AMAL ISSUES STILL

not long ago I got some good info from all of you regarding setting up the carbs on a 1970 Norton commando and I got some good points do I followed all the guides cleaned the carbs drilled and tapped out the access points to clean the jets etch and put them back on the bike heres what's going on now

the bike starts but only runs for a very short period like it runs out of gas like it can't draw fuel into the engine I'm now lost as to what to do any ideas guys?

Hi Archer
I had a similar problem, which turned out to be two separate issues, the first was the rubber in the main fuel cock had turned not allowing enough petrol in, (open both cocks),the second problem was in the tank cap, the air relief had blocked and (on a full tank,especially) I just opened the cap then closed it. Maybe not your problem but worth checking.
Peter

Sounds like not enough fuel is getting into the float bowls.

Remove the float bowls, one at a time, put a small tin underneath it,
open the fuel tap and observe that you get a good flow out of each.

Check carefully too the fuel inlet needle and seat.
Any problems there. ?
There was some chat about viton tipped fuel needles a while back, maybe someone can elaborate.

ozbowhunter said:

the bike starts but only runs for a very short period like it runs out of gas like it can't draw fuel into the engine I'm now lost as to what to do any ideas guys?

Click to expand...

What do you mean by it runs for " a very short time"?? 10 seconds?? 1 minute?? 5 minutes??

Once it starts, does it respond to the throttle? or just die when you throttle it??

ok it starts it will rev a few times but only runs about 15 - 20 seconds then dies

When you tickle it, does the fuel dribble out the little overflow hole ?
Easily ?
What happens if you keep trying to tickle it when it does start.

Fuel would seem to be the solution here. ?

does your gas tank have a breather in the cap so when gas flows down to the carb bowls you don't actually create a vaccum in the gas tank?? You could start the bike, then open the cap and see if it stays running... If it does then you need to have a way to let air enter your gas tank to displace the gas as it feeds the carbs.


...... but here's another possible scenario... You push the carb bleeders to fill the bowls to start it, so you know you have gas in the bowls. You kick the bike, it starts and it runs until the bowls are empty and so it dies of gas starvation...

Try this. Push both the bleeders til both your carb bowls puke a little gas. kick and start the bike. Let it run 10 seconds then pump the bleeders a few seconds and see if it helps the bike continues to run.. If it starts to die, pump the bleeders again.... If pumping the bleeders keeps the bike running, you have a gas starvation problem. related to your floats, float needles, needle seat height, gas tank vacuum.

Did you really drill out your carbs to clean your idle jet? a guitar string does the trick to clean the idle jets for me with no drilling...

** Argh, I see Rohan beat me to the "tickle the bleeder" test...

yep drilled and tapped them out as per the instructions
ok here where I am
after all adjustments I got it to start but it wont idle it still seems to die I checked for gas flow and it keeps flowing through wit no apparent vacuum in tank

today I got it running and I have flames back through the right carb and cannt get it to adjust idle I moved needles to last slot and it ran but again still backfiring through carb on right I just don't know what to do I got my triumph running perfect with same set up
could this be timing ???

Yes it could be timing.
The commando is easy to check, just needs a strobe and the little plug removed on the lhs to show the degree scale,
and you are away.

It could also be VERY worthwhile to check the valve clearances, especially on that backfiring carb.
If the valve is held open, or burnt or bent, its not going to run well.
If the jets in the carb are still not clean on the idle circuit though, it can do that.

Could also be dirty plugs, or dirty points if you still have points...
hopethishelps.

PS I'm a little nervous about this mention of 'drilling' your amals.
What instructions are these, and where did you drill.
Cleaning and drilling are not quite the same thing.
Amals can be quite pernickety to get thoroughly clean inside the idle passages.

this is what I followed
http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

will check carbs again but always seems to be the right so maybe other issues

maybe smear some grease around the screw that covers the hole you drilled to make sure it's not sucking air into your carb. Any air leak at that screw would mess up your idle circuit adjustment.

Backfiring back through the carbs is usually too much ignition advance. Even if you think it's correct now, retard it a few degrees temporarily to see if that helps eliminate the backfiring. If you only have backfiring on one cylinder, it may be an issue related to the intake valve on that cylinder not closing properly.... (as rohan stated previously) Sometimes, the floats in the bowl hang up on the bowl gasket. If your float is hanging up causing a lean condition on one cylinder, that can cause a backfire if your timing is advanced. People trim the inside edges off the bowl gasket sometimes if they think the float is hanging up against the gasket.

I had one float hanging up recently in the down position and when I opened the gas tank petcock a flood of fuel came flowing out the bleeder hole continuously. I took it apart 5 times and still it hung up when I reassmbled it. Eventually I just gave it a "Rap" with a screw driver handle and the float free'd itself and the needle seated. The floats can sticking in the closed postion in your case, so when it runs out of fuel, the lean mixture causes the backfire.

What ignition are you running ?? points? electronic ignition??

running electronic ignition will go over it all again today

ozbowhunter said:

running electronic ignition will go over it all again today

Click to expand...

Some electronic ignitions are sensitive to battery voltage and will throw a spark irradically if you have low voltage. Some other EI's are less prone to that... so test voltage too

Had an issue like this awhile back. The o-rings in my petcock swelled (possibly due to ethanol in the gas?) and were letting very little fuel through.

Easy to check, just disconnect the fuel line, open the petcocks and let them run into a catch can. You'll quickly see whether there is free flow or a dribble.

I took off the petcocks, ran a drill bit through the petcocks by hand to scrape out the excess rubber, blew them out with compressed air, and reinstalled. They've been fine for several years now.

Cheers, Will

Back fire out the carby also = too lean a mixture, back fire out the exhaust too rich a mixture.
Sounds like fuel starvation, pilot circuit?
Burgs