Yet another way to install Gen 1 Carb Diaphrams

[safetyguy]

Just to add to the knowledge base here on the subject of carb diaphragms --

 

1. I was able to get the original screws off the side carb cover. I sprayed each screw with PB Blaster. This was based on information that these screws get frozen at the juncture of the head and carb cover plate (and the threads inside the carb body are fine). I had to use a impact driver on all and I also used a T-25 Torx security bit to get the "special" screw off. All screws came off in one piece and were later reinstalled.

 

2. After removing each cover, each (and I mean all four of mine) carb slide was in pieces. If you look at the first picture, all the pieces shown were in this disassembled state when the cover came off. The center metal keeper was loose and the old diaphragm was off the slide, Somewhere mentioned that parts on the carb slide "come apart" (I believe it was Condor who said he had experienced this a few times). I know the previous owner of this one owner bike, and it never had carb work done since new. It must be the nature of the beast that these slides parts came apart.

 

3. For the first two carbs, I followed the recommended procedure to disassemble everything including the carb needle/holder assembly. I found that reinserting the plastic screw that holds the small spring and carb needle to be a slightly tricky task. Since I wasn't replacing the white spacer (as some have for "improved" fuel mileage), I omitted this step for Carb 3 and 4. This omission saves considerable time. (5-10 minutes each)

 

4. I cleaned all the parts with carb cleaner and installed the parts together. I used the SD-1 diaphragms from Sirus. In photo 2, you can see the white plastic washer on the keeper part. (You don't need a screw driver like in the photo, it just made taking the photo easier).

 

5. The next part installed was the diaphragm itself, there is no need to stretch it over the slide in this assembly scenario. The gray washer goes on next and the groove side goes against the diaphragm. See photo 3.

 

6. Slide the reassembled keeper part into the black plastic slide assembly. See photo 4.

 

7. Lastly, there have been many questions about the orientation slide to the tabbed portion of the diaphragm. If you look into the slide, there appears to be a vent hole or something at the bottom. In my four, one was at 1 o' clock (or pointing at the tab portion in the upper right corner), one was at 4 o'clock, one was at 6 o' clock, and the last was 9 o'clock. As you push the keepers into the slides in step #6 above, you can rotate the diaphragm to get it into the position you want. As far as I can tell, there is no standard position. Does anyone know the answer?

 

So the conclusion is, if your slide/diaphragm unit is "split, this is the way to assemble it. This may end up being the preferred way to install new diaphragms. If the keeper can be removed from your slides -- it allows for a thorough cleaning of pieces and avoids the possibility of ripping the diaphragm when you slip them into place (and use the fingernail method like skydoc17 does). This is probably more critical for people who reuse and recoat old diaphragms where they could easily be damaged by stretching.

 

There is no need to take the carb needle out if you are just replacing the diaphragms. Seriously!

 

The SD-1 diaphragms fit well. We will see if they stand up to the test of time.

 

Incidentially, my old diaphragms showed wear (and fabric) along the outer edges but I couldn't spot any pin hole leaks elsewhere.

[oldandcrotchety]

Good information. I copied your post to my files. Thanks.

[Condor]

Like Mike stated I've had a couple of diaphragm assemblies come out in pieces when inspecting. Not sure why it would happen, but it did. The brass 'keeper' that slides inside the plastic and holds the two plastic washers together over time seems to loose it's grip. Maybe poor assemble of the plastic slide by what ever method they used. I had a broken slide once that took an act of God to pull the keeper out... so don't try it... When the assembly is put together, whatever they use is effective. I've thought about roughing up the inside of the slider and the brass keeper and using Super Glue maybe to re-install the keeper as a fix?? My 2Cents....

[skydoc_17]

Hey Mike,

Thanks for posting about the condition of your sliders as they pertain to the installation of the new Carb. Diaphragms. Because I work on other peoples bike for hire, the two times I opened up a Carb. body and found the sliders to be separated the way you have shown in your pics I have replaced the entire slider assembly. I considered these sliders to be sub-standard. I was wondering how you re crimped the brass retaining ring back to the plastic slider body and was also wondering if it came apart the first time under normal use, (which it is not supposed to do) what method did you use to reattach the retaining ring so it will not come apart again under normal use?

As to the question of the clocking of the Diaphragm to the slider body according to the service tech. at my local Yamaha dealership, there appears to be no significance in the orientation of the Diaphragm and the slider body. He did mention that it is very important to have the tab on the outer most diameter of the Diaphragm engaged into the slot of the Carb. body so that the cap will attach tightly.

You appear to be a very detail oriented and tidy mechanic (as am I) and I like that very much. I would like very much to "compare notes" on the 30 or so Carb. Diaphragm replacements I have done to the Carb. Diaphragm replacements you have done. I think we would have some interesting information to share with each other.

Thanks for your post,

Earl

[safetyguy]

I just pressed the parts together by hand and they seemed relatively tight and I would call it a snug fit. I read elsewhere in another thread that someone ran across this problem before and they just pushed all the pieces back together (as I did) and it worked fine for them. In fact, I liked the fact that I could push the retainer piece in far enough to be tight on the diaphragm as well.

 

As for crimping the keeper/retainer to the plastic slide, I did not. The big end of the retainer only comes in contact with the white washer that is on top of the diaphragm. It is what holds the whole shebang together (see my picture 2 & 3). The metal retainer piece does not appear to be structural to the slide. It seems that its purpose is to hold the diaphragm lip between the two plastic washers.

 

Again all 4 carbs were in this state upon disassembly-- what are the chances of 4 bad slides? And if all 4 were bad, why has the bike been running for 21 years (including up to the time of disassembly)

 

The true test would be to take a new slide assembly and see if the metal keeper can be pulled out easily. I suspect that it can be and that older slide units are stuck for other reasons. I should have tried to reassemble the slide units with the old diaphragms. Maybe the old ones had shriveled up to the point that the retainer was no longer a tight fit in the plastic slide body but the new diaphragm is. It would have been nice if I had thought of this sooner -- I could have tested my hypothesis before I put this all back together.

 

Here are my results - I only was able to test ride my VR for about 20 miles after installation and carb synching with a Morgan Carbtune. It seemed to run well but I will see how it really does this weekend on a longer ride. I ran it at speeds that some law enforcement types may have issue with and no ill effects were noted even close to redline rpms.

 

Like some previous posters in some other threads have stated, it seemed like there is a little less power on the low end of the power curve but I have more at the high rpm range with the new diaphragms. The difference wasn't much between my old and new diaphragms -- it may be all in my imagination anyway. This may be because the leaks in my old diaphragms were really small compared to what others have described. I was getting about 35-37 MPG before the change - one up and heavy with the throttle hand, running 10% ethanol blends (all that is available by law around here and not my choice).

 

Earl -- thanks for the info on the positioning of the vent hole. Interesting that it makes no difference. I agree with you that you need to make sure that the tab is lined up correctly in the carb body. The cover goes right into place when it is in its proper place.

Edited June 20, 2009 by safetyguy