[Stroked 82 El Camino]

Ihave a 383 and no matter what i have done i cannot get rid of this missfire,it only happens at cruzing speeds but its at 3,000 rpm every single time.Any advice?

10:5:1 comp, edelbrock per rpm 64cc heads,comp cams XE 294/306duration
519/523lift,victor jr intake,edel 750,hei w/6a???????????

 

[Bob West]

Too lean? Have you changed jets/rods in your Edelbrock carburetor? I personally have tried and do not like the Edelbrock carb for performance applications, but I'm sure they can be tuned to work okay. How do you have the timing set? How much advance and total timing? Usually at cruising speeds its a lean condition.

 

[69-CHVL]

As Bob suggested try upping your jetting a touch - I don't know how that works on an eddy.

When my jetting was lean, I had a tip-in stumble that no amount of accelerator/timing adjustment could fix.

And put a timing light on there to make sure your advance is working smoothly.

 

[forcd ind]

you might try a little stronger springs on the metering rods-with vacume, the rods are sucked down, using the fatter part of the metering rods-as you lose vacume, the springs overcome the vacume, lifting the rods to a thinner part, allowing more fuel-the heavier the spring, the sooner the enrichment-this may not be the problem, i would also ck vacume @ idle, it may not be very good with the cam, causing a rich condition, and a fouled plug can cause the same problem, the spark is weak when more power is needed, causing a misfire-the edelbrock carb is a great carb to tune on, you can move the fuel curve all around-of course, it can always be ignition related, but i would mess with the carb first-by the way, someone didnt leave a 3k chip in the rev limiter, right(dont laugh, i have seen it happen) good luck
this would be neat to have an LM-1 meter hooked up to ck a/f ratio

 

[vrooom3440]

This is an area where a wide band O2 setup is very useful... as well as a vacuum gauge.

What carb are you running specifically (manual or electric choke model)? What rods and jets are you running on the primaries?

I doubt that the springs in the carb are the issue here as you really do not want them popping into rich under basic cruise. They also do not affect idle/transition mixture at all. What is your vacuum during this cruise mis-fire condition?

I have built an Excel spreadsheet that lists all of the available jets and rods for the Edelbrock Performers and calculates the effective jet sizes for cruise and power settings. Using it I can find combinations that Edelbrock does not list in their tuning pages and/or see how far apart variations are. The jetting is really not that complicated, it is just area of jet minus area of rod.

You are pretty far up the cam space and I would guess you run a fairly low vacuum at idle? Probably less than 8"? That can play havoc with the idle/transition circuit and idle speed settings on the Edelbrock carbs. I suspect that their calibration is optimized around a 350 with perhaps a 270 cam and dual plane intake. I find that my 750 stops flowing fuel from the transition circuit right about 7" of vacuum making for a huge stumble coming off standing starts.

Based on my experience, and this echos what has been said, your stumble probably correlates with a lean AFR. A rod/jet change may be in order.

 

[Jerry70]

Maybe a timing issue? If you're running a lot of timing and it's coming in about then it could be detonation. With a loud exhaust you might not hear it but you'll sure feel it. If it's only at cruise (not wot) and you're running vacuum advance, try disconnecting the vacuum advance for a test.

 

[SS4speed]

Stroked,

If you find that it doesn't seem to be the carb, take a look at what Jerry stated. I was asked to look at a 383 that was doing the exact same thing. It turned out to be the springs on the weights in the hei dist, they were too strong. Once we had changed the out to lighter springs, the surge was gone and it ran one heck of a lot better in the upper rpm too. It was about the same engine without the 6A.

Fred.

 

[Stroked 82 El Camino]

Jerry Is Rite On Cuz If I Disconnect The Vac. Advance Its Better .if It Matters I Just Put The Edel. On.i Removed A Holley 650 D Pumper W Mech Sec And Same Issue.CAN U GUYS TELL ME YOUR OPINION ON THIS SET UP, PRESENTLY IM BUILDING A 383 W A ROLLER 350 BLOCK(1 REAR MAIN)AND I WANT THIS TO BE RITE ON THE MONEY IF I GET MY DREAMCAR "69 CHEVELLE SS"PLEASE LET ME KNOW IF ANYBODY HAS ONE FOR SALE.THANKS FOR ALL YOUR HELP.

 

[Bob West]

LOSE THE CAPS!!! A lean condition causes detonation too!!! you edited your post cuz you forgot

 

[69-CHVL]

How about trying ported advance vs. manifold...may give you a little less advance at cruise.

 

[vrooom3440]

How about trying ported advance vs. manifold...may give you a little less advance at cruise.

That would be some cruise to get the throttle closed enough to close the vacuum port. Heck I use the vacuum port to set my throttle blade idle position. I back out the idle speed screw until the vacuum goes away on that port. So you have to pretty darn close to idle before that port closes.