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Bike back firing

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hondacb750fourk6:
Hi I had a problem with my Honda CB750 Four K1 last month I went to a show bike was running good when I left the bike show bike was running good I had about 3 miles before going through dartford tunnel bike started to back fire like it was only firing on 3 cylinders and no throttle response loosing power I thought I was running out of petrol so switched the petrol tap over to reserve didn’t make a difference so pulled to the left lay by to open the filler cap on the petrol tank to see if the tank was empty plenty of fuel managed to get it home so did some checks checked the points and removed all spark plugs when I pulled no2 spark plug cap off it came off the ht lead tried to screw it back on was too loose so had to cut the ht lead back a bit removed all spark plugs to check if there were all firing they was so put them all back started bike back up it seemed ok so went out this morning on it started it up it wasn’t running right it was back firing a lot there was lot of back firing in no 4 exhaust pipe so turned back round went back home put  the bike away went to check the bike removed the points cover started the bike up there was a lot of back firing coming from the bike I noticed there was big sparks coming from the points on the right side big flashes could this be the condensers shorting out causing this problem as this bike has never broke down on me since I had it I have a new Boyer brandstan micro ignition system which I won at a bike show going back 2015 never got round to fitting it how easy would this to fit it as says in the instruction manual remove the cam weights off the rotor as I can’t find any videos on YouTube someone fitting a Boyer ignition system on a Honda CB750 Four thanks

Bryanj:
If the points faces are clean it does sound like condenser is bad, havent fitted a boyer for 45 years so cant remember how

neat street:
the `flashing` definatly suggests the condensers.

royhall:
Can weights are just 2 circlips to remove them. Then the Boyer bits fit as the instructions. The hardest part of a Boyer is finding somewhere to fit the control box. Got a Boyer on my 750K5 and it is superb. Bike runs lovely. Bit of a strange procedure to strobe the timing as you have to rev the engine to 5000rpm to set the full advance.

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hondacb750fourk6:

--- Quote from: neat street on July 29, 2025, 08:01:15 AM ---the `flashing` definatly suggests the condensers.

--- End quote ---
ok I thought it was the condensers will replace them thanks

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