deja Posted July 27, 2006 Share Posted July 27, 2006 I know this is an almost impossible question to answer but thought I'd give it a shot. I have a late GEN 1 350. It has a bit of a cam but since I didn't build it I have no clue about the specs. Its running stock manifolds, no headers. Its running a 725 cfm type 4150 # 4118 Holley on an Edelbrock dual plane manifold. The engine has been running rich since I got it. I'm planning a LT1 swap so I haven't really addressed the rich condition. But now I've decide to attempt to fix it. The plugs don't really look that bad, a little dark. I looked at the jets and power valve, they are the ones that come stock with this carb, 725 (F)68,®78 power valve 8.5. Obviously whoever built the engine didn't do any fine tuning. I don't have an exhaust analyzer and doing all out runs on the street and plug reading isn't something I'm going to get away with where I live. Is there a best guess for jetting this carb with what little engine information I have? I hate to have to buy a whole jet kit for this to shotgun it. Summit wants $42 for a whole kit and $7 for a single set. Quote Link to comment Share on other sites More sharing options...
Twoeightnine Posted July 27, 2006 Share Posted July 27, 2006 I know this my sound simplistic but, with the stock intake manafold, prob stock heads, and no header, your engine is over carburated. Drop back to at least 600cfm, maybe even more, jetted for your altitude and I will venture to bet... she loves it! You can always go ol school after that and check your exhaust pipe color. gray...is OK. Quote Link to comment Share on other sites More sharing options...
Mike kZ Posted July 27, 2006 Share Posted July 27, 2006 Try switching to a hotter spark plug, see if that helps any. Quote Link to comment Share on other sites More sharing options...
jnjdragracing Posted July 27, 2006 Share Posted July 27, 2006 Make sure you are pulling enough vacumn at idle to keep the power valve closed, if it is an 8.5 you need at least 9.5 vacumn. Also check the power valve to make sure it is not busted. This would cause rich condition if it is broke. John Quote Link to comment Share on other sites More sharing options...
deja Posted July 27, 2006 Author Share Posted July 27, 2006 I know this my sound simplistic but' date=' with the stock intake manafold, prob stock heads, and no header, your engine is over carburated.Drop back to at least 600cfm, maybe even more, jetted for your altitude and I will venture to bet... she loves it! You can always go ol school after that and check your exhaust pipe color. gray...is OK.[/quote'] The carb probably is too big, but this engine won't be in this car long enough to justify buying a new carb, anybody want to trade? LOL. Altitude may be a point since Atlanta is at 1000 ft. Quote Link to comment Share on other sites More sharing options...
deja Posted July 27, 2006 Author Share Posted July 27, 2006 Make sure you are pulling enough vacumn at idle to keep the power valve closed' date=' if it is an 8.5 you need at least 9.5 vacumn. Also check the power valve to make sure it is not busted. This would cause rich condition if it is broke. John[/quote'] Power valve was a 8.5 which I just replaced thinking maybe that was the problem because when I first got this car it had ignition issues and backfired a lot. I'll see if I can get my hands on a vacuum gauge. Quote Link to comment Share on other sites More sharing options...
deja Posted July 27, 2006 Author Share Posted July 27, 2006 Try switching to a hotter spark plug, see if that helps any. hmmm I'm using Autotlite 25's now, any suggestions? Quote Link to comment Share on other sites More sharing options...
John Scott Posted July 27, 2006 Share Posted July 27, 2006 Running rich usually makes the plugs a sooty black. If they are just a little dark you are probably in the ballpark. Holley stock jetting are darn close at or around sea level. reduce 1 jet/ 2000' gain is the rule of thumb. Also, for every 35 degree drop in temp using 70 degree benchmark, jet up a number. So if you are running around 100 F, like we are in the summer you probably can go another jet leaner. (our track temps were 144 the other evening, bleh!) Nothing wrong with trying to jet a couple of numbers down on the primary side. When you feel the engine (lean) surging at part throttle cruise, then go up a number. Secondary side, about the only sure way is with a/f guage or best mph in 1/4. Track access is great for tuning, I picked up 2 mph with secondary jetting and 1 on the primary. Big difference in wheel hp. For a standard trans, a 6.5 is a great universal PV, thats why they come in so many dbl pumprs, Automatic with low stall require more tuning, but always a number or two lower than vacuum at idle in gear. You can seat of pants tune a Holley, to acceptable levels, but remeber rich carb might = fouled plug, but too lean might cost an engine. Quote Link to comment Share on other sites More sharing options...
deja Posted July 27, 2006 Author Share Posted July 27, 2006 Running rich usually makes the plugs a sooty black. If they are just a little dark you are probably in the ballpark. but remember rich carb might = fouled plug' date=' but too lean might cost an engine.[/quote'] The plugs didn't look all that bad, a little dark but not black at all. One looked like there may be a seal or ring issue, bummer. I know I don't want to get too lean, I've seen what that can do to an engine. One other thing that has been tough to get rid on is the bucking of the engine when I slow down and the RPMs drop to around 2000. I've tweaked on the idle screws which has helped a lot but it still happens a little. Back in the day I had a 950 3 barrel on my 70 AMX and it was very easy to tune right, but this one is a bitch. Quote Link to comment Share on other sites More sharing options...
John Scott Posted July 27, 2006 Share Posted July 27, 2006 The plugs didn't look all that bad' date=' a little dark but not black at all. One looked like there may be a seal or ring issue, bummer. I know I don't want to get too lean, I've seen what that can do to an engine. One other thing that has been tough to get rid on is the bucking of the engine when I slow down and the RPMs drop to around 2000. I've tweaked on the idle screws which has helped a lot but it still happens a little. Back in the day I had a 950 3 barrel on my 70 AMX and it was very easy to tune right, but this one is a bitch.[/quote'] I'd bet you are close enough on the jetting to leave alone. Again you might try a step leaner. If your plugs where showing no color then, no. Bucking might be due to a longer duration cam. More initial timing gives a little more low end response and can clean up the idle a bit.. Most will set initial around 16-18, but then you need to be concerned about 36-38 total. Might help. Good luck! Quote Link to comment Share on other sites More sharing options...
deja Posted July 27, 2006 Author Share Posted July 27, 2006 I'd bet you are close enough on the jetting to leave alone. Again you might try a step leaner. If your plugs where showing no color then, no. Bucking might be due to a longer duration cam. More initial timing gives a little more low end response and can clean up the idle a bit.. Most will set initial around 16-18, but then you need to be concerned about 36-38 total. Might help. Good luck! My timing is set at 12, but I don't know what the total is. I need to get a better timing light or degree wheel. Quote Link to comment Share on other sites More sharing options...
Pyro Posted July 27, 2006 Share Posted July 27, 2006 I run a holley 750 on my 350, 454, 396. And they all needed 68 to 69's on the primarys and 72's to 74's in the secondary. So I think a set of jets ranging from 67 to 74 should cover it. A "bit of a cam" may require a 6.5 power valve Change the primarys jets based on the amount of soot around the metal base ring at the bottom of the threads. A soot ring that goes 1/2 way around the base ring is a good mixture. The "base ring" is the flat surface at the bottom of the threads that is perpendicular to the threads. Then if you see black smoke blowing out the tail pipe during WOT, then jet down the secondarys until the smoke stops. Use a vacuum gage on the ported vacuum source and if there is more than 1 or 2 inhg then the throttle blades are openned too far into the main idle circuit. This will make the idle mixture screws do almost nothing to correct the idle mixture. If you have this conditon, two 0.060" holes drilled in the front throttle plate will allow more air into the engine with the throttle blades in a more closed position. This will make the idle mixture screws work correctly, then adjust the idle mixture when the engine is hot to the highest idle vacuum. You may need to drill a 0.070, 0.080, or even a 0.090 to correct the problem. Do a web search on how to tune a holley. There is a lot of free information out there. Quote Link to comment Share on other sites More sharing options...
deja Posted July 27, 2006 Author Share Posted July 27, 2006 I run a holley 750 on my 350' date=' 454, 396. And they all needed 68 to 69's on the primarys and 72's to 74's in the secondary. So I think a set of jets ranging from 67 to 74 should cover it. A "bit of a cam" may require a 6.5 power valve Change the primarys jets based on the amount of soot around the metal base ring at the bottom of the threads. A soot ring that goes 1/2 way around the base ring is a good mixture. The "base ring" is the flat surface at the bottom of the threads that is perpendicular to the threads. Then if you see black smoke blowing out the tail pipe during WOT, then jet down the secondarys until the smoke stops. Use a vacuum gage on the ported vacuum source and if there is more than 1 or 2 inhg then the throttle blades are openned too far into the main idle circuit. This will make the idle mixture screws do almost nothing to correct the idle mixture. If you have this conditon, two 0.060" holes drilled in the front throttle plate will allow more air into the engine with the throttle blades in a more closed position. This will make the idle mixture screws work correctly, then adjust the idle mixture when the engine is hot to the highest idle vacuum. You may need to drill a 0.070, 0.080, or even a 0.090 to correct the problem. Do a web search on how to tune a holley. There is a lot of free information out there.[/quote'] Thanks. The idle screws do seem to be almost useless. And I scout g=for a different PV and read the plugs again since I just changed them. Quote Link to comment Share on other sites More sharing options...
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