Forum: HoseHeads Sprint Car General Forum (go)
Moderators: dirtonly  /  dmantx  /  hosehead

Curious on what is the accurate procedure on leaking down a barrel valve. I have seen it described two different ways but you get different results.

First way is to bring your leak down gauge up to 100 lbs and insert the hose to your barrel valve. You read your leakdown on the right hand gauge but the left hand gauge is actually dropped as well and is no longer at 100 lbs.

Second way is to readjust your left gauge back up to 100 lbs before the final adjustment of the barrel valve.

When I do it the first way I am much leaner and the motor is getting hot really quick. The second way does make the motor richer and doesn't get hot as quick but I just worry about dumping to much fuel and contaminating the oil with to much fuel. I am wanting around 18%, Correct?

Thanks for any suggestions and helpful tips!

P.S. I know that the BEST way to get it dialed in is to have it flowed but that is not a viable option at this time and would like some other suggestions that can be made in the shop.

Lots of sites on Google....

Search "leaking down a barrel valve"

Chuck.....

Here is some food for thought.....

Not all gauges are created equal. I have seen gauges that were off as much as 10-12 psi. Also many people tend to struggle with some of those economy dual gauge set-ups. But that doesn't mean that you can't use yours.

18% on your barrel valve is a average random number, kind of like a 70 main jet. It sure leaves a lot of other factors out like fuel pump quality, injector size, nozzle size, camshaft selection, etc.

I suppose the first thing to do is to really look at what the function of what the barrel valve does. It is almost hard to believe that all of the fuel that goes to each cylinder has to pass over that tiny little ramp but it does! The barrel valve's job is to supply fuel at idle and part throttle until the butterflies are wide open. Even then the fuel is passing through it to the nozzles.

My barrel valve setting really serves two purposes. Snappy throttle response and proper fueling - cooling under yellow conditions. If I did not have a leak down gauge to go off of, I would set my barrel valve like this:

• Set all of my butterflies/idle screws so that with a .0025" brass feeler gauge I had a slight drag between the butterfly and injector.
• Take the fitting out of the barrel valve housing and make sure that hole that goes to the secondary is showing along with the opening side of the ramp on the spool. As you open the throttle the hole should start to disappear and the ramp should get larger.
• Start the engine and with the fuel valve full on, adjust the barrel valve lean/rich until my idle was about 1200 rpm.
• Then, slowly close the fuel shut off valve until the idle rpm increase to about 1800-2000 rpm. It should take about 5-7 minutes to get the engine to warm up to 180 degrees.
• Next turn the fuel valve full on. The idle rpm should return to about 1200 and the water temp should start to fall off a bit. Now you are close.

I guess what I am getting at is that with the fuel valve full on your engine should want to cool a bit at idle. That way if you are racing and running 210-220 degrees and they have a yellow, the idle circuit should help cool the engine back down to 190 - 200 degrees. If you are still building temp with the fuel full on under yellow your barrel valve is probably set too lean.

Take off issues: This is probably the most difficult item to diagnose. Because if you are too lean it will stumble and if you are too rich it will blubber. Many people have a hard time telling the difference. The easiest way to diagnose this problem is with the fuel shut off valve. If your barrel valve is too lean and is lean stumbling, if you close the fuel shut off valve about half way and try to take off the engine will either continue tol lean stumble or act like it wants to die or have a dead spot before it gets going. If your barrel valve is too rich and it blubbers on take off, if you close the fuel shut off about half way and it takes off better, you were too rich.

Ultimately, you want to find a balance between having to warm up the engine with the fuel valve partially closed, cooling on yellows with it wide open and good throttle response. Once you have those things dialed in, THEN I would use your gauge(s) to check the percentage of leakage and make a note of it for that particular engine.

A few notes:

• Make sure your secondary is capped off when you check the barrel valve leak percentage
• ALWAYS blow the fuel out of the barrel valve and blow some light oil or mineral spirits through it to displace the alcohol. Alcohol is VERY corrosive! Also it is really hard to get ALL of it out of your pump, barrel valve, by-passes etc.

Good luck!

Rome wasn't built in a day......but they sure didn't
waste any time burning it down!

Mark all I can say is WOW!! Thanks for all that great info. Actually makes me feel kinda dumb to think there was a generic number that would work on every motor. Gonna put your tips to work today and get it dialed in.

Thanks!

Mark, when your leakdown is satifactory (or correct ) shouldnt a driver lean off the motor on yellows to avoid stumbeling, fouling ,or contanimation of oil, while on pace/yellow laps? I think a point missed thus far, is the ambient temprature your trying to warm your motor at, as well as engine heaters helping out in todays pits , what a differance in starting ... thanks for the explaination Mark, well done.. and helpfull..

mark above has given info that is hard to argue or add to, but i can maybe give a simple answer to your qustion. make sure your gauge that shows line pressure reads 100# when you are pluged into the injectors and have the system pressurized. if you set it at 100 and it drops when you plug into the injectors as it will, re-ajust it back to 100. also make sure both gauges on the tool are reading the same! meaning that when you adjust the gauges before you plug into the injectors, run the pressure up to maybe 50 then 80 then 100 making sure both gauges read accuate to each other. it is always nice to have leak down gauges that are accurate to other gauges, but in a leak down situation you are not looking for a pressure, you are just looking for a difference in pressure and how much that difference is. so as long as the gauges are accurate to themselves, you should be good. if you only use the gauges for leak down and they are a few lbs off of say what your pop off gauge reads, i wouldn't be too worried. i would want my pop off gauge to be as accurate as possible. (actually, i am picky and want ALL my gauges to read correctly! lol) i use a .0015 feeler gauge instead of a .0025, but that is just me maybe because i have found that works best for me. also something to check is what your main pill spring is set at. you want some minimum pressure on the spring, say 5-7 lbs. that will help the car to start easier and will give your system a good floor pressure so you will have good idle pressure behind the barrel valve and the system can recover better when you open the throttle. did mark say to disconnect the cross over linkage when you set the injectors with the feeler gauge when you sync both sides of the injectors? i usually do that. also remember to plug the secondary by-pass when you leak down. i also re-check and re-set leak down after starting the motor and setting idle and side by side. then as mark says, you may have to make some at the track adjustments to get things fine tuned and working so that you can idle and take off and race and all that. then just make sure you keep track of your leak down number. you can also re check butterflies with feeler gauge to keep track of your leak down compared to throttle position when sitting on the idle stops after you have raced and made adjustments. if you know how far your butterflies are open and what your leak down is at that point, you should be able to duplicate and keep track of that part of your fuel system setup.

to indy and beyond!!