Starfire Problem

[bikerbob]

I have recently bought a Starfire which has been standing unused for about 4 months that I know of could be more. I put fresh petrol in started no problem ticks over well but after about a minute or so it just stops no missing or spluttering just stops, couple of kicks and it starts up again then once again after about a minute or so it stops. I have done this about 4 times before I decided to put it back in the garage and find out what the cause is. have checked the points they are ok as is the plug so am wondering if this could be carb issue it has the concentric carb fitted but this is the first bike that I have owned that has a concentric carb fitted all my previous bikes had monoblocs. Am looking for advice thanks.

[rhyatt]

doing what your bike is doing is usually indicative of a dodgy electrical component.
they are cold when when you turn the bike on and warm up electrically after a while - generally failing when hot.

the 1st and cheapest place to start is the condenser which is across the points

replace that 1st and clean/rest the points while your'e there

[Barney Rubble]

Might also be the fuel tank breather or float bowl breather is blocked.

[bikerbob]

Thanks for those replies. Not at the moment convinced it is a petrol problem as bike starts and ticks over OK and when it stops you can start it up straight away either first or second kick. Have been looking on line about testing the condenser with a multimeter. you discharge the condenser first  then set the multimeter to ohms but online they do say at what setting to set on the scale mine has setting from 200 2000 20k 200k 2000k which none do I use. Then you set the meter to DC volts but once again do not know which setting to use my meter says 200m 2000m 20 200 600 which setting do I use when testing the battery  for volts I use the 20 setting

[rhyatt]

For what the condenser costs, I never bother testing them.
Just stick a new 1 on
If your condenser is external to the points, you can use a car condenser mounted conveniently near the coil, usually cheaper components

[Greenfield]

Testing with a multimeter is quick and easy. I've just fitted a new one on my B40 as the test results were hit and miss. The original spec is unavailable, so I've fitted one from an early mini (half the price) under the seat next to the coil. If you do this make sure it has a good earth.

[bikerbob]

Thanks for that on my Starfie the condenser is under the seat bolted to the rear of the toolbox like you say I think I will just buy a new one and go on from there.

[rhyatt]

The new one goes across the contact breaker wire on the coil to earth.
Check polarity of coil whilst your there.
If bike is neg earth, then points wire will go to neg on the coil along with condenser wire.

[neil1964]

Condensers tend to fail when the engine is being stressed at high RPM manifest by a misfire.
Points failing tend to give you a slow speed, just pulling away misfire.  I totally agree that a component getting warm can fail but surprises me that it could get hot that quickly and fail that way.
I've had issues with modern fuels deteriorating causing rust in the tanks, grit and rust in the fuels. 
I suggest removing the tank and washing it out thoroughly.
Strip the carb (taking care to note the pilot setting and needle setting as you go. Blast the small passage ways with carb cleaner and then compressed air (particularly the tiny compensating hole just inside the main choke - usual caveats re no wire or drills down jets).
Check the fuel filter inside the tank on the tap is intact and not clogged.
Reassemble with new gaskets and washers (o-rings rarely fail) and take care not to overtighten flange nuts (lock washers, self locking nuts preferred) and fresh low ethanol high octane fuel (premium) eg Esso Synergy  Supreme this is ethanol fee at moment but will go E5 soon.
Also if laying it up might be best to slosh some 2stroke mix around the tank to add a little oil to the surface and then wash/dilute out before using again.

[bikerbob]

Thanks for those replies I will work through the suggestions,however I am not convinced at this stage it is a petrol problem I am 81 years old have been riding bikes since I was 16 not continuosly but continuos since 1995 I have restored an A10 a C12 A65 A7 so I have had numerous problems both fuel and electrical which at times have caused a few headaches. In my experience if it is fuel related then you normally get some warning missing spluttering that kind of thing. In all those years I cannot ever remember having a blocked main jet but have had a number of pilot jet blockages  plus other carb problems you usually get some symptoms like with a blocked pilot jet normally the bike will try to start but will not and if it does start then it will be missing and spluttering. Now electrical that is my weak point they have always caused me the most headaches like now trying to test the condenser have watched videos on line  the first one I watched a guy set the ohms on the multimeter to 20k then putting one lead on the connecter the other on the body if you get a high reading of 18-19 then condenser is OK if you get a low reading 1-2 then condenser is faulty. Using that test on my condenser I get no reading at all. The only thing with Starfire is this is the first time I have ever had a bike with a concentric carb all my other bikes have had Amal Monoblocs maybe concentrics react differently,the main reason that I suspect an electrical problem is the sudden stop of the engine no prior warning it is like switching your light off at home it is that sudden but you can start the bike up again with just a couple kicks and the whole saga starts again runs perfect for about a minute then suddenly stops. I do appreciate the help that I am getting Thanks.

[neil1964]

You have a long experience with old machines.
When you restart do you tickle the carb again?
I've had exactly the same issue with 1036 Mk1 concentric on a Goldie.
Start up with tickler, run for 20 seconds or so then dies, phut!
I cleaned the carb thoroughly and found blocked compensator jet with rust bits (my main tap filter was ok but my reserve tap filter had a small hole in the fine mesh hence the grit).

I have the electronic test gear so cap testing is easy just with Fluke Multimeter and they are a bit of kit well worth having (so no need for me to use either Tel-Ohmike or the Hunts CRB!!

But of course for a few pennies by all means buy another cap but a lot of car caps and points available now coming from the far east are total rubbish and I'd go electronic at drop of a hat if I planned using it regularly.

[bikerbob]

No Idid not tickle the carb just kicked it over and couple kicks bike restarted. Have got the tank off and have done multimeter test on the coil using the ohms setting at 200 I get a reading 0f 5.2 changing the ohms setting to 20k and taking a reading from either connector to the plug lead hole I am getting a reading of 8.76. From what I have checked on line the reading across the connectors should be .4 to 2 and from the connectors to the plug hole 6k to 20k. Is the coil OK or do I need a new one. Thanks. I will be next taking the carb off and checking that over but because of other things may not get around to that till the weekend. Thanks

[rhyatt]

When testing, the component to be tested must be discon totally from everything else.
Primary , across the 2 lite terminals should be around 4 ish ohms.
Secondary , 1 little terminal and the other probe down inside the ht tower, about 12k ohms ish.
I say ish but these are ball park.
The ht lead should be pure copper therefore 0 ohms and the suppressed plug cap around  10k.

Just try the condenser 1st, easy and potentially quick solution

[bikerbob]

Thanks for that the coil was still attached to the bike when I did the tests will take it off tomorrow and try again. While waiting for the condenser to come I thought I might as well take the carb off  check it out, the inside was spotless no signs of any dirt blew compressed air through all holes all OK. The airscrew position has got me thinking, now with a mono bloc carb the starting point for tuning is one and a half turns out, on this concentric carb the screw was not quite a half turn out are concentric carbs different. Also the needle position the Amal catalogue says posotion 2 but  in the library I checked the instruction book for my model and it says position one, now I don't think this would contribute to my problem but I would like to get it correct when I put it back together not sure what position was before I stripped it as when trying to compress the spring to release the throttle cable somehow disturbed the needle clip and the needle fell out getting a bit clumsy in my old age.

[rhyatt]

The 1.5 turns out is a starting point for concentrics as well.
Needle position as you say, won't affect this problem, but put it in whichever clip your bsa manual says or failing that ring Burlen in Salisbury , they took over all things Amal and are a mine of information.
Check the ht cap resistance as age can make these caps difficult for the spark to penetrate.
Your coil readings weren't far off fine anyway.