timing degrees

[frankyjoet]

Have an RV cam, what tdc degrees should be set. i have it now at 10 tdc. it pops thru the exhaust. I have had this exhaust setup since 1998. 73 gmc 3/4 ton 350 sb 4.0 headers edlebrk carb and manifold manual shift on floor (old granny trans). i adjusted the jets to more rich. I don't drive truck, just start it up in the driveway. Still restoring. Thanks in advance for any help. frankyjoet

[rich weyand]

More rich is probably wrong. Edelbrock carbs are rich as stink out of the box for sbcs.

Base timing will depend on your distributor settings. Is it the stock distributor? That would give you +20* mechanical advance at rpm. Sweet spot for base timing + mechanical advance is 36* BTDC, so subtract your mechanical advance to get best base timing.

A couple posts you might want to read:
http://67-72chevytrucks.com/vboard/s...d.php?t=689321
http://www.fullsizechevy.com/forum/g...ml#post5758323

[frankyjoet]

Thanks Rich that's a lot to read. i have an aftermarket HEI dist. My timing tag doesn't go above 16*. i am going to set it at 16* and get back to you. thanks frankyjoet 73 gmc man trans. How do i hook up the rpm tester. thanks for any help.

[MikeB]

Originally Posted by frankyjoet

i am going to set it at 16* and get back to you. .

Be sure to do that at idle with the vacuum advance line plugged. Then when you rev the engine you should see the timing advance way past 16 degrees.

I'd say go back to stock jets, rods, and springs, which will at least get you in the ballpark. Then adjust idle mixture for max vacuum at idle.

Also, how much manifold vacuum do you have at idle? With a generic RV cam, I'd expect to see 18 inches or more. And when you reconnect the vacuum advance line after setting timing, do you see the timing advance?

[rich weyand]

WHICH aftermarket HEI distributor? It matters.

[frankyjoet]

rich i have a High Performance super 65k volt for gen 1 engines. bought on Ebay from skip white performance parts in Kingsport, Tennesee. i don't have vaccum gauge tester. i need help using the RPM tester. this distrib has a life time warranty. thanks for any help
frankyjoet

[rich weyand]

That has an adjustable advance can. How did you adjust it?

[cadillac_al]

Is this a new cam? What changed to make the exhaust pop? Crossed plug wires will make it pop.

[frankyjoet]

i don't know about the advanced can. where is it located. yes the cam is a new RV. the wires are ok. fairly new. it pops once on startup, but when engine gets warm it doesn't pop. i hope this helps. frankyjoet

[rich weyand]

The vacuum canister is on the side of the distributor, toward the front. Engine vacuum sucks on the canister and pulls the ignition timing advanced. When the throttle is opened, the vacuum disappears, and the timing goes back to its base setting.

It is important that the vacuum can have the right tension on the spring, which sets how much vacuum it takes to overcome the spring and pull the ignition advanced, and how far advanced it pulls, which is set by a stroke adjustment on the canister pull lever.

You bought a "performance" distributor, which means it is probably set up all wrong for an engine that pulls as much vacuum as a normal or RV cam will pull. Which means that you are probably running in vacuum advance all the time.

I am hoping that the Skip White distributor accepts a standard HEI distributor vacuum can. (Anyone on here know?) If it does, replace the adjustable can, which you don't need, with an AR23/VC1853 advance canister, which is locked in to the values you need for that engine.

[frankyjoet]

Rich , i contacted Skip white co. and the tech said "the distributor vacuum should be disconnected, plugged and plug at carburetor. In other words he said you don't need it. An another alternative is change tension springs that came with it. I also have to add a timing tape on the h-balancer. i think this h-performance damper has numbers stamped on it. Timing should be at 34* btdc. i am going to try this and get back to you. thanks again frankyjoet

[rich weyand]

OK, so they don't know what they are talking about. No vacuum advance is fine for a race car, sucks for a street car. You will suffer huge performance losses at low and mid throttle settings, because the spark will be retarded from where it should be. Maybe all that guy knows is race cars. They never use vacuum advance, at least not the circle-trackers I know.

TOTAL timing should be 34-36* BTDC. That is, at 3000 rpm, the timing should be 34-36* BTDC. At idle, with the vacuum advance disconnected, it should be more like 14-16* BTDC.

Just put on the AR23 vacuum advance can. You can thank me later.

[MikeB]

Originally Posted by frankyjoet

Rich , i contacted Skip white co. and the tech said "the distributor vacuum should be disconnected, plugged and plug at carburetor. In other words he said you don't need it.

I second what Rich said. The guy's a moron.

Skip White parts are the cheapest of cheap Chinese crap, and his customer support guys are worthless. There's a reason his distributors cost $49 instead of $150-$300.

I bought a power steering pump bracket from them that didn't come close to fitting properly, and wouldn't work with a 2-groove pulley. Their standard answer: "We've sold over 800 of those and you're the first person to have a problem."

Ended up buying one that cost twice as much from Alan Grove Components. It fit perfectly and worked with a 2-groove pulley. Trying to save money will cost you time and money every time!

[TrybalRage]

I bought one of those Skip White distributors, to replace my ESC unit when it started freaking out on me. Did the bypass for a while but finally just decided to swap out the whole thing.

It runs pretty well on my otherwise stock engine (full emissions in place with exception of faulty air temp sensor). I have the adjustable vacuum advance hooked up, and since changing out the dizzy I have seen a ridiculous improvement in gas mileage.

One thing I had to do was run it on ported vacuum instead of manifold. I tried both, but the manifold source had a very noticeable dip in power just off-idle that I don't have with ported. Perhaps it might be better with the 'correct' vacuum advance on manifold, but for now it's running really well.

I do need to get a proper timing tape for the balancer and a better timing light to see if I can really dial it in.

[frankyjoet]

rich checked classic industries for part, they have a cross referenced part dv1853 which fits 76-78 v8 5.7l. will that work? i am going to plug at dist. and plug at carb. My ports on the edlebrock 1406 are side by side. i had the advance hooked up to the closest port the left side. i am not sure which side is port and manifold. i remember port on the ship as left side. vet of 8 yrs NAVY. 1955-1963 hope this helps. will get back to you after i tried to bypass and reset timing to 16* btdc. hope this helps frankyjoe

[rich weyand]

Not sure about that advance canister because they don't say anything about the operating specs. This one I know is right.
http://www.napaonline.com/Catalog/Ca...853_0168354142

It should be connected to the vacuum port on the driver's side front of the Edelbrock. (Note, when denoting left and right on the vehicle, it should be while facing forward. You say you have it on the "closest port, the left side". That's looking aft on the truck right? Navy parlance, it should be on the port side port.)

[Jake Wade]

Here is a nice distributor when the time comes:

http://www.summitracing.com/parts/NAL-93440806/

[cadillac_al]

Originally Posted by Jake Wade

Here is a nice distributor when the time comes:

http://www.summitracing.com/parts/NAL-93440806/

Even that expensive distributor has a bad review. You can get a dud now and again with anything. It's hard to figure out what is going on with the OP's truck because it doesn't leave the yard. Vacuum advance shouldn't be too critical just starting a vehicle in the yard. I'll bet it will come out of it once you start driving it.

[rich weyand]

If he has somebody's idea of a "performance" distributor, it may kick in the advance at as little as 7" of vacuum, in which case he will never get out of advance with an engine that will pull 18 to 20 inches at idle.

He needs the right vacuum advance can for a 350 with an RV cam.

Or he can use one of those fully adjustable ones, in which case he has to fully adjust it, which can be painful. Easier just to put on the right can.

[rich weyand]

Here is a thread on another forum, where the vacuum canister turned out to be the culprit. Same sort of scenario.

http://www.gm***************/forum/s...ad.php?t=14572

[frankyjoet]

rich, the edlebrock i have looking from front of the engine aft, 3 ports 1 on left with vacuum hose and 1 on right plugged and the other in the MIDDLE to pcv and channeled off with Y connector to the emissions cannister. On the rear of carburetor the center port is plugged. The vacuum advance at Classic Ind is set and non-adjustable. i will try the plug method, reset timing. hope this helps. frankyjoe

[frankyjoet]

rich the thread you posted doesn't open, get web page not available frankyjoe

[Jake Wade]

Originally Posted by cadillac_al

Even that expensive distributor has a bad review.

Its a quality distributor with 1 bad review, module most likely. Like you said, you can get a dud ever now and then. I will take it over a Skip whiter any day.

I agree that the OP needs to take it out and run it to clean the plugs up.

[rich weyand]

Originally Posted by frankyjoet

rich, the edlebrock i have looking from front of the engine aft, 3 ports 1 on left with vacuum hose and 1 on right plugged and the other in the MIDDLE to pcv and channeled off with Y connector to the emissions cannister. On the rear of carburetor the center port is plugged. The vacuum advance at Classic Ind is set and non-adjustable. i will try the plug method, reset timing. hope this helps. frankyjoe

When you say the one on the left, is that PORTSIDE (left facing forward)(a.k.a. the drivers side), or left facing AFT, i.e. STARBOARD?

Plugging everything and running without vacuum advance is no better than running with the wrong vacuum advance. Studebaker introduced vacuum advance in 1938, and it was put on all GM vehicles beginning in 1939. Why you would want to plug it off beats hell out of me.

[rich weyand]

Originally Posted by frankyjoet

rich the thread you posted doesn't open, get web page not available frankyjoe

That's because TPTB don't like me pointing to another forum.

Try this:
https://www.google.com/?gws_rd=ssl#q...tion+timing%22