Board index Flathead Power-Technical Questions, Answers, and Suggestions Knuckles Dual plug heads

Dual plug heads

Post Fri May 16, 2008 11:12 pm

Posts: 77
Location: Custer Wa.
I have seen a knuckle in Daytona that had daul plugs. Seen a lot of shovels that where done.I have never used dual plugs.More compression more power? Any feed back.

Ride to live Tshoe

Post Sat May 17, 2008 6:42 am

Posts: 732
Location: nekoosa,wisconsin,usa

Less prone to detonation, can run lees advance, smoother low end .

Post Sat May 17, 2008 12:09 pm

Posts: 1654
does it improve the starting?
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Sat May 17, 2008 2:23 pm

Posts: 732
Location: nekoosa,wisconsin,usa

It doesn't improve the starting enough to make it worth the price for that alone. Proper tune ........ no starting problems anyway.

Post Sun May 18, 2008 1:35 am

Posts: 1654
oh ok.. that's the main reason I got rid of my panhead, I could never start the thing reliably, hot, warm or cold, in any weather. Plenty of people who were supposed to know their stuff had a go, and all ended up telling me that 'they are like that'. I went back to a shovelhead with an electric foot and had no further problems.

that's one good things about 45 flatheads,they start straight off....
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Sun May 18, 2008 8:03 am

Posts: 377
Location: madison wisconsin usa
i saw john's 4 plugger at a recent rally, it certainly makes you look twice the first time you see it! not many of them around.

45brit, i still cannot agree with your opinion with pans. every one i have encountered is mild mannered and easy to start. -except- for mine when i first got it as a screwed up chopper with a faulty magneto and a leaky carb!

i assume you understand the math in regards to starting them? take the number of onlookers when you attempt a start, and multiply by 5 that equals the number of kicks required!! :D

the closer i have made it to stock the better it behaves.

take care,


Post Sun May 18, 2008 12:23 pm

Posts: 1654
wellllllll................. it may just be their general rarity and the resulting lack of experience, but pans have a very poor reputation over here when it comes to starting. Even so, I have a lot of experience of big ol' Brit bikes, including the Matchless Model X 100cc sidevalve vee-twin ( yes, the Brit industry made big ol' flatheads too.. BSA had the G14, Royal Enfield their 1150cc brute, and of course the 1150cc Brough sidevalve ) and I suspect that our cold, wet climate is not kind to the 6v coil ignition. 6v coil ignition on Brit bikes was largely confined to small cheap run-abouts like the Red Panther or BSA C10, and that may be the reason. Someone is going to point out the Ariel Square 4 as the exception to prove the rule no doubt.. but with 4 x 250cc cylinders, starting would be easy with any sort of ignition system

I would also comment that the BSA M20 and M21, 500cc and 600cc sidevalve singles, are very different bikes despite their apparent similarity. The later Panther 600cc and 650cc variants were generally considered inferior to the earlier 500cc ones. I did own a 61-inch panhead and much preferred it to my 74-inch one. I wish I'd kept it, for various reasons. I have rather come to feel that for bikes of that type, 1000cc is the 'optimum' size, just as 45" seems to be the optimum for sv vee-twins. The longevity of the WL is proverbial, not so the UL and its related models. The Indian Scout would be another bike in that class, of course..
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Sun May 18, 2008 5:03 pm

Posts: 732
Location: nekoosa,wisconsin,usa

I'm going to beat Tom Cotten to the punch here. I've had a terrible time starting one of my Knuckles one season. I fiddled with everything but the the right thing. I have my Knuckles converted to the o-ring style intake manifold the the Pans use. It turned out the one o my o-rings had deteriorated and was the root of all evil. One I replaced it Dago Red returned to being a 1-2 kick starter. Before giving up make sure that you have no intake leaks. Pressurize the intake system with 14 PSI. Use a good leak detectant ( Snoop ). Do not settle til you have zero bubbles. I'll bet the Pan becomes your best friend !
Call on God, but row away from the rocks.

Post Sun May 18, 2008 6:06 pm

Posts: 77
Location: Custer Wa.
John have any pictures of your dual plug heads? plug location, inside or outside

Thanks Tom

Post Mon May 19, 2008 3:43 am

Posts: 732
Location: nekoosa,wisconsin,usa

Post Mon May 19, 2008 8:13 am

Posts: 62
Location: Texas' Big Bend country
Howdy Folks,

During the '80's I machined quite a few dual-plug conversions on Shovels, iron-head Sportsters, and BMW air-cooled Boxers. John's is the first dual-plug Knuckle I've seen. We did the conversions because, with the disappearance of leaded premium gasoline, many of these motors that had high-compression pistons installed began to have over-heating and detonation problems. You had to change out the coils to get the correct impedence unless you ran a dual-fire ignition. We ran both points and electronic ignitions as well as single-fire and dual-fire setups. It was also necessary to retard the timing considerably, due to the faster burn time in the combustion chamber provided by two flame fronts, and as the stock timing marks were no longer correct, we had to work with ignition timing and carb jetting to get the best results. It was a fairly successful cure for the problem; one of my mechanics, Manny Avila, ran a 92" stroker Pan/Shovel with dual-plug heads and 9:1 compression ratio forged pistons without problems. The bike mounted a S&S Super carb to which we had fitted an adjustable main jet and a Mikuni accellerator pump, and a Panhead dual-point ignition timer with a pair of standard H-D dual-lead coils. It was usually easy to start, although on occasion it could be balky. I still think its a pretty good option for Beemers and iron-head Spportsters. There are cams available now for big twins that work about as well with high-compression pistons with less modification required then dual-plugs.

--- Randall

Post Mon May 19, 2008 9:38 am

Posts: 1676
Location: Interlaken, NY USA

JohnHD, I'd have tgo agree with you that you can screw up a Pan enough to make it an evil starting machine. I've had 3 over the years, and generally, the onlookers rule prevails :-) Mine have been 6V, 12V, Linkert, SU, DC Linkert, and Mikuni carbed. The jekel and Hyde is the latest, a '65 s&s stroked to 84". With an Andrews "A", it was miserable to start, I was ready to push it off the cliff. Installed an Andrews "B", and it transformed to a first kick machine. Must be the extra overlap and light wheels or something.
On all the carbs I've used, all worked well, but the VM Mikuni with the "enrichener" has made all my bikes first kick machines, NO PRIMING NEEDED! And that I like, no need to explain to newbies about "priming", etc, it, just , starts.

Post Sat Jul 12, 2008 8:25 am

Posts: 15
Location: Dallas, Texas
I also have a 84 inch panhead that I rebuilt about 2800 miles ago. I'm wondering what type lifters do you have? What compression pistons did you use? Any headwork done or pretty much stock?
I noticed a night and day difference in starting when I changed from solids to Velva-Touch hydraulics. Now she starts hot, or cold, anytime.

Interesting about your experience with an Andrews 'A'. I was planning to go back to an 'A' after trying a Crane 296A (which I don't care much for at all). I hesitate to change anything but I do like Andrews cams and the 'A' has been a favorite for many years. Sounds like maybe an 'B' is better suited to an 84 inch motor??? I'm tempted to try it.

Do I read right that you're using a VM Mikuni on that 84" pan? Is that a VM 38?
I stuck a Mikuni 42 on my pan and after a little re-jetting it runs great. I get hellacious gas mileage now.
Those VM Mikunis sure are great carbs!

Post Sat Jul 12, 2008 8:12 pm

Posts: 1676
Location: Interlaken, NY USA

KR, I've been running solids for years. I never could get hydraulics to work. :cry: On the A grind, I bought one for my first pan, a 49 pretty much stock engine, and it ran great. SU carb on that one. Then the '62, same, ran great, that bike with 8.5:1 pistons, and the cam as a rigid bobber, would do 125. Must have been a Wednesday bike. The '65 got stroked right away, 8.5's. A grind, auto advance, and was a pig to start, as I mentioned. Chucked the auto advance, clapped out, finally switched the cam to the B, and it was transformed. With the stocker 74 flywheels, the A grind was great. Really liked it. The B comes on a little higher in the rev range, as you would expect with more overlap.
Yes, I'm using the 38 VM on the 84" pan, seems to work o.k., a little rich off idle, other wise, it's fine through the rev range. I'm temped to work on that, drop the idle jet down a size, and then see if a different cutaway on the slide is needed to smooth up off idle. It may just be the overlap and I'm stuck with it. We'll see,

Post Sun Jul 13, 2008 4:36 pm

Posts: 219
Location: Georgia
When a Shovel or Pan is double plugged the timing is backed up to 28 to 32 degrees. I am sure a Knuckle is the same. When that is done the initial timing is backed up also. That is the most of the kick start problems with them. If the mechanal advance is modified to raise the inital timing the kick start problems disapear.

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