890A using Tapatalk

>and that'd be full roto start application because there's no way in heck my little butt is kicking that

not at that CR, for sure! can you just see it, the saw is ready, on a stand... and up comes the starter guy... just like a digger.... engages starter unit, pilot (chain saw operator calls: CONTACT!... and "clear chain!") squirts in some alky - and then... WWRRRR-R-R-R-R... and ignition-ON...and Whampussss! and the lil stinger lites off.... comes to life... and cracks on the alky... poppin' an pissn' like a mean 'ol nasty bull just hunting for someone or some thing... to snarl at!

and the crowd hoots n hollars...

 

[HuskyHeadDave]

Big plug looks ashy to me...?