Running rich

[Yoshi823]

If #1 & #2 are wetting the plugs, I would be inclined to look at the points gap & timing. It may be that the points have closed up & the plugs arn't producing a spark. As the carbs are more difficult to access, check the ignition first...with a timing light preferably.

[bluemouse1006]

Hi
been reading this and have similar problem the plugs are like a black  burnt biscuit wonder if anyone knows which way to turn the mixture screws to weaken off a touch ? it doesn't like running on choke at all so have to take it off as soon as it starts

cheers

Amos

[mick]

If I remember right Amos its in to make it richer & out to make it weaker  cheers Mick.

[adrian58]

Ok checked float heights and if anything a bit low. Looked at all 4 plugs and Nos 1+2 showing sooty and a bit wet 2+3 pretty much ok. I'm now thinking have I got an intermittent/ weak spark as 1+2 share the same coil ? If I'm right, maybe that could also be the reason she's a bugger to start sometimes. It's on a Boyer so no points etc and all the plugs are new. Any thoughts help much appreciated . ps wouldn't start today then stripped 6 teeth of the starter reduction gear. Grrrrrrrrrrrrrrrrrrrrrrrrr

[hairygit]

Almost certainly NOT ignition related, 1and 4 share the same coil, 2 and 3 share a coil, so if 1 and 2 are sooting up, it's fuel related

[adrian58]

Sorry meant to say 1and 4 share the same coil.

[adrian58]

Sorry screwed  todays  first post up. It's 1+4 plugs wet and sooty 2+3 ok and as they use the same coil thinking that could be cause. Brain fried after the started gear saga.

[hairygit]

Okay, so it probably IS ignition related. I have no experience of boyer ignitions other than taking them off and binning them and refitting points plates, but you may want to have a look at your coils/leads before blaming the boyer.

[adrian58]

Wondering if maybe it's the plug caps. The No4 one has been changed at some time. Anyone else had probs with the coils or plug caps ? Am I right in guessing they are resistor caps ?

[hairygit]

If you suspect the ht caps, (unlikely 2 would fail together) try replacing them, but I'm more inclined to suspect the coil, or the wiring to it. Pop the tank off and have a good look at the coils themselves (looking for cracks or anything leaking from them) the security of the ht leads into the coils, and particularly the low tension wiring to the coil (corrosion in the bullet connectors can cause a lot of difficult to trace hassle, and check the connection is tight) If you don't see anything obvious, try swapping the low tension leads to the opposie coils (the blue wire to the yellow and vice versa, and use the ht leads that are currently on cyl 2+3 on 1+4 and vice versa. If the problem moves to cyls 2+3 it's got to be an ignition system fault,so put the wiring back to how you started, then you need to think about borrowing a coil to try, if the problem goes away, happy days, you need a replacement coil, if not, then start to suspect the boyer (I'm assuming you've already checked the wiring fron the points cover to the coils for continuity, particularly the join at the back of the motor, that joint is well known for being a pain in the arse!)

[adrian58]

Will the H/T leads be long enough to swop ? Didn't think about L/T leads and connectors. When you say the one at the back of the motor where is that ? Can get a new aftermarket coil for £20 but will look at all the things you said first. Just seems odd to me that the previous owner (who seemed to know his stuff) stripped and set the carbs with 2+3 being  pretty much spot on and 1+4 way out. As for the plug caps, one has been changed at some time and thinking that 1+4 are more exposed to the elements. Can the resistors break down  in them ? Thanks again for all your help. Adrian.

[Yoshi823]

I had Boyer-Bransden electronic ignition on my CB750F2 & the only time that I ever had problems with it was when I binned the bike on the right side & the Rickman engine bars bent & partially severed one of the two wires going from the points side up to the wiring loom by the removeable engine mount by the clutch cover. I never suspected that as a fault until one day it wouldn't run on all four at all. I buzzed through from the ignition back plate to the end of either the yellow or the blue wire...I forget which as it was back in the late '70s, & lo & behold I found the break. I bought a second hand shrouded pair from a breakers & that was it...sorted.

At one time I visited the small factory of Boyer-Bransden when they were situated near to my work at Elmers End. They said that in the vast majority of situations it was a connector problem with their system & not a fault of the black boxes themselves. In all of the years that I had it fitted to my 750 it was faultless.

[adrian58]

Found at least one very dodgy connection (fell apart when I took the tape off). About 4 others with crap connectors so going to renew the lot. Can't understand why previous owner spent £100 + on a Boyer then for the sake of about £2 fitted crap connectors. Pretty sure it's either a connector or the coil not the Boyer.