Howdy all, so I've been dinking around with my '81 F150 as described in my signature, and I'm having an issue with the timing...or is it the carb? I've set the timing to about 7 degrees advanced and the vacuum port on my Holley 2bbl is showing me 6-10" of hg at an idle of 800 (the cam is rated for 1000-5000 RPM's) and that number increases as the motor wraps out. I've been told that my primary plates are too far open which would cause my timing port to be pulling vacuum. So if I go adjust my idle down to close those plates, that's going to (of course) cut my fuel and the engine will wanna die. should a guy adjust the timing accordingly to compensate for that? Or am i on the completely wrong train of thought? Anybody else run into this problem before or have a better idea of what's going on with this thing? Thanks in advance for any and all input.

-Kenny

 

Should be pulling about 17-19hg on full manifold vacuum. Several things to try. 1. Set the timing with the dizzy disconnected and the vacuum port plugged and turning the dizzy until you obtain the highest steady reading and then back off 1-2hg. 2. Adjust the idle mix screws using the vacuum gauge the same as you did for the timing. 3. Then adjust the idle speed. Do it again starting with 1. Reconnect the dizzy vac and take for a test drive. Readjust as necessary.

I found with my engine that it was best to run connected to full manifold vacuum. When connected to the timed port on the carb the throttle plates had to be opened quite a bit to get it to idle.

I have the same cam in my engine and can idle down to 500 rpm with no problem although I have the idle set at about 650 rpm and pull 18+ hg at about 2000' elevation where I live. At sea level it will pull 20 hg.

 

Yep, what Harte3 said.
Adjust the timing as he described.

Also, are you sure you have the vacuum gauge on full manifold vacuum and not ported vacuum? The full manifold vacuum should be on the base of the carb, or on a port on the intake itself.

Then, your next step is to adjust the idle mixture. If you bring the RPMs down, and it dies, the idle is set wrong. As a starting point, with the engine off, turn the idle screw all the way in (don't ever tighten it snug), and then back it out 1 1/2 turns.

Start the engine and look at your vacuum. Adjust the idle mixture screw out until the vacuum starts to drop. Then, turn it the other way (slowly, so the vacuum can readjust) and turn it in until the vacuum starts to drop again. Turn it back out slightly until you reach that peak vacuum again. Readjust the idle back down to 650 RPMs, and repeat the adjustment with the idle mixture. Repeat idle adjustment. Over and over again until no adjustments bring it any closer. As said, should be around 17 - 20hg.

 

Ya, I've triple checked that one haha, my Holley model 2300 only has 2 ports...the "timing advance port", as Holley describes it, up on the choke side of the carb and the full manifold vacuum port that I use for my brake booster, but have kept it capped off for all of these timing/carb adjustments.

Here's what I've accomplished (or lack thereof ) so far:

I adjusted the timing as per the method you both suggested and checked it with my timing light. I have it set at about 10 degrees at an idle with the vacuum advance disconnected and plugged. When I lean into the throttle, the mechanical advance shoots the timing to about 25 degrees keeping in mind that the vacuum advance is still disabled. At this point I adjusted my carb down til I finally had 0 vacuum at the timing port, an idle of 500 RPM and my timing still at 10 degrees. My manifold vacuum read about 16-18" hg. I then re-enabled the vacuum advance and it still showed 10 degrees at idle, but when i leaned into the throttle, it shot to somewhere between 45-50 degrees...

I disabled the vacuum advance again and took the truck out for a drive just to see what it would do...the motor seemed weak trying to start out from a dead stop (had to use 1st gear, and used to always start in 2nd before the rebuild) but when I put the wood to her, she seemed to have some power...but after about 10 or 15 minutes of driving up and down my (steep hill, quarter mile long) driveway, it started having trouble running....it would kinda chuck while trying to drive it and didn't really wanna do anything except run full bore. It certainly didn't want to idle and it died on me a number of times...on the last time in died, it cranked hard and didn't wanna start, like the battery was discharged. I let it sit for about 5 or so minutes and she fired right up.

I've never had trouble with an engine like this before, so it's definitely throwing me for a loop...is it all a problem with my carb, is it a bad distributor, or a sad and sorry combination of the both of them? Just seems to me that it oughta be a little easier than this...some suggested swapping in a Chevy H.E.I. ignition in place on my DS I but I'm not so sure that will cure the problem I am having right now...or will it?

Thanks guys,
-Kenny

 

Hrmm.... The timing jumping that far up doesn't sound abnormal. It can go pretty high when there's a lot of vacuum and a lot of RPMs (high speed, no load). Mine goes up to around 40 or so.
Have you tried driving it around as you have it set now with the advance hooked up? If it doesn't ping, there shouldn't be any issues.

Also, have you tried setting the idle? When you set the idle, you'll want to do it with the advance hooked up, as that's how it'll be idling on a daily basis.

If the above symptoms persist, you might have a different issue than your idle and timing.

 

Sounds like it's time to bump the timing back a couple degrees, and hook up the vac advance.
Kicking back against the starter when warm is indicative of too much initial timing.

Also, what ignition system is in use? If it has the factory DS2, does it have a genuine motorcraft brand module? The cheap aftermarket modules usually don't include the "start-retard" feature found in the motorcraft units. Ford really over-engineered the DS2 system.....

 

My brainbox on the fender just says Duraspark, doesn't say I or II anywhere, so should I assume that its still I? If it is still I, should I upgrade to II?

I suppose that the engine could advance as far as 40 or 50 degrees, but it's doing it just off of idle, like about 1500 RPM's instead of full bore when it should be...and I've driven the truck with and without the vacuum advance hooked up at several different initial timing settings...the problem persists only in different degrees of severity...

I did finally figure something out for sure though...the sensing port in the barrel for the timing port on the carb is drilled below my throttle plate and the Holley rep I've been emailing says it should be above the plate...he recommended drilling holes through my plate, but I'm thinking that's B.S....I'm thinking that it got machined wrong at the factory and I oughta have them send me a different one. I'm also beginning to think that the carb is either running lean or rich and that my fuel pump isn't keeping it fed either....that would explain why it runs ok (w/o vacuum advance) for 10 or 15 minutes and then it starts acting up on me, it's burnt through all its available fuel in the bowl. I think tomorrow I'm going to test my fuel pressure and maybe borrow a different carb from a friend and see how it works to either eliminate or confirm a carb issue once and for all.

Thoughts? Thanks for all the replies everyone, by the way! I appreciate the help!

-Kenny

 

One thing, I hate to say, is that I've found out Holley tech support doesn't know a darn thing. I've had 100% disappointment with their "help", and when I've shared their advice and recommendations with others, it's been laughed at.

I'm not trying to spread bad vibes about Holley, but from my experience, their tech support recommendations, aside from basic tuning, are rubbish. He may very well be right in this case, but my point is to be sure and double (triple) check their recommendations with someone else before going through with them.

40 - 50 degrees advance is a lot by 1500 RPMs under any circumstances, at least I think so. The ignition module doesn't have anything to do with the timing advance though on a DS setup. It's all weights and vacuum. The idle base timing is set by the rotation of the distributor. The mechanical advance from RPMs is set by weights inside, with their speed of increase limited by springs. And the vacuum advance is set by an arm that is pulled by vacuum.

To me, it sounds like a springs inside the distributor has given out, or are weak. Is the distributor new? I know when I was recurving my distributor, I had the spring tension wrong, and it advanced way too quickly.

 

Good thought about the advance springs. If one is broke/missing, it will certainly allow the timing to advance way too quickly.
Here's another rare, but certainly possible problem. The vacuum advance arm can come loose from the internals of the dist. A buddy of mine was chasing down an erratic timing condition, and thought I was crazy when I suggested he check for that, till he (finally) did and found it was unhooked......

The box having duraspark on it usually indicates it's a motorcraft brand. As far as I know, ford/motorcraft owns the exclusive rights to use that name, and aftermarket manufacturers are not allowed to put it on their parts. Of course, there's always the possibility of counterfeit parts making into the country...

Holley tech support is about as flakey as their carbs are, in my opinion. I don't care for either. The advance port being misdrilled wouldn't surprise me one bit, since 90% of the shadetree hotrodders don't even bother with using the vacuum advance, and racers tend to focus only on total timing @ a specific RPM and therefore don't utilize the vacuum advance at all.

 

Ah yes, I had this problem too. It was the other way around though. In a mishandling, the arm had been slightly bent, and made it bind in place. So, the vacuum from the carb's advance was able to pull the arm to increase timing, but since the arm was bent, it would bind and wouldn't return. Made me push 40 or so advance at idle.

Easy to check by disconnecting the vacuum line from the carb (not the distributor), and put the other end either on a handheld vacuum pump if you have one, or just in your mouth. Put a good amount of suction on it and watch the arm move on the advance. If it moves and then moves back when you relieve the suction, the arm's movement is okay.

Check the internal workings by putting a timing light on the engine and do the suction again. You should see the timing advance and then drop when the suction stops.

 

if you are still running all the smog equip then run the vac adv off the timed port

if you are running no smog stuff then you want it off full manifold vacuum.

http://www.corvette-restoration.com/.../Timing101.pdf

i know its on a vette forum but still good information....

 

Never run a non-computerized carb/ignition system off manifold vacuum for the vacuum advance. Doing so makes it run full advance at idle, and retards as soon as you open the throttle. In other words, it becomes a vacuum retard.
Anyone that says to use manifold vacuum for the vacuum advance is wrong. Period.

 

Timed or ported vacuum has zero vacuum at idle, right? Then why does your idle rpm drop if you disconnect the advance on the factory setup? Why must you disconnect the vacuum advance to set base timing?

 

No way in heck do you want to drill out throttle plates. That will only make the idle problem worse

If you've got the vacuum advance hooked to manifold vacuum that's why it's idling at 1,000. Like AB said, the engine speed should increase under vacuum.

I've seen hot rods with the advance on manifold vacuum, but only to help off idle with a big - like 230+ @.050 big - cam.

Get the mechanical advance curve dialed in first, then hook the vacuum to a ported source.

 

Because the idle speed *can* hold the throttle plate open slightly, allowing a small percentage of venturi vacuum to occur. Unhooking the vac advance takes this possibility out of the equation, eliminating the variables.