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Holley carb.

Coloradodave, thanks for the video. I have watched it several times before and again just now. Still gives you now idea of what the entire selection of colored pump cams will do. I just got another Holley book and have gotten into it already. Nothing replaces direct experience. I moved my cam position up one click and started the engine the first time since assembly. Started right up, but idled at 2500 rpm. Shut it down and backed off on all idle adjustments. Still 2,000. Moved primary cam back to #1 position and idle cam right in at 800. Had to rally loosen the primary accel pump to no contact, but still giving shot when throttle first starts to open. Vibration was indeed causing a small shot to feed the venturis at that initial fast idle. I think the experience of this exercise has given me incite, feel, for what needs to be done on the primary. The secondary, I had this too tight as well. It was shooting fuel into the venturi at that fast idle, so I backed off on it until it no longer added fuel to carb when not wanting it, but still opening when the throttle called for it to open. I have not used the feeler gauge to set either the primary or the secondary, but am making sure the accel pump diaphragm is not being jammed at WOT. I made sure the arm still had some play.
I do have a question. Someone said they set the idle using the secondary idle adjustment screw. I believe the engine builder moved the adjustment screw to the top of the throttle lever. Not sure when to use this to adjust idle as opposed to just using the primary idle adjustment screw. Do they both do the same thing? Do they have an effect on timing, on the idle adjustment mixture settings? I found in the Haynes Holley book that one should tighten the secondary idle adjustment screw until it just touches the secondary throttle lever and go one more turn. Anyone disagree? If I am correct and the adjustment screw has been inverted so you can make adjustment from top of carb, will I have to back off on the screw instead of "adding one turn"?
Cornpatch MO, Thanks for your input and reference to cam video on Summit.
Garys1969RR....OK, I took out the primary mains......74s......what should I buy if I was buying a set of say 10 sizes? I did not pull the secondaries and look at them. Would you expect them to be different? Do you still think that I need to richen by going to 88s? When I pulled my plugs, a couple looked ok, but more than half were sooty. Not a big build up, but covered with soot.
Some one mentioned that they had success using the blue cam. Any agreement or disagreement? Again, what I am looking for it slow to med range response. I'll leave burn out and top end to the racers. Thanks again for all the time being devoted to helping me get up on that learning curve. Give me back my Alfas with mechanical fuel injection or a set of Webers and I would be more comfortable, however, with all your advice I think I will get there on the 440 with dbl pumpers. Thanks.
 
Sputnik I think you need to slow down & go over all your settings again. I only used one 850dbl pumper & that was racing. If I remember right my stallspeed was 4-4500& I would power brake at 15-2000rpm and then nail it, so my acc.pumps were set up for a delay right off idle; not what you want in a street car. I never remember setting either pri or sec changing the other side AND no carb setting will ever change the timing.
 
Jim, The main thing to remember is to adjust the arm so that ANY movement of the throttle when accelerating from normal hot idle, choke off, moves the accelerator pump arm. If there is any slack you will get a hesitation as the engine goes lean before the accelerator pump shot comes in. The other important thing is that when the throttle is WIDE OPEN, there is .015" that the arm could still move, insuring that it is not bottoming out the diaphragm. You can achieve this by moving the accelerator pump cam from one hole to the other, changing the cam profile or even bending the arm where it rides on the cam. After these basic adjustments are done, everything else is peculiar to your combination. What someone else runs has no bearing on what will work for your engine.
As far as the secondary idle adjustment screw, you want to back it out so the throttle blades are completely closed, then screw it in until it contacts the linkage and then 1/2 to 1 turn more. This is to insure that the throttle blades don't get stuck in the bores, although not likely in a double pumper, due to mechanical linkage. Very important on a carburetor with vacuum secondaries.
Tuning is all about putting in the time and experimenting with different combinations. If it's not your cup of tea, you can take the car to a chassis dyno shop and pay them to make it razor sharp...as always, it's time verses money. Good luck.
 
Dave, thank you for your input. I will finish the set up tomorrow. Got the valves adjusted, intake manifold back on (not so easy with one old, short person), the carb on, bought a accel pump cam kit and set timing and idles. I thought I'd be ready to rumble but I lost fuel pressure and had to trace it down and go to town to fine parts for the gauge set up. I must have over tightened the new gauge and cracked the area at the top of the threads. Bought brass. Always something, and usually self inflicted. My wife thinks I should call it quits, take it to the race mechanic (I live in the Ozark and people here think a Dyno is another prehistoric critter) and just drive the Viper (garage Queen). Question.....is there any problem with running one cam on the primary and a different cam on the secondary. I don't see why not, but I thought I better ask. I could not verify that in the Holley book. Any suggestion on what color of cam(s) to start with?
 
Dave, thank you for your input. I will finish the set up tomorrow. Got the valves adjusted, intake manifold back on (not so easy with one old, short person), the carb on, bought a accel pump cam kit and set timing and idles. I thought I'd be ready to rumble but I lost fuel pressure and had to trace it down and go to town to fine parts for the gauge set up. I must have over tightened the new gauge and cracked the area at the top of the threads. Bought brass. Always something, and usually self inflicted. My wife thinks I should call it quits, take it to the race mechanic (I live in the Ozark and people here think a Dyno is another prehistoric critter) and just drive the Viper (garage Queen). Question.....is there any problem with running one cam on the primary and a different cam on the secondary. I don't see why not, but I thought I better ask. I could not verify that in the Holley book. Any suggestion on what color of cam(s) to start with?
Notice--- there are specs for the different colored cams in some of the Holley books. However, They are for the 50cc accelerator pumps. The book I have doesn't go into the 50cc pumps very much . I would guess that for a mechanical secondary 4250, you could put a 50cc pump kit on just the secondary ?
I have to rethink my power valve requirements. For some reason, I thought my vacume was very low, like about 3-4 inches at idle . I didn't check it with mu gauge and just went ahead and put a 2.5 power valve in. Bad on me. I still have a bad stumble at low RPM when I punch the throttle in low gear. So, I found my vac. gauge and I actually have 12.5 inches of vacume at idle. Drops and then recovers quickly when I blip the throttle all the way-- no load.
How do I determine what power valve I should use?......Thanks.......................MO
 
General rule of thumb on a power valve, is that you want it to be about half of what manifold vacuum is at idle. So being that you have 12.5" vacuum, you should have a 5.5 or 6.5 P/V. I'm not surprised that you get a stumble at part throttle with a 2.5 power valve. It's opening way too late.
 
General rule of thumb on a power valve, is that you want it to be about half of what manifold vacuum is at idle. So being that you have 12.5" vacuum, you should have a 5.5 or 6.5 P/V. I'm not surprised that you get a stumble at part throttle with a 2.5 power valve. It's opening way too late.
It gets confusing. Vacume holds the power valve closed which blocks off additional gas. Dropping the vacume because of acceleration opens the power valve ( the " at rest" position) and lets additional gas into the venturies. So in a 2.5 power valve, any vacume above that holds the valve shut--no additional gas .
After adjusting the idle mixture screws ( 4 of them in a 4250) my vacume at 650 RPM is 12-13 inches. I installed a 6.5 power valve. So that means when the vacume drops to below 6.5 inches , the power valve opens , and lets additional gas into the venturies.
I have read several things about adjusting the accelerator pump , and some of them are a little confusing as to where and how much to set some clearance. I set mine so that at rest, (idle) there is no clearance where the pump arm contacts the pump lever. however there is supposed to be .015 clearance at full throttle to keep from rupturing the diaphram or bending linkage.
Bad storms here including tornados. the wifey and the dogs went to the under-house storm celler, and I was close by! So, I weill try out my carb changes tomorrow.
 
Is there a way to test to see if the power valve is operating as it should? .....................MO
 
Is there a way to test to see if the power valve is operating as it should? .....................MO

Any speed shop or performance oriented auto parts store will have a vacuum tester for the Holley power valves. Unfortunately, it only tests the diaphragm, not when it opens. I used to push the valve end in and put my tongue on the diaphragm side and then let go. If the diaphragm is good, it will hold vacuum against your tongue.
Mo: Your adjustments should get you in the ballpark.
Jim: You can mix and match pump cams. Not a problem.
 
Any speed shop or performance oriented auto parts store will have a vacuum tester for the Holley power valves. Unfortunately, it only tests the diaphragm, not when it opens. I used to push the valve end in and put my tongue on the diaphragm side and then let go. If the diaphragm is good, it will hold vacuum against your tongue.
Mo: Your adjustments should get you in the ballpark.
Jim: You can mix and match pump cams. Not a problem.
That is what I did. I had several power valves, but the size rating marking is so bad, you can't see them even with a magnifying glass. The new 2.5 valve was clearly marked.
I read that you can take a hand vacume pump that has a built in vacume gauge , and not only test if it is working, but also the inches of vacume when it closes-opens. ..............MO
 
Sorry if I am posting to much on someone elses thread, but hopeing my experiences now, is helping someone.
I took Brutus out on a test run, and what I have done has helped a lot. Next thing to do is check the float level this afternoon, and start playing with main jet sizes later. I can not get this thing to show running rich at any time, and the squirter nozzles are plenty big. (.042) I may need a 50cc accelerator pump and experiment with the pump cams. ..............................MO
 
Mo the 50cc pump only gives you a longer (time) shot, the amount coming out is all dependant on nozzle size.
 
Also the 50cc pump only works with good with certain of the acc.pump cams if I remember right.
 
Sorry if I am posting to much on someone elses thread, but hopeing my experiences now, is helping someone.
I took Brutus out on a test run, and what I have done has helped a lot. Next thing to do is check the float level this afternoon, and start playing with main jet sizes later. I can not get this thing to show running rich at any time, and the squirter nozzles are plenty big. (.042) I may need a 50cc accelerator pump and experiment with the pump cams. ..............................MO
Try to make just a little improvement, and everything goes to he**! I tried adjusting the front float. Couldn't get gas to come up to the bottom of sight plug. In so doing, the needle and seat flats for the adjust nut got so far down, I couldn't get them back up again. Finally got it back up again to catch the adjuster nut flats. Then the engine would not idle at evem 1000+ RPM. Ran real rough, like way to much gas entering. backed off the accelerator pumps a little. Did I blow the power valve? I could not get the gas level in the bowl to stop running out the sight plug. Must be the needle and seat not shutting off the fuel and dumping it into the carb. So I take off the fuel bowl and take out the needle and seat. Power valve is working OK. Maybe there was something in the needle and seat , but I couldn't find anything. So, it sits on my bench until tomorrow and a better attitude from me !.I think I will make sure the float does not have gas inside of it. ................MO
 
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