trouble tuning mild 351c with holley 3310

[87fox72mach]

so my idle was a issue. I changed the advance slot by putting a sleeve over the peg. got 20 deg of mechanical advance. somehow though I think I ruined my vac advance unit as whether I connect it or not timing doesn't change at all. this is connected to manifold vacuum. timing seems to stick then at 1800 rpm it begins advancing. kinda curious of this seems I'm not out of the woods yet

 

[Don C]

Remove the distributor cap and make sure it's still connected.

While you have the cap off make sure the breaker plate moves freely.

You may have backed it off too much, try turning the adjustment a couple of turns clockwise.

Pull the vacuum hose off the carburetor and connect it to a vacuum pump, or just suck on it, to see if it holds vacuum.

 

[87fox72mach]

It doesnt seem to hold vacuum. Dont know how i could have possibly ruined it lol

 

[clevelandcoupe]

I think it's the distributor gremlins again, lol

Good job Alex, now I can set up the Distributors in the model a and mustang !!!

Thanks, Jay

 

[Stanglover]

I'm putting this in here as it relates to the issue. Hope it helps.

In 80 degree weather, I took my car out for a drive today and ran it through some hard acceleration. Still thinking I can get a bit more out of it, I did a little timing change. Also I realized that depending on what angle I held my full adjustable timing light, I could get slightly different results for the initial set-up. My damper mark has a thin white paint line on it and so does the pointer. The paint line needs to be thinner still, barely any more than the groove at 0* if you follow me.

Anyway, my initial was 14* with 20* on the crank (34* total) mechanical @ 3000 rpm, plus about 3-4* vacuum and it ran quite well at that. Sooooo, I bumped the initial up to 16*, reset the idle to 800 (manual trans). The vacuum gauge showed 18"Hg, right were it should be with my cam. I took it out and ran it hard through the gears and it pulled well, BUT when I let the revs drop in 4th and then hit the gas, it spark knocked like crazy. Didn't do that before, so I guess the sweet spot for my engine is where I had it before. My choices are a, cut the crank degrees down to 18 ish and set the initial at 16*, b, leave it alone or c, change and / or reset the spring tension to slow the advance down a tad.

So guys, what do you think. Leave it or play with it some more?

 

[Don C]

Before I did anything, I would check to make sure the vacuum advance and breaker plate move freely. It's possible the big jump in vacuum when you let off on it did something. Strange that it would just knock after you had already run through the gears and then backed off on it.

 

[midlife]

Before I did anything, I would check to make sure the vacuum advance and breaker plate move freely. It's possible the big jump in vacuum when you let off on it did something. Strange that it would just knock after you had already run through the gears and then backed off on it.

I think you mis-read his post.  He backed off and then nailed the gas in 4th gear.  That's the best condition to see if knocking is occurring.

 

[87fox72mach]

I feel ill just keep it at thr safe sweet spot. I dont need every ounce of performance. Car looks and sounds great. As long ad i dobt havr spark knock ill be content. Dont understand why vacuum advancr is necessary but i ordered a new vacuum unit

 

[TommyK]

I feel ill just keep it at thr safe sweet spot.  I dont need every ounce of performance.  Car looks and sounds great.  As long ad i dobt havr spark knock ill be content.  Dont understand why vacuum advancr is necessary but i ordered a new vacuum unit

It provides for better part throttle performance and better gas mileage at cruise.

 

[Stanglover]

Before I did anything, I would check to make sure the vacuum advance and breaker plate move freely. It's possible the big jump in vacuum when you let off on it did something. Strange that it would just knock after you had already run through the gears and then backed off on it.

I think you mis-read his post.  He backed off and then nailed the gas in 4th gear.  That's the best condition to see if knocking is occurring.

  Yes, Don did misread it. The distributor internals are working, all new, no sticking, new vacuum can. It's all in the set up and that was the point I was trying to get across for the benefit of 87fox72mach.

 Today I plan on re-setting it and try again. If not it's going back where it was and call it a day. The plug read was light to mid brown, so I'm not too worried about fuel/air ratio either, although I'd love to put a meter on it just to be sure.

It sounds like our friend has it very close now. Perhaps he should run it for a while and if possible in different temperatures to see if that makes any change. Mine ran very strong when it was cooler, no pinging at all.

 

[Stanglover]

I feel ill just keep it at thr safe sweet spot.  I dont need every ounce of performance.  Car looks and sounds great.  As long ad i dobt havr spark knock ill be content.  Dont understand why vacuum advancr is necessary but i ordered a new vacuum unit

+ 1 on the sweet spot. If that is where it like it, leave it. Do you have a vacuum gauge attached while you're working with it? If not make sure that the tee for the air cleaner is capped off, assuming you have a stock air cleaner.

 On the vacuum canister, make sure it is adjustable!!! There are cheap Chines crap ones that are not. I buy a lot of my stuff from RockAuto, same products way better prices. The one I bought was; Standard Motor Products, VC-31 Distributor Vacuum Advance.

Good fortune my friend,

Geoff.

 

[c9zx]

I know we are way into this thread to be asking the following question but, what octane fuel and plug heat range plugs are being used in these cars? Chuck

 

[Stanglover]

I've spent some time today re-reading a post I made on June 5th 2016, "Which aftermarket distributor to buy - 351C4V"

First, thanks to everyone who helped me get an understanding on the subject of curving a distributor. I've learned a lot and still very much learning.

So, I'm putting this here to refer interested parties back to that thread as I'm going to continue MY experience there rather than overshadow 87fox72mach's post and question on this subject, which would be inappropriate.

Geoff.

 

[87fox72mach]

Hey Chuck im running 93 fuel and autolite 25. Also geoff ur input has been very helpful! I got my new vacuum advance installed. I have 12 base and 4 advance. Total is 36 deg. I gotta drive the car now and see how it does

 

[Stanglover]

Hey Chuck im running 93 fuel and autolite 25.     Also geoff ur input has been very helpful!   I got my new vacuum advance installed.  I have 12 base and 4 advance.  Total is 36 deg.  I gotta drive the car now and see how it does

 Thanks 87fox..... I appreciate that you got something out of my experiences. I'm glad to learn that you are getting on top of this "timing thing". It can be pretty daunting to say the least, but becomes easier as we start to understand.

I'm continuing my own post on this until I am satisfied with my engine and results.

Geoff.

 

[TommyK]

Hey Chuck im running 93 fuel and autolite 25.     Also geoff ur input has been very helpful!   I got my new vacuum advance installed.  I have 12 base and 4 advance.  Total is 36 deg.  I gotta drive the car now and see how it does

You are running a plug that is one step hotter than stock which may be part of the problem. Try 24's.

 

[Stanglover]

Hey Chuck im running 93 fuel and autolite 25.     Also geoff ur input has been very helpful!   I got my new vacuum advance installed.  I have 12 base and 4 advance.  Total is 36 deg.  I gotta drive the car now and see how it does

You are running a plug that is one step hotter than stock which may be part of the problem. Try 24's.

 Interesting comment Tommy, That is also where I'm at. Going to switch back to 24's today as while I now have my timing pretty much sorted, I didn't like the plug read, a little too lean for my liking. I'm running the best gas I can get non-ethanol Shell 91 V power.

More on my own thread later.

Geoff.

 

[c9zx]

+1 on the 24s. Chuck

 

[87fox72mach]

Ugh i had 24s in it a while ago. They r all carboned up. Ill have to get a set

 

[MeZapU]

I have had significant trouble with Autolite spark plugs in the recent past stemming from the inconsistency in their quality control. Ever since they stared being made over the boarder(Mexico/China) and no longer made in the USA they have had issues. Not just in the #25 and #24 plugs but also their their #45, #3923 and #3924's. These used to be the go-to plugs for the community. It seems so hit or miss with the quality of the plugs I see from Autolite anymore. My experience is that they run well for a day or two, then start misfiring, and that leads to plug fouling. After a fresh plug swap, all seems well but this cycle continues. In the mean time all the tuning you try and perform is time chasing your tail because you are just going in circles.

I have made the switch to NGK spark plugs and could not be happier. I literally had the above scenario going on on my 85 GT's 408w for over a year before I figured it out. I would post pictures but with the recent Photobucket debacle I no longer can. I have converted many a non-believer and have fixed many many issues in peoples cars I have diagnosed simply by switching away from the Autolites. Not saying NGK's are the be-all end-all plug, but Autolites are just not what they used to be.

I whole heartedly recommend NGK plug #6630 for your 351c.