Re: balancing carbs on R90/6

gabe2004@xxxxxxxxx wrote:
Hi. I posted to this group a while ago about my R90/6. I have taken
it out of the garage this year and amd determined to get it running
well. It first it was very hard to start and when it did, ran on one
cylinder. I cleaned both carbs and also replaced the air filter and
it's running much better. However, there is a lag between when I open
up the throttle and the engine responds. It's very noticible. I was
thinking that the carbs might need to be balanced. I've never done it
before. Any advice on the best way to do it?

Two basic techniques (bear with me if I'm missing an R90 peculiarity)

1) Vacuum balance. You attach a vacuum gauge to a little port on
the underside of the carb and fiddle with the idle adjustments
until the two carbs are drawing equal vacuum. You can make
a differential vacuum guage out of $5-10 worth of plastic tubing
and drip irrigation widgets.

2) Shorting the plugs. You cobble up an extension to the spark
plug thread such that there's a length of exposed metal running
between the plug and connector.Using an insulated screwdriver,
you short out one plug at a time, observing the RPMs and
adjusting the idle until the RPM for each cylinder matches.

In either case, you probably want the idle richness screws about
1/2 to 3/4 of a turn out from fully screwed in, then play with the idle
speed screw on each carb. The richness adjustment screw is (I think)
on the underside of your carb. The speed adjust would be on the top
or side. I don't recall much about the exact Bing carb you have,
so you'll need to examine it to find these screws.

You probably want a Haynes and/or Clymer manual. I prefer having both
so I can compare and contrast the instructions.

I usually use plug shorting because it's easy and works fine for me.
You can use an old spoke end or buy a 4mm tap and some 1/8"
aluminum spacers to make the plug extensions. I also built a
differential
guage but don't use it much because it's more of a PITA to set up.

Check out the airheads and ibmwr websites for some good tech articles
on both techniques.

.

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