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Old 11-01-2009, 02:14 PM   #1
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Default Pressure Line Question

I just lengthened my fuel line to make sure I don't have issues when I am upside down. However, my car has recently become hard to start. I think it is because I have less pressure now because of the added fuel line. Assuming I am right, should I shortened or lengthen the pressure line or leave it as is and try and re-tune. What changes should I expect when the fuel line has been lengthened?

Also, my car has started faming out at pit stops. Is this related or something completely different?

Last edited by petevette; 11-01-2009 at 04:29 PM.
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Old 11-01-2009, 02:46 PM   #2
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There are so many factors that can cause the symptoms you have described. How many gallons is through the engine, what engine, how is your glow plug, how soon does it flame out after you flip, how is your clutch (Shoes, springs, bearings).

I think I read somewhere the pressure line should be half the length of the fuel line, but i could totally be wrong. I just have my lines nice and clean and tight, sorta like my racing line
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Old 11-01-2009, 04:38 PM   #3
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The engine has 1 gallon and runs well. I haven't had a flameout problem when upside down, but wanted to prevent getting one since we have some slow turn marahalls. I haven't checked the plug in a few races.

The flameouts come only on refuel once my car has been dropped and I gun it. Half way out of the pit it stalls. Oh, on warms up I heard a sound twice like a backfire.
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Old 11-01-2009, 04:59 PM   #4
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i found that longer fuel line is worse for slow marshalls, if they are slow then there is a bigger bubble in the line once they flip it and you flame out every time. just tune your motor right and it should idle fine upside down, if you sit there and rev the motor it sucks more air into the line quicker. the best solution is a clunk style tank, like losi, and this mod can be done to any tank very easily (as long as the tank does not have really tall internal chambers that can make the clunk stick on top higher than the fuel) with the use of an airplane tank clunk and a drill bit that is about 2mm smaller than the od of the fuel line used.
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Old 11-01-2009, 05:13 PM   #5
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Changing fuel line length alters your tune. Retune.

Don't overdo it. The line routing in AE's or XRay's instructions is about right for most cars. I keep my pressure line as short as possible, about 8 inches as I want its bends to be smooth.

Fresh air filter, fresh clutch and bearings, fresh DUBRO fuel line, fresh glow plug and retune with fresh fuel.

You engine will change tune at 1 gallon and again at 2. It's hard to recommend stuff without being there, take it to the track, make a fellow racer help you tune by holding him at gunpoint.
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Old 11-01-2009, 05:22 PM   #6
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Originally Posted by j_blaze14 View Post
just tune your motor right and it should idle fine upside down
x2. My Grenade idled beautifully yesterday while it was upside down. I took my time and walked off the drivers stand, onto the track marshalling myself. Never did the engine rev or bog.
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Old 11-01-2009, 06:04 PM   #7
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Originally Posted by petevette View Post
The engine has 1 gallon and runs well. I haven't had a flameout problem when upside down, but wanted to prevent getting one since we have some slow turn marahalls. I haven't checked the plug in a few races.

The flameouts come only on refuel once my car has been dropped and I gun it. Half way out of the pit it stalls. Oh, on warms up I heard a sound twice like a backfire.
A backfire ussualy means you are too rich. And just b/c your glow plug lights it doesnt mean its good. Get your truck started and at a good operating temp, bring it back in and while the engine is still running put on your glow ignitor, if you hear a change in idle, your plug is not at 100% working order.
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Old 11-01-2009, 08:40 PM   #8
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Great input guys, I will check/try some of this stuff next time out.

So to summarize, the shorter the pressure line the better? Meaning that the shorter the line the higher the pressure?
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Old 11-03-2009, 03:05 PM   #9
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Great input guys, I will check/try some of this stuff next time out.

So to summarize, the shorter the pressure line the better? Meaning that the shorter the line the higher the pressure?
Too short of a pressure line can cause an inconsistant tune. You want between 6-8 inches to equalize the pressure, too short and the pressure in the tank will pulsate. Too long and you can't get enough pressure consistantly.

Also, if your fuel line is too long it will cause problems. Imagine if you hook up a hose to a hose bib and turn the water on. If you add another hose you lose pressure at the end. Keep adding hoses and eventually the water will just dribble out. The pressure at the source has to push more and more fluid at once.
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Old 11-03-2009, 07:57 PM   #10
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After reading everyones suggestions I would add taking a look at your fuel tank itself! Sometimes the rubber seal thats in the lid goes bad causing all kinds of problems! Suberse it in water leaving the lines connected to the tank out of the water and blow in your pressure line. If bubbles appear around the lid you've got a bad seal.
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Old 11-03-2009, 09:02 PM   #11
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what engine and tune pipe you are running ?
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Old 11-03-2009, 09:43 PM   #12
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...it sounds like your low speed needle is rich, and /or your glow plug is pooched ( backfire )
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Old 11-04-2009, 05:54 AM   #13
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Quote:
Originally Posted by NitroFreakManHo View Post
...it sounds like your low speed needle is rich, and /or your glow plug is pooched ( backfire )
+1.......when your pit crew refueling and before he drop your car on the pit lane, try rev your engine to clean up your low end and this I feel can solve your stalling problem after refueling. Looking to hear from you soon what you find. I also learning.
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Old 11-04-2009, 06:59 AM   #14
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Default 8 " Pressure 8" supply

My engine guy (Monty Houston) swers by that rule. I haven't had any issues with mine when she's turtled. I just cycle the throttle to keep the pressure up. If your clunk has a line long enough to keep it picking up fuel I dont think the motor cares which way it is as long as you give it fuel. just remember to let off the throttle while the marshaller picks it up.
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