petcock question

[Drumagician]

What is the difference between the PRI and RESERVE position?

[Incubus]

Reserve feeds through a lower pipe and is used when you run low on gas on RUN. Prime bypasses the vacuum closure function and allows fuel to flow unimpeded. You could run on PRI, but then when you run out of gas you are done. PRI is normally used to refill the carbs when you have drained them completely, either by neglect or on purpose.

Patrick

[DGXSER]

Reserve lets you use the last bit of fuel in the tank. It is intended to give you a warning that your about out of fuel and better head to the petrol station.

Prime is the bypass to the vacuum valve. It is intended to let the empty carb bowls fill with fuel after carb work or perhaps sitting for a while where some of the gas in the bowls might have evaporated. Another key point is that PRIME eliminates the reserve function, as in when your running on PRIME, and the bikes gives you subtle sputtering to say "switch to reserve", there ain't nothing left, it drained the reserve part of the tank to.

[Drumagician]

I guess that leads me to another question that I have been wondering about. I have no vacuum function on my bike. No vacuum line on the petcocks, and I have read that when there is no vac line there is supposed to be a octy mounted to the carbs. Well, I don't have that either. Just straight gravity to the carbs. This is ok right?

[DGXSER]

Looks liek you have the Special model. Which means your petcocks are four function, ON, PRIME, RESERVE, and OFF. They also have two outlet nipples in each petcock. When mounted to the correct side of the bike (they have an L and an R on the petcocks to indicate which side they go on) the rear outlet is the ON and RESERVE outlet, the front is the PRIME outlet.

Straight from the factory the bike had a vacuum operated duel feed and dual outlet fuel valve that is vacuum operated, comonly called the OCTY. The purpose was to cut the fuel flow to the carbs when the engine was not running. It can be problematic, so alot of folks eliminate it and just run the fuel straight to the carbs from the ON/RESERVE outlet of the petcocks. Some folks T the PRIME outlet into the line to the carbs, some just plug it off and never use PRIME again. In the process of eliminating the OCTY, the ON function is now the same as PRIME anyway.

Is it OK? Well, it has worked well for me on every Special I have owned and worked on.

[Drumagician]

sweet. That sums it up very well. I will cap that pri off and eliminate some spaghetti.
Thanks!!

[DGXSER]

If you do run without the Octy, I DO receommend turning the fuel petcocks to OFF when not riding. The carb float valves SHOULD keep the fuel from overflowing if they are left on. However, they can fail and leave a rather large pool of fuel ont he bike and the floor, and even cause a nice fire. So, yeah, turn them to OFF when not riding/running the engine.

[bikerphil]

Not to mention a crankcase full of fuel and oil mix.