Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: hondacb750fourk6 on July 27, 2025, 06:56:16 PM
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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
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If the points faces are clean it does sound like condenser is bad, havent fitted a boyer for 45 years so cant remember how
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the `flashing` definatly suggests the condensers.
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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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the `flashing` definatly suggests the condensers.
ok I thought it was the condensers will replace them thanks
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Carefull what you buy, new daichi are notoriously bad
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I have OEM TEC condensers in stock. I also have about 15 sets of OEM handlebar grips in stock, I over ordered 😁😁😁😁
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the `flashing` definatly suggests the condensers.
ok thanks
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Carefull what you buy, new daichi are notoriously bad
the points and condensers I bought from David Silvers in 2014 were patten parts I fitted to the Honda so have lasted well so going to buy from him again thanks
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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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yes Boyer is a good ignition system had them fitted to two of my Triumph T140s and my Trident T150 yes you have to do that to the triumphs Rev it up to 3000rpm as on the T150s and T160s they had 3 sets of points fitted as I still have my Trident T160 when I first got it ,it had a Boyer fitted to it as I had a lucas Rita ignition which I bought for the T150 I got my mate to fit it to my T160 as he’s good at rebuilding T160 engines it always started first time on the button might get him to fit it to my Honda thanks
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I have OEM TEC condensers in stock. I also have about 15 sets of OEM handlebar grips in stock, I over ordered 😁😁😁😁
ok thanks going to buy them from David Silvers for now a bike show I went to in May bank holiday at Ashford market Ashford Kent a stall holder mentioned your name said you had a lot of Honda parts always best to keep spares for these bikes as you never no when you might need them but all these bike jumbles I go to you don’t find much Honda CB750 four parts found a few genuine Honda oil filters there is more Triumph parts there thanks