Tank fitmint issues

[Fjfreude]

Im having some tank troubles. I have a 1979 xs650 special and I wanted to swap tanks out. So, I bought a 1977 xs650 standard tank of ebay and tried to mount it but it wont fit! When I put the rubber spacer bits in the front part the petcocks just sit on the frame. So i took them out and one of the petcocks still wont go. I even reversed the petcocks to see if that would make more room. No go.

Any ideas? I though the standard tanks fit right on the specials whats going on here?

 

[Fjfreude]

Heres a pic of the tank (not mounted). Just maybe its an odd year or something.

 

[650Skull]

A pic showing the problem would have been better.

That being said...........All XS650 tanks from 74 to 84 will interchange on a standard or Special bike with the standard carb and normal bike set up without any changes to the frame rails. If the tank has had aftermarket petcocks fitted this may also be a contributing factor

Any deviation from an original set up may cause a problem..............The reason i state this is there has been modifications done to your bike and you have not stated what has been done that could be causing the particular problem..................Again a pic of the tank in position....................and the petcocks..............

Sometime, (especially if the rubbers are new), the rubbers are hard to get into the cups, this will cause the tank to not seat properly. A firm and harder firm push is needed.

 

[Fjfreude]

Thanks! So, i went back in after I made the post to take a pic. Thinking, as you said, an actual picture would be better. I got it! Turns out the owner who did all the mods installed a 2-1 manifold and single carb setup. To do this he cut the frame tube in the center and added two new frame tubes off to the side. I just thought of it last minute and had to do some searching for images of stock frames to check. Its these tubes that are causing the problem Ill have to fab something to get it solved. Always up for a good challenge!

Thanks for the help. I appreciate it.

 

[fredintoon]

Hi Fjfreude,
on reading your first post I thought "WTF? My Standard tank fits on my Special no problem." but yeah, the photo tells me why.
That neat frame modification does get in the gas taps' way, eh?
But the Special tank has it's gas taps in much the same place so how did it's gas taps fit?
OK, you'll need to either modify the frame tubes which will be a cut'n'weld job or move the gas tap slots which will involve a cut'n'weld on thin sheet steel plus wrecking the tank's nice paint job.
Or make adapters to move the gas taps. Let me think - - -
Piece of rectangular section aluminum bar drilled to bolt onto the gas tap access.
Holes drilled through the bar from the tank and another from the side to met inside the bar an L-shape.
Tank hole one side has a standoff tube for normal fuel supply, T'other side has a plain hole for reserve.
Holes from both sides have a threaded to fuel tube spigot elbow.
Fuel line to in-line on/off gas taps then lines Teed together to the single carb.

 

[650Skull]

Figured it had to have had some frame modification.

That tank looks real nice, may pay to resell and look for a US XS750/850 tripe tank. They have a wider tunnel and the petcocks should miss the frame. There is some modification to the front mount but an easy fix, easier than messing with the frame.just get some measurements for the width between the petcocks if you go this way.

 

[arcticXS]

I wish Yamaha had built the frame like that in the first place. Then it would be easy to use longer inlet manifolds, even with linked dual carbs. I mean, even the early 2-strokes had this type of frame design after all.

 

[Brassneck]

I'd make a plug for one of the petcocks, and then make a plug with a port for the other side..then a fuel hose/and in-line petcock to the carbs. Simple.

 

[fredintoon]

Figured it had to have had some frame modification.
That tank looks real nice, may pay to resell and look for a US XS750/850 tripe tank. They have a wider tunnel and the petcocks should miss the frame. There is some modification to the front mount but an easy fix, easier than messing with the frame.just get some measurements for the width between the petcocks if you go this way.

FWIW an XS11 gas tank (I don't have an XS750/850 tank to measure) carries it's petcocks at 8-7/8" between centres vs an XS650 tank's 5-1/2". As I remember, the XS750/850/1100 tank front mounts are all forward facing cups vs the XS650s knobs & hockey pucks.
All you'd need to mount them is two back to back pairs of hockey pucks for an XS750/850 tank and two really wide pairs for an XS1100 tank.
But yeah, a set of petcock adapters for the XS650 Standard tank is the easiest way.

 

[Fjfreude]

Turns out if I switch the petcocks the right fits on the left and the tank goes on fine. However that's without using the rubber bumpers. I'm gonna plug the right hand side so I'm using a single petcock and use some hosing for bumpers. Brassneck, that's not a bad idea either.

Thanks for the tank info, though. I may end up needing it.

 

[Fjfreude]

After atitle fabbing of a block plate to seal up the right side, hose sections for the inner bumpers, and minor rubber trimming it fits like a glove.

Thanks for the input!