Gas tank swap?

[Paul1965]

I picked up a gas tank from a 90 FJ and want to swap it onto my 84. Will it work? I know the petcocks are different but not what the difference is (is it just that one has a handle the other doesn't?), and the 90 has a protective bracket for the fuel filter. I'm wondering if I can cut the bracket off and relocate the filter? Also, what about the vent tube that's on the back end of the tank, under the front of the seat. What is that for?

[Pat Conlon]

While the '90 tank will physically fit on your '84, the petcocks are different. The petcocks are different because the fuel delivery systems are different.
The '90's petcock was designed for fuel pump systems and has no shut off feature when used without a fuel pump. You need to be able to shut off your fuel.
The '84 petcock has the fuel shutoff feature (via engine vacuum) but will not fit on the '90 tank. The petcock mounting base is different between the 84 and 90.

A couple of options for fitting a 90 tank on a '84:
1) use the oem petcock on the 90 tank and convert the '84 over to a fuel pump system
2) install a manual lever type petcock on the 90 tank and figure a way to make the lever accessable.
3) use the oem petcock on the '90 tank and install a Pingel Vacuum shut off valve on the fuel line.

I am looking at converting my gravity flow '84 over to a fuel pump system, that way I can install a real honest to God fuel filter in the system (instead of a screen) Something I think will be needed (if not now, then in the near future) as the eathnol blend fuels play havoc with our tanks and fuel systems.

The only way a proper filter will work on a FJ is with a positive displacement fuel pump pulling the fuel through the filter. Just like on the '89 and newer FJ which have a fuel pump and filter.
Head pressure from Gravity flow (84-87FJ's) will not produce enough pressure to push the gas thru the filter, you need a pump.

You can not use a fuel filter on your gravity flow '84, a simple screen: yes, a filter: no. Don't confuse the two.

The '90 tank has a recessed fuel cap with a spiffy feature to drain off any fuel you might spill in this recessed area. The drain stub at the back of the tank is connected to the recessed drain and it's where the hose connects to drain this spilled fuel away from the bike.

Cheers Pat

[Paul1965]

While the '90 tank will physically fit on your '84, the petcocks are different. The petcocks are different because the fuel delivery systems are different.
The '90's petcock was designed for fuel pump systems and has no shut off feature when used without a fuel pump. You need to be able to shut off your fuel.
The '84 petcock has the fuel shutoff feature (via engine vacuum) but will not fit on the '90 tank. The petcock mounting base is different between the 84 and 90
A couple of options for fitting a 90 tank on a '84
1) use the oem petcock on the 90 tank and convert the '84 over to a fuel pump system
2) install a manual lever type petcock on the 90 tank and figure a way to make the lever accessable.
3) use the oem petcock on the '90 tank and install a Pingel Vacuum shut off valve on the fuel line.

I am looking at converting my gravity flow '84 over to a fuel pump system, that way I can install a real honest to God fuel filter in the system (instead of a screen) Something I think will be needed (if not now, then in the near future) as the eathnol blend fuels play havoc with our tanks and fuel systems.

The only way a proper filter will work on a FJ is with a positive displacement fuel pump pulling the fuel through the filter. Just like on the '89 and newer FJ which have a fuel pump and filter.
Head pressure from Gravity flow (84-87FJ's) will not produce enough pressure to push the gas thru the filter, you need a pump.

You can not use a fuel filter on your gravity flow '84, a simple screen: yes, a filter: no. Don't confuse the two.

The '90 tank has a recessed fuel cap with a spiffy feature to drain off any fuel you might spill in this recessed area. The drain stub at the back of the tank is connected to the recessed drain and it's where the hose connects to drain this spilled fuel away from the bike.

Cheers Pat

That's awesome info Pat, thanks for taking the time to go in depth. I will check on what the vac valve costs and go from there.

[Pat Conlon]

Glad to help.

[movenon]

While the '90 tank will physically fit on your '84 the petcocks are different.
The '90's petcock was designed for fuel pump systems and has no shut off feature when used without a fuel pump. You need to be able to shut off your fuel.
The '84 petcock has the fuel shutoff feature (via engine vacuum) but will not fit on the '90 tank. The petcock mounting base is different between the 84 and 90
A couple of options for fitting a 90 tank on a '84
1) use the oem petcock on the 90 tank and convert the '84 over to a fuel pump system
2) install a manual lever type petcock on the 90 tank and figure a way to make the lever accessable.
3) use the oem petcock on the '90 tank and install a Pingel Vacuum shut off valve on the fuel line.

I am looking at converting my gravity flow '84 over to a fuel pump system, that way I can install a real honest to God fuel filter in the system (instead of a screen) Something I think will be needed (if not now, then in the near future) as the ethanol blend fuels play havoc with our tanks and fuel systems.

The only way a proper filter will work on a FJ is with a positive displacement fuel pump pulling the fuel through the filter. Just like on the '89 and newer FJ which have a fuel pump and filter.
Head pressure from Gravity flow (84-87FJ's) will not produce enough pressure to push the gas thru the filter, you need a pump.

You can not use a fuel filter on your gravity flow '84, a simple screen: yes, a filter: no. Don't confuse the two.

The '90 tank has a recessed fuel cap with a spiffy feature to drain off any fuel you might spill in this recessed area. The drain stub at the back of the tank is connected to the recessed drain and it's where the hose connects to drain this spilled fuel away from the bike.

Cheers Pat

I vote for #1  

The black line/hose you are referring to is a an air vent line. It ends up under your fuel cap providing positive pressure for the flapper valve built into the fuel cap which in turn feeds air pressure into the fuel tank as fuel is used. Also if you over fill fuel it will leak out of it. If you want to use your ignition key with your new gas cap PM me and I can probably help you do that.

As just an opinion, some remove the flapper valve. I personally wouldn't recommend it. Ethanol manufactures strongly recommend to store the fuel in an air tight environment. The alcohol in it is a water magnet and will absorb water from ambient air. The local small engine shop ran an informal test with a jar of sealed ethanol and an unsealed jar of ethanol and after 6 months the sealed jar was still clear and the other a dirty brown color.  As a note they don't recommend storing ethanol for more than 90 days.

Why do you want to relocate the filter location Paul ? If you run a filter you will probably need a fuel pump.. Also as a note the 1990 petcock uses 7mm/ 1/4inch fuel line.

George

[Paul1965]

While the '90 tank will physically fit on your '84 the petcocks are different.
The '90's petcock was designed for fuel pump systems and has no shut off feature when used without a fuel pump. You need to be able to shut off your fuel.
The '84 petcock has the fuel shutoff feature (via engine vacuum) but will not fit on the '90 tank. The petcock mounting base is different between the 84 and 90
A couple of options for fitting a 90 tank on a '84
1) use the oem petcock on the 90 tank and convert the '84 over to a fuel pump system
2) install a manual lever type petcock on the 90 tank and figure a way to make the lever accessable.
3) use the oem petcock on the '90 tank and install a Pingel Vacuum shut off valve on the fuel line.

I am looking at converting my gravity flow '84 over to a fuel pump system, that way I can install a real honest to God fuel filter in the system (instead of a screen) Something I think will be needed (if not now, then in the near future) as the ethanol blend fuels play havoc with our tanks and fuel systems.

The only way a proper filter will work on a FJ is with a positive displacement fuel pump pulling the fuel through the filter. Just like on the '89 and newer FJ which have a fuel pump and filter.
Head pressure from Gravity flow (84-87FJ's) will not produce enough pressure to push the gas thru the filter, you need a pump.

You can not use a fuel filter on your gravity flow '84, a simple screen: yes, a filter: no. Don't confuse the two.

The '90 tank has a recessed fuel cap with a spiffy feature to drain off any fuel you might spill in this recessed area. The drain stub at the back of the tank is connected to the recessed drain and it's where the hose connects to drain this spilled fuel away from the bike.

Cheers Pat

I vote for #1  

The black line/hose you are referring to is a an air vent line. It ends up under your fuel cap providing positive pressure for the flapper valve built into the fuel cap which in turn feeds air pressure into the fuel tank as fuel is used. Also if you over fill fuel it will leak out of it. If you want to use your ignition key with your new gas cap PM me and I can probably help you do that.

As just an opinion, some remove the flapper valve. I personally wouldn't recommend it. Ethanol manufactures strongly recommend to store the fuel in an air tight environment. The alcohol in it is a water magnet and will absorb water from ambient air. The local small engine shop ran an informal test with a jar of sealed ethanol and an unsealed jar of ethanol and after 6 months the sealed jar was still clear and the other a dirty brown color.  As a note they don't recommend storing ethanol for more than 90 days.

Why do you want to relocate the filter location Paul ? If you run a filter you will probably need a fuel pump.. Also as a note the 1990 petcock uses 7mm/ 1/4inch fuel line.

George

My bike doesn't have the clearance for the filter mounting bracket, so for the tank to work I'd have to remove it. I did notice that the petcock mounting boss is the same size on both tanks, but the petcocks are physically different (the 90 is smaller). One option could be to elongate the petcock opening and drill/tap a new mounting hole for the 84 petcock.

[Paul1965]

Glad to help.

What kind of fuel pressure does an FJ fuel pump put out? Can a regular universal type inline fuel pump be used?

[Pat Conlon]

George is the guy to answer this question.......

[Pat Conlon]

.........I did notice that the petcock mounting boss is the same size on both tanks, but the petcocks are physically different (the 90 is smaller). One option could be to elongate the petcock opening and drill/tap a new mounting hole for the 84 petcock.

You know, now that I think about it, if you can do this ^^ it would be your best option.

I forgot that the '90's petcock and fuel line are only 1/4", which is (obviously) just fine for fuel pumps...
You see that the 84's gravity flow petcock outlet and fuel line are larger...around 3/8" or so...
I would be worried about starving my fuel bowls (at high rpm) with a gravity flow system running on low head pressure (from a low fuel level in the tank) and fed by a fuel delivery system choked down to 1/4"

Take pictures for us...show us the way.....Oh yea, Don't forget to safety wire that '84 petcock.  Cheers. Pat

[movenon]

Glad to help.

What kind of fuel pressure does an FJ fuel pump put out? Can a regular universal type inline fuel pump be used?

Its a low pressure pump. I haven't measured the pressure so I can't give you an exact answer. Randy has a pump listed on his sight and there are a number of aftermarket pumps that will work. Randy's indicates 2.5 to 4 PSI.

http://www.rpmracingca.com/proddetail.asp?prod=fuelsystem%3AFP

Here is a link to a KTM site they change there Mitsubishi pump for a Facet 40171. A lot of other bikes have used this pumps also.

http://www.ktm950.info/how/Orange%20Garage/Engine/fuel_pump/facet_40171/facet_40171_install.html

Here are some spec's. They sell the pumps for less than 50.00. And the filters are cheap at less than 10.00. (also the filter screws into the pump so it wouldn't be under your tank. If you convert you should install a fuel pump relay. The 40171 has a fuel shut off built in when no power is on the pump which is a must feature.

http://www.aircraftspruce.com/catalog/eppages/facetpumps.php

Here is a good thread to read also.

http://www.fjowners.com/index.php?topic=9724.0

More to study and I will get back on to the other project next week Paul... I get distracted easy.....  
George

[movenon]

Oh and into the mix of things Paul. The carb needle and seat valves in the fuel pump models are a smaller diameter.
1.5mm for fuel pump vs 2.3mm for gravity feed.

http://www.rpmracingca.com/products.asp?cat=24&pg=3

I am guessing for a parts list to convert would be:
Fuel pump
Filter
Fuel pump relay
7mm / 1/4 inch fuel line
4 needle and seat valves

For a start anyhow.  You should look into the fuel inputs at the carbs also.
George

[Paul1965]

Oh and into the mix of things Paul. The carb needle and seat valves in the fuel pump models are a smaller diameter.
1.5mm for fuel pump vs 2.3mm for gravity feed.

http://www.rpmracingca.com/products.asp?cat=24&pg=3

I am guessing for a parts list to convert would be:
Fuel pump
Filter
Fuel pump relay
7mm / 1/4 inch fuel line
4 needle and seat valves

For a start anyhow.  You should look into the fuel inputs at the carbs also.
George

Well this is looking like it will be a lot more work than I care for. I found some pretty decent priced fuel pumps on eBay, but I think the best option is to try modifying the 90 tank to accept the 84 petcock instead as I really don't feel like messing with the carbs. Thanks to everyone for all the valuable info!

[Pat Conlon]

Pictures, pictures!  (we will put them in the Files for future reference)

[giantkiller]

Someone needs to work out all the details. For the fuel pump conversion. And post it up so, I can convert my 86 over to a pump.
I'm so sick of having to clean out tiny bits of varnish that get in my carbs every couple hundred miles. I've cleaned the tank out three times. But it still keeps happening. 

[Paul1965]

Someone needs to work out all the details. For the fuel pump conversion. And post it up so, I can convert my 86 over to a pump.
I'm so sick of having to clean out tiny bits of varnish that get in my carbs every couple hundred miles. I've cleaned the tank out three times. But it still keeps happening. 

Nice hijack.