1970 440-6 miss??

Posted By: Anonymous

1970 440-6 miss?? - 07/13/08 11:43 PM

I drove my cuda for the first time yesterday with no miles on it. It seems I am getting a steady miss or surge. It almost feels like I am driving into an eighty mile per hour wind. I moved the timing from 10*BTDC to 6*BTDC to see if that will help but have not had a chance to test drive. Does anyone have an idea as to what may be wrong. Everything on this car is brand new, less than forty miles.

Posted By: W5Duster436

Re: 1970 440-6 miss?? - 07/13/08 11:48 PM

I can almost guarantee you that you'll need around 20 degrees of initial advance and 16 mechanical.

What cam specs etc? We need to know as much information as possible for your setup.

Posted By: Anonymous

Re: 1970 440-6 miss?? - 07/13/08 11:52 PM

when we did the engine we bored 30 over, went with a stock cam, used the original crank. I did nothing special tried to keep the engine original but not happy with the way it runs. It does not seem to miss or run funky on acceration and it also starts very easy. Are you guys saying I should set the timing with the vsacuum plugged at 16* BTDC

Posted By: UCUDANT

Re: 1970 440-6 miss?? - 07/13/08 11:56 PM

Yes block the vacuum while setting timing. He means 20 degrees BTDC intial timing and mechanical advance should be limited to 16 for a total of 36 max. I think the general rule is 34 degress max total for small blocks and 38 for big blocks.

Posted By: W5Duster436

Re: 1970 440-6 miss?? - 07/13/08 11:57 PM

Quote:

when we did the engine we bored 30 over, went with a stock cam, used the original crank. I did nothing special tried to keep the engine original but not happy with the way it runs. It does not seem to miss or run funky on acceration and it also starts very easy. Are you guys saying I should set the timing with the vsacuum plugged at 16* BTDC

You want to put as much initial timing close to 20 degrees in it as it will take before it drags the starter while cranking. Do this at idle with the vacuum unplugged/blocked. What type of distributor are you running? Stock, mopar performance etc? Basically you want 36 degrees total advance using the initial + mechanical advance. You may have to modify your mechanical to limit it since stock timing was much less. Usually this must be done because of larger cams but also because gas is basically crap now compared to yesteryears.

Does it not seem to have any power? What are the symptoms exactly? Your mechanical timing may be off too. With a 440+6 you should be able to hammer it and break the tires loose easily.

I guess another question is did you break the cam in? I know this isn't stuff you want to hear but if you just started the car up on the initial startup and didn't let it run at 2500+ rpms and throttling it for 20+ minutes you may have damaged the cam. This could potentially wipe a cam lobe which would definitely make it run like that. You would also tend to notice it feeling like it was running on 7 cylinders though too.

Posted By: Anonymous

Re: 1970 440-6 miss?? - 07/14/08 12:05 AM

I have a mopar perf distrib in it with no points and a flame thrower coil. As for exactly what it does is it starts easy and idles great. As I accelarate it seems like I am driving into a very strong wind and when I get up to speed and hold at a steady speed the car seems to surge or miss I am having a haed time telling. I pulled all the wires and plugs this morning and everything looks great but as I said I had the timoing right at 10*BTDC abd now moved it to 6* but have not driven yet. I will try m oving it to 20*BTDC and try that, do you agree?

Posted By: Anonymous

Re: 1970 440-6 miss?? - 07/14/08 12:07 AM

broke the cam in correctly and used additives recomended by the outfit that helped me rebuild the engine

Posted By: W5Duster436

Re: 1970 440-6 miss?? - 07/14/08 12:15 AM

Since you have mopar performance distrib there's really no reason to run the vacuum at all. You'll just set your initial timing at 20 BTDC for now and then see how much total timing you have at 3500 rpm or so. Do you have an adjustable timing light so that you can dial in? That is a necessity to check your total timing.

Even at 10 BTDC you should have not felt a power loss. I would also look at fuel pressure and make sure you don't have a kinked line or something. Make sure your float levels are correct and your linkage is not binding on the secondary carbs. Sounds like it may be running majorly lean too so definitely double check the carb float levels.

After that I would also run a compression test just to be sure that you didn't wipe a lobe. If it idles smooth though you're probably okay. You would tend to hear it if the cam got smoked. Remember the '78-'79 chevy camaro with the lobes that wiped? Nearly everyone I knew with one had the cam go south. Even the trucks tanked. I can still remember hearing them and the sound the engine made with wiped lobes.

Posted By: Anonymous

Re: 1970 440-6 miss?? - 07/14/08 12:40 AM

I thought of one more symptom. I noticed yerterday that I got a backfire through the exhaust at idle once in a while

Posted By: torkrules

Re: 1970 440-6 miss?? - 07/14/08 02:32 AM

Quote:

I drove my cuda for the first time yesterday with no miles on it. It seems I am getting a steady miss or surge. It almost feels like I am driving into an eighty mile per hour wind. I moved the timing from 10*BTDC to 6*BTDC to see if that will help but have not had a chance to test drive. Does anyone have an idea as to what may be wrong. Everything on this car is brand new, less than forty miles.

Wow, I had the same problem with the Hemi in my Roadrunner. i found it was a combination of things (took me a few MONTHS to figure it out). Today was the first day it was surge/miss free.

Too much advance
Too quick an advance curve
Transition circuit in the carb was too rich

The figuring out part sometimes takes a lot of experimenting. Heres my

Advance: Normally wedge motors like between 34-38 degrees total timing. As someone mentioned, try to run about 14-18 initial advance. The rest will be mechanical (vacuum unplugged). If you have a newer style MP distributor, the mechanical advance is adjustable. If it's the old style, you have to weld up the slots or get the kit from the guys at "four seconds flat".

The curve should be all in by 2600-3000 rpm. For a drag car than 1500-2000. Too quick a curve will cause missing/surging, pinging, etc. This is accomplished by changing the spring in the dizzy. Sometime it won't like the vacuum advance. If it's a newer MP dizzy, they are adjustable. You may need to leave it disconnected.

The last item is mixture. Since you have a six pak, you'll be messing with the middle carb. Set up the mixture screws using a vacuum gauge (highest vacuum). Take the carb off and look at the the slot near the throttle plates. Only about .020" of the slot should be showing once the idle speed is set.

Make sure the power valve is good and has the correct opening point. Read the highest vacuum at idle and go a couple of point lower.

Are the stock jets in the carb? If not, install the stock jets and try it again. You may need to go up and down a couple of sizes from stock to see if it has any effect.

Good luck and let us know how you make out.

Posted By: W5Duster436

Re: 1970 440-6 miss?? - 07/15/08 05:51 PM

any progress?