Just started to drive my Roadster here in Sweden Specs: Chevy 454 Holley strip dominator intake 049 oval port heads BG 750 racedeamon carb, ( mech. secondarys ) Compcams 270H, specs: 224* 224* @ 050 510 - 510 lift Lobe sep 110* Intake vaccum at idle are 12 in-hg Runs very nice on idle and slow driving Need some advice on main jets and power valves Later on i drive it with a broadband lambda i have welded in the bungs in the headers
Hello from Alabama, USA. We'll need a little more information about any problems you're having. Does it have a bog/flat spot coming off the line under hard accleration? Etc.........
Above app. 2000rpm ( no tacho yet ) The 454 are runnin rich I have not check the jets size or power valves in hg Just want some andvice for a starting point at jets and valves ( I dont know where the carb have been before )
is it running rich just under full throttle above 2k or is it also running rich cruising at 2k? Whats your vacuum at cruise at say 2200rpm? Is this on flat ground or cruising up a mountain? I would think as a starting point it would have somewhere in the 72-76 for jets. Your powervalve just nds to be low enough so you arent opening it up just cruising around normal and at cruise, so maybe a 6 just for starters. the power valve should have a number stamped on teh side of it, that is how many inches of vacuum it opens up at. thats a real mild cam, so should make good vacuum just about all the time. putting in a low number will ensure you arent opening up too early, but it will depend on your driving style,gearing, trans etc...
Its the first ride with this 32 If i just hold it at 2000 rpm , maybe 2500 at PARK I can hear and see down in the carb, runnin rich ! I have dont check the vacuum when driving or above idle I check what jets and valves in it ...
If this info OK ? -- I goggled 12 In Hg-- The number stamped on a power valve, such as 65, indicates the manifold vacuum below which the power valve is operational. In this case, all manifold vacuums below 6.5 Hg, the power valve is operating. Generally a 65 power valve is sufficient for most high performance applications that have a manifold vacuum of 12 Hg or higher. However, some problems can result with radically cammed machines equipped with automatic transmissions. These vehicles often idle at 2000 rpm, approx. 6.0 Hg. At this point the main nozzles are starting to feed and richen the mixture (supplied by the power valve) and the engine will probably load up. To correct this problem, install a 45 or 35 power valve. If the engine has a manifold vacuum of 12 Hg or less, a good way to determine power valve size is take the manifold vacuum at idle and divide that number by two. The answer is the power valve size. This will provide idling and proper fuel flow under wide open throttle conditions when manifold vacuums seldom rise above 1 Hg.
As your google search indicated, as well as my post, a 6.5 pv is a good start. You dont need to worry about the radical cam part as your 270h is a mild cam. First thing to do is to check the power valve...as well as make sure the choke(if it has one )cant close when running and lastly you might try a short drive without your aircleaner to make sure its not a resrtriction causing it to run rich. At least blow your filter out with compressed air from the inside...
I have check the jets and PV´s Primary: 85-85 jets, PV 4,5 Secondary: 86-86 jets, PV 4,5 What is normal for my engine ?
My advice is plug the PV, and run 84 square...Thats what I do anyways. You could also run a 2.5 pv and 84 square as well... Running a PV plug will allow tune ability. Many disagree on this topic, but there is a reason Holley offers plugs. I swear by them.. Keep in mind, fuel atomization is crucial for HP and TQ. running to lean say in the low 70s for jets in a 750 will do nothing but hurt you, perhaps burn a valve on the freeway. The best way to tune is with a o2 sensor device, but they are pricey for a one time use. I am assuming that over 2000 rpms your not into the secodnarys, so you have a PV opening causing your rich mixture. That is why I say 2.5 or plug.....I am also assuming your plugs are thr right heat range, and your ignition is good...
Wth an automatic, idle speed in gear. Check main manifold vacume port reading and divide by 2. This should be your power valve number. This is per Holly tech guy.
If plugs are black & sooted the you need to troubleshoot. You are not tuning. The tuning begins when you have problem solved. What you have is raw fuel running into the engine from a blown powervalve or wrong meteringblock gasket or powervalve gasket installed wrong. Once you have solved the raw fuel problem then you'll need fresh plugs, new store bought ones, and the you can tune. Show us pictures of your metering block, the metering block gasket and the face of the throttle body - i believe that carb takes a special gasket - does it have aluminum metering blocks? it might be sending idle circuit fuel right into a vacuum port dribble into the engine under the base plate.
The jets was to big Primary: 85-85 jets, PV 4,5 Secondary: 86-86 jets, PV 4,5 I changed to 78-78 in primary , much better That was jets i had at home Maybe needs some 72-76 as advice before in this thread
absolutely !!... Tuneablity / driveability The reason I say do this, is. If you go to small on the jets, your fuel atomization in the venturi's will be lean, and your cylinders will run hot. Normaly when you plug the PV, you jump 4 jet sizes, to offset on the strip, but on the street, if you are already running rich, you can square the jets, say at 84, retaining fuel atomization, in the venturis. If you have a PV opening for what ever reason, you now take out that variable. Which ever you decide, make sure you check with Holley about running a small jet, say down into the mid to low 70's, you dont want to burn a valve.
Later on i drive it with a broadband lambda i have welded in the bungs in the headers I just wanted a good starting point in jets and PV´s
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