viperjesse

I'm running a Holley 650 double pump mechanical secondary carb.
Which vacuum port do I use for the vacuum advance? There are 2 on the passenger side, 1 high and 1 low. I have it on the low one and I'm having a lot of difficulty getting my engine to start and run.
It's a new and built engine so I'm still trying to set everything. The Carb Dr. says to use the top port for vacuum advance.
This is the port that gives no vacuum at idle and full vacuum during midrange. The bottom port gives vacuum at idle and none during acceleration.
Could this be screwing up my startup?

I have perfect TDC by using a manometer and all my wires are correct but I still get puffing and small fires in my new carb when trying to start.
Any help is greatly appreciated.
Thanks
JZ

P.S. I'm Running Comp Extreme cam 294/306 duration 519/523 lift, 2.08 Iron Eagle heads, Air Gap intake and have 10:1 compression.

lars

With a cam like that and a stock setup Holley, you have a little tuning to do to get your combo to work right.

First, you need to get your mechanical timing set up for 36 degrees total advance. With 36 total, your cam combo is going to need about 16-18 degree initial timing. Once you have the timing spread set up and the total advance dialed in to slam in fully by 2500 rpm, you can play a little with the vacuum advance.

There is no set rule on whether to use ported vacuum or manifold vacuum: you use the one that provides best quality idle for your specific engine combination. Best quality idle is not necessarily fastest idle: you're looking for the smoothest and best idle quality. This may be ported or manifold on any given engine. Most performance engines will respond best with manifold vacuum, but there are exceptions. Use the two ports as tuning tools and take it from there. If you need more info on the subject, drop me an e-mail and I'll send you a detailed paper on vacuum advance control.

The vacuum advance will not affect ease of engine starting or your backfire problems. The mechanical timing, as initially described, will.

Once you have your mechanical total timing, timing advance, intial timing and the vacuum advance figured out, make sure you balance out the primary and secondary throttle blade angles on that Holley: they're never set up right from the factory, and this has a big effect on idle quality, throttle response, and off-idle performance. Again, if you need specific instructions, drop me an e-mail for a how-to paper.

cw823

Top port, passenger side.

lars

Top port passenger side is ported vacuum. This may not produce the best quality idle for your 294 cam. However, if you choose to use manifold vacuum (any port other than the top port passenger side) make sure your vacuum advance control unit is one that will pull in its full advance range at the vacuum reading you get at idle. If not, change it out with one that will.

viperjesse

Thanks Guys. LARS you da man!
My theory/thinking was if I have my vac adv on a port that creates vac at idle, I'm pulling the advance curve in at idle and I'm not getting it on acceleration as needed. It makes sense to connect to a port with no vac at idle to preserve my base timing, then allow the vac to advance as needed thru acceleration??

As is, when it was running it ran and started best when my base timing showed 30deg. I had a Holley 750 on it and it would die below 2000 so I bought the 650. I had it idling the other evening at 800-900 rpm.
Could any of this situation be coming from my new carb? Like float adjustment?
Again, Thanks guys.
JZ

lars

Vac advance does not operate during acceleration (vacuum advance is fully retarded during acceleration regardless of the port used), so it does not matter if you have it hooked to ported or manifold. The vacuum port selection only effects operation at idle. Use the port that produces best quality idle. This does not effect cruise or acceleration modes at all.

If you have 30 degrees initial timing, you are grossly over-advanced. Check your total timing and set it to 36. Initial timing (without vacuum advance hooked up) should be no more than about 18 with the maximum total mechanical advance at 36. If you're running 30 base (initial) timing, you probably have about 45 total, and this is way too much to make any power at WOT.

Float adjustment has minimal effect. You need to balance your throttle blade angles in order to get the idle set up right.

stingr69

JZ,

The vacuum advance does nothing while starting the car so that is not the issue. The hose can be hooked up to either connection but for starters, I would hook it up to the upper "ported" connection until you get the rest sorted out. It is more goof-proof there.

As Lars stated, it is important to get the ignition curve right first and then go from there. Any new carb should have the float setting verified when installed. I have seen threads where people expect that the carb will not need any adjustments out of the box and I would dissagree. You need to set the floats and the idle mixture screws and idle speed screws at the minimum. The jets and power valves can come later but the basics are not optional in my opinion. The car will start and run if these are in the ballpark. Mixture screws at about 1.5 turns out from lightly seated. The floats on the 650 DP need to have a slight trickle coming out from the float bowl sight hole with the engine idling and the idle speed screw needs to be cracked so that the transfer slot on the baseplate is partialy exposed. If the slot looks like a square, you are close enough to run.

Be sure to verify the firing order and the ignition timing while cranking. Have a friend crank the engine while you observe the timing light. If the indicator is close to the top of the tab, it should fire. She should be growling and snarling in no time.

-Mark.

6T5RUSH

viperjesse,

Sorry to steal your thread but I am interested in how to balance out the primary and secondary throttle blade angles. Is this something I can do with the carb already mounted on the motor? Background: the carb was totally rebuilt and all pieces machined/checked for flatness (no warping). All bushings replaced and the carb was assembled after replating then test run on a mule motor. I just picked up on your comment regarding the blade angles and need to know if there is an easy check on these.

Thanks in advance for your insight on this and thanks again to you viperjesse for starting this thread.

Regards,

Jim

lars

Jim -
The setup and balancing of the throttle blade angles is something that needs to be done on Holleys and BGs. For a complete description on this, drop me an e-mail and I'll send you a copy of the setup paper that describes this process in detail:
V8FastCars@msn.com

viperjesse

Jim, the more the merrier.
I'm gonna try Lars procedure tonight with the timing, I'll check my float levels first.
I have a buddy here at work who's been racing and building for 20 years now. He will be coming by to give me a hand setting this engine up.
From what I've seen of it running so far it's going to be quite a beast.
Thanks guys I'll let you know how it turns out.
JZ

viperjesse

After another unsuccessful attempt to start this engine I inspected the distributor. It's a new Mallory HEI.
The engine tries to start but seems like it doesn't have enough spark to ignite. It cranks and fires spuraticly (sp).
The distributor housing moves within the block opening approx 1/8" like the diameter is too small. I checked the rotor. It rocks front to back approx 3/32" and the mechanism under the rotor also is very sloppy. I'm not talking about the advance movement. It seems like the shaft fit inside the hsg is very loose. Also the brass contact on the rotor is bent slightly CCW. This means that it hit while spinning. I found no damage to the cap contacts, just discoloration.

COULD this be the culprit? How much slop is acceptable in a distributor? I always thought you couldn't have any.
Thanks guys
JZ

viperjesse

ttt

bobs77vet

not sure i fully understand you ... if you are talking about movement under the bracket that is on the intake manifold this is a real problem.... i'm not sure how it would affect starting.... but it probably would create some wobble factor to throw off timing... i think the bigger issue with this is that it may reduce oil flow to the upper half of the engine... i'm not sure where the wobble is but you need a tight fit or an oil galley will not be sealed reducing flow to the upper half...you need to figure this out before you crank the engine any more to make sure the oil galley is properly sealed....