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Accelerator pump shot #1302243
09/11/12 07:25 PM
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General 68 Offline OP
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My 5 year old Edelbrock AVS 800 Thunder has developed a off-idle- and idle-to-WOT bog I can not tune out. I checked the pump shot and found that the throttle has to be opened some before it squirts. Shouldn't the pump squirt immediately when the primairies start to open?
The pump diaphragm has no obvious damage and the spring and ball under the squirter are ok. There is tension to the pump at idle.
It idles smooth with steady vacuum.
The carb is clean and the car pulls strong other than this bog. It used to run good with the same settings before.
Any ideas? Do the diaphragms tend to go bad this early?

Re: Accelerator pump shot [Re: General 68] #1302244
09/11/12 07:47 PM
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Quote:

the throttle has to be opened some before it squirts. Shouldn't the pump squirt immediately when the primairies start to open?
It used to run good with the same settings before. Any ideas? Do the diaphragms tend to go bad this early?


replace the AP. I believe someone said that the leather cups are better than the neoprene ones if they make a leather one for your application (or if a leather one can be adapted to fit). What do you have for fuel over there? Ethanol blend?


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Re: Accelerator pump shot [Re: RapidRobert] #1302245
09/12/12 05:50 PM
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General 68 Offline OP
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I just ordered a new diaphragm. Not sure why the old one doesn't work.
It made a good shot but not before the butterflies had opened a little. Anything else that can cause this?
I do not know much about the fuel avilable but have not heard others having problems. I'll throw in the new pump diaphragm and see how it works. Thanks!

Re: Accelerator pump shot [Re: General 68] #1302246
09/12/12 07:21 PM
09/12/12 07:21 PM
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At WOT, the top of the plunger should be flush with the top edge of the carb body. If not, the pump could potentially be higher than the fuel and not push anything but air for the first bit of travel. Tweak the bendable arm to correct this.

Also, if the floats are too low the top of the pump could also be out of the fuel.


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Re: Accelerator pump shot [Re: General 68] #1302247
09/13/12 11:23 AM
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Quote:

I'll throw in the new pump diaphragm and see how it works.


Let us know how it goes


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Re: Accelerator pump shot [Re: RapidRobert] #1302248
09/20/12 11:12 AM
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Update: I put in a new accelerator pump plunger and the small delay is the same. Raised the float level a little and adjusted the pump rod and drove the car till it was fully warm. Tested idle to wot and it bogged. Then I had to take care of a few other things so the car sat for 30 minutes. Took it out again and after making sure the choke was fully open I smashed the pedal a few times without getting a bog! Throttle respons was crisp and clean! Tried som more an all was fine. Took the car for a drive and after about 5 minutes of driving i tried cracking the throttle wide open again and it bogs
Seems like something in the ignition circuit is not up to the task. I'll start with the ballast and eventually follow up with ecu and coil as I have spares. Briefly explained the car will bog when it has been driven for a while. After cooling down for 30 minutes it does not bog. Drive some and it bogs again. I'll see if I get some time to dig into this tonight. Please let me know if you see things I haven't thought about. (Ampere meter is by-passed and wiring checks out good to ballast.

Last edited by General 68; 09/20/12 02:49 PM.
Re: Accelerator pump shot [Re: General 68] #1302249
09/21/12 06:55 AM
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Quote:

Update: I put in a new accelerator pump plunger and the small delay is the same. Raised the float level a little and adjusted the pump rod and drove the car till it was fully warm. Tested idle to wot and it bogged. Then I had to take care of a few other things so the car sat for 30 minutes. Took it out again and after making sure the choke was fully open I smashed the pedal a few times without getting a bog! Throttle respons was crisp and clean! Tried som more an all was fine. Took the car for a drive and after about 5 minutes of driving i tried cracking the throttle wide open again and it bogs
Seems like something in the ignition circuit is not up to the task. I'll start with the ballast and eventually follow up with ecu and coil as I have spares. Briefly explained the car will bog when it has been driven for a while. After cooling down for 30 minutes it does not bog. Drive some and it bogs again. I'll see if I get some time to dig into this tonight. Please let me know if you see things I haven't thought about. (Ampere meter is by-passed and wiring checks out good to ballast.




Just to eliminate the possibilities-
You say it ran fine and then developed this problem...
Have they switched to a higher ethanol-blend of gas? Like an E-15 or greater? AVS's don't like the alcohol gas as the aluminum bodies tend to transmit heat faster and therefore evaporate the fuel quicker...
Next question-
Are you running a carb spacer/heat shield? All my AVS's I run with a some kind of phenolic spacer or with a heat shield for the reasons stated above...
Also- on an AVS the fuel should come out of the squirter IMMEDIATELY- there should be NO delay. I would check the pump squirter for a blockage of some kind that would be creating the delay- or the adjustment of the linkage rod that controls the travel of the pump. You may just have a linkage that is loose, worn or bent.

And- if it's ignition-
Check your ignition box- they can go bad over time. I had an Orange Box that croaked after 3 years on the car- it looked just fine, but one day I'm going up the road and -zap- engine shuts off like I turned the key. Swapped a new box on and drove off.....

Finally- The AP diaphram needs time submerged in fuel/oil to swell and fit the bore of the pump chamber. With a leather diaphram, I would soak it in oil overnight before installing it. With the rubber version that currently is used, I'd probably do the same thing, but I don't like the rubber ones.


Good Luck,
CC

Re: Accelerator pump shot [Re: chargincharles] #1302250
09/21/12 05:29 PM
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Gas is good. I have never had any trouble around that. The pump shot is strong and steady but does not come in until the throttle cable/lever is moved almost 1/8". When looking down the carb while flipping the throttle I see the throttle blades open a tiny amount before the nozzle squirts. Slow or fast movement the first 1/8" does not matter. A little longer blip of the throttle and it squirts strong.
One thing that puzzles me is that I only read 5,5 volts out of the ballast resistor when having 12V going in. On a different car I have I read 9V out to coil. I swapped the ballast from this car over and got only 4,5V out. I went further and swapped the ECU too and still the same. I run a 5 year old FBO system and hav a spare coil wich I also swapped in. Same low reading. I jumped all wires between ecu/coil/distributor and still the same. The only time I get a good voltage reading at coil (9V) is when I swap the coil from the different car. Then I basically have swapped the whole ignition system from that car over. I also did the same tests with the coil secoundary wire and the distributor unplugged without any difference.
What am I missing here? Both FBO coils takes the voltage reading out of ballast/in to coil down to 5,5V. These are coils meant to be run with a ballast resistor.

Re: Accelerator pump shot [Re: General 68] #1302251
09/22/12 12:07 AM
09/22/12 12:07 AM
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I'm not sure about your ignition

but on the carb, i would look closely at the checkball under the squirter sealing. that check ball is there to hold fuel near the squirter, if there is any gunk buildup, it may be bleading down.

another thought is when the engine gets hot, todays fuel boils very easily, while your driving, boiling gas may be pushed out the squirters and you don't know it then when you mash the pedal there is no gas sitting above the check ball

another thought, is the weather may have turned cooler and the carb seems leaner to the engine and you may need to open the A/F screws a bit.

If you have the balls to take drill bits to the carb, PM me and I will tell you how to take care of the bog forever


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Re: Accelerator pump shot [Re: sixpackgut] #1302252
09/22/12 09:41 AM
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Check ball and spring seems ok. No dirt or sticking as far as I can see. I have not checked for fuel over the ball. I guess fuel is supposed to be found over the check ball when I remove the squirter nozzle. I do not run any spacer under the carb but the car runs cool with huge fuel- and return lines. Temps have cooled some here now and I get this bog after a short drive, even befor the engine reaches operating temperature. The only time it might be gone is after the car has sit for a few minutes and gets started back up. After a short amount of time the bog is back. I have rechecked the idle mixture settings but still no go.

Re: Accelerator pump shot [Re: hooziewhatsit] #1302253
09/22/12 07:08 PM
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Quote:

At WOT, the top of the plunger should be flush with the top edge of the carb body. If not, the pump could potentially be higher than the fuel and not push anything but air for the first bit of travel. Tweak the bendable arm to correct this.

Also, if the floats are too low the top of the pump could also be out of the fuel.






Did you make the adjustment as was stated by hossiewhatsit?

Last edited by 540DUSTER; 09/22/12 07:09 PM.
Re: Accelerator pump shot [Re: 540DUSTER] #1302254
09/24/12 06:17 PM
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Yes the pump plunger is flush with the carb body at wot. It was a little high but adjusting it did not make any difference.

Ignition opdate: After swapping out the FBO coil for a known good old coil the car runs smoother than ever. The two FBO coils I have around measure the same impedance and the same voltage drop after ballast resistor. 12V in measures 5,5V at coil. Ballast came with the FBO kit and is marked 0.8 ohms. With the known good coil in the circuit I get 9V at coil. So are the FBO coils both bad or can't the ballast take the load they create or should the ballast for the FBO coils simply have less resistance? These are questions I would like to shine a light on!

The coil swap worked wonders but the engine still bogs. Here is a summary from tonights test runs: Warmed the enging - smash the throttle several times an it bogs every time. Stop the engine and do some tweaking, start up an NO BOG! Drive a minute, smash it an IT BOGS. Actually it will always bog after being driven, but after a short stop or just idling for a minute the throttle can be smashed many times in a row without making the engine bog.

Hmm.. fuel boiling ? Weather is rather chilly here now and I believe the fuel actually should be cooler when driving than after the engine has been shut off for a minute. The engine starts really easy after being shut off for a while.
Floats too low? I set them at factory settings but raised them some last time i thinkered with the car. Not sure what to try next. I do have a 1/2 inch phenolic carb spacer I could try but the air filter box won't allow the hood to be closed. Ideas?

Last edited by General 68; 09/24/12 06:25 PM.
Re: Accelerator pump shot [Re: General 68] #1302255
09/24/12 06:38 PM
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With the new plunger do you get immediate tip in? and repeatedly pulling the throttle gets the same immediate tip in? this is with eng off & visual down the throat. I would put 2 strips of clean rag past the nozzles to catch the raw gas to do this check. On a seperate note the 2 FBO coils show 5.5V and the "known good coil" shows 9V using the same ballast? What's the ohms (pri/sec) difference between the FBO coils and the known good coil? EDIT I'm thinking there's a fuel starvation issue of some sort. worn pushrod (BB)/partly plugged sock/pinhole in gas line/partly plugged filter/internal carb issue. Keep on it

Last edited by RapidRobert; 09/24/12 06:52 PM.
Re: Accelerator pump shot [Re: RapidRobert] #1302256
09/24/12 06:56 PM
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Always a strong steady shot but the throttle blades move a little before the nozzles squirt. The new pump diaphragm did not change anything. Even when I move the throttle lever fast this small distance it will not squirt. I assume the fuel should come out the nozzles as soon as the lever is moved? On the other hand the throttle responce is good as long as I don't floor it completely. The engine takes a 2/3 throttle smash but not more without hesitation.

I have not measured the good coil but I'll do that tomorrow just to see what we have here. Same ballast for all readings.

Another idea: is it possible that something is leaking inside the carb when the throttle is held open some, as when driving, and the engine then needs some time to clear up? This will mean that I have a rich bog. The fact that the bog is gone after the engine has been shut off for a minute really puzzles me.

I run an electric fuel pump with 1/2" fuel- and return lines and dual 3/8 lines from regulator to carb. Fuel pressure is currantly 4,5 PSI, maybe a tad on the low side but I can not see that this should create this problem. The car pulls strong up the RPM's.

Last edited by General 68; 09/24/12 07:05 PM.
Re: Accelerator pump shot [Re: General 68] #1302257
09/24/12 07:03 PM
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ANY chance you could borrow another known good carb for a day to see if you could pin it down to the carb or to the fuel delivery? Got an idea, might take off the squirter & see if the check valve underneath is free & might spray it all out and the nozzle with starting fluid,could be a piece of debris

Last edited by RapidRobert; 09/24/12 07:11 PM.

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Re: Accelerator pump shot [Re: RapidRobert] #1302258
09/24/12 07:12 PM
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I do not have access to any suitable carb around here. Checked the needles and seats and blew compressed air through the metal screens and the rest of the air horn the other day. No difference afterwards. Float level was set according to Edelbrocks manual and I raised it a little without any effect.

Re: Accelerator pump shot [Re: General 68] #1302259
09/25/12 03:11 AM
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Quote:

Always a strong steady shot but the throttle blades move a little before the nozzles squirt. The new pump diaphragm did not change anything. Even when I move the throttle lever fast this small distance it will not squirt. I assume the fuel should come out the nozzles as soon as the lever is moved? On the other hand the throttle responce is good as long as I don't floor it completely. The engine takes a 2/3 throttle smash but not more without hesitation.

I have not measured the good coil but I'll do that tomorrow just to see what we have here. Same ballast for all readings.

Another idea: is it possible that something is leaking inside the carb when the throttle is held open some, as when driving, and the engine then needs some time to clear up? This will mean that I have a rich bog. The fact that the bog is gone after the engine has been shut off for a minute really puzzles me.

I run an electric fuel pump with 1/2" fuel- and return lines and dual 3/8 lines from regulator to carb. Fuel pressure is currantly 4,5 PSI, maybe a tad on the low side but I can not see that this should create this problem. The car pulls strong up the RPM's.






If the engine is bogging when you smash the pedal,it could be that the opening rate of the secondaries needs to be adjusted.I am not sure about the new thunder carbs,but there should be a spring on the air door you can adjust.Try to tighten the spring and see what happens.

Re: Accelerator pump shot [Re: 540DUSTER] #1302260
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I have played with the air door and it seems like I can tune out a bog by tightening it a bit more than two turns from closed, but then the secondaryie won't kick in. Best result the other way is around 1,4 turns after closed. I sure can try it even lighter but I can not see how this should affect the fact that the bog goes away if I stop the engine and restart after a couple of minutes. After warmed up the engine will bog from idle but if stopped for a short time and restarted the throttle responce is crisp and clean. Drive it a mile an the bog is back. Even letting it idle for a minute seems to take away most of the bog.
Can this be a choke problem? Just thinking. The choke pull-off is adjusted to specs and I have tried different settings for the spring tension. The car starts really easy but runs a little rough until the choke is open wich with the currant setting happends after about two minutes. I sure can wind up the choke spring to delay the choke some but it will still run rough.

Last edited by General 68; 09/26/12 05:33 PM.
Re: Accelerator pump shot [Re: RapidRobert] #1302261
09/26/12 05:42 PM
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Rapid Robert- The Fbo coils measure pri 0,7ohms/sec 11,8 kohms.
The old OEM coil measures pri 1,8ohms/sec 10,2 kohms.
Ignition is checked out and when warm the car runs super other than hving this bog problem.

Re: Accelerator pump shot [Re: General 68] #1302262
09/26/12 06:26 PM
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Find the AVS adjustment procedure and do it by the book and you should solve your problem.The correct pump adjustment is with the throttle plates closed and the measured recommended height from top of air horm to top of accelerator pump shaft is how you adjust the pump.

Re: Accelerator pump shot [Re: General 68] #1302263
09/27/12 12:12 AM
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Quote:

The Fbo coils measure pri 0,7ohms/sec 11,8 kohms.
The old OEM coil measures pri 1,8ohms/sec 10,2 kohms.


Just from the specs I'd think with the FBO coil drawing more primary current from the lower ohm value that it'd run better with that


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Re: Accelerator pump shot [Re: RapidRobert] #1302264
09/27/12 02:32 AM
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Yes, by the specs measured at the fbo coil, I agree. Too much resistance through the supplied ballast maybe. I still have plenty of juice to ignite the fuel as the engine screams other than the mentioned wot bog. I also agree this seems to be some kind of fuel starvation somewhere inside the carb. It should not be flooding as it seems to clear up some after idling a minute. Or could it actually be lifter pump up that makes a valve or two not seating 100% as the bog disappears during shutdown? I do not know how this should feel. Also have in mind that idling (with less oil pressure) clears it up some. I can not get more than 11" of vacuum at 850 rpm idle. Vacuum is is not pulsating and power brakes work great. This is with a Lunati 60303 cam, .226/.234 @ 50, adv. dur. 268. I will have to double check that with a different vacuum gauge thou. And mayb monitoring the vacuum when running to see if it pulsates at first when going back to idle.

Last edited by General 68; 09/27/12 03:12 AM.
Re: Accelerator pump shot [Re: General 68] #1302265
09/30/12 05:38 PM
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Update: I hooked up a timing light to check that I was at 18 degrees at idle, and I was. But the timing does not start to advance intil 2000 rpm. This can not be right, ok? I run a distributor recurved by FBO to 18 initial, 34 total, all in by 3000 rpm. The timing advances fast after starting at 2000 rpm.
Anyways, I bumped the initial to 20 and hooked up a digital tach to monitor exactly idle rpm. I then realized that my in-car tach reads a little high so my idle has been low. I let the idle stay where it ended after bumping the timing wich was 780 and got 12"hg - 1hg more than I had prior to advancing initial timing. With these settings the bog is completely gone (!) but I need to dig into the distributor. I think I need some guiding to work through the advancing curve. Shouldn't the distributor start to advance earlier? Duration at 50 is 226/234, advertised 268/276. All tests with the vacuum advance plugged. The vacuum advance says to be 10 degrees at 16"hg.

Re: Accelerator pump shot [Re: General 68] #1302266
09/30/12 07:04 PM
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Quote:

. But the timing does not start to advance intil 2000 rpm. This can not be right, ok? With these settings the bog is completely gone


(1) that's not right (2) success on the bog! Keep experimenting


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Re: Accelerator pump shot [Re: RapidRobert] #1302267
10/01/12 07:59 AM
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I'll be away for a few days but hopefully I get time to play with the distributor next weekend. thanks all for your help so far! I really appreciate your input!

Re: Accelerator pump shot [Re: General 68] #1302268
10/02/12 05:41 AM
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Not sure if this is the right thread to ask but do you have any advice for a proper timing/advance figure for the 60303 cam? 68 Charger, 440/ported 915's, cr around 10:1, 5-speed, torker 2, 2" headers, 3" exhaust with x-pipe, 4.10 rear, mostly street driven.
I took apart the distributor and everything seems ok and moves smooth.
One dark/black spring and one silver. Mechanic advance doesn't start to come in until 2000rpm.

Re: Accelerator pump shot [Re: General 68] #1302269
10/02/12 11:54 AM
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Yes it's always a good idea to keep it all in the same thread. I'd set the initial with the "vacuum gauge" method then with that figure in hand shorten the slots to get 36 total then go with a lighter spring combo that keeps you just under the pinging point at WOT up thru the gears on your hottest/driest (most likely to ping) day and which starts advancing a bit above your in gear idle RPM. Vac adv (if used) is capped to set initial and total if working with ported vac adv. If going with full manifold vacuum then it'd be plugged in to set the idle timing but not the total. If ported then after the initial/total/springs are set plug in vac adv (if used) and work with it in everyday part throttle operation around town staying just under the pinging point. A 3/32" allen wrench CCW slows the onset of its' curve


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Re: Accelerator pump shot [Re: RapidRobert] #1302270
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Ok. My distributor is set up with 16 degrees of mechanical advance. So initial 20 will be 36 total. All in at 3000rpm. Wich springs are avilable and what is their rating? T what rpm should I get the advance started? I want to check the advance curve again to verify that nothing was stuck in there prior to disasembling the distributor. I find it hard to believe that FBO set it up to not start advancing until 2000rpm.

Re: Accelerator pump shot [Re: General 68] #1302271
10/05/12 10:44 PM
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RapidRobert Offline
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RapidRobert  Offline
Circle Track
R

Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
Is this a newer type Mallory built MP dist that I think uses special (I've never owned one) springs? If it's a regular type (70's) dist MP has a light spring set as does Mr Gasket & on those (70's dists') keeping the stock light spring and tossing the heavy spring with the long loop on one end & subbing in (1) mr gasket or MP spring would be a good start. Want to stay just under the pinging point at WOT up thru the gears on your hottest/driest day and want the curve to start a bit above your in gear idle speed


live every 24 hour block of time like it's your last day on earth
Re: Accelerator pump shot [Re: RapidRobert] #1302272
10/06/12 12:49 PM
10/06/12 12:49 PM
Joined: Jan 2007
Posts: 401
Norway
G
General 68 Offline OP
mopar
General 68  Offline OP
mopar
G

Joined: Jan 2007
Posts: 401
Norway
Thanks RR! Really appreciate your input! Not sure who made my distributor. I purchased it from FBO 2006. So for a stick car that idles aroun 800rpm the advance curve could start around 900-1000rpm or so? and then tweak it to stay just under the pinging spot up to fully advanced?

Re: Accelerator pump shot [Re: General 68] #1302273
10/06/12 11:19 PM
10/06/12 11:19 PM
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
R
RapidRobert Offline
Circle Track
RapidRobert  Offline
Circle Track
R

Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
Quote:

Not sure who made my distributor. So for a stick car that idles aroun 800rpm the advance curve could start around 900-1000rpm or so? and then tweak it to stay just under the pinging spot up to fully advanced?


I think on the Mallory built MP dist you can see the adjustable slots. Yes a bit above idle speed. Set initial with the vac gauge method then with that figure in hand shorten/lengthen the slots to get 35 total (SB), 36-38 BB, (initial and total set with vac adv capped) then play with spring tension, mix and match so you're just under the pinging point at WOT up thru the gears on your hottest/driest day and as said it starts advancing a 100 or so rpm above your idle speed, THEN plug in vac adv & work with it (CCW slows its' curve onset) and with it your wanting to stay just under the pinging point at high vac steady cruise on the highway on your hottest/driest day at an RPM at or above the rpm where the mechanical curve is maxed out so every system is at max advance AND no ping in everyday driving


live every 24 hour block of time like it's your last day on earth
Re: Accelerator pump shot [Re: General 68] #1302274
10/07/12 09:25 AM
10/07/12 09:25 AM
Joined: Apr 2005
Posts: 46
Detroit, USA.
M
MagnumGT Offline
member
MagnumGT  Offline
member
M

Joined: Apr 2005
Posts: 46
Detroit, USA.
Just my two cents... As simple as this sounds, take off the cap and see if there any I MEAN ANY play back and forth on the rotor. I have had my idle act weird only to find the tip of the distributor worn and a tiny bit of play causing timing changes but only "sometimes".
Lots of great people on this board!

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