AMeatHead
XS400 Enthusiast
Does anyone have a lead on brand new replacement carburetors that can be used on 79-82 XS400, Xs400J and XS400JR and the like?
If your petcock has a vacuum line connect to the intake manifold boot. The petcock is a vacuum assisted fuel flow to the carburetor. Direct flow has no vacuum to assist in flowing fuel to the carbs.
Ok I may not have been clear or I should use terms you understand. Manual fueled carbs mean the petcock has no vacuum line. manual petcock = direct fuel, vacuum assist petcock fueled carbs may have been a better way or manual petcock fueled carbs.
Like bench sync = static sync. Manual fueled=direct fueled and that has to do more with the petcock than the carb.
As many of us have learned the XS400J/RJ using the BS-34 series type carbs that when the engine is off fuel still will flow to your carbs even when the engine is off and the petcock left in a on position. that is how many of us found out our float needles needed replacement as the carbs would fill and then flow into the firing chamber then into the crank case via the oil ports and around the rings. causing no or poor starting and oil/fuel mixture to flow through the vent hose into the airbox onto the ground.
My vacuum hose from the petcock to the intake manifold boot breaths I can watch it suck in and expand out as the intake valve opens and closes. I read either here in another thread about this vacuum assist type of petcock and that some were replacing them with direct fuel / manual petcocks and eliminating vacuum line all together. and they stated they found it better. So I wanted to find out more but no one responded so I asked the question here if anyone knew more on this.
I wanted to point out that the carbs that came stock were off a line not one of them was jetted for each bike they were being placed on. So the stock carbs were jetted to a specific range and ratio for the bike and its type of air intake. In the case of the 81-83 XS400J/RJ the carbs were all jetted the same and installed on thousands of bikes. At that time we could simply buy another set of BS-34 carbs and would have to only sync them.
Being it is 30 years later and those carbs are no longer produced I was looking for a new carb replacements jetted to the stock specifications that would mount to the XS400J/RJ, K/RK, H/RH bikes. the BS-34 carbs were sold to Yamaha, Kawasaki and Suzuki during those years. But depending on the Bike manufacturer those carbs are jetted differently. So an 82 set of BS-34 carbs off an 82 Suzuki will not run well on an 82 Yamaha and vise versa. But you could switch them from one 82 Yamaha to another of the same model no problem.
to make a long story short does anyone manufacture replacement carbs with the stock specifications that would work on these older bikes?
A friend of mine was able to buy a brand new set of carbs for his 68 Harley. He put them on synced them and they work fine. But when I look for a set for my Yamaha I cant find any or I am not looking in the right places.
the Ethanol is destroying the alloy and the jets in the BS-34 carbs and even if you rebuild them they never work the same. You will have problems getting the carbs to work if they have been run for any length of time on unleaded that contains Ethanol. and don't trust the 10% octane stickers on the pump the ratio is even higher than that sometimes up to 30%. The law only requires they put the minimal amount on the pump.
I am currently in that dilemma though I am now using fuel stabilizer and regular leaded gas with petroleum octane boost to make a high octane regular gas.
I sure wish they still made leaded premium gasoline.