Rebuilt engine only firing on one side

stelrad · Post by **stelrad** » Mon Sep 29, 2008 9:22 am

Hi guys - My first posting and a plea for help. My CB77 only seems to firing on the right hand cylinder. I've rebuilt the engine with new pistons and rings etc and tuned it as per Ed Moores tuning recipe. The left hand cyclinder is popping and spitting and barely running at all. If I remove the left hand plug cap the engine hardly misses a beat. When I replace it the popping and misfiring returns. If the right plug cap is removed the engine stops straight away. I've double checked the ignition timing and this appears spot on. As a double check I swapped the coils and HT leads over and tried new plugs but this made no difference. I cut the HT leads back by a quarter of an inch at each end as per the forums suggestion. There is plenty of compression and the with my hand over the intake of the carb, plenty of suck. as last resort I disconnect the choke rod and swapped the carbs over. The left cyclinder now seems to run (silencer and downpipe hot) with the right not running. I've stripped the carbs and put back the original jets and needles as I'd fitted overhaul kits to them but still cannot it get the left carb to run. If I put full choke on the left carb only it fires and runs. Any help would be appreciated.

e3steve · Post by **e3steve** » Mon Sep 29, 2008 10:16 am

Welcome along; grab a straitjacket!

It seems you've isolated the problem to the l/h carb -- now, presumably, bolted to the right port. Sounds to me like there's shite blocking one of the drillings. Have you stripped it completely and shot the body through with an air-line? Or, better, do you have a spare carb?

Check in later with results...?

G'luck!

stelrad · Post by **stelrad** » Mon Sep 29, 2008 10:42 am

Thanks for the quick reply. I've blown the carb out with carb cleaner and put back the original jets but cannot see anything obvious - it all looks clean. As you say maybe try another carb - if I can locate one. It's got to be something obvious but after two and a half days of messing about with it I'm a liitle frustrated to say the least.

e3steve · Post by **e3steve** » Mon Sep 29, 2008 10:54 am

Hey bro', frustration goes with the territory on these delightful, older machines sometimes! The end result is always worth the head-banging though; don't lose heart.

I'd still say there's probably an obstruction, possibly too well lodged, in one of the jet drillings. High pressure air nozzle may be the only remedy.

Another obvious check: is there petrol in the float bowl of the errant carb? Remove the tin valley cover, place a suitably-shaped container* beneath the misbehaving bugger and whip the float bowl off. Turn on the petcock and see if the old junglejuice flows. Also, don't forget Ed's tip about squeezing the floats together 'twixt thumb & forefinger to ensure that they don't bind on the bowl, body or gasket.

*Cut the bottom off a used plastic bottle or other container.

e3steve · Post by **e3steve** » Mon Sep 29, 2008 11:01 am

Just a thought: was there any 'varnishy goo' in the float bowls when you rebuilt the carbs? This would indicate that the bike had been stood a good while before your sterling efforts. Some of this muck could have ended up well ensconced within the carb body's passages.

stelrad · Post by **stelrad** » Mon Sep 29, 2008 1:58 pm

Thanks Steve - The float bowl has petrol in it - when you unscrew the brass screw it pours out - not sure if there's enough in it though. I suppose the bottom of the jet has to be below the level of the petrol in the float?

I was in Mallorca last week

e3steve · Post by **e3steve** » Mon Sep 29, 2008 5:58 pm

Getoutahere! You were here in sunny Majorca? Where's your homeport then?

Float heights are crucial -- if Ed (LM) has read this thread, he'll bloody flip! See following pics. I made a 22.5mm height template (23.5mm, allowing for the recess) from printer card stock. With the bowl off and the carb inverted you can hold the float, just touching the needle-valve plunger, with a forefinger on the fulcrum pin. The correct height, h, is measured as shown; but the datum is from the lip that circumvents the float bowl seal, not from the recess found in said lip alongside the bowl retainer clip's swivel drilling, shown in pic 1 as a red line. My jewel-encrusted, Cartier-designed, make-a-gold-Rolex-Yachtmaster-look-inexpensive '67 carbs have this recess; I can't remember if my original '64s had them. Scott Pargett may be able to answer, as he has those now.

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Rebuilt engine only firing on one side

Rebuilt engine only firing on one side

Engine only firing on one side