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Cleaned carbs. Nothing found in jets or filter in banjo fuel inlet. Drained all gas using inline filter, didn't see anything in filter. Removed petcocks and found both filters rotted away. Ordered new petcocks w/filters due to not sure if old ones are opening all the way. Seemed to flow good but want to be sure. I want to clean tank out in case there is debris from old filters in it. Would alcohol be OK to rinse it out with?

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Do you have a tool for cleaning the pilot jet yet? Despite everything I'm thinking this is your problem.
Put the chokes back on. You will need them for the cold starts this fall.
Do you have the Stock OIF filters or after market pancake filters?
Are the coils original. Did you check them with an Ohm meter?

Be careful tightening the nuts on those carb flanges. Too much will bend the flange causing air leaks and stuck slides. How much is too much? I turn the nut down till the lock washer is *just* flat and go 1/16th of a turn more and no farther. Same for the float bowl. if you are worried about the nuts or screws backing off then a drop of purple locktite will ease you mind. Make sure the o-ring on the carb flange is new and paper gaskets on both side of the phenolic spacer.

The bike was running before but you did say it was running hot.

1) Carb set up should start with setting the fuel height in the float bowl. See my post somewhere in this thread: https://www.britbike.com/forums/ubbthreads.php/topics/860468/concentric-mk1-setting-float#Post860468

Last edited by Semper Gumby; 10/16/21 9:02 pm.
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Cleaned carbs and jets best I possibly could. Replaced petcocks (old ones were about half plugged up and filters were disintegrated) and Replaced all fuel lines. Still, no start. Haven't got to electrical parts yet, will be next thing to check. Gonna also check timing.
Thanks for all the help and info here. Much appreciated.

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Has OIF air filters. No idea how old coils or ignition system (pazon sure fire) is since it was on bike when I purchased it last year. Looking now to see how to check coils. Then go from there.

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The only way to properly clean the pilot jets is a # 78 drill, anything less , spray, guitar string, wont cut it.

Clipped this from vintage bike mag.
"pilot jet can be cleaned using a #78 drill (.016″ diameter). It will have to be securely mounted in in a brass tube or equivalent. It is a confounded nuisance when the drill gets stuck in the pilot jet and comes out of the brass tube! Twirl it between your fingers in a clockwise rotation and it will draw any “swarf” down stream of the fuel flow and help prevent the drill from becoming stuck.

Yes, a guitar string can remove “swarf” from the pilot jet orifice. It doesn’t insure the jet orifice is returned to its proper size. Also the “swarf” in the jet is pushed up stream of the flow of fuel. This allows the “swarf” to flow back into the jet and potentially partially block the orifice. The guitar string technique works only if you modify the carburetor where the body is drilled and tapped to accept a modified pilot air screw opposite the working air screw. This way you can push the “swarf” down stream of the orifice. See AMAL’s web site to see this modification."

The whole article is here. http://vintagebikemagazine.com/technical-articles/AMAL/


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
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Since 90 % of carb faults are electrical, have you tried hot wiring the ignition so the key switch is by passed. i have owned my 71 A65 for nearly 40 years, its on its third ignition switch, these are low quality switches located in a terrible place .


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
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What's the easiest way to bypass ignition switch? As you said it's in a poor location. Bent 2 keys kicking it, may be switch.

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At the back of the switch , pull the brown/blue wire ( feed from battery), pull the white wire ( goes to ignition system), join these together.

If you have an ohm meter, check the resistance between the spades at the back of the switch, it should be zero when " on " , infinity when open, if you see wavering numbers when on, its defo the switch.

Also , open up the fuse holder in the brown/ blue line , give it some love, clean any oxides off the contacts .

Get a #78 drill, they are not expensive, buy more than one. If you have an AMAL Concentric this is an essential tool.
1971 BSA A65 workshop manuals are also still available. try e bay.
https://www.ebay.co.uk/itm/271386641948?hash=item3f2fe7861c:g:ir8AAOSwvMVcjNk0

Last edited by gavin eisler; 10/18/21 11:14 pm.

71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
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Thanks for the info Gavin. Think I'm gonna relocate switch with new one anyway, so I don't break key off. I'll post if it was switch.
Thanks again👍

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