Timing Question

[Chaparralman1974]

Morning everyone!

I am trying to dial in my timing and wanted to get some feedback from the experts. :-)

My motor is a 327 with a mild Isky R/V cam, stock quadrajet, and the stock dizzy but with a Pertronix module and coil installed. The plugs and wires are stock for a regular dizzy (7.5 mm wires if I remember) and the plugs are gapped to .040" on the recommendation of the guy that redid my dizzy. The truck is a manual transmission as well.

Right now, I have the timing set to 10* BTDC. It runs, but it does stumble a little bit and the exhaust smells like unburned fuel. The initial start when cold seems to always fire right up, but sometimes (not always) after it has been running, it will want to crank a little longer before catching.

I have not yet adjusted the mixture screws. I have a vacuum gauge, but I was under the impression that I needed to get the timing and idle all set first before adjusting the idle mixture.

Given my setup with a manual tranny, what is the ideal idle speed, and where should I set my initial timing? I read somewhere that "327's like a lot of timing"....I don't know if that is true or not, but it seems like it could run a lot better than it is now.


Thanks, Clay

[67C10Step]

I would say you need to be at least 12-14 on the initial timing with the vacuum advance blocked. At 3000-3200 rpm the full advance should be 34-38 degrees or so.

My little, stock 283 seems happy at about 13 degrees initial and 35 all in. Mine is manual and the idle is 750-800 rpm.

[sixty8HDC30]

How many miles on it? The timing chain can stretch over time causing the recommended timing to not work the best, it can also cause inconsistent timing. You can also try timing it by ear for best performance. There are several how to time by ear videos on youtube specifically for the small block chevy.

I'm not an expert but I hope this helps.

[Chaparralman1974]

Originally Posted by sixty8HDC30

How many miles on it? The timing chain can stretch over time causing the recommended timing to not work the best, it can also cause inconsistent timing. You can also try timing it by ear for best performance. There are several how to time by ear videos on youtube specifically for the small block chevy.

I'm not an expert but I hope this helps.

The motor is essentially brand new. The entire truck is in the middle of a frame off restoration. I have finally gotten it to the point where it is running and moving. I am trying to now tune it properly.


Thanks, Clay

[Chaparralman1974]

Originally Posted by 67C10Step

I would say you need to be at least 12-14 on the initial timing with the vacuum advance blocked. At 3000-3200 rpm the full advance should be 34-38 degrees or so.

My little, stock 283 seems happy at about 13 degrees initial and 35 all in. Mine is manual and the idle is 750-800 rpm.

Thanks much! That gives me a good place to start. I will start at 12* at 800 RPM and see what that does.

Clay

[kaycee]

My warm 327 loves it at 16* gaped the plugs at 40 and set the idle/air mixture and got rid of the rich smell.

[Chaparralman1974]

Ok, I set my timing at 15* and it seems to be a little smoother. I am also trying to figure out the idle mixture screws. I got a vacuum gauge from Harbor Freight, but it bounces all over the place and I can't really tell what is going on. It doesn't seem to make a big difference when I turn in the mixture screws.

I turned the screws all the way in, then backed them out 3 full turns. I tried to turn them in 1/4 turn at a time (started with the driver side screw first) while looking at the vacuum gauge, but it really didn't seem to do much. I have my idle set at about 800RPM now. I am using an Innova timing light that I got at O'reilly's but I am not sure I trust it....the idle is all over the place. I am going to exchange it and see if that helps any.


Clay

[geezer#99]

Turn your idle down to 600 rpm.
See what that does for you.

[1970cstblazer]

Ensure the Q-Jet's throttle shafts are not leaking air. You will never get a really good idle with a vacuum leak.

[Steeveedee]

Needle bouncing all over the place indicates leaky valve guides.

[Willshook]

Timing curve for the GEN I SBC is very, very well-established. Unless the engine is pretty hot, the standard curve applies.

Yes, always establish the timing curve before moving on to other adjustments.

15 BTDC is a lot of initial advance for a mild engine.

https://outintheshop.com/faq/Lars%20timing%20.pdf

Q-jets are often FUBARd from unskilled hands at some point or simply wear.

[Classics Fan]

Originally Posted by 1970cstblazer

Ensure the Q-Jet's throttle shafts are not leaking air. You will never get a really good idle with a vacuum leak.

x2. My 350 had a stumble that I could not tune out. After rebuilding the original Qjet with a kit I got from Cliff Ruggles that included a throttle shaft bushing kit it runs like brand new. The fact the idle air mixture screws don’t have much if any affect is also an indication of worn throttle shafts that are allowing unregulated air into the carb idle circuit.

[geezer#99]

Originally Posted by Willshook

15 BTDC is a lot of initial advance for a mild engine.

Sure, 15 might be a bit much. Barely.
But at 800 rpm some of that might be coming from mechanical timing kicking in.
That’s why I suggest idle nearer 600 rpm.

[Chaparralman1974]

Well, as an update....

My timing light died on me...I bought one of those fancy Innova deals that does the tach and advance, and all that other crap.....it died within 5 minutes of using it. I just ordered a cheap one that will hopefully be here tomorrow.

Also, my vacuum gauge is garbage....I never paid attention to the fact that it wasn't even zeroed. There is no way to calibrate it either. Unfortunately, I didn't pay attention to the harbor freight reviews, so lesson learned there.

I have since ordered a new timing light and a Lisle vacuum gauge (I have always had decent luck with Lisle tools).

I misspoke in an earlier post about the vacuum gauge bouncing....It really wasn't bouncing, but going from one number to the next and just hanging there. I don't trust the gauge at all, so I need to ensure that I have good tools before doing anything else.

My motor is all new and the machine and head work were done by a competent shop, so I am really hoping that what I am dealing with here is just bad tools and improper adjustment. Additionally, I had the dizzy and the carburetor completely rebuilt / restored by a competent guy out here who does nothing but these things. He is an old timer (probably 80 years old) that has been in business for over 50 years here in peoria. So, I am confident that those were done right.

Once I get the new timing light and vacuum gauge, I will give these suggestions a try and report back.

Clay

[geezer#99]

A side thought on your motor.
Was a proper break in done on it?
Did it get the normal 20 minute 2000 rpm operation?

[Chaparralman1974]

Yeah, I made sure to do the proper cam break in.

Clay

Originally Posted by geezer#99

A side thought on your motor.
Was a proper break in done on it?
Did it get the normal 20 minute 2000 rpm operation?

[70STOVEBOLT]

Set it for 12 degrees and then advance it in small increments until the engine starts to detonate under a load, then back it off slightly. Also, connect the vac hose from the distributor to manifold vacuum, which is any vac port on the carb that is below the throttle plates, or you can connect it directly to the intake manifold. Always set timing with the distributor vac hose disconnected from the carb and plug the port on the carb (or intake manifold) where it was connected. 600 rpm should be good for the idle unless you have a pretty big cam, then you may need to set it a little higher. If you want to know your total timing without having to get an expensive, dial-back light, you can use a timing tape on the damper.

[Rust_never_sleeps]

This guy started selling his own timing lights. Not always in stock, but for $40 pretty sweet
https://carburetedinnovations.com/pr...k-timing-light

thunderhead289 on YouTube. He's got some good videos on timing and carb tuning, but mostly a Ford guy

[71CHEVYSHORTBED402]

Elevation apparently matters. I have 1967 HP 396 heads on a 402 block, Delco HEI and plugs gapped .045. Rebuilt Rochester 4B, new vacuum hose, A/C☺. 4800’ elevation; and it's set at 14. Think I read 14 is the recommended max for this elevation, and it's never run better.

I didn't dial in the carb., two old timers did, along with the timing. One of these days I'd like working experience to dial in a carb, with vacuum gauge, seems that's the best or one method? along with the usual steps like presets. I also need working experience for maintaining the original choke. Both guys I knew no longer tune carbs, dying, and bad health will do that. Same these tasks are ancient

Originally Posted by Rust_never_sleeps

This guy started selling his own timing lights. Not always in stock, but for $40 pretty sweet
https://carburetedinnovations.com/pr...k-timing-light

thunderhead289 on YouTube. He's got some good videos on timing and carb tuning, but mostly a Ford guy

Very cool. I can't listen to him though Fix Or Replace Daily

Originally Posted by 70STOVEBOLT

Set it for 12 degrees and then advance it in small increments until the engine starts to detonate under a load, then back it off slightly. Also, connect the vac hose from the distributor to manifold vacuum, which is any vac port on the carb that is below the throttle plates, or you can connect it directly to the intake manifold. Always set timing with the distributor vac hose disconnected from the carb and plug the port on the carb (or intake manifold) where it was connected. 600 rpm should be good for the idle unless you have a pretty big cam, then you may need to set it a little higher. If you want to know your total timing without having to get an expensive, dial-back light, you can use a timing tape on the damper.

Man, I need to link this thread. Thanks

[Chaparralman1974]

Ok, just an update....

I have been fiddling around with the motor and it seems to want A LOT of advance. Right now, I have the initial advance (no vacuum advance hooked up) set at 18* BTDC. Just for giggles, I hooked it up to manifold vacuum vs. ported vacuum and it smoothed out big time. But, at idle when I put the timing light on it, it was showing around 30* advanced. Again the truck was running super smooth at this point. I turned it of and on a few times and there was no kick back when I restarted the motor.

Also, I got my new vacuum gauge and I am pulling 15" on the gauge. I was under the impression that I had to have 20". I tried to fiddle with the mixture screws, but it wouldn't go any higher.....it would drop and the motor would stumble when I screwed them in too far and then I would back them out again and it would level out at 15". I do have an Isky Supercam 262 (RV Cam). I don't have all the specs on it.....The cam was brand new when I bought the block and heads and I decided to use it versus the stock cam that cam with the rebuild kit. Will an RV Cam cause these kinds of issues with timing? It seems to be way too high as far as advance is concerned, but it is also running fairly smooth.


Thanks, Clay

[geezer#99]

What’s your idle rpm when at 18 initial?

While at idle can you slowly turn in either mix screw all the way in and it doesn’t die?

[Chaparralman1974]

I have the idle set at 600RPM. I didn't turn the mixture screw (one at a time) all the way in, but close.....it was stumbling when I did that like it wanted to die. I can try that and see what it does.


Clay

Originally Posted by geezer#99

What’s your idle rpm when at 18 initial?

While at idle can you slowly turn in either mix screw all the way in and it doesn’t die?

[Chaparralman1974]

Just as a recap..

The motor is new. I did the build myself, so it is entirely possible that I screwed something up....:-) I am an IT guy and not an engine builder. I did have the heads rebuilt by a competent builder in town.

I have a new balancer on the motor and a timing cover with marks. I went ahead and ordered a piston stop so that I can 100% confirm that everything lines up as it should.

My Cam is an Isky Supercam. I don't recall the exact specs, but when I was building the motor, I called Isky and gave them the part number on it and the guy told me that it wasn't a radical cam or anything. I told him the application it was going in and he just stated that it was a mild RV cam not that far off from stock. I installed it using the stock timing gears and chain that came with the kit.

The carb and distributor have been completely redone....the distributor was recurved on a Sun machine, and it has a Pertronix ignition system with the 40,000 volt coil. I have set my plug gap at .040"

I revved the motor up to about 3000 RPM's and stuck the timing light on it and the total timing was about 32* or so.....I couldn't get it to go any higher.

I can't hear any pinging or knocking....my hearing is total toast though...... I was a Mortarman in the Marines.....used cigarette buts for ear plugs....bad idea....you get the picture. :-) But it sure does sound smooth when it is running. I am not at the point in the restoration where I can drive it down the road at high speeds, so I can't test under load at the moment.....all this is being done with the truck in the garage.


Clay

[geezer#99]

Good idea on the piston stop.
Your cam is very mild. Rated at 215 degrees and .435 lift.

Do you have the timing specs on your recurved distributor?

[Chaparralman1974]

Here is a picture of the Isky cam that I have.