91 VFR750 carb. throttle slide/ diaphragm source

Discussion in 'Mechanics Garage' started by John carnahan, Oct 8, 2018.

  1. John carnahan

    John carnahan New Member

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    3 of the 4 diaphragms on my new 91 Interceptor are bad. Anyone know of a source for new ones.

    Also, has anyone ever tried to repair. Just a wild idea, I have a gal. of Flex Seal I used to repair my roof. I wonder....they claim it will seal anything and everything. Just hate to be stopped along the road when it gives up. :-(

    Thanks,

    Jack
     
  2. John carnahan

    John carnahan New Member

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    Maybe an intro. I rode English bikes in the 60-70's. Sure wish I kept the 72 factory 810 Dunstall Norton. Had a couple bikes in the 80's for a short time but actually quit until 2003 when I got a used 2001 SV650. Made a best new best friend-ex pro road racer who taught me how to ride. Bought a GSXR100o but kept the SV. Managed to stay alive for a year/12K miles ripping around WV at much too high speeds. Did several track days but at 58 at the time got smart and sold/traded the GXSR for $ and two FZR400 racer/track bikes(should have kept them too) Anyway I've kept the SV650 ever since and have put 50K on it. Love it although the shocks are wasted but at 72 I've slowed down anyway.

    On my way to bible study one evening I saw a used sport bike along the road 5 miles from home. It was there on the way home so I stopped. It was a 91 VFR750 with wasted plastic but running for $350 so I bought it w/o knowing anything about it. Was surprised to learn it was a V4. Went to fetch it the next day and couldn't find my handle bar strap so I put the SV tag on it and rode it home noticing it would only go about 60 mph and lacked power. BTW only 26K miles. Anyway I started looking for used plastic, mainly needed the left upper and found prices on ebay crazy so I ordered Airtech one piece upper. (Have I mentioned I should have found this forum sooner) Decent price but %$#$^ shipping from the left coast was almost as much as the fairing. Of coarse the fairing stay was also bent and bought another one, still bent but not as bad. The Airtech is well made but a problematic fit with OEM lowers.

    Got it together and painted and was going to get tags but ran it first and now find the diaphragms are my problem. Found a complete carb. assembly cleaned and garrenteed for $200 that may be a good bet???? Hopping to be on the road CHEAP. Oh did I mention I own two homebuilt aircraft. The red/white biplane has a sick 180 horse Lycoming that I'm rebuilding and just found the crank case is cracked(about $3500 to replace) so no $ for the poor VFR. I need to sell an airplane but have to get it in the air first....Oh well

    Regards,

    Jack
     
  3. 34468 Randy

    34468 Randy Member

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    Flex Seal. Are you talking about the stuff advertised on TV? It does seal well but like everything else, it has a life time. And it is quite short with that stuff. I have bought that stuff for a few things and to be perfectly honest with you, they are robbing you for what you get. Can you use it on your diaphragms. I have no idea for sure, but I would not.

    BTW. We like pix of your rides here. Even the none VFR ones. Good to see someone older than me come along once in a while. Makes me feel like a kid again for a while anyways.
     
  4. Allyance

    Allyance Insider

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    The part you want is called a vacuum piston (rubber diaphragm is bonded to metal piston) is listed on partzilla.com, part # for your year is 16111-MR7-004 and is listed as "NOT AVAILABLE" and if they were, they would be $112 each, making them more expensive than your entire bike! They are very delicate and provide little resistance to vacuum, that is what the springs are for. If you can repair them with minimal change in flexibility, go for it. It is the vacuum seal that is important, the rubber also keeps the needle/piston centered as it moves up and down. Note, springs are different for the front two carbs vs the rear two carbs.

    You might want to experiment with some rubber cement thinner (light fluid will work) to see if you can thin the flex seal and make it more pliable.
     
    Last edited: Oct 8, 2018
  5. OOTV

    OOTV Member

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    Squirrelman seems to be quite knowledgeable about carburetors and has worked on a few carb sets for members, perhaps he knows a good source. A PM to him might not be a bad idea?
     
  6. John carnahan

    John carnahan New Member

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    Thanks guys. I was mostly kidding about the Flex seal but was told by my friend/mentor who is an experienced mechanic that if available the vacuum pistons would be expensive. I took the carb set to him and he only took a quick look, he observed me push the slides up and they snapped back "suggesting" they were bad. It was late and I went home. Today he was out but I went to the shop and pulled the pistons one at a time and they looked fine "to me" anyway. I'll let him make a final say-along with I'm sure equal experienced mechanics on this forum. Frankly.....as you will note I have only a vague idea of how carbs. work-almost black magic to me. I'm amazed at the carbs on my SV650(and others) after 50K miles and 17 years, never serviced and let sit every winter with mostly 10% ethanol and they run perfect. I do try to run them as often as possible but nothing special.

    Thanks for the hint about different springs

    I'll keep you posted. Sorry no pictures yet. I have a new Kodak, old one I understood broke, the new one is a mystery so far......

    Jack
     
  7. John carnahan

    John carnahan New Member

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    Maybe start at the beginning, what the bike does. It has no power will only go 55-60 mph. I ran it with air cleaner off and it will struggle to make 9000 rpm full throttle. The vacuum pistons do NOT open. One quivers a bit, the other 3 don't move at all.......

    Gas flows free from tank and fuel pump seems to be working well although I didn't measure flow.

    I can only say I "think" the vacuum pistons are the issue but I'm certainly not sure.

    Jack
     
  8. squirrelman

    squirrelman Member

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    best bet for newer diaphragms is buying individually or a carb set on ebay. if you blow air into the right hole, good diaphragms will lift that slide, best way to test.

    i have a good set of gen3 carbs freshly cleaned and adjusted for sale in the classified section.

    or you could box your carbs and send them to me for inspection and/or repair. PM for questions, please.
     
    Last edited: Oct 8, 2018
  9. 34468 Randy

    34468 Randy Member

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    I was wondering if you were just kidding or not about the flexseal. But we do have a couple real winners here. One has a nick handle of SOW.
     
  10. John carnahan

    John carnahan New Member

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    I was working on the airplane and getting my bi-annual flight review and my mechanic friend was bow hunting or sighting in his rifle(it's that time of year again...everything else almost stops here in WV) anyway didn't get a chance to look at the carbs again.

    If I may ask , which hole do you blow in to raise the slide?

    Thanks,

    Jack

    PS- I'll just pop a big fat doe down in the pasture when the time comes to fill the freezer-no longer make a big deal out of it.
     
  11. squirrelman

    squirrelman Member

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    we already know the diaphragms are shot. hole is about 1/2" diameter black hose.
     
  12. John carnahan

    John carnahan New Member

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    It seems I might have been to quick deciding the pistons were shot. After we gently blew air into the "1/2" dia. black hose" and observed all 4 pistons react Dave and I dug into the carbs. There was some very rubbery sludge in the bottom of the bowls and two of the pilot jets were problematic. The big error was two of the needles were under, not attached to the floats. It was obvious someone had been into them. After a day of raking leaves and working on the airplane before working on the carbs and then helping Dave put the deck back on his mower before riding home in the dark with less than adequate jacket I haven't tried them yet. I'm hopeful. My sincere thanks to all. VFR owners sure seem to have a great forum. (I no longer usually ride at night around here. Too many deer and my eyes aren't as good as they use to be)

    Jack
     
  13. John carnahan

    John carnahan New Member

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    You learn something every day. I've been riding several Japanese bikes for 15 years now butt mostly just ride them.....

    Put the carbs. back on and it ran worse . Talked to my friend/mechanic Dave and first thing he ask was did I run it with the airbox installed? No. So I went home and put it completely back together and bingo it now runs, or ran perfect. I rode it down the lane and it straightened my arms out. And then it quit. Pushed it 200 yards home, at least it was downhill. Dejected I had something to eat. Was going to leave it but took a look. Dumbass(me) had managed to get that heavy wire that holds the fuel line right under the tank too close to the shut off valve and it had somehow turned the fuel off. Either that or I bumped it most off installing the tank and it vibrated the rest of the way closed since that wire was right against the valve. Whatever it sure runs better with the fuel on.

    Thanks again,

    Jack
     
  14. squirrelman

    squirrelman Member

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    u can't make many mistakes like that in an airplane, old timer. :Eek:
     
  15. John carnahan

    John carnahan New Member

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    Please don't think I haven't thought about that! At least my rather vintage aircraft designs are simple compared to modern cycles. But age may be catching up with me? Dave asked me several weeks ag how many miles on the SV650? When I said almost 50K he replied that the suspension must me about wiped out. I admitted it didn't handle very well. Yesterday it was cold when I set out and it really handled bad, like wouldn't hardly turn at low speed. Then I remembered I hadn't checked the tire PSI for a long time. I stopped at Dave's and found 15# in the front and 18# in the rear. Putting air in the tires made a new bike out of her. So yes while I check and double check the airplanes, one can't take maintaining a motorcycle for granted either. I use to check tire pressure every day when riding the GSXR rather aggressively but have been treating the old SV like Marcia treats her car....turn the key and go. Not good.

    I've been patting myself on the back for still being able to get my leg over the seat of my bike and being able to climb in/out of a open cockpit biplane. If I don't keep my mind right too something bad might happen.

    Thanks,

    Jack
     
    Last edited: Oct 13, 2018 at 1:08 AM
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