Tuning with pressure line length?

[Silent]

Can the pressure line from the pipe to the tank be TOO LONG? I had lengthen'd it a couple race days ago for a more consistent pressure.... but I think thats when my problems started. Two V-Specs have exibited high lean-rev characteristics.

New theory: Longer pressure line actually reduces fuel pressure to the carb, making you adjust it richer.... then the motor does this rev thing, even when your off the throttle...... Weird and very hard to fine the tune.

Gonna shorten it next time out, but thought I would bounce it off you guys.

-Paul (MBX5-T w/non-modded .21 V-Spec)
btw, the pressure line now wraps around the tank twice.

 

[Rolex]

Yes, it CAN be too long. I believe the recommended maximum is 8".

 

[jetmechG550]

Just as it can be too short it can be too long. You're correct in thinking the longer length will smooth out the pressure waves and when you hit the optimal length it will help with a more consistent tune throughout a tank of fuel BUT too long and you get what you are experiencing. On my 5T the line is prolly no more than 5", right off the nipple through clip on the front of the tank I mounted and to the cap, enough slack that it won't pull off or get damaged during a pit stop.

 

[ohmygahitscoby]

Woah, I never knew this. What's the max and shortest length the inline and return can be?

 

[olds97_lss]

Well... there was a lengthy discussion at one point that it isn't even necessary to run a pressure line... It was something done more to assist the fuel to the engine on extended WOT runs and for starting... or something like that.

As for myself, on a small block rig, I haven't had many issues running 4"-8" pressure lines with 4"-8" fuel line. I typically run 8"-10" pressure line on BB rigs with about the same for fuel line.

I've found if I run much longer fuel line or pressure line on SB, the tune gets picky and lean. Same for the BB's.

 

[Silent]

Suspicions confirmed! I got curious as to what I had on there, so I took a measure of the pressure line....... 23" !!!! Whoa. LOL :surrender

 

[jetmechG550]

LOL, cut it down and you'll have plenty of extra for your pit box!

 

[Silent]

The funny this is, neatly wrapped around the tank twice... it looked ok, I had no idea. But I guess buying 2' of fuel tubing, then not having enough to do the fuel side.. should have been a clue. DOH

Thanks guys.

 

[hamz9561]

Along these same lines, would a fuel filter inline on the pressure line keep the pulses down?

 

[olds97_lss]

It may help as it adds capacity to the air in the line.

 

[Rolex]

Along these same lines, would a fuel filter inline on the pressure line keep the pulses down?

It's like having a tank inline with your airbrush. If you run straight off the compressor it sprays in puffs. Add a tank and you have a smooth flow.

 

[pitbull14218]

Now my truck(savage 25) idles funny too, my tank to carb fuel line is just long enough to reach the carb its not tight agaisnt the head but is close, also has fuel filter in it. now my tank to pipe is longer, you think they should be the same lengeth? maybe thats the problem?

 

[Cupooterluvr]

You should make the line to the carb longer because it gives you extra lid time if it flips.

 

[pitbull14218]

See my fuel lines a lil in this picture, but i dont think its that any more, i flipped it a few times and it didnt stall but i ran up to it, but it took probly like 10 seconds to get to it.