The carbs on the ‘78 XS500 are very similar to the ‘80-‘84 XS650 34mm Mikunis. There are some subtle differences, but you can rebuild them using the ‘80-‘84 XS650 34mm parts. I had to modify the float bowl gaskets slightly to accommodate the older 34s. All the main jets and pilot jets are interchangeable. The needle valve seat is different so you can use the seat you have if it isn’t wore out. Mine was fine so I just swapped out the needle valve.
The slide diaphragms were shot and being a cheap bastard I did not want to pop for the whole assembly. They sell at MikesXS for sixty-nine bucks a piece. There is a guy that sells replacement diaphragms on ebay for $49.00 plus $10.00 shipping. You have to wait for the auction to end which may drive the price up considerably. I opted to go with JBM’s products. He resurrected a old rubber press and makes diaphragms for a few different sizes of Mikuni carbs. The 34mm of the XS500 and the ‘80-‘84 XS650 have the same 73mm diameter and they fit my carbs like a nice pair of leather gloves. As far as I can tell, JBM is the best choice by far, a quality part for a great price. Only $39.00 for a pair and just $3.00 shipping on top of that. They are a snap to insatall and they have easy to follow instructions on their site. I highly recommend them.
I’m not going to be running stock filters and exhaust, so I bumped up the main(132.5) and pilot (42.5) jets to 140 and 42.5 respectively . Plus I bought one size up from there145, and 47.5 just to be on the safe side if the bike doesn’t run well with this set up. Just a note, When buying from MikesXS, have your total order ready when you purchase. If you forget something they charge you $7.00 shipping on all orders even if the part your buying is only a buck. If you do forget a part, if you get the order on the new one before the first order ships, they will add it to the first order at no additional cost. It would be nice if they had a phone number in addition to the checkout, just saying.
The total for rebuilding the carbs including the extra jets comes to $105.95
float bowl gaskets $4.00 X2 $8.00
132.5 main jet pr. $6.00 $6.00
140.0 main jet.pr $6.00 $6.00
145.0 main jet pr. $6.00 $6.00
42.5 pilot jet pr. $6.00 $6.00
47.5 pilot jet pr. $6.00 $6.00
Float Valve $9.00 X2 $18.00
Shipping $7.95
slide diaphragms Pair $39.00
Shipping $ 3.00
Total $105.95
After getting the carbs sorted out and mounting them on the bike there seems to be electrical issues as well. I ordered a new fuse block from Mikes ($24.00 plus shipping) and have to diagnose why else she is not putting out any fire. So it will take awhile for me to track down the electrical problems as this is where I shine the least. I will lean on J.J. and see if he can make any sense of it. It’s not too bad so far I’m only into it for just over a saw buck.
Till Next Time................................
