Question about 1977 Yamaha XS 650 D
Its not any obvious reasons like a stuck throttle cable or dirty pod filters. could it be a sticky auto advancing unit? or could it be a vacuum leak somewhere? i have already torn down carbs and replaced all jets and cleaned properly. what do i need to try next?
Probably the vacumn slides are hanging up, Not because they are stuck, But because the idle screw is set too high to get to idle. The idle will usually hang up at 3,000 rpms. Set the idle mixtures at 1 1/4 turns out & make sure the throttle cable has play. Now back the carb idle down till it just idles about 1,100 rpms. with choke off. If the carb sync is way off, I will hang up on 1 carb when hot. You need a vacumn guage set to make sure they are balanced. To check the spark advance (which I doubt), Put a timing light on the LH plug wire & shine it at the timing marks behaind the LH cover on motor at botton covering the generator. It should be on the F marks at idle & at the unmarked line aprox 1 " over which is full advanced when reved up to 1/2 throttle. But yes a air leak at the intake manifold could cause it to rev, But will be a very erratic idle at 1,100 rpms. If the idle circuits are working correctly, You should be able to kill each cylinder with turning in the mixture screws one at a time. That checks the idle jet circuits.
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Posted on Jan 02, 2017
Have you checked the float level in the float chamber?
I guess you may have to reset the float pin adjustment, its allowing more gas to pass through thn required and thus the overflow!
Not bad too, when you are working on the float assembly take the opportunity to blow out the fuel line from petcock to the carburator via the seat for the float pin,any foreign particals there would stop the float pin to seal up and thus overflow.
Fit in an inline fuel filter , this will help keep out the dirt or whatever.
Hope this helps.
Knight (Yamaha Seca XJ750A 1981)
Posted on Feb 13, 2009
If I understand your problem correctly this may help. There should be a spring just a bit smaller diameter than the slide that mounts between the top of the slide and the bottom of the carb cap. No spring means no snap-back. I am assuming there are no kinks in the cable and the cable was routed correctly when installed. Lots of times if the cable is not routed properly the gas tank will "stretch" the cable when the tank is re-mounted. Route the cable properly and the problem goes away..... As far as the slack in the cable, there is a an adjusting screw on the top of the carb (where the cable ends) and an adjuster screw at the hand throttle also where the cable ends. Some bikes have an extra adjuster mid cable but I don't think yours does, (working from memory here). If none of the above work then my guess is that the parts counter handed you the wrong part.
Posted on Mar 14, 2009
sounds like carbs not cleaned right, oh try changing fuel filter, does fuel pump run constantly. if you cant hear it you can feel it, up behind the ignition. Berrymans B12 fuel additive works wonders. double dose add to gas run bike til hot then let stand overnight, pray a lot and try it again.
here is a free pdf service manual too http://www.carlsalter.com/aaman/Yamaha_VSTAR_650_MAIN_MAN.pdf
Posted on Apr 04, 2009
SOURCE: Cleaning Carb Jets
not to a trained ear also go by rpm and spark plug color
NOTE: use copper wire to clean jets, sync is just thottles are same position as all carb's just leave them adjustments alone will be fine if are out use a 1/8 drill an place in between piston/butterfly to carb bore to sync/calibrate
better use a manometer for adjusting screws
depends on condition of org parts
worn = richer running
new = lean an clean
also if changed the exhaust system need to
re-calibrate carbs for max performance
Posted on May 09, 2009
SOURCE: how to clean carb on yz125?
ALWAYS have a fire extinguisher on hand when working on carburetors.
Remove the water trap bowl at the bottom of the petcock, (gas valve). Is there any water or trash in the bowl? Drain a cup of gas from the tank. Is there any water or trash in the cup? Dump it, clean it and re-mount it, ( not all bikes have a water trap bowl ).
Drain the carburetor. There should be a large plug on the bottom of the carb float bowl. Remove the plug then replace it after the fuel drains. Turn the gas back on and wait a minute for the carb to fill with gas. If the bike doesn't start and run properly then shut off the gas and remove the carburetor from the engine.
Remove the float bowl and clean the entire carb with a spray carb cleaner from the auto parts store. Wear protective goggles to avoid getting spray in your eyes. Spray into all the little airways and fittings in the carb. Remove the idle screw and the air screw on the outside throat of the carb and spray into the screw holes as well.
< < READ CLOSELY > >
Be sure to put these two screws back in the same hole they came out of. IMPORTANT > do not tighten these two adjusters down. Only screw these in until they LIGHTLY seat. Now turn each adjuster one and one half turns outward. Put the rest of the carb back together, clean the air filter and install the carb. Let the float bowl fill then start the engine. This process should get you back on the road. Post a comment to get back to me if it doesn't.
A “very helpful” rating for this answer? Thanks
Posted on Jun 16, 2009
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