Cylinder 1 misfire

[ray bear]

Hi All, I have purchased a second 79 unfortunately it comes with a misfireing number 1 cylinder that doesnt run at idle but when riding you open the throttle to the same position every time about quarter throttle it runs good and when in neutral you have to bring the revs up to about 3000 for it to cut in.
I did find a vacuum leak at the air cut off valve by using acetalene torch and when the gas found the leak it run ok but fixed that and still have the problem.
Have blown out the jets , checked mount rubbers & clamps and did find 2 washers and o rings stuck in the pilot jet & fixed that but still have fault. tried to syncronise with gauges and happy with result however doubt accuracy with misfire & did try swapping plugs, leads & coils but no result so Im sure its carb related . It seems like a pilot / slow run jet fault but i would like to think I cleaned it ok perhaps I will have to remove it ,My old CBX has been my daily ride for many years and never required any more than tyres and battery so am not as schooled up in this area as I would like to be ..HELP PLEASE ...bill

[CopperCollar]

My inexperienced 2 cents....... idle circuit is still in need of cleaning.

These carbs are notorious for gummed up idle circuits and accelerator nozzles.

Can't count how many times I thought I had the circuits clean only to find they weren't and this after the hassle of installing then on the bike.

Mike

[EMS]

Let's hope for the best and that it is indeed just a plugged carb circuit at No 1 and not the dreaded "hydrolock" syndrome....
Take the plugs out and rotate the motor by hand. Stick a longer (welding-) rod into the cylinder and compare how far No 1 piston comes up towards tdc.

[ray bear]

I measured the difference between #1 & #6 however did not set engine to TDC but shouldnt matter for the experiment and was getting 39.40mm average between the 2 but was difficult as some slight lip at top of plug thread made it difficult for verniers to sit accurately on top of head but feel confident at the readings I obtained and feel that all is well in that department but am interested to know how far do they normally bend the rods ?? can some one tell me .
Also done a compression test of all 6 with with only a few lb difference and #1 & #6 were almost identical so hopefully back to cleaning a blocked jet ..Please dont scare me with any bent con rod stories ..Im sure theres plenty as well as tears. Thanks Bill

[daves79x]

Bill:

The most a rod can bend and have the engine still run is maybe a mm or two. Enough that you'd see the difference in measurement. Compression equal also rules that out.

I'm with the rest in that you've got a still-plugged idle circuit. #1 can be fiddled with while still on the bike, and you can try that, but you really need to make sure all circuits and air bleeds are open. That for sure is your problem.

Dave