Just balanced my carbs, how much vacuum should I see?

HndaTch627

I just balanced the carbs using, i believe, xsjohn's idea of 2 vacuum guages and fish tank turn off valves. with the valves turned down to stop the large power pulses i get 5-7 inHg. Bike seems to run better although it seems like it's popping in the exhaust a little more at idle.

What would a normal range of vaccum be on these bikes? I am used to cars where a healthy motor draws 18-20inHg. If i open the valves up the needle does go all the way to 20inHg but it's almost impossible to get it consistent.

Jeremy

xsjohn

Jereme my 80 gets 8-9 inches.............just need one vacuum guage.......check the valves and set them at 4 thousands intake and 6 exhaust.....book says .0025 thousands on the intake......way too close and will hurt vacuum and idol....and performance......and valve tips...

Can set the intake at a "simi" snug 4 thou to help keep the tapping down.....when you open the valve clearances you are retarding the cam timing.....interesting that the vacuum went up......

often wondered why such a bit of vacuum.......believe it is the way these XS's are camed....for revs....

need to be able to set the mix screws also..........and if you ever get into setting the carbs right I make a kit for them....

when done connect the vacuum barbs together with 3/16" ID tubing.........

These seem to run the best at about 1/8" retarded from the F mark....if left on the F mark they are cranky at the lower rpms and will kick the F out of you....the breakoff screws can be ground off and replacedwith screws so youcan moove the pickup coil....the break off screws are thredded...........these things you can take to the bank.......

xsjohn

pamcopete

HndaTch627

Well, if you have real dual exhausts (no crossover) you can also try adjusting the sync screw a tad towards the popping cylinder until both exhausts sound the same and the popping is gone. Turn the sync screw no more than an 1/8th turn one way or the other. Retrim the idle revs with the left idle adjust screw when you got the exhausts sounding the same. Try this before you cross over the vacuum barbs.

Retiredgentleman

I get 7" Hg vacuum on my 78SE. Yes, these engines are quite a bit lower than a car.

HndaTch627

xsjohn wrote:

Jereme my 80 gets 8-9 inches.............just need one vacuum guage.......check the valves and set them at 4 thousands intake and 6 exhaust.....book says .0025 thousands on the intake......way too close and will hurt vacuum and idol....and performance......and valve tips...

Can set the intake at a "simi" snug 4 thou to help keep the tapping down.....when you open the valve clearances you are retarding the cam timing.....interesting that the vacuum went up......

often wondered why such a bit of vacuum.......believe it is the way these XS's are camed....for revs....

need to be able to set the mix screws also..........and if you ever get into setting the carbs right I make a kit for them....

when done connect the vacuum barbs together with 3/16" ID tubing.........

These seem to run the best at about 1/8" retarded from the F mark....if left on the F mark they are cranky at the lower rpms and will kick the F out of you....the breakoff screws can be ground off and replacedwith screws so youcan moove the pickup coil....the break off screws are thredded...........these things you can take to the bank.......

xsjohn

I think the next step is adjusting the carbs as i am pretty sure the last person that touched them had NO clue what they were doing with it. One question though, what's the advantage of connecting the vacuum barbs together over just capping off the right bank and using the left bank for the petcock(until that fails and then i'll just cap that off)? It's pretty obvious the cams on these bikes run some fairly decent overlap on duration. I am going to check the timing tomorrow.

Pete: that was what i did initially but i believe the bike is just currently running too rich(the carbs had already been tampered with when I got the bike). I got them fairly balanced and the motor seemed much healthier overall under load. Initially the right bank was drawing 7-9inHg and the left bank was in the 5-7inHg range. Now both are @ 5-7inHg.

Jeremy

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