[zipchip]

Hi, need some help with a diagnosis....just recently completed 70 454 (full Ls6 specs) full restoration with aftermarket Holley 850 dbl pumper, elec chock disabled, choke wide open. Carb rebuilt about 24 mos ago, ran in cam/engine, then carb sat for 12 mos before final re-install. Car has only 15 miles on it....plugs look fine, timing at usual 4 btdc.

Cold start is just fine, idle is good at around 750, no hesitation, float levels good...when engine is hot having two issues

1- Engine diesels loudly at shut down (rpm at 750)
2- Hot restart is a problem, engine cranks and acts and smells like it is flooded, will start with pedal to the floor.

Any suggestions? Also need a book or website on tuning and adjustments for a 850 dbl pump.

Thanks

 

[Twins Fan]

Crank the timing up on that thing. Try setting the initial at about 16* and see how it runs then. You also want to know where your total is, so you know what your advance is.

The search function here on TC is probably better than any book for Holley's and timing. There is a good Holley book out there, though. I got it at Barnes & Noble, it's called Tuning Holley Carburetors, or something similar to that.

 

[bbmusclecars427]

There may be trash in the needle seat(s).These are at the bowl(s) to ajust the float level(s)Also the float levels could be too high.The fuel level should be bearly trickling out the fuel level inspection hole(s).

 

[Mike]

http://www.holley.com/data/Products/Technical/199R7923-2.pdf

 

[zipchip]

Thanks guys will recheck the float levels and reset timing to 16 BTDC. As I said I am at 4 BTDC now and vacuum advance is capped/fixed at 20 initial. I was told need to be at 36 total (20+16) not 24 (20+4) where I am now....

 

[Mike]

vacuum advance is capped/fixed at 20 initial

Your not using vacuum advance in your total are you ?
The centrifugal (mechanical) advance should be set to a max of 20 and the initial set to 16.
The vacuum advance doesn't count in the total timing.

 

[Twins Fan]

I'm also not sure on your timing remarks, Tom. Post how you set the timing for us. What kind of distributor do you have anyway (HEI, points, stock, aftermarket)?

Hopefully it sounds something like this. With the vacuum advance disconnected and plugged/blocked, get the idle low around 600 or so, then set the initial timing to 16* BTDC. Then check your total timing and hopefully it ends up at 36* BTDC all in by 3000 rpm.

Don't even be concerned with the vacuum while setting the timing. When all is said and done, you will probably have like 54* of total timing with the vacuum advance included.

Get the timing squared away first before you start on the carb.

 

[zipchip]

The distributor was/is stock GM points. (I had the distributor checked and recurved to LS6 specs.)

I was told it was re-curved (LS6 specs) and set to 20 degrees mechanical advance and the vacuum advance was permanently plugged. I was not told (clearly) about going to 16 btdc on the damper but now it makes sense.

I am at 4 btdc now, as per your suggestions, I will back down the idle RPM (600 or so) and set the timing to 16 btdc, probably in two steps (ie: 4 > 10 btdc then 10 > 16 btdc) with an idle adjust between each to finish with 16 BTDC on the damper. Will also recheck the dwell.

How does this sound.....

 

[zipchip]

Thanks Guys, problems seems to be solved with that timing adjustment as suggested.