Topic: Tank, Frame, Harness-- Something's Not Right? photo

[Popwood]

I have my tank off for repainting so I'm looking a lot more closely what's going on immediately below the tank that's usually out of site.  Oh, yeah, this is a '75 750K. Here are the problems:

1) The wiring harness is routed to the inside of the left side frame member. With the wiring harness in this location, a full twist of the throttle the mechanism above the carb that lifts the needle actually has no clear path straight up. The harness interferes with it's free travel and pushes it slightly to one side. This can't be right. So what is the correct harness routing?

2) I find it odd that there would be rub marks on the bottom both sides of the tank where it is contacting both the left and right frame members about the same place more or less directly above the carbs. The tank rests on the regular rubber knobs on the front and has a standard rubber holder at the back just below the seat. I would think the tank would be fully suspected and not rub the frame.

I've attached a photo. One thing I've wondered about is why the line of the bottom of the tank is not in line with the bottom of the seat. The tank seems to ride higher. Do I have a "frankentank" here or something? Looks like a 750K tank to me.

[andy750]

Tank should look like this when on the bike (shown is a 74 750)...maybe its not seating on the front two tank rubbers properly or the rear rubber is somehow incorrect? Tank looks fine - Is the petcock touching anything?



for more reference - foreground bike is a 75...



Wire harness routing - look in the online manual -shows very clearly how to attach wire harness - a pic of your issue would also help.

Here is mine...sorry for the bad pic...



cheers
Andy

[Popwood]

Thanks Andy, and yes, I know those trim strips on the bottom of the tank and seat should be a continuous line. I'll grab a photo tonight after work and post. The petcock is not touching anything, but it does project out to the left at a bit of an angle as opposed to projecting straight down from below the tank.

The front seats on the front rubbers OK, but there seems to be a bit of play side to side. More than I think there should be. Also, when front wheel/forks are turned full right, it just kisses the front of the tank as the fork hits the travel/turn limitter. This does not happen when fully turned to left. When I study the photo of my tank vs. your's, it seems as though mine is angled with a downward slope to the front. Hmmmm.

[andy750]

If you can take a bunch of photos of the tank rubbers, rear rubber, harness-carb clearance we can figure it out for you. Sorry I dont have better pics! Ill take some more tonight since both my bikes are stripped at the moment.

cheers
Andy

[MickeyX]

From the pic you've posted, your tank seems slightly bigger than andy's. Like... fatter/taller at the back where it meets the seat? Or is it just an illusion? To me, they look like different tanks.

[Toxic]

From the pic you've posted, your tank seems slightly bigger than andy's. Like... fatter/taller at the back where it meets the seat? Or is it just an illusion? To me, they look like different tanks.

+1 from me too.

The tanks don't look the same, or maybe it is just the angle of the pic.

I think you have a tank from another bike.

how about some close up pic of the side and top.

[mystic_1]

This may help.

mystic_1

[mlinder]

It's an optical illusion. The tank is a standard k 750.My guess is something isn't lined up just right, so the tank isn't sitting where it's supposed to.

[andy750]

It's an optical illusion. The tank is a standard k 750.My guess is something isn't lined up just right, so the tank isn't sitting where it's supposed to.

+1

[Toxic]

post a side shot like Andy's pic so we can compare.

There is not a heck of alot to "not" line up. He says it is sitting on the front and rear mounts correctly and the petcock is not binding the thing up so what could it possibly be?

You know the rear metal tang on the tank doen't sit on top of the rubber mount but slides into the center.

Also I've had 4 different early CB tanks on my frame and there never has been any lateral movement on the front mounts.

something is not right

[Popwood]

Hey, everyone, thanks for the help. I'm posting a bunch more photos here. Clearly, the wiring harness needs to be routed and secured to the top frame member, as Mystic_1's illustration suggests. That takes care of that problem.

Still wonder why the rub marks on the frame r and l frame members and why the tank doesn't line up properly with the seat. Please check out the photos and let me know what you think. Appreciate the help.

[Toxic]

Lets try this:

On my tanks the distance between the front mounting cups is 3 3/8" as measured at the back of the cups.  The wideth of the tunnel at the widest point is 6 1/8". ( measured 6" from the back of the mounting cups ).

Where you have rub marks on the frame rails above the carbs i have 1/4" of clearance.

i wish I could be of more help

[Popwood]

Toxic, just to make sure we are apples to apples, we're both referencing a 750K, yes? Not exactly sure how you are taking your measurements, but here's a photo showing the distance between the "cups" at the most narrow point (at the "back of the 'C' shape of the cup, you might say), and I'm getting a measurement of 4+". Is this where you are getting a 3 3/8"?

The second photo shows two places on the bottom of the tank at the ends of the "pointer" which could be a flat spot where a rubber mount might rest(?) or could have someting to do with the mold shape that was used when the bottom of the tank was stamped/molded. Is this typical of a 750K tank?

[mystic_1]

Your rear mounting rubber is backwards, I think.  On mine, the triangular piece at the top faces towards the back of the bike.  Dunno if this would cause your problem, but it's something.

mystic_1

[Popwood]

Makes sense, Mystic_1, as the triangular tab to grab would be pointed to the rear of the bike where you could actually get a grip on it. I'll switch to see if helps. Ahh, PO's. I didn't put that on, or route the harness. I'm just working backwards from problems that I find. Good learning process though.

[Toxic]

Yes, 750K.

Where you have 4+" is exactly where I have 3 3/8" on all three of my "K" model tanks.

[Toxic]

In the second photo those round dents are on my tank as well. They don't sit on anything.

The wide ruler at the back of the tank is centered above the round dents your second pic is pointing to ... the edge to edge measure is 11 1/4

The two white rulers are 6" wide.

There is something way different with the front mounting points on your tank.  Should be 3  3/8"

[Popwood]

Toxic  I'd say the bottom of your tank looks very different from mine. Your's is a very smooth stamping while mine has distinct ripples from the molding process.  And clearly different dimensions at the front mounting cups. So just why do I have here? I'm prepared to believe it's not stock for this model year, but what then is it?

Anyone want to throw in here?

[HondaMan]

Starting with the K5, the tanks and the frame mounts moved a little bit. Installing a K4 or K3 tank on a K5 frame will cause the tank to sit lower, hitting the frame where you describe. The curl brackets in the front were located about 4mm further back on the K3-K4 tank, as compared to the K5-K6 tank, so the tank will sit further forward, causing the fork ear tubes to touch (or even dent) the tank "lapels".

There are 2 things you can try that will help:
1. Get the larger "donut" rubbers for the K3-K4 tank (the round knobs up front).This will push the tank back about 2-3mm.
2. Try to locate a K1-K4 rear tank rubber mount: it is taller under the "slit" where the tank's tab mount resides. The overall height is the same. You can recognize these by the thinner top   part of the strap (often broken on one side). Honda moved the "slit" down into the center of the rear block and lowered the tab's angle on the tank to suit, because the rubber strap on top often broke: moving the "slit" downward let the edges become stronger. But, the tank had to change so the carbs would not hit it, etc...

In short, it looks like you have a K4 tank on a K5 frame...

[Popwood]

Hondaman, you very we'll have nailed it-- thanks! Would seem using the front rubber mounts to both raise and push back the tank, thus changing the geometry, could help resolve some, if not all the tank problems.
Unless anyone out there wants to do a tank trade? I'm near done rehabbing this tank interior- wasn't bad to begin with-- but I'd be up for a trade before I start painting!!

[andy750]

I think Hondaman has it - the front mount rubbers look very odd angle to me. Another thing is your coils appear to be asymmetrical with your ignition connector maybe be getting in the way as well. try rerouting the harness to where it should be and then try tank again once coils are more symmetrical.

good luck!
Andy

[mystic_1]

Another thing is your coils appear to be asymmetrical

Noticed that too, don't think the coils are actually mounted in that pic, I don't see the mounting band that goes around the upper backbone tube.

mystic_1

[Toxic]

Starting with the K5, the tanks and the frame mounts moved a little bit. Installing a K4 or K3 tank on a K5 frame will cause the tank to sit lower, hitting the frame where you describe. The curl brackets in the front were located about 4mm further back on the K3-K4 tank, as compared to the K5-K6 tank, so the tank will sit further forward, causing the fork ear tubes to touch (or even dent) the tank "lapels".

Awesome, that is why my fork ear tubes touch the tank.  I going to put is a small screw to act as a "bumb stop"

There are 2 things you can try that will help:
1. Get the larger "donut" rubbers for the K3-K4 tank (the round knobs up front).This will push the tank back about 2-3mm.
2. Try to locate a K1-K4 rear tank rubber mount: it is taller under the "slit" where the tank's tab mount resides. The overall height is the same. You can recognize these by the thinner top   part of the strap (often broken on one side). Honda moved the "slit" down into the center of the rear block and lowered the tab's angle on the tank to suit, because the rubber strap on top often broke: moving the "slit" downward let the edges become stronger. But, the tank had to change so the carbs would not hit it, etc...

In short, it looks like you have a K4 tank on a K5 frame...

This is great info but tell be why the distance between the front "curl bracket" on his tank is over 4' and on all 3 of mine it is 3 3/8" measured at the same spot. Something is still not right.
Try these suggestions and let us know.  Curious about this one.

I've been reading this forum for over a year and never new this so thanks again.

[xenoscr]

The tank in your photos looks like it's been sat on. Or someone pried the bottom apart. I have a K0-K4 style tank (purple) and a tank from a K5 (black) sitting around and took some photos. Hope they help:

XenosCR

[6adan]

Looks like the tank has expanded for some reason. Maybe from setting in the sun.