helping a mate with the above bike. He has recently acquired it and has the above problem. The carb has been stripped and ultrasonically cleaned. All the jets are clear and correct for the year. New plugs fitted. Spark is good. Starts easily but when the choke is removed, it runs very badly, requiring lots of throttle to keep going.
However, it has had some mods over the years. It is fitted with simease pipes like an RGS, has a bell mouth fitted to the carb.
I wondered if this machine should be fitted with an air filter (UK bike).
I know I need to check the carb flange for straightness and air leaks ther, but any other suggestions would be gratefully received. I will be having another look at it in the next week or so.
Many thanks for and thoughts
Hi Seamus,
Definitely check the carb to head joint for flatness and do not over tighten. The torque on these should be 10 ft/lbs.
Also, there would have been a filter fitted so running a bell mouth will make the mixture a bit weaker but I would expect it run but a bit lumpy at low revs. What does the plug look like? Even though ultrasonic cleaning is very good, it is still possible to have bit of a blockage. Try some carb cleaner and an air line.
You may be able to tune the pilot screw to get it a bit better otherwise it may need a slide with a smaller cut away to slightly richen the mixture.
The pipes will not have really have any affect especially at tick over/slow running.
Dave.
I know this is going to sound like a stupid question but when you say remove the choke does that mean taking the choke off to run normal (choke on/choke off) or stripping it off the bike completely.
If it means taking the choke off to run normally are you moving it the right way? They work different to a car choke (please feel free to ignore as you see fit if it really was a stupid question!)😀
That sounds like the most probable reason. Very easy to get the choke operation wrong! The choke cable is tensioned to turn the choke off.
:) :) :) :)
Hi.
Please do not be offended by this post.
Using the normal choke lever, the choke is off when the lever is fully open. In other words the choke is held in the off posn by the cable.
I found this out in the stupidest way after trying to ride around with the choke lever 'closed'
Take care and enjoy
Mike 8) 8) 8) 8) 8)
sounds very much like a pilot jet blockage . Did you poke a wire through the passages .
The difference in the carb jettings with or without a air filter is in the size of the main jet. It sounds like a blocked idle jet. The jet should be number 25.
Be interesting to see what the issue was. I'd check the obvious first before I stripped stuff and get into a whole world of pain and expense!
Had the same problem on a bike with a Monobloc carb. I found that I had not tightened the main jet sufficiently and it was loose on its thread. Presumably the vibration caused the petrol not to flow through properly.
Thanks for the ideas chaaps. The choke is operating the correct way, as I thought that was the problem, when my mate told me the trouble. I have also got an A10, but a different version.
Think the carb may have to come off again as I did not get time to check the flatness of the flange. Guess that is my first job.
I had poked out the pilot jet (no 25) with fine copper wire prior to ultrasonic cleaning. Suspect the bike has not been run properly for some time as all the jets were pretty mucky, hence the ultrasonic treatment. Thought I looked up the pilot jet hole and saw light, but i could be mistaken. Did not really get a lot of time as he was keen to see if it was sorted. Plugs were new and only run with choke and a bit off choke. 10 mins max, so don't imagine I will get much from them. Will look anyway.
Will not get a chance to look again till I finish my isolation as I had a positive test yeaterday.
Will keep you posted of progress
Hope all goes well with the isolation and you aren't too ill with it.
Guess we all have to wait another week to find out...good luck 😀
:) :) :) :)
Someting I have done with varying degrees of success. Strip carb. take out slides and jets then boil it gently in a mixture of water and every day kitchen soda, for about half hour. (haven't considered Coca Cole but might next time). Then fit new jets cost relatively little or even use a complete repair kit.
Mike 8) 8) 8)
Hi,
There comes a point with an old carb when no amount of cleaning or fitting of new bits works. Sometimes it is more economical to buy a new one.
Dave.
I am watching this thread with great interest. My friend has a Triumph tiger 100 with the same problem. He has bought and fitted a new carb with no success.
I am at a loss too but looking for leaks between the carb and head sounds a great idea.
Johm
Hi,
The new carb. is very unlikely to not be perfectly flat but it is till worth checking. The face on the head could be the problem. If the carb is still fitted then as a quick check wrap some tape very tightly around the joint to make it air tight. It may help to identify the issue and then the job can be done properly.
Make sure that the carb. nuts are not over tightened.
Dave.
Just fire the bike up and spray some wd40 or easy start on the carb to manifold joint. Any change in engine note means you have a leak.
Thanks again gentlemen. Some good ideas there.
Hope to get round when I get a couple of negative tests. Luckily. I don't feel really bad. Bit like a cold.
Cheers all
Resurecting this thread as I had a bit of time and a suitable day to test. Carb stripped again, it has no number stamped on the flange, but I measured it at 1 1/16 choke size, guess a 376 ype as fitted to 55 to 59 gold flash. This is a 60/61 bike and should have an 1 1/8 carb. I have assumed if the jets are correct for the earlier carb, it should run ok. The carb has been stripped again, poked and prodded, washed out with carb cleaner and everything appears to flow fine.
All reassembled and a pancake air filter fitted.
Running the bike, it idles well and revs fine on choke. Off choke, it will idle and when trying to rev, it missfires and seems to be running on one cylinder. Difficult to see which cylinder it is not running on as both exhausts are hot by then.
Will try starting on choke to warm up a bit, then remove one ht lead and start on choke, take off choke and see how it runs, then swap over. At least it will eliminate the ignition side.
Should have more time to play with it as th weather is getting warmer
The earlier A10 was fitted with a 376 carb with 240 main jet whereas the 60-61 A10 was fitted with a 389 carb and 250 main jet. Assuming it's got a 60-61 head on then it probably should be run with the 250 main jet also assuming it's got an air filter attached. If not, an even bigger main jet is required.
The fact that it revs with the choke on would indicate that it's running very weak. Assuming that the main jet is the right size, a possible reason for it running weak can be a worn throttle slide or throttle body allowing air to enter past the slide. The slide should be a snug fit as you move it up and down in the body with no free play discernable. If there is significant free play, a new slide might be enough to cure the problem otherwise, unfortunately, the carb may be worn out.
The other problem may be a weak spark. A weak magneto will fire a rich mixture but when weakened and the engine reved it will tend to blow out the spark. Had this problem a few years ago with a Shooting Star. Worth checking how far the spark will jump.
Hi Seamus,
Can you confirm the colour of the plugs after idling and revving with the choke slide in the lowered 'on' position. Then after cleaning, the colour with the choke slide raised in the 'off' position after idling and then trying to rev.
Also, how much are you opening the throttle to get it to rev? Have you tried opening the throttle to about 3/4 + to see what happens?
Dave.
Thanks again for the suggestions. Unfortunately, my mate is off on holiday for a couple of weeks so I will not have access to the bike.
Found a working colourtune plug in my box of bits and will try that in one cylinder at a time and see if I can judge the mixture from that.
Rechecked the jets and founf pilot 25, main 250 and needle at 106, so should be in the right ballpark. Carb flange is flat (checked on a surface table) O ring is new and squirting carb cleaner through the pilot holes, comes our in a good flow.
See what happens and will report back
8) 8) 8) 8)
Hi
Coca Cola doesn't work---honest
Mike 8) 8) 8) 8)
Hi,
'Colortune' is a great tool. Although the engine will not be under load, the full range of throttle openings can be assessed. Also the affect of quickly opening the throttle can be seen as well as the affect of using the choke.
Dave.
Seamus
How are you getting on. My friend's T100 problem was cured with screwing in the air screw fully then out by 1 1/4 turns. Started and ran ok without choke! Adjusted the air screw following Amal instructions.
Too simple? Perhaps just my ignorance.
John