1982 Yamaha xj 650 maxim - petrol tap pipes?

[Daz1977]

Hi

Can anyone shed some light on something which should be obvious, I bought a 82 yam 650 maxim[as a bitsa project] which needed a rebuild, but there is something I can't figure out, I inspected the petrol tank and tap, the tap has two pipe fittings one main and one reserve, ok, I found the obvious main one to the carbs, but can't find where the other one is supposed to fit to the carbs ....or does it go somewhere else, air box, or wot???, or do I have the wrong carbs?

I hope I have made sense, I bought a haynes but doesn't discuss anything about the second pipe???

Can any one help??

[Newbie bike builder]

Daz

[YPVS TONE]

If the tap is the same as a UK spec XJ650 what you have is a main fuel pipe which as you say goes to the carbs but the other smaller pipe is actually a vacum pipe which runs from the tap and goes to a stub on one of the inlet manifolds between the carbs and cylinder head,which i think is N03 cylinder counting from the left as you sit on the bike.If you look at the tap you should have 3 positons marked on it i.e ON,RESERVE and PRIME.The idea is under normal running you leave the tap in the ON position so when the engine is running it creates a vacum in the tap which opens the diaphragm in the tap which then lets fuel to flow.The prime positon bypasses the vacum side and lets fuel flow out without the engine running so you can fill the carbs when they are empty.The reserve position should only be used when you run out of fuel in the ON position but should be turned back to ON when you fill up the tank again.The other inlet stubs i.e 1,2 and 4 should have a black blanking cap fitted to them as these are only removed when you are balancing the carbs with vacum gauges. Hope this is some help. Tony.

[Airhead]

+1 the above

Might be an idea to test your fuel tap at this stage too! Switch it to prime, hold a comtainer under the fuel pipe and you should get a flow., Now switch it to 'Run' the flow should stop. Now place the vacuum pipe in your mouth and suck on it, the flow should resume...JOB DONE

[Daz1977]

If the tap is the same as a UK spec XJ650 what you have is a main fuel pipe which as you say goes to the carbs but the other smaller pipe is actually a vacum pipe which runs from the tap and goes to a stub on one of the inlet manifolds between the carbs and cylinder head,which i think is N03 cylinder counting from the left as you sit on the bike.If you look at the tap you should have 3 positons marked on it i.e ON,RESERVE and PRIME.The idea is under normal running you leave the tap in the ON position so when the engine is running it creates a vacum in the tap which opens the diaphragm in the tap which then lets fuel to flow.The prime positon bypasses the vacum side and lets fuel flow out without the engine running so you can fill the carbs when they are empty.The reserve position should only be used when you run out of fuel in the ON position but should be turned back to ON when you fill up the tank again.The other inlet stubs i.e 1,2 and 4 should have a black blanking cap fitted to them as these are only removed when you are balancing the carbs with vacum gauges. Hope this is some help. Tony.

Thanks Tony it does!!

I'll let you know when I have this baby running

Daz

[Daz1977]

+1 the above

Might be an idea to test your fuel tap at this stage too! Switch it to prime, hold a comtainer under the fuel pipe and you should get a flow., Now switch it to 'Run' the flow should stop. Now place the vacuum pipe in your mouth and suck on it, the flow should resume...JOB DONE

Cheers oldgitonabike

I'll try this too

can't wait till this baby is on the road!!

Daz