Rough Idle

[pipeline010]

pulled the carb. the ring around the power valve was totally dry. I swapped with the old one and the only change (on test drive) was that the truck dragged a little a$$ on speedy acceleration. Seems the new PV was doing its job. Too dark, so I'll swap back tomorrow.

Ok good to know about that blue thing. I'll pull it, I'm all about clean engine bays these days.

Plugs are the ones I've used since getting the truck. Prior to the new diz it ran absolutely perfect. I don't think its the plugs.

vacuum is good. holds with a very slightly bouncy needle at 20-22. The only vacuum items I have are standard and simple. Booster, PCV, etc.

vacuum advance is attached to the port on the left side of the carb (facing from front of truck). It works exceptionally well, tons of movement at speed.

I feel like I've done pretty much everything at this point..

 

[pipeline010]

ok, so my local mechanic (who visits me from time to time) thinks the issue is sticking valves. encourages mystery oil to hopefully get them moving freely and proper. otherwise we'll need to pull open the block and put new valves in. this is according to the mechanic.

recapping the truck:
-69 sport
-original 302
-motorcraft 2100 2bbl recently rebuilt
-new pertronix ii ignition system w/ coil

recapping the issues:
-->idle (800rpm) sounds horrid, popping sputter, backfiring.
-high rpm tons of horsepower, you'd never know there was an issue.
-->at coast (letting off throttle) popping/sputter returns.
-from slowing down/coasting to acceleration tons of HP, no issues.
-vacuum at 20-22 with fast bouncy needle.
-timing set and proper.
-fuel delivery at 4-5 psi.
-power valve checked, good and not leaking.
-spark plugs new, spark wires new.

also to note: the truck drove and idled absolutely perfectly as of 6 days ago. timing correctly set, everything was as it should have been. I drive it every single day.

so....stuck valves? that's the answer?

edit: i did go out and do the paper on the tailpipe thing and, indeed, the paper was having some sucking into the pipe. each pipe actually. dual exhaust, so both sides?)

 

[Justafordguy]

I find it hard to believe you have bad/stuck valves with that high of a vacuum reading.

Also, what did you mean by a "yellow" spark? A new performance ignition should have a hot white/blue spark. I know my HEI does.

 

[pipeline010]

spark was yellow against the engine block. the way I understand it is that that is simply an effect of there being a lot of sodium in the air (I live on a barrier island). On a spark tester it should be blue, but I was just field testing.

I keep coming back to the things I just changed. It's certainly possible I'm having internal engine trouble (gotten worse today), but I always assume the issue is due to whatever we just changed:

distributor - from duralast module / points >>> pertronix II
coil - from duralast >>> pertronix II
brake booster >> from none to horsepower sales
rebuilt carb autolite 2100 <> by ME, a total amateur.....
new plugs and wires


issues:
-idle super rough, feels like I'm killing it just turning it on.
-misfires, possibly lean, but random.
-HAD aggressive acceleration as needed until yesterday when it was re-timed [by mechanic on site, with timing light]. now kinda weak on pickup but ok.
-vacuum yesterday was a super bouncy 20-22, today (different guage) super bouncy 15-18. But my guage is likely just a POS.

???????????????????????????????????????????????????????

 

[pipeline010]

started to slowly undo some stuff to see what might get better.

1. replaced PCV valve.
2. checked w/ vacuum guage using same hose as booster (eliminating that as the issue).
3. changed some spark plugs. probably were just fine.
4. switched back to the previous spark wires I had been using before. they were decrepit, but no change.
-----------------------------------------
learned? nothing new. altho i did pull 2 plug wires while the engine was running and it seemed to make literally no change to the behavior of the idle engine. Yes, 2...at the same time...i think it may have stalled out had i pulled 3, but never tried.

haven't checked:
new coil (not even with ohmeter).
new distributor. no idea how I would even do this or bother, the timing is perfect.
have no yet pulled carburetor and pulled it completely apart, but I have checked power valve. It appeared intact, but didn't do drip test.
--> I did test for a power valve leak by turning the carb screws (both of them) all the way in. It lasted about 30 seconds with them all the way in, struggled in and out, thought it might recover, but then died. I assume this means PV is intact, but it did last a good while.

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I'm literally pricing valves and crate engines. i'm losing it....

 

[Joe473]

started to slowly undo some stuff to see what might get better.

1. replaced PCV valve.
2. checked w/ vacuum guage using same hose as booster (eliminating that as the issue).
3. changed some spark plugs. probably were just fine.
4. switched back to the previous spark wires I had been using before. they were decrepit, but no change.
-----------------------------------------
learned? nothing new. altho i did pull 2 plug wires while the engine was running and it seemed to make literally no change to the behavior of the idle engine. Yes, 2...at the same time...i think it may have stalled out had i pulled 3, but never tried.

haven't checked:
new coil (not even with ohmeter).
new distributor. no idea how I would even do this or bother, the timing is perfect.
have no yet pulled carburetor and pulled it completely apart, but I have checked power valve. It appeared intact, but didn't do drip test.
--> I did test for a power valve leak by turning the carb screws (both of them) all the way in. It lasted about 30 seconds with them all the way in, struggled in and out, thought it might recover, but then died. I assume this means PV is intact, but it did last a good while.

---------------------
I'm literally pricing valves and crate engines. i'm losing it....

Sounds like you have 2 dead holes and it's not ignition related. This is a good find. Pull 1 at a time. Make sure you have spark and identify all those that dont result in a change.

I asked a couple of responses back about leak down test. Dont freak out just yet and dont tear things apart until you find a real issue. Something has changed and although you said it was done I would do it again. If it's a burned valve or other compression problem a leak down and compression check will lead us to it. You can rent a kit you just need a compressor. Write down numbers for each cylinder and compare.

A sticky valve as you described is Usually what I would call a collapsed lifter or something seriously wrong in the valvtrain. This will be noisy and result in lots of valve lash you can hear. More common is a rocker arm stud that pulls out due to aftermarket higher lift cam and possible heavier springs without treating the heads to a good rebuild. Also a worn out cam lobe can cause a dead hole. May not exhibit valve lash or fail leakdown but should result in loss of compression.



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[pipeline010]

hp99f is looking like an attractive option right about now.

although so is a moderate amount of c-4....and I don't mean the transmission.

 

[Joe473]

hp99f is looking like an attractive option right about now.

although so is a moderate amount of c-4.

Take a break. Then go back to it. If it wasn't isnt smoking or burning oil I would hold off on new engine or C4.

Do the compression and leakdown test before doing other stuff or buying any more parts.

I ran this mess for 2 years burning oil and tapping even made a few long 500 mile road trips before doing my engine.

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[gr8scott]

I envy you guys in CONUS...free shipping. If it were me I'd get one with a roller cam.
But do like Joe said and get compression and leak down tests done.

 

[Powerbyford]

With the engine running at idle, look down in the carb for gas dribbling from the boosters. They should be dry or you have a carb float problem or excess fuel pressure flooding it.

 

[pipeline010]

will do. I took some advice and got away from the truck for a few days. cleaned up the whole house and got my wife happy with me and played mummies with the kids. yep.

today I'm going back in, gonna pull the carb and do a breakdown and then put it all back together. It's certainly possible something went wrong with my rebuild and, although it spent 3 days running perfectly, something may have shifted loose causing my current issue. i was very careful not to over-tighten anything, maybe I was too careful.

planning a compression and leakdown test later in the week, but if they're foul I'm not replacing valves.

1k for a valve replacement or 1800 for a new HO 302 motor where I can use a lot of my same dressing is a no brainer. add a rebuilt used OD and my driveline is as perfect as I'd ever need it to be for under 5k. not a bullet I wanted to bite, but one that's always been on the horizon. This is my worst case scenario.

 

[pipeline010]

I've opened a side thread to particularly rule out any issue with my carburetor as my the cause of this horrible idle.

http://classicbroncos.com/forums/showthread.php?p=3132831#post3132831

 

[pipeline010]

so, finally went out and grabbed a proper multimeter. For those who like to read really long stuff you'll notice my mechanic checked the voltage level going TO the coil to verify it had over 12v as needed for the pertronix ii flamethrower. But he didn't check the coil itself.

So I just did. Does something here seem jump out to anyone or am I missing something?

 

[pipeline010]

Solved! finally......

the coil was indeed blasted open on the secondary. put in a duralast coil that made little difference. I also ran a compression test and found pretty much 150psi from 1>8. So what was the cause, then?

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Joe473 was on to it almost immediately, and a diagram from waynep712222 at reddit really made it obvious that I needed to check the carburetor a little more carefully.

The autolite 2100 (and I assume all other carburetors) access very different ports for fuel when you are driving/throttling vs when you are idling. Seeing as how my truck ran absolutely perfect at drive and trash at idle, once I had this illustrated to me it was clear the carb venturi was the issue. I pulled it and found what you see in my image below.

The emulsion rod provides the gas at idle. Mine was snapped and barely holding within the main tube.

Thanks to delconick sourcing a very particular venturi size (and looked like brand new!!), a day to ship, and 25 minutes of work my truck is no longer a Bronco.

I know it's not a Bronco cause it's purring like a kitty cat right now.

https://imgur.com/a/siLJ7