Motorcycle Repair: 1998 1500 suzuki intruder LC, rubber diaphragm, suzuki intruder

Question
I have a 1998 1500 suzuki intruder LC,the back cylinder is running real rich,enough to foul out the plug,it also backfires some and cutsout at idle and low speeds,runs pretty good at hiway speeds,also get bad fuel mileage

Answer
Hi Wade,

There are various things to look for
when one cylinder is running rich.

One is cylinder compression or leak down.
Sometimes it is oil blowby fouling things up.
If your plug is oily it might be this.

Too tight valve clearance can lower the engines
compression when idling or low speeds.

If you have a vacuum line from the
rear cylinder to the fuel valve
it might be sucking fuel in
through a bad rubber diaphragm
in the fuel valve.

The float level in the carb may be too high,
the float bottom should be 7mm from the carb
when it just touches the float shut off needle.
A leaking float needle can cause flooding.

Also on these bikes the valve under the
float shut off needle has a small o-ring
which could allow fuel to leak into
the float bowl overfilling it.

The carbs also have a coaster valve
on the side which has a small rubber
diaphragm. It is designed to prevent
backfiring. It is under a small
plate with a couple of screws holding
it on.

Usual stuff like plugged air filters
or intake can cause rich running problems.

I have even seen the brass idle or main jets in the
carbs fall out into the float bowl
and cause a really rich scenario.

Last resort might be weak spark,
it should jump about 6-8 mm gap
and be strong blue colors.
Could be a bad plug cap etc.

Take your pick, all these should
keep you busy awhile ;)

Good luck!
Wayne S.
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