• Welcome to the forum website of the Vincent H.R.D. Owners Club.

    Should you have any questions relating to the Vincent H.R.D. Owners Club, or Vincent H.R.D. motorcycles in general, please contact Graham Smith, Online Forum Webmaster by calling 07977 001 025 or please CLICK HERE.

    You are unrecognised, and therefore, only have VERY restricted access to the many features of this forum website.

    If you have previously registered to use this forum website, you should log in now. CLICK HERE.

    If you have never registered to use this forum website before, please CLICK HERE.

Ignition timing for twin plug heads

vince998

Well Known and Active Forum Website User
VOC Member
Hi All,
Has anybody out there experience with ignition timing for twin plug heads?

Series "D" Shadow, 1.3/16 inlets with 32mm MKI concentrics (200 main jets), MKII cams, 7.2:1 compresion (changing to 8:1 this winter), although putting a second plug in makes a farce of the theoretical compression ratios in my opinion, look at the amount of space between plug body and electrode insulator!! :D

I´ve run between 24° - 29° BTDC and not really felt a difference.
I´m running 29° BTDC (7° BTDC retarded) at the moment (because tickover is very solid) and it´ll do an indicated 110 slightly down hill and will pull 100 on the flat if i lay on the tank.
Can i expect much more?
I´m not a speed demon, i just want the bike to be giving its full potential

I know when i got the bike from my father with 9:1 pistons,MKIIs, 1.3/16 monoblocks and single plugs running at 34°BTDC, it´d pull an indicated 120 with me sitting upright?

is it all to do with compression ratios, or where am i going wrong?

Thanks
 
Last edited:

Mark Fisher

Well Known and Active Forum Website User
VOC Member
My Egli has Terry prince twin plug heads and when we started the motor after a rebuild it ran horribly and after a couple of starts it broke the pin in the starter. We had set it to 38deg BTDC but in order to get it to run right we had to back off to about 27deg BTDC so you are probably pretty close on timing. I haven't had much more than a 100mph out of mine either, but I haven't tried too hard recently. Maybe I should take it on the interstate this weekend and see what it will do, it is fully run in now. I can tell you that the bike starts, runs and idles beautifully the way it is set up right now, but I am tempted to try a bigger main jet on the mikunis just to see if it changes anything at the top end. Maybe take a look at carboration instead of ignition?
thanks
mark
 

Bracker1

Well Known and Active Forum Website User
VOC Member
Find a dyno and see what happens at top end. The infamous plug chop test doesn't work too well with modern fuel. 200 jets might be a bit small for wide open runs, try going up a size.. Also check fuel flow from petcocks, may be fuel starved. Let us know how it goes. . Cheers, Dan
 

Howard

Well Known and Active Forum Website User
VOC Member
Find a dyno and see what happens at top end. The infamous plug chop test doesn't work too well with modern fuel. 200 jets might be a bit small for wide open runs, try going up a size.. Also check fuel flow from petcocks, may be fuel starved. Let us know how it goes. . Cheers, Dan

Hi Dan

I'm just building up the courage to do a plug chop test on my main jets - I've always found it earie travelling at 80 plus with no engine noise.
What are the problems you've encountered?
I've heard that setting on a dyno still needs modding for the road conditions, so I haven't tried that route.

H
 

Bracker1

Well Known and Active Forum Website User
VOC Member
The chop tests I've done always result with the plug looking different at every read. I can't get any consistancy. My thought is , you are good for the specific RPM you cut the motor at, but have no idea how it is behaving getting to full throttle. Slides, needle, etc. may be wrong. The new fuels without lead are designed to burn "cleaner" so the deposit shouldn't be there anyhow. The same goes for the colortune plugs, they glow different if you use Av fuel vs. unleaded. So, if you use a plug chop test, use the leaded and beware of getting a ticket running the bike to wide open. I think the dyno will give a pretty accurate assesment of settings. Cheers, Dan
 

vince998

Well Known and Active Forum Website User
VOC Member
Hi Mark,
Mine runs O.k, starts and idles well to, but i´ve been given three diffirent ignition advance figures from 3 different people?:confused:
Obviously depending on how your using it (race or road)depends on your advance figures?

Dan, 200 jets to small? I was told that 180 where normal for MKI concentrics (i had 320 main jets in my monoblocks and the bike was quick, but that was a different carb). I´ve tried the plug chop, and the plug body is sooty black and the electrode brown.
i can empty a full fuel tank in 15 minutes into a jerry can allowing the fuel to run through the fuel lines (with the banjos still connected) so i don´t think i´ve got fuel starvation problems (carbs and jets are also internally clean)

H, i don´t have any other problems except the bike pulls like a train form 2800rpm (with the throttle fully open so running of the main jets) but then seems to tail off quite a bit at around 3900/4000rpm. Maybe this is normal for a Vincent (not having ridden another one for comparison i don´t know) but i thought i´d check for ignition settings first.
On open roads, i try not to run the engine below 2500rpm as it takes a while to get get it spinning again (especially in 3rd & 4th gear). Could this be ignition settings (to much advance) or just a characteristic of MKII cams?
Maybe just the characteristics of a 50+ year old bike ;-)

Cheers guys
 
Last edited:

timetraveller

Well Known and Active Forum Website User
VOC Member
It's the Mk II cams. They were designed to give power at racing revs, not touring revs, and torque (flexibility) will be reduced below about 4,000 rpm. Good luck.
 

Bill Thomas

Well Known and Active Forum Website User
VOC Member
Hello Vince, I can't talk about twin plugs but 200 main jets are too small. Like Norman says at 4000 revs the mk11s should start to go fast not slow off, But I run them with 9 to1s and mine pulls like a train from 1500 in top. Vins are over geared so if you want to go fast buss it in 3rd 6000 = 110 mph then take 4th, Some people run Comet gearing. I don't know how you blokes run such low ign timing , when I ran 26 deg with 12 to 1s on 5 star petrol in the 1970s I had to pack the bob weights out in the D distributor or at tickover it was the other side of T.D.C. May be thats why your bike don't like below 2500?. Have you changed the silencer since your dads time? Some have small holes inside = very bad !!. All The Best Bill.
 

vince998

Well Known and Active Forum Website User
VOC Member
Hello Vince, I can't talk about twin plugs but 200 main jets are too small. Like Norman says at 4000 revs the mk11s should start to go fast not slow off, But I run them with 9 to1s and mine pulls like a train from 1500 in top. Vins are over geared so if you want to go fast buss it in 3rd 6000 = 110 mph then take 4th, Some people run Comet gearing. I don't know how you blokes run such low ign timing , when I ran 26 deg with 12 to 1s on 5 star petrol in the 1970s I had to pack the bob weights out in the D distributor or at tickover it was the other side of T.D.C. May be thats why your bike don't like below 2500?. Have you changed the silencer since your dads time? Some have small holes inside = very bad !!. All The Best Bill.


Hi Bill,
My bob weights have reduced movement (22° in total).
The ignition system is from Francois Grosset and set up for twin plug heads.
I´m running two 3 ohm Double Dyna coils, wasted spark. (on a re-wound 12 volt lucas E3L, electronic regulator and a 7 amp hour AGM battery. (Balances at 2000rpm with the the lights on full :cool:. Who needs modern generators)

Funny you should mention the silencer :). My dads was just a hollow tube (now on a mates egli i built cos he likes it noisy)
I changed it for one from russel with a really small hole in the middle, then changed it again (cos the bike ran like poo) for one with a slightly larger hole (but still not straight through).
In the midst of converting to electronic ignition/twin plug heads/MKI concentrics, i´d forgotten about that:eek:

Time to make some noise then.
 

vince998

Well Known and Active Forum Website User
VOC Member
Hello Vince, I can't talk about twin plugs but 200 main jets are too small. Like Norman says at 4000 revs the mk11s should start to go fast not slow off, But I run them with 9 to1s and mine pulls like a train from 1500 in top. Vins are over geared so if you want to go fast buss it in 3rd 6000 = 110 mph then take 4th, Some people run Comet gearing. I don't know how you blokes run such low ign timing , when I ran 26 deg with 12 to 1s on 5 star petrol in the 1970s I had to pack the bob weights out in the D distributor or at tickover it was the other side of T.D.C. May be thats why your bike don't like below 2500?. Have you changed the silencer since your dads time? Some have small holes inside = very bad !!. All The Best Bill.


What size main jets would you recommend for MKI concentrics Bill?
Thanks
 
Warning! This thread is more than 12yrs ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.
Top