I have a 74 455 I'm trying to get running properly. It has a large vacuum leak since the gauge reads zero. I've plugged or replaced all the hoses I could find.
Obviously, I will have to continue my hunt but my question is are there any
notorious causes for this other than hoses? The compression is not bad ranging from 142 to 160 all round. Timing is 12D at idle and 26D at centripetal advance.

Thanks,
Randy

 

Check the carb. Check the torque specs and make sure it's tight enough.

 

if the reading is ZERO it's not hooked up right a a faulty gage.

 

The engine won't run with zero vacuum, except at full throttle.

If you're looking for a large vacuum leak, consider the brake booster.

- Eric

 

With no vacuum it would running way worse than improperly. You must have your gauge hooked to the wrong port or a bad gauge. You can test your vacuum gauge just by sucking on the hose real hard and see if the needle moves.
As far as external leaks you can find them with regular old carb cleaner, just spray around everything and the engine idle will go up when you hit a vacuum leak. Internal leaks you can find by clipping a pair of vise grips on individual vacuum lines and the idle should decrease when you find a vacuum leak.

 

Thanks Guys, sorry for the late reply I was away for the weekend. So I haven't had a chance to spray the carb yet. But the gauge works. The motor starts and idles nice and revs well in park but still has no vacuum. It will not rev up while driving. I've tried various ports and felt the manifold tees and there is no vacuum there either. I'm wondering if they are plugged so I'll have to take them off and run a wire through or something. When I figure it out I'll post what I find.

I just wondered if anything else could cause the vacuum problem then hoses.

 

OK, so I need to read a little more. Since this engine is a 1974 is had an EGR valve that I had plugged. This rendered the vacuum to close to NIL. After hooking up the EGR I now have good vacuum but bounces from 20 to 22. Not sure if that is serious movement or not. The engine has been sitting a lot. So now it runs much better but still backfires on heavy throttle in park. I assumed the vacuum advance was not working but now I'm not sure. Any help on the backfiring would be appreciated. I'm still rusty on all this. Thanks.

 

Offhand, sounds lean to me. Since you're talking about Park, you probably mean a fast blip - consider your accelerator pump and your power valve.

- Eric

 

Thanks Eric, when I get it resolved, I'll confirm.

 

So I rebuilt the carb after reading Cliff's book several times. The car now idles OK and runs/starts well. I still get a stumble and a back fire with throttle blips in park. I'm kind of at a loss on what to do next. There is a bit of a miss on the driver's side which I'm hoping some new plugs will cure. Any ideas on the backfire? Thx.

 

Is it backfiring through the exhaust or the carb?

 

Eric: It backfires through the carb. I originally had a 1969 quadrajet on it, I then purchased a 1976 quadrajet and installed it and it also back fired through the carb. I then rebuilt the 76 carb and it runs and idles better but still back fires. I have arbitrarily set the primary idle screws to 3 turns, then 5 turns and finally turns. It seems to run the best at 5 turns. Starts and idles great but hesitates and eventually backfires on throttle blips. Timing is good as mentioned above. I am using premium 91 octane for now.

 

You may need another quarter to half a turn of the secondary air valve tension screw.
-- See Cliff's book.

- Eric

 

Do you have a points distributor or electronic ignition ie HEI? In many cases I have seen the points and especially the condenser the culprits of hesitation and some spitting back thru the carb.

 

Timing?

 

OK, here's where I'm at. I've rebuilt the carb. The car idles well, the timing is 12d advanced at idle. I cannot seem to adjust the dwell past 15d and the timing light goes out when I try to throttle in neutral. I have ordered a new set of points/wires/plugs but I think I may have a bad ignition coil. I believe this would explain the timing light going away as I try to throttle up. Any advice before I order a new one? Thanks.

 

Years ago my neighbor had a 67 vette and the editors of mustang monthly and super ford and muscle car review and corvette fever magazines were all at his house, they rebuilt his holley twice! then bought a new holley and it still did not work it kept spitting at higher revs, I went over put the old carb on and put in a condensor told him to give me 5 dollars and to take it for a spin. All the magazine guys were gone to the store to take back the new carb and buy a new set of wires cap and points. It ran great just that condenser When they came back they could not believe that condenser gave all the problems to the car. So I always check condenser first then plugs, wires cap rotor then points then timing. any weakness in the chain will cause it to run bad.

 

Remember when you set your dwell you have to reset your timing and then recheck your dwell. I hope you get her running perfect soon! Good luck

 

+1.


If the engine stalls and stops running as you rev it, then it may be the coil (or the condenser, or the wires, or the cap, or the rotor...), but if all that happens is that the timing light conks out, then it's probably the timing light (leaky condenser in the xenon strobe discharge circuit).

- Eric

 

Thanks guys, I'll get back to this next week and give you an update once resolved. One thing good it's idling very nicely, like a true BB. I'm getting excited to finally drive it.

 

Dwell is supposed to be 30. Did you mean you can't get past 15 degrees of advance? Not sure, but if the distributor is not installed at the correct location, the vacuum advance tank will hit and limit advance of the distributor.

 

Was wondering that too. Do you have the dwell meter set to 8 cylinder? If so are you reading the 8 cylinder scale? .018" -.020" point set gap = 30* dwell angle on a dwell meter. If you have the dwell set at half of the required 30* this will cause the symptom you have. Agreed with all the suggestions on making sure the basic settings are in spec...pay attention to the centrifugal and vacuum advances too. Read your plugs.
If your still experiencing the symptom after the ignition systems dialed in then Id look at tip-in problems with the carb. If you have Ruggles book you should see that discussed.

 

Yes, while adjusting the dwell with the dwell meter attached, the best I could do was 15* (for 8 cyl.). If I adjusted the dwell (using an allen key) either way it would start to run poorly.
I decided to change out the standard distributor (awaiting parts) with a new HEI I had purchased to see if either the condensor/coil/ or points were the culprit and of course now I have to get new plugs wires because the old ones don't fit the HEI cap. I'll get back to you guys once I've cleared up my backlog of errors and part requirements.

 

To top it all off I've ordered the following points from Rockauto and the points that were actually in the car (could be a 1974 dist) had the condensor attached. The ignition coil also had a condensor attached. I check my manual and it only shows the 6 cyl.distributor without the condensor. Can anyone tell me which set of points (woth ot w/o condensor) and if it's OK to have 2 condensors (one on the coil and one in the dist.) Sorry to be a pain but my 1969 manual isn't clarifying and I can't trust the existing set-up because it may be a meld between the 1969 and 1974 set-ups.

 

So I just checked and 442.com says this is a 1973 or 1974 distributor.

Quote:1"112197 1973232 455-4V L-75 MT Cutlass [engine UD]
1112197 1973232 455-4V L-74 & L-75 AT Cutlass, 88, 98 [engines UA,UB,US,UT]"

Being part no 112197 I guess I've ordered the wrong points. Judging from this there appears to be a duplication of condensors on my current set-up. I'm thinking that could be part of my problem. Can anyone confirm I should be using just one condensor and abandon the one on the coil? Thanks.

 

Dont worry about the condenser on the coil its only for static in your radio and the points with the condenser attached is just for convenience so you dont have to put the condenser in and then the points it just makes it easy to install but I have put them in and they did not work brand new out of the box! with only 15 degrees of dwell I can understand why it doesnt run good oh it will idle but when you put a load on it Kablam!! I am not a fan of the HEI as they limit the amount you can turn one and often times are very tight fitting if you have an aftermarket intake. MSD is the king in my opinion, they come with a GM factory looking cap and you can buy them from MSD in Black. Worth every penny!!

 

Your problem with the dwell is your timing.

At some point, the rubbing block wore, the dwell was way off, and somebody reset the timing without setting the dwell.
Now, when you try to set the dwell correctly, the timing goes right out the window.

Put the distributor back in.
Gap it roughly to 0.016" (thickness of a matchbook cover).
Crank it over with the dwell meter attached. Tweek the dwell if it's significantly off.
Crank it again with the timing light on it. Watch for that ONE occasional flash that will show where you are on the scale. If you don't see the line, pull the cap, turn the motor over to TDC on the scale, with the rotor facing the #1 wire, put a test light between the (-) coil terminal and ground, and slowly rotate the distributor clockwise until the light just goes out (if it doesn't light at all, start a bit further counterclockwise from where you were).
Now put it back together and look for that line with the timing light again.
Put the distributor about where you want it (5°BTDC is always a good place), start her up, and finish setting the dwell and then the timing.

- Eric

 

Dave- Oh the things I've forgotten... Of course that's for the radio static. Appreciate the lesson on forgotten facts. I will look into the MSD, I have the HEI in now and might as well give it a shot when I get the new wires. Much appreciate the clarification/explanations.
Eric - Yes I guess my dwell is so far off it won't adjust to 30d with 12d advance.

Thanks for the input guys, I think I'll have this all cleaned up. Once I get the new parts and everything is tickety boo, I'll post the results.

 

OK, I went to the wrecker today and picked up a fairly new set of wires for my HEI. I plan on putting the points dist back in later. Anyway, aside from having a bit of trouble setting up my choke causing hard starting it's running much better. I'm able to rev it up in neutral nicely (haven't taken it for a test drive yet-not licensed) but I'm getting an off idle stumble. I'll have to read my quadrajet book again. Thanks for the help and any further advice on the stumble would be appreciated.

 

Eureka, I've found all of the gremlins (touch wood). I switch to HEI wich solved my electrical gremlin (broken wire insulation under the distributor). I rebuilt my 69 carb as well and switched from the 76 carb requiring me to make a block off plate for the EGR.
It now runs pretty darn good considering it still needs plugs. Everything you guys said was bang on. Bottom line, spark,fuel,vacuum and timing. Oh by the way the with all the screwing around I also ran out of gas. I was fit to be tied. Gauge doesn't work. Next job...

Thanks again.

 

Good to hear, let us know how she runs when the plugs and wires are changed and you fill that empty tank with some high test! She should be able to burn the tires off!!