vacum reading

[Torque]

I've got of 7-8 inHg(needle moving but only an inch)Timing is set,re tourqued carb and intake manifold,all vacum hoses new.Got to pick up some carb cleaner to test for leaks.Is there anything else I should check for?Engine recently rebuilt along with carb.

[Ernzo]

You have 7-8 manifold at idle? IF so, there has to be a leak or the guage is bad, if the motor is known to be good. You can try locating and restricting, pinching off, the other manifold vacuum lines, not sure what you have. IF pinching off one makes more vacuum, then you can trace the leak. I use a 3/8 inch piece of fuel line to listen for a hisss. Never could get the carb cleaner to work.

[Desert Beast]

havent tried this but it was in a 4wheeler i believe, get a propane torch and with it UNLIT, turn it on and pass it over the vacuum lines if theres a leak the propane should be sucked in thus increasing idle. be careful about it around the carb though, as it might be sucked in through there giving you false readings. never tried it but it seems like it would work.

[turtlejoe]

I have heard others that have successfully used acetylene as well, and I've even had success with carb cleaner. Just be sure to protect your eyes!

[LRRH]

it definately sounds like the is a leak. 7-8 is NOT a good reading...you should have a steady 15 at minimum. I also believe that fluttering is caused by sticking valves.

[Torque]

Thanks guys,
Had to work late so didnt get a chance tonight. First I'll check the gauge againt another one(re-checking test equiptment always good).Got some carb cleaner so I'll give that a shot first,did try the vacum hose trick but couldn't hear any leaks.
The book says that a low but steady reading at idle indicates late ignition or valve timing,or a uniformaly close setting of the valve lash.
The ignition timming is set,how do I check the valve timing?

[oddfire]

do you have your engine timed at factory spec? they pretty much go out the window with a rebuilt engine. try advancing your timing and see what happens.my factory spec is 8*btdc but I'm running 19* and have steady 21" of vacuum...........phil

[Torque]

The timing is set at 11BTDC..specs(underhood lable) says 10BTDC +/- 2.
So in setting my 'new' timing what do I do?I'll mark the current setting so I can find it again. The tricky part(for me)is to know how far to advance it and what to use as feed back to know when I've reached the new proper timing

[oddfire]

What i would do is mark it first like you mentioned, then try advancing it to about 15*-16* btdc, let it warm up and take it for a spin, preferably up a fairly steep hill. Listen closly for any pinging or rattling coming from the engine, sure sign of preignition. If it does not ping and runs good, try the vacuum gauge again and see what you get. If it does ping, back down the timing a degree or two and take it for a ride again. After I did my rebuild it was a game to find the right set-up. Advance the timing as far as I could without getting any detonation, then back it of a degree or two, then readjust my idle RPM, then hook up the vacuum gauge and adjust the carb idle mixture till I got the highest possible vacuum reading, then recheck the timing to verify that it hasn't changed, then recheck the idle RPMs.
All this can take a while so I threw the timing lite, the vac guage and my special 9/16 distributer wrench in the rig so I could make any adjustments on the spot. It took a few days of trial and error, but I got it dialed in now and it runs great, even at the 13,000 ft passes in Ouray..........phil

[Torque]

Where I'm at...
1-vacum gauge tested and working
2-sprayed carb cleaner and no leaks found
made the following observations...
1-vacum reading seems to indicate ignition timing prob
2-Oddfires observation about the need to advance the timing
3-connecting/disconecting the vacum advance didnt change the timing
4-after messing around with the truck(warmed up) I shut her down and she didn't want to start(sounded on the verge)using the Haynes troublehooting guide this is a symptom of distrib prob
Solution time to upgrade to a TFI,it certinly cant hurt

[oddfire]

Torque,
Although a TFI conversion is a good idea,{I did one myself before the D.U.I. I have now} it will do nothing to increase your vac readings. Also, there are a bunch of places for vac leaks to develope. The QT switch and lines under the dash, the heater controls, the tranny modulator lines,the brake booster, are all places for vac leaks. Any doubts, remove and plug the line at the manifold and check again. Try this quickie. 1. with the vac guage hooked up, and engine warm,advance your timing till you get the highest vac reading.
2.back off timing a degree or two
3.adjust idle RPMs
4.take for test drive, listen for ping.
5. if no ping, fine tune vac reading by adjusting idle mix and idle RPM till you get highest vac reading.
6. if engine pings back off timing
7. if engine runs on, idle too high
8. if engine doesnt want to crank, back off timing
I'm taking for granted that you do know the correct proceedures for adjusting timing and you do know how to set idle mix and idle RPM and that you do know how to hook up the vac guage. if you've got questions on these, do a search on those topics here and youll find lotsa info...dont give up, were here for ya man....phil

[Torque]

Thanks Phil,
Havent checked all the under dash stuff,didnt even think about it.As for upgrading the ignition system its more to do with inconsistant performance.By upgrading its another link in the chain that has been strenghtened.Its hard to tune/set up when it wont start hot but does when cold.On the bright side I've got plenty of steep hills for testing.It will take a couple days to round everything up an install,work doesn't understand that to some of us our truck is like the child and when sick we need time off to heal her.
thanks all

[krob725]

1. where are you connecting the gauge? is it a constant manifold vac source?
2.are you running a larger than stock cam?
3. you can check the hoses going to the soup cans and plastic ball, cruise control etc
4. not to a smart Great Googley MoogleyGreat Googley MoogleyGreat Googley MoogleyGreat Googley MoogleyGreat Googley Moogley, but are you sure your gauge isn't metric, it might be 7-8 bar~ ?
krob725

[oddfire]

Torque, keep us posted with your findings and results.........phil

[Torque]

Krob,
Valid question as much of our stuff up here is metric but unfortunly I had the right scale.Ahh the money I would have saved not having to buy both metricand inch tools.
The plan of attack is check and service distibutor,TFI upgrade,recheck rpm and idle mixture setting,check rest of unchecked vacum systems(under dash stuff),dial in timing using Oddfire's info(timing light and vacum gauge)followed by test driving.Arent those distrib wrenches great!!

[Torque]

I'm running a RV cam,so its a bit hotter than factory but not a big change(or so I thinK)

[Torque]

So some update...
Discovered that both CTO's were hooped.Passed the carb cleaner test but not the vacum pump test. Didn't get to start it up yet as I'm also upgrading the ignition and just plain ran out of time.So here's hoping that replacing the CTO'swill solve the vacum thing