Hesitation/bog Problems on my 86

[rockable]

My 86 C10 w/ 305 has bugged me since I bought it.  It is stock with the exception of the air pump being removed.  I put a rebuilt factory correct Q jet on it and fixed all the vacuum leaks after I got it.  The timing is 4 degrees BTDC at 550 rpm idle speed.  I just adjusted the idle mixture again and put new plugs on it.

From idle, when you just ease down on the throttle it hesitates or bogs momentarily before finally accelerating.  When you look at the timing, the advance is working but it is controlled by the esc.  It doesn't advance until the engine gets to maybe 1200-1500 rpm.  So, when you crack the throttle, it bogs, doesn't advance and then revs and advances. 

I'm convinced that timing is the main culprit here but don't know how to fix it.  Has anyone else encountered this and come up with a fix?

[Fairlane514]

I would get rid of the ESC, get a straight HEI distributor  and set your initial timing at 10-12 degrees advance.

I have an 84 with a Goodwrench 350, I removed the ESC distributor and put in a Summit regular HEI with an adjustable vacuum advance. I turned the adjusting screw all the way clockwise and then 8 turns back CCW. I set my initial timing (with vacuum disconnected and plugged) at 12 degrees and then then used a full manifold vacuum source on my Qjet for an additional 10 degrees advance (with vacuum advance)  at idle. Its runs great with no hesitation.

550 rpm seems a little low for an automatic ( I assume), especially with A/C

[87454westernhauler]

i had the exact same problem with my 86 that had the ESC on it and i just bought a hei distributor and put it in and set the timing around 12* and that solved the problem. it rilly had me confuesed.

[454Man]

I thought about buying another distributor but I figured why not see what everyone is talking about with the 375 center plates and 41 weights from a 80s suburban. I spliced the black and green wires going to the esc controller, then later found the center plate and weights that give 20° of mechanical timing and limited my vac advance to 10°. I also used the medium springs from the moroso kit which bring my timing all in@3200 rpm. This truck is a total different beast. It feels like I picked up a ton more tq and hp through out the entire rpm range. It idles smooth all the way down to 350 rpm with a lope like I have a bigger cam. Truck doesn't shake a bit. Ill try to get a video clip going if anyone its interested. Even if I do get another hei I would still use the same center plate and weights.

[Stewart G Griffin]

rebuilt factory correct by who?

[rockable]

If you put a straight HEI unit in, does that mess up the ECM in any way?  I know it will also take the knock sensor out of the loop.  I still have all the multitude of vacuum lines connected to my EGR and I don't want that to malfunction in any way.   

550 RPM is spec with the AC off.  It's at 650 with the AC on.

Mountain Man Fuel Systems - Ted, rebuilt the carburetor.  He does nice work.

[rockable]

Ok, after some research I realize that what I called the ECM only controls the distributor and timing for the most part.  I am putting a straight HEI in it as soon as possible and will let you know if that fixed it. 

After that, I may remove the EGR and all those giggered vacuum lines, now that I understand how the TCC is signaled.

[rockable]

Put a standard HEI distributor on and it improved the acceleration and throttle response.  I still have a slight hesitation but it is better.  Overall, the engine runs much better with a stock HEI distributor.  Wish I had done it long ago.

Recently replaced the stock catalytic perverter, too.  The new one made a big improvement in performance and sound.

[Fairlane514]

What is your initial timing?

[rockable]

8 degrees.  12 was too much.  8 seems ok.  Connect the vacuum to the timed port, not the full vacuum port.

[Fairlane514]

Why was 12 too much?    Did you try the vacuum advance on full manifold vacuum?

[rockable]

Pre ignition and knocking like heck under load.  Same deal with full manifold vacuum.  Idle timing at 34 degrees BTDC is too much.  That's what I had with full vacuum.

[Fairlane514]

Ok, sounds right.  You might try using a vacuum gauge on full manifold vacuum to tune the idle mixture screws on the quadrajet. You want the highest reading on the gauge.

[454Man]

34° should be initial+ mechanical and not initial, mechanical, and vac. How many regress do you have in mechanical? the reason you can only go with 8°btdc is because there is too much mechanical advance built in. if you lower the mechanical  your initial can be raised.

[rockable]

I set it with the vacuum disconnected to 36-37 degrees.  That was too much.  Backed it down 4 degrees and was all good.

How do you change the mechanical?  Change weight and springs?  Forget it. Its running so much better than it was, I'm good.