Life Expectancy of Carb Diaphragms?

[kbert777]

I would like to hear some opinions on the life expectancy of 1st Gen carb diaphragms...

 

Last week I received a set of four new ones from Sirius Consolidated in Kitchener. They appear to be really nice quality, probably on par with the stuff Yamaha sells. I had some problems getting the carbs synched right last time I tried, fairly consistent in idle, huge difference at 2000 and 3000 rpm's. Ordered new diaphragms just to have them on hand in case a problem arose.

 

Anyway, the diaphragms were replaced about 18k miles ago when a dealer in San Bernardino county rebuilt the carburetors. I have the receipt for almost $900 in parts and labor from the PO.

 

Imagine my surprise when I removed the covers, all four diaphragms have significant holes in them, same amount and pattern in all four. So how long are these things supposed to last???

 

The bike runs much better now, lot more top end power, noticed that my trusty old Mercury MotionPro must have been damaged last weekend and ended up ordering a Morgan Carbtune...

 

Klaus

[jasonm.]

Here is the main reason for the holes in the middle area of the rubber...not the edge or slide area. Look at the carb cover that's over the diaphragm. You will see stops cast into the cover. These stops rub the diaphragm when you hammer the throttle. Thus holes deveplope. I took my dremel tool and ground them away and sanded all baby butt smooth. But normally the diaphragms should last a minimum of 30k or 7 years. Unless you have some real bad gas out your way that hurts the rubber. Mine are 7 years old with not many miles and look like new. Most of my originals went ~50k. With only one going bad at 35k because the cap let go that holds the slide to the diaphragm, but no holes.

[Snaggletooth]

The bike I bought was a one owner '84. He had all the paperwork for repairs and service on the bike since new. No record of the slides or diaphrams ever being replaced. Still had the original tamper proof screws in all four covers to.

 

So I'd say 25 years can be expected from stock ones. I bought a set of replacement diaphrams to but holding out for a reason to change. Mine are still solid and working well.

 

I'm curious myself on how long these replacement will survive.

[MiCarl]

the diaphragms were ALLEGEDLY replaced about 18k miles ago when a dealer in San Bernardino county WAS PAID TO rebuilD the carburetors.

 

How's that look?

[Snaggletooth]

MiCarl does make an interesting point. That's why so many of us learn to do our own work.

 

That's why we call them "stealers". It's hard to trust them sometimes.

[skydoc_17]

Hey Mike,

When I replaced my Carb. Diaphragms I only did the rubber portion, not the sliders. The big difference I noted was the stock Yamaha Diaphragms appeared to be a woven material that was coated. I will say that they lasted 21 years and 70,000 miles! The aftermarket Diaphragms appear to be solid rubber and don't "bunch up" as much as the stock ones, very much like the "cone" of a speaker. I find the throttle response better with the aftermarket Diaphragms and so far I have about 6,000 miles and 1 year on them with them functioning perfectly. Plus, with them being under $100.00 with shipping it is probably the best "bang for the buck" I did to my VR.

Hope this answers your question,

Earl

Edited May 10, 2009 by skydoc_17

[kbert777]

the diaphragms were ALLEGEDLY replaced about 18k miles ago when a dealer in San Bernardino county WAS PAID TO rebuilD the carburetors.

 

How's that look?

 

Yeah, I thought about that myself...

But here is the deal. I bought the bike with 62k miles, one owner with all the maintenance receipts, now the clock shows a little more then 78k miles. About 80% of the receipts are from the same San Bernardino shop, everything adds up well over $15k in maintenance, repairs and extras. So far I did not find any discrepancies between what was billed and what was performed. I also pulled an older set of carbs apart a while back with supposedly much lower mileage and the original bolts still in the covers and the diaphragms were almost torn to shreds.

 

Makes sense that the diaphragms rub against inside of the lid during heavy acceleration, I guess I will pull the covers back off and take another look.

 

Klaus

[skydoc_17]

Hey Klaus,

Take a look at this older thread:

 

http://www.venturerider.org/forum/showthread.php?t=32052

 

This thread shows how to replace just the rubber Diaphragm and not the sliders. You can do this for under $100.00 for all four carbs!

I found this to be an economical alternative to the Yamaha replacement parts which cost in the $600.00 range. As I stated above I am at 6000 miles+ and a year into these new parts with excellent performance.

This thread shows where to get the Diaphragms, be sure to mention VentureRider.Org for your discount!

 

http://www.venturerider.org/forum/showthread.php?t=32943

 

Hope this helps,

Earl