Interpol 2 uneven running

[jgn]

Hello, I have an Interpol 2, which presents a few problems for me. When picking up speed from slowing down for a turn or for a crossroad, it runs very uneven - I have to turn the throttle, increase rpm and slip the clutch in order to get it going.
When running at constant speed, 50-60 mph, it misfires occationally, but acceleration when at speed is no problem, and idling is also fine. Spark plugs are new.
I have renewed the O-rings for the large suction tubes and also the O-rings in the carburetors for the idling tubes. I have also checked the float levels this Winter but found them inside limits.
Can anyone help me on this matter?
Kind regards
Jorn Gaardsvig Nielsen
Denmark

[johnbirchjar]

Has this problem occurred since you fitted new plugs?and what electronic Ignition box is fitted to you bike?J.B.

[Interpol2471]

Have you serviced the carbs especially replacing the choke o rings?

[Anthony Duffield]

Jorn,

Your comments, below seem to contradict each other:

When picking up speed from slowing down for a turn or for a crossroad, it runs very uneven - I have to turn the throttle, increase rpm and slip the clutch in order to get it going. I would have said that this was a fuelling issue, turning the throttle causes the pistons to rise increasing fuel.

When running at constant speed, 50-60 mph, it misfires occasionally, but acceleration when at speed is no problem, and idling is also fine. Spark plugs are new. But as acceleration when at speed is no problem it would suggest fuelling is OK??

However I would still suggest that the issue is fuelling, when slowing down for a crossroad the pistons will be at their lowest point, turning the throttle to increase the vacuum to lift the pistons to provide enough fuel and to quickly pick up speed seems to be the issues, unlike when at constant speed the pistons are someway up the suction chamber so able to provide enough fuel to increase speed.

I would inspect the movement of the pistons in the suction chamber, they need to be free to move, check the springs they should be the same length, make sure that the oil in the dash pots is the same as you use in the tank i.e. SAE 40 and while you have the carbs off give everything a good clean check the needles are not varnished and the jets are clear and blow everything through with carb cleaner and compressed air.

And as suggested by Interpol 2471, make sure that the choke (fuel enrichment valve) is clean and the O Rings are renewed.

Good luck

[jgn]

Thank you all for your replies and tips - I will take a look at the carburetors and the O-rings at the chokes - I have not renewed them.
With respect to the ignition unit, it is a Minimag unit.
Jorn

[Interpol2471]

Minimags are normally pretty good and if not sure can be tested by mini magneto on the IOW

[Ian Mc]

Is the problem only when the engine is hot ? Sounds like it could be an air leak. Make sure the idle pipes are fully into the engine casing, a light tap with a blunt screwdriver will do. Try a smear of instant gasket around the pipe to see if it helps. If your bike has the crank case drain modification, disconnect it and block both ends to see if that helps, you will see a second pipe coming off the left hand spigot if fitted. It can allow air to leak into the inlet. Make sure the oil scavenge pipe is tight on the spigot.

[jgn]

Hello Everyone,
I have checked all the pipes, O-rings and also choke levers this Winter, and I believe that I have no leaks anywhere in the intake system. The problem still exists, and I'm now wondering if the problem could be the spark plugs. I'm using NGK C8E together with the Minimag ignition unit. Does anyone know, if resistor plugs should be used with the ignition unit?

[johnbirchjar]

Nope,you are using the correct plugs,I bought resister plugs once by mistake,once was enough,took them out after about 2 miles and threw them away,dreadful things,the engine was running all over the place,J.B.

[jgn]

Thanks for the input, John.
After having read Grahams info on the Norton Owners Club webpage I have now changed the plugs to CR7E, and that solved all problems. The CR7E were readily available from a local dealer, but I will get hold on a set of C7E plugs instead.
But maybe the root cause has been, that my oil pump setting has been a bit too rich, as I was afraid of running with too little oil with fairly new seals and bearings.
I have reset the oil setting now, and I will later try to swith back to C8E plugs.

[mick695]

There seems to be a lot of dodgy NGK spark plugs doing the rounds at the moment...

My 750 Commando seen off a new pair of NGKs in less than 120 miles, plenty of others at our local Classic club reporting problems with NGK plugs.

By the way, I've also gone back to C7E plugs too.

Mick

[johnbirchjar]

I seem to remember about 5/6?years ago there were reports of quite a few dodgy NGK plugs being sold,(and these were being sold by reputable sources) then during covid the reports seemed to dry up,bikes not being used I suppose,not heard anything since though,J.B.

[Ageing Rotarian]

Gents, ‘piggy backing on Jorn’s post, my bike has always been very temperamental when cold, coming off idle up to about 2500rpm plus. The bike surges slightly until the bike gets thoroughly warm/hot but then settles down to an even tickover and pulls clean from junctions. Is this typical as I have another bike number (classic no33) and is a lot smoother and is a lot more civilised?
I have had to rebuild the carbs due to them being full of a black deposit after being stood for some considerable amount of time. Only thing is, like an eejit I didn’t change the cold start seals and maybe this is the long standing problem. Does anyone’s else’s bike ‘play up a little until warm? Bike in question is a classic replica ie interplod.
Any feedback would be appreciated.
Regards
Roy

[johnbirchjar]

I remember way way back(20+years?) when my Classic was returned to me from Shenstone after it's 1st engine re=build(long painful story )and I couldn't get the engine to run evenly between cold start and warm ,all over the place until about 90c.I eventually found the problem was the Idle Rod had been adjusted entirely wrong ,took me ages of trial and error to finally get it to run from cold start on choke(two clothes pegs ,then one c/peg to nice even running when warm,no c/pegs .
Other bikers often asked me at various biker events throughout the years"Clothes Pegs"?
Could this be your problem?J.B.

[Ageing Rotarian]

Maybe John, I haven’t set the choke rod with too much thought only to ensure the rod fully returns as at one time the bike was hanging up, but maybe it requires a bit more attention.
Just noticeable that the two bikes are quite different, was the classic set up to give a more civilised ride or is there no difference between these and the interplods?
Also was wondering if anyone has changed the fuel enrichment seals and what affect they had?
Thanks for responding and I will ask the boss if she will donate a peg or two.
Regards
Roy

[johnbirchjar]

Having never ridden a Interplod,I can't comment,but I seem to remember reading somewhere that the Classic was the softer tuned of the two(a couple of BHP if memory serves)J.B.