Engine Help

[Jeremy]

I was driving today and had changed shock settings and thought I would see how this affected hard braking. I hit them pretty hard and the engine died. It would not start no matter what I tried. It had done this to me the last time I braked hard but started and ran like crap. When I checked the timing the distributor had slipped retarding timing.

I had it towed home and about three hours later I was able to get it started but I had to advance the distributor as far as it would go. I have been able to back the timing down a bit but no where near where it needs to be. I have it idling at about 1500 with a lot of advance but it has under 10 HG of vaccuum and it had 17 before today. I have taken the carb (Edelbrock) apart and checked the floats. The were a little out of spec, but I fixed that and everything is working.

I figured the car flooded and thus the reason it wouldn't start but I figured it would have cleared up by now. IF I turn on the AC the car can't handle the load and dies. If I lower the timing or idle speed it dies and I have to max the advance again to get it started.

I have looked for anything that could have come loose and haven't found it.

I appreciate any help as I am at a loss. I also need to car up and running for day to day use and a show this Sat. Thanks.

[Jeremy]

Some things I can rule out are any accessory that uses vaccuum as I pulled and plugged every line coming from the engine. No change.

I ran it tody and it started right up. I let it run and the most it would pull was 6 inches of vaccuum. I am still running way too much timing but if I back it down the motor dies.

It can't take any load at all. If I turn on the AC the vaccuum drops to 0 and the motor will die in a few seconds.

If I ease the throttle open, the rpms and vaccuum will increase. If I try to open them quick, it wants to die.

Someone give me some ideas. My bet is on something internal in the carb, but I can't for the life of me guess what it would be.

I can pull a 3/8 vaccuum line and leave it off with no change. I can cover the air horn with my hand and no change.

[malihoochie]

It would seem to be vacuum leak related, especially since pulling a vacuum line and adding a leak doesn't affect the motors running. Putting your hand on top and blocking air only adds to this thought as it seems to be getting air elsewhere. Edelbrock carbs do not have many internal parts to fall, move, or break & the vent "tubes" are on the sides of the air horn - so a sudden stop (going forward) should not cause fuel to choke out the engine.
I suggest looking on the manifold for missing or damaged vacuum plugs, hoses, etc.

[malihoochie]

How about taking a good look at the fitting at the back of the base of the carb? It is often hard to see and may be your issue.

[Jeremy]

I checked all the vaccuum lines and plugs and all is good there. I checked the EGR valve, removed and plugged it (wasn't hooked up anyway) and no change.

I drove it around the block today and if I kept it above 2K rpm it ran like it should, it just can't take any load under this point.

I noticed when I had the carb apart there was some sediment of some sort in the bottom of the bowls. Could this have gotten into something on the idle circuit?

When I tried to drive it, it felt and the air/fuel meter showed that it was not getting fuel. Above 2K the gauge was right at the lean/rich line where it had always been.

I had noticed that it seemed to surge a bit at low load when it should be cruising on the idle circuit prior to this, if that helps.

[LS6 Tommy]

Sounds like you blew the diaphragm on the brake booster. Is the brake pedal any harder? If so, try disconnecting the booster line and capping the port. You might want to try it even if the pedal is the same.

Tommy

[Jeremy]

I've pulled and capped the line, no change.

I put on a new fuel filter and PCV today. No change. I put on a new Edelbrock 600 CFM carb (750 originally). Once I got it started I was able to at least drive it. The AFR was showing max rich at low engine speed. Once the car got going, it actually ran fairly well, just not much vaccuum although it got better the longer I drove it.

For the most part the AFR was very rich throughout all situations which struck me as odd as the carb was much smaller than what it replaced. At least with the smaller carb the AFR would come off of max rich.

[David Pozzi]

Try a compression test on a few cylinders.
I'm wondering if you had the cam timing slip or perhaps the cam to distributor gears jumped a tooth. The GM nylon tooth cam sprockets get brittle and break with age, what shape is yours in? I'm not sure how hitting the brakes would cause it but something happened!

David

[Jim Nilsen]

I'll second the timing problem and it being the chain. Get out the timing light and see what you get?

[Jeremy]

I pulled the intake to reseal it figuring it was relatively cheap and found that the bottom of the intake manifold had a 3 inch crack in it. I am betting that the crack is the cource of the vaccuum leak.

I also think that the intake gaskets were leaking a bit as well as I spray carb cleaner along the gaskets before pulling the intake and the engine speed picked up. Several spots on the gaskets were wet leading me to believe that the gaskets may have been leaking and the carb cleaner got pulled in.

The new intake will be here in a few days and hopefully that will take car of everything.

[Jeremy]

The new intake did not fix the problem, although I am happy to have one without a crack in it.

I pulled the distributor and found that the mechanical advance could not move. I could not get it to move with a hammer. It was rusted solid. When I started to disassemble the distributor to try and fix it it was missing a tanged washer on the bottom as well.

The shaft also had a lot of resistance to spinning so I ordered a new distributor and it will be here tomorrow.

Just to make sure, on replacing a distributor, you turn the motor over by hand until you feel air coming out of the #1 cylinder and then keep going until the timing mark is lined up, correct? This should be top dead center, right?

I know it is a simple question, but I want to make sure. This is how I staged the motor for the new distributor.

[evan]

...Just to make sure, on replacing a distributor, you turn the motor over by hand until you feel air coming out of the #1 cylinder and then keep going until the timing mark is lined up, correct? This should be top dead center, right?

I know it is a simple question, but I want to make sure. This is how I staged the motor for the new distributor.

I don't have an answer for you, but I hope someone does. With all that persistence (and money) you deserve to have this work for you.

[Jeremy]

I replaced the distributor today and it fired right up and the timing was in the range that it should be. It idled very rough and would backfire through the carb.

From what I have read about through carb backfires, I am geussing that this means I have a valve problem or problems? I would assume a stuck valve would contribute to the low vaccuum.

Any thoughts?

[Jeremy]

I advanced the distributor and it idled smooth at 1250 but still only pulled 7 - 10 inches of vaccuum. I was able to drive it around the block and it didn't drive bad considering there is something wrong. The AFR is fine at idle, and then dances around a bit while driving. I know it is a little lean on the primary side given the smaller carb and I haven't jetted up yet.

It backfired out the carb twice while I drove it but I don't know if that was because it was lean or not. When I let off the throttle with it in gear the vaccuum will jump to 15 to17.

I am going to do a compression check next as I can't think of nothing else to check.

I tried a can of sea foam as I figured it couldn't hurt at this point. It seemd to smooth things out but no change in vaccuum.

Here is what I know to this point.

The carb is new

The intake is new and sealed properly

The distributor is new and installed as it should with the motor at TDC

Vaccuum is too low

The motor only runs with a high amount of initial advance

The motor turns slow when warm but will start. This seems consistent to me with a motor running a lot of advance.

The motor actually runs smooth at higher rpms. A vibration I had before is no longer noticeable.

The motor doesn't make any odd sounds.

The problem started when I slammed on the brakes and the motor died.

Come on guys, there are a bunch of knowledgable folks here and someone has to have some thoughts.

[Vegas69]

Do a compression check as suggested. I also like the suggestion of the timing chain.

[JEFFTATE]

Check Cam timing.
Do a compression test.
Do a leakdown test.

[Jeremy]

I found a timing chain test on line that said to watch for rotor movement while turing the motor the opposite direction. According to the article one should see the rotor move in 3 to 5 degrees.

Doing this I checked mine twice and got 14 degrees of movement on the first test and 18 degrees on the second test.

Am I safe to asume that the timing chain is stretched and causing the problems?

The timing chain in the motor is an unknown brand that came with the PAW rebuild kit. The local Oreilly's can get me a Cloyes heavy duty set for a good price. Is Cloyes a good brand?

In further reading on stretched timing chains, I found that this will cause low cylinder pressure in all cylinders which I believe should lead to the consistent, steady low vaccuum reading I am getting.

[Jim Nilsen]

Yes Cloyes is a good brand and 18degrees is way too much for a chain and is probably worn a nice line in your timing cover. I had one once that wore a line that started to leak before it decide to jump time. This is a common problem.

[Jeremy]

I'll find out this weekend as I the timign set will be in tomorrow and I hope to have some time here and there to tear into it.

I believe the set I ordered as three settings for 4 deg advance, straight up, and 4 deg retarded. What does everyone recommend to set it at.

I was thinking the 4 deg advanced might be a good idea. I have 6x heads with a 068 cam and I think it is a little low on compression and cylinder pressure. I have always had to run a lot of initial advance on the combo and think that the 4 deg would help.

[David Pozzi]

Advancing will bring peak HP at a lower rpm, not a lot but maybe 500 rpm's lower. Be very careful indexing the crank sprocket. The symbols Cloyes uses is a triangle, square and "O". The O and square can get mixed up fairly easily. I had a buddy with a new engine that they installed the gear with square on the keyway, but indexed off the "O" on the tooth, it ran terrible, got up to 3000 and fell flat on it's face.

I hope you didn't bend a valve, do a compression test or better yet do a leakdown test after you get the new chain on the car and don't turn the crank much without the cam turning or you can bend a valve that way. If you do have to turn the engine farther than it takes to get the gear on, back off the rockers first.
David