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Discussion Starter #1
IM just checking , I built my carb, went with recommended jets and PV, and it had some drivability issues, a slight stumble on initial light acceleration, and intermittant stuttering when opening secondarys.

So I finally went down to my friends shop, and set the timing to 36 degrees total

I disconnected my vac advace, plugged the line, ran her up to 3000-3500 RPM had set my light to 36 degrees, and turned the dist till the timing mark was at zero and set it. Then rehookup the vac advance. now its running 20 degrees cooler, seems to pull a lot harder Still has a few drivability issues, but now I need to play with jetting and squirter issues to dial it in.

The point of the telling, is is this the logical way to have went about this?


Steve

Thanx in Advace

Steve
 

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I had a question and tried to send you a pm but your message inbox is full and won't accept any new messages until it's cleared out.
 

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What was the timing before?
 

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Discussion Starter #5
It was set basically by ear

id drive it, see how it ran, move back and forth until the engine seems to perform, well, but it ended up way advanced, to the point it wasnt starting well, didnt detonate because I run 94 octane, for the cruise this weekend, im gonna add 5 gallons of 100LL


So the doing it correctly, retarded it significantly


S
 

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I disconnected my vac advace, plugged the line, ran her up to 3000-3500 RPM had set my light to 36 degrees, and turned the dist till the timing mark was at zero and set it. Then rehookup the vac advance. now its running 20 degrees cooler, seems to pull a lot harder Still has a few drivability issues, but now I need to play with jetting and squirter issues to dial it in.

The point of the telling, is is this the logical way to have went about this?


Steve

Thanx in Advace

Steve
You shouldn't get hung-up on any pre-conceived advance "number" like 36 degrees or any other for that matter. 36 will usually put you in the ballpark but is by no means the "magic" number for every engine. You need to fully experiment with the timing and get it optimized before fooling with the carb (as far as changing components) too much.

My engine likes 38 degrees total advance. 36 doesn't quite cut it but is pretty-close. At 38 it runs absolutely fantastic. You need to play around some more before automatically assuming you have to change something in your carb. Find your upper limit as far as advance goes. After that, you may want to play with the curve some. If you go right to 36 degrees and don't experiment any further, there's a chance you're not going to get the most out of your engine and could make things worse by jumping to the carb and changing out jets and squirters and power valves prematurely.
 

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You set it at 36 degrees total but where did your initial end up? How much vacume advance are you pulling?

It seems like the most common thing people do is stab in the lightest springs then dial up the initial for a good idle and response then end up with too much total and a curve that's faster than the engine wants-let the bucking begin. When you finally get the curve right and the inital and total optimized you'll be able to stab the gas pedal at any speed or rpm and have it just pull crisp and clean. Forget about adding vacume advance untill you get the mechanical curve, initial, and total optimized- then add a little vacume advance to the mix just a little at a time to see just how much the combination likes at cruize and under slight load. JMO
 

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As was posted, timing totally depends on the engine combination. There is no "magic" number. We run our 632 at 32* initial advance and take it down in the low teens with nitrous. A friend has a 892 ci engine and his is set at 26*. Learn how to read plugs...they are what really tell you how happy the engine is.
 

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As was posted, timing totally depends on the engine combination. There is no "magic" number. We run our 632 at 32* initial advance and take it down in the low teens with nitrous. A friend has a 892 ci engine and his is set at 26*. Learn how to read plugs...they are what really tell you how happy the engine is.
X2..... i built two motors alomost idetical, only dirreance was the carbs. on the dyno one loved 42 deg. of timing (distributor locked out) and the other only liked 38 deg. total. im not sure of your combo but i dont like running the vac. adv. i always plug mine off even in street motors. not saying you should but maybe if you try it it might like it. find out where it likes to run (take it to a dyno if possible) there you can get a for sure reading instead of just seat of the pants.

on a side note we did the ol timing buy ear thing in a buddys 69 chevelle while we were waiting for the light to show up, we went out and made a pass and the car ran better than ever. got the light there and checked it.....64 deg of timing in that thing lol!:eek: we backed it back down to 44 in fear of to much detination. good luck and i hope you find the sweet spot.
 

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Discussion Starter #12
well im somewhat limited

after I set the 36, I idled it back down, and I believe it was 8 BTDC, then the carb was needing readustement as far as idle mixture, I couldent find my god blessed Vaccum gauge, But my engines pretty much out of the box ZZ350, even the speed shop said I would be wasting my time with a dyno tune, I actually considered that.

So a basic from the factory 1992 ZZ350, at idle, vac advance disconnected should run what timing? I asked that months ago and no one replied....

The 36 Degrees, made sense, and whern I did it, it was a huge improvement, last night I set the accel pump clearance, reset the idle mix, I go in, till it breaks up, then out 1/2 turn. Now the stumble is gone, once in awhile itll barely stumble when I hit the secondarys, so Im thinking narrowing the jet gap from primary to secondary from 9 to about 4 or 5.. I do not have a secondary power valve.

I appreciate all your suggestions, Im just not sure which way to go, is there someone with a very similar combination that can tell me how they are setup?

I have 9.8 to one
a Bowtie Performeresque intake
510 Lift Cam
650DP
68 Pri Jets 79 Secondary Jets
HEI, Accell Hi Perf Coil
Headers, full exhaust with the one flowmaster in stock location
Roller cam, Crane 1.5 Roller Rockers
Aluminum GM Heads, 57CC ( Nothing Special )
4 Speed
373 Gears


Its actually running outstanding now,. IM not quite sure its maximized, but it doesnt detonate, and it runs 20 degrees cooler at 36 degrees Total

So I appreciate all the input, but lordie, makes me appreciate you guys that have this down pat. Im not above just taking it somewhere and having them do it LOL

Im an Expert Aircraft Mechanic, but this aint no Airplane
LOL



As far as recurving, the centrifigual advance, thats gotta be a hit and miss deal, my plugs are light brown

Thanx for all the good advice gentlemen Ill take it, and go a step at a time

Steve
 

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Steve, did you try 37* of timing yet?.....it might like alittle bit more...My 355 runs great with 40* total (mallory unilite dist)....jmo (never hurts to try) :yes:
 

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Discussion Starter #14
Saturday before the cruise

Ill check it out, shoulda just brought my light home with me


thanx man
Steve
 

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36 total is probably just fine, but it will probably wake up with more initial timing, so you're going to have to limit the total advance.
With only 9.8-1 compression I probably wouldn't even run 91 octane fuel--89 is about all I'd use. I run 91 in my 410" that has just under 12-1. If the engine doesn't need the octane, you're just wasting money and losing power.
 

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Your cranking compression will give some clues as to what octane it might like. With the throttle blades open and the spark disconnected do a compression check and see what she's pumping. If you're using octane higher than needed then that will also screw with what spark advance it seems to need- higher octane needs more advance. I learned this the hard way many years ago when running AV gas in an engine that didn't need the higher octane-that motor needed 52degrees of total timing to run right with the aviation fuel (105 back then) and it made less power than pump gas.

If you're at 8 on initial and 36 total I'm sure you'll need to limit the mechanical advance so you can dial in more initial for optimum results. My guess would be that it'll like somewhere around 12-14 initial and 22-26 mechanical but you'll need to burn all that fuel out and fill her up with straight pump gas to work on it now otherwise you're just chasing your tail. If I'm not mistaken the ZZ4 engines burn fairly efficient and usually like around 35 total. This is where a quality aftermarket distributor with an adjustable advance curve shines-way easier than modifying an HEI.
 
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