400 Tuning
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Elder User
Joined: Jun 2013
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400 Tuning
Good evening guys!
400
4 speed
headers/cam/ intake, 3" exhaust/ 600cfm 1406 eldelbrock carb
So I am finally getting around to getting my engine fine tuned. Today I put a timing light and vacuum gauge on it. After some adjustment I was able to get just under 11lbs of vacuum. The truck was set with a frozen distributor at 32 degrees initial timing. It has been taken down now, but I don't recall to what degree. I think the guy helping me set it at 12 degrees.
The truck is still stumbling around 3,000rpm like it has a miss. It did have some backfiring while getting the timing dialed in.
The plugs look to me like they are running hot and are gapped between .038 and .045. I plan to get some colder plugs this weekend in the truck. They are Motorcraft platinum ASF 42p
So my questions:
1) What timing should I shoot for?
2) What plug should I buy for a colder burn?
3) What vacuum level should I shoot for?
400
4 speed
headers/cam/ intake, 3" exhaust/ 600cfm 1406 eldelbrock carb
So I am finally getting around to getting my engine fine tuned. Today I put a timing light and vacuum gauge on it. After some adjustment I was able to get just under 11lbs of vacuum. The truck was set with a frozen distributor at 32 degrees initial timing. It has been taken down now, but I don't recall to what degree. I think the guy helping me set it at 12 degrees.
The truck is still stumbling around 3,000rpm like it has a miss. It did have some backfiring while getting the timing dialed in.
The plugs look to me like they are running hot and are gapped between .038 and .045. I plan to get some colder plugs this weekend in the truck. They are Motorcraft platinum ASF 42p
So my questions:
1) What timing should I shoot for?
2) What plug should I buy for a colder burn?
3) What vacuum level should I shoot for?
Senior User
Joined: Sep 2012
Posts: 372
Likes: 4
From: New Mexico
12 degrees initial (vacuum advance plugged) may be a reasonable place to start, but it depends on your total advance which you should check. I'm currently running 16 which was optimized for MPG. You could also set your initial timing based on maximizing your idle vacuum. My vacuum is 16, but I'm a mile high in altitude. If you're going to tweak the carb, I strongly suggest getting an AFR gauge. We don't have the same carb, but here's my experience tuning my 351m:
https://www.ford-trucks.com/forums/1...g-project.html
https://www.ford-trucks.com/forums/1...g-project.html
Tuned
Joined: Nov 2010
Posts: 426
Likes: 1
From: Caledon ON
By the looks of the plugs you are lean. With only 11 inches of vacuum I would say you have either a vacuum leak or a pretty radical cam with a very tight lobe separation. I would suspect a vacuum leak though, it should be around 18 inch's. 12 degrees initial is good with the vacuum advance plugged.
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Elder User
Joined: Jun 2013
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Thanks for the response guys
We did a check on the vacuum lines and some of the hoses were a thin wall type that were collapsing under pressure. Those got swapped out for a thicker hose with a nylon core. I don't think there are any more leaks, but with these trucks who knows.
I will try to get a timing light on it again and set the timing to 16 like you said. What is a good number for total timing?
An AFR gauge would be nice. Do I need to plum an O2 censor for one of those?
Although I don't know any of the specs on the cam, it is a rather radical idle. Purely from sound it reminds me of Comp's Mothr thumpr or big mothr thumpr cam.
Im not familiar with using a piston stop and how it relates to tuning. Could you elaborate?
The one of the guys helping me tune the truck called me back this morning with an idea of why the truck would have the popping and missing at higher rpm. The truck has an MSD ignition box and coil, but factory type pug wires and rotor button. He seems to think that the pug wires are breaking down at high rpm and not sending enough spark.
We did a check on the vacuum lines and some of the hoses were a thin wall type that were collapsing under pressure. Those got swapped out for a thicker hose with a nylon core. I don't think there are any more leaks, but with these trucks who knows.
I will try to get a timing light on it again and set the timing to 16 like you said. What is a good number for total timing?
An AFR gauge would be nice. Do I need to plum an O2 censor for one of those?
Although I don't know any of the specs on the cam, it is a rather radical idle. Purely from sound it reminds me of Comp's Mothr thumpr or big mothr thumpr cam.
Im not familiar with using a piston stop and how it relates to tuning. Could you elaborate?
The one of the guys helping me tune the truck called me back this morning with an idea of why the truck would have the popping and missing at higher rpm. The truck has an MSD ignition box and coil, but factory type pug wires and rotor button. He seems to think that the pug wires are breaking down at high rpm and not sending enough spark.
Lead Driver
Joined: Nov 2006
Posts: 5,217
Likes: 506
From: Pa.
You will get a piston stop equivalent to your spark plug thread ..
It will be screwed into the #1 spark plug hole after you've verified your on the compression stroke .. set the screw shaft at the top of the stroke and mark the harmonic balancer at the pointer .. Now turn the crank in the opposite direction gently until it hits the stop .. Now mark the harmonic balancer again .. Absolute TDC will be the mid point between the two marks .. From there you can begin your tuning process with confidence otherwise all the hard work of fine tuning could be for not ..
It will be screwed into the #1 spark plug hole after you've verified your on the compression stroke .. set the screw shaft at the top of the stroke and mark the harmonic balancer at the pointer .. Now turn the crank in the opposite direction gently until it hits the stop .. Now mark the harmonic balancer again .. Absolute TDC will be the mid point between the two marks .. From there you can begin your tuning process with confidence otherwise all the hard work of fine tuning could be for not ..
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Elder User
Joined: Jun 2013
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Okay I will have to pick one of those up. Right now I am judging by one paint park on the harmonic balancer. Who knows if that it is at all correct. How do I know its on the compression stroke?
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Lead Driver
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Senior User
Joined: Sep 2012
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From: New Mexico
Most of the AFR gauges come as part of a kit including an O2 sensor. You then weld or clamp a bung onto the header collector.
If the plug wires are suspect, I think you'd see issues at all RPMs. You could check for breakdown by looking for arcs or corona with the engine running in the dark.
Once you verify TDC and it matches the timing mark, I'd map out the advance curve with and without the advance and see what that looks like. Something like 36 total without the vacuum advance would be reasonable and this should be all in by 3000 RPM.
As skidoodave noted, your plugs suggest the engine is running lean. The AFR gauge would certainly confirm this. If the timing is all good, then I'd start looking at the carb and fuel delivery.
If the plug wires are suspect, I think you'd see issues at all RPMs. You could check for breakdown by looking for arcs or corona with the engine running in the dark.
Once you verify TDC and it matches the timing mark, I'd map out the advance curve with and without the advance and see what that looks like. Something like 36 total without the vacuum advance would be reasonable and this should be all in by 3000 RPM.
As skidoodave noted, your plugs suggest the engine is running lean. The AFR gauge would certainly confirm this. If the timing is all good, then I'd start looking at the carb and fuel delivery.
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Elder User
Joined: Jun 2013
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Thanks for the info guys, its helping a lot. For now I will have to do without the AFR gauge for price reasons.
Any suggestions on what plug I should be running? I was told that I need a colder plug
Any suggestions on what plug I should be running? I was told that I need a colder plug
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