1973 TX650 Carburettor Woes

Ilbikes · New Member Joined: Oct 25, 2006 Posts: 6

Hello fellas.

I could really use some advice. I've got a 5,000 mile original TX650 that I'm trying to sort out. I've completely been through the carbs, soaked them, blown through every orfice and passage. I replaced all of the jets with factory new ones, I replaced both floats, new float valves and seats, checked both needles for stock size, confirmed they were in the 4th slot from the top, and put in a NOS choke valve, gasket, and cap in the left carb, plus checked the cross-over tube between the two. I can turn the right-hand air/idle screw all of the way in and the idle speed runs it's highest. Something is not right when the air bleed screw can be shut off. I'm getting air in there somehow.

Also, the right cylinder is running 20-25 degrees hotter than the left, an indication of a lean mixture. I suspect the right cylinder is trying to do all of the work (with it's slide opened fully) and that the left carb is somehow losing slide vacume through the choke system. The 2 carbs are identical except for the enrichment circuit. The air for that enrichment circuit comes from the "atmospheric pressure" side of the diaphram. My slide diaphrams are perfect and not leaking, but I do see the slide dropping faster on the left carb than the right one does when you cover the atmospheric air inlet while the enrichener is closed and the slide pushed up by hand. This is what led me to the choke valve. Before I buy NOS carbs or close off that enrichner circuit, what am I missin here. I've had 3 650's in 30 years and none ran perfectly. There has always been something amiss with these vacume carbs.

I've worked on many bikes and own/operate several today. This is the first time I've been stumped in many years. Your help/input will certainly be appreciated.

Thanks,
Gordon

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

deleted

Ilbikes · New Member Joined: Oct 25, 2006 Posts: 6

Thanks for the reply. I've re-posted this in the more read, discussions forum.

The screw is actually a "mixture" screw and regulates the 14:1 air/fuel mixture after it comes from the jet. I purchased the new jets from Speed and Sport using the parts fiche fo rthe 1973 TX, but I will check to see if they're correct. I am not convinced though that my problems are pilot jet related. Since this screw completely cuts off the 14:1 mix to the cylinder when screwed all of the way in, I'm more and more convinced it has to be in that left-side choke/enrichment circuit.

Here is a pic of the factory shop repair manual - page 73 where the idle circuit is explained in detail -

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