Tri power / timing questions - Pontiac GTO Forum
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post #1 of 36 (permalink) Old 08-07-2017, 01:06 PM Thread Starter
 
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Tri power / timing questions

Hello all. I will start with saying that this is my first post. I have been reading much here and have found answers to some of my questions. There are many knowledgeable and helpful folks here.

So now my questions. First, do the harmonic balancers on these Pontiac spin ? To further detail my question, I have a 65 389 with the thin balancer. Do they have the rubber ring like the chevy? I know that the Chevy balancers have been known to spin and for that reason some just power time the engine rather than use a timing light.

And my next question. I recently installed a tri power setup and I am having a hard time getting the engine idle speed low enough to use my vacuum advance. I can only get the rpms down to 800 range with vacuum advance Un hooked but plugged.. If I hook the vacuum line up to the vacuum advance it speeds the engine rpms to nearly 1000 and I have no further way to lower the rpms ( idle screw backed out as far as possible and butterflies closed to max allowable)

The only way I can get rpms any lower is to retard timing to a undesirable setting ( below 6 initial) or I can lean my idle screws but then I get a lean idle ( starts to get a lean miss at idle) .

I've talked to the carb builder many times and he recommended that I run the car with out using the vacuum advance. He claims that I simply will not get my idle rpms low enough with the vacuum advance pulling.

Anyone else have similar experience? ?? Thanks in advance.
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post #2 of 36 (permalink) Old 08-07-2017, 09:26 PM
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Yes, Pontiac balancers are 2-piece and if you have any suspicion that the ring might have slipped, replace it. You don't want to take a chance on that outer ring coming completely off at rpm and dancing around in your engine compartment. It can do a ton of damage as you might suspect.

Tripowers can be difficult. Getting the throttle plates to align and seal can be a challenge. If there's any air at all leaking past the plates on your end carbs when they're supposed to be shut that will make everything off, and hard to manage. You might want to consider shipping it off to a shop that specializes in rebuilding them to make sure it's "right".
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post #3 of 36 (permalink) Old 08-08-2017, 06:23 AM
 
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Great points by bear on that carb.....on your timing, and vac advance as you add advance your idle will increase as you have found.

But the most likely problem you have is the Vac advance is pulling in wayyyy to much timing as they usually all do...When I pull those cans and test them on my distributor machine they often have 20 or 30 degrees of timing advance....way too much. Even the lowest pulling points Dist can pulls 16 degrees, still too much.....

You can read the can and look up the specs, or test it with your timing light hooked up and disconnected and you will see how much timing it pulls at idle....if it is more than 10 or 12 it is too much.

If you are running a points Dist, get a B26 Vac Can ......rock auto...SMP VC 181...NAPA calls it a VC 1808....

Then email [email protected] and get one his Vacumn correctors and knock that vac back to 10* and hook to full manifold Vacumn

If you are running HEI it is different.....But I gave you the points stuff because that is what the car came with and the tri power have little room for the big discs.

If you have already done this, than you need to work on the carb like Bear said , if not do this first then go to the carb....

Good Luck...You will get it!
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post #4 of 36 (permalink) Old 08-08-2017, 04:36 PM Thread Starter
 
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Thanks for the replies.
The reason I asked about the balancer was so I would know if I was getting my timing accurate with the light. After posting this I do believe that the balancer has Not spun. I set the timing at 0 with the light and I could hear some "woofs" out the exhaust indicating retarded timing, so I now believe the light.

And with the carbs, they are freshly rebuilt. I checked everything for vacuum leaks with wd40, no leaks. My next step was to remove and block off the secondary carbs and run the car on just the center carb. I still couldn't get the idle low enough for the vacuum advance. I spoke to the carb builder and he claims that I won't because the gasoline of today as compared with the gasoline back in 65. It does run pretty good but if I use my vacuum advance it idles to high for my liking.
I have a new pertronix distributor with the latest version number 3 ignition. It does pull a ton of advance at idle. I will have to check how much. I believe that it was about 12 to 14 on top of my initial 6 or 8 to bring it to around 20 at idle.

Maybe to much advance at idle???
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post #5 of 36 (permalink) Old 08-08-2017, 04:43 PM
 
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20 at idle is perfect as long as it is 10 from vac and 10 from base.........close to that is what you want for smooth driving

26 more inside distributor..would make it 36...perfect
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post #6 of 36 (permalink) Old 08-08-2017, 05:26 PM Thread Starter
 
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I will keep at it. I will get it one way or another.
I did run it with the new tri power setup on the road. I ran it without the vacuum advance. Just plugged the hose. I have to say it didn't run bad.
That tri power sounds awesome, but it does bother me that I can't get it with the vacuum advance.
What's your thoughts about running it without vacuum advance? ??
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post #7 of 36 (permalink) Old 08-08-2017, 06:15 PM
 
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Originally Posted by My65goat View Post
I will keep at it. I will get it one way or another.
I did run it with the new tri power setup on the road. I ran it without the vacuum advance. Just plugged the hose. I have to say it didn't run bad.
That tri power sounds awesome, but it does bother me that I can't get it with the vacuum advance.
What's your thoughts about running it without vacuum advance? ??

You can run an engine without vacuum advance - many early factory HP cars typically had the dual points without vacuum advance and racers run their cars without vacuum advance.

I ran a 409CI with the factory Mallory dual point distributor and no vacuum advance -no issues. The key is to get the initial timing and advance curve set-up correctly for your engine application and this can mean a little trial and error work for you or taking it to a shop/guy with a distributor machine who can dial it in for you. Your gas mileage will drop a lot and your engine may run hot.

As BearGFR puts it, "The purpose of the vacuum advance is to add ADDITIONAL advance under light throttle, light load conditions only. This helps with both fuel economy and with engine cooling. For power, it is never a factor."
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post #8 of 36 (permalink) Old 08-09-2017, 07:17 AM
 
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wAll said is correct a as Vacumn advance hooked up and set correctly has no detrimental effect on full power or throttle down operations....

But that said, it has many advantages at light throttle and idle and overall response of the car in street driving as the advanced spark fires the light mixture early for strong power with barely touching the throttle,...responsiveness...

As an example,....take two cars, say with trans with no overdrive, 65 mph at 2800 RPM?..

The car with no vac advance under light throttle,..at cruise of 65 mph has 36 degrees of timing advance....it's top limit...

The car with vac advance under light throttle...at cruise of 65 has 46 degrees of timing advance.....it's top limit.....

If they both hammer down to increase speed..
....
..they both then have 36 degrees of timing advance.......you lose nothing for power but gain an increase to fire the lean mixtures at idle and light throttle......this make's your pedal very responsive..

Also, both of those cars at that 65 cruise have different throttle down applied angles, the car without vac will have to have the pedal down more.....because it needs more fuel to get the same speed......with 46 degrees of advance the lean mixture fires sooner and the applied throttle is very light.....less gas runs cooler with more advance, because it it more efficient.

My AFR meter, two widebands in each exhaust will show 14.3 to 14.7 AFR at that light throttle, on a carb.....14.7 is a complete burn of every gas molecule,..a perfect burn, all modern computers cars constantly change the fuel injectors and air flow to get that 14.7. they do it for emissions.....

Power comes at the 11.5 to 12.5 say AFR as you pedal down, a car with no vac advance would have a richer burn at cruise,...like 12.8 or 13 depends on the car.....or lower.

What happens when you set-up with no vac advance your timing is limited to 36 or 38... if you go higher you ping and knock,..

Vac advance let's you go with more timing, but none of the negatives effects. It also add idle cooling if hooked to full manifold vac...

It can be done many ways, racers have their purposes and know their cars,...some don't like it because they never had it set up right,...they had a vac can with too much advance so they declared them all bad...

My friends say "my car is running great", but when we pull the Dist it will have 65 degrees of advance from Base, cent and vac...so that is not possible,...it is just what they thought was great...

I am a Believer in Vac advance when set up correctly,....it loses you nothing and gains you more timing advance, more efficiently, better gas mileage, more responsive throttle, better engine cooling even at idle.....why would you give that up?

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post #9 of 36 (permalink) Old 08-09-2017, 04:06 PM Thread Starter
 
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Great information. Yes, I do want to use the vacuum advance but just can't get the engine rims low enough. I'm getting pretty frustrated. ..
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post #10 of 36 (permalink) Old 08-09-2017, 06:56 PM
 
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Check your throttle springs are they new and strong enough to pull throttle plates back to full close on end carbs?

Can you seal off end carbs and set base at 20 vac disconnected and plugged to engine?

Will it idle then at 750?
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