heavy bog under acell

-

DustyDan

Member
Joined
Sep 11, 2014
Messages
17
Reaction score
0
Location
Millville, Massachusetts
Hi everyone, I'm new here to the forum.
About me: Dan from Massachusetts, Mopar or no Car. full time mechanic (91B) in the RI National guard. Been a mechanic for 12 year mostly working on fuel injection, have a Neon srt4 as a DD. Back in July picked up my first old Mopar a 73 duster 340 4 speed.

About the car: stock 340 from what I can tell ( vin on motor and trans matches car, )
Holley 750 vac sec 74 jets stock plate on rear .35 squirter, blue squirter cam, a weiand stealth dual plane
Stock electronic ignition, new mopar performance distributor, 16* btdc initial, vac advance connected to ported source, 5 pin ignition box, accell super stock coil, msd sf wires auto lite 65s at .040 gap.
8.25 open 3:23 rear
Hi po exhaust manifolds tti head pipes and x-pipe.

Problem: under moderate to heavy throttle off idle or at cruise I have a huge bog, if I ease into it no bog pulls good. At idle if you rev it no bog although it doesn't sound that crisp, a slight delay. I adjusted the carb with a vac gauge best I got was ~12 hg so I put a 6.5 pv.

What I've tried: bigger and smaller squirter, (clearance on linkage good about 0.015) different pump cam. Neither had any change.

My thoughts are maybe pv too low, timing or vac advance maybe, any thoughts or advice appreciated

Other notes:
When I got the car she had headers which were leaking so I swapped them out to manifolds. Since then the problem showed up, probably a coincidence.
 
a bog is generally a lean condition so with that in mind l'd say you would want to check out the power valve which at 12 hg. it will stay shut until the vacuum drops below 6.5. you may need one closer to your 12hg. secondly check the vacuum pod to see if it's opening to fast. if it is it will create a bog because there is not enough vacuum to pull gas up the emulsion tubes so you have to install a heavier spring in the pod. try to put our mits on a holley book to get some really good tuning information.
 
You may also want to raise your float levels a bit. Most of mine like the fuel a little higher than the bottom of the sight plug.
 
Have you checked the pump shot. With the engine not running, crack the throttle as if your flooring it quickly while looking down in the carb and be sure you're getting instant fuel.
 
Yeah one of my first thoughts was the pump shot, I adjusted the arm, my question on that is it you want to see a .015 gap when WOT and pushing down on the lever. I'm gonna try and go up a couple sizes on the power valve and see what happens. I will also check plugs and see how they look. As far as the vacuum pod right now it has the plain spring which I think is the middle one. I'll check for vacuum leaks as well. Thanks for the suggestions I will keep you posted.
 
Probably not an issue here but I once had an Accel coil that didn't completely fail but the secondary voltage was so low that to get any power at all I had to run 42 degrees of timing. On the scope it wouldn't peak over about 12KV.
 
Coil? i just tossed my new Accell super coil, left me stranded in the middle of the intersection! all sorts of issues i put a stock coil back on problom solved.
 
It's probably the blue (#427, right?) Pump cam. Too much shot. Also will make gear changes
herky jerky. The old white (218) cam is best for probably 90% of cars and now they're becoming
hard to come by. Your stick car doesn't need quick, agressive squirt like a lot of
automatic cars do. Try 218 cam if you got one, or a black or orange.
 
I don't know how smiley face jumped in there, but that was supposed to say 218!
 
And by the way, you don't want Any clearance in pump arm at idle- what you
want is .015 travel left in pump arm at wot. That's probably your biggest problem right there.
 
Blue pump cam usually maxs' out pump to the point of not having any travel left and puts
stress on pump diaphram.
 
Here's a Holley vid on setting up the accel pump.. You should see a strong, consistant stream of fluid outta the squirter nozzles THE VERY INSTANT you move the throttle...There should be NO PLAY in the accel linkages at idle..

[ame="http://www.youtube.com/watch?feature=player_embedded&v=k-Nx5HEzvlY"]How To Adjust The Accelerator Pump On Holley Carburetors - YouTube[/ame]

hope it helps
 
Yeah some signs point to too much fuel, for example it smells pig rich at idle, in the garage running after I minute your eyes will burn, only gets about 10 mpg and that's driving normal, but the plugs looked lean so that's why I upped the Jets from 72 to 74. Also I have a hot start issue. After driving at normal operating temp if I stop and shut the car off for a few minutes, like to get gas, when I go to restart I have to hold the pedal to the floor and crank the motor longer. It cranks fine doesn't kick back because of timing or anything, just seems flooded. I put a heat insulator gasket on helped a little. Idk. Alot of trial and error I guess. The car is an improvement from when I first got it. I used to idle really rough like it had a crazy cam, and was only getting 6 mpg. So I know what I've done has helped. I would just like to get her "dialed" in better.
 
The eyes running, is a tip off your power valves may be punctured/leaking,, and the long cranking would suggest the carb is dripping after you shut it off,, possible high float level,, here's a vid on setting float..

[ame="http://www.youtube.com/watch?feature=player_embedded&v=ge-mIk6nEYQ"]How To Adjust Fuel And Float Level On Holley Carbs - YouTube[/ame]

hope it helps
 
If your throttle is cracked open too far at idle, your motor will be idling on transition and main
circuits causing rich idle. Do your mixture screws work? If you turn mixture screws all the way in,
does' motor die?
 
The heat thing is a big problem for guys like us. The gasoline companies used to put additives in the
gas to help prevent vapor lock and gas boiling in carb from heat soak when you turn engine off.
Also, most Holley carbs used to have a flapper valve on the primary bowl that vented boiling gas
vapors into the atmosphere when the throttle was clos
ed. You want to try to keep carb as cool as
possible. Thick heat spacer, exhaust heat blocked from manifold. Maybe a scoop on hood, or
anything you can think.
 
Also, when you replaced headers w/exhaust manifolds, did you keep heat riser valve or
eliminate it? I would have eliminated.
 
Modern fuel injected cars' system works at high pressure, so additive is
n't as important to them as it is to people that drive "antiques".
 
Yeah removed heat riser, going to Change intake gaskets with one that has black off for cross over, also have a 1" phenolic spacer I will put on. When ever I fill up for fuel I always put the Lucas additive that combats the ethanol effects of the new gas. I had a huge problem on the neon when ever In boost at WOT it would knock, once I started running the additive it cleared it up.

Progress on bog: Adjusted the accel pump linkage, like the guy In the video with the carb that had the hoses in the vent holes. The bog improved but still has a slight bog.(maybe go up on size on squirter? current size is 35) One thing I noticed it with the blades closed the arm that pushes on the pump doesn't make contact with the cam, (not sure if its normal or its bent, it's an orange cam). Mixture screws work if I run one side in car will stall. When looking at the carb from underneath the transition slots are "squared" I had to open the rears slightly because before I'd have to run the idle screw down alot to get to idle at 850-900.

Next trial: I have 2 other power valves 7.5 and 8.5, I will try them and see how it acts. I will also pick up a pump cam kit and experiment with different colors.
 
One thing I noticed it with the blades closed the arm that pushes on the pump doesn't make contact with the cam, (not sure if its normal or its bent, it's an orange cam).

There's your bog.. as mentioned earlier, get rid of any play in the linkages that cause there to be any delay in the start of the squirt.. The plastic cam has 2 screw holes for adjustment, try moving the cam to the alternate hole,, and adjust the "spring/screw" till the play is ALL gone... Bending the arm is not out of the question,, if the play can't be adjusted out..
 
Okay so I did some tinkering with the car this weekend, most of the bog is gone now,(slightly bogs now) I put a 7.5 pv In, however I think that is too high, because after I let off the throttle from wide open, it takes a little for the rpm to some down, drives like I got cruise control, there is no binding with throttle linkage, so my guess would be pv hanging open. (Now i know this is the wrong way), but I connected the vac advance to manifold vac, noticed that the rev at idle is alot more crisp. So my thoughts would be adjust timing? Currently timing is initial 10* btdc 34* btdc @3000. If I set base to 20* the idle is cleaner vacuum is higher, but with a 24* mechanical I end up with way too much timing. I have verified true tdc in reference to balancer, and all is well there. So maybe just need to recurve distributor.
 
Not sure what cam you have but my j head 340 270H cam 3.23 gear 93 octane runs its best at 26* initial, 35* mech total, 48* vac adv. on ported vac. Crisp throttle, no ping.
Also Summit sells their brand of AFR kit for $165 that is made by AEM. You can dial in a carb with ease and no guessing. Every change made is easy to see. I dialed in my thermoquad and the car is running like a 340 should. Get your timing curve dialed in first, then dial in the carb.
For heat soak you can also make a heat shield to help keep the fuel bowls cooler and insulate the fuel line as room allows.
 

Attachments

  • 000_0045 (640x480).jpg
    50.4 KB · Views: 139
  • 000_0044 (640x480).jpg
    49.4 KB · Views: 129
Definetly have to "modify" distributor. Have to shorten up amount of advance. If you're not
familiar w/ distributor, just to let you know, there is a wire clip under the felt wick on top of shaft
that must be removed. I use long nose plyers. A little tricky to remove and reinstall.
 
Also power valve not responsible for "cruise control". That's probably related to vacuum advance.
 
Also, in case you didn't know, vacuum advance is adjustable with allen wrench through hose
connection hole. I would tune motor not even using vacuum advance, then add and tune after
curve & carb are straightened out. You want a quick curve and probably end up using very little
vacuum advance.
 
-
Back
Top