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Post by dogbunny on Apr 20, 2011 9:26:48 GMT -5
Thanks for the reply.
After some study, I decided that yes, you should use a gasket.
The JBM boot is exactly the same thickness as the stock boot. If you don't use a gasket, then the carb is too close to the engine -- you need the gasket to get the correct spacing as intended by the Yamaha engineers.
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Post by grizld1 on Apr 20, 2011 10:01:01 GMT -5
If you really think the thickness of a gasket is going to make a significant difference in intake length, you know a lot more than I do.
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Post by dogbunny on Apr 20, 2011 11:43:52 GMT -5
The intake gaskets are about 3/32" when compressed, almost 1/8".
No, I don't know if that makes a difference, but why take chances?
From what I gather from this forum, moving the carb closer to the manifold improves top end but decreases low end power, and vice-versa for moving the carb away from the manifold. I need low end power, so I don't want the carb any closer to the manifold then the engineers intended.
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Post by 5twins on Apr 20, 2011 15:41:38 GMT -5
The original gasket is quite thick and besides sealing, may have been designed to help insulate the manifolds from engine heat and vibration. I think I'd be inclined to use them. I put a narrow ring of sealer on the gasket between it and the manifold so it comes off with the boot any time I remove it. I don't use sealer on the engine side. I don't know if you've ever had the pleasure of cleaning a cemented intake gasket off the motor but take it from me, it's no fun, lol.
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Post by scabber on Jul 4, 2011 13:23:08 GMT -5
I lost a vacuum cap my own fault put a new mikes cap last summ er should have replaced and forgot. Due to the fact the the JBM boots uses the 1/8 tube ID small hole the ride home wasn"t all that bad some backfire. the bike ran ok considering. Bought a box of 25 from Fastenal $ 8.16 part no 162602 not than I will ever need them. autoparts store out they wanted close $4.00 pack of 5 .They are not going to come off a little hard to get all the way on used a screwdriver last half. They don't pry off easy.I doubt I would have been riding anywhere with a stock boot. use the right caps you will not have any problems. They were designed by motorcycle people. ;D
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Post by ShakerNorm on Jul 4, 2011 18:40:09 GMT -5
I got something similar and used zip-ties to make sure they never come off..... LOL
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Post by 10ecjed on Jul 9, 2011 21:17:46 GMT -5
I got a set of boots from JBM. They don't have vacuum barbs installed. I thought they did. I checked the web site and it says that they stopped putting barbs on fro strenght purposes. I guess I have to try to pull the barbs from my old ones and drill these.
He told me I do not need a gasket. If I need a gasket I guess I wont be riding tomorrow. I am very disapointed.
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Post by preston on Jul 9, 2011 22:03:31 GMT -5
10: I would not drill them, or put your barbs in them,, ( they may break, due to lack of strength purposes ??) there is another way to do that.....I think by putting a port, in the carb, take out a screw, put in little port ? I know your dealing 34's i may be mixed up,with my 38s... and you have those famous "vacuum" pets cocks, or did you get converted to old style ? ( and you may need barbs) If you need gaskets, call me,, PM, or e-mail me, (Sunday - day light hours) and i will go out in the garage, see if I have two extra, ( I think I do) Drove down 194 today, never have I seen so many cars, at your carnival !.  Preston |
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Post by dogbunny on Jul 9, 2011 22:16:17 GMT -5
I do think you need gaskets for the reasons that 5twins stated in his last post in this thread.
However -- and I will probably get flack for this -- I think snyching with a manometer is over-rated. You can get a very close sync with the paper slip method. Put a thin strip of paper under an almost-closed throttle plate. Adjust the plate until the paper pulls out with a slight drag. Do the other plate the same way.
I have used this method (on a few different BS38s), and then tested it with a manometer, and the paper method was almost perfect every time.
It is my understanding that synching only has an appreciable effect at low rpm anyway.
Now, if you need the barbs to operate vacuum petcocks, that may be a different story.
I would be very reluctant to drill holes in my brand new boots, especially if the guy who makes them thinks it is a bad idea and won't do it.
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Post by jefferytodd on Jul 9, 2011 22:52:33 GMT -5
I have the JBM carb boots too and am very satisfied and did not want to drill them. I have a set of stock 77 carbs and got the nipple fittings from 650 Central that allows me to screw them directly into the carbs for carb syncing. When not syncing I remove the fittings and just replace the stock screws to block it off thereby not having to worry about a cap that could get dislodged.
jtc
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Post by grizld1 on Jul 9, 2011 23:02:03 GMT -5
You'll catch no flack from me on either point, DB; I use doubled gaskets with JBM boots because of clearance issues on my TM36/68 carbies, and when it comes to synch, there's more than one way to skin that cat. And right you are re. synch error having greatest effect at low throttle openings--the difference between throttles makes up a far greater proportion of area exposed to engine vacuum at idle than it does at WOT. But synch error, if large enough, can make a difference in the cruising range, causing increased vibration, overheating on the side that's overworked, and excessive fuel consumption.
The manometer can yield diagnostic information while you're setting synch. For example, if synch wanders significantly off-idle, that can be a symptom of an intake valve going bad, and you can then confirm by other means. And it's faster to hook up the manometer than it is to pull the carbs and gauge the throttle plates.
I don't know why Don thinks it's a bad idea to drill the boots for barbs; the metal core is very thick, and there's more than enough material for you to tap for a pair of 5 mm. barbs and Loctite them in. I discovered just how thick the material is when the barb pulled out of one of my JBM boots and I enlarged the hole halfway down to give a bit of space for JB Weld to set up in--that barb hasn't misbehaved since.
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Post by kopcicle on Jul 10, 2011 14:06:37 GMT -5
I'd rather drill and tap the head for vacuum access but that's just me .
~kop
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Post by ShakerNorm on Jul 10, 2011 15:32:26 GMT -5
Threads are much more reliable than jbweld.
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Post by grizld1 on Jul 10, 2011 23:16:06 GMT -5
Sometimes you have to make judgment calls, Norm. If you're going to use the vac barbs with a manometer, it's best to keep dimensions the same. I preferred repairing one boot with what was on hand to modifying both. The repair is as strong as it needs to be.
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Post by 10ecjed on Jul 28, 2011 18:37:20 GMT -5
I am going to try to get the old barbs out and then drill. We'll see. I am going to use Prestons gaskets because the carbs just barely make it to the stock air cleaners. I made a thin set of gaskets with some gasket material I had laying around. They sealed up ok but not thick enough. Had to pull it apart anyway since it started missing again last wed. on the way home from work. It is so intermittant that it is driving me crazy. I am really beginning to think it is electrical.
BTW.. Thanks for the gaskets Preston. Will repay you soon.
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