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?
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NEW Replacement Carburetors
- Thread starter AMeatHead
- Start date
XSLeo
XS400 Junkie
With proper jetting, needles and slides I think you can get Mikuni VM 34 carbs to work. Try talking to Micheal Morse at 650central.com
He is mostly XS650 stuff but might be able to help you with XS400 stuff.
Leo
He is mostly XS650 stuff but might be able to help you with XS400 stuff.
Leo
AMeatHead
XS400 Enthusiast
I would like to get a brand new set of carbs with my specific jetting needs. Is there company I can contact to get a new set that fit my bike with my jetting specs?
And what do you all know about direct fueled carbs compared to vacuum assist fueled carbs? Is that all about a new type of petcock and stopping the vacuum ports?
And what do you all know about direct fueled carbs compared to vacuum assist fueled carbs? Is that all about a new type of petcock and stopping the vacuum ports?
This may come across as being rude or condescending, but that isn't the intention...
There's no reasonable way that anyone can setup a pair of carbs jetted for your specific needs. They may be able to setup the carbs to be somewhat close, but final tuning will have to be done by you (or someone else), on your bike, at the location you ride. Even if you provide a shop with detailed information (engine displacement, volumetric efficiency, max RPM, etc), the calculated jets will only be close to what is actually required. Close, but not correct. Final tuning will be required.
I'm sorry, but I don't understand what you are referring to when you describe direct fueled and vacuum assist carbs. http://en.wikipedia.org/wiki/Carburetor may help you.
The petcock is a valve, and the vacuum supplied to it is used to open it when the engine is running, and close it when the engine is stopped. Nothing more.
I hope this helps, at least a bit...
There's no reasonable way that anyone can setup a pair of carbs jetted for your specific needs. They may be able to setup the carbs to be somewhat close, but final tuning will have to be done by you (or someone else), on your bike, at the location you ride. Even if you provide a shop with detailed information (engine displacement, volumetric efficiency, max RPM, etc), the calculated jets will only be close to what is actually required. Close, but not correct. Final tuning will be required.
I'm sorry, but I don't understand what you are referring to when you describe direct fueled and vacuum assist carbs. http://en.wikipedia.org/wiki/Carburetor may help you.
The petcock is a valve, and the vacuum supplied to it is used to open it when the engine is running, and close it when the engine is stopped. Nothing more.
I hope this helps, at least a bit...
AMeatHead
XS400 Enthusiast
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.
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.
Last edited:
AMeatHead
XS400 Enthusiast
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.
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.
I think they make lead subsitutes that you can add to your gas.Dont know if its rue or not but somebody on here said you can buy ethanol free gas from boat marinas.It cost $1.50 higher per gallon here anyways.
I'm afraid that you are mistaken. The vacuum petcock on XS400's is nothing more than vacuum opening of the petcock when it is in the on or run position with the engine running. There is no pumping action or anything else. Remove the vacuum (engine stopped) and it is supposed to shut off the fuel flow. If it doesn't, then it needs to be rebuilt. This is a safety and convenience thing.
If your vacuum hose is pulsing, then it isn't vacuum hose. Probably automotive windshield washer tubing. If you'd prefer a manual petcock, there are some available that will fit the tank without modification.
AMeatHead
XS400 Enthusiast
yeah I need to rebuild my petcock that is for sure.
No the tube is a new type of fuel line used on some small 100's and it is thin walled handles the heat but to soft for using on the vacuum line. I finally was able to buy a foot of original OEM line from Yamaha and replaced it. It doesn't breath anymore I was worried it close off. But I closed the vacuum line off and drove it around and had no problem with it, it ran just fine without it being hooked to the petcock.
No the tube is a new type of fuel line used on some small 100's and it is thin walled handles the heat but to soft for using on the vacuum line. I finally was able to buy a foot of original OEM line from Yamaha and replaced it. It doesn't breath anymore I was worried it close off. But I closed the vacuum line off and drove it around and had no problem with it, it ran just fine without it being hooked to the petcock.
The stock carbs were obviously jetted for the bike as it was designed. Was it perfect for each bike? No, but it was close enough for most. Dealers often had to re-jet the carbs to meet operating conditions. e.g. high altitude locations or cold weather.
Have you looked at MikesXS.net? http://www.mikesxs.net/products-82.html#products I believe that they offer parts to convert this kit to XS400's. They will however require jetting and tuning.
I can't disagree about ethanol in gasoline. It is one of the worst con jobs hoisted on us by governments and big businesses.
In Canada we can still get Shell's Gold 92 octane unleaded gasoline that does NOT contain ethanol. 
And our pumps are stickered to indicate the maximum percentage of ethanol the fuel may have. Leaded gasoline is not required or recommended for our bikes. And 87 octane is fine in a stock engine, if it is jetted correctly.AMeatHead
XS400 Enthusiast
My hibernated for 16 years also and only a little over 5000 miles. but the carbs have been the problem.
the original owner had nothing but problems and the original dealer was no help to him. the Yamaha shop guys back then never found the problem.
When I got the bike and sonic cleaned the carbs of all the lacquered fuel that had dried in it it took two days to get it cleaned. I was getting ready to replaced all the needle valves and jets. when I got ready to remove the float needle valve and I saw this dirty hair I thought was still there and it turned out to be a crack. I bet it had been the problem the whole time. I replaced the right hand carb because of that. But I am sure it could run better than it does.
I had the tank cleaned and zinc electroplated. so I don't worry about the tank ever rusting again It really was not that bad. The petcock does need to be rebuild but as long as I shut it off at each stop I am fine with it.
It bogs when trying to accelerate and sometimes gives me trouble idling untilo it is very warm. then it idles high.
the original owner had nothing but problems and the original dealer was no help to him. the Yamaha shop guys back then never found the problem.
When I got the bike and sonic cleaned the carbs of all the lacquered fuel that had dried in it it took two days to get it cleaned. I was getting ready to replaced all the needle valves and jets. when I got ready to remove the float needle valve and I saw this dirty hair I thought was still there and it turned out to be a crack. I bet it had been the problem the whole time. I replaced the right hand carb because of that. But I am sure it could run better than it does.
I had the tank cleaned and zinc electroplated. so I don't worry about the tank ever rusting again It really was not that bad. The petcock does need to be rebuild but as long as I shut it off at each stop I am fine with it.
It bogs when trying to accelerate and sometimes gives me trouble idling untilo it is very warm. then it idles high.
Okay! Now we are getting to the root of the problem! 
Sounds to me like your idle mixture is way too lean. This can be caused by the pilot (idle mixture) screws not being adjusted correctly, damaged or missing o-rings on the pilot screws, undersized pilot jets, or vacuum leaks. It is also quite possible that the pilot circuit passages in the carbs are still plugged up despite the cleaning.
Valve adjustment should also be checked because if they are too tight, all kinds of performance issues will occur.
So, my suggestions are:
- Remove and completely disassemble the carbs and clean them again, being sure to also probe all passages with a fine wire.
- Clean the carbs with a mild acid (lemon juice, vinegar, tub and tile cleaner, etc) to remove any corrosion.
- Replace the o-rings on the pilot screws.
- Increase the pilot jets one size.
Hopefully doing all this will get your bike running as it should and save you lots of $ as well!
Sounds to me like your idle mixture is way too lean. This can be caused by the pilot (idle mixture) screws not being adjusted correctly, damaged or missing o-rings on the pilot screws, undersized pilot jets, or vacuum leaks. It is also quite possible that the pilot circuit passages in the carbs are still plugged up despite the cleaning.
Valve adjustment should also be checked because if they are too tight, all kinds of performance issues will occur.
So, my suggestions are:
- Remove and completely disassemble the carbs and clean them again, being sure to also probe all passages with a fine wire.
- Clean the carbs with a mild acid (lemon juice, vinegar, tub and tile cleaner, etc) to remove any corrosion.
- Replace the o-rings on the pilot screws.
- Increase the pilot jets one size.
Hopefully doing all this will get your bike running as it should and save you lots of $ as well!
Those behaviours happened to me until I adjusted my valve clearances. As the valves expanded and opened up, the engine behaviour changed dramatically...
Back to carbs - why not just buy a set of stock jets? Heck, you can have mine if that's what you're after...
Back to carbs - why not just buy a set of stock jets? Heck, you can have mine if that's what you're after...
AMeatHead
XS400 Enthusiast
the valve clearances are spot on.
you got a link to where to buy stock jets?
you got a link to where to buy stock jets?
I'll mail you mine. PM me your address. You're still using the stock air box, right?
AMeatHead
XS400 Enthusiast
yes I am still using the stock carbs.
see PM
see PM
