When vacpipe is off fuel tap the fuel stops comeing out of the back of the carbs and when its on the fuel tap comes from overflo pipes on the two carbs. also the bike starts when cold but when its hot its will not start. the rd350 ypvs runs ok with the vacpipe off but will not start with it off. can any help???????????????
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Is the tap vacuum operated? There will be a pipe from the carb to the tap if there is, and when the engine is running the vacuum from the carb pulls on a diaphragm and opens the flow.
If this is the case, the 3 positions are "PRIME", "MAIN" and "RESERVE".
Disconnect the pipe from the outlet of the tap, but be prepared for fuel to come out. If it does, then the tap is set in the prime position so move it to another setting to stop it. If it doesn't start flowing then the tap is set to main or reserve.
Main and reserve are self explanatory and are standard on most bikes, but prime is not on as many. Never ride on prime as this just allows fuel to flow freely and is only used to start a long standing bike or one that has been run to empty. It does what it says and primes the carb. Once running switch over immediately to main or reserve.
Hi... if you have vacuum cabs... Have you checked to see if the vacuum on the fuel tap is working correctly.. Take the fuel pipe of the carbs, put the fuel tap to on.. If its a vacuum tap there should be no fuel coming out. Put the pipe in your mouth and suck on the pipe, if fuel comes out then stops it seems to be working. Also check the diaphragms in the top of the carbs are not split or have any pin holes in them. You can do this but holding the diaphragm up to the light.. (If they are vacuum carbs).. You can aso check to see if the carb rubbers are leaking between the carbs and the engine.. You can do this by starting the bike up and leave it ticking over. Get some carb cleaner or WD40 and spray it onto the rubbers between the carbs and engine. If the engine pics up speed (revs go higher) then the rubbers need to be changed.. Hope this helps you out...
from memory a fuel line( runs to a fitting on carbs which feeds all carbs with a common tube) a vacumn line to opperate the fuel tap(slightly larger diameter comes off the manifold) a tank breather line
1) This might sound daft but check if there is actually fuel in the tank. Many bikes have been stripped down by the hard of thinking only to find the tank was empty...or the tap was off... or should be on reserve...
2) Assuming this is a gravity tap (one main pipe) and not a vacuum tap (one main pipe and one smaller pipe at the side) Turn tap to off and remove pipe from tap. Turn tap on and see if fuel flows. If yes, then replace fuel pipe (this should sort it, try again with the pipe off at the carb end and see if fuel comes out. If it does but the bike still won't start then the carb jets are blocked.), if it still doesn't flow then go to3)
3) If there is fuel in the tank then remove tank and pour it out into a can. Remove tap from tank by unscrewing with the correct spanner.
4) Examine the guaze filter, it is probably full of crud and muck. Clean with fresh petrol and replace.
Hopefully that should sort it.
it may just be sticky flotes or you may need to change the fule pipes as they could have rotted away
turn on the fule and try tapping the carbs to see if it stops leeking fule out the carbs but dont hit the carbs very hard just tap them! if it stops the fule leek strip carbs and clean the flote needels so they can move freely
Did you clean the pilot & main jets in the carb & set the float height to standard? There is also an over flow in the carb which should stop fuel flooding into the air filter - did you check? Make sure there are no splits in the fuel pipes & the smaller vacuum pipe that goes from the side of the auto fuel tap, also check pipes connect well By your description it sounds like the carb is filling very slowly, 1 bowlful would get you around 2 miles & then plug would be dry when trying to start it, leaving it overnight the carb would fill up & flood air filter due to a leaky fuel tap
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the fuel line(the bigger of the two)which will come from either between the carbs or offthe left hand carb,is connected to the main fuel tap(larger outlet) and the vacuum line will come from the front of one of the carbs(on the engine side)and should be tapped into the inlet manifold,this pipe (smaller dia)goes to the other outlet on the fuel tap,these are a vacuum pump inside the fuel tap assembly