Reserve setting on petcock not working

[vanbiker]

I'm very frustrated with this problem, but I would like to know more about the fuel line arrangement out of the gas tank on my 1970 CB750. I have a very low (60 miles or so) effective range because when my fuel level gets lower the engine stalls because of low fuel flow, I switch to reserve and no help, but there is plenty of fuel in the tank. I removed the petcock and cleaned and checked all ports and it seems clear, I cleaned the brass filter screen, replaced the fuel lines and cleaned out the inline filters, still no luck. When I disconnect the fuel lines from the tank and turn on the petcock to reserve, fuel flows fine. There are two fuel lines coming out of the petcock routed to the fuel bar next to the carbs....are they the same? Is one for reserve only? I'm confused!

 

[Staubig]

I'm very frustrated with this problem, but I would like to know more about the fuel line arrangement out of the gas tank on my 1970 CB750. I have a very low (60 miles or so) effective range because when my fuel level gets lower the engine stalls because of low fuel flow, I switch to reserve and no help, but there is plenty of fuel in the tank. I removed the petcock and cleaned and checked all ports and it seems clear, I cleaned the brass filter screen, replaced the fuel lines and cleaned out the inline filters, still no luck. When I disconnect the fuel lines from the tank and turn on the petcock to reserve, fuel flows fine. There are two fuel lines coming out of the petcock routed to the fuel bar next to the carbs....are they the same? Is one for reserve only? I'm confused!

This bike is a little further back than my knowledge covers, but do the two fuel lines go to the two different carbs?

 

[tommycarl]

Maybe a stab in the dark, but is there a chance that the vent on your gas cap isn't working? If not, gas could just stop flowing after a relatively long ride. If you've opened the cap to check fuel and it still doesn't flow, the vent is likely not the problem.

 

[vanbiker]

This bike is a little further back than my knowledge covers, but do the two fuel lines go to the two different carbs?

It seems both lines go to a fuel rail that is between two of the four carbs.

 

[vanbiker]

I don't think that is it, since being warm is not related, just being low enough on fuel to stop flowing through the regular setting on the petcock. When on reserve, the engine sort of runs-like it is starved for fuel but is getting enough to start.

 

[dan1951]

The two outlet lines going to the carbs come from one internal outlet in the petcock, The only difference is in the on position the fuel is fed down the riser tube in petcock which is approx. 3" long below that it will run out of fuel, Turned to the reserve position fuel is drawn at the bottom of the petcock. I had a problem running Wix model number 33011 filters that would not flow below half a tank, I just removed them and it would run till the tank was empty. Kinda weird but true.

 

[vanbiker]

The two outlet lines going to the carbs come from one internal outlet in the petcock, The only difference is in the on position the fuel is fed down the riser tube in petcock which is approx. 3" long below that it will run out of fuel, Turned to the reserve position fuel is drawn at the bottom of the petcock. I had a problem running Wix model number 33011 filters that would not flow below half a tank, I just removed them and it would run till the tank was empty. Kinda weird but true.

Ah, that seems to have worked, yeah! Thanks for the tip. But now I'm concerned about clogging up the carbs, since my tanks has some rust on the inside. Are there other filters that may work that you know of? Is the screen filter in the petcock sufficient to protect the carbs? Were filters in the gas line original equipment? Many thanks!

 

[dan1951]

The early models We have did not come with external filters, I do not know about the newer models. Perhaps someone using inline filters could help us both out. Take Care.

 

[dirtdigger]

I have always used inline filters and have never had an issue. I have used the wix filter before also, but it is long and you normally have to have a big fuel line loop to get it to fit and that can cause problems with slow fuel flow. Normally the fine mesh screen inside is enough to catch anything that will cause an issue. With the gravity feed anything you put in line will cause a reduction in flow to the carbs. The lower the fuel level the lower your flow because you have less pressure from the lower fuel height in the tank. If your tank is rusty then I suggest cleaning it out so you dont have to worry about the rust and just use the screen inside the tank.

 

[dan1951]

Thanks Digger, I just use Your advice and keep the petcock filter clean.