Years back, I owned a 2000, Intruder 1500.  It broke down and I towed it home.  The rear cylinder was full of raw fuel.  The o-ring in the carburetor needle/seat insert was bad.  Recently, I sold a 2017 Boulevard S40 with 1,500 original miles.  The new owner didn’t make it the 60 miles home.  The same o-ring was again bad in the Mikuni carb.  I just corrected a mechanical problem in a friend’s S40 by replacing the needle/seat o-ring.   My mechanic said these o-rings should be changed every two years, and that the wear is from exposure time, not miles.   For years, the standard method for seating a needle/seat in a carb was threads and a washer in all bikes and four wheel vehicles.  I’ve owned many Suzukis over the years, beginning with a new1966 T20, X6 Hustler.  I presently ride a 2013 Boulevard M50.  Suzuki makes fine machines.  But in my opinion, employing the Mikuni carb with the o-ring type needle/seat was a huge disservice to motorcycle riders.  It replaced a time-proven, screw-down needle/seat connection with an unnecessary (and what I consider foreseeable) mechanical flaw.

Regular or premium fuel at Valero, Union or Safeway (CA).  Of the four o-rings I've had to replace, none have been deteriorating.  They've all just lost enough resilience to let fuel by the seat.  Thanks for responding.

The content of gasoline varies from state to state, and it is likely some areas have fuel that is harder on rubber parts than in other areas.  In some states the Premium fuel doesn't have any ethanol - and some of the major cities have "Reformulated Fuel" to help cut down on the air pollution.  

Some of our bikes are getting a bit old.....and it is very likely that some rubber parts are showing the age.  I have rebuilt a few carbs that needed the TEV diaphragm replaced as the rubber was no longer very flexible.  As the original post suggests....the rubber O-ring on the needle/seat is also an area where age shows up - as well as the diaphragm in the vacuum petcock.  The rubber boot between the air cleaner and carb is very stiff on the older bikes - and the same is true for the rubber flange between the carb and cylinder (I have replaced one that was split from age on an 87 engine).

I replace my fuel line every 2-3 years as it shrinks and becomes stiff.

If you have an older bike, store it outside or in a garage that gets really hot in the summer, or ride a lot in hot weather - you might want to consider inspecting the rubber parts for age and replacing them.  This bike has been around for 30 years and is pretty durable - but rubber parts do age and will need to be replaced eventually.

I appreciate the productive responses that obviously came from experience.  My main point was that the screwed-in needle valve seat and gasket can last the life of the carburetor, and engineering and dependability-wise, and the o-ring feature is inferior.

Most folks (including me) who own the Savage/S40 love them.  If Suzuki would spend the money to re-design the bike with alloy wheels, EFI, self adjusting valves, a little larger tank, a sixth gear and a long life cam tensioner, I think they'd sell more of them.  I bought my 2017 100 miles from home and rode it home.  I'd have no problem riding it cross country.  But it feels like you're winding it up at 60.  (I wish my M50 had a sixth gear now too.)  Anyhow, no more carbs for me, except my old Harley.

RickNeal wrote on 12/15/20 at 22:27:03:

Pretty sure if I had a sixth gear, I'd want a seventh  

Absolutely.  Carbs are fine.  They've fueled millions of engines for a 100+ years.  I've worked on them at home for 60.  But that o-ring needle and seat has let me down on the road three times.   In my years of driving, I've never had a seat unscrew itself from the carb body.  My point is, the o-ring is an unnecessary design flaw, perhaps intentional, like taking the dipstick out of automatic transmissions.  It's a design to make it tougher on the layman and more lucrative for the mechanic.

Gary_in_NJ wrote on 12/17/20 at 10:51:50:


Same with me.......I have not had the carb off my Savage since the bike was converted into the Cafe' bike and had the maiden voyage in the spring of 2013.  The bike is stored indoors and at the end of each riding season the fuel is drained from the tank and the carb.

I believe most carb problems are not caused by riding - but by improper storage.