Misfiring and overheating NG 350

[MikeCrook]

Bike runs fine for about 10 miles then looses power and misfires , overheats also.
I have replaced plug , checked points and timing, operation of the advance /retard and choke.
The oil pump is working and fuel runs clean.
Any suggestions please.

Thanks

[robjameson]

Have you checked if you are getting an induction air leak?

If not, get an aerosol of brake cleaner and spray it on the carb flange at idle, if you have an air leak then the revs will increase.

Could just be a case of it being too lean

[chris.shearwood]

Bike runs fine for about 10 miles then looses power and misfires , overheats also.
I have replaced plug , checked points and timing, operation of the advance /retard and choke.
The oil pump is working and fuel runs clean.
Any suggestions please.

Thanks

What do you do when it loses power and misfires? Stop the motor? Will it start again before it cools off? Maybe the condenser in the magneto is becoming defective?

[RalphM]

Have you got the carb set up right jet sizes needle in the right notch and so on
sounds like it could be running weak.

[JohnnyBeckett]

hi can it be the mag condenser when it gets hot it starts missing

[MikeCrook]

The engine faulters and misfires with blowback through the carb. The motor starts to stall and by closing the throttle it just about keeps running it might pick up for a few moments but without power to move the bike. When it stalls it is possible after a few minutes to restart the engine with out any improvement. Can't detect any leaks at carb manifold , I have not reset the carb notch etc .
Is there a way to test the condenser ?

Thanks for the replys.

[will_curry]

Do you know any history of the magneto?

If it were mine I think I'd be looking at that next.

[RalphM]

It could well be the condenser I missed the 10 miles
Bit in your first post but it may be worth checking if the fuel cap breather is clear.

[ian williams]

id go for fuel cap breather or lack of a hole in the cap .
if you have an indian made fuel tank cap it wont have a breather hole in it , but needs one .
you should have a small hole in centre of cap , its around 1.2mm diameter thats all , and you should be able to get some air through it .
the original ariel cap bolt has a hole passing down so far and then it turns at 90 degs and comes out side of bolt just below top of cap in the area that you will see a small funnel shaped part of the underside of cap .

on my NH i had similar issue to you but it was 7 miles for me , cough bang and engine stopped, then wait a minute and it would fire up and go for another 7 miles until cough bang pop .

i found i had no breather hole in my indian tank cap and that was the problem , i drilled necessary holes and all has been well since .

on my AJS twin i had similar issue recently but ive had bike for years and it wasnt tank cap , but i found some debris in bottom of fuel pipe right at the elbow/banjo to the amal carb which had blocked flow of fuel , the banjo fitting has much smaller hole than the 1/4" pipe and bits can get trapped here which impede or block fuel flow from tank to carb .

sometimes the filter under the carb banjo fills with crud and could block fuel passing , so it needs a clean out once in a while .

choke/air lever needs to be checked so it cant work its way shut while riding , just needs the screw tightening once in a while and checking .

ignition points need checking where the thread goes into the rotatiing carrier , they can be done up too tight when locking the points up and will pull out or work their way out of the zinc casting and make the gap close up .

if you do find problem here at the points and need to bush the threaded hole you can use a brass threaded sleeve from an old metal mains wall socket as they are the same thread something like 3.5x0.6mm

one other thing i can think of is float in carb sticking when its down , you may have type of float which slides up a rod and i have had this issue on my flat tanker which has a senspray carb on it which has similar float bowl to the older type amal carbs and i have to flick the tickle button every so often to make the float "pop up " and let fuel in .

regards
ian

[MikeCrook]

Thanks for all the ideas ,

The bike had been running well since beginning of the year.

I will work through the list.

With the capacitor can they be tested ditto the mag ? Or do i just fit a new capacitor?

Thans again all.
Regards

Mike