Twin Plugging

[Rob Farmer]

Got my twin plugged heads back on tonight, what a difference, the bikes now got loads more umph at lower revs and pulls harder all through the rev range...dead chuffed.

I decided to go for the simple "back it off 3°" setting for the ignition for no other reason than Mick Barr and Jim Cray go for that method while Andrew Sexton does a mod on the ignition module that limits the advance by a few degrees.

Total cost came out to around £160 including the coils, replacement gaskets etc

Highly recomended

 

[Rugged Path]

Hi Rob,
Twin plugging has always been an idea in my head from the days the 'Ultimate Source' used to sell them at a hefty price. Way above my UK salary.

Times they have a changed and with the money saved from not paying UK tax, I have a project plan to refurbish an old 'A' reg RIOORS in bits I've had for 15 years in the coal shed.

Looking to where I can get the engine overhauled and put performance engine parts into it. I have been told 40mm Mikuni carbs are better than the old Bing type. Where did you get your heads machined for the twin plug conversion?

Are there any books in english or web sites for getting info on boxer projects?

 

[Howard Millichap]

I have been told 40mm Mikuni carbs are better than the old Bing type.

I don't think so. Look at what the desert racers used; Bing carbs. They are so simple they don't go wrong. Why go through all the expense and setting up agro?

 

[MATKAT]

bing or bling

yes, the mikuni carbs are good but why change the bings??? if you twin plug it and (I believe just altering the advance retard is n ot the best solution) have the advance retard unit modded properly.........then it will go like stink anyway.
Andrew Sexton is a great source on modding, mikuni's and all, certainly for doing heads etc he does top quality work. MY 100gs went like a rocket after he did the work twin plugging gasflowing heads etc.
He does a mod to the advance retard for about 30 quid. Motoelektric do a modded unit as well and they like many other specilaist tuners say the unit needs modding, of course you will get improved performance but you wont get the full potential of the twin plug conversion

 

[Rob Farmer]

Rugged Path,

I used a local guy, Mick Barr, to do the machining. Cost was £30 a head - Mick does the kit for Motobins so if you went to them for the complete package he'd do your heads anyway. If you have an earlier boxer then you can buy a twin plug ignition module from Boyer.

Matkat,

I agree with your comments on the Ignition unit, there isn't that much info for doing these mods yourself or what settings/alterations to make to get the best from the bike, Mick Barr told me to just alter the timing a few degrees which is just a compromise, I've now found the best settings for the timing but now need to modify the ignition unit to allow more advance at higher revs. Andrew Sexton just knocks the tabs that limit the advance in the beancan out of the way so that theres more advance above 3k...Dead easy to do and just a few minutes work according to Steptoe, I'll give it a go as soon as I get a chance.

I think the only gain with fitting Mikuni carbs would be to remove the slight throttle delay you get with the Constant velocity Bings.
I know somebody used to make a small unit called a "ThunderJet" that fitted to the bings and did a similar job.

 

[MATKAT]

Mods

interested in your comments.and of course I will always accept Steptoe's knowledge and his always sound advice!!
it has given me a thought though, as the only thing I havent done to my little demon is twin plug it. I have the dyna coils etc but am finding it hard to justify spending the dosh on converting, valve guides and all. I know Mick Barr does good work, were all the original valves guides springs etc re- usable, what has it cost you all up to do the conversion??
I am just in the process of re-wiring mine and also finally fitting the supertrapp silencer and s/steel exhausts. If I thought I could twin plug it at very low cost I would do it now. So it really would be rocking at Lehinch.

 

[Rob Farmer]

My valves and guides didn't have any wear on them at all (46k) so it was just the cost of maching the heads, buying the coils and gaskets. I've got receipts for a fraction over £180 but that included spare gaskets and a couple of bits and bobs for the 1150.
If you already have the coils then you can knock £65 off that price. You could always just have the heads machined, put the second plug in and do the rest of the work at a later date.

Give Mick a call if you want some info 01162 419316