355 Poor Performance

[1976Scottsdale]

If all that don't work, plug ur brake booster hose off and drive it and see how it does.  Be VERY CAREFUL as the brakes are gonna be a real bear to stop with.  If you still have issues your booster is okay.  Mine did the same, no leaks at chek valve or anywhere on hoses, had an internal one some where.  I ended up setting mine at 4 degrees without the vaccum advance.  Runs like a champ.

[78ScottsdaleK20]

Dinked around with it some more. My total timing is at 28 degrees. 12 BTDC and at 3,000 RPM it took 16 degrees on the gun to hit the 12 degree mark on the indicator.

How do I get more advance at 3,000? Change weights or springs. I have a weight and springs set. Came with three sets of springs and one set of weights. I havent mucked with the adjustable vacuum advance since I dont know which way does what, so I would have to check but think its at around 5 turns out.

Installed a thick Holley carb spacer/gasket, (one you would install to keep the fuel colder) and cleaned up the interior of the distributor and under side of rotor (was pretty dirty), also installed spring loaded needle and seats, so I can keep her running when wheeling. END RESULT: better vacuum readings, the needle does not violently flicker, stays steady at 15". Adjusted carb with the gauge and got it to 16" at idle. This made the A/F really rich, so I dropped 1 1/2 stages lean for the power and cruise mode. Re-adjusted for highest vacuum with new metering rods and jets, still rich, but not as bad.

It seems I am getting closer, its still running pretty fat, both at idle and cruise, but the part throttle stills stumbles a little.

The engine ground strap is the same as when I bought the rig, and looking pretty old. Might replace this and install another one on the other side of the motor. Currentlly there is only one from the pass rear header bolt to the cab.

Might take the dist. into have it put on a machine and have the guy dial it for my application. After all, it might be worth the little $30 investment to know that it is right.

[VileZambonie]

  I'm confused. Don't you have a zero mark on your timing tab? Aim for zero and whatever your gun reads to make the mark line up with zero is what your timing is at. Don't worry about base timing right now. Advance the distributor (rotate it counterclockwise) until you have 36° total advance.

[78ScottsdaleK20]

Maybe I am confused too...instructions say to take base timing (12) then take readings again advancing the gun to line up the balancer mark to where the base was set at. It took 16 degrees to get the balancer to line up with the mark from the base reading and then add the two totalling 28.

Maybe this is incorrect. I will try again. If I advance that distributor any more the terminal for the BAT and TACH will hit the firewall, and the vacuum advance is going to hit the Intake. Should be able to positon the cap in any position as long as your not off a tooth, and the rotor is pointing to the correct wire right? I need to reposition the cap so I can advance it more.

[VileZambonie]

Do you have a body lift or drop or something funky going on? Your distributor should not hit the firewall. If the vacuum advance hits the intake so you can't get 36° then your distributor is off one tooth.

[78ScottsdaleK20]

Took more timing readings, and it took 51 degrees advance to get the mark on the balancer to line up with the zero on the tab. Took timing with everything hooked up as normal running operation.

This seems wrong, and yes the vacuum advance will run into the Intake with a little more turn. Could the dist. be off one tooth and still run pretty good, just not perfect? This may be the cause of the miss (I thought it was carburetion).

Also I noticed that my fuel pressure fluctuates...Like my RPM's it will flutter sometimes, dropping to 3 psi then go back up to the 5 psi I set it at. Needle will flicker. The fuel in the filter (clear) gargles / bubbles and there is little fuel in it. The filter itself is of a bigger kind and is positioned just before the pressure regulator.

When I get enough time I will yank the valve covers off and verify valve lash.

Thanks for the replies, it helps.

[VileZambonie]

If it reads 51° total advance you might want to verify your TDC mark. Bring the #1 piston to TDC visually (pull the spark plug) and see if your mark lines up on the damper with your timing pointer.

51° is over advanced.

As far as fuel pressure goes -with a carburetor pressure isn't as important as volume unless pressure gets too high. Anything over 9 PSIG can easily force the needle off of the seat and flood the carburetor. But if you see it bouncing around like crazy I would do a fuel volume test with the regulator installed.

[78ScottsdaleK20]

So I am tired of working on this heap out in the cold so I took a break. Sometimes you gotta just walk away from it

I retarded the timing back to 8 BTDC (from 12) and total timing as anyone would expect fell 4 degrees to 47 @ 3,000 RPM's. Quick math would tell me that if I wanted to get 36 total I would have to retard the timing all the way down to 3 degrees ATDC. That cant be right.

As far as verifying TDC with the mark on the balancer and the indicator, the engine builder set TDC and I havent mucked with it. I verified TDC with the balancer mark and indicator when I put the dist. back in when the Intake gasket was done, and I know that I didnt set it for cylinder #6. As far as being a tooth off, anytime I dropped the dist. in it would only go in matching the oil chamfer. If I went one way or the other, (one tooth over) the dist. would drop but not seat on the Intake. So I should be spot on.

I have set the carb up with the vacuum gauge, and since then I have set the idle mixture screws way fat from where I used to have it. A/F improved a little and driveability, but has the infamous stumble at the low end during part throttle.

I found the tech article on CK5 forum about "timing & advance timing 101 tech post" and is informative, almost to the point complicated to a shade tree mechanic as myself. However I did take advice and disconnected my vacuum advance from the timed port on the carb and hooked it up to direct manifold vacuum. It seems this helped a little with the above mentioned A/F and driveability.

Soooo...at this point it seems I will muck around with weights and springs in the dist. to get the correct timing set. If that all fails, IM PUNTING!!! Let somebody else do it.    Sometimes its just nice to learn yourself...Also will set correct valve lash this weekend when I get the time...

Thanks again Vile for your continued support!

[VileZambonie]

A good aftermarket distributor should really help you nail down your timing. Get rid of the vacuum advance distributor all together if it's in your budget. It sounds like your distributor is in right since you can range up over 50° before it hits.

[VileZambonie]

Also did you pull the air horn off and pull out those sock screens then readjust your float level/float drop?

[78ScottsdaleK20]

I heard that one whould stay away from teh dist. without vacuum advance from that tech 101 page writtenb by an X-GM engineer. It mentioned that most street driven engines really benefit from them, if used correctly.

So far when changing timing, I dont have any knocking or pinging, so I am thinking of advancing the timing til I hear some pinging then backing it down. This may bring me to where I was or more advanced then before, but install different springs to slow the centrifugal timing down. Its my understanding that experimentation is the best way here if you dont have a dist machine.

I did not take out the sock filters, as there was quite a bit of debris found in one of them, and I felt if these were removed I would have more problems with erratic A/F metering if any of that debris goes through the metering system. My thought is, better to stop it there than have it clog up the jets and all little orifices in the carb. Should I still remove these? Do you recommend doing this if dirt is found consistently in the fuel bowls?

[VileZambonie]

If you are using a good quality inline fuel filter they are a catch can for a lot of crap. If you have a good filter the smallest particles will pass through and not build up in the fuel inlet. I've always eliminated them but at the very least clean them and the passage way.

As far as vac advance goes- If you are running a really good aftermarket ignition system and it's more of a toy than a DD I would kick it to the curb. If you are daily driving you will probably want a good vac adv dist.

[78ScottsdaleK20]

Followed valve lash instructions verbatum using the method of marking the balancer every 90 degrees, and starting with #1 following the firing order. Loosened the rocker arm until lash was felt (up and down movement of rod) then tightening locking nut until lash is zero, then half a turn.

I felt side to side play in the rocker arm and the push rod spins easily. Should the rocker arm be snug with no movement, and the push rod able to spin easily? I thought no, so I adjusted the rocker nut until all rockers were snug and a little spinning of the rod. Some took 1/2 turn, and some took 2 full turns.

Started truck up (engine cold-outside temp 28) and heard a little excessive valvetrain noise until engine fully warmed up. Still can hear the slight "typewriter" sound once fully warmed up.

I also verified somem more ignition components. One test for the pick up coil continuity between the two leads. Suppose to be between 800-1500 ohms resistence with no break in continuity when actuating the vacuum advance arm. The reading I got was 804 with the reading dropping down to 795 when moving the vacuum advance arm. I gues this little difference is ok as long as its not a big break. Also took the weights and springs out of the dist. and cleaned off a little gunk from the bushings.

However, the engine performance feels a little better, like the valve timing has improved. Still have the infamous low end stumble (though it seems not as bad as before), I imagine is from fuel metering. Still runs rich at idle and cruise, and lean at part throttle when throttle is just opened up but not quite in the power mode. It seems I have to run this in the power mode so its not in lean mode stumbling around.

I will continue to search for this common problem in the forum and other forums like Hotrodders and CK5 and fumble around with carburetion to see if I can correct the low RPM stumble. I shouldnt have to live in the power mode to drive this thing around, unless I like stopping at every gas station.

[VileZambonie]

One full turn from zero lash is what you wanted to do. Yes the rockers will be able to move and if lubricated the pushrods will spin without much effort so you'll need to readjust your valves. Start that one over from the beginning or you'll be bending pushrods.

P/U coil is 500-1500 and usually you'll find around 800ohms. The pick up coil will either work or it wont. So rule that out or you'd most likely be dealing with an intermittent no start.

Re-adjust your valves again

[78ScottsdaleK20]

If I tightened the rocker nuts too tight, there is a possibility of the following?

1. Bend a rod
2. Damage a lifter or rocker arm even braek a spring
3. Wear the cam lobe down

If they are too tight, will I hear some noise of the above mentioned?

Since I tighten the rocker nut enough to take out the side to side play in it, but the push rod is still able to be spun, is this so tight, that I could do damage?

The next time I will have time to redo this is tomorrow. Not sure if I should be driving this thing around... I drove it around last night and a little this morning, and I did not hear any bad noises...

I will re-adjust the lash again just to make sure. When I get to zero lash (rod to rocker arm) its one full turn. If the rocker arm still has movement, is this acceptable. I thought maybe thats where you get the valvetrain noise from...?

I am sure you are aware of, there is many different amounts of "turns" to correctly set the lash, from 1/8 of a turn to Chiltons 1 1/4 turn. Last question, how do you know how much turn you need?

Thanks again for your support and help, its appreciated!