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WildBill79 · 05:42 PM

I tried out the vacuum gauge today and the gauge would hover around 10 then shoot up to close to 15 when the engine surged. It seemed like the more it revved the more vacuum I got. There was one point for about 20 seconds where the motor sounded good. The gauge showed a pretty steady 18 then it went back to surging and sounding terrible again with about 10 on the gauge. What do you think all this is tellimg me?

Old Goat 67 · 10-11-2011, 05:24 PM

It trying to tell you that you have a darn good vacuum leak.

WildBill79 · 10-11-2011, 07:26 PM

I figured that much. I guess I should get some carb cleaner and spray that around and replace the intake manifold gasket. Maybe I will get lucky. Is there anything else I should check before doing this that may cause my issue with the rough idle, surging, stalling. Why would vacuum increase when I give it gas?

Old Goat 67 · 10-11-2011, 08:15 PM

First, disconnect ALL external hoses leading off of the carb or manifold to eliminate them! Brakes, HVAC, vacuum advance on the dist, etc.

THEN, if it's still present, you will have to diagnose and repair the carb or the intake on the engine to cure it.

Old Goat 67 · 10-11-2011, 08:17 PM

Youre looking for a steady 18 at idle.

PontGuy · 10-12-2011, 08:35 AM

Wow that is really low. What RPM were you measuring at, and was the brake booster line disconnected and plugged when you got those readings? It would take a pretty big leak to drop it that far. Be sure to check the PVC valve and hose in addition to all the carb connections.

If nothing obvious jumps out I would do a compression test on all cylinders as a quick check to make sure the valve train is OK.

WildBill79 · 10-12-2011, 08:46 AM

The numbers I got were with all vacuum lines capped off at about 800 rpm. When it surged, the RPMs went up and so did the vacuum. I am starting to think there is a messed up valve. I'll try the carb spray test and maybe a compression test before I start taking things apart.

wilcar · 10-12-2011, 09:57 AM

You might want to check your fuel pressure with a gauge mounted at the carb and see what happens when it starts to surge. Are you running headers?? They can cause a big increase in underhood temps causing fuel percolation and a condition that your engine seems to have. On my 455 65 GTO with dual Edel. 600's I had no surging but when the car sat for awhile after a long ride it was very hard to start. I later found that the intake was so hot that it was boiling the fuel in the carbs and was causing the problem. I bought some Mr. Gasket spacer plates and installed under the carbs and that solved the problem. When I lived in Fla. and raced the car in the nice, humid, 95* heat I was getting fuel starvation at higher speeds. I was running an electric pump in back through a mechancial pump up front and what we found was that the mechanical pump was getting hot enough to cause fuel percolation in the fuel line and the starvatiion. I removed the mechanical pump and the problem went away. You may want to check your float levels in the Edel. carb and see if you have them set to factory specs. Your problem sure seems to point to some sort of fuel problem caused by heat. On my buddy's 81 Vette he was having the same symptons as your car, ran fine when cold but once it warmed up the car would start to surge and finally just quit. He changed the distributor, wires, etc. but still had the problem. He had headers and chrome engine parts and a small engine compartment. He wrapped his headers and added an electric fuel pump and no more problems. He still has his stock fuel pump(which may be defective) but I think the electric pump alone would be just fine.

ta man · 10-12-2011, 11:57 AM

Quote:

Originally Posted by WildBill79

I did several things today. Once I put everything back together I wired the coil straight to the battery. This didn't seem to do anything. I then ran the line going to the fuel pump into a can of fresh gas. This didn't to to much either. So then I put in a known good fuel pump from my project car and this didn't really do anything as well. Finally, I capped the vacuum line going to the brake booster. This time it fired up and actually ran. The timing does not seem to jump around as bad so I was able to set it and let it idle for quite a while. It does surge and sputter frequently and now when I put my hand on the carb the idle will shoot up. It also seems to be running really rich from the amount of fuel missing from the can. I guess maybe I have a big vacuum leak?

Sounds like the brakebooster is bad.

WildBill79 · 10-12-2011, 02:31 PM

Its hard to say since I still have such a bad leak with the booster capped off. Once i get this problem fixed, I'll hook up the booster and get another reading.

Old Goat 67 · 10-12-2011, 02:46 PM

Vacuum advance on distributor capped???

Timing should NOT jump around.

WildBill79 · 10-12-2011, 02:50 PM

Yes, everything was capped except what the gauge was hooked to. I hooked the gauge to the transmission modulator port on the manifold and the pcv valve port on the carb and got the same readings.

Stuckinda60s · 10-12-2011, 03:17 PM

IIf nothing is hooked to the engine and the vacuum drops and rebounds, you must have a sticking valve. Probably as well as the bad booster.

Does the engine turn over evenly on the starter or does it change speed? R-R-R-R-R-R-R-R or R R-R-R-R-R-R-R-R-R-R?

Do you have an adjustable valve-train? At any rate, it appears to be time to pull the valve covers and inspect the valve train, you may be able to see something amiss. You may have a sticking or misadjusted valve. If it's not backfiring through the carb, it's more than likely an exhaust. A broken valve spring is also a possibility.

WildBill79 · 10-12-2011, 03:26 PM

Now that you mention it, sometimes the starter does sound funny. Occasionally, it will turn over normally, then hesitate, the start turning over normally again. Sometimes it hesitates bad, almost like the battery is dead, but the battery is new. I'll pull the valve covers today and see if anything is obvious. Can you turn these motors over or run it with the valve covers off or will it shoot oil everywhere?
The valve train is stock, it is probably even original. It will sometimes backfire through the carb, but it may be because I was flooding it trying to keep it running or adjusted the timing too much.

69Customs · 10-12-2011, 04:16 PM

http://www.secondchancegarage.com/public/186.cfm

ta man · 10-12-2011, 05:26 PM

Timing chain?

PontGuy · 10-12-2011, 05:37 PM

Nice link 69 Customs!

It is really hard to debug problems like these over the internet, best we can do is offer suggestions. Going through the whole post it sounds like you have done all the obvious checks plus a bunch more, and the carb and distributor are known good because you tested them on another engine. The only tests that I see missing are fuel pressure (to confirm there is no blockage in the line from the tank) and compression check (which may or may not indicate a valve train problem).

Recapping the symptoms-

Engine runs with very low vacuum, and surges even with all vacuum lines plugged
Engine dies when it warms up and does not want to re-start
Timing jumps around a bit- enough so that setting the timing is tricky

If it is an internal problem I am back to timing chain or cam end play as most likely because at least these would also explain the timing moving around. Sticking valves would not affect the timing. Not really recommending that you open it up just yet, but at a loss as to where else to look.

An afterthought- a plugged exhaust system would also give you some of these symptoms. Not very common for a car without a cat though, unless a pipe has somehow gotten crushed.

Stuckinda60s · 10-12-2011, 06:23 PM

If the distributor springs are too light, timing will move around if something happens to cause the rpm's to fall. In other words, if the springs are light enough that there's advance already in the distributor at idle, and the rpm's drop, so will the timing.

What is the cause and what is the effect? Rpm dropped and idle followed or timing changed and rpm followed? Valve stuck, vacuum dropped, rpm dropped and timing followed, see how it might work? Plus, if vacuum advance is hooked up and the vacuum drops, timing has to follow.

PontGuy · 10-12-2011, 06:44 PM

Good point about the advance springs. Just assumed that the springs are heavy enough since the distributor worked OK in the other engine. Springs that are light enough to put a bunch of advance in at idle can cause all sorts of fun tuning problems. Yes, another thing to consider.

WildBill79 · 10-13-2011, 07:36 AM

Thanks for the link 69 customs. That is better than what I was working with. Based on that link it would look like a valve issue or head gasket.

PontGuy pretty much summed everything up. One thing I can add is that this issue started with a surge at idle and progressively got worse.

Stuckinda60s, I am starting to think the jumping timing is due to the main problem because when the engine does run fine for a few seconds, the timing is solid. I just don't really know how to link the two yet.

I didn't get time to do much of anything yesterday. I just removed the driver's side valve cover and of course everything looked fine. I won't get to the compression check until this weekend. Can I do that with the valve covers off or at least without valve cover gaskets. The drivers side one was cork and was destroyed.

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