FBO plate over advancing

[Agent_Orange]

I've worn out the search bar to the point where I'm seeing the same posts over and over, not finding much chatter about this issue, so it's safe to say I messed up somewhere.

318 w/ vac advance, eddy 1406, mild cam with original springs, headers, 2.5" exhaust w/ mufflers, 727, 3.73 rear.

Timing done with an Innova 3568 dial back light.

After timing test, the engine wants 18* initial, and 34* mechanical. Bought a FBO plate and spring kit, assembled the distributor with both light springs from kit and the plate set on the 16* tabs.

dropped the dizzy in, warmed the engine up and locked initial in at 18*. Next, with vac advanced disconnected, I mapped my curve by setting my dial back at 20* jot down rpm, then 22*, 24* all the way until I ran out of advance. I hit my target of 34* total (initial+mech) @ 2110 rpm, yet the advance kept going. The engine quit advancing 42* @ 2800 rpm. 8 degrees more than the fbo plate should have allowed.

I read one thread on here from a while ago with a similar issue of over advancing with a fbo plate, and the verdict was to replace the ignition module, but I didn't have this issue a few days ago when I tested the stock distributor with that same ignition.

 

[4spdragtop]

No help, but watching.

 

[Cuda416]

Safe to assume when you let it idle again it goes back down to 18@780?

 

[Agent_Orange]

Safe to assume when you let it idle again it goes back down to 18@780?

Yes sir

 

[Cuda416]

Yes sir

Ok, I was trying to eliminate the dizzy rotating a bit.

I don't have an FBO plate, but you could measure the slots to make sure it's the correct slot. I know they are marked but it's something else to eliminate.

dist. degrees / slot size
6.............. .340
7............... .355
8............... .375
9............... .390
10.............. .405
11.5 ........... .420
12.............. .435
13.............. .445
14.............. .460
15.............. .475
16.............. .490
17.............. .505
18.............. .520

 

[Dana67Dart]

Are the posts clean without slits from years of wear?

 

[sabre67]

learning

 

[RustyRatRod]

Ok, I was trying to eliminate the dizzy rotating a bit.

I don't have an FBO plate, but you could measure the slots to make sure it's the correct slot. I know they are marked but it's something else to eliminate.

dist. degrees / slot size
6.............. .340
7............... .355
8............... .375
9............... .390
10.............. .405
11.5 ........... .420
12.............. .435
13.............. .445
14.............. .460
15.............. .475
16.............. .490
17.............. .505
18.............. .520

I too have found the FBO plates to be inaccurate on both slant sixes and V8s and I've made mention of it here before, but was run over like a freight train with disagreement when I said something about it, so I just kept quiet after that. My experience on the slant 6 was the same as what's presented here. It was getting way too much advance for the given slot length. If you think about it, from the slant 6 to the V8s, those slot lengths should be the same for a given advance amount, since the distributors are the same in that regard. .....and now people with no experience there will come out to argue with me again. But I've done actual measurements and comparisons. Even done some parts swapping between slant 6 and V8 distributors and there was no difference.

 

[Agent_Orange]

Ok, I was trying to eliminate the dizzy rotating a bit.

I don't have an FBO plate, but you could measure the slots to make sure it's the correct slot. I know they are marked but it's something else to eliminate.

dist. degrees / slot size
6.............. .340
7............... .355
8............... .375
9............... .390
10.............. .405
11.5 ........... .420
12.............. .435
13.............. .445
14.............. .460
15.............. .475
16.............. .490
17.............. .505
18.............. .520

undoubtedly, the distributor will be torn back down, I will post the FBO slot readings when that happens.

Are the posts clean without slits from years of wear?

by posts, are you referring to the cap posts? If so, the cap looked okay from over the fender. New cap and cables were installed probably 10-15 years ago and basically sat until this summer. I will pull it off this evening and do a better inspection.

In my head at least, that cap worked fine 3 days ago ... but if I knew, I wouldn't be here, so there's that.

 

[PRH]

I used to braze up the slots and file the length as required.
Seems like most distributors I messed with had the slot plate marked something like 15(30* at the crank).
If you limit the travel of the pin to about 1/2 of what it is stock, it should get you close to 15-16* at the crank.

 

[memike]

@halifaxhops

 

[Agent_Orange]

I too have found the FBO plates to be inaccurate on both slant sixes and V8s and I've made mention of it here before, but was run over like a freight train with disagreement when I said something about it, so I just kept quiet after that. My experience on the slant 6 was the same as what's presented here. It was getting way too much advance for the given slot length. If you think about it, from the slant 6 to the V8s, those slot lengths should be the same for a given advance amount, since the distributors are the same in that regard. .....and now people with no experience there will come out to argue with me again. But I've done actual measurements and comparisons. Even done some parts swapping between slant 6 and V8 distributors and there was no difference.

I grew up in the fuel injection Era, so my experience in this world of distributors and carbs is growing by the day. Luckily, I built this car with dad 24 years ago and I'm even more blessed that he kept it in the corner all those years while I was busy being irresponsible.

I've spent a lot of time within this site's search function, and from my point of view, I know who on here has helped fix and improve my favorite car. You guys are appreciated.

 

[Cuda416]

I used to braze up the slots and file the length as required.
Seems like most distributors I messed with had the slot plate marked something like 15(30* at the crank).
If you limit the travel of the pin to about 1/2 of what it is stock, it should get you close to 15-16* at the crank.

That's essentially what I did but using a mig. Then filed out to 14deg (0.460 slot length)

I think the posts being referred to are the posts that fit into the adv limiter slots. If they are "grooved" then the weights would move too far.

 

[Agent_Orange]

That's essentially what I did but using a mig. Then filed out to 14deg (0.460 slot length)

I think the posts being referred to are the posts that fit into the adv limiter slots. If they are "grooved" then the weights would move too far.

Oh... okay I'm following, added to my distributor inspection list.

 

[69FBCuda]

What gains do you expect from all of this effort. Me.. run it stock

 

[Agent_Orange]

What gains do you expect from all of this effort. Me.. run it stock

I just want it to run efficiently, not smell as bad at idle, increase off idle response, and to learn to time a distributor before moving onto building my 340.

 

[Dana67Dart]

by posts, are you referring to the cap posts

No, I was meaning the posts that the limiter stops on.

If they are warn the limiter will not stop at the correct deg

 

[Agent_Orange]

So I wasn't very productive in the garage this evening. Had to finish mowing the yard ~1.5 hours, played soccer with my son for an hour or so, dinner.. ect.



however, I did pull my distributor, and found I was able to move the fbo plate while the t-bar was still attached.




the center hole on the FBO plate is machined to use that lip, that I'm pointing to on the t-bar, as it's centering device. I can't speak on all t-bars, but this lip is minimal. If the t-bar lifts out of that centering hole, the pins on the weights and the slimmer armature shaft are holding the plate in place. Allowing a slight amount of float in the plate.




So my assumption is that on my original assembly of the plate, I overlooked the importance of that shoulder on the t-bar. And failed to properly seat the 2 pieces. Reinstalled plate at 16*, warmed up engine, set idle at 18*, verified 18* after a couple bumps of the throttle. Timing appeared to stop advancing at 36* @ 2400 rpm.. by this time it's, after 9pm, kids are going to bed and I decided against reving anymore tonight.

Below is a picture of those studs on the weights, there is a slight wear, not sure on what the tolerance would be in this situation.

 

[RustyRatRod]

I grew up in the fuel injection Era, so my experience in this world of distributors and carbs is growing by the day. Luckily, I built this car with dad 24 years ago and I'm even more blessed that he kept it in the corner all those years while I was busy being irresponsible.

I've spent a lot of time within this site's search function, and from my point of view, I know who on here has helped fix and improve my favorite car. You guys are appreciated.

When I first began as a mechanic in high school auto shop in 1980, front wheel drive was coming into vogue and anything with EFI on it was a total POS, since it was still in its finite stages. I've worked in just about every dealership in Macon and some others in outlying areas in my career as a mechanic and I must say I still hate EFI. It's never made sense to me that a fuel pump failure on EFI means dead in the water "wherever" you are when a fuel pump failure on a carburetor might mean if you're easy on the gas, you might can make it home. I've never seen it as an upgrade and I never will.

 

[Agent_Orange]

When I first began as a mechanic in high school auto shop in 1980, front wheel drive was coming into vogue and anything with EFI on it was a total POS, since it was still in its finite stages. I've worked in just about every dealership in Macon and some others in outlying areas in my career as a mechanic and I must say I still hate EFI. It's never made sense to me that a fuel pump failure on EFI means dead in the water "wherever" you are when a fuel pump failure on a carburetor might mean if you're easy on the gas, you might can make it home. I've never seen it as an upgrade and I never will.

I haven't driven an old car with an efi system installed. But I'm not interested either. The engine is the same regardless of carb or efi bolted in place. So any gain in performance or response with efi would have to be minimal.

 

[RustyRatRod]

I haven't driven an old car with an efi system installed. But I'm not interested either. The engine is the same regardless of carb or efi bolted in place. So any gain in performance or response with efi would have to be minimal.

I agree. .....and I'm no expert on the differences, BUT, everything I've read and heard people say who KNOW the differences say that carburetors make more peak power every time. .......and the EFI crowd always blows up. lol

 

[halifaxhops]

Sounds like you're on the right track. I have said this hundreds of times. DO NOT TRUST A DIAL BACK TIMING LIGHT unless the advance mode is verified. Heck I have seen 0 off also. The potentiometers wear out and gives assuming results. Check it with a timing tape or against a digital light or it will drive you nuts. Also that advance cam will only give you 15 dist degrees maximum The FBO plate can only keep that or go lower something to keep in mind also.

 

[Agent_Orange]

Sounds like you're on the right track. I have said this hundreds of times. DO NOT TRUST A DIAL BACK TIMING LIGHT unless the advance mode is verified. Heck I have seen 0 off also. The potentiometers wear out and gives assuming results. Check it with a timing tape or against a digital light or it will drive you nuts. Also that advance cam will only give you 15 dist degrees maximum The FBO plate can only keep that or go lower something to keep in mind also.

And I'm looking for around 8* in the distributor. So I'm good there. Timing lights are what they are. Get me close and I can go by feel from there. Find what it likes then weld/file the slots. I don't think I will be able to trust the plate for the long term.

 

[Agent_Orange]

one more observation:

Halifax got me thinking, my tbar is a 15, so 30* at the crank. I wanted 16* at the crank, so roughly half the slot. The picture below has the 16* slots under the tbar. The inside of both pieces are flush, the fbo plate should restrict the travel by more than it does.

my micrometer needs a new battery, so I wasn't able to get slot readings last night

 

[halifaxhops]

I am not sure if the numbers on the FBO plates are dist degrees or crank. I never use them.