is this too much initial timing on a newly rebuilt engine with performance cam?

[oldrock]

My son got his charger  back from the machine shop with a total rebuild including a mild performance cam, porting job, alum performer intake, holley 650 dblpumper and electronic ignition. Car has a nasty hesitation runs crappy when cold and even when warm has a nasty hesitation accelerating from idle to about 2000rpm. We have idle set at 850rpms and the initial timing set at 16 degrees. I did experiment with advancing the timing and it seemed to accelerate better at 20 degrees but I was concerned that would be too much initial timing. What do you guys think? Is initial timing of 20 degrees too much? I wanted to get the timing set before I start jacking with the accelerator pump nozzles and jet sizes.

[John_Kunkel]

What is the total timing? 20° initial might be OK if the total with the vacuum advance (if equipped) blocked isn't over 34-38°.

[b5blue]

If the dist. is a re-man it may be junk, I bought 2 before giving up and getting new Mopar. Set up a timing light and "map it's curve". Check the springs and function along with the bearing by removing the cap and twisting the rotor, it should snap back nicely and have no side play when grabbed and wiggled side to side, both A-1 Cardone dist I bought failed one or both tests. There was no adjustment that helped with these problems. (just saying COULD be an issue)

[oldrock]

I haven't had a chance to map the curve yet but did bump it up to 20 degrees initial timing and the acceleration off idle is much better than 16 degrees. I also did some minor adjustment to the primary accelerator pump arm to get a stronger shot which might have also helped a bit. I'll see if I'll check the timing curve at a few different rpm settings to see what is happening. BTW, I have an aftermarket electronic distrib in there. It looks like a HEI but does not have the built in coil so we are running a accel supercoil on it.

With the 20 degrees timing setting, the idle is much smoother than with 16 degrees and accelerating thru the primaries is pretty good although still a little slow to ramp up rpms. Also when we let off the gas after accelerating, it does do some backfiring thru the exhaust. Even at 20 degrees initial timing, idle is still pretty crappy till it warms up. The 650 dblpumper has manual choke and we don't even have a cable for it yet so gonna have to live with crappy idle on cold starts till we get a manual cable hooked up. Not a huge deal, just have to manually advance the idle to about 1200rpms for a couple mins for it to warm up. After that, it will hold about 850-875rpms at idle.

Oh one more bit of info, just doing some testing by putting the auto tranny in drive, it kills the engine at 16 degrees every time. With the timing at 20 degrees, it will lug the engine down to maybe 650-700rpms but not kill it. So not sure if maybe we have an additional issue with the torque converter or if it will work better once we have the carb adn timing all sorted out.   

[68r/t]

Check the true top dead center, maybe the outer ring on your harmonic balancer has moved and your not getting an accurate reading.

[oldrock]

did that when we put the distributer in and it looked correct to me (eyeballing the #1 piston movement while hand turning the engine). I'll check out the timing curve tomorrow and report back what I find. I have a mityvac gauge so will also check vacuum at idle to make sure I don't have vac leaks. 

[femtnmax]

You might need larger diameter accelerator pump nozzles on the carburetor.   The accelerator nozzle assy is simple to change and would affect cold and warm engine conditions.  Just a thought and worth a try IMO.
I had such a hassle dialing in the replacement carb on my work truck at my elevation, I ended up buying an Edelbrock O2 sensor kit from Summit.  Has a simple set of lights that tell you the fuel mixture at any engine rpm.  Was accurate enough to set all fuel circuits of the carburetor including idle, transfer ports, main metering, secondaries, and accel pump shot.  Engine runs great now.  Several experienced car mechanics have smiled as they listen to it run.

The 16-20 degrees initial timing sound like too much, with the distributor vacuum advance disconnected.   Should have about 34-36 degrees total timing at 2500-3000 rpm.  Todays cylinder heads with more efficient quench type combustion chambers do not need all that initial timing advance.

[BSB67]

Have you checked for a vacuum leak?  How large is the cam?, and what is the initial timing with the car idling in gear?

[oldrock]

Re accelerator nozzle, I was hoping to hold off on changing AP nozzles or jets until I check the other stuff first.

Re vac leaks, I didn't hear any leaks around the base of the carb or intake but other than that, I haven't checked. I'll check for leaks tomorrow to make sure that isn't the issue.  

Re cam, I don't have the full specs on the cam. I guess i could call the owner of the machine shop that did the rebuild to get the full specs for the cam if i need to. I just know we wanted a cam that would give us best possible torque while still running on 89-91 octane. We didn't go for anything too radical.

Re idle while in gear, it was doing 850-875rpms in park and dropped to 650rpms when in drive with brake on.  

[firefighter3931]

What are the cam specs ? Duration @ .050 ? LSA ? What tq converter ?

The engine is telling you it likes 20* of base timing so leave it....but check the total. If you're running vacuum advance get rid of it. 


Ron

[oldrock]

did a video of it this morning doing a cold start up so you experts can take a listen and give me your thoughts.
http://www.youtube.com/watch?v=z0vD34FwBZ4

[charger Downunder]

I thought it sounded like there is a leak in the exhaust. The popping on back off is probably unburnt fuel in the exhaust.

[oldrock]

could be a leak in the exhaust. We put new exhaust manifold gaskets on but didn't mess with anything else since Josh wants to upgrade to larger exhaust in the near future. Any thoughts on the acceleration lag or idle speed not holding as low as we want?

[charger Downunder]

I would pull the carb off and clean it inside with carby cleaner and have a close look at everything, replace needle and seat and the mixture screw gaskets cork o rings they could be pulling air in if worn. Reset float and the mixture screws on the side. Adjust idle hook up the manual choke and fix the exchaust leak.

[oldrock]

I can't hook up manual choke till my son buys one and we run the cable. That shouldn't be an issue though once the carb warms up a few minutes I don't think. Least it has never been an issue on the 750 dblpumper on my mustang.

I installed a full rebuild kit on the 650 dblpump while the engine was in the machine shop. I did a pretty thorough job on it and have done it a few times so don't think that is the issue although it could have been. I sprayed around the intake today and didn't find any leaks. I plugged the carb vacuum line for on the distributer so that isn't an issue.

One thing I didnt do is hook the PCV valve up. The PCV valve is in the valve cover but I dont' have it hooked up since I didn't have a connection for it on the new setup. DO you think that could be an issue with the setup? The power brake booster does have a second valve on it so I could try running a line to that but was concerned it would take too much vacuum from the brake booster.

[charger Downunder]

Yes get a pcv valve and hook it up. Try this get the car running and block of the pcv valve hose with your finger and see if it runs smoother i would say this is the problem.

[oldrock]

tried the PCV valve block thing and no difference in idle. Also tried connecting it to the extra valve on the brake booster and no difference.

I went ahead and got some timing readings at different rpms so thought I would post them up to see what you guys think might be going on. These are with the electronic ignition setup and the vacuum advance is capped off on the carb and on the distrib. Base idle was 950rpm and max seemed to be at 2350 and 37 degrees.

RPMS timing
950 -  20
1500 - 23
1750 - 29
1900 - 32
2150 - 36
2350 - 37

I was looking around in the engine bay and thought I should also report that fuel regulator is inline and set to 4. Doesn't seem to be starved for fuel at higher revs so figured that was ok but sure would like to get that idle down. Also don't like the fact it dies when put in drive unless I have it at least 950-975rpms. When in drive or reverse, rpms drop from 950 to 650 and rough.

[Paul G]

Can you borrow another carb, known to run right, from someone to try? I have had fits with carbs that just wont run right. Holleys are not the most friendly thing to tune. Idle adjustment effects accelerator pump and on and on. Was this carb on the engine prior to rebuild? How did it run?

[oldrock]

I bought the carb and intake used as a set. Guy said it was running but who really knows on that stuff. Only other carb I have is the 750 dblpump on my mustang and think it would be way too much for the charger. It is really getting me down. Car is ready to go if it weren't for the crappy idle. My son wants to drive his charger badly but it would not be safe to let him till we can get the car idling properly. I thought about maybe buying a carb but that would really add alot of cost to the rebuild so hoping we can get the holley sorted out. I am a holley fan and the 750 on my mustang runs great. Don't understand why the charger doesn't run great too. 

[oldrock]

was doing some research online and might have found something out about my problem. There was a post about a guy with a similar problem with his 318 and he decided it was because the aftermarket pointless distributer and supercoil he put on needed the full 12 volts for proper operation. So what he did was a fairly elaborate rewiring of his harness to emininate the ballast resistor. I am wondering if I could not do a simple fix to test that theory and just rig up a short jumper wire to bypass the resistor by running the wire from the ignition side directly to the positive on the coil. Before I try it and mess something up, I thought I should run it by the experts first. Is that a way to do it or is there another better way to bypass the ballast resistor? The other thing I can think of is to just attach a jumper between the two wires on the resistor. 

[oldrock]

I have great news!!! I soldered up a little jumper to put between the two leads on the ballast resistor and it worked like a charm. Now the car idles nice and slow and no more dying when I put it in drive or reverse. Apparently the lower voltage thru that resistor was messing with low speed operation and the way it accelerates. Hard to believe a homemade 50 cent jumper fixed the fast idle and poor acceleration issues. Josh drove the car when he got home from school and we both were grinning ear to ear 

Still need to sort out some minor stuff such as a proper brake bleed and do a few minor tweaks but that rebuilt motor sounds great and the HP increase is very noticable to say the least. Thanks for all the help guys... looks like the new improved charger is back on the road.

[FLG]

Is that coil meant to be run at 12v?

Because if its not your going to fry it.

[oldrock]

it is an accel superstock 42k volt coil and says 12 volts so I think it should be fine but i guess time will tell. The car is running SOOO much better now though that even if it shortened the life of the coil, I'd leave it set up this way and just replace the coil when it crapped out. 

[Paul G]

You fixed it, great.

I am running an MSD 6A box with a Mopar distributor. I removed the resistor and associated wiring just to clean up the firewall.

[elacruze]

The ballast resistor is only there to protect points and condenser. You don't need it with an electronic ignition.
Your Accel supercoil draws more current than a stock coil too, which is another reason it was weak at low rpm. As rpm goes up, so does alternator output and system voltage.
Nice catch, by the way.