Rebuild my BS38's or Keihin Carb Kit

[rfk74650]

Need advice from you Guru's please.
My 74 TX650 randomly dies like it is getting no fuel.
Looking at the carb ID info on Mikes XS page, my carbs are the stock BS 38's with separate throttle cables. I have had them apart a dozen times and cleaned them and also put in rebuild kits from Mikes but it still doesnt quite run right. It randomly shuts off like it runs out of gas then will eventually restart. I replaced both fuel petcocks and installed inline clear fuel filters. There is always gas in the filters so I know it is flowing from the tank. The plugs are dry when this happens so I am convinced it is a carb issue. I have installed a Pamco kit last summer which made a huge improvement over the old stock ignition. I am looking for advice to either have my stock carbs rebuilt by someone with more knowledge than me or go with the Keihin Carb Kit.
Thanks!

 

[650Skull]

Have you checked the vent hole in the gas cap. If it is blocked or partially blocked it crates a vacuum and starves the motor of fuel.

Buy the way real nice bike

 

[rfk74650]

Yes, the cap appears to fine. Would there be fuel in the filters if it was blocked?

 

[littlebill31]

Check the floats. The float needle might be sticking. Or you can send 'em to me.

 

[ReycleBill]

Have you actually tried riding it with the gas cap open? You could still have gas in the lines but not have flow to the carbs if the tank vent isn't working.

 

[XSLeo]

Too low an idle? Should be at least 1200 rpm, 1500 a bit better.

 

[pamcopete]

rfk,

I have found that some fuel filters work too good and will actually restrict the flow of gas when the tank is low. That causes the engine to quit when riding at higher speeds because the gas is not being fed to the carbs fast enough. If you stop and wait a few seconds, the flow fills the bowls and the engine will run just fine again until you burn more fuel than the filters will allow to pass.

To see if you have this problem, do a flow test by draining the tank through the filter in the prime position or on position of the pet cock. You may find that the flow actually stops as you get to the reserve level because the pressure is at its lowest just before you are in the reserve level. Some filters will stop completely and you cannot use the reserve.

Generally, these filters are of the paper type and the condition gets worse once the filter has been used a bit and it is saturated. The filter may in fact pass the flow test when it is new , but stop flowing after a few hundred miles.

So, I have stopped using paper filters.

 

[retiredgentleman]

Have you considered a loss of power to the ignition? Your fuse,kill switch or ignition switch may be intermittant.

 

[bluebikerblan]

Along the lines of the previous two gents comments....I'd bet on restricted flow of filters and/or a plugged gas cap vent. Also, your manual petcocks each have a brass screen internal filter which is easily/often blocked with sediment/tank crud as well.

Petcock Filter with attached filter screen. Petcock Filter with attached filter screen.
Fits: Original Yamaha manual Petcocks Only. Part #20-6421$4.50 USD EaAdd to Cart

I've been refurbishing a number of petcock sets and converting vacuum to manuals as well. It's amazing how much flow is restricted by these blocked filters & screens. Easy to check as the filter screen unit screws right out. Might want to take the back plate off the petcock to take a look inside that as well. Blue