My latest Flat Head build

J

Jay_Wrix

New Member
#1
#1
Figured I would post some pictures of my latest all out flathead build,

Should make some real good power when I get her dialed in when the warm weather comes!

Does anyone have experience in timing a dual plug? I have some ideas....

It has

full port and polish
eyebrow removal
Dual spark plug head
"long arc rod"
weisco piston
Stainless valves
undiscclosed cam
supporting valve springs
copper head gasket
mikuni carb
custom aluminum manifold
Robertson Torque Tube header, built for a Rupp Roadster


assembled.jpg 20141221_121034.jpg eyebrowed.jpg dualplugcoil.jpg 20141226_164014.jpg
 
H

Havasu Dave

Moderator
#4
#4
CarPlayLB said:
That head is crazy! looks OEM! ...and where do you find a coil like that? Did it come from a 2 cylinder Briggs?
Click to expand...
Yep. Twins. They burn out quickly, so Briggs recommends gapping both plugs at .015 instead of .030. I assume timing would be the same, and no idea why this is needed, except it looks cool.
 
125ccCrazy

125ccCrazy

Well-Known Member
#5
#5
Welcome back Jay, I wondered whatever happen to you,,, do you still have the funnel style intake manifold you got from me?

as far as I understand both leads fire at the same time so timing should be set as recommended for the cam... one lead doesn't spark and then the next..I may be inaccurate but I'm pretty sure on the twin the coil fires on the opposite stroke of each cylinder...so each cylinder gets fire twice per complete cycle..... anyone with different thoughts or information correct me if I;m wrong..

bandit 40 said:
Whats the benefit of a dual plug and wire ?
Click to expand...
Mark it's to burn more of the air/fuel mix being dumped into the engine so the theory (fact) is the more air and fuel you can cram in an engine, compress and burn effectively the more power the engine will make.
 
J

Jay_Wrix

New Member
#6
#6
the Dual plug is to gain a better burn and high speed running stability and smoothness, in theory at least, it was an OE head at one point of its life. it was machined to have a dual plug electrode.

The coil is off of a V twin flatty, it needed to be adapted to fit onto the briggs 5 horse mounting points.

Thanks for the information on Gapping plugs, I didnt realize that. the reason I assume the timing is different is because the of the location of the fire directed to crankshaft angle, i dont know where in the dwell time a stocker fires, but i assume i have to have a slight delay for the front, I know the leads are different so I was wondering if i could get that milisecond delay to fire the front plug by using a longer lead. Its still too cold to do as much trial as I would like, I would hate to kill a long rod monster briggs with a shirt skirter from predetonation.

125ccCrazy

Im alive and doing fine, took a break from minis for college, then found a career, and no I am pursuing from being a chemist to going into full time sales, anyone need any Phosphates and reactive lubricants?! lol

I still have the funnel intake, and the carb. I actually had it on this motor and was going to attempt to run it. I currently might use the manifold to mount up a vintage Posa injection carb on it for some vintage cafe look on my nasty rat rupp!
 
Tiki_Todd

Tiki_Todd

Member
#7
#7
Old Triumphs run on a lost spark system (both cylinders rotate at the same time, but only one fires), you should be able to run any dual coil like harleys or you could run two coils wired up together. you timing should still be the same since its a single cylinder and they will both fire at the same time. its quite simple actually. well in my head if that make any sence.
 
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