Holy Cow ... Sputters and stumbles at 4000+ rpm

[msampsel]

Well I installed a new fuel pump and a regulator and sitting at ~ 3 psi into the rear or second carb.
Car is still sluggish. Checked for spark at each plug and get it.

Car starts fine but idles rough. Pull on dogbone to rev engine and it is missing and sluggish.
Hold dogbones up high enough and the engine seems to catch up. Might need to do this test again too hot to do it
more than once today

This seems to point to carbs or is there something else? Also removed gas cap for the venting test and
no change.

Somewhere I saw exhaust system blockage caused some weird stuff, I know mine has some
shaky metal in the muffler. Anyone experience exhaust blockage problem?

[msampsel]

After the way lean inputs I received from some of the members herein,
I cleaned the carbs etc and set the mixture to 1/4 turn richer and made sure I have 3 psi.
The car vacillates from 400 to 1600 rpm as gas added. And now the plugs look like this (3, 2, 1 cylinders):

P1040018.JPG

They were like this on 5/15.

P1040007.JPG

I must be mistaken right, only 1/4 turn and I get this change??

Keith (AKA CKtrap) .... Unused JT68 SS Exhaust system heading to eBay soon (check often and early)

Thinking maybe my coil voltage is weak. Does not seem to be fuel pressure.
Plugs looked like todays plugs once before and I adjusted the ADQ needles to set a leaner idle.
Seems maybe this was not the issue though ... doh!

Heck we can't all have perfect roadsters else no need to donate to S Allen!

[cktrap]

Keep me posted but I'd rather hear it on yours! I'm about four weeks from sticking my engine. Hope to install the dash next weekend. Most of the interior is done. I need to get the seats off to have the covers put on. I'm seeing light at the end of the tunnel. It's been a year since I've driven it. Starting to jones.
Keith

[fj20spl311]

GIVE UP and Buy a MSD, I like the 6AL but the Street Fire looks good.

[Daryl Smith]

Just a thought....Are all your electrical connections and grounds good and solid?

[Gregs672000]

The plugs are telling you that you have too much fuel. That is being caused by either a spark/ignition issue, or a carb issue. It cannot be too LEAN a condition if those plugs represent how the engine is burning fuel in all condition, so we know it's not fuel pressure or anything that relates to making enough fuel available to the system, right?
So either the engine is not firing the fuel properly, thusly fouling the plugs, or the carbs are way overfueling. I'm guessing we have a spark problem.
So, let's first put the carbs back to "last known good" settings (lean a 1/4 turn?). Then let's check timing and confirm advance. Then let's eval the distributor (points or EI?), coil, etc. May swap out a couple things like the coil. Let's also confirm a few other things, like making sure the valves are openning and adjusted/set as expected (cam went flat? Probably not, but ya never know, and that would likely result in some poor fuel burning). Time to be automatic systematic! The plugs are speaking to you. Unfortunately, with out that ol A/F wideband meter I've been pushing at you ( ) we don't know if your high speed running issues are due to a lean condition or not...
But right now, she's way rich and you need to figure that out first.

[Gregs672000]

You also mentioned back pressure in the exhaust. So how hard does it push your hand if you take a thick rag and cover your exhaust?

[msampsel]

The plugs are telling you that you have too much fuel. That is being caused by either a spark/ignition issue, or a carb issue. It cannot be too LEAN a condition if those plugs represent how the engine is burning fuel in all condition, so we know it's not fuel pressure or anything that relates to making enough fuel available to the system, right?
So either the engine is not firing the fuel properly, thusly fouling the plugs, or the carbs are way overfueling. I'm guessing we have a spark problem.
So, let's first put the carbs back to "last known good" settings (lean a 1/4 turn?). Then let's check timing and confirm advance. Then let's eval the distributor (points or EI?), coil, etc. May swap out a couple things like the coil. Let's also confirm a few other things, like making sure the valves are openning and adjusted/set as expected (cam went flat? Probably not, but ya never know, and that would likely result in some poor fuel burning). Time to be automatic systematic! The plugs are speaking to you. Unfortunately, with out that ol A/F wideband meter I've been pushing at you ( ) we don't know if your high speed running issues are due to a lean condition or not...
But right now, she's way rich and you need to figure that out first.

I checked timing quick with advance connected and at 1000 rpm I see 20 deg BTDC. The total advance was 35 degrees.
This does not appear to be an issue.

Right it is a "wee" too rich. Will go back to 1 turn off closed for the mixture.
New plugs and fingers crossed. Want to get engine warm and check the compression again which was 175, 175. 177, 180 just 100 miles ago.
Will run the crank to TDC and verify both valves on number 1 are closed.

Points are new, 300 miles, they should be fine, but I'll check them. I tried two different condensers too. Same result. Both
have very few miles on them.

Leaning towards getting MSD coil (45 K volt) and CD system at the moment

[msampsel]

Just a thought....Are all your electrical connections and grounds good and solid?

Sure think so Daryl, I'll glance at em again. 12.5 volts at the condenser connection with points open and ignition on.
No rust were the ground attaches to the frame. Seems good there.

[Gregs672000]

I've run the MSD coil before, worked well. My favorite spark box was the Jacobs Pro-Street set up with the Ultra coil. Not made anymore, but far superior to my old MSD 6A.

OK, so timing is right, question is she sparking consistently then? If spark checks out, then the next step is fuel ratio as you indicated. I would still pull the plugs and hand rotate the engine while watching the valve springs and making sure they are all compressing the same (no cam flat spots or lobes going away). You have a high lift cam and it should be obvious that the springs are compressing fully. Just a guess. Did you check your theory on exhaust back pressure?

[Linda]

IMHO I would revisit setting the carbs to the "magic number" in the Wiki and see what you have. Then adjust them as necessary by number only, not the 1/4 turn method, as I have found that way can be inexact and excessive.
Using a ColorTune is good too.
Linda

[msampsel]

IMHO I would revisit setting the carbs to the "magic number" in the Wiki and see what you have. Then adjust them as necessary by number only, not the 1/4 turn method, as I have found that way can be inexact and excessive.
Using a ColorTune is good too.
Linda

Linda,

Magic is something I need! The magic number you refer to Linda ... is this the offset between the jet (or nozzle) and the
the round brass piece in the carb body?

Amazed there is a way to measure this to 3 one thousandths of an inch (i.e. the 0.087 inches vs 0.09 inches quoted)
What caliper measures this distance? No picture of the caliper used to measure the offset. Maybe done under the carb body ...

So under the carb (using the spare I have) I find 2 full turns of the mixture knob is approximately the "magic number" 0.09 inches.

I found other hints at starting at 2 full turns for HS carbs.
here as example
http://www.nicoclub.com/archives/2-writ ... carbs.html
Seem to recall someone suggesting this and painting the richness knob. Mine do not have the bumps on them
So I've painted the knobs with different colors every 90 degrees (this has done me a lot of good as you can tell by this thread of epic proportions ... (keeps me off the streets!).

Certainly has me thinking still ... a lot richer than the 1.125 turns which caused overly rich looking plugs.

[Linda]

Just get yourself a Harbor Freight digital caliper ( and a free flashlight ) which can measure accurately with the little extending piece from the end. Insert it down into the bottom of the opening that the nozzle comes thru and measure. Get that .086, or .087 measurement (whatever the magic number) on each carb ( you have of course taken the domes off). Now you are even and can start from there. You might measure both of them first, just to see how uneven you actually were to begin with.
Drive the car after reassembly and pull the plugs. Too rich or lean, then readjust by number and measurement to be most accurate. Yes, I know it is a pain, but this way you maintain balance. Most of the time the magic number is all you need. All my experience, YMMV.
I was way uneven on adjustment when I first did this, which is why I only use this method now.
Be sure there is no binding of the needles by tightening the domes slowly and evenly and checking for free movement.

Linda

[Daryl Smith]

"For posterity I did all the electrical adjusting with dwell at 48 now, took it for a spin or two.
Still stumbling at high rpm, pulled the choke and no change, and the car dies at times and when it dies the turn signals do not work
and the fuel pump quits too."

The above still has me thinking there is a possible loose connection somewhere.....
I would check the connections around the starter and fusebox to start with...you've been in and out of the distributor so those/that connection should be good...but that wouldn't affect the signals/fuel pump....

[Gregs672000]

"For posterity I did all the electrical adjusting with dwell at 48 now, took it for a spin or two.
Still stumbling at high rpm, pulled the choke and no change, and the car dies at times and when it dies the turn signals do not work
and the fuel pump quits too."

The above still has me thinking there is a possible loose connection somewhere.....
I would check the connections around the starter and fusebox to start with...you've been in and out of the distributor so those/that connection should be good...but that wouldn't affect the signals/fuel pump....

Didnt see this info before... I must have skipped over it. I agree.