Need second opinion vacuum advance issue.

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72HCODE

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Been driving my car quite a bit this year and I've been making more rolling tweaks and changes as I have almost daily drove it.

2 times in the past I've noted my vacuum advance hose has been disconnected after a long drive, I chalked it up to mechanic error in forgetting to reattach it during tuning, however I now know that was not the case my vacuum hose for my advance had popped off again and I didn't know it. The last time it popped it also popped the orange cap that caps off the dual advance for cars that do not use it. So that is telling me it is popping that hose with some amount of force most likely under hard acceleration however I do not hear a back fire under heavy acceleration.

I have some ideas but I want some second opinion, one possibility is the secondaries opening too fast.

I know for sure it popped off yesterday when I drove it because I heard something under the hood which I thought was the AC compressor kicking off but now I know it was the advance hose popping off problem is I don't remember if it was during acceleration or deceleration when it happened.

I was going to pull the plugs and see what they have to say and also swap them for a hotter set because the motor is running too cold my thermostat hasn't even kicked off this year. And the temp stays on the low side of the gauge. I tested the advance as well the diaphram is not blown.

So toss me ideas for a vacuum advance where the vacuum hose keeps popping off.

 
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Far as I know only a backfire can create pressure to dislodge a vacuum hose.

(also sometimes when u try to start a car and it does not catch and the motor turns backwards)

Perhaps others will have other ideas.

Good Luck!

Paul


Adding on...

I bet it is just old sloppy fitting vacuum hoses in play here.

First thing I did was change ALL vacuum lines on my horse.

 
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Interesting problem... Which port do you have it connected to? I know there's a lot of debate as to which one is proper, ported or manifold?
I second this question. For it to pop the other cap off you're talking about a pretty serious pressure wave to create a force on the other side of that diaphragm

 

72HCODE

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it is connected to ported.

This is why i didn't notice it. Ported vacuum is off at Idle. so the vacuum leak occurred when i accelerated. so i didn't notice the leak when i started up the car, my idle is very high as is so the small leak i might of had was not noticed. the last drive when i parked it i did notice my idle was slightly lower then usual, so that all makes sense now.

the hose is not easy to pop off either, so it must be repeated slight backfires that slowly pushes the hose off the connector on the carb. It must be happening on accleration i'm thinking with the AC on... I might need to up my accelerator shooter 1-2 sizes, but i never heard detonation at that point..

I could also turn my vacuum advance down 1-2 turns, and reduce the timing.

I agree its a substantial possible back fire. Not only do i know now that the hose was popping off, but it actaully popped the orange cap off the distributor advance, my car has a history of carb lean backfire to the point i have blown the aircleaner filter off and i had to replace the vacuum booster. however i thought i solved it since i do not hear ping detonation like i used to. the carb is set pretty rich right now, it was so rich on the last drive that i backed off the idle screws a little, that was when i saw the orange cap was blown off and the hose was disconnected under the air cleaner base.

 

metalfan302

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Honestly these issuse should be treated sepretly yet together if that makes sence. Let me explain the issues you are having are tied to gether yet not one matches up yet causes your problem. First Question when were your heads last redone. If you have a history of back firing that would be where i would look first, compression test that shit. After you must lean out your carb bro, you are flooding your plugs. Now this is one thing i have had problems with up till now with the tuning, put the air/fuel screws in and work them out 1/4 to a 1/2 till it runs right. Just my opinion.

 

72HCODE

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Trust me been through it with the engine, compression is good.

Heads are new. I'll be pulling the plugs and looking how white they are still.

It's a combination of parts problems because my engine builder didn't listen to me when he rebuilt my engine. I've been through it with that guy enough.

She will still lean stumble slightly when cold, it has been much better so I thought I could live with it but the engine can't I've been going over the last couple 100 miles in my head and I think that hose popped off at least 2 drives ago..

I remembered I've been getting a cloud of smoke on heavy acceleration lately because I lost my advance since the hose was disconnected. I made a note it was a little odd, and kept an eye on it. It was another reason I dropped the air bleeds to see if I went too far but looks like it was the vacuum leak that was the problem.

I have hotter plugs I need to try out and I know that will increase the lean misfire. So I'll be doing some testing with the advance disabled, and engine cold.

I have options so I'm exploring them.

 
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72HCODE,

How long ago was your engine rebuilt? I was researching your threads and found the 07-06-2011 thread. Is this the time frame?

I also found this small article, "Why does my engine spit or backfire?"

http://www.badasscars.com/index.cfm/page/ptype=product/product_id=95/category_id=13/mode=prod/prd95.htm

2CarPros- Engine Backfire

http://www.2carpros.com/articles/what-is-an-engine-backfire

My first initial thought was, How well was the distributor to TDC aligned? Next one was, What carburetor are you using? The newer or modern Holley Carburetors are suppose to have protection a mechanism to protect the power valves. Could his power valve be blown? How well is the accelerator pump on the carburetor adjusted? How old is the carburetor?

This is a head scratcher here. I will be following this thread to see what the final solution is.

mustang7173

 
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Engines need the additional advance afforded by manifold vacuum to compensate for lean idle conditions.

Ported vacuum comes from above the throttle plates and shouldn't be affected by backfiring, but your engine stumbling may cause fluctuations in vacuum and pressure at the ported vacuum location.

I agree with the other post about old hoses falling off, just the engine movements caused by the stumbling may be shaking the hose loose.

 

72HCODE

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engine was rebuilt in 2008, then needed head attention in 2011.

Initial timing is 10 degrees.

compression is fine.

carb holley 750 DP, with modified accelerator pump circuit to 50CC from 30cc Brown Cam.

the power valve protection just protects the power valve from a carb backfire everything else does not have protection.

carb is 2008 and I've gone through it making changes numerous times.

hooking up a Vacuum gauge again is on the list.

I know shes still lean on acceleration, so i'm going to have to do some cold tuning adding more accelerator pump shot.

But, i'm pulling #1 plug and seeing what it looks like.

otherwise the car has been running very well this year.

looking back i can see the hose has popped off in past years.

the only time there would be enough back pressure to move a hose or pop a vacuum cap has to be with a carb lean backfire, it must happen when the engine has still not fully warmed up and i gun it to get on the highway or from a stop light. I can't see it happening at cruise. under heavy load she used to ping but i changed the power valve and took care of that.

changed from a 6.5HG to a 9HG on the power valve. she would ping just off cruise otherwise. i had to fill the gap between the pump shot and jets so i opened the power valve earlier.

I made some exhaust back pressure changes and then i ended up leaning the carb out slightly after that.

when i have a chance to pull the plug i'm betting it will be bone white again, but we shall see. i have to be really close since the car used to sound like a box of marbles bouncing around in the exhaust.

72HCODE,

How long ago was your engine rebuilt? I was researching your threads and found the 07-06-2011 thread. Is this the time frame?

I also found this small article, "Why does my engine spit or backfire?"

http://www.badasscars.com/index.cfm/page/ptype=product/product_id=95/category_id=13/mode=prod/prd95.htm

2CarPros- Engine Backfire

http://www.2carpros.com/articles/what-is-an-engine-backfire

My first initial thought was, How well was the distributor to TDC aligned? Next one was, What carburetor are you using? The newer or modern Holley Carburetors are suppose to have protection a mechanism to protect the power valves. Could his power valve be blown? How well is the accelerator pump on the carburetor adjusted? How old is the carburetor?

This is a head scratcher here. I will be following this thread to see what the final solution is.

mustang7173
 

72HCODE

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ported vac has a plate on the throttle arm that blocks off the vacuum port at idle only, so at idle when using ported there is no vacuum advance, 0 HG.

when you open the throttle to increase RPMs then ported becomes full manifold Vacuum. using full manifold vaccum at idle has the mechanical off and vaccum advance on, since HG at idle is 18-20HG then you have a lot of advance at idle, that means higher rpms and lower exhaust temps. that translates into faster off the line acceleration, your starting at a higher level so to speak.

the idea with ported is just to decrease emissions at idle, retarded Timing means hotter Exhaust manifold and that burns off emissions gasses at idle.

the vacuum advance itself is setup to make use of extra rich condition in the engine while accelerating under full mechanical advance, so if you have an adjustable advance you can crank more timing into the engine when it can tolerate it. if the advance is disabled when an engine was tuned to use it then you get a rich condition. this is what i saw, the vacuum leak would cause a lean condition but was tiny and since my engine requires a huge dump of gas to not carb back fire i ended up with a Monster smoke cloud of unburnt gas out the back as my engine was massively retarded on timing at that point.

the back side of my car was covered in soot the last drive so i know it was hyper rich thanks to the loss of the advance since the hose fell off. funny thing i didn't feel it at all inside the car.

2 clues, smoke cloud out the back when i gunned it and slightly lower idle maybe 50 rpms when the hose came off.

the hose itself is on there tight and isn't an old hose i replaced it a few years ago it is still soft.

what this is telling me is that the hose was blown off and didn't slowly fall off because of the missing Dual vacuum advance cap, the back fire was strong enough to pop that cap off and pop that hose off so the diaphragm saw a positive pressure wave at some point over the last 500 miles.

problem is i never heard it or felt it.

So its getting covered up by engine noise and i know when the motor is cold she misses on acceleration.

again i will need to investigate further. I'm rather happy the hose popped off because it released pressure. better the hose then the diaphragm.

total mechanical should be 34ish,, have to check it again i limited it a couple years ago.

Engines need the additional advance afforded by manifold vacuum to compensate for lean idle conditions.

Ported vacuum comes from above the throttle plates and shouldn't be affected by backfiring, but your engine stumbling may cause fluctuations in vacuum and pressure at the ported vacuum location.

I agree with the other post about old hoses falling off, just the engine movements caused by the stumbling may be shaking the hose loose.
 
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72HCODE,

Since your Holley is a 2008 model, then you have the Power valve protection system built in. Was it brand new? Could it be something wrong with the internal body of the carburetor due to its age? So, I went back to the Engine, Drive train, performance forum to look for threads related to carburetor sizing and cfm flow rates. I was able to locate your thread on your carburetor upgrade process. The Holley 750 DP is pretty much a mute point here. One other thing to look and eliminate is the PVC valve and tube. I remember having an non-factory tube to the PCV valve and when I revved the engine, the vacuum collapsed the tube thus choking off the PVC valve. Just a thought.

We will keep plug'n away at this.

mustang7173

 

MotoArts

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In regards to the plugs...

Heat range change will not make the engine run hotter or colder.

If the center porcelain is already white, the engine could be burning lean. A little color is good. It's OK if the outer metal "ring" is black. It should be, it is where the heat is dissipated into the cylinder heads.

Do not mask a bad carb/timing tune with changing plug heat ranges.

True, plugs are harder to read with today's unleaded gas, but nonetheless try these guides:

http://www.ngk.com.au/spark-plugs/technical-information/heat-range-explanation

https://www.google.com/search?q=how+to+read+spark+plug+color&client=firefox-a&hs=vsk&rls=org.mozilla:en-US:eek:fficial&channel=sb&tbm=isch&tbo=u&source=univ&sa=X&ei=5f38U6jYJcrMsQTUm4GADQ&ved=0CB8QsAQ&biw=1088&bih=482

As for a potential cause for intake backfire, check all of the other vac lines for splits, or slipped intake gasket (especially common on Cleveland engines from what I understand) sucking air/oil from the lifter valley (potential source for your "soot").

As a big "swing of the bat", I'd bump the primary mains up a number and try it.

Another (not too common) big swing would be doing a leakdown check, looking for a potential sticking intake valve, or burned intake seat.

My money... without actually seeing/hearing... is going to be on an intake gasket issue. When you pull all 8 plugs and compare colors, if there are 1 or 2 dark ones... :-/

 
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72HCODE

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ok here is the update...

always make small changes.

Problem #1 i'm not sure when the hose popped off, my money is it happened back in June.

I spoke to a neighbor that is a mechanic he works on hotrods and i explained what happened and my theory on why.

short story since May i've been making changes to the car as i drove it more and more to adjust for problems and short comings.

He agreed with me about the lean misfire. we agreed on upping the pump shot, and a couple other things to try later.

got home.

yesterday i discovered the hose was popped off. when i put it back on i readjusted the idle bleeds down .5 turn.

today: Pulled air cleaner. took a good look around. pulled Plug #1 the plug was a little fat on idle, everything else looked good REALLY good. reinstalled plug hooked up ignition wire.

inspected for blown read valves on A/C vacuum canistor and vaccum booster, both checked out A-OK.

Based on conversation with mechanic buddy i looked at the pump shot. I looked through my car notes and i had actaully installed a .35 shooter last year, Upped to .37 Shooter.

installed Vac gauge, installed timing light, capped vac advance.

started motor, ran good,, looked at Vac gauge she read 19"HG at idle,, she never read that high before, Timing Dead on mark for initial 10 degs, checked max mechanical dead on mark at 34 degrees. checked fire on plugs all normal.

pulled vac gauge, pulled timing light, reinstalled Vac advance, reinstalled air base.

went for Drive, it was awesome. the dame idle was smooth as glass. had no issues. I gunned it a bunch of times with the A/C running. came home inspected Vac hose it was still fully seated.

car ran dare i say perfect. now i will be keeping an eye on that hose.

So update in the future.

forgot to mention.

I ran the engine on autolite 24s for a couple of reasons and i wanted to change to autolite 25s.

ran 24s because. engine was close to overheating in 2008, there were major problems, including detonation after rebuild.

the old A/C compressor had a major problem and locked up the engine 2 times and stalled it. on a 90 degree day the car started to overheat. this was with 24s colder heat range. the idea was run the engine cold until i could iron out the endless problems. most likely this saved the engine from grenadeing itself.

the 24s run the engine very cold. so on a 90 degree day after fixing all the problems even with the new A/C compressor running, the engine will not get hot enough to turn on the thermostat at 192 degrees, it most likely is getting the coolant to 160 degrees, the minimum to activate the intake air snorkel warm to cold air intake servo, the engine isn't reaching proper temperature with the 24s. the thought was with the engine running better(before the hose popping off discovery) i wanted to swap to 25s and increase combustion temp and block temp to get the engine in the 190 range for good drivability and better fuel burn. 25s will increase the chance of a ping/detonation... so i'm holding off messing with the 25s, now we take it easy for a while drive the car and keep an eye on that hose.

 
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