Gas tank swap?

[Pat Conlon]

George, thanks for the reminder on the shut-off. Having been in the automotive field for 30+ plus years, I'm use to a fuel pump that stops when you kill the ignition.

No, that's not what he is referring to. When the pump is electrically shut off, the pump internals should hold back the gravity weight of the fuel from the tank. In other words, when shut off, no gas should dribble from the pump.

[Paul1965]

George, thanks for the reminder on the shut-off. Having been in the automotive field for 30+ plus years, I'm use to a fuel pump that stops when you kill the ignition.

No, that's not what he is referring to. When the pump is electrically shut off, the pump internals should hold back the gravity weight of the fuel from the tank. In other words, when shut off, no gas should dribble from the pump.

Actually that's what I meant, I just didn't say it right

[movenon]

Paul I have a box of carb parts in my garage I might have the n/s you need.If nothing else you could look at them and see whats up.I hope to be pulling the engine out of the Civic in the next few days I think I have a buyer for it.I can help you with your carbs if you need help but im sure you can do it once you take a look at them.I know where to get mikuni parts in elgin if need be as well.I have bought jets there a couple of times.

Thanks Scott, I think I saw that box of parts lol...If you need some help pulling the engine let me know.

George, thanks for the reminder on the shut-off. Having been in the automotive field for 30+ plus years, I'm use to a fuel pump that stops when you kill the ignition.

Not just stop, but a check valve preventing fuel flow. Not a problem with cars because the fuel is located below the pump. I know you are aware of all this I just wanted to make the statement clear

Here is a good if not the best link on the carbs  http://www.fjowners.com/index.php?topic=4281.0...
George  

Thanks Pat you were quicker than me 

[racerrad8]

...and the fuel pump I sell does that; stops fuel flow.

Randy - RPM

[Paul1965]

...and the fuel pump I sell does that; stops fuel flow.

Randy - RPM

True, but if I'm going to attempt to keep my stock carb setup, yours will flow too much (and sorry, it's also outside of my budget). I think my best bet for now is to measure the flow of the stock petcock (unless someone already knows it) and try to match a pump up to that.

[movenon]

...and the fuel pump I sell does that; stops fuel flow.

Randy - RPM

True, but if I'm going to attempt to keep my stock carb setup, yours will flow too much (and sorry, it's also outside of my budget). I think my best bet for now is to measure the flow of the stock petcock (unless someone already knows it) and try to match a pump up to that.

At my best "WAG" a gravity feed tank in an FJ is probably doing good to deliver .2 to .4 PSI. Not much. I think a number of .4 lbs at 1 foot fuel tank height was an estimate. The FJ has less height than that.

As far as the volume or rate ? Another WAG way of looking at things. Can you totally empty your fuel tank in 1 hour of running ? That's about 5.5 gallons ?
There is a lot more to it than that. We are just talking steady rate of flow. But anyhow it would be hard to use 5 gallons of fuel in an hour with the typical FJ rider. But you could build in a WAG factor for that... Skymasters is going to love this "engineering"   Farmers way of looking at things....


Paul if is any help I have 4 needle and seats out of my carbs from when I rebuilt them that I can give you. They were not leaking in my carbs I just replaced them because I did a total rebuild. I also can give you 4 new needle and seat O rings (Viton O rings 7.1 x 1.6mm).

George

[Paul1965]

...and the fuel pump I sell does that; stops fuel flow.

Randy - RPM

True, but if I'm going to attempt to keep my stock carb setup, yours will flow too much (and sorry, it's also outside of my budget). I think my best bet for now is to measure the flow of the stock petcock (unless someone already knows it) and try to match a pump up to that.

At my best "WAG" a gravity feed tank in an FJ is probably doing good to deliver .2 to .4 PSI. Not much. I think a number of .4 lbs at 1 foot fuel tank height was an estimate. The FJ has less height than that.

As far as the volume or rate ? Another WAG way of looking at things. Can you totally empty your fuel tank in 1 hour of running ? That's about 5.5 gallons ?
There is a lot more to it than that. We are just talking steady rate of flow. But anyhow it would be hard to use 5 gallons of fuel in an hour with the typical FJ rider. But you could build in a WAG factor for that... Skymasters is going to love this "engineering"   Farmers way of looking at things....


Paul if is any help I have 4 needle and seats out of my carbs from when I rebuilt them that I can give you. They were not leaking in my carbs I just replaced them because I did a total rebuild. I also can give you 4 new needle and seat O rings (Viton O rings 7.1 x 1.6mm).

George

Thanks George, that's very generous of you. But I think I'll get with the Flying Scottsman first since he's local and has already offered up some of his carb parts. If he doesn't have what I need I'll shoot you a PM with an offer, as I really don't want to get something for nothing. You guys have been a tremendous help with this project!

[racerrad8]

...yours will flow too much

Nope, it has nothing to do with flow. It has to due with the line pressure applied to the float needle tip and the requirement of the smaller needle seat.

Put the new tank on, add in inline electric shut off valve and ride the thing.

Unless you are going to be riding at 100+mph on a sustained basis I doubt you will have any problem.

Randy - RPM

[movenon]

Paul, don't worry about "something for nothing". They are just old back up ones. A couple of years ago I got all new parts from RPM and just rat holed the take out parts. The O rings I special ordered and come in packs of 25... So I used 4 and the rest is just stuff on hand.
George

[Paul1965]

...yours will flow too much

Nope, it has nothing to do with flow. It has to due with the line pressure applied to the float needle tip and the requirement of the smaller needle seat.

Put the new tank on, add in inline electric shut off valve and ride the thing.

Unless you are going to be riding at 100+mph on a sustained basis I doubt you will have any problem.

Randy - RPM

I think I've come up with a better idea...

[Derek Young]

Hey Paul.  Getting into this a little late, but I'll tell you what I did with my 86.  The original tank had some rust and a very poor Kreem tank coating in it. Dropped it on its side in the shop and a little crease in the metal just happened to hit a rusty spot and she started leaking... Did an epoxy gas tank repair and started looking for a new tank. Ebay had only newer model tanks available at the time, so i bought a 91 tank.

If you look at the first picture you posted, you will see 2 spot welds on the flat spot where the petcock mounts.  Those welds hold a doubler plate on the inside of the tank with a matching slot and tapped holes to match the petcocks. I drilled out the spot welds on both tanks and removed the doubler plates. I used the existing front hole, elongated the slot and drilled a new hole in the thin metal tank and two holes for plug welds.  From there I bolted the new doubler in place and plug welded it in. A little sanding and the fabrication was done.  The fuel filter bracket on the bottom of the tank was in the way and had to be cut off as well to fit on the bike.

Of course the paint didn't match, so This was done after I completely stripped the tank with aviation paint stripper. Adapting the petcock was a very small part of the much larger repaint project. It was much easier to adapt the tank to the bike than to adapt the bike to the new tank.

Derek

[Paul1965]

Hey Paul.  Getting into this a little late, but I'll tell you what I did with my 86.  The original tank had some rust and a very poor Kreem tank coating in it. Dropped it on its side in the shop and a little crease in the metal just happened to hit a rusty spot and she started leaking... Did an epoxy gas tank repair and started looking for a new tank. Ebay had only newer model tanks available at the time, so i bought a 91 tank.

If you look at the first picture you posted, you will see 2 spot welds on the flat spot where the petcock mounts.  Those welds hold a doubler plate on the inside of the tank with a matching slot and tapped holes to match the petcocks. I drilled out the spot welds on both tanks and removed the doubler plates. I used the existing front hole, elongated the slot and drilled a new hole in the thin metal tank and two holes for plug welds.  From there I bolted the new doubler in place and plug welded it in. A little sanding and the fabrication was done.  The fuel filter bracket on the bottom of the tank was in the way and had to be cut off as well to fit on the bike.

Of course the paint didn't match, so This was done after I completely stripped the tank with aviation paint stripper. Adapting the petcock was a very small part of the much larger repaint project. It was much easier to adapt the tank to the bike than to adapt the bike to the new tank.

Derek

Hi Derek, thanks for the great info on how you did the tank mod. However I really don't feel like taking the chance of doing any welding on the gas tank. I think my best option will be to make a simple adapter plate instead and think a piece of 1/4" aluminum stock will work fine. It will have 3 mounting holes, one for the original front screw, one countersunk hole for the original rear mounting screw, then a third for the rear mounting screw of the 84 petcock (the adapter itself will be tapped to accept the rear screw). I should be able to use cork gasket on the tank side of the adapter plate and retain the original rubber seal on the petcock side of the adapter. I think 1/4" stock will be thick enough to drill and tap and get good screw retention. If not, I'll drill a countersink hole on the top side of the rear screw so I can drop a nut into it.

[Pat Conlon]

1/4" steel will give you stronger threads but be harder to work with.....

Whatever....you *do not* want that petcock to rattle loose.......kaaaablamm

[Paul1965]

1/4" steel will give you stronger threads but be harder to work with.....

Whatever....you *do not* want that petcock to rattle loose.......kaaaablamm

Ha, no doubt Pat!!!

[Derek Young]

I also have concerns about leaking.  Steel would be a better choice for strength on the threads.  Having said that, I have built lots of fuel tanks from aluminum, many of them with fuel gauge sending units that have a bolt flange attaching it to the tank. I usually tack weld a 1/4"plate on the inside of the tank, as many of them are only 1/8"thick, and drill and tap the six small bolt holes.  This isn't a huge concern for leakage considering it's located on the top of the tank.  On a motorcycle tank, the petcock MUST be sealed...

If you do use aluminum, ensure you follow the tap drill size chart to make sure you have the proper thread depth.

Derek