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Old 07-29-2005, 07:53 AM
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Idle adjustment - holley 650 dp 4777

I got my timing issue worked out, set at 36* total. The previous cam (edel Perf rpm) needed some help from the secondaries for it to idle in gear. And, I changed from a Holley red to a Holley 110gph mechanical fuel pump. Right now the engine is very responsive to the gas pedal and fires right up upon the turn of the key. The problem I have is that I can't get it to idle below 1200 rpm. The curb idle is all the way out, I also turned out the secondaries. ( I am going to try to turn the secondaries the whole way out and then bottom the screw + 1/4 turn) The air bleeds were bottomed and turned 1.5 turns out, but to get it to idle down slightly, it turned them in about .75. In addition to this, I have 2 light springs on the distributor, which I am going to leave alone until I get this issue worked out. That being said: I can see fuel dropping from the primaries as it is idling. I have a 3.5 power valve in right now, because I had little vacuum with the old cam, but it looks like that won't be an issue with this cam. The PV won't cause me any issues until I "street tune". I am going to attack the float level first. I have sight plugs on the fuel bowls, but they have clouded over a bit and are hard to see. In addition, they don't seem to want to pull out. The fuel pressure seems to be around 7psi at idle (fluid filled gauge goes to 0 as the car warms up, I need to drain a bit of fluid out of the gauge)
So my analysis of potential problems are as follows: 1) Float level too high, coupled with 7psi fuel pressure may be pushing fuel into carb at idle. (I do have pressure regulator from elec fuel pump if necessary) 2) Throttle linkage may be sticking (throttle cable too tight etc) 3) Light springs in distributor causing timing to come in too early. 4) The most hated, vacuum leak The new cam is a Crane solid 116841 112 LCA, 280/288, 518/536. Eddy was 112 LCA, 308/318, 488/510.
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Old 07-29-2005, 04:28 PM
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#2 and #4 are the most likely. Did you make sure that the idle speed stop on the throttle lever is hitting the idle speed screw? If the cable is too short turning the screw won't change a thing. Check for vacuum leaks by spraying suspect areas with wd-40 while the engine is idling. If the rpm drops you've found your leak. If this hasn't found your problem try removing the vacuum lines and plugging them off one at a time.
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Old 07-29-2005, 04:58 PM
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RE: Holley 650

The Holley 650DP 4777 is an excellent carb , I run a modified one on my SBC and it works great. The old 4777 needs modification to work better, 2 corner idle and the old style metering blocks are not acceptable on todays performance engines. That being said, you have other problems--your post doesn't make sense. If you have the primary curb idle turned out all the way, the throttle blades would be closed, shutting off all air flow. The carb linkage is sticking or the throttle linkage of the car is sticking or misadjusted. Also you stated there is a "vacuum leak"--stop the leak before you try to tune the carb. Trash those useless clear sight plugs and use the Holley brass float bowl plugs. Set your float level and adjust your fuel pressure to stop fuel from dripping out of the boosters at idle. Fuel should just barely trickle out of the sight hole at idle. Then try to set your mixture screws with a vacuum gauge to obtain the highest vacuum reading at idle for the best idle with your cam. Make sure your primary throttle blades are set to expose .020 of the transfer slot or close to it and make your final idle RPM adjustment with the secondary speed screw.
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Old 07-30-2005, 06:45 AM
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Walt B - Are you saying that 7 psi is too much for the carb? Is a Holley mechanical fuel pump adjustable? I didn't say I have a vacumm leak, but that it may (always) be a potential problem. My game plan for today is to remove the sight plugs & get the floats adjusted. Pull the throttle cable & see if that's causing the problem. Is there anything else I can use on my newly painted engine & manifold besides WD40 to check for vac leaks? I'm going at it now & hope to have it running well this afternoon. thanks
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Old 07-30-2005, 08:32 AM
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You could use an automotive stethescope, the type with a long needle style probe rather than a bell, to listen for vacuum leaks. Some people use ether or propane to find vacuum leaks but these are really bad ideas.
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Old 07-30-2005, 07:07 PM
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Well, I found my problem this morning. After taking Walt B's advice & trashing the sight plugs (about a 2 hour process to drill out & retap Good advice, I'm sorry I ever used them. It was really simple, & I am only writing this to maybe help someone else in the future. (If not, I may be the worst carb tuner ever ) Anyway, after I pulled the carb and tried to figure out why the primary butterflys were open, but the curb idle screw was not touching the stop. I traced it down to the..........choke side fast idle screw. It didn't make a difference with the last cam because of the overlap & idle speed necessary, but it really gave me fits. Anyway, put the carb back on, air bleeds 1.5 turns out, and a vacuum gauge, I have about 16 inches of vaccum after an additional 3/4 turn, it idles in drive at about 800 rpm, and seem to have a good deal of power. Set the timing to about 36* total. All is well. My plans for any future changes are to reset the air bleed to 1.5 turns from bottom, closing the primary curb idle until the transfer slot looks square, and just opening the secondarys a tiny bit and then start tuning from there.
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