Norton JPS F1 dropping a cylinder on idle (running rich)

[au_carl]

Hi All,I have just stumbled across your group and see that there are a lot of Norton enthusiasts present.I have a Norton JPS F1 and Suzuki RE5 and hope that I can both obtain some guidance on my bikes as well as contribute.Now my problem with the JPS F1:This is an original unmolested bike of 3,600 miles that spent several years unused, I recommissioned it several years ago and now ride it occasionally. Often when I ride it it runs rich at idle and drops to one cylinder, the slightest opening of the throttle clears it. This has bugged me for years and I still haven't fixed it. I have checked and eliminated:The fuel circuit/micro switch and three way solenoid are all good - I have feed to the tank, tank internal overflow and gravity feed to the carburetor at idle.At around 2,000-2,500 rpm this switches to pressure feed direct to the carburetors.I have stripped the carburetors and checked the float, needle and seat and O ring behind the seat, I replaced one O ring (as it looked a bit dodgy) with no improvement - I suspected maybe fuel leakage between the seat and carburetor body past the o ring.I am pretty much convinced that the fuel pump/lines/solenoids and micro switch are all OK as are the floats, needle and seat.I am also pretty much convinced that I have an internal carburetor leakage problem on one cylinder that leads to excessively rich idle after a period of idling and wondered could I have a problem with leakage around the Mikuki carburetor chokes - I really don't understand how the choke mechanism works so trying to understand how it could be faulty is really hard.So I have a great bike, that I like riding, that I often have to hold on a fast idle at traffic lights (to keep it running as if it stutters and stops its flooded and a pig to start), I ride in Perth Western Australia where its often hot so I end up getting a inherently hot running bike even hotter by the fast idle.I am keen to fix the problem but I have run out of ideas as to what to now look for, any ideas??Thanks for any help/advice that anybody can offer.As my contribution to the Forum anybody interested in an SU Carby conversion to a RE5 then I have created a series of posts on another forum here:http://re5rotary.proboards.com/thread/1 ... -years-why

[Dell Boy]

My experience with my F.1. was that when stationary, at say traffic lights, the heat from the collector box evaporated the fuel in one or both carbs/fuellines & the bike would stop halfway across the junction. It would restart on the button but it drove me to distraction, as well as being very embarrasing, so I passed the bike on.Derek Fox.

[Wayne]

hi allI had a problem with my f1 not ticking over after a few minuits it would dye similar to how derick discribed, i tried new ignitions no difrance, evan a brand new set of carbs no diferance, i noticed if i took all the bodywork off and it would tick over reliaby, then it hapend the ballast resitor totaly faild, fited a new one and the tick over problem rectifyed its selfI belive heat when stood at traffick lights ect heat hit the ballast resistor causing expansion on the rivets, it did get to the point i had to let the bike for longer and longer periods till it totaly faild.Second if the fuel had evaporated (in my case) from the carbs and fuele lines it would not start imidiatly on the start buton, second after it stalled i imidatly opend the throttle and the fuele pump stopped, again indicating fuel was presant in the carbs.I have had problems with the in line non return valve, i cure ths after winter storage with a blast of carb cleaner.Like derick the problem drove me nuts till i found it, however i was luck in that my problem apeard after 7 years of ownership so i new it could be cured.My advise would be open the throttle after it stalls and see howmany clicks the pump makes till it stops 2 to 3 clicks and you have fuel in the bowelsRegards Wayne

[au_carl]

Hi Dell Boy & Wayne,Thanks for your suggestions and I will check those items out but having looked at the problem now for a few years and checked many things I am almost 100% confident that I have a fuel flooding problem to one rotor. My bike comes clean (firing on both cylinders) immediately after opening the throttle slightly - to me this makes ignition and fuel starvation as being possible causes as unlikely and inconsistent with what I am experiencing.

[Wayne]

Opening the throttle should almost imidatly switch the carbs to fuel direct from the pump not header tank. The setting for the miro switch is a couple of mm from memory is set by measurement not rpm.Also when you open the throttle with the ignition on but the engine not running dose your fuel pump stop or dose it Cary on pumping, if it Cary's on pumping it will pump and pump or petrol will appear from the oil pump cover.Assuming the pump runs withe throttle open If no petrol appears from the oil pump cover after a few Minuits suspect the non return valve, this is easy tested as nip the pipe befor the valve and the pump stops the valve is passing throttle in open position for the test

[Charles Wilson]

au_carl-If you have questions on your RE-5, I'll be happy to fog things up for you.I owned an RE-5 (Still have ~ 1 1/2 engines...) and collected a lot of material on it.CW

[au_carl]

Hi Wayne/CharlesWayne The reference to rpm when the fuel pump solenoid changes over from overflow to direct flow was an estimate by me the micro switch is adjusted as per the Norton commissioning book. My bike idles OK and then after a while starts to falter and drop to one cylinder, when the throttle is opened little (more air) it comes good and fires on both cylinders. The fuel pump and solenoids do not seem to be the problems, I have gravity feed at idle when the problems occurs and when I revert to pressure feed off idle the problem goes away - I am 100% sure that I am not pressure feeding the carburetors at idle, I have confirmed this by connecting extension lines to the fuel delivery hoses and placing them in separate containers. On Idle the lead going to the fuel tank (and overflow weir) pumps, off idle the other one pumps - I have no leakage from the pressure direct line at idle. I seem to have a gravity fed leakage to the float bowls or choke to one of the carburetors.Charles,Thanks for the offer of info on the RE5 but (fingers crossed) my RE5 has been a regular ride for me for the past 10 years or more and apart from a shorted wire in the headlight case it has been 100% reliable and trouble free.