Looking for some advice on what to set this engine at for Timing and the Quadrajet. I had the carb rebuilt last year but I have never been able to set it just right and now want to dig into this to get it running perfect. The carb is a 800cfm, 77 jets, 55p rods, cv sec rods, idle circuit was opened up a bit and a new elec choke installed.

-Olds 455
-KB 277 30 over pistons (comp around 9.8:1)
-Cam 298/306 on a 110, with .568 lift on both (thanks Cutlassefi)
-Comp Roller Rockers/Guide Plates/Studs
-Large Valve 2.07/1.72 G heads light porting job, crossover filled, center divider levelled
-Edelbrock Performer 2151 intake
-Hooker Comp non-tuned Headers 3902 / 3 inch Pypes dual exhaust
-Olds HEI Distributor, rebuilt with a Mallory CD Ignition

Right now I find the problem is it smells really rich upon initial startup, it gets better as it warms up, so my choke may need some adjusting, somebody was telling me to use a different oil pressure switch to run the choke?

The throttle is responsive but I think between the timing and adjusting the carb that I could get it to run better, I also find I have to keep the idle up near 900 rpm otherwise it will stall at lights...

It is also a little hard to start cold, I normally have to pump the pedal a few times and crank it for 5 seconds before it kicks.

What do you think of the carb setup? What should I set the initial timing at?

 

I would run as much timing as you can, till it gets hard to start, or pings, then back it up just a little. Try for total,34-36, all in by 2500 RPMs. Also with performance cams, need all the timing you can get, and also performance cams usually always smell, and run rich

 

I believe total is right around 36 all in close to that maybe a little higher 2,700 rpm. Like I said the car performs well when the pedal is pushed, just more so the high idle that I was trying to get down without it stalling... It does not ping either. Thats good to know that a larger cam tends to run rich, I had thought the carb might have been jetted too high or improperly set.

There's 2 screws on the front of the carb, I tried hooking up a vac gauge to get the highest reading, trouble was I really found very little difference if I turned them, even with them closed vs opened 3 or 4 turns, I ended up leaving them at 1-3/4 turns out but not sure if I need to do this differently.

Also I think the choke might be the culprit but I have no clue how to set it so maybe I need to check that out first.

 

If the 2 idle fuel screws have no effect on your vacuum gauge and you can turn them all the way in, your idle is probably too high and your out of the idle circuit. Another possible cause is vacuum leaks.

 

Please don't generalize. ALL "performance" cams run rich? Really? No matter what? Not so.
And technically they need more fuel due to overlap, but they're not all the same.
Also, how do you know his application wants all the timing in by 2500? The last time I did that on the dyno I lost almost 10hp. Do you know for sure those numbers are correct for his combo?
No you don't. And if you don't want to have to potentially buy him new pistons you may not want to recommend such an aggressive timing curve right off the bat.
Just sayin.

 

So what should I start looking at first the carb or the timing?

 

The carb, whats your idle speed?

 

Cold idle is 950, in gear is 750 and it almost stalls.
Hot (180 on temp) idle is 1,050, in gear is 850.

 

I am also wondering if my vacuum connections to the carb might be incorrect.

Front of carb has:
-upper left to distributor
-lower left to pcv
-lower right to TH400

Back of Carb has:
-large hose to brake booster
-other hose to vacuum bulb for heater/vent controls, car has a/c removed

 

When you set your timing, was the vacuum advance disconnected? Is there vacuum on the line at idle? IMO you idle is too high, at what rpm did you set it.

 

Hi Eric, yes distributor vacuum was disconnected when I set it but I am thinking there may be vacuum at idle, I need to test that to see if it is ported or manifold vacuum. My understanding is there should be no vacuum at idle going to the distributor but when the pedal is pushed you want vacuum, is that right?

As for the idle, yes it is high, but if I turn it down then the car wants to stall. Thinking this could be caused by the distributor vacuum or something else in the carb/timing.

Thanks for your help

 

The argument on running manifold vacuum to the distributor is endless. Some engines like it some don't. I'd like to know what your initial timing is set to at 750 rpm , even though you stated your total without vacuum advance is all in at around 36.

 

I'll pull out the timing gun tonight or tomorrow and get some exact readings, I think my initial was set around 12. I am also at about 3,000 feet above sea level so what would you expect me to have for initial and total (without vacuum)?

 

I'm assuming this is your setup from another post:
My build will should deliver around 425hp/500ft lb also.
-Olds 455
-KB 277 30 over pistons (comp around 9.8:1)
-stock rods & crank ground 10 under/align honed/balanced
-Cam 298/306 on a 110, with .568 lift on both (thanks Cutlassefi)
-Comp Roller Rockers/Guide Plates/Studs
-Large Valve 2.07/1.72 G heads light porting job, crossover filled, center divider levelled
-Edelbrock Performer 2151 intake / Quadrajet jetted to match engine
-Hooker Comp non-tuned Headers 3902 / 3 inch Pypes dual exhaust
-HEI Distributor
-TH400 trans, red alto perf rebuild with Transgo 400-1&2
-Rear end is a 3.70 posi
-2,500 Freakshow Performance stall

Although 3000 ft creates additional issues, I would assume your initial should be higher that 12

 

Yep thats my exact build

 

I'd get rid of that air cleaner. Have you tried running your engine without the spacer under your carb?

 

Spacer is already gone, it caused the air cleaner to touch the hood so once I got into painting the car it was removed, yes I heard that air cleaner was bad from another guy to, I plan on gettign a regular round chrome one too.

 

see if you can find the posts on how I fixed this issue on the high compression 403 with HEI

12 timing was not enough
had to alter the HEI to limit advance therein and run manifold vacuum to dist'r

therefore the vacuum stayed high at idle and it did not richen and die.

You should see it run now.

http://s19.photobucket.com/user/Rock...qmat1.mp4.html

 

That's good feedback to as I need to look at what the vacuum is addign for advance and also what the weights are doing. More to come on what its at now then we can start moving it around with the advice you guys have given me.

 

In most cases HEI's have around 18 degrees of mechanical advance. So generally an 18 degree initial gives you a 36 degree total. At 3000 feet that may not work.

 

With elevation would you expect it to need more or less advance?

As for the vacuum advance, what amount should it be adding at idle zero or ? And is there a limit or ballpark that I should be aiming for with the vacuum advance at a certain rpm?

I know this is all tough as each engine is different but I am just looking for a starting point.

 

At the higher altitudes you need to lean the carb out and timing might be a bit more advanced. I generally limit it to 10 for a total with vacuum advance of 46-48 where I'm at in Texas. For now I would disconnect and plug it until you have your distributor ironed out.

 

Will try to get some current initial/total numbers tonight or tomorrow night, will post back with what I find.

 

I used the common adjustable vacuum can, adjusted to min. travel, which was 11-12 degrees.

I had the exact symptoms you describe plus low power and severe overheating after a 2 mile test run. Idle adjust screws did nothing, gagging rich exhaust, low vacuum at idle which I assume allowed the power piston to rise, further richening the mixtrure, then even lower vacuum, then stall. Search the web for HEI tweaking clues. Learn to measure mechanical and vacuum advance. I ended up using math and calipers and a pointer and such.

PS most carb jet combos I see have about a 0.030" difference between jet and needle, you are more like 20. I parted a Chevy truck carb and found the needles to give me a 30 difference and though you would think even richer would be worse, it now works great.

 

Here's the results of the tests:
-initial timing was at 18 degrees (no vac to distributor)
-mechanical advance added 16 more degrees so 34 total

My neighbor came over, he's a Chevelle guy and a mechanic so he's a good guy to have around, we dropped the initial down to 8 degrees, left the vac advance disconnected, so now its seeing a total of 24 degrees. Adjusted the idle down to 800 which is about 650 in gear and it sounds way different in a much better badass way. Took it for a drive and it ran pretty good, had lots of power and the idle is down quite a bit now.

Not sure on the vac advance though if I leave it off or hook it back up, we'll see how the car starts cold next time as I am hoping it will start easier without it...

I may also try to go up a few degrees on the initial maybe to 10 or 12 and see how it acts.

 

Give this a read:
http://www.lbfun.com/warehouse/tech_...t%20Timing.pdf

 

That's an interesting read, lots of good info in there, I need to test my vac advance to see how much it is adding at idle as I think that was part of the problem also. I may be able to go back up on the initial if I leave the vac off or limit the vac as I can adjust it with an allen key.

Thanks for all the help guys, I sure know a heck of alot more about timing and carbs now that I did a week ago!

 

are you sure you have 77 jets and 55 rods in that carb? that sounds like the jet/rod configuration for a large main air bleed smog chevy carb.
What is the carb ID number?
77/55 sounds weird. It should not be necesary to put that big jets/rods in the carb. I can see the carb is a BOP unit, so it will most likely have small main air bleeds. I just finished a Qjet for a high compression Buick 455 with a 236/241@.050 cam and headers. That one ended up a bit rich with that APT screw putting the rods right at the upper edge of that taper: leanest possible setting.

 

Carb id is 17059253 2798 BZA I believe it is originally off a 1979 Trans Am with a 403. Not sure on the exact mods that were done to it but I did have it rebuilt by http://www.carbrebuilders.com by Don Oake in Oshawa, Ontario.

Is this not a good Quadrajet to have?

 

ohh, that is one of the best Qjet-units you could use :-)
I am pretty sure that unit is a small main air bleed unit, so using 77 jets and 55 rods sounds weird. It aint right... unless the builder opened up the air bleeds ( which would be a bit of a weird move ), that jet/rod combo is way off.

 

hmmmm the only thing I know that was modified was that the idle circuit was opened up to allow more fuel, so would that be what you mean by the air bleeds?

He did ask me for my engine specs so he could match the carb to the engine, and I did see some good reviews from his carb business think it has been rebuilding carbs since the 70's so I assumed he knew his stuff.

 

I dont know the guy and dont mean to spread doubt on his work!
Sounds good that he opened up the idle circuit. That would certainly be necesary with that cam. Both the idle circuit and the main circuit has upper and lower air bleeds / emulsion bleeds. The size of these bleeds has a great impact on the total amount of fuel metered to the engine.
77 jets would be very big, but throw in a pair of 55 rods and the jetting is pretty lean all of a sudden. It just sounds fishy, is all. Maybe it aint. Maybe he calibrated it for your altitude, that would mean leaner jetting than normal.
In order not to leave power on the table, due to improper tuning, I would definately check up on jetting, either by measuring these two air bleeds or by checking AFR with a wideband.

 

I appreciate you sharing that with the detailed explanation on the circuits and air bleeds. My plan is to get the car dyno'd soon so we'll be able to fine tune it at that time also.

 

your'e welcome :-) It just caught my eyes. Maybe everything is good.
If you can remember, please do let me know what AFR's the carb gave, once you have it dyno'd :-)