wallaby Posted September 30, 2014 Share Posted September 30, 2014 I am still trying to sort out the tuning on my new 468. The timing and fuel ratios and such. For the longest time something didn't seem right, and I was blaming an exaggerated dyno sheet and inside I was cursing my builder. Then I found this handy guide for general settings to get you in the ballpark. For me, it worked wonders. If you are running a big-block, you can probably run the lower end of the timing figures. This is a great thing to reprint and tack to your garage wall next to the periodic table of the elements, the rotational lathe speeds for different metals poster, the tap/die/drill guide, and the Chevrolet firing order chart. It reads:... 10 to 12 degrees of initial timing when the camshaft duration is less than 220° @ 0.050, 14 to 16° of initial timing with less than 240° @ 0.050; and 18 to 20° of initial timing with a cam with less than 260° @ 0.050. For those of you with air/fuel meters, here are the general ratios to target: ...Starting points when you are setting the air/fuel mixtures of a generic engine are: Idle: 1% to 3 % CO or a 14.1-13.4 to 1 air/fuel mixture, Cruise RPM: 1% to 3 % CO or a 14.2 –14.0 to 1 air/fuel mixture, Power Mixture and Acceleration: 6.6% CO or a 12.0-1 air/fuel mixture. Some high performance engines with fast burn cylinder heads may use a slightly leaner power mixture of 4% CO or a 13.0 to 1 air/fuel ratio. I was at 12 degrees initial with a cam with 236/244 duration @ .050... Advancing the timing up to 17 made a WORLD of difference. Now for those with know-how, why is it that as my engine gets to the fully warm state it leans out at idle? I can drive for about 30 min on the freeway and it might get to about 170 degrees, and when I exit into stop/go traffic the idle goes way lean (15-16/1) and it idles rough and puts out obnoxious fumes. It idled fine with good ratios at 160 degrees...(160 T-stat, choke long ago fully open). I'm wondering if it might be the underhood heat that the engine is intaking....thoughts? Should I just readjust the idle mixture when the engine is fully-fully hot and live with the resulting rich "normal" temp ratios? Quote Link to comment Share on other sites More sharing options...
Murphy Posted September 30, 2014 Share Posted September 30, 2014 This is a great thing to reprint and tack to your garage wall next to the periodic table of the elements, the rotational lathe speeds for different metals poster, the tap/die/drill guide, and the Chevrolet firing order chart. I don't know what all the facts & figures are you stated in your post but I wear this shirt in the garage all the time... The wifes impressed..........that's what counts! I really envy those of you who get deep into the operation of the combustion engine! Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted September 30, 2014 Share Posted September 30, 2014 are those air/fuel ratios for 100% gasoline? with the ethenol crap we have now will change them Quote Link to comment Share on other sites More sharing options...
LIL' Mac Posted September 30, 2014 Share Posted September 30, 2014 Murphy, the firing order on my '55 is 18736542, so that shirt would not apply. I used a Howard's 4-7 swap circle track cam in that motor. Have to swap the wires. Quote Link to comment Share on other sites More sharing options...
Rock Posted October 1, 2014 Share Posted October 1, 2014 Originally Posted By: wallaby This is a great thing to reprint and tack to your garage wall next to the periodic table of the elements, the rotational lathe speeds for different metals poster, the tap/die/drill guide, and the Chevrolet firing order chart. I don't know what all the facts & figures are you stated in your post but I wear this shirt in the garage all the time... The wifes impressed..........that's what counts! I really envy those of you who get deep into the operation of the combustion engine! I want that shirt.... Quote Link to comment Share on other sites More sharing options...
7tonemonte Posted October 1, 2014 Share Posted October 1, 2014 I love the shirt too! Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted October 1, 2014 Share Posted October 1, 2014 Mark. fully warmed up means... oil up to temp, intake coolant and heads too I feel your combustion temps are low and not burning all the fuel, then once you drive it and get the temps up, it goes lean for a street driven car! you should put a higher temp thermostat in it, get the combustion temps up, these engines were designed to have a 195 thermostat originally running a big block or small block @ 190 to 200 certainly isn't going to hurt it, I've found that mine actually runs much better all today's new cars are running around 210, everybody freaks out if the temps go over 180...why? Quote Link to comment Share on other sites More sharing options...
LIL' Mac Posted October 1, 2014 Share Posted October 1, 2014 Exactly Sam. IMO, anything 220 and under is fine. All the years I worked in a garage, most cars as I recall ran 220, and then the fans kick on, IF I remember correctly. Has been awhile. Like you said, the warmer the better, to a certain degree that is. Quote Link to comment Share on other sites More sharing options...
Murphy Posted October 1, 2014 Share Posted October 1, 2014 You can order these shirts at http://teespring.com/18436572order I saw the ad on CL last winter and had to have one......$20. Quote Link to comment Share on other sites More sharing options...
wallaby Posted October 1, 2014 Author Share Posted October 1, 2014 Ok, I used a 160 stat because it was a requirement for my engine warranty. That has expired time-wise, so I'll try a 180. My normal scenario is I drive to work in the wee hours of the morning (like 3am) and it behaves beautiful...even when I get there and it has to idle. But the same drive in the other direction is a different story. This trip is done in the late afternoon and it isn't as smooth, even at cruise. Idle in traffic, and it goes way lean. I got home today and tried to richen the idle mixture while it was still hot and idling lean, and found that the screws are essentially all the way out already. Backing them out further made no difference. I tried cupping a rag over the primaries and got little or no response. I then tried the rag over the secondaries...and it stumbled and nearly stalled. I thought maybe it was my giant rag (a towel) covering the bowl vents, so I made sure to avoid those and tried again. This time it stopped the engine dead in its tracks. From this I'm guessing that I have a vacuum leak...probably the secondary plates not fully closing. That would explain why the idle screws are all the way out and the idle is so unpredictable. Anyone had this issue with a Holley? This is the first Holley I've ever run and it's brand new. It's a street avenger vacuum secondary carb with electric choke. Again, a recommendation from my builder. So far I'm not real impressed. Oh, and that Tee shirt should be printed backwards so you can look in the mirror for reference. And if your computer asks for a new password, and helps by suggesting "What's your favorite restaurant?" Don't do it because everybody knows it's Red Lobster. Quote Link to comment Share on other sites More sharing options...
Leghome Posted October 1, 2014 Share Posted October 1, 2014 Mark I had a similar problem with the 350 crate motor in my 72. My son in-law and I checked everything and rechecked and could find no problem. Finally I got to looking at the base of my Holley carb and thought the base looked bent causing it to suck air. Took a straight edge and in the center of the base there was almost an 1/8" gap in the center of the base. Some one had over tightened the carb or something like that. Took the Holley off and put an Eldebrock 1406 on it ran perfect right out of the box. Mine would just about choke when ever you mashed the accelerator on take off and it had to be feathered until you got up to speed. Similar to your problem but still quite a bit different. Good luck on figuring it out. Quote Link to comment Share on other sites More sharing options...
wallaby Posted October 2, 2014 Author Share Posted October 2, 2014 Alright, I made some progress. I pulled the carb and the baseplate was flat. Next I checked the secondary throttle plates and found them to be open a bit. I did some checking online and found that there is a secondary stop screw designed to hold them open a bit. Strange. On a Q-jet you drill tiny holes in the primary plates to get a good idle with a lopey cam, but Holley has a screw to do the same thing. The idea is to have the primary plates nearly closed so they don't expose too much of the transition slot. Once that slot gets too much exposure the carb starts running on the main metering system and your mixture screws loose their ability to adjust. That was where I was. I had the idle adjustment set too high to let the mixture screws do their lob. The solution was to open the secondary plates a bit with the "bugger to get to" screw, and then slow down the idle with the idle speed screw. It's a bit of a balancing act, but I think I got it. Quote Link to comment Share on other sites More sharing options...
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