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Author Topic:   FUEL PRESSURE
GRTWallbanger
Dirt Maniac

Total posts: 196
posted April 23, 2005 01:59 PM  
Was suppose to have practise today but the car runs so ****ty we did not go.I think the thing loads up and floods out the minute you try to idle or take your foot off the gas.Running alky with a by-pass regulator at the back of the fuel log.I can adjust the pressure with the regulator but it does not move more than 1 to 2 lbs when i rev it up.I was told 10psi @ 4,000 rpm.I cant get 10psi unless i idle at 10?Any ideas??

dirtmod0
Dirt Maniac

Total posts: 143
posted April 23, 2005 02:27 PM  
I would first look at the float level and maybe make the regulator is working properly.
I'm no engine guroo but thats where i would start.

James Birmingham
Dirt Full Roller

Total posts: 28
posted April 24, 2005 08:03 AM  
Is it a 2 stage bypass? What fuel pump is it. Most of the big needles and seats won't hold much at idle 3 lbs maybe. In order to flow more they are so big it increases the area that the fuel pushes on and the poor float just ain't got the balls to keep it shut. Not to mention the pulsations that are going on in the pump.

#13 mod
Dirt Full Roller

Total posts: 72
posted April 24, 2005 11:02 AM  
what type of fuel pump do you have? the type of by-pass you have only works with a belt drive fuel pump.

GRTWallbanger
Dirt Maniac

Total posts: 196
posted April 24, 2005 01:47 PM  
I run a mechancial fuel pump (edelbrock)
Just talked to a buddy that runs the same set-up.His psi is around 4 to 5 all the time?I thought you need 10psi at wide open throttle?

49mtmod
Dirt Maniac

Total posts: 127
posted April 24, 2005 03:37 PM  
I've run the mechanical pump like yours with the same set up and set it at 9 lbs. However, my carb would handle 9lbs at idle, it would not handle 10. I definitely would not try 4 or 5.

If your carb will not handle the pressure at idle you may want to try a set up like the C&S mechanical bypass - I've also run one of those and it worked great.


racer50
Dirt Roller

Total posts: 24
posted April 24, 2005 04:36 PM  
Willys has a regulator that is vacume operated. At idle when you have vacume it opens the regulator and you get 4-5psi, when you get on the throttle vacume goes away, shuts regulator 9-10 psi. Also is suppose to help throttle response coming off the corner by not loading up the engine with fuel when you get out of the gas entering a corner. 2 races on ours seems to work pretty well. price about $195 but thats a lot less than burnt pistons

GRTWallbanger
Dirt Maniac

Total posts: 196
posted April 24, 2005 05:10 PM  
How do yo know what the carb can handle at idle???If the needle and seat are not blowing off is that mean it can handle it?I was afraid of running to much pressure at idle and washing the rings down or flooding out when setting at idle for a few minutes?

49mtmod
Dirt Maniac

Total posts: 127
posted April 25, 2005 06:50 AM  
At 9lbs mine would idle like it does at lower pressures - nothing blowing past the needles and seats. We did notice a little fuel would run out immediately after shutting the car off. A quick snap of the throttle to rev the motor up while shutting the car off cured that.

Has anyone ever tried the bypass with idle jet with a mechanical pump?

rpm20
Dirt Freak

Total posts: 338
posted April 25, 2005 06:57 AM  
last year we had the same issue with a mech pump. had to close the reg. completely. didnt need anything except the idle jet on the regulator. it worked great. we now run a tandem pump and have to screw the setting all the way out due to too much pressure. the secondaries made a old faithful immitation when we revved her up, cool but not good.

Dman
Dirt Freak

Total posts: 270
posted April 25, 2005 07:31 AM  
We tried running a by-pass regulator with a mech. pump. I had to put a larger jet in the by-pass to get the pressure down to 4 psi at idle but I could only get 7 psi at 3500 rpm.
Pump mans. say to use a barrel valve type bypass like C&S or Barry Grants.The BG unit is pricey and still doesn't handle the pulsations at idle (will still flood).
I am going to try the new "Racepump"piston pump
designed by Howard Stewart.He says to put the by-pass regulator back at the tank with a regular low pressure fuel line from the fuel log to the by-pass at the tank. The fuel line will then absorb the pulsations from the pump curing the flooding at idle.
The race pump is still cheaper,lighter and simpler than a belt drive set-up. We'll find out.

dgb
Dirt Full Roller

Total posts: 70
posted April 25, 2005 07:44 AM  
Some type of two stage regulator setup is best, but I've always gotten by just running about 4 psi for all engine speeds. Any more than that would sink the float and flood it out. In fact it's iffy getting it to work at 4, but I didn't have the guts to go any under that. With alcohol, 9 psi at anything other than WOT is probably way too much in my experience.

Rat Trap
Dirt Maniac

Total posts: 129
posted April 25, 2005 02:47 PM  
i'm running the same fuel pump as you are, but we were told to put our regulator in the front of the fuel log, we run around 10 at idle and have had no problems.

GRTWallbanger
Dirt Maniac

Total posts: 196
posted April 25, 2005 06:24 PM  
Rat Trap?Does your regulator have a jet in it?And then do you still run a return line to the tank?I actually thought about trying the reg, there but was afraid of such high pressure at idle?I even ran the motor with no regulator and no return line.I had 14psi at idle.

Scottavery
Dirt Roller

Total posts: 18
posted April 25, 2005 06:43 PM  
For 7 years we have run a Nuyten carb with Holly regulator at 6.5 lbs pressure. He uses a ball type seat instead of a neddle seat. The "only" time I have ever had a problem is when I forgot to put top oil lube in the fuel. I use Klotz Uplon top lube and this stuff is great. You will not have any corrosion problems and we have never had an alky stain on a cylinder wall or anything like that.

Rat Trap
Dirt Maniac

Total posts: 129
posted April 25, 2005 06:49 PM  
I don't know exactly what you mean by a jet, but it is adjustable. It has one inlet and 3 outlets. one outlet goes to the fuel log and one outlet is the return line, we actually run our return line back to our filter instead of the tank, but that won't make a difference where your concerned. the other outlet we put a plug in. It also has a vacuum on it, but it isn't used and nothing has to be done to it. Go to summit.com and put this pn into the search. AEI-13301 that is the one we have, didn't buy it from summit but thats it. Hope this helps.

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