New 4180 Carb Rebuild, Low Vacuum, Need some help...

[clintonvillian]

For starters let me say that I have no clue what has been done to this motor. I'm trying to figure out what the PO installed.

It came with an aluminum "Ford" 4 barrel intake, 4180 Carb, E7 or E7TE heads.

I checked the lift at the pushrod, it measures .210", at the intake valve it measures .340". Seems to be a stock Cam, right?

Compression is even across all cylinders.

At 6 degrees timing, it is pulling 7 inHG. I advanced it to 12 degrees, and it is pulling 13 inHG.



Now Monday evening I advanced the timing to around 20 degrees, and had it tuned pretty decent. Still only pulling 13-14 inHG. Some guys reccomended I disconnect the PCV valve (it is aftermarket) and check readings at factory timing. This is where the issues started happening. I couldn't get the hose off of the pcv valve or off the nipple on the carb spacer. So I just pulled the PCV out of the valve cover...engine died immediately. tried to restart it, and nothing.

Pushed it back into the cover, and it starts and idles fine. So I think okay I will pull the hose off. Pulled the hose off the PCV and plugged it. Pulled the PCV out of the valve cover.

Engine starts, sputters surges really hard, starts knocking. I grab the test light, and put it on the balancer. The vacuum advance kicked in and timing is probably 40-50 degrees. At this time, I panic and grab the distributor and twist it back down...a little to fast and retard the timing below 0 degrees and cut the ignition. As this is going on I look up and fuel is pouring out of the accelerator pump.

I cleaned everything up, plugged the PCV back in, set everything back to where I had it the night before, fires right up. I now have a small leak at the accelerator pump, that sprays fuel when I hit it. But the engine runs....except now I think I have a permanent knock near cylinder 8.

What are your all's thoughts?

No vacuum leaks (that I can find). Would a small leak at the accelerator pump cause this? Or is there maybe an internal vacuum leak somewhere? I just put new intake manifold gaskets on, as well as the carb rebuild.

 

[pcf_mark]

There is a lot going on all at once. I would fix your fuel leak first so it is safe. A 4180 should to really spray fuel I am note sure I follow your fuel leak. Is it coming out of the fuel vent on top of the carb? If it is coming out of the vent the either the float level is too high, the float is stuck or dirt has clogged the needle and seat and the engine is being flooded.

Watch this

https://www.google.com/search?q=che...me&ie=UTF-8#kpvalbx=_nXu3YLO4GMSp1QHJpbzoDg18

I have seen a Holley weep fuel from the accelerator pump that is on the bottom of the float bowl but never squirt. It is possible! If your leak is from the diaphragm on the bottom then you need to put a new accel pump diaphragm in. Easy way is to lift the carb off and unscrew it , put a new one in.

Another great video on how the accel pump works and how to adjust it

https://www.youtube.com/watch?v=w3F3ssOb8lg

 

[clintonvillian]

There is a lot going on all at once. I would fix your fuel leak first so it is safe. A 4180 should to really spray fuel I am note sure I follow your fuel leak. Is it coming out of the fuel vent on top of the carb? If it is coming out of the vent the either the float level is too high, the float is stuck or dirt has clogged the needle and seat and the engine is being flooded.

Watch this

https://www.google.com/search?q=che...me&ie=UTF-8#kpvalbx=_nXu3YLO4GMSp1QHJpbzoDg18

I have seen a Holley weep fuel from the accelerator pump that is on the bottom of the float bowl but never squirt. It is possible! If your leak is from the diaphragm on the bottom then you need to put a new accel pump diaphragm in. Easy way is to lift the carb off and unscrew it , put a new one in.

Another great video on how the accel pump works and how to adjust it

https://www.youtube.com/watch?v=w3F3ssOb8lg

The pump is adjusted properly. It is squirting out just above the pump arm. It makes me think the pump gasket split just above the arm. This initially wasn't an issue. It literally started when the engine was surging. Would the surging have anything to do with the accelerator pump?

Or are we looking at tow different issues that just happened to occur around the same time. I know a backfire will blow out the power valve, and even the diaphragm in the distributor. I was curious if thats a similar possibility with the diaphragm pump.

 

[pcf_mark]

Next up disconnect every vacuum hose from the carb - including power brakes if equipped and distributor vacuum advance and PCV. Then go along the bottom of the carb and plug every single vacuum port. Check for a big one on the back, small one on the front corner etc. Look carefully. Given you have 14-15" inches you are in pretty good but not stock.

Start it up and keep it running - it may need some help w/o vacuum advance. Check the engine vacuum while holding it at idle speed. If it is the same 14-15 inches - that is what you are going to have until you get into some carb tuning and you probably do not have a leak. BUT if it climbs up to 16+ steady you have a leak from either a missed port or the power brakes or PCV leak. I recommend removing the PCV for all of your tuning.

Once you confirm or sort out your vacuum leak go back to basic on the distributor. Set the base timing to 10-12 degrees with the vacuum advance disconnected. Then connect the vacuum advance to ported vacuum (the one on the passenger side of the metering block). You should have close to the same vacuum reading from your previous test. How does it run? Probably ok but not very snappy.

 

[pcf_mark]

The pump is adjusted properly. It is squirting out just above the pump arm. It makes me think the pump gasket split just above the arm. This initially wasn't an issue. It literally started when the engine was surging. Would the surging have anything to do with the accelerator pump?

Or are we looking at tow different issues that just happened to occur around the same time. I know a backfire will blow out the power valve, and even the diaphragm in the distributor. I was curious if thats a similar possibility with the diaphragm pump.

Sounds like a bad diaphragm. Fuel sits in there all the time so they crap out with modern material and ethanol gas. If the pump is leaking it will not take throttle smooth will usually backfire. Don't worry about a power valve getting blown out that is an old wives tale.

 

[pcf_mark]

When the engine changes substantially by disconnecting and plugging the PCV the air leak of the PCV is impacting the tune of the carburetor. If your engine is so rich that it needs the air leak from the PCV to idle decent you have a carb that is way out of adjustment. To keep tuning with that is going to make for a very inefficient tune. I would disconnect and plug that before doing much more you will be chasing odd stuff like the throttle blades being closed but it is still idling at 900 rpm.

Set the idle mixture screws to 1 1/2 turns out both sides from lightly seated. With the engine off peak into the carb throat and see if there are any holes drilled int the throttle blades too. Also engine off look at the idle screw touching the linkage. Is it making contact? Does it touch and is it 1 to 2 turns down? These two should get you running smoothly with 10 degrees of timing.

 

[clintonvillian]

All 4 mix screws were at 1.5 turns. Went to 2 full turns to clear idle up. It idled fine, sounded good. Vacuum was still low which is what got me looking at the PCV, and Timing.

I am going to check it with a second vacuum gauge and verify the gauge is fine. Also need to get my tach hooked up.

Does the lift on the cam posted above seem to be stock?

 

[clintonvillian]

A side note...I am running a 10.5 power valve. BECAUSE when I rebuilt it I assumed I would be pulling around 20 inHG.

Could that be causing a rich condition? Also I am 2000 ft above sea level, in theory my inHG should be a few inches higher, correct?

 

[clintonvillian]

Any chance the 600 cfm is too big for the stock camshaft and causing the low vacuum numbers?

 

[pcf_mark]

Carb size is fine because of the vacuum secondary. You may never us the full potential but it will not harm you.

The power valve size is fine - that circuit is not in use while you are idling in the garage. Cruising down the road you have 12-14 anyway you get on the gas, vacuum drops, power valve opens. Tune that later on a flat road.


.340 lift is a pretty small cam I would say close to stock.

4 mix screws is interesting. That is a 4 corner idle carb I did not think they have vacuum secondary 4 corner idle models.

If you are confident on your timing set up try this. Put the vac gage on and let it get steady. Then turn each idle mix screw in slowly until the vac drops then slowly back it out a tiny bit at a time until you reach max vacuum on the gauge (don't listen, use the gauge). Do this for all 4 screws. This should bring your vac up and make it steady.

I may get flamed for this but for stick shift trucks you can do this. Set your base timing (no advance connected) to 8-12. Then connect the vac port to manifold vacuum. This will pull in the vacuum can in right away and give you 10-12 more degrees of timing. Reset the idle speed down and go for a drive. It should be snappy off idle and have good vacuum.

 

[MS73HD302]

Check out thunderhead289 on YouTube great videos on dialing in Holley style carbs

 

[jckkys]

After '79 Ford made the idle mixture adjustment very difficult on 4180s. Did you or a PO pull the plugs out of the holes containing the adjustment screws? Another question is what year and engine is the carb mounted on? Ford only installed the 4180s on 302s called 5.0 Liter 4V HO on Mustangs from '83-'85. The cams changed in this period. The '85s got the roller cam. So lobe lift changed over the years. The 4180s came with a 2 stage power valve that would be preferable to the one you installed. Reinstalling the OE power valve would be a good idea. The accelerator pump diaphragm is the same as any 4160, 4150, or 2300 Holley and can be found at most parts stores. Do you know if the diaphragm is perforated or the cover was over tightened bending it, to create the leak? The diaphragm IS the gasket and back fires have no effect on it. The 4180 and the spacer have multiple vacuum connections. All are in the front. To isolate a vacuum leak, all have to be plugged. An EGR valve can also be stuck open creating another vacuum leak. Any of these could explain low idle vacuum. The PVC escapades make no sense. Pulling it out of the valve cover usually makes no difference to the engine. Also in my experience 20 degrees of initial timing advance works well on stock 302s. If we have more specifics, we can better answer your questions.

 

[DC_Gearhead]

Check out thunderhead289 on YouTube great videos on dialing in Holley style carbs

+1


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[clintonvillian]

Well,

When it rain it pours...

The accelerator housing was bent, allowing fuel to spurt between the gasket and diaphragm.

I guess it hadn't shown up sooner because I had been pretty much at idle. Speed up the engine created more fuel. which is why it was spraying at higher rpms, and only squirting when I pumped the throttle. I sanded it back down flat and reinstalled.

I switched out to a 6.5 inHG power valve. With the current low vacuum readings, I felt better about this, because I know it will not be opening while tuning the idle mix.

Yes I have access to all four screws, plugs were pulled and I had to replace a mix screw spring. PO was using it without....on a fresh rebuild.

Now, I get the carb back together, back on...hit the ignition, turns over and nothing... I'm thinking I flooded it, so I wait, again same result.

Doesn't sound like it is firing. Pull a plug, sure enough. No fire. Chase everything down...Coil checks, voltage checks, grounds check.

So now I think the pertronix went bad.

I had been testing circuits on the heater, so my tester was laying in the seat, when I went to get it, I noticed water in the floor board. The freaking heater core is leaking....

 

[pcf_mark]

You're luck is not the greatest! That 6.5 is probably going to be awful on the road. You will get this huge dead spot / bog waiting for that to open and think it is your accel pump.

Throw the pertronix in the bin they are unreliable in my experience.

 

[jckkys]

The 2 stage power valve was designed to bridge the lean flat spot with a metered first stage that opens at about 10"Hg. In my experience it worked well. Here is Holley's 4180 rebuild instruction;https://documents.holley.com/199r10060rev.pdf. The ignition failure would be best addressed with a Duraspark II conversion.

 

[broncogt]

Worst case you should think about your timing chain...could it be 1 tooth off???

 

[clintonvillian]

The 2 stage power valve was designed to bridge the lean flat spot with a metered first stage that opens at about 10"Hg. In my experience it worked well. Here is Holley's 4180 rebuild instruction;https://documents.holley.com/199r10060rev.pdf. The ignition failure would be best addressed with a Duraspark II conversion.

I was going to go with Duraspark, just for the parts availability. I am now pretty sure the pertronix failure was my fault, and have ordered another one. Apparently you cannot leave the ignition switch on for an extended period of time or it will fry the unit. The new ones are supposed to have this fixed. I left my ignition on whil working the carb and was just starting it by jumping the solenoid.

I now have a 6.5, 7.5, and 10.5 single stage valve. I cannot determine what the dual stage installed with the carb was. The rebuild kit came with what appears to be marked as an 8 dual stage valve.

At some point I will have to swap them out. I just went with the 6.5 to basically ensure there was nothing going on/opening while trying to tune at 13 inHG. I have to figure this low vac issue out.

I am hoping the accelerator pump was causing the vacuum leak but I really doubt it. I certainly hope that the timing chain isn't off a tooth... I am really not looking forward to pulling the cover.

 

[jckkys]

Ford and Holley were secretive about the vacuum ratings of the 4180 2 stage power valves. I found the part without the rating here; https://www.ebay.com/itm/253566013895.

 

[pcf_mark]

Get the ignition working and set up correctly first. Too many moving parts you will get lost.

Then go after the vacuum to see if you have a problem or not. 13" may be what you have. Tuning for that is easy.