Hi all, I am getting rather frustrated with my timing on this thing, and I am at a loss? I have a cammed 350, HEI converted, T/A Stage intake, 10:1 Compression. I have full advance timing at 30 deg, at about 3000 RPM's(Poston book says 35). I am running 93 Oct gas, and I get detonation at high RPM's, and at cruising speeds(cruising meaning 75MPH). The carb is a Holley 750 vac with 65 jets in primaries, and 76 jets in 2nds. Am I overlooking something here? What could be causing my fine little motor to sound like a Buick Diesel? Thanks, -Jon
Sounds like I have about the same set up here. TA 212 hyd. cam with stage 1 intake, everything else is pretty much stock, still running quadrajet also. I also just switched to HEI, and an Accel super coil and Accel spiral wound wires. I am running 25* inital and 34* total timing with the timing coming in at about 1800rpm. I can run 91 octane without ping right now, but if the weather was hotter (90+) I would have to use a few gallons of 110 octane to mix in. I might be inclined to think that the 93 octane may not actually be 93, more like 90-91. It wouldn't be the first time they did that. You might try backing the timing to 20* initial and see if that does any better, or try a little octane booster. If the octane booster does the trick.....I would doubt that the fuel is actually 93 octane. What was your initial timing set at? Do you have a curve kit in the dist? Mike
Have you verified that your TDC mark on the timing tab is actually correct with the cyl. head off or with a TDC stop in the plug hole?
I have verified the timing mark with a new balancer from Poston, and used a piston stop to mark the TDC position. My initial timing at idle is 12 deg, I have a curve kit in the dist, but I have to run the heaviest springs cause its pinging. I have two possible ideas here? Either I am running too lean, (but it doesn't make sense at cruising sppeds), or I noticed last night my thermostat is sticking, and gettign the engine pretty darn hot. I have replaced that thing like 5 times already.... ticking me off! :af: One other thing I have thought of here is that my weights might be getting stuck, and when I am checking full advance, they might not be coming out as far as they would on a cruise speed or laying the pedal down? Nothing I try works, and I have used gas from all the stations around here. I really wanted your set up Mike, to have my full advance coming out at 1800. I love the torque you can get back at low RPM by doing that! Thanks, -Jon
Have you tried to richen it up? How do the plugs look? Are you running vac advance? Which holley 750 carb? Does it have power valve in back? I think you are way too lean on the primaries. Jim Burek
Mixture Hi Jim, vaccum advance is disconnected. I have a 4160 Holley 750. The primaries are 65, and 2nds are 76. I just realized my power valve is WAY too rich, and I have been reducing the primaries to compensate for that bog, so you could be onto something. . I have 6-7 vaccume at idle in gear, and my power valve was a 6-5. I have the correct power valve to install this evening, I chose a 3.5 to start. My question is what controls the cruise mixture on these Holley's? Does it come through the primaries like it does on a q-jet? When I am cruising, I get detonation if I accelerate at all. I am new to the Holley carbs, so assume I know nothingo No: The plugs are clean.. too clean I think? Oh, I am also running a cold plug in this engine. Thanks, -Jon
Re: Re: Timing Question Good call Jim, I think you hit the nail on the head. I remember adjusting mine a little on the rich side (Qjet). You should be able to pull a plug or two and read what's going on there. If you want the timing comig in sooner, just use the gold springs.
Re: Mixture I think definately too lean on the primary. During cruise, you are already on the jet circuit. Jim Burek
Will let you know on Monday Ok, thanks for the input, it gives me some things to try over the weekend. I will jet it upward, and see what it does to the motor. I appreciate all the input here. This board is the best find next to my Buick :beer Hopefully I will get to meet some of you Northerners at the Nationals this year. Havent been since 2000.... Thanks, -Jon
Thanks Jim and Mike, Richening the mixture and jetting it/power valve adjustments made all the difference. Now I can play with puling my timing out a little sooner. I am looking forward to thei years Nats and meeting some of you Northerners. I of course will have a 5 gallon keg of home brew to distribute. :beer Nothing like beer to make friends! -Jon