The intake boot O-ring problem, in pictures! 

(Stainless steel fasteners are HERE:)

Between the cylinder head and the intake boot (aka intake tube), there's an O-ring that seals the intake path.  This seal is essential to proper engine & carburetor operation.  Over time, the O-ring loses its elasticity and starts to harden.  As soon as this happens, it starts to leak vacuum.  Eventually they harden up like dry uncooked spaghetti.

I've seen this problem on bikes that were only 5 years old, so unless you're certain of how old they are, you need a new set.

Sometimes, this component cracks, probably from thermal expansion & contraction that it can't handle anymore, because it's no longer flexible.  This generates a gaping intake leak that's impossible to see, and the effects are numerous.

Either way, you wind up with a temperamental engine; it'll run fine under some conditions, but it'll be crabby & lethargic other times.  A classic symptom is an unstable idle speed.  If your bike's idle runs way up after it's warm, this is the likely cause.  It can be hard-starting and will run hot.  It leans out the mixture, can cause your valves to burn, and generally causes annoyance.  It is an absolute waste of time trying to tune a motorcycle with an intake leak, as you're aiming at a moving target.

Worst of all, it mimics a host of other problems that you could spent money trying to correct until hell freezes over, while simply detracting from the otherwise enjoyable experience of owning a motorcycle.  Soon, out come the whiskey and firearms, and there's a real mess to clean up.
 

Here's the cylinder head's view of this problem:

cylinder head's view

Aha!  Look at the escape path at around 11:00.  Three of the four in my engine were cracked like this.  Note also that the O-ring is completely flat; these should have a perfectly round cross-section.  It's taken a poster-child 'compression set'.


Here's the poor, neglected offender:

crack.jpg

shot

And the solution is... replacement, of course.


For most Suzukis, the part numbers you're looking for are:

09280-32006 (32mm = 'Small')  for '79 and older 750 & larger
 09280-38004 (38mm = 'Large') for most '80 and later bikes.

Usually available at your dealership, as well as here.

77-79 750's, 850's and 1000's use 32mm o-rings and 16mm screws.
79 425's use 40mm O-rings and oddball 6x35 screws, which I don't carry. **
77-79 550's use 28mm O-rings and 16mm screws.
80 & 81 1100E and 750's don't use intake O-rings or screws (so you're off the hook!)
80 & 81 1000's use 40mm O-rings and 16mm screws.  **
80 and later 850's use 38mm O-rings and 20mm screws.
81-83 650's use 38mm O-rings and 16mm screws.
80-82 550's "                                                           "
80-82 450E's use 40mm O-rings and 20mm screws.
82 & 83 1100's (2-valve) use 40mm O-rings and 16mm screws.
83-86 550's use a siamesed setup; they take 30mm O-rings, and five 16mm screws and one 20mm screw.  There's a 'medley' screw set on the order page for these bikes.
85 700 uses 38mm O-rings and 20mm screws.

For the '80 - '82 450's, I have carb kits and intake parts here:
(No other model years.  Sorry.)

Order the larger or smaller HERE:

 Prices are:  $3.30 for a set of 4 small,  and
           $3.91 for a set of 4 large.


Note:  Do not just grab O-rings from an assortment.  They'll burn.  You need a fairly special material (called Viton) that can withstand the heat of the cylinder head.  Nitrile O-rings, no matter how well they fit, wouldn't hold up.

The only tough part of changing these will be getting those Phillips head screws out.  If your trusty hand impact tool doesn't get the job done, you can use a Dremel tool with a fiberglass reinforced cutoff wheel.   If you carve a deep slot into the screw head, you can use a large slotted screwdriver with a wrench on the shaft.   Plug the intake paths first!  You don't want metal fragments getting in there.

Cutoff wheel

Because these screws are difficult to remove, and because they usually wind up badly mangled, it's become S.O.P. to replace them with stainless steel allen head (cap) screws.  They also look a whole lot nicer on the bike.  I decided to sell these as well, with matching stainless steel washers, for one-stop intake shopping.  I strongly recommend using anti-seize compound on these.   Here's the M6 x 1 x 20mm:

Wow, nice shiny fasteners!

See the table above for sizes.

 Some bikes use 16mm screws.  These include everything pre-1980, the '80 & '81 GS1000 E & G,  and the '82 & '83 1100G's and 650's.  The 16mm screws aren't quite as chrome-looking.  The 80 & later 850's, the '83 750's, and the '80 and '81 450 all use the 20mm.  So does the '85 700.  If I didn't list your bike, check with an online parts retailer like Flatout.  Get the part number for the screw and email me.  Some bikes ('80 & '81 1100's & 750's and others)  use gaskets instead of intake boot O-rings, so check the exploded diagrams carefully.

You can order these HERE.  These are priced at $4.85 for the set of eight screws and eight washers.    Postage   is $2.25, mainly because I have to use a padded envelope.