Am I lean?...or should I go bigger?...HELP!!!

[Falcon Ranch]

Hey guys...first post here...
I am having an issue with my Holley 350 carb...or it could be an ignition problem...I am not sure because everything is brand new except for the original distributor which is in great condition...no slop on the shaft.

I will start from the beginning...the motor;
**200 4bm bored 60 over
**Comp cam 260 dur. with .500 lift
**72 truck head with 78 size valves and new springs/seats/guides
**1.6 roller rockers w/chrome molly push rods
**Tri-Y header w/2.5" exhaust
**Igniter points replacements with hotter coil, stock cap/rotor/wires all new!
**New outta the box Holley 350cfm carb 2300series
**Trans-adapt adapter plate to fit Holley to intake

When I first took the carb out of the box I replaced the stock jets(61) with some 55's, thinking that the 61's would be too rich...started up the motor and it shook pretty bad, hard to stay running, gotta keep feathering the pedal...after 5 minutes of warm up the engine settled down to a fairly smooth idle...I believe the cam is causing the shakes cuz the exhaust tone at the tail pipe is singing a nice steady rumble...so I let it idle for awhile and it looked good so far...I cracked the throttle plate and it stumbled upon itself...if I crack it open about 10-15 degrees it has a terrible miss and shakes worse...if I give the throttle a good shove to full throttle and let off it runs smooth cuz of the accelerator pump adding extra fuel...so I called Holley tech department and they told me that I should of left the 61's in the carb and went from there.

Well, this morning I put the 61's back in and fired up the motor...same thing, I had to keep feathering the pedal and working the choke...after it warmed up it settled into a nice steady idle with only a slight shake...when I crack it open 10-15 degrees it does the same thing but not as bad as before...so does this mean that I need to go even bigger?

The idle jets are set at 1.5 turns...the exhaust doesn't smell rich at all...the calculations show that this carb is ideal in size for the cubic inches I have...isn't this 61 size jet ideal for this carb or is it an in-between size meaning that I could go bigger then what the Holley came with

Any racer experience in tuning or size recommendations would be very helpful...Thanx

 

[gtm1086]

Seems to me I went up to around a 65 or so high speed jet. Also check your vacuum at idle.If you confirm that you have no leaks and it is low you may have to go to a smaller power valve.

Once dialed in this is a great carb for your motor

 

[Falcon Ranch]

Thanks so much for the quick reply gtm1086

I did call tech support again and they said for me to change my power valve with the car in drive...so I went out and found the sweet spot with the timing...then adjusted my mixture screws again...after the mixture screws killed the motor, I backed them out to the setting before it died plus another 1/8 turn out...vacuum reading was 13"s

Once the motor was warmed up, I was able to get a vacuum reading while in drive...reading 7.5-8"s...so I believe that a 3.5 power valve is in order.

I believe I will also take you up on the jet size advise too...what the heck, can't hurt anything.
Thanx again!

 

[gtm1086]

Here's another thing give the motor as much timing as it will take.

Also one of the best things you can do is to go eletronic ignition either a Dura Spark unit or get one of the DUI units Mikes sells at classic inlines. I'm running a Mallory with a Mallory high five just to be different.

 

[Falcon Ranch]

Well, this is where I am so for...I'm up to #69 jets and I still have this misfire at constant speed...at this point it's not as bad as before but think that either another step down from the 3.5 power valve to a 2.5 or 3 might fix this...but I have spent 50 bucks so far on jets and the new power valve...I also have this new roller rocker assembly that I have adjusted twice but still am getting rocker noise.

So would the valves being out of adjustment even a little bit cause this misfire I keep getting?..I am almost at my wits end here...I am desperate for an answer...all I know is that only when I gun the throttle does it run good, no miss at all...to me it does seem carb related because at idle, it runs pretty good but does shake a little...I think it is cam related but not sure.

I called a shop yesterday that did performance work and dyno tuning...when I told him what I had he had said if it didn't have a computer he didn't want to work on it...can you believe that!?

As frustrated as i am at this point, I am almost positive that the problem is something absolutely stupid simple...I will take a break from this for awhile and wait to here from some experts here.

Also, does anyone here know anyone in El Paso that can dyno tune this beast?

 

[Falcon Ranch]

Here's another thing give the motor as much timing as it will take.

Also one of the best things you can do is to go eletronic ignition either a Dura Spark unit or get one of the DUI units Mikes sells at classic inlines. I'm running a Mallory with a Mallory high five just to be different.

I did check today about getting a Mallery distributor but the shop wanted $430 bucks for one!...also when I advance the timing it does seem to run a bit smoother but kills the motor when I put the car in drive...it doesn't like that much timing I don't think...it seems that the motor is loosing too much vacuum.

 

[wallaka]

Here's another thing give the motor as much timing as it will take.

Also one of the best things you can do is to go eletronic ignition either a Dura Spark unit or get one of the DUI units Mikes sells at classic inlines. I'm running a Mallory with a Mallory high five just to be different.

I did check today about getting a Mallery distributor but the shop wanted $430 bucks for one!...also when I advance the timing it does seem to run a bit smoother but kills the motor when I put the car in drive...it doesn't like that much timing I don't think...it seems that the motor is loosing too much vacuum.

Wow, for that price, there is NO reason not to get a DUI. That is a ridiculous price for a distributor.

The only reason I don't have a DUI is that a used MSD 6 + DS2 was 100 bucks.

 

[gtm1086]

I bought my Mallory on E-Bay for around $150 new. With that said I sure would recommend looking at either the Dura Spark or the DUI from Mike. Your motor will like it very much

As for a dropping to a lower power valve I don't think you need to. Try going up to a #71 jet and once again take a real good look at updating your ignition system

 

[Falcon Ranch]

OK...I pulled the plugs and found them to be glossy black on the face...which means that I am still too rich...so what I did was jump not only the power valve size but also the jets...so all this time I was thinking it was a lean misfire was actually a foul miss...so I will try going back down on the jets while playing with the #35 PV...I should eventually find what works...I will be back with results after X-mas...thanks for all the tech advise you guys are giving.

Dave

 

[Inline6Merc]

Your motor should be pulling about 17-21" of vacuum not 13". I would say you have an improper seal (vacuum leak) between the carb, carb base, and or intake. just my two cents!