[Badrat496]

My combo
BBC 454
stroker crank 4.25
10.2 compression
ultradyne hydraulic roller 245/253 @ .050 650/650 lift 110 lc
850 holley DP
Team G single plain
MSD Ign.
Everthing is new on this motor.
My problem is it was running pretty good but I had to have the idle set higher than normal for it to idle. I know transfer slots exposed to much and running rich but it still had a smooth but lopey idle and reved smoothly. All the sudden it started running rough no matter what rpm. I changed the plugs no change. I sprayed the intake and carb looking for vacuum leaks no change. Vacuum gauge on it and it jumps from 5 to 7 inches at idle 1200 rpm. So I locked out my dist. at 35 degrees to get more vacuum and idle no change. Pulled the valve covers and the springs looked fine. Placed timing light on all wires and all were firing ok. Checked rotor and cap still look new. Help!

 

[69-CHVL]

Sounds like something is off, I figure you should have around 10" at least, at around 1000rpms or less. I would check your valve adjustment, sounds like one maybe too tight. Vacuum gauge should be relatively stable.

 

[Badrat496]

But why would the valve adjustment change after say 50 miles? I run Comp. Cams gold roller rockers and locks.

 

[69-CHVL]

I dunno....maybe a polylock came loose, lifter failing, lobe wearing down, valve seizing in the guide, etc, etc. Is the timing stable...dizzy gear could be wearing. Lotta things to check.

 

[Badrat496]

Got to crash for awhile but I hope someone out there can shed some light on my problem. Thanks in advance and to 69-CHVL for the quick reply.

 

[Badrat496]

Timing is stable. Polylocks are tight. I was hopeing to find something on the outside but may have to pull the intake anyway. Thanks. I will check back in the morning.

 

[kettbo]

If your transfer slot is outa whack...sounds like not enough initial timing...
If 18 degs initial does not do it, crack open the secondary blades a bit.....

 

[Badrat496]

Timing is locked out at 35 degrees

 

[Jason Snyder]

are the boosters dripping fuel ?

Another question , what do you mean by runs rough ? like sputtering ,loading up , missing ...............there are so many ways to be roough !

 

[Badrat496]

No dripping just doesn't rev as smooth like a bad plug wire. I changed carbs and it seemed to smooth out some and my idle vacuum is at 7 inches steady now. But I still have to turn the idle screw way down to get it to idle at a 1000 rpm and the mixture screws do nothing at this point due to not being on the idle circuit.

 

[jmarkaudio]

You can try turning the secondary blades up a little to get the primaries down, otherwise you may need to drill a couple holes in the primary blades. Start at 3/32 and reset the idle. If that still isn't enough put a pair in the secondaries. It will not run right trying to idle in the transition circuit.

 

[Badrat496]

Does this mean its running lean as it is?

 

[kettbo]

Listen up.
You already identified your problem....the throttle blades too high on the transfer slot.
If it is not adjusted right, the idle circuit will not work right and you will have poor idle quality.

Unlock the distributor and set the vacuum advance back up...probably not talking race car with a HR cam... You want 18-20 degs adv in the distributor.

As I posted in another thread this week, here is the fix.
Warm the car up. Shut it off when warm.
Unwind the idle speed screw so the blade closes. Go back in 1.5 turns exactly. This sets the edge of your front blade on your transfer slot perfectly. Loosen the dist hold down a bit. Start the car and advance the timing until you have a good idle low idle.
Tighten the distributor down. Set your idle mix screws. Re-install your vacuum advance. The idle should come up a bit (use a full vacuum source, not ported vacuum).

 

[Badrat496]

The distributor is a MSD 85551 and does not have vacuum advance so I locked it out at 35 degrees in hopes of more idle RPM and vacuum and I still only see 7 inches at idle.

 

[kettbo]

ok, let me think....
DId you crack open the secondaries so you could lower the front of the primary blade?
Drilling the throttle blades is a last resort.....

 

[Badrat496]

I opened the secondaries to .020 and it seemed to help but the primary slot is still like
.080 or more showing.

 

[Badrat496]

Thanks for all the replys so far I have to get some sleep so I can work on this thing again in the morning. I will check back here to see if you have any more suggestions.

 

[kettbo]

I opened the secondaries to .020 and it seemed to help but the primary slot is still like
.080 or more showing.

OMG...horrible!!!!!!

 

[Badrat496]

What do you think of drilling the throttle blades?

 

[oldtimr]

What do you think of drilling the throttle blades?

hard(but not impossible) to undo. You always feel like your 'repair' is either going to go down the engines throat or is interfering with smooth flow etc.

for just a quickee test to see if this thing wants more air open a large vacuum hose and restrict or regulate the air with your thumb, and if it likes it then you know you will be able to tweak it back into the idle circuit.

The use of the secondary butterflies is what I usually do.