Timing frustrations

[Big Red Mach 1]

Big RED & Geoff.

I figured that all of the shafts are and were always steel.

There are bushings (plastic) both older and present carbs, but the older Holley's were Zinc .

Now most all are aluminum and that will wear faster than zinc period...

I am not an engineer but I can drive a train ! (sorry I just wanted to say that on the internet.)

Yes I really can drive a train.

Boilermaster

I love trains!! I watch YouTube videos of train hops all the time. Would love to do that even though you can get busted for it. LOL

I went on the summit site and asked what the bushings were made of. I assumed Teflon or Bronze. We'll see what king of answer I get back. 

 

[Don C]

Holleys don't come with bushings, either. The throttle bodies do have thicker aluminum casting around the throttle shafts. I believe the throttle shafts used to be made from bronze, don't know about now.

 

[Stanglover]

Big RED & Geoff.

I figured that all of the shafts are and were always steel.

There are bushings (plastic) both older and present carbs, but the older Holley's were Zinc .

Now most all are aluminum and that will wear faster than zinc period...

I am not an engineer but I can drive a train ! (sorry I just wanted to say that on the internet.)

Yes I really can drive a train.

Boilermaster

 Okay, I have to admit I'm not thinking too much these days. probably most carb bodies are die cast Zinc alloy. That's a reason they're not polished as aluminum can be. As for bushings on the shafts, I have not paid too much attention to that detail, but if none are used, then for sure the zinc will stand up better over time. These things are not made to last a lifetime.

Thanks for your knowledge and input.

On a side note, my brother (in England) is a part owner of a steam engine in Poland and goes there to drive it once a year. I too love steam engines!!

 

[Big Red Mach 1]

Little update. For the most part, I really like the carb. Coming from no choke, I like how well the electric choke works, The annular boosters certainly do much better at atomizing the fuel. I like that it came with a fuel rail too. I like how easy it is to swap the Power Valves. Not that it's hard by any stretch on a Holley, but this carb with the PV's below use one gasket and 4 tiny screws. Don't need the 2 large gaskets for both sides of the metering block like you do on a Holley. It also does come pretty darn ready to run out of the box. It's amazingly lightweight being all aluminum.

HOWEVER. There are some oddities.

I hooked it up, and once again, I'm still at 10Hg and running pig rich. Was almost like I never took the Holley off. Adjusting the mixture screws did absolutely nothing for me. Which told me I'm once again getting fuel from elsewhere in the idle circuit. The power valve of course. So at 10Hg, by rule, my primary PV should be a 4.5 since Holley doesn't have a 5. So let's open it up and see what I have inside... A 6.5. Okay, not a surprise. Let's see the secondary PV...9.5. That's a large PV for a secondary, no??? Once the secondary circuit kicks in, at or near WOT you're at or near no vacuum left right? So Why a 9.5? Just to make sure there is a ton of fuel waiting once you hit WOT?

I know most carbs have no PV on the secondary side. Just larger jets. But when you run a secondary PV, should it really be that big??? Is there a benefit at all to that?

Back to the primary, I popped in a 5.5 (just to see if it got a little better) and really couldn't get any adjustment out of it still. Probably still opening up just enough to screw me up. So I jumped down to a 4.5 and was able to get a little adjustment, and a little more vacuum at 11. Still running a tad more rich than I'd like. But better. I know that I need to be adjusting using a wideband if I want to get it any better. I'm just not going to get it fully dialed in without one.

Back to that 9.5 secondary, what do you carb whisperers think about that?

 

[Don C]

Have you checked your oil for gas in it? After all of the rich running your oil may have a lot of gas in it and as the engine warms the fuel vapors are pulled through the PCV causing a rich idle. I had this happen once on a car that belonged to a friend that I was talked into looking at.

 

[Big Red Mach 1]

No. I have not. However, I have literally nothing at all hooked up to the carb other than the vac gauge. Absolutely everything else is plugged off.

 

[boilermaster]

Big Red Mach 1,

If you put a vacuum gauge in the cockpit and watched it you WILL understand.

Hammer the go fast pedal to the floor and vacuum drops, as the engine accelerates and you gain speed you get some of that vacuum back,

even at full throttle, that is how the secondary's open in the first place.

Depending on the secondary's spring rating will determine at what rpm the secondary's open.

Put in a really weak spring you will get a LEAN bog not a rich one.

When the secondary's start to open they don't just slam open, they open gradually based on a vacuum signal.

Start thinking of these power valves as a load switch and you may better understand them.

That secondary power valves rating is only PART of the air fuel supply, you also have accelerator pump circuit, main jets, power valves and power valve restriction channel to consider here, and oh AIR, lots of air.

If and or when you hook up wide band o2 and watch it in a high gear cruise, you will see it start out rich and get progressively leaner as rpm's increase, (because you are only using the main jets)  as your rpm increases you are adding more and more air making it leaner and leaner.

as this happens your vacuum becomes lower and lower, then viola, that power valve brings you back richer once again.

Now gain some more vacuum and we start all over again with the secondary's.

That rear power valve is based on a lot more than just it's vacuum threshold, consider jet size, secondary spring rate, venture size and throttle bore size.

Boilermaster

 

[boilermaster]

Good point Don c. on the crankcase vapors.

Big Red,

I would STILL like to see you bump the timing in 2 degree increments until you get just the hint of spark knock and then back off 2 degrees.

That divot on # 1 piston is there for a reason, either valve timing or ignition timing.

Boilermaster

 

[Big Red Mach 1]

Understood, and some brilliant points about the size of they valve they chose being part of the overall architecture of the carb. I really didn't consider any of that when thinking about the size.

I do understand that I build vacuum under mild acceleration, but I dump most of it going to WOT quickly, and slowly build some of it back cruising. And, yes, I've seen the secondaries CREEP open, on vacuum secondaries in particular.

The car will have a wideband and a vac gauge in it where the console clock currently is. I'll be excited to get that project underway as well. : )

 

[Big Red Mach 1]

Good point Don c. on the crankcase vapors.

Big Red,

I would STILL like to see you bump the timing in 2 degree increments until you get just the hint of spark knock and then back off 2 degrees.

That divot on # 1 piston is there for a reason, either valve timing or ignition timing.

Boilermaster

I will certainly do that.

Please don't remind me of the divot though.   :shootself: rofl

 

[Don C]

Because the stock 4V 351C has an idle spec of 13 inches at sea level, and because you are not at sea level and because your engine apparently has a hotter than stock camshaft, 11 inches of vacuum at idle may be realistic.

 

[Big Red Mach 1]

Because the stock 4V 351C has an idle spec of 13 inches at sea level, and because you are not at sea level and because your engine apparently has a hotter than stock camshaft, 11 inches of vacuum at idle may be realistic.

Agree completely Don. I've given up on the hope for more. 11 maybe 12 on a good day is all I expect to get with this cam and where I live.

I accepted that reality this morning. 

 

[c9zx]

Little update. For the most part, I really like the carb. Coming from no choke, I like how well the electric choke works, The annular boosters certainly do much better at atomizing the fuel. I like that it came with a fuel rail too. I like how easy it is to swap the Power Valves. Not that it's hard by any stretch on a Holley, but this carb with the PV's below use one gasket and 4 tiny screws. Don't need the 2 large gaskets for both sides of the metering block like you do on a Holley. It also does come pretty darn ready to run out of the box. It's amazingly lightweight being all aluminum.

HOWEVER. There are some oddities.

I hooked it up, and once again, I'm still at 10Hg and running pig rich. Was almost like I never took the Holley off. Adjusting the mixture screws did absolutely nothing for me. Which told me I'm once again getting fuel from elsewhere in the idle circuit. The power valve of course. So at 10Hg, by rule, my primary PV should be a 4.5 since Holley doesn't have a 5. So let's open it up and see what I have inside... A 6.5. Okay, not a surprise. Let's see the secondary PV...9.5. That's a large PV for a secondary, no??? Once the secondary circuit kicks in, at or near WOT you're at or near no vacuum left right? So Why a 9.5? Just to make sure there is a ton of fuel waiting once you hit WOT?

I know most carbs have no PV on the secondary side. Just larger jets. But when you run a secondary PV, should it really be that big??? Is there a benefit at all to that?

Back to the primary, I popped in a 5.5 (just to see if it got a little better) and really couldn't get any adjustment out of it still. Probably still opening up just enough to screw me up. So I jumped down to a 4.5 and was able to get a little adjustment, and a little more vacuum at 11. Still running a tad more rich than I'd like. But better. I know that I need to be adjusting using a wideband if I want to get it any better. I'm just not going to get it fully dialed in without one.

Back to that 9.5 secondary, what do you carb whisperers think about that?

Was the "9" stamped on one side of the Sec PV and the "5" stamped 180 degrees out on the other side? perhaps the "9" is a "6". I know of no reason why the PRI PV would be 6.5 and the Sec PV be 9.5 in/hg to be fully closed/starting to open. Do you have a "Mighty Vac", or similar, to test the PVs? A VAC SEC carb diaphragm is activated by PRI venturi vacuum (negative pressure), not to be confused with manifold vacuum. As the throttle is opened manifold pressure drops and venturi vacuum (flow) increases causing the VAC SEC diaphragm to open at a rate determined by venturi vacuum and VAC SEC spring rate. If the SEC PV really is a 9.5 someone messed up. Contact Summit tech for out of the box calibrations. Are you sure that this is the same intake and engine that was in the car when Fast Eddy owned the car? IIRC he had a Blue Thunder Intake on the engine. I can't believe he would run an Offey intake. I do think Boilermaster is right about the timing issue. Since you have no accurate way to verify damper ring position/pointer position his idea to advance until slight ping and back off 2 degrees is a good idea. The AFR meter is a good idea but, if the timing is not right you will adjust to a wrong target. The AFR meter is a great tool, as I have recently leaned, but if an aggressive cam is used the reading at idle can be misleading due to overlap. P.S. don't worry about the #1 piston dimple. I'm almost certain it it was put there by a piston stop and a forgetful engine assembler.  Keep us updated. This is a good thread, or whatever it is called. Chuck

 

[Big Red Mach 1]

It's really 9.5. They show it in their specs. I'll call Summit Monday and have them confirm what they should be. Eddie loves the Blue Thunder, but believe it or not, he did switch to this intake at some point. Although he still says Blue Thunder is his favorite.

 

[jpaz]

Could the camshaft be giving you these issues? If I remember you have a comp cams 270h cam. I use to have the same one in my 351c. I got about the same kinda low vacuum readings as you, and it always ran rich. I had a couple different carbs on it and got about the same results. The second carb was the QF that I’m running now. I know that cam is a single pattern and Cleveland’s like a dual pattern better. I think it was Hemikiller who said this is the worst possible cam for a 351. But you would think that you should be able to tune the carb so it doesn’t run so rich, but I never could. 

Probably not the issue, but I had about the same problems and I thought I’d let you know.

I have rebuilt my engine with a different cam, but same carb, and I have none of the endless rich conditions anymore.

 

[boilermaster]

Jpaz, 

Funny thing is that I decided to call comp's tech division where they ask for all of your engine specs and then select a bumpstick for you.

Guess what they selected for me ? yup you got it.

I did not take the bait and gave comp MY specs and had one built for me.

This cam is not that far from the 270 but with split lift and duration and a lot less overlap and I make 17hg.@ warm idle.

Boilermaster

 

[c9zx]

Jpaz, 

Funny thing is that I decided to call comp's tech division where they ask for all of your engine specs and then select a bumpstick for you.

Guess what they selected for me ? yup you got it.

I did not take the bait and gave comp MY specs and had one built for me.

This cam is not that far from the 270 but with split lift and duration and a lot less overlap and I make 17hg.@ warm idle.

Boilermaster

The PV situation is very odd. I would try to get to an actual carb tech at summit to ask why. The cam is not well suited to a 4V Cleveland but, the overlap is only 50 degrees. It has a 110 lobe separation, a little on the tight side, which can make the idle choppy and lower manifold vacuum. However, I would expect vacuum in the 14 in/hg range. If the cam was not degreed in it could be installed retarded which would give the symptoms you describe. Unfortunately there is no easy way to check this. Chuck

 

[boilermaster]

C9zx,

The nice thing about comp cams is that they list lobe lift @ tdc , so no degree wheel needed if you actually know where true tdc  is.

Just look up your lobe profile in their master catalog and they give you the spec.

from there you can do the math to figure out exactly where you are.

I must admit that finding my lobes in the pdf catalog was a pain, but no degree wheel needed, just a dial indicator.

So one can actually CHECK cam timing without removing the timing cover, unfortunately changing cam timing is a little more involved.

Boilermaster

 

[c9zx]

The info about lift at TDC from comp is a good thing to know, thanks. I thought that early in the thread the damper ring position was in question so true TDC was unknown. I may just be having a false recollection. Chuck

 

[Big Red Mach 1]

Well, either way, the cam I have is the cam I'm going to have to live with for a while.

I'll bump the timing up 2 degrees until I start to ping and then back it off 2 as suggested and see where I land. I'll also call Summit and ask about their secondary PV choice. There has to be a reason behind it. I've been doing some more reading in other places around the web as well, and it seems like of the folks who choose to keep a secondary PV like to match the primary. Not sure what the logic behind that is. Doesn't seem to be a particular rule of thumb on the subject.

More importantly I have a lot of PVs from Quick Fuel coming that I can use and play around with and see what seems to work best from a drive-ability standpoint. They even have whole numbers. so I've got some 4s, 4.5s, 5s, and 5.5s coming. We'll see what actually performs best for me, and then further dial it in when I do the wideband.

No matter what Summit says about the secondary PV, I'm keeping the carb. Again, I love the choke, and how easy it is to change PV's and other items. The car also idles way smoother than it ever did with the Holley, and it's a lot more responsive to throttle input as well. Probably due to the annular boosters. I'll get it fully dialed in as can be eventually.