351m tuning project
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Joined: Sep 2012
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From: New Mexico
Some of our recent below normal cold weather mornings have been useful for learning. While my lean modifications worked very well in warm weather, I think they've effectively made the carb too small in cold. By that I mean it's hard to find a choke setting that will keep the engine running for the first few minutes. I need the choke to richen up the mixture, but getting it too something like 12 or 13:1 requires so much choke the engine is starved of air. I have to repetitively tap the accelerator for a few minutes before it will idle on it's own. Also I'm running leaner for longer (17 or 18:1) until the engine gets fully warm. Hence I'm going to change the air bleeds to richen the mixture lest I burn a valve.
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From: Northeast, OK
When mine gets to 18 it falls on its face. And the way I have the choke adjusted it comes off just a tad too early and the AFR goes right on up. I'm hoping the hot air off the exhaust and a touch more choke will solve that.
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I'm beginning to think that an EFI throttle body might not be a terrible investment. Not like I can't swap it on to a different vehicle. I'm going to have an old car or truck until I no longer have a say in the matter. I'm still happily tinkering with my Holley, but EFI is looking nice. I might get over my mechanical leanings for my Comet and have some electronics on the car.
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Still trucking...
I got my mileage up to 11.5 consistent, mixed driving, then set the timing where I wasn't quite pushing it as hard, got 10.6. I cranked the timing up again, got back up to mid 11s but the thing won't crank when it is cold.
I'm going to tear into the dizzy later and see what the advance is set to.
So far it seems the 390 likes a ton of timing, so I was thinking about going with pretty high initial (16-22ish) and a pretty small advance + vacuum advance, but she doesn't like to start with high timing when cold.
Previous experience was that high timing caused hard starts when warm. This engine is completely opposite.
I got my mileage up to 11.5 consistent, mixed driving, then set the timing where I wasn't quite pushing it as hard, got 10.6. I cranked the timing up again, got back up to mid 11s but the thing won't crank when it is cold.
I'm going to tear into the dizzy later and see what the advance is set to.
So far it seems the 390 likes a ton of timing, so I was thinking about going with pretty high initial (16-22ish) and a pretty small advance + vacuum advance, but she doesn't like to start with high timing when cold.
Previous experience was that high timing caused hard starts when warm. This engine is completely opposite.
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I think that is why I got such good mileage out of my 302. 8:1 compression allows for some pretty extreme ignition timing. Initial was 22.
What I can't figure out is why it will start hot but not cold, unless it is because the engine spins easier when warm.
What I can't figure out is why it will start hot but not cold, unless it is because the engine spins easier when warm.
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NMFirstF2504X4, did you ever change your timing curve?
I finally started tinkering again, trying to get my timing as far advanced as I can without pinging. 14* initial, 40* total + vacuum, should come in around 3000. I'm going to swap the springs for a softer set and see how it likes total timing around 2500.
I finally started tinkering again, trying to get my timing as far advanced as I can without pinging. 14* initial, 40* total + vacuum, should come in around 3000. I'm going to swap the springs for a softer set and see how it likes total timing around 2500.
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From: New Mexico
0ldman - sorry to not reply sooner - I haven't had much time to do anything with the truck other than drive it and post the 2 year rustoleum paint job update.
I've not done anything with the carb or ignition beyond my last posts here. Until I come up with some better diagnostics, I don't want to invest a lot of time and gas trying to optimize further. For example, on my long range list of projects are ways to measure real-time fuel flow and measure real-time spark advance. Right now I have higher priority (and easier) projects for when I do find some time and $.
Glad to see your still tinkering!
I've not done anything with the carb or ignition beyond my last posts here. Until I come up with some better diagnostics, I don't want to invest a lot of time and gas trying to optimize further. For example, on my long range list of projects are ways to measure real-time fuel flow and measure real-time spark advance. Right now I have higher priority (and easier) projects for when I do find some time and $.
Glad to see your still tinkering!
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I was mostly just checking in to see if you had to richen it up again, see if it is maintaining the mileage decently.
I'm still stuck at 11.6 mixed, but picking up my daughter from school kinda kills it. I've still got to get my tires finished to do much highway driving. I finally swapped in a clutch fan, haven't checked the mileage yet though. Had some carb issues so the numbers are going to be skewed.
I'm still stuck at 11.6 mixed, but picking up my daughter from school kinda kills it. I've still got to get my tires finished to do much highway driving. I finally swapped in a clutch fan, haven't checked the mileage yet though. Had some carb issues so the numbers are going to be skewed.
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