right hand cylinder spluttering

[graciesdadpaul]

hello everyone.

I recently rebuilt my 72 J model engine after the bike was left sitting for many many years, crank rebuild, new seals, re-bore new pistons, carbs cleaned and seals renewed etc etc. The left and centre cylinder seem to be running ok and there is a nice colour to the plugs so i thinks all is well there. However the right hand cylinder is a different story. Its seems to be only firing every other time and sort of splutters and spits.(fourstroking?) The plug is fouling up a little as well. When riding the bike it bucks and splutters on closed or very low throttle and feels bloody horrible to ride.
Ive tried cleaning the carb about half a dozen time, ive taken out all the jets and cleaned all the galleries and as far as i can tell there are no blockages. the jets are standard size and the needle and pilot screws are set as per the manual. ive tried adjusting the pilot screw but that does absolutely nothing. thought maybe it's getting too much fuel and so dropped the needle one clip from standard to lean it off and no change.

So then i looked at the ignition side of things, the timing seems spot on, I swapped coils over and that made no difference, i swapped the points and condenser and still no change.

I cant find a garage in my area ( home counties north of London) who will even entertain looking at it as its too much hassle for them it seems. Has anyone with experience of the J/K models and their particular idiosyncrasies have any ideas as to what could be the cause of this.

thanks

[barney01]

Here's one suggestion for you. Check that the choke is adjusted properly and is closing fully when switched off. If you look at the base of the choke piston check that the seal on the bottom is not perished. You can still buy a new replacement.
The pilot circuit of these carbs have a branch that leads to the mouth which has a non adjustable metered hole which is essential but difficult to clear.
Good luck
https://youtu.be/O9VRh3odYDk
https://youtu.be/gice81XPjP4
https://youtu.be/O9VRh3odYDk

[canaletto5]

What temperature plugs are you using?

[graciesdadpaul]

Hi again thanks for the responses, i have swapped the middle carb for the right carb yesterday and that made no difference but i didn't change or check the choke plunger, I'll have a look at that and see if there a problem by swapping these over and seeing if the misfire moves to the other cylinder.
The plugs im using are the standard rating as per the manual B7ES i think from memory. im not sure how that works which way do I go with the numbers if the plug is oiling up?

[canaletto5]

Hi

Double check your plugs, I thought B8s were standard. A hotter plug is a lesser number, so if you have sevens fitted it might be worth fitting sixes to see if it helps but be careful about over heating and holing a piston

[teazer]

Double check the pilot jets. If they are pre-owned they may be oversize and if new it's possible that one or more is wrong size.

But you swapped the carbs side to side, so that suggests that it's not the carbs. Perhaps that side flooded or the check valves in the oiling leaks allowing a build up of oil in that cylinder that can't be burned off because the bike hasn't been ridden hard enough.

[graciesdadpaul]

the saga continues. i looked at the choke plunger and the one for the right hand cylinder did look at little warn so i swapped it for the one from the middle cylinder and it didn't change.
the manual says the plugs are 7s but i may try a 6 and see if that makes a difference and keep a very careful eye on it . Im beginning so suspect the check valve on the octopus is leaking as suggested and that is the only thing remaining i havent looked at yet. how easy are they to change, from memory they appear to be pretty much impossible to get off.
The other thing that occurs is could it be something to do this the exhaust pipe. its the original standard pipe but there is something rattling in there if you give it a tap. are there internal baffles that have come loose maybe?
seems to me that the exhaust gases arent getting out of the cylinder in time for the next charge to combust fully and it only seems to fire every 2nd go. Also on closed throttle it will surge indicating that some mixture remain in the chamber and is being ignited as soon as the exhaust clears but i dont know why at the moment.

[canaletto5]

It could be as basic as the exhaust pipe being blocked with carbon. It might be worth dropping the baffle out and checking the condition. Kev

[barney01]

Also, just checking, you aren't running with resistor plug caps by any chance.?

[graciesdadpaul]

hi again, the baffles are new and it only done about 200mls since the rebuild and i dont know if the cap have resistors, they are red NGKs . I've just noticed there is a black oily deposit leaking out of the exhaust where it meets the cylinder head and also what looks like a small amount of clean gearbox oil around the weep hole at the bottom of the generator cover. I'm going to strip the exhaust of and see what's going on and clean it out , ive ordered a new gasket, and i'll remove the generator to see where that leak is coming from as well, Could I have found the issue! I'll let you know.