New 383 runs really bad/Please Help

maddart said:

Rj12yc

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have you pulled the plugs to see what they look like? if fouled.. go with the RJ14YC (typical 400ci 2bbl plug), but its a hotter plug.

have you tried a different carburetor as of yet?

I'll bring this up again, is it 180 degrees off? Its easy to do and even good mechanics can do it. Those symptoms you are describing are like what happened to my car which was 180 degrees off. Either that or probably a vacuum leak?

After i timed it to 12 degrees BTC it seems to run much better. No more rough idle. I am still concerned about a vac leak tho-How do i check for that?
Need to have mufflers put on this first then i will check plugs for lean/rich condition.

A quick easy way is to put both hands or a rag over the carb while the car is running.If it dies right away no vaccum leak if it does not die you got a vaccum leak.

either needs to be jetted fatter or use a colder plug

Kind of wondering about your guys suggestions on his carb situation??
I read things like "changing jets to make up differances in cfm"?,
"450 cfm needed at idle"?
"750cfm being to much carb for a 383cid"?
I'm pretty sure these are all incorrect.... SORRY GUYS,,, NOT TRYING TO PICK ON ANYONE!
You can never make up CFM differances through jetting...... You can only match the correct parts of fuel to a specific ratio of air. It's called air fuel ratio, and remains a theoretical constant on all naturaly aspirated engines " at least thats the goal".
If you define 450cfm required at idle, wouldn't it stand to reason that the CFM or cubic feet per minute would also increase with RPM revolutions per minute?? lets say somewhere around 750cfm??? Thats why we have a throttle plate in the carb.
Listen,, there are a lot of things one can do to "fine tune" engine performance but this guy was on step 5,,, some of you are talking about step 500......
Lets get the basics figured out "or al least try to assist" and help prevent this guy from destroying his engine by having something fail internaly.
Start with basics,,, verify top dead center on comp stroke for ingition timing base line.
inspect the valve train "it's just a couple gaskets". While your in there, verify your valves to be closed at TDC #1 cyl using a degree wheel and a positive piston stop "maybe it's assembled incorrectly". Make sure your dist is tightend down all the way "not moving around on you"
When you get it running after checking things out carefully use a can of carb cleaner to check for vacuum leaks "spray around carb base and intake" If you hear a change in RPM you got a leak.
Did you do anything with the weights and springs in your distributor? Is the air gap between the pickup unit and the reluctor set correctly?
How about good grounding for the ign module?
Dont leave any stone un turned and for god sakes, dont run the thing for any length of time when you know it's not right... you'll only make things worse on yourself.
There are a laundry list of things for you to inspect and verify,,, just make sure you don't overlook something thinking "it couldnt be that" or " I'm sure that's ok"...
Put you hands on it,,, feel it,,,, look at it.....EVERYTHING! And then my friend,, you will have your answers... they are all under the hood of that car waiting to be found...
Good luck!

67 B-body said:

Kind of wondering about your guys suggestions on his carb situation??
I read things like "changing jets to make up differances in cfm"?,
"450 cfm needed at idle"?
"750cfm being to much carb for a 383cid"?
I'm pretty sure these are all incorrect.... SORRY GUYS,,, NOT TRYING TO PICK ON ANYONE!
You can never make up CFM differances through jetting...... You can only match the correct parts of fuel to a specific ratio of air. It's called air fuel ratio, and remains a theoretical constant on all naturaly aspirated engines " at least thats the goal".
If you define 450cfm required at idle, wouldn't it stand to reason that the CFM or cubic feet per minute would also increase with RPM revolutions per minute?? lets say somewhere around 750cfm??? Thats why we have a throttle plate in the carb.
Listen,, there are a lot of things one can do to "fine tune" engine performance but this guy was on step 5,,, some of you are talking about step 500......
Lets get the basics figured out "or al least try to assist" and help prevent this guy from destroying his engine by having something fail internaly.
Start with basics,,, verify top dead center on comp stroke for ingition timing base line.
inspect the valve train "it's just a couple gaskets". While your in there, verify your valves to be closed at TDC #1 cyl using a degree wheel and a positive piston stop "maybe it's assembled incorrectly". Make sure your dist is tightend down all the way "not moving around on you"
When you get it running after checking things out carefully use a can of carb cleaner to check for vacuum leaks "spray around carb base and intake" If you hear a change in RPM you got a leak.
Did you do anything with the weights and springs in your distributor? Is the air gap between the pickup unit and the reluctor set correctly?
How about good grounding for the ign module?
Dont leave any stone un turned and for god sakes, dont run the thing for any length of time when you know it's not right... you'll only make things worse on yourself.
There are a laundry list of things for you to inspect and verify,,, just make sure you don't overlook something thinking "it couldnt be that" or " I'm sure that's ok"...
Put you hands on it,,, feel it,,,, look at it.....EVERYTHING! And then my friend,, you will have your answers... they are all under the hood of that car waiting to be found...
Good luck!

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LOL... I don't think anyone said anything about 450 cfm at idle, or changing jets to make up differences in CFM.
Maybe you should read a little more carefully before dogging everyones helpful advice. :thatswck:

I think that there are many things that could be tried before completely tearing the engine apart. He said it was built by a professional... and never mentioned that he didn't trust the work of that professional.

"put your hands on it... feel it... look at it..." ??? Best advice advice I have ever heard for making an engine run better. :werd:

dont know much about carbs , first things i would check from the sound of decription is plugs , timing , vacume leaks , cross plug wire,after that i need help lol, hope you get it lined out and enjoy it

68ChargerAG said:

LOL... I don't think anyone said anything about 450 cfm at idle, or changing jets to make up differences in CFM.
Maybe you should read a little more carefully before dogging everyones helpful advice. :thatswck:

I think that there are many things that could be tried before completely tearing the engine apart. He said it was built by a professional... and never mentioned that he didn't trust the work of that professional.

"put your hands on it... feel it... look at it..." ??? Best advice advice I have ever heard for making an engine run better. :werd:

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Whatever,,, If you've got it all figured out, then you'll just give him all of his answers and the problem is solved!

Here is the video of the engine running. Actually seems pretty strong at this point although I can't get the vacuum over 15 inches. The carb idle mixture allows me to decrease vacuum and become choppy but its pretty smooth where its at.
http://www.youtube.com/watch?v=2zQ0y2W1rzo

I think I had my 284/484 cam at 106* and ran 13-14* advance.

Since you seem to be doing better at 12* I think you are moving in the right direction.

I just kept adding advance until it started pinging under load and then backed off a hair.

This may change every time you put gas in. I tuned for 89 octane.

Air fuel ratio constant is correct. Isn't it 14.7:1?

You should have that at 400CFM and at 780CFM, at least you should try to.

Isn't that what adjusting the jetting is supposed to allow you to do?

yes adjusting jets does give you the ability to change a "ratio" but not make up a differance in going smaller in carb as suggested in a earlier post.
And yes somewhere around 14.7 to 1.... however, there are some arguing that "fact" recently?

68ChargerAG said:

LOL... I don't think anyone said anything about 450 cfm at idle, or changing jets to make up differences in CFM.
Maybe you should read a little more carefully before dogging everyones helpful advice. :thatswck:

I think that there are many things that could be tried before completely tearing the engine apart. He said it was built by a professional... and never mentioned that he didn't trust the work of that professional.

"put your hands on it... feel it... look at it..." ??? Best advice advice I have ever heard for making an engine run better. :werd:

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Maybe you should read more carefully.... No one mention completely tearing an engine apart...:bootyshake:
and yes I guess the "at idle" was a miss quote on my part "sorry", but never the less 750 is not to small for this engine! Hell from the factory slant six engines ran four bbbl carbs. Can anyone tell us what size the factory carter AVS or AFB or thermoquad would have been on this engine displacement????:werd:

Oh BTW giving credit to professionals,,,, Hmm you mocked me for getting passionate about him looking at EVERYTHING,,, and doing this by saying touching,, getting his hands on everything,,,, well guess what... I am a professional with all the certifications and degrees you could imagine a "professional" might have!! You see, this is how we "professionals" do things.. We are passionate and have fewer problems because of it!
However,, our poster is not... Now then, I'll attempt to place this passion and attention to detail into anyone wanting or asking assitance from an open forumn such as this..
Enough said on the topic!

69 383 had a 625cfm AVS on it

67 B-body I agree that everyone's opinion is what makes this forum so great. Many ideas can be brought up by others with similar experiences, and everyones input helps.

I only brought your post up because you were mis-quoting what others said (and still are), and were dogging everyone's input... then just throwing something out there like holding and feeling the engine.

No need for you to get so emotional about it... LOL... :eusa_boohoo:

68ChargerAG said:

67 B-body I agree that everyone's opinion is what makes this forum so great. Many ideas can be brought up by others with similar experiences, and everyones input helps.

I only brought your post up because you were mis-quoting what others said (and still are), and were dogging everyone's input... then just throwing something out there like holding and feeling the engine.

No need for you to get so emotional about it... LOL... :eusa_boohoo:

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And I guess you miss quoting will continue to go unspoken:angel1: (and still is)...
Get it??? :eusa_boohoo:

Dang, all this love reminds me of another site I used to visit lol

Hey, maddart...ask the builder what the cam is degreed in at and post the numbers.

I watched your video, and (in no particular order) I'll tell you the problems I see.

1st. you are running a carb that is designed for a PVC valve, but you don't have a PVC hooked up. This can be done, but the carb would need to be jetted down substantially, as the PVC provides a controlled vacuum leak that the carb is jetted for.

There is no good reason not to have a PVC hooked up, and unless you do so, you are shooting in the dark as far as tunning goes.

You can take a piece of hose and hook it to the carbs PVC nipple, with the PVC valve hooked into the end of it. Just make sure that the PVC valve has the open end pointed down as it uses gravity to open the valve. It doesn't matter if it is in the valve cover (for tuning purposes), but it must be able to function properly.

From that point, it sounds like your timing is about 10 degrees retarded. I recommend using a vacuum guage hooked to manifold vacuum while you turn the distributor to reach maximum vacuum.

You will need to readjust your idle speed (as it should be much higher as timing/vacuum increases), then adjust the timing (as described above) again. This can take 3 or 4 times till the idle vs. timing advance is maxed. Ignore the timing marks at this point.

From there, back the distributor off till the vacuum drops by about a point or so. readjust the idle, then you can actually start tuning.

You can then check for vacuum leaks by using 91% rubbing alcohol in a spray bottle, while spraying it on all the mating surfaces (manifold/carb/etc). while listening for a change in idle. Don't spray it on the PVC valve if it's open to the atmosphere as it will change the idle, but isn't relevant at this point.

Fix any vacuum leaks you may find, then repeat the whole process again till you have any vacuum leaks fixed, and the timing/idle set.

At this point you should be happy with the responsiveness of the engine, and I would suggest driving it and moving on to the road test/re-set method of adjustment, but I have to address a few other potential problems with your particular build first.

If your posting of cam specs and compression are accurate, you will need some serious octane in order to keep it from pinging its guts out. The cam is way small for the compression. So you will probably have to back the timing way off in order to keep it from pinging if you drive it, or better yet, add some race gas to continue tunning.

Your air filter is ridiculously small in both diameter and height, and should be tossed in the dumpster, as it will cause a ton of tunning problems for you, and will ultimately reduce performance.

With no fan shroud, and the fan so far away from the radiator, you will probably run into heating problems, which will cause tunning problems.

If you can stabilize all the built in problems, you can then start tuning.

If you really don't want the PVC, you will need to drive the car to an emissions station and have them test the fuel/air ratio at the exhaust pipe with the PVC disconnected and plugged. This will give you an idea of how far down you will need to jet the carb in order to achieve a good fuel/air ratio. --- Better yet, hook up the PVC as it only does positive thing for your engine from every standpoint.

The carb is definitely not to big, and from that standpoint is not your problem,

At this point, a timing light is useless, as you can adjust the timing by hand as you drive in order to find the point where the timing is advanced as as far as it can be without pinging under load. Do this with the vacuum advance connected. --- This probably goes without saying, but this is done by trial and error by advancing or retarding the distributor a bit at a time while stopped, then driving and listening, stopping and adjusting etc.

You can then use the light to see what the engine is set at (what it likes), vacuum advance disconnected and plugged, and make minor adjustments from there.

This sounds complicated, but it really only takes about 10 minutes to find the best timing setting. From that point you can fine tune everything (jetting if needed, distributor advance, initial timing, timing/octane/manifold vacuum balance, etc).

I can see you have some serious time and money invested in your car, so doing it right will make all that pay off.

Good luck.

Btw, it's a PCV ...Positive Crankcase Ventilation....but it's easy to call it PVC. I still like to know where the cam is at. A 'pro' builder should always degree in a cam no matter how small it is. It takes care of two things. 1), you know exactly where the cam is and 2), you find out if it's ground right and if the sprockets are marked correctly. I know way too many that just lined up the dots and went ahead and bent up a bunch of valves...or it ran like chit.

67 b-body's advice is the best, along with the 180 degree comment. You can do all the checks & tweaks and whatnot... but if your cam timing is off actual TDC, NOTHING else will solve the problem. Period.