Perplexing problem - ignition vs. carburetors
Posted: Wed Aug 09, 2023 1:35 pm
Hello all,
I bought a nicely kept 1979 CBX the year before last. It was always difficult to start, but since I bought it in November, just before temperatures fall below -20C in Canada, I didn't think too much of it, as I wasn't going to be able to do much before spring of last year.
The bike had been 'restored' by the previous owner, and cosmetically was in beautiful condition. The obvious maintenance items (drive chain and sprockets, brake pads etc) were new, and everything was clean and shiny. The seller said that the engine had been stripped down and rebuilt, and the carburetors also stripped and rebuilt. I couldn't see anything externally to suggest anything had been butchered.
The bike remained difficult to start, and often felt like it was dropping a cylinder or two at times. It was not noticeably worse either hot or cold - just intermittent. By the end of summer I thought I had pinned it down to cylinders 1 and 6, but using a temperature 'gun' cylinders 1 and 6 were much cooler, while 2 and 4 were cooler than 3 and 5 (ie, NOT 2/5 vs. 3/4). Bear with me here - I'm getting there...!
I figured it was likely the igniters, but thought that the easiest route would be to replace the entire ignition system, so I installed a Sachse system from Italy. By the time it arrived and got installed, it was December and snowing heavily, so the bike was put to bed for the winter again.
Back to 2023 - I couldn't get it to start at all, but confirmed the ignition was at least making sparks. I had been reading some horror stories of gummed up carburetors, and wondered if the so-called 'rebuild' actually included the carbs, so, I got a set of Keyster kits and stripped and rebuilt the carburetors myself. I was hoping to find all kinds of gunk blocking jets etc. but the carbs were actually very clean looking, and no sign of any bad handywork was apparent. Jetting and needles were correct for stock. I got the carbs back on the bike last week, and got the bike to run - but without the assistance of cylinders 1 and 6. Even though I could see healthy sparks from the plugs on all cyclinders, I ordered some new coils, and replaced the 1 and 6 coil. Result - exactly the same - will fire up 2,3,4 and 5 but cylinders 1 and 6 are not getting hot!
I am kind of struggling to figure out what could be wrong at this point. I have trimmed the ends of the ignition leads and refitted them with new plug caps. Still seeing sparks at 1 and 6, but no actual ignition. The plugs appear to be getting fuel. Is there something obvious that I am missing here? Any and all suggestions would be appreciated.
I bought a nicely kept 1979 CBX the year before last. It was always difficult to start, but since I bought it in November, just before temperatures fall below -20C in Canada, I didn't think too much of it, as I wasn't going to be able to do much before spring of last year.
The bike had been 'restored' by the previous owner, and cosmetically was in beautiful condition. The obvious maintenance items (drive chain and sprockets, brake pads etc) were new, and everything was clean and shiny. The seller said that the engine had been stripped down and rebuilt, and the carburetors also stripped and rebuilt. I couldn't see anything externally to suggest anything had been butchered.
The bike remained difficult to start, and often felt like it was dropping a cylinder or two at times. It was not noticeably worse either hot or cold - just intermittent. By the end of summer I thought I had pinned it down to cylinders 1 and 6, but using a temperature 'gun' cylinders 1 and 6 were much cooler, while 2 and 4 were cooler than 3 and 5 (ie, NOT 2/5 vs. 3/4). Bear with me here - I'm getting there...!
I figured it was likely the igniters, but thought that the easiest route would be to replace the entire ignition system, so I installed a Sachse system from Italy. By the time it arrived and got installed, it was December and snowing heavily, so the bike was put to bed for the winter again.
Back to 2023 - I couldn't get it to start at all, but confirmed the ignition was at least making sparks. I had been reading some horror stories of gummed up carburetors, and wondered if the so-called 'rebuild' actually included the carbs, so, I got a set of Keyster kits and stripped and rebuilt the carburetors myself. I was hoping to find all kinds of gunk blocking jets etc. but the carbs were actually very clean looking, and no sign of any bad handywork was apparent. Jetting and needles were correct for stock. I got the carbs back on the bike last week, and got the bike to run - but without the assistance of cylinders 1 and 6. Even though I could see healthy sparks from the plugs on all cyclinders, I ordered some new coils, and replaced the 1 and 6 coil. Result - exactly the same - will fire up 2,3,4 and 5 but cylinders 1 and 6 are not getting hot!
I am kind of struggling to figure out what could be wrong at this point. I have trimmed the ends of the ignition leads and refitted them with new plug caps. Still seeing sparks at 1 and 6, but no actual ignition. The plugs appear to be getting fuel. Is there something obvious that I am missing here? Any and all suggestions would be appreciated.