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Unread 09-19-2013, 10:04 AM   #1
ForestJeep89
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1989 YJ Wrangler 
 
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vacuum readings question

I am fine tuning the holley 390[there when I bought the jeep] and the DUI [just purchased] and have some weird vacuum action. Was wondering if anyone had any thoughts or possibilities to share. My initial timing is @ 8* and with the carb tuned off manifold I had it all setup with a very nice 19.5-20 " when warm then I noticed the gauge fell to around 15" and stayed there. Thought this was weird and started looking for leaks with propane and things and i couldn't find a leak. I glanced up @ the gauge and it was reading normal again [19.5]. I figured that me tightening things on the manifold musta fixed the leak or something and thought i was good to go...A few days later i was drivin round takin ptc readings inside my cab to ascertain which power valve to use and when i was on my way home the vacuum dropped down again to the 15" mark and stayed there all the way till i parked in me garage. Now im confused by this reading as it appears to be intermittent, so the charts of vacuum readings have me going in many different directions. Anybody have any ideas here as to what might most likely be the best direction to look at? Anybody have this intermittent thing b4?

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Unread 09-19-2013, 11:21 AM   #2
superj
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Maybe its when the line in the cab is open, the one for the heater door? Or your 4x4 has a leak somewhere that shows up when you hit a bump a certain way?

I can only get 17-17.5 out of my holley 450. It doesn't fluctuate though
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Unread 09-19-2013, 02:22 PM   #3
Old4X
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Check all vac related items. PCV valve, EGR valve, vapor cannister, brake booster, axle disconnect, vacuum reservoir, heater door vac motor, and all the other vac lines hooked to the manifold.

A loose carb mount or worn throttle shaft can do it as well.
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Unread 09-19-2013, 04:13 PM   #4
ForestJeep89
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Hmm interesting... I never did check the 4x4 system thoroughly and so I will right away.The egr system is neutered @the exhaust by a weld tack and the manifold is an offenhauser so that couldn't be it I guess..unless the weld is leaking[will check].The "heater" system has been set to "vent" lately so I better check that vacuum line..Carb mount has recently been torqued..pcv will get rechecked.. hmm ,good ideas lemme go check em ,thanx!
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Unread 09-19-2013, 08:46 PM   #5
ForestJeep89
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update: pvc is good w/idle decrease when hose pinched,
4x4 system seems good w/idle decrease when pinched [although the green line HAD come out!]..plugged it back up but symptoms remain on vacuum gauge,
brake has strong pull at manifold,hose good,check valve good,brake booster test with pedal to floor good.Sealed up check valve with gasket maker just in case ..
Vacuum gauge starts out at 19.5 and slowly goes down to 15 then climbs back up and goes down to 15...takes 7 seconds to drop...
the exhaust restriction test says I have no restriction but I did get the vacuum to hang out at 26 for 4-5 seconds b4 slowly going down 2-3 times but cannot repeat these results,so idk if exhaust is clogged...
temperature @ beginning of cat is less than the exit so it seems ok...muffler is rusty and tailpipe has holes but I have mass power so idk.
I have holley @ 3/4 a turn out[wonder if im lean,will try that tomorrow],wonder if my timing is retarded will try that tomorrow....
I don't have a vacuum reservoir I just have some small aftermarket charcoal bulb with one manifold line going in.....the "heater" door vacuum SEEMS ok and actuating the lever shows NO vacuum effect so idk
the last reading on the gauge was holdin steady at 19.5 but im not fooled by that im sure the drop will return with me tomorrow...tx!
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Unread 09-19-2013, 09:25 PM   #6
Old4X
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Vac res is under the battery if it is still there.

Also, intake and exhaust manifold bolts torqued? They tend to loosen up on these engines
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Unread 09-20-2013, 04:03 AM   #7
roadyrob
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have you checked the timing when the vac. drops? just guessing that it could be a distributor problem. I run the holley 390, list 8007 and vacuum holds steady at 20.5
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Unread 09-20-2013, 07:31 PM   #8
ForestJeep89
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so today I start er up and she is hangin out @ around 15"----

I wanna look @ the timing while the vacuum is down [as suggested]and sure enuff the timing lost 4 degrees! I do the timing chain slack test by watching the rotor while turning crankshaft but after several tries my "slack" is right @ 4 degrees. I check to see if my dizzy hold down is tight and I CAN tighten it down more so I set the timing @ 9* btc and do tighten it down very much this time----I don't really know how much to tighten that clamp but today I 2 fisted it and it still had some turn left in it when I stopped----The thing is very tight but im not sure if the bolt should bottom out er wut?Also I chose to use the clamp supplied with the DUI and idk if maybe it isn't right----Everyone I know complains constantly about me overtightenin things so im just not sure on this clamp as I am always leaving things half tight for the sake of other's sensibilities. There was a lil oil on the lil gasket dui gives out for the dizzy base.
After this I went back to checkin and tighten other things and fired er up to get 19.5" again and then went after miss Holley and got the vacuum up to 20.5",steady!
I went for a test drive and it dropped back to 15" steady and so I started again,eesh----
I was mistaken on the reservoir issue as I do have the original it is simply hooked to manifold and teed up with red 4x4,the "other"port is unused now.My charcoal system is present but ,port,mani,tank vent and carb are all disconnected.
I had hand tightened the intake/exhaust studs b4 but decided to do them again by whackin the wrench with a rubber mallet this time and got considerable movement. A deepwell 9/16 socket is first on the shoppin list for tomorrow so I can torque em proper though.
I did a lot and then wanted to check the timing again only to find my cheep amazon.com timing light zap out in my hand! hoy shaboy! A new light is on the list now----
Thinkin bout buyin a cigar to check fer vacuum leaks but im a reformed smoker so idk.:}
Also the dui I bought arrived with a near dead coil so I sent it back and they said the coil should be fine [.3 pfft!]but that the reluctor was out of phase[and presumably fixed that] but when I put it in it didn't work till I had them send me a workin coil. so idk if this issue of the reluctor is related or not. I am a novice with vehicles and distributors haven't formed their complete schematic in my brain yet.
Try try again I guess, we shall see ,tx!
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Unread 09-20-2013, 08:42 PM   #9
Old4X
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" timing lost 4 degrees"

You have a bad distrubutor.

Hei isn't magic,with a stock pre smog dizzy, chevy ICM, the team rush and nutter, you get at least as good performance with way better heat tolerance and coil grounding.
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Unread 09-20-2013, 11:14 PM   #10
ForestJeep89
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Well I just might have a bad dizzy,i havnt replicated that loss in timing yet until I get a new light and re-test after having tightened the clamp.
I wasn't looking for magic ,it was actually better gas mileage, quality, and simplicity ,ironically.
So far I am utterly un-impressed with dui.The results positive, have been VERY smooth power and lots of it but the negatives on Davis are customer service,build quality and frankly what appears to be a company resting very heavily on its laurels.I had read such good things on this forum about davis but so far the thing might as well have just been made in china and the customer service based out of india[out of site out of mind].It is a paradox really cuz the unit is great and buggy at the same time and the service is timely and helpful yet cheap and argumentative as well as shady.
There is a huge back story to all this ramble but suffice to say I have been without my Jeep all summer sending things back and forth with them and I was actually waiting for long term results to do an in depth ,full spectrum review on Davis.As it stands, b4 I even know if it is bad now ,the final conclusion is pending.I mean the thing has only been running a few hours...and crappy @ that. tx!
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Unread 09-23-2013, 09:48 AM   #11
ForestJeep89
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Well I got a new timing light and thought id update this post instead of just letting it die for those interested. The timing is currently ok and holding steady .We went on a mass steep mountain trail the other weekend and it musta come loose I guess.
The drop in vacuum remains .I got some ether and was able to almost kill the engine @ the throttle shaft,and was able to kill the engine by pushing down and sideways on the pump diaphragm arm thingy.
I got the book Holley Rebuilding and Modifying (Workbench Book) by J Williams so im gonna take the carb off and look for diaphragm leaks[though the shooter is workin perfectly on time] and look for worn throttle shaft[not sure if I can replace this?].I will also look for baseplate cracks or gasket issues.
I did have some loose manifolds[intake/exhaust,not carb] nuts but upon torqueing the vacuum issue didn't go away.
I wonder if a leak @ the carb would cause a 5" vacuum loss?
Never rebuilt a carb but this should be fun as I REALLY love carbs and think they are genius!
Wonder if I cant replace throttle shaft if Holley will re-man my carb?----well anyways tx!
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Unread 09-23-2013, 10:32 AM   #12
Old4X
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The fix for loose throttle shaft is to install bushings and ream to fit. Kits are sold for this.
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Unread 09-23-2013, 10:41 AM   #13
SeanB95YJ
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can't help you on the timing loss other than what was said above you might have a bad dizzy

but for vacuum issues:
I use a handheld propane (or MAPP, acetelyne, etc. whatever I have handy at the time) torch to check for vacuum leaks. with the gas on (but NOT LIT!!!) slowly move the torch tip around, following all vacuum lines from end to end, and around gasket surfaces.

the little bit that gets drawn in will change the idle enough to be obvious, but it's not enough to do any harm.

good luck
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[FONT="Comic Sans MS"][COLOR="Blue"]Sean B. - Schenectady, NY - 95 YJ, 350/700r4/NP241, JB Shorty SYE, 8.8 rear, 2" BDS, 1" homebrew shackles, Daystar 1" BL, TJ flares, 35x12.50 General Grabber AT2 on 15x10 Bart D-Truckers, Polyshield polycarbonate windshield, HD over/under crossover steering
[/COLOR] [COLOR="Red"]swap/build thread: [url]http://www.jeepforum.com/forum/f22/after-almost-4-years-finally-my-own-build-swap-thread-1542284/[/url][/COLOR][/FONT]
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Unread 09-23-2013, 01:24 PM   #14
ForestJeep89
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Thanx old 4x . Ill git er taken down and see whats what.
Sean I knew about the others but wasn't sure if I could use my map,so tx fer that. Nice Amanita muscaria btw! we are just winding down on King bolete season here.anyhoo
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Unread 09-27-2013, 07:54 PM   #15
ForestJeep89
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Well I got the Holley taken off and fiddled with er a lil.
The manifold gasket was somewhat rotted and discolored at the throttle positions, there was too much play in the throttle shafts[I got like a 450 rpm drop when spraying ether here],and my umbrella check valve in the accelerator pump housing was in half[I think maybe I did this when fiddling].
An educated guess [borrowed knowledge] would be that the throttle shafts are worn cuz of the Teflon used by holley and that possibly someone over tightened the carb before I got it thus accelerating wear on those shafts and maybe even warping the baseplate.

I wanted to take my time and enjoy rebuilding my first carb and I need the vehicle ready for winter so I just went ahead and ordered a refurbished 390 from Holley's eBay storefront.It was basically a hundred bucks off new carb price but they said the carb wasn't actually used but a return job from a customer that changed his mind or whatever so may have blemishes or whatever .They say it has been flow tested and what not so im hopin it is all good[over 12,000 sales this year and only 5 negative comments,most of which were infantile].Has a 90 day warranty and customer support and what not

I cant really afford anything different right now[either more or less!] so at least I will have spare parts if I need them or sumthin .Should be here within a week so we shall see if it totally fixes the vacuum variation.

Anyone have any knowledge on exactly how to get a torque wrench on intake/exhaust manifold bolts 3 and 4? I don't know about stock but with the offy all I can do is barely get an open end on there.The rest torqued fine.
TX!
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