Lightning,easy starter,can be set to a nice idle but on the road,anything after quarter throttle,it drops a pot,change up,all ok then it goes off again...any clues? Electronic ignition and a charged battery.
I'm hoping you get some reply's to this! I soon will be rebuilding a Lightning (all in bits at the moment) where I will be putting a cutting torch through the rear end and making a bobber out of it so anything with issues like yours I'd like to know about just encase I have similar issues and just before anyone shouts out "what you doing that for you idiot" I want a bike that I can sit on with both feet flat on the ground. I know each to there own!
BobM
Assuming its a Boyer Bransden Electronic ignition, then it sparks on both cylinders at the same time so it's unlikely to be that.
if its the same pot that cuts out then its the carb on that side so that's the place to look. If the needle position and jets are all to spec then one thing to consider is the two tiny holes in the choke bore either side of the front (forward edge) of the throttle slide. If they are blocked, that will cause the symptom you mentioned. Poke a thin strand of copper wire down them and squirt carb cleaner through. If they are clear watch out as the carb cleaner will hit you in the eye. (Dont ask me how I know.....etc.).
Worth a try.
Chris
If it is after quarter throttle it is demanding more fuel from the jets. I agree, pull the carb right down, there are some Amal cleaning video's on Youtube. Those pilot jet drillings have always been a pain, but do all jets whilst it is in bits.
Thanks for that,just what I needed some clues. Will let you know how it goes.
An update, bought a sonic cleaner and cleaned the carbs and jets out and refitted everything. Big improvement but it still gives a bit of a hunt through the revs but if I give it a touch of choke,off it goes. When I rebuilt the carbs I fitted new jets, main 270,pilot 25 and the needle is now in position 5 to give it more fuel. Are these sizes correct? Amal 389 carbs.
Hi Willie
Amal spec is carb nos, 389/228 and 689/228 with 1.5/32" Bores main jet 270, pilot jet 25 and needle jet 106. Slide is cut away 3. Needle position 3. If yours meet that, except for the needle of course then worth checking the float chamber level. It should be level with the pip on the end cap. Before then, perhaps you could do a plug chop after a stint at 1/4-1/2 throttle (Needle Jet phase) and see what colour the plugs are.
I had the needle set to three and lifted it to see if it helped. Tried a plug check but as its running on choke they are black.....
You're running with the choke on? Could be an air leak somewhere on intake.
Tried spraying brake cleaner around the joints but it did not get drawn in,tearing my hair out now. Got one amazing backfire through the exhaust which is a new developement as it never did that before.....
Hi Willie,
Try checking the tappet clearance.
Best wishes...
backfire in exhaust? excess fuel not been burnt normally timing out.
Hi Willie Dee,
Are your slide cutaways the same on both carbs? Should be No.3 according to specs.
Regards
An update...as it would run on choke,my take was short of fuel so I ordered up a couple of bigger main jets 340 and stuck them in,I also followed a tuning guide by Bushman which was,I think,a good way to do it...no joy. Had beer,then a sleep and thought about it. The bike was now running rich,so,dropped the needles to the lowest position (highest notch) and ........wait for it...BINGO,! It now can be driven and revs all the way. A bit more fine tuning needed but it's a different bike now. What was the issue? Not sure,mainly me,I think but the bushman guide pointed me in the right direction. Thanks everyone for their advice,it was all good....now,let's cancel the 2 new carbs!!
Just a final comment. Did you replace the needle jets for new ones? Reason for asking is, people think that as there is a taper on the needle it doesn't make contact so should never need replacing.
I reality, with intermittent air flow the needles are constantly rattling against the inside diameter of the jets and this makes them oval i.e bigger than they should be and therefore delivering more juice resulting in richness.
If not been replaced then worth a try to see if any difference.
Chris
Yeh the needles were replaced,actually everything was replaced that could be. I bought all the bits from Amal but they are a bit "vague" on the 2 new carbs I ordered,anyone had any bother with them? They have been great so far.
well, Amal have history in carbs for many years and many vehicles. they know what they are doing, unfortunately, in todays world they have to be competative. this means us old machinists (40+ years) are getting near retirement age. 10 years ago we had 120+ machinists turning out £2 million a year, now we do £7 million with 25 people. one of our former machinists works for Amal now but not machining.
the machining of the bodies is carried out in India. The assembly is done in Salisbury, the only problem Ive had is a 600 series carb was machined wrong and had to go back to India for correcting, this held up a customer rebuild. that said, the recent 289G/1at I got for a B33 got the engine running and starts second kick now.3
Wassells do their own 6 and 9 series carbs cheaper, Ive fitted to my Triumph 500 no problem, but some would say not original. shape is coating isnt but do the job.