[PatM]

Plug the lead from the carb. The vacuum can on the distributor can stay open to atmospheric pressure.

Pat

[jankinnu]

I'm still having trouble with engine bog at 4000rpm. After that I disassembled the carb, removed the choke tower and smoothened the sharp edges. I changed new gaskets and power valve, size 65 (earlier was size 50). Accelerator pump shooter size is 25. Is this too small? Primary jets are size 72. The check ball in the vac secondary housing was missing so installed new one.

After that I adjusted the float levels and idle circuit so that the idle is highest. The idle mixture screws are 1 1/4 turns open. I don't have vacuum meter.

I checked timing. It was 15deg at idle and 24@2000rpm with vacuum hose disconnected and plugged from carb. Maybe my distributor mechanical advance springs are too stiff? I'm gonna check the timing @3000rpm to see if it's changing. Maybe 36deg@3000rpm would be ok?

I try to do some tests today with the new setup. Will see how it works.

[F-BIRD'88]

If the motor is bogging down while winging the throttle and reving the motor up in neutral this has nothing to do with the power valve,, jetting or timing curve.
You have a severe ignition problem or a severe fuel delivery problem. (blockage, restriction, crap pump ???

Distributor magnetic pick up tiny/thin wire leads is suspect. (Does it suddenly work fine of you leave the vacuum advance disconnected and rev the motor?)
Replace the pick up coil assembley. Check the pick up reluctor air gaps on the pick up assembly (plastic feeler gauge). Check the distributor advance plate mounting screws.

Ignition coil is suspect. Add a ground strap between the engine and firewall. ( don't ask) Did you add a after market coil but forget to replace the distributor cap center piece. (the carbon resistor type runs way too hot with a hi output aftermarket HEI coil) get a steel one)

Timing should be 16 to 24deg at idle (more is better) and advance smoothly to a maximum of 34-36deg BTDC between 3000 and 3500rpm. (advance maxed out)
Total combined mechanical max + vacuum advance should not exceed 51 degress.

[jankinnu]

Fuel pump is new, model Carter 4070 (electric). I have a decent grounding between the motor and the frame.

Ignition coil is new Accel super coil with new Accel high temp wires:
http://i130.photobucket.com/albums/p.../P1010238_.jpg

The distributor is old. I just bought a new original distributor cap and the rotating part. So this carbon cap center piece is still there. Just to make sure, is it the one in the picture with red circle around it?

Fuel line fits directly into 3/8" hose.

Here's some pictures of the distributor:
http://i130.photobucket.com/albums/p...u/P1010237.jpg
http://i130.photobucket.com/albums/p...u/P1010239.jpg
http://i130.photobucket.com/albums/p...u/P7270150.jpg
http://i130.photobucket.com/albums/p...u/P7270148.jpg
http://i130.photobucket.com/albums/p...u/P7270149.jpg

How much the gap in the magnetic pickup should be?

[F-BIRD'88]

Looks like a pre1974 GM Delco points distributor that has had a electronic points eliminator kit installed. Don;t recognise it by brand.
Don;t know the exact mag pick up /star wheel gap but .015" should be good.
See if the distributor shaft is loose. ( back and forth shaft play).
try reving he motor up with the vacuum advance disconnected. Does the spark mis fault disappear with the vacuum advance disconnected?
The cap center post is fine as long as you have the recomended OHM rating ballast resistor for the Accel super coil.

I thought you were using a 1975 up GM HEI distributor. (big cap with internal coil)

check the shaft end play Excessive end play will allow the starwheel to contact the mag pick up at rpm. (green arrows)

Sometimes the mag pick up (blue arrow craps out) sometimes the small wires become intermident (purple arrows) The coil or ballast resistor could be defective (even if new) check the supply voltage at the ballast resister. Must be a full 12v before the resistor.

[jankinnu]

I may have found the problem. If I rev the engine at neutral with partial throttle, it revs nicely up to rev limiter 6000rpm. When I push the pedal to the metal, it bogs and stays around 4000rpm.

I opened the hood and removed the air filter. The secondaries were all wet. Gas was also over the air filter. So the secondaries are flooding for some reason. I checked the float levels, they're ok. I have no idea why the secondaries are pouring way too much fuel.

I take a picture tomorrow of my carb. The previous owner had already made some modifications (choke removed, I removed the choke tower, the two pipes in the carb centerline coming out of main and secondary fuel bowls are shortened very short. I don't know why.

[F-BIRD'88]

Possible the secondary metering emulsion tube passages in the metering block are plugged up.
Or the secondary air bleeds or passages in the main body are plugged.

[jankinnu]

I had courage to go underhood and rev it at neutral. With WOT it looks like the engine backfires from primaries. If I lift the gas pedal a bit, the engine revs up to 6000rpm rev limiter. Is the mixture too lean? I think I didn't see any flames, more likely just gas steam. The secondaries won't even open and I think they shouldn't open without load.

How do I know if I have vacuum leak? Maybe I gotta buy a vacuum cauge.

[jankinnu]

I finally bought a vacuum gauge.

Here's some measurements for warmed up engine (thermostat 82degC/180F):

I first measured the vacuum readings, with idle mixture screws 1 1/2 turns open:
14" , gear in P, 800rpm (engine temp was around 70degC/158F).
9-10", gear in D, 600rpm

Then I adjusted idle mixture screws until the vacuum reading was highest @ mixture screws 1 1/4 turn open (engine temp 82degC/180F):
15", gear in P, 800rpm
11-12 inHg, gear in D, 600rpm
20 inHg, gear in P, 2000rpm
19 inHg, gear in P, 3000rpm

I adjusted the timing to 20deg @ idle 800rpm with vacuum hose connected. What worries me is that the total timing with vacuum connected was 53@2000rpm and 56@2500rpm.

After these changes the car runs quite well at lower rpms, but backfire from the Holley 3310-2 carb primaries is still there.

I tried without vacuum. 15deg initial and 36deg total. Still after 4000rpm backfire during acceleration. I have to change new rear tires before the next tests Getting bored with symptoms.


- Can too much timing cause this backfire from the carb?
-How do I know if I have a vacuum leak? Maybe some leak detection spray?
-Is it possible that the camshaft is one tooth off from the correct position?

[jankinnu]

I didn't find any back and forth shaft play from the distributor. There is about 1.5mm clearance if I jerk the shaft up and down. Normal? I found this kind of serial number from the side of the distributor:

III2005 1F10

I think I'm gonna start saving to a new distributor. Any recommendations with the MSD 6AL ignition box?

[jankinnu]

I got some suggestions from my friend for the cause of my engine symptoms. He said that either the head gasket is leaking to the intake manifold or one of the intake valves leak causing pressure to the intake.

I bought new intake gaskets and head gaskets. I'm gonna remove the heads to see if the head gaskets have markings of leaking. I will check the condition of the heads also. How do I see from the intake valves if they are leaking?

[F-BIRD'88]

Do a simple compression test. This is always the place to start. Then apply compressed air to the cylinders and listen at the carb and at the tail pipe for leaky valves. while looking in the rad cap for bubbles (head gasket)
Get a manifold vacuum gauge and read the directions on how to use it for engine trouble shooting. Its your eyes inside the motor.

Do a simple cylinder balance test with the vacuum gauge at idle to find the weak running cylinder(s)

[ernkazern]

Beg, borrow or steal a known good carb, put that on your car and see how it runs. You've got a carb on there that some yahooo screwed around with, cut pieces off of etc and you wonder why the car hesitates? You haven't thought to replace it yet???? Is the guy a tuner for Hendrick (sp?) Motor Sports in Nascar or maybe Kenny Bernstein? What the f$#& are you thinking man?

[jankinnu]

I did a compression test for cold engine:

cylinders 1,2,3,5,7,8:
10.5bar/152psi. Spark plugs brown colored.

I couldn't measure cylinder 6 because my headers are modified so tight in the engine compartment.

Number 4 cylinder had only 5.5bar/80psi pressure. So I think either my intake valve is leaking or I have a leak between cylinders 4 & 6.

I'll borrow a dial indicator to check also the actual lift of the camshaft lobes. I didn't see any difference visually when I ran the engine without valve covers.

[jankinnu]

I decided to disassemble the motor due to the low compression in one cylinder. Old iron heads will be replaced by some new aluminum heads. I just don't know which ones to buy. I am also replacing the pistons to flat tops, so I can use 64cc heads.

I have looked lots of heads and their flow numbers. At the moment, I have lift of 0.52" at the valve, so the heads should handle at least 0.6" lift for future modifications.

Car will have about 1000 miles a year in road trips so the new heads should last at least a couple of years without machine shop.

I have a budget of about 1200USD for the heads + seals, pistons, balancing, machining etc. Any suggestions? I have found a couple of used high flowing moderate price heads but don't have courage to buy used ones from abroad.