4th gen replacement carb vacuum piston diaphragms

Discussion in '3rd & 4th Generation 1990-1997' started by YoshiHNS, Aug 1, 2018.

  1. YoshiHNS

    YoshiHNS New Member

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    Main thread will be kept up on the VFRD site. Here's the copy and paste

    Looking to put together a group buy for replacement 4th gen carb vacuum pistons. These are the rubber diaphragm that moves the needle up and down. You cannot buy OEM replacements, and I'm not sure if you ever really could. If you have a torn diaphragm, or yours are just old and dry from being 20+ years old, this is for you.


    [​IMG]

    I met with Paul from JBM industries. Paul manufactures OEM replacement parts for many carbureted bikes, including isolator boots. Mike Norman used them on his NC35, and if they are good enough for him, they must be pretty good. He is confident in being able to make replacements. Because these diaphragms are only applicable for the 4th gen VFR, he would need a full order to cover his costs to make the initial batch. If you know other bikes that use these same diaphragms, let me know.

    http://jbmindustries.com/

    Only the rubber diaphragm will be provided. Read through JBM's page on replacement instructions, but these will involve clipping the plastic ring off and gluing the new rubber on. He will mold in extra thickness to have the rubber replace the ring, as he has done with over parts. If you are not confident on replacing them yourself, we can work on having someone replace them for you.

    I will be providing a sacrificial set of parts for him to do his prototyping on if we make the orders.

    For Paul to go through with this, he needs a commitment of 30 sets at $80 per set of 4. This does not include shipping. He normally handles production of new molds and products at the beginning of winter, but will confirm if we get sufficient orders. Sign up, ask around, lets see if we can make this happen.
     
  2. YoshiHNS

    YoshiHNS New Member

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  3. YoshiHNS

    YoshiHNS New Member

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    Bump. Setting October 1st as the deadline.
     
  4. Billy C

    Billy C New Member

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    I am confused. The 94-97 VFR750F RC36 is the 4th Gen VFR according to my reading. It does not have a round aluminum piston as shown in the pic. It has a black plastic flat slide and there is a big loop on the diap. See pic.
     

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  5. YoshiHNS

    YoshiHNS New Member

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    Well aware. the image was just an example from JBM Industries of a random piston.
     
  6. Billy C

    Billy C New Member

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    Ah! Are you the guy who was trying to push this buy thru with JBM? How much do you know about doing the actual swap? They will not swap as do the 1st Gen V4 slides where you cut out the retaining rings and slide on the new diaps. The existing retaining rings must be left in place and appear to be cast as part of the piston assy. I did a cutaway pic from an old slide and it shows no seams where the retaining ring can be removed and later reinstalled on top of a new diap. I sacrificed a couple used bodies experimenting and getting the old diaps out is nigh impossible without damaging the ring. Getting the new diap in and the tab aligned looks daunting as well. IMaybe you are familiar with my name (Billy C) from other forums? I am a long time V4 carb rebuilder. Been doing biz with Paul Csornok and the guy he bought the biz from for many years. My point is this is not my 1st rodeo and I am stumped. I am looking for anyone who wants to discuss a possible solution. Convince me that these diaps can be swapped out on the old pistons and I will commit to a buy of 10 sets to help get this thing going.
    Billy C
    903-567-1543
    cp 903.340.6009
     

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  7. YoshiHNS

    YoshiHNS New Member

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    Yes, I am the one trying to organize this with Paul. He lives only a few miles from me, so I was able to show him the piston in person. I don't remember exactly what the solution was, but I believe he was thinking he could mold the rubber thick at the mount and not have to worry about a new retaining ring. Use adhesives instead. Still have to make sure the rubber is oriented correctly when you replace it. I'd have to look at it again, as the pictures I have don't have enough contrast to really see what's what. But I agree that it isn't as easy or straightforward as some other versions.

    I know who you are. Years ago when I was just starting into motorcycles I had you rebuild a set of 4th gen carbs.

    The diaphragms I have are all still functional, so I havent tried taking one apart myself. The VTR250 diaphragms I have are torn, so those can be destroyed further, but they are different from the VFR ones, and Paul already has a part for that.
     
  8. Billy C

    Billy C New Member

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  9. YoshiHNS

    YoshiHNS New Member

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    Those look pretty close. The part numbers are different, but that could be any minor difference in the slide. I see there is a CBR900 complete slide listed as well. Gong to take the risk of buying one (either diaphragm only or the whole assembly) and seeing if it fits?

    If the diaphragms are the same, then that actually makes it more appealing for Paul to make these for us (expanded market and all). If some CBR900 guys need them, it would help push us over the minimum order Paul required.
     
  10. Billy C

    Billy C New Member

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    The seller lists the same diaps for 3 or 4 other models. CBR600 CBR1000 CB250 and a CB400. So apparently Honda used the same diap, maybe slide for several models which would follow what I have seen with Honda parts practice. This seller is not making these like Paul does. He is buying them elsewhere. If I can find his source (China) I think we are talking a few dollars each. And yes, I would rather buy from JBM.
    I have one diap on order to confirm fit. Will proceed from there.
     
  11. YoshiHNS

    YoshiHNS New Member

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    I did a search on the plastic top cover, and it is shared by the CBR F3, F4, 900RR and 1000F. VFR is not listed. So the diaphragm might be close, but not exact. I have an F3 carb that I can pull to compare with the VFR. I'll try and make time this weekend.
     
  12. Billy C

    Billy C New Member

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    I got the CBR900 diap in the mail. I test fit it on a 94-03 3rd gen Magna and it fits like it was made for it. I have a 94 VFR rack I will pull out and check fit on it.
    The R&R part is still a problem.
     

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  13. NorcalBoy

    NorcalBoy Member

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  14. COS_VFR

    COS_VFR New Member

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  15. NorcalBoy

    NorcalBoy Member

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    Think about that....there are very good reasons for it. Anybody who thinks an older machine is going to be cheap or easy to find cheap parts for is in for an ugly surprise. Caviar is never on the dollar menu.
     
    Last edited: Oct 25, 2018
  16. Billy C

    Billy C New Member

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    Many of us oldtimers consider these old V4s cheap horsepower. I am more a 1st Gen guy and can install 4 new vacuum slide diaphragms for $88.00. That siad money is relative and some folks have so much of it that $800 for a set of new slides is not something they waste a second moment thinking about, they just hit Buy It Now. A lot of us in the middle class economic strata pride our selves on being cheap bastards or frugal if you prefer and will go to great extremes to pay less. Some of my customers are in the lower burger flipping class and absolutely can not afford to drop $800 on a set of slide assys.

    I rebuild carbs for customers. I am looking for the cheap fix. Keeps prices down. They seem to like that. Rarely do I meet a guy who asks if he can pay more (never actually). Keeps these old bikes on the road. As COS said, just because they have them listed does not mean they have them. Honda has discontinued them. It will be a short time before folks are cannibalizing running bikes for these parts to keep their own ride going and that is not a satisfactory solution.
     
  17. squirrelman

    squirrelman Member

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    Economy has always been my goal on the carbs i rebuild, too.

    Instead of just tearing carb sets down, i usually speak with my clients about their problems first, then jump in until i locate the probable cause before a real cleanup. i do alot of tests before i start cleaning, looking for problems.

    none of my rebuild clients want to buy new floats, float valves, new jets, new needle valves every time their carbs are opened up, so i reuse everything that tests good and isn't worn or damaged, keeping parts costs low or zero. a typical dealership mechanic would replace everything, and that's good insurance and more profit. most frequently, the parts i find need replacing are needle valves +new viton float bowl gaskets, sometimes idle jets if they can't be cleaned and don't meet my testing specs.

    ordering replacement parts for a rebuild, i never charge customers $$ over what i paid, no mark-up, doesn't seem fair to me. also, i try my best to get jobs turned around and shipped back within 10 days almost every time.

    have a small stock of bits and pieces for VF's and VFR's to aid rebuilds. separate carbs are available for both and 2 sets of good '85 VF500 slides that are waiting to go somewhere.

    about half the time, professional carb fixers find a few signs of abuse by inept fools with bad tools who never read the FSM..... to the point where some damage is expected about 40% of the time.:Cry::Cry: the only sets that come in totally undamaged are the ones never worked on before! :Pound:

    my work is priced for the low-budget rider cuz i are one. since my first bike in 1988, i couldn't afford a bike unless i could do all the rapair/mainrenance work myself.

    my carb work is guaranteed for 30 days ** (more could have the idle jets clogging) and have had only one return, fixed for free, after years and years.

    I want to be able to test any VFR rebuild i've done on one of my bikes under real riding conditions, top speed included. However, even after 32 years of working on VFR's, i haven't developed enough facility to do any quick or easy carb mounting, and it's sweat on the brow every time.



    ** only if you promise to drain and FLUSH your tank b4 mounting carbs, new filter too !
     
    Last edited: Oct 25, 2018
  18. Billy C

    Billy C New Member

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    I have been doing V4 rebuilds about 15 yrs now. I have some real carb horror stories and some that are just funny. I think by now I have touched just about every 1st Gen rack out there, OK it only seems like it. Done a lot of 2nd Gen Super Mags and 3rd Gen Magnas have been coming thru increasingly over the past 3 years. Don't see a lot of VFR racks.
    10 days is a great turnaround time. By the time May rolls around I am starting to get quite a backlog. I easily get to 4 weeks by peak season. I have tried all sorts of rebuild models over the years. I have finally settled on a complete teardown and email with notes if I find stuff abnormal that require replacement. I may add to that right thru the cleaning and final assy phases. I inspect at every stage but one can never know til all parts are thoroughly cleaned and going together again. I always replace all seals because I do not want customers coming back complaining a fuel tube started leaking. I don't do quickie cleans either. Complete teardown and rebuild or look elsewhere is my model. This is just how I do it and not the only way but it has worked out well for us.
    I figure on doing rebuilds until I am too old to do them (I am getting there quick) or the bikes die off before me (even money bet). These damned slides could really speed up the process. Got to figure these out or get the Chinese to start making them. I have put the diap project on low heat while I finish up a few racks for customers and catch up on some important honey do projects around the home front. I'll keep working on it though. Still hoping a hero comes thru with a solution.
     
  19. MechTech

    MechTech New Member

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    I recently had my carbs apart to change main jets and reset the needles for higher altitude riding. The rubber diaphrams were in good shape and i took the opportunity to rub a bit og silicone grease into them to enhance their pliability and keep them from drying out. They are performing well so far. Any suggestions for something better than silicone grease to extend the life of the diaphragm sliders? I have a 92 750F. IMG_20180912_204135.jpg
     
  20. Billy C

    Billy C New Member

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    I wish I had a clear answer for that question. Diaps I believe are made from some variety of nitrile rubber. aka NBR. aka Buna N. etc. Silicone is a different sort of rubber entirely and as such a silicone treatment probably is a waste and may even have some negative effects. Not sure about that so do your own research. Rubbers turn into a needed degree in chemistry real quick.
    There is a product called Wurth Rubber Care Stick that comes highly recommended for weatherstripping on cars. I have yet to find a source that confirms what they are made of but believe them to be either NBR or more likely HNBR which has better ozone and UV resistance. So possibly Wurth is good for our diaps. Perhaps not. It works quite well on cars.
    So you got 3 short paragraphs of 'I think' and 'I don't know'. I have researched this topic over the years and never found a satisfactory answer.
     
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