tuning a 500 inch stroker for 91 pump gas

[68charger440]

The play in the shaft can be corrected but not cost effective to have it bushed. New baseplates are available too. Just not cheap. I would get the engine running as best as possible, spray some carb cleaner around the baseplate and shaft and see if the engine rpm changes significantly.

I'll try that tomorrow.

[68charger440]

Would the leakage around the secondary shaft cause the idle mixture screws to be ineffective whether closed all of the way or opened?

[c00nhunterjoe]

Spray carb and choke cleaner on it while idling. If its leaking the rpm will change.

[68charger440]

Spray carb and choke cleaner on it while idling. If its leaking the rpm will change.

It does change the idle, but the Holley tech I have been emailing back and forth with said that a small amount of vacuum leak at the shaft is built into the design.  I just Don,t know if mine is at an acceptable level or not.

[68charger440]

OK, I took a detour to deal with a couple of problems that were preventing me from tuning the motor. 
One was a low voltage to the coil  problem that was giving such a low voltage that the spark was weak and would cause a misfire.  After much frustration and digging I bypassed the ammeter which was fried to the point where it was acting as an resistor and giving low voltage to everything downstream including the ignition switch, coil etc. 
The second issue was the carburetor itself and trying to get it to respond to the mixture screws.  For that I ended up having to drill the throttle blades to regain control of the mixture.  The carb has very loose secondary throttle shaft and the blades don't seem to seat as well as they should, so that may have played into my need to drill the blades.  I still may replace the base plate or the carb entirely if I have to.
I addressed both of those issues through separate threads to keep from getting too far into the weeds on this thread.

Right now it has a fairly good 700 rpm idle, but I still want to try to tune out the detonation if possible.  If I can't tune it out then I will either put a thicker head gasket or aluminum heads on it.  Fixing the electrical problems above helped, but upon further review it is still there. 
I want to try backing off the timing even at the loss of power as long as it won't damage the motor.  I need some advice on how to go about this., and probably understanding in more depth how it all comes together.  I am thinking if I go to manifold vacuum instead of the carb ported vac then I will be able to set the initial more retarded and let the idle vacuum bring it to where it needs to be at idle, whereas with the ported vac it has little or no effect at idle.  I am thinking of backing the initial off from 17* now to 12 with the vac disconnected, and then  when it starts and has full vacuum at idle through the manifold it will get the the vac advance from the MSD dizzy..Am I way off base or what?

[firefighter3931]

Here's what i would try ;

Disconnect the vacuum advance and plug it off. Set the total timing to 34* and let the initial timing fall where it does. 

I'm assuming that you are using the black bushing in your MSD RTR distributor ?


note: If it's sucking air from the secondary throttle shaft, that will create a lean AFR and contribute to your detonation headaches. A wideband O2 sensor and air/fuel guage would tell the whole story. 



Ron

[68charger440]

Here's what i would try ;

Disconnect the vacuum advance and plug it off. Set the total timing to 34* and let the initial timing fall where it does. 

I'm assuming that you are using the black bushing in your MSD RTR distributor ?


note: If it's sucking air from the secondary throttle shaft, that will create a lean AFR and contribute to your detonation headaches. A wideband O2 sensor and air/fuel guage would tell the whole story. 



Ron

I am running the black bushing.
Should I leave the vacuum advance plugged permanently, or reconnect it after setting the 34* total timing?

[firefighter3931]

Here's what i would try ;

Disconnect the vacuum advance and plug it off. Set the total timing to 34* and let the initial timing fall where it does. 

I'm assuming that you are using the black bushing in your MSD RTR distributor ?


note: If it's sucking air from the secondary throttle shaft, that will create a lean AFR and contribute to your detonation headaches. A wideband O2 sensor and air/fuel guage would tell the whole story. 



Ron

I am running the black bushing.
Should I leave the vacuum advance plugged permanently, or reconnect it after setting the 34* total timing?

For now I would leave it blocked off. Drive it for awhile and see if the detonation goes away. The black bushing gives you 18* of mechanical advance so setting the initial at 16* should put you right at 34* total.

Something else that may help is a heavier set of advance springs....to slow down the curve and reduce advance timing under heavy load. Try it first with the advance plugged and the timing at 16/34 and see what happens. 



Ron

[68charger440]

OK, I was already pretty close to 16* initial and 34 total timing, so that didn't get me anything, but I borrowed a friends narrow band o2 meter.  It only read lean or rich, but it was good enough to show me I was real lean.  I played with the jetting until I got it looking pretty good and a bit on the rich side.  When the smoke cleared I had jetted it up 6 sizes. The pinging is gone on light and medium load now.  I couldn't test heavy load because I had some slipping between 2nd and third and didn't want to push it.  I didn't hear any detonation at all so I think we've got it.   Thanks so much for the help everyone and Ron in particular.  Now I have to try to adjust the kickdown linkage and hope that is causing the rev between 2nd and third.  I didn't see a sticky on adjusting the kickdown on the 68 Charger 727.  Do you know of a thread that I missed that covers it?

[firefighter3931]

Good work....wow 6 jet sizes sure explains the detonation issue. Those A/F gauges are awesome for sorting this stuff out 

The way I've adjusted the KD linkage is to open the throttle all the way and snug up the adjustment so that the KD has a small amount of travel after the carb is at WOT. Basicly the throttle and KD are synchronized to be full open at the same time....hope that makes sense.

The trans might also need a band adjustment to firm up the shifts and reduce overlap.



Ron

[BSB67]

From May 8:

"You should first do a cranking cylinder pressure test.  This will help us where you are at relative to the altitude. 

Things that can help: Cooler plugs, cooler thermostat, make sure you don't have a lean condition, heat crossover blocked, slower timing curve.

Your cam is pretty small too.  Larger cam with a larger LSA will help your cranking cylinder pressure but maintain a very docile idle."

[Cooter]

From May 8:

"You should first do a cranking cylinder pressure test.  This will help us where you are at relative to the altitude. 

Things that can help: Cooler plugs, cooler thermostat, make sure you don't have a lean condition, heat crossover blocked, slower timing curve.

Your cam is pretty small too.  Larger cam with a larger LSA will help your cranking cylinder pressure but maintain a very docile idle."

He did say thanks to all.....dontcha hate that???

[68charger440]

From May 8:

"You should first do a cranking cylinder pressure test.  This will help us where you are at relative to the altitude. 

Things that can help: Cooler plugs, cooler thermostat, make sure you don't have a lean condition, heat crossover blocked, slower timing curve.

Your cam is pretty small too.  Larger cam with a larger LSA will help your cranking cylinder pressure but maintain a very docile idle."

He did say thanks to all.....dontcha hate that???

My apologies if I have offended anyone by not naming them specifically for contributing to my ultimate solution.  I really do appreciate all of you!  I just singled out Ron because he held my hand every step of the way.   I'll be better next time in acknowledging everyone!