Fuel tank size

[Melnic]

So, I had been wanting to do some tests with the tanks on my older bikes and I did so today.
I have a 1 gallon measuring cup so I dumped fuel from the petcocks (through a filter) into gas cans to measure how much fuel before needing to run reserve. Here is what I got with the 78 special. I have a dual petcock setup and I did this on the center stand. At the end, I leveled out the front tire to match the rear and angled it to also compensate for sag and the results were not much different, only a few more oz came out. I'll also note that when the left petcock went dry while on RES, moving to the right petcock only yielded 8oz (about 3 miles of gas).

1978 Special
ON : 2.65gal (10L)
RES : 0.5gal (1.9L)
Total 3.15gal (approx 12L)

 

[bosco659]

So, I had been wanting to do some tests with the tanks on my older bikes and I did so today.
I have a 1 gallon measuring cup so I dumped fuel from the petcocks (through a filter) into gas cans to measure how much fuel before needing to run reserve. Here is what I got with the 78 special. I have a dual petcock setup and I did this on the center stand. At the end, I leveled out the front tire to match the rear and angled it to also compensate for sag and the results were not much different, only a few more oz came out. I'll also note that when the left petcock went dry while on RES, moving to the right petcock only yielded 8oz (about 3 miles of gas).

1978 Special
ON : 2.65gal (10L)
RES : 0.5gal (1.9L)
Total 3.15gal (approx 12L)

Great info thx. This supports the 2L reserve theory. That said, on my ‘76 which should be a 15L tank, I should have 13L of “ON” fuel, which should give me 260+ km of range. Sounds right.

 

[Melnic]

One thing that can alter results is if anyone is using after market Petcocks. I’m using rebuilt stock petcocks

 

[Kevin Werner]

One thing that can alter results is if anyone is using after market Petcocks. I’m using rebuilt stock petcocks

Yes, aftermarket petcocks may have differing fuel pick-up heights on the main ON position.

 

[bosco659]

Yes, aftermarket petcocks may have differing fuel pick-up heights on the main ON position.

Ok I believe mine are aftermarket so I’ll conduct the same experiment as @Melnic

 

[bosco659]

My right petcock is stiff to turn (but doesn’t leak) so when I drain my tank I suppose I should replace that round rubber seal / gasket. Does the OEM seal work or do you need to replace it with an aftermarket seal?

 

[gggGary]

strongly suggest oem for the four port valve.
PS I believe the standpipe length differs from standard to special tanks

 

[bosco659]

strongly suggest oem for the four port valve.
PS I believe the standpipe length differs from standard to special tanks

K thx. I’ll have to order from my bit so local dealer. Unfortunately all the close Yamaha shops are no longer in business. Closest is about 1/2 hour away. I’ll see if I can order on line.

 

[bosco659]

strongly suggest oem for the four port valve.
PS I believe the standpipe length differs from standard to special tanks

@gggGary , will the OEM four port valve rubber seal work on an aftermarket petcock?

 

[gggGary]

@gggGary , will the OEM four port valve rubber seal work on an aftermarket petcock?

great question!