700 Maxim-X Petcock "Leak-by" -- what's up with that???

OK, Max-X drivers. What's going on here?? I don't have any experience on Maxim-X (700). Although the bike seems like a Xerox copy of the 750 ... there's something haunting it; and I can't seem to iron it out.
The petcock fails to shut-off with No vacuum. There's good flow on Prime. Good flow on Reserve. You'd expect the flow to be shut-off on Fuel / On ... the straight up-'n-down position.
It trickles. I pulled-of the vacuum valve and it "Looked" OK ... I guess! I thought the vacuum operated shut-off was about the same on all these bikes. There's and O-ring at the end of the small valve body ... and, it seems to look just fine under the magnifying glass.

Yet ... the petcock won't shut off.

I dove-in through the front and inspected the rubber metering wafer, too. Looked OK ... replaced it anyway.

Does the 700 Max-X have a petcock unlike others. I don't think it does from the look of it.
The vacuum valve. Is that unlike others? My gut feeling is that it must be ... because the one in this petcock -- (after being rebuilt by a dealer) -- leaks like a sieve.

OK ... give me the 4-1-1

RickCoMatic

 

There have been problems with the K&L rebuild kit. Mainly that the oring is too small. Another thing that may work is to stretch the spring. It seems 3 things keep it from sealing, the oring is bad, trash blocks the oring from the seat and the spring doesn't push hard enough to seal it. A cracked diaphraghm can cause leaking but that should have been fixed or at least checked by the dealer. But knowing dealers like we do......

 

I vacuum tested it. Opens full under vacuum. Leaks-by under NO vacuum.

Following is text from owner with same experience:
++++++++++

If it has been rebuilt recently and if they have put in an
aftermarket rubber vacuum/plunger assembly chances are that the
plunger might be a fraction short. I had this problem when I got one
off eBay. Couldn't figure it out initially. I ended up putting my
old moth eaten rubber diaphragm&plunger back in the petcock and it
worked fine. Put in the new one and out came the petrol. Finally
figured out that it was too short. A couple of fixes...shave some of
the facia in the petcock assembly so the plunger seats more deeply. (***There's NO WAY I'd do this -- ever. NEVER alter. Fix it right! ***)
This should do it. Or try to stretch the rubber diaphragm (not
recommended)to see if that assists with stemmimg the flow.
++++++++++

I'm making some calls ... getting the right kit!

RickCoMatic don't hack!

 

I've tried a new rubber wafer made no diff. Bought a K&L repair kit as well which proved to be useless because the O rings were too big. Tried a a washer behing the spring and a spring from a ballpoint pen as suggested by a fellow member and it still seeps petrol.

Mick Faighaigh.

 

Have you checked for a hairline crack in the petcock, sometimes they are hard to see, it may be gracked and leaking.

 

Having same problem.

Haven't started to repair the petcock yet, but Im watching this thread carefully to find a solution, so keep at it.

 

Well (he said smugly) I won a S/H petcock on ebay which I shall try once it arrive. Hopefully that will be one of my problems sorted.

Mick Faighaigh.

 

Can you buy just any petcock? Or do you need a specific one (OEM)? What Im saying if I see a petcock on ebay, does it have to be for a yamaha Maxim X?

 

Yes and no! How's that for a strong stand on the issue?
The pingel petcocks are round at the base. Our's have that oval base with the oval oring. Why? to cover that damn oval hole they cut in the tank. So you would have to modify it somehow.
However when mine went bad I replaced it with a new one off of an ATV. The dealer checked my old one with what he had in stock and it has worked very well since.

 

NEWS FLASH ...

AUTHORITIES INVESTIGATING MISSING PETCOCKS ON ATV'S

 

Hey Rick,

I wasn't sure if that rebuild kit I sent you from oldbikesbarn is the right one for the 700. Did you see the photo of it? Should I order this one? Let me know and I'll get right on it. Precious riding days are slipping by as we speak!

Thanks,
Cheryl

 

Forensic exam of leaking petcock.

Fuel "Leak-by" vacuum valve.
Side-by-side comparison with known good petcock.

The aftermarket kit's valve piston does not allow O-ring to seat.
A possible mod would be:
Chamfering the end of the vacuum valve piston to allow the O-ring to be pushed further into the tapered seat.

Theroy untested at this writing.
Experiment to get underway -- shortly.
Results to be posted here.

Stay tuned.

 

So should I buy the rebuild kit? It seems if the rebuild piston doesn't allow the O-ring to seat, then it's too short (which is what we originally suspected). If this is the case, then do you think YamaRobber actually installed the wrong kit?

 

Wolfmajor ... Come and get your bike ... it's FIXED !!!

Everybody else with that "Vacuum valve leak-by" ... Do this for the fix!

Pull the Vacuum valve off the petcock.
Using a 19mm socket as "The Table" and a Standard Small "C-clamp" as the Press ... PRESS the Center Spring Retaining Rod- ON THE ALUMINUM DISC SIDE -- IN ... .015 - .020mm Causing the aluminum disc to form a slightly concaved surface ... thereby moving the opposite side of that rod ... where the O-ring attaches ... to be moved .015 - .020mm further into the recieving taper of the valves O-ring seat. FIXED! DONE.

This is "The Fix" ... for "Petcock Leak-by"

Just another in the long list of inovations brought to you by the World Leader in XJ-Series restoration techniques and shop tricks.

RickCoMatic ... They don't call me "RickCoMatic" for 'nuthin!

'Cuz wenn dat boa gots iz mo-jo woikin' ... yeh jess no sumpin' good gunna appin' ...

Kin ah gits ah Hey-men on DAT!

I fixed it ...
Copyright Aug 21 2006
Richard E Massey
Billerica, MA
The RickCoMatic Leak Fix

 

Rick - YOU ROCK!!!! Unbelievable, man! I'm not sure I follow what you had written out as the fix, but I'm sure it will make more sense when we meet in person and you tell me (again) what you did to make this work. Invaluable information. This deserves a patent.

I'm going to make a few calls to see who might be available to bring me back to your place to get the "finely tuned Maxim." What are the best days/times for you???

Again, the XJ community is a very unique one, indeed. Rick is one (shining) example of what the love of this beautiful bike will do. Pay it forward in the best possible ways.

Thanks again, Rick!
wolfmajor

 

Wolfmajor ... You got mail ... PM

 

any way to get some schematics of what your doing for the petcock? simple draw program example would be good, just so I can visuallize what you did better.

Thanks

 

Just for reference, in case someone gets tired of rebuilding petcocks, I found that a Pingel petcock, model 4111-AH4 for the Yamaha YZ-80 for $79.80 was a perfect fit on my XS1100 Midnight Special. It comes with the oval mounting plate and I think it fits the 750 Seca too. Not sure about the 700 but it might fit if the mounting holes are spaced 34mm apart. There's a photo here near the bottom of the page so scroll down most of the way.
http://www.arizonasteve.netfirms.com/XS1100Carbs/

 

Hi.

Well the S/H petcock has arrived and it will probably fit ok but it's different to the existing petcock. On this one the fuel line and the vac hose both run out of the same side on the existing one fuel runs out from the right and the vac runs out from the left. Busy day today but if I can I'll fit it tonight and see what happens.

Re: the K & L petcock repair kit, I forgot to mention that as well as over-sized o-rings it came with a large round O-ring but both the petcocks I have need ovals.

Mick Faighaigh.

 

Mick, Are you sure they are meant to be oval? Old ones often look oval due to the years of pressure.

Which one are you specifically refering to?

From Memory there is only two o-rings. -small one on the vacuum port and a large one around the tap mechanism.

 

Yamaha Petcock-to-tank O-rings are OVAL. Aftermarket Petcock-to-tank O-rings are round -- but, the correct size to fit.

This is what tipped me off to Wolfmajors petcock being overhauled with an aftermarket kit. I think they grabbed any kit they had and threw it in there ... that's why it was leaking-by ... even with NO vacuum!

Does anyone have a part Number for either the OEM or correct fitting Aftermarket kit. I want to get wolfmajor's bike straightened-out, once and for all. It's got to be frustrating spending $$$ at the pro-shop and getting less than you pay for!!!

 

Morning.

Made an attempt at fitting the petcock I bought on ebay but the old sod already fitted refuses to come of the tank, in fact I now have a leak from the one of the screws due to the washer falling apart under pressure.

So the old one is still in place but I stripped the new arrival and used all the parts, the result is that I now have a decent flow on prime and zilch on run or reserve. All I need to do now is cure the leak and get the squealing noise sorted.

Have put a couple of pics on my gallery, one showing the oval O ring and the other showing what arrived as a K & L repair kit. I think the size difference of the O rings can be seen, the lower one is the original.

Mick Faighaigh.

 

I have an 82 XJ750 Maxim, and the local shop couldn't find a diaphragm, or full rebuild kit (w/diaphragm) for this model.

I have a leak when running, so I think it would be the diaphragm. I was hoping for a simple fix. Does anyone know if there is a kit or diaphragm available for the XJ 750 J? The books show for the 650 and Seca 750, but not Maxim...

 

The following info came from the XJ CD in the Carbs and Fuel Systems section:


For those of you that are interested, I managed to obtain a Kawasaki replacement part for my XJ650RJ.
Part# 430281021 – This the Diaphram Assembly including:
>-Square Plastic body
>-2 square rubber gaskets
>-Metal Plunger with small O ring
Source Kawasaki Bike is the KZ650-H2 ’81-’82 H1/H2

 

i was experiencing very similar problems with fuel leaking out around the petcock. my solution was pretty but has ended the dreaded drip.

went to a checker autoparts store and found some grey gasket that moto bike riders use for quick gasket jobs. its gas resistant and heat resistant.

slathered the damn petcock in the stuff, put a little bit on the inside to create a seal and let it dry. doesn't look pretty but i haven't had any gas dribble out of it since.

 

I'd sure like to find an aftermarket company (like Pingle) that will fit an XJ Maxim that had a setting for OFF- RUN- RES
that would replace ours and dosent cost a fortune to buy and not look aftermarket. (adapter plates and such).

 

nice work man. just got the kit and tore my petcock apart. of course i read this after i put it in. lol. my question is where can i come up with a spring for inside there. mine never had one in it. any ideas?
thanks

 

OK, so I'm a little late on my post for this string, but thought that RickCoMatic would like to know that his 19mm socket trick worked way out here on the west coast too!

My petcock hasn't worked right since the last time I "fixed" it about 6 years ago. Didn't worry much as it was just always getting gas. Since I'm doing a bunch of other work, I thought "what the hell, why not start something else too?" Though I'd seen this string, and was deciding on what kit to try and get, I went with whatever the local bike shop had......the dreaded K&L. I thought to myself, "I could shop around, but surely I'll have better luck than everyone else has had."

You guessed, it....it leaked like a sieve when I put the new diaphrams in. I came back in and read RickCoMatic's suggestion carefully, and went back to the garage. About 5 minutes later, I was testing it out, and it stopped the flow without vacuum, but with vacuum, worked just fine.

Just had to post my success story (they're actually quite rare), and thought that someone else might be willing to try knowing that it worked on more that one occasion. Thanks!

Brett

 

Just read this article as I’m fixing mine and the rebuild kit was still leaking. You guys are awesome! I knew I’d find the answer here

 

when a problem comes along, you must whip it, whip it good.

 

Followed the instructions and no more leaks!! Thanks