Fuel tap options

[Digs]

Ahh okay! Well that’s good to know! Cheers for the heads up 

[Digs]

Also now tried a second tank that I know is good with two different fuel taps. Same issue. 

[coombehouse]

Part of the issue maybe because you are not comparing like with like.

The auxiliary tank @ 1m above the bike will provide a much greater head pressure than 1-2l of fuel in the actual tank. No doubt the fuel tap flow is marginal however you may find the problem vanishes with a full tank of fuel.

[DAZ]

20 hours ago, Upshotknothole said:

Make sure the lines aren't getting pinched under the tank when it's back on? Don't need much fuel in the tank to rev it in the garage.

Different tanks and taps same issue ,so get some new pipe , the fancy clearish one that's ethanol proof , someone told me old pipes can degrade internally and cause issues. Top to bottom eliminate the possibility cap,vent,tap,hose you know it runs on the auxiliary tank so it shouldn't be carbs 

Edit it's called tygon hose 

Edited July 12, 2023 by DAZ
Added text

[Digs]

2 hours ago, coombehouse said:

Part of the issue maybe because you are not comparing like with like.

The auxiliary tank @ 1m above the bike will provide a much greater head pressure than 1-2l of fuel in the actual tank. No doubt the fuel tap flow is marginal however you may find the problem vanishes with a full tank of fuel.

That's a good shout, either way I want enough fuel flow at low fuel levels so that I can at least limp it to a petrol station if needs be. 

1 hour ago, DAZ said:

Different tanks and taps same issue ,so get some new pipe , the fancy clearish one that's ethanol proof , someone told me old pipes can degrade internally and cause issues. Top to bottom eliminate the possibility cap,vent,tap,hose you know it runs on the auxiliary tank so it shouldn't be carbs 

Edit it's called tygon hose 

So the hoses are 8mm ID and less than a week old so they shouldn't be an issue.

I have found a few things that seem to have mostly resolved the problem:

• Shorter vac line with a slightly smaller ID
• Different routing of the fuel lines  (not sure really if that has made much of a difference)
• fully charged battery, the CDI doesn't like to spark with a low battery

 

[Upshotknothole]

30 minutes ago, Digs said:

That's a good shout, either way I want enough fuel flow at low fuel levels so that I can at least limp it to a petrol station if needs be. 

So the hoses are 8mm ID and less than a week old so they shouldn't be an issue.

I have found a few things that seem to have mostly resolved the problem:

• Shorter vac line with a slightly smaller ID
• Different routing of the fuel lines  (not sure really if that has made much of a difference)
• fully charged battery, the CDI doesn't like to spark with a low battery

 

With as tight as everything is between the tank and the carbs on these bikes, fuel line routing is very important. It's super easy to pinch a fuel line when putting the tank back on. Clear fuel line makes it a lot easier to troubleshoot, at the very least some clear fuel filters will help you see what's going on.

[coombehouse]

3 minutes ago, Upshotknothole said:

With as tight as everything is between the tank and the carbs on these bikes, fuel line routing is very important. It's super easy to pinch a fuel line when putting the tank back on. Clear fuel line makes it a lot easier to troubleshoot, at the very least some clear fuel filters will help you see what's going on.

Problem with filters is that they often are a restriction themselves, particularly the cheap ones readily available. Not ideal if everything is marginal. Nothing is easy!

[Joseph]

Indeed you must not use inline car type filters on gravity fed systems

[Digs]

2 hours ago, Upshotknothole said:

With as tight as everything is between the tank and the carbs on these bikes, fuel line routing is very important. It's super easy to pinch a fuel line when putting the tank back on. Clear fuel line makes it a lot easier to troubleshoot, at the very least some clear fuel filters will help you see what's going on.

May well have to give the tygon a go then, nothing to loose! 
 

 

[Digs]

All sorted and running well, here’s a cold start. 

Thanks every one for all the advice and help. I’m delighted it’s a simple fix. 

[Wagola]

and the answer was ??

[DAZ]

Pinched fuel line ? 

[Digs]

So the difficult thing is there was no one thing that made a massive difference.  

if I had to say it was probably a mixture of a worn fuel tap and the ID of the vac lines. I’ve re-routed the fuel lines and shortened them, but I was having the same issue with tank sitting above the bike on the frame. 
 

[baldrick]

the fuel lines are easily pinched, and some rubber lines restrict flow on bends...... the standard bike came with springs around the lines to prevent this. 

im also using tygon lines, theyre a bit expensive, but worth it, as they dont solidify over time or degrade from the inside , over time, especially with the crappy fuel we have to put up with these days.

 

anyway, good you got it sorted

[Upshotknothole]

I usually try and stick with OEM vacuum lines as there's not a ton of vacuum coming off the intake to open up the petcock. Glad you got it sorted.