Intake manifold

[retiredgentleman]

Starting about 3 years ago, I had intermittant "chirping", which I knew was an air leak. In 2008 I replaced both the throttle shaft seals and the intake manifolds. The intake manifolds were from Mikesxs. The "chirping" would go away and then return at random.

I have finally traced the leak to the right intake manifold. I removed them and made some careful measurements with a vernier caliper.

Mikesxs manifold I.D.=1.866"
Yamaha stock manifold (original from 1978) I.D.= 1.795"
BS38 carb O.D.= 1.840"

The stock Yamaha manifolds are an interference fit and the rubber must stretch .045" to go over the carbs. This ensures a very tight, leak free fit.

The Mikesxs manifolds are .026" too large, which results in a loose fit. Now depending on how well the clamping works, you end up with intermittant air leaks, causing hovering idle and "chirping".

My conclusion is that Mikesxs intake manifolds were molded with incorrect I.D. and will not seal properly. Mine were bought in 2008, which could mean there was a bad production run at that time, or maybe they are still being manufactured out of spec.

When I re-installed my 32 year old (original) manifolds, I could tell that it was an interference fit with the carbs, as it was a much tighter fit. The "chirping" is gone and the engine has never run better. The quality of Yamaha OEM manifolds is quite impressive...............engineered and manufactured to be leak free!!

If buying manifolds from Mikesxs (or are now having air leakage), it would be wise to carefully measure the inside diameter of your manifolds.

I would be interested if someone would post the manifold I.D. for a Mikesxs product from a recent purchase. The I.D. of a JBM would also be good to know.

 

[5twins]

I just managed to find some N.O.S. originals on eBay, about $45 for the pair. I've been running a set I got from Mike's 4 or 5 years ago and they seem to be holding up OK. Obviously a better batch than his recent ones as I run gasohol all the time.

I highly recommend replacing the Philips screws on the manifold clamps with Allens. Once the original screws get buggered up a bit, you can't tighten them enough. On the 38 manifolds anyway, if you don't tighten the clamps all the way so the two clamp halves touch, they may not be tight enough.

 

[retiredgentleman]

I agree 5twins, ...............I use allen head cap screws everywhere I can on the bike.........carb clamping, float bowls, rectifier mounting on heat sink, alternator small side cover etc. I used to use them as well on the points plates before I changed over to a Pamco unit.

That's a great buy, N.O.S. Yamaha manifolds.................they are clearly a superior product . After looking carefully at my 32 year old originals, I find they have no cracking or hardning and seal perfectly. Just think.............guys are throwing out original Yamaha manifolds for inferior Mikexs products!

I suspect that the quality and fit of Mikesxs manifolds varies with different production batches. Its a bit of a crap shoot.............caveat emptor.

As I mentioned, I'm curious as to the I.D. of current Mikesxs and JBM products.

 

[grizld1]

4 or 5 years ago Mike's XS sold Tour Max boots, which were and are excellent. That's no longer the case. Don't be concerned about the ID of the JBM boots. I'm using a pair with relatively heavy TM36/68 4-stroke pumpers; when Don James says the boots are designed to hold the carbs with no back support, he's telling it straight. The boots are produced right here in the USA by a man who knows rubber, not at Peoples Big Joy Condom Recycling Collective.

Edit: Oops--I meant Tour Max. Thanks, 5twins.

 

[5twins]

Yes, mine were Tour Max and seem OK. But one may be leaking a little at the gasket. My bike runs well but I have a slight misfire at idle on the left side. I noticed some discoloring on the manifold gasket there. I think it's leaking a bit. I don't know, maybe I'm picking nits, but I'm going to try the new factory ones and see.

 

[grizld1]

The last time I went nit picking over an idle stumble the cause turned out to be a 20% leak on an intake valve. I hope your issue is just an air leak!

 

[KentMoney]

I have Mikes XS manifolds I bought maybe 5 months ago for my 1981 with bs34s. I went on my first group ride yesterday only to find that after the first leg of the trip my carbs had completely slipped out of the manifolds!!!

so this has started to bother me and I'm in the market for new manifolds. I'm going to rummage around for the original boots but from what I recall they were pretty worn which is why I bought new ones to begin with. Perhaps the JBMs will be my only solution...

 

[5twins]

Did you tighten the clamping screws completely until the 2 clamp halves touched? You have to or the carbs can pop out, especially if you get a backfire while starting.

 

[KentMoney]

it seemed that if I overtightened the clamps that it would essentially 'squeeze' the carbs out of the manifold. I will double check this today, however.

 

[5twins]

Sounds like you didn't seat the carbs fully into the manifolds. There's a groove on the intake spigot of the carbs and a corresponding ridge of rubber on the I.D. of the manifold that "snaps" into it. Do that and tightening the clamps fully won't squeeze the carbs out. As you install the carb set, rock it up and down as you force it in. Lube the boot I.D.s with some WD40 or a thin smear of white lithium grease.

 

[bluebikerblan]

Gentlemen.....Firstly, The strength of the JBM Carburetor boots is derived from the quality of the TSR rubber compound, the metal insert, the chemical bonding of the rubber to a specifically designed steel metal insert within the boot and the excellence of both in process high pressure heated molding and post molding oven cure.

By design...only enough pressure to hold the clamping band in place on the molded rubber surface is needed. Moreover, excessive clamp pressure can distort the boot shape and even cut the rubber surface. Specifically, too much clamping pressure can and has caused cuts, damage and leaks and is referenced in Don James instructions and counsel as to be avoided.

Remember.... there is no longer that protective metal shroud around the boot and between the clamp as with the OEM design. We have found that just enough pressure to prevent the boot from being able to be hand rotated on the carb exit is about right. Moreover, only enough to prevent the boot from expanding enough for the locking lip to slip out of the channel, is required.

Watch for and avoid distortion of the boot by excessive clamping band pressure.

I have done some work with Don James on this matter and if there is any doubt I would
suggest re-reading his instruction and/or seeking his counsel on the matter.

Best, Blue

 

[CDNTX650]

JBM ones are fantastic. Dont even consider putting them in the same sentance as mikes ones. 2 years on mine and they look like new still, mikes ones got me a month or two.

Dont bash one of out GOOD parts suppliers please.

 

[bored0987]

Hello folks you guys are great...I have not owned a motorcycle yet but my father has a 1977 xs650d with the bs38 i believe ..He live in another state and can not use a computer well, he has a very limited income.. he needs Intake Manifold 447-13555-01-00 and Carburetor Joint 447-13565-01-00.. I need some help trying to figure out which of these will work,. or if they will work.. I found these at bikebandit http://www.bikebandit.com/mikuni-mounting-flange?m=147213.If you guys could help me i would greatly appreciate it..Please remember I am no biker yet and have no experience with bikes yet ..

i hope i put this in the right place

P.S. I built that rectifier for him works great..

 

[Olie]

In my experience, universal usually means universally sucks. The ones you want are from JBM here. Hope you're not in a hurry though because they won't be in for another month.

 

[grizld1]

When it comes to XS650 carb mounts (which are NOT "manifolds" unless they're 2-1's, as a manifold by definition blends two or more tracts into one) there's a weird tendency to make things a lot harder than they need to be.

Except for the first two years (XS1 and XS1B), original equipment mounts (AKA boots) are still available. They are still made by the original manufacturer, ARS, and they are are sold by 650 Central and any dealer who does business with K&L Supply under the Tour Max label. Quality is excellent, and they hold up to decades of 10% ethanol. The only issue is that the BS38 version is no longer produced with vacuum barbs to support 1978-79 vacuum petcocks.

JBM boots are fine, but experience has forced me to qualify my opinion of them. If they're used without the OE airbox or some added support, the heavy OE carbs will eventually crack them right around the spigot stops. The cracks will begin internally, you won't see them until it's too late unless you inspect. This is due to the lack of metal shrouds to support the spigots (note that the same thing will happen with OEM mounts if they are used without shrouds). JBM mounts should last indefinitely when used with light VM36 carburetors (BS34 version fits them) or with well supported OE carbs.

 

[bored0987]

I want to thank you all for your help I have explained this to my father.., and you know riders., he cant wait a month.. so i found this..for the quick fix he wants http://www.georgefixs.com/servlet/the-1316/NEW-74-dsh-77-XS650-TX650/Detail
Also thank you olie, grizld1 his bike is a 77 so he does not have to worry about the petcocks (i assume)because the ones that were on there didnt have them, and everything else is original.. except the rectifier i built him ..also he does not use ethanol fuel..Plus he never rides far. you know around the lake in his area or to the closest urbanized city..The farthest he really rides it is to come see me which is a couple of hours away.. So he hasn't been in the situation where he has to use the ethanol fuel..

If these will not work let me know.. I wont be ordering them for a few days..

Wait nevermind I told him the one from 650cental were from original manufacture and he wants those so thank you very much...
He is like this and wants to be like this

 

[grizld1]

If those really are Japanese made, they're likely to be ARS boots. If so, you'll find the trademark cast into the rubber. Don't order more until you've checked them out. Good luck to you and your father on the refurb work! You're doing your "due diligence," which puts you way out in front of the pack.