Rubber carb joints (XJ750) - Repair rather than replace?

Hey all,

I've had an XJ for all of three days, so bear with me.

The bike is an '83 Seca 750. It has been running recently, but is hard to start, and has a bit of a miss at idle. (More than that, I can't tell you.) I am midway through doing the valve adjustment, after which I assume I'll need to do the 'Nine Yards' carb treatment.

On to my question: I understand that the "carburetor joints" - the rubber pieces between the carbs and the head - are a potential source of intake leaks, which would cause that cylinder to run lean / hot.

On my bike, a superficial look shows that #1 and #4 are checked / have small cracks; #2 and #3 look pretty good. I'm guessing they're not UV

Now, as I understand it, there are two part numbers; slightly different shapes? Inner and outer? Are they A / B / B / A, or A / A / B / B or A / B / A / B?

Anyway... I was a little shocked to find out these things are $80 a piece! Before I drop an extra $320 on the bike... Has anyone tried sealing the carb joints, to prolong their life? I was thinking rubber cement, rubber paint, self-sealing tape?

Stock pic attached, just so we're all talking about the same thing.

 

The cracks probably don't go all the way through. have you checked? Mine are ugly on the outside, but don't leak one bit. There is a mess of stuff you could try to make it look better, but it won't change much.

 

Bicycle inner tube bedded on clear silicone, makes a neat repair, but if you have the beans buy new.

 

have you checked with chacal about the parts? $80 a piece seems awful steep.

CN

 

Cool, thanks for the replies guys.

 

Hi temp silicone went on mine an is fine for now til I buy new.

 

Hi temp silicone went on mine an is fine for now til I buy new.

 

repair is fine by me, but if your curious the cheapest I have found for genuine Yamaha ones is 45ish partshark.com also I think there is an ebay seller too. plus another 5ish for the gasket to head side.

 

Warning:

Attempting to remove Intake Manifolds from the Cylinder Head has a VERY Serious down-side.

The Manifolds are fastened to the Head with Non-hardened Steel Cap Screws.
More often than not, ... they are seized do to Galvanic Corrosion. Sometimes referred to as "Galling".

They will act like they are being removed.
But, they twist easily and sheer right off.

Breaking an Intake Bolt is the beginning of an avalanche of headaches.


Ask anyone who has broken one off.

 

X2

But as others have said, the cracks probably do not go all the way through.

Spray some starting fluid on/around the boots with the bike running, if the rpms change, you have a leak. If not, you're all good for now.

 

I just talked about this yesterday in my thread:

I used regular old bicycle inner tube from Walmart. I got the biggest one I could (though diameter of the wheel doesn't seem to change the cross-section diameter of the tube itself). I also bought Silicone caulk/glue/sealant to put in between the tube and the boot, but it's so tight on there that it would have been a sticky mess. Glue would have been everywhere. I opted to leave it at just the tube + boot until it becomes a problem again.

I would suggest starting with the tube right-side out, and inverting it as you roll it on. The outside is essentially tacky, and the inside is treated with a powder to keep it from sticking to itself. Dragging it on without flipping it inside out is really tough, but inverting it lets you take advantage of the powder.

Also, you'll have to get clever when it comes to making a hole for the stems. Poking a hole, then stretching, tends to lead to tearing the hole bigger if not clean through. I waited until I had pulled up enough slack that I could poke a hole and place it with the least tugging.

Oh, and take the caps off the stems as you do this!

Also,

It should also be noted that I cut the section long so that I could trim off excess when I was done wrestling with it. Minus the hole-punch part, the end result should look like this.
[/quote]

 

Mine are all horribly cracked (both 550s) but none of the cracks go all the way through so I packed them with black adhesive RTV and they've been fine for over 4 seasons now.

On the YICS-motor bikes, the manifolds are oriented / / \ \ (as in the pic above) which is why there are two part numbers.

 

inner tube and black rtv is my preferred way. BTW, Baldy....you did a very nice job with yours!

dave

 

Muchas gracias, Señor Fiddles.

 

Doesn't look like anyone posted the original boot repair thread: http://xjbikes.com/Forums/viewtopic/p=3 ... tml#330799

Somewhat related and looking at baldwonder's picture about: does it matter if you install your carb's vacuum hose on the 2nd or 3rd boot? I thought the 3rd one was correct, as it's a shorter distance to the tank nipple.

 

I found new ones on boats.com. $100 for all 4.

 

Mine's always been on #2 (since before I got it anyway), it's fine

 

Are you sure it was boats.com?

 

Very sorry. I found my receipt. It was boats.net and they were $199

 

Here's the diagram for a 1982 XJ650J.

I find it interesting that the diagram shows boot #3 as not having a stem cap. I don't doubt that pulling vacuum from any of them is probably fine, but nice to see possible confirmation that it was designed to be #3.

 

On my bike the reserve gas line goes into the stem on 3.

 

Pretty sure you'll find that's the vac hose whch activates your petcock, just like everyone elses................. unless I missed the joke?

 

I opted to leave it alone, figuring he'd realize it's not a reserve line eventually.

 

On the 550s and 600s, the vac line was originally connected to intake boot #2.

On the 650/750 series, it was connected to #3.

It only matters on some of the later 600s, their #2 carb was jetted slightly differently, and I'm assuming that to be the reason why.

 

Wasn't trying to but ended up being the ass of it. I'm new to bikes so I assumed thats what it was. So I took it off and haven't had a issue since, which had been about 6 months.

 

Bald wonder, nice job. Perhaps ky jelly would assist the fitting process and a heated rod to make the stem holes?

 

iirc thejewishguy suggested using a single hole punch to make the the hole. Imo it's a good idea.

 

This is great!
My boots are bad and budgets is tight.
I don't have RTV but do have Pliobond.

I believe it would work swimmingly well.. . Anyone know other wise?

 

Go to the auto parts store. AutoZone, O-Reilly's, whatever.

Find black, adhesive high-temp RTV. It's made for certain automotive applications where they simply glue the cover on; there is no gasket. I discovered it because it's how you install the end cover on a Dodge/Mitsubishi 3.3L automatic transmission. Mean stuff, kinda silvery-black.

It'll cost you maybe $7 ~$8 for the tube. Screw Pliobond. Use it to fix your flip-flops. You gotta think automotive with this kinda stuff; not kitchen-drawer - hardware store.

 

Got the RTV adhesive sealant and did the deed.
Went really well, easier than expected, stretched right over the nipple and then a small puncture allowed the nipple to poke through without ripping.

Weird thing, boots 1 & 4 had no cracks, 2 & 3 were cracked up pretty good.
Any thoughts as to why that would have happened?

Thinking of maybe moving the insides to the outsides (1 swaps with 2 and 3 swaps with 4). Good thought? Bad thought?

P.S. flip-flops are now good for another 10,000 miles :lol:

 

Maybe it's because water can't evaporate as readily from the middle as it can from the sides and that aged the rubber faster. Or maybe the outer manifolds get more airflow than the inner and that keeps them cooler. I don't know, just throwing out some guesses. I'd be interested in hearing what the more informed have to say about it.

Either way, I'd advise against removing the manifolds, there are so many horror stories around these threads about those galvanized screws snapping. Plus, why would you want to put the ugly cracked manifolds on the outside?? XD

 

My guess is that a PO took the time to apply some kind of rubber restorer/protector on the outer two, but didn't want to get dirty and reach for the inner two.

 

Stump, I also had two that looked great and two that were checked, but it was my outers that looked rough; I'm guessing that someone on either your bike or mine swapped them over, and that it's either a function of engine heat (inners) or UV light (outers).

I guess the takeaway is, if you're really cheap... you should be able to make one nice set out of the manifolds from two parts bikes!

 

If you removed the vacuum hose on the stock petrooster and still running you will have a problem soon. The vacuum allows the petcock to stop the fuel flow when the bike is not running. You may end up with gas flooding the carbs and your engine. You may need to rebuild, or replace your pet rooster sooner rather than later.

 

To reply to multiple people without sounding to disjointed . . .

I already removed the intake boots - mine came off easy - actually too easy. Almost like the bolts weren't torqued properly - the gaskets were crispy and thin, so maybe 33 years ago they were torqued proper and then the aging gaskets created a 'looseness'.

Rubber restorer put on the outside boots kinda makes sense especially given that it sounds like something the PO might have done. Can't really see him skipping the inner ones - but they are a little tricky to get to if you don't remove the gas tank . . .

Heat, kind of make sense - the inner two boots are tucked inside - but one would ass-u-me that there is still enough air flow around the whole bike to keep things nominally cool.

I am going to flip-flop (not the footwear) 1 & 2 and 3 & 4 when I reassemble.

 

Looks like Im kinda late on this post, but it would seem cylinder #3 would be the best for the vacuum hose. My thinking is that all the carbs are syncronized with #3.