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340 Six Pack vacuum advance

Posted By: Aar1064

340 Six Pack vacuum advance - 02/20/18 04:07 PM

I'm working on some issues with carbs and timing and was wondering these things:

1. What is a good baseline for hg measurement for the distributor vacuum advance hose out of the center carb?
2. Is there any adjustment on the vacuum canister for a stock dual point distributor?

When hose is plugged into the distributor car will not idle correctly because it's advancing. If I unplug hose, engine will die. Seems to run better when hose is off and plugged.

Distributor has been gone thru and setup by Jeff at Advanced Distributors so I'm pretty confident it's in order.

I'd really like to use vacuum advance as it's intended but it's not a deal breaker and I was thinking I could just make it non operational but it makes me wonder if something else is going on that's causing the high vacuum.

Thanks for the help.............
Posted By: Cab_Burge

Re: 340 Six Pack vacuum advance - 02/20/18 07:45 PM

It sounds like you have the vacuum advance hook into manifold vacuum port instead of above the throttle plates for ported vacuum like they came stock scope
Which carb numbers are you using, OEM Holley or after market carbs like the BG six shooters or ?
Posted By: RapidRobert

Re: 340 Six Pack vacuum advance - 02/20/18 08:55 PM

we need all related specs; initial timing. in hg vacuum. ported or manifold. how much timing when you plug the hose in. Rotor phasing OK?
Posted By: Aar1064

Re: 340 Six Pack vacuum advance - 02/20/18 11:07 PM

Originally Posted By Cab_Burge
It sounds like you have the vacuum advance hook into manifold vacuum port instead of above the throttle plates for ported vacuum like they came stock scope
Which carb numbers are you using, OEM Holley or after market carbs like the BG six shooters or ?


OEM original Holley carbs restored by Scott. It's plugged into the ported one on center carb.
Posted By: Aar1064

Re: 340 Six Pack vacuum advance - 02/20/18 11:24 PM

Originally Posted By RapidRobert
we need all related specs; initial timing. in hg vacuum. ported or manifold. how much timing when you plug the hose in. Rotor phasing OK?


I need to start out by saying that this is a fresh restoration and I'm working out a few kinks. Engine maybe has 15 hours on it.

Stock build 340 TA with original carbs.
Initial @18
ported
with hose plugged in it's at 18* when it settles down to an idle.

After reading more about it and talking to Jeff this morning, it may not be the vacuum just a carb adjustment issue. I've followed every guide I've found related to these carbs in particular the one that Tom Quad put out but I'm getting nowhere.

I've got all the gauges needed to perform a top quality tune and the only thing missing is the experience. Lol.

From what I've read about transient (run) and idle circuits it seems it's having a tough time moving from run to idle. When I gas and release it, it will set at around 1400 to 1500 RPM's and crawl back down and may or may not idle. Takes about 10 seconds or so. Scott restored them and outboard fuel air screws are setting where they were when they left his shop.

I have no hair left after this weekend. Argh
Posted By: RapidRobert

Re: 340 Six Pack vacuum advance - 02/21/18 12:59 AM

it almost sounds like the throttle shaft/butterflies are hanging up in the bores. I'm assuming the dist weights ain't sticking. yes this hobby has made more men go bald than any other (but we wouldn't trade it for nuthin).
Posted By: Cab_Burge

Re: 340 Six Pack vacuum advance - 02/21/18 03:44 AM

Originally Posted By Aar1064
Originally Posted By Cab_Burge
It sounds like you have the vacuum advance hook into manifold vacuum port instead of above the throttle plates for ported vacuum like they came stock scope
Which carb numbers are you using, OEM Holley or after market carbs like the BG six shooters or ?


OEM original Holley carbs restored by Scott. It's plugged into the ported one on center carb.

If my memory is serving me correct, it's been over 30 yrs since I worked on a stock set of OEM Holley 340 six pack carbs blush, the vacuum advance hose should be on the nipple on the passenger side of metering block, not on any other one scope
I've work on a bunch of 440 six packs since then but not in the last 5 yrs whiney whistling grin
Six packs rock when set up correctly, no matter what the doubters say runaway grin
Posted By: Mopar Guy

Re: 340 Six Pack vacuum advance - 02/21/18 05:07 AM

You probably have to adjust idel mix on the outboard carbs to becaus there is no way Scott can pre adjust those Spot on for your engine ! There is an realy great artikel by Jerry Binder that is realy good that i can email you if you like !?
Posted By: Mopar Guy

Re: 340 Six Pack vacuum advance - 02/21/18 05:10 AM

You also might whant to look for air leaks on intake and carbs befor adjusting to mutch.
Posted By: Aar1064

Re: 340 Six Pack vacuum advance - 02/21/18 05:42 PM

Checked butterflies last night and they are closing all the way. Weights shouldn't be sticking because of fresh rebuild by Jeff @ Advanced Distributors. With vacuum unplugged from distributor, engine idles down correctly.

I also checked for vacuum leaks and didn't find any.
Posted By: Aar1064

Re: 340 Six Pack vacuum advance - 02/21/18 05:51 PM

I may have read it but please send it anyway.

Yes I realize that and Scott has been great and continues to be helpful as I'm dealing with this. There's no doubt that they were running great when they left his shop with only minor changes needed on my end.

They were running good on my car and on run stand (with electronic distributor) until I started dealing with ignition issues. I'm just not giving up on yet on points.

I started messing with carb things before realizing that I was having ignition issues hence the reason for sending it in and getting it setup.

Thanks for the help
Posted By: RapidRobert

Re: 340 Six Pack vacuum advance - 02/21/18 06:37 PM

Quote:
With vacuum unplugged from distributor, engine idles down correctly. I also checked for vacuum leaks and didn't find any.
that tells me that it is dist related, either a vac leak as of yet undiscovered or weights hanging up. I'm assuming you've vacuum pumped the can/hose & I would go inside the dist & go over it.
Posted By: Sixpak

Re: 340 Six Pack vacuum advance - 02/21/18 07:28 PM

Make sure the fast idle cam adjustment on the center carb is correct. On a sixpak carb it's not a screw adjustment - you have to physically bend a sheet metal tab that contacts the cam in order to move it. There's a little slot in the part to insert a small screwdriver to bend the link. I had a similar issue where I could not get a 340 sixpak to behave at idle. Found that the fast idle cam was getting hung up on the linkage meant to engage it. Some careful adjustments by bending the link fixed it. Make sure the choke is working and the choke pull off is working too. Your car MUST idle off of all 3 carbs, and not just the center carb. That means adjusting the idle on all 3 carbs in order to get it to idle properly.
If your idle rpm is much above 1000 rpm you may start pulling vacuum thru the port to the distributor. Insure the fast idle cam isn't hanging up, then end carbs are closed at idle (adjust linkage properly) then adjust the idle mixture screws, starting at 1 5/8 turns out on all 3 carbs for a starting point. Do all adjustments with vacuum hose to distributor disconnected.
I found on that same setup the best idle quality I got was having all three carbs have the idle mixture screws turned out 1 5/8 turns. Use that as a start and adjust each mixture screw on the center, and end carbs by covering the air bleed nearest to that mixture screw and checking the idle quality. Covering the bleed should have no effect on idle rpm. If the rpm falls it's too fat, turn in 1/8 turn and try again. Speeds up means it's too lean, turn out 1/8 turn and try again. You may have to take the back carb off to get at the mixture screws. I like to adjust the front carb so it's working well and then swap the front carb to the back. Once you get it to idle cleanly around 950 - 1000 rpm, hook the hose up, then adjust the center carb idle screw; the one on the long arm that usually contacts the idle solenoid, to lower the idle if it picks up.
Posted By: Mopar Mitch

Re: 340 Six Pack vacuum advance - 02/22/18 09:12 PM

I recommend the PROMAX outboard base plates... allows easy adjustment! Its the way it should've been designed in the first place (at least for the rear where you can't get to it with the carbs installed).
Posted By: Mopar Guy

Re: 340 Six Pack vacuum advance - 02/22/18 09:51 PM

I would NOT recomend Pro Max !
Posted By: Mopar Mitch

Re: 340 Six Pack vacuum advance - 03/02/18 09:36 PM

My PROMAX setup offers easy fine tuning; the factory setup does not. My carbs run perfectly. I've never heard any negatives about PROMAX products.
Posted By: Tommy D

Re: 340 Six Pack vacuum advance - 03/02/18 11:41 PM

I second the Promax metering blocks. Work great for me.

When checking that the butterflies are closing all the way, have a friend rev the engine while you're working on the engine. Assuming the rpm's will stay high with this method...when allowing the engine to return to idle, but while still idling higher than wanted, press the two outboard throttle shaft attachment points for the secondaries. If it goes back to normal rpm, that is your problem. This stumped me for a long time. I had to grind a sharp edge onto both outboard carbs butterflies in order to fix. All good now.

Another thing to check...don't over tighten the carbs to the manifold. They only need hand tightening with a ratchet extension. You do not need the ratchet. Too tight and the aluminum bodies will warp. That's likely what happened to mine. Once warped, they'll need the fix in my top paragraph. Good luck.
Posted By: BradH

Re: 340 Six Pack vacuum advance - 03/03/18 12:28 AM

Originally Posted By Mopar Guy
I would NOT recomend Pro Max !


Originally Posted By Mopar Mitch
... I've never heard any negatives about PROMAX products.


I'll be curious to see if this expands beyond the above two comments. work
Posted By: Aar1064

Re: 340 Six Pack vacuum advance - 03/05/18 07:12 PM

Sorry it's been so long reporting back but I've been busy trying to resolve this. I think I have a serious vacuum leak. A friend has a smoke machine and I'd like to hook it up to see what the results are. In order to do this, I'll need to block off all the ports. I can think of a few and want to make sure I'm not missing anything.

1. Ported vacuum on middle carb
2. Intake port
3. PVC port on middle carb

What else is there?

Some will say spray carb cleaner but I'm too afraid to do that. Others will say use propane but since fan is on engine, I'm not sure how reliable that is.

BTW-Over the weekend I replaced the intake gaskets and this didn't help or it did and I have another leak.

Thanks for the help
Posted By: ademon

Re: 340 Six Pack vacuum advance - 03/13/18 03:16 AM

That's a high initial at 18* for a stock build, sure your throttle blades have enough of the transfer slot exposed???
Posted By: Cab_Burge

Re: 340 Six Pack vacuum advance - 03/13/18 08:39 AM

Originally Posted By ademon
That's a high initial at 18* for a stock build, sure your throttle blades have enough of the transfer slot exposed???

There is no way I would ever make any carb. idle on the transfer circuit port, NEVER tsk
The idle circuit should and will control the idle mixture and RPM when set up properly up scope
Ultimately the AFR and amount of air allowed into the motor controls the RPM at idle or at WOT work twocents
OP, my 518 C.I. 400 block pump gas six pack stroker motor would idle at 850 RPM in gear and gain 100 to 150 RPM going from in gear to in neutral, all on the idle circuit with no vacuum advance with the timing set at 14 BTDC at idle and under 1200 RPM with a big solid roller race cam in it shruggy up It had a mix set of original 440 carbs. on that motor modded by C&J Engr, in Whittier, CA
It took a little work and time on my part to get it to work like that so you may need to try and test some different things on yours also up
You CAN do THIS up
Now, get to work whistling wrench grin
Posted By: ademon

Re: 340 Six Pack vacuum advance - 03/13/18 11:37 AM

Try dropping your initial to 10 or 12, and resetting your idle.
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