Not a cobra, but I need some FE help

[d_ford]

Hey everyone,
I haven't posted here in quite some time since I sold my last ERA but I've been busy building a 68 mustang fastback with a 427 tunnelport engine. I finished the car and have driven it some but it has an issue I just haven't been able to figure out. It starts and idles great, drives very nicely as long as I accelerate slowly but as soon as I step down on the gas it starts cackling through the exhaust and doesn't really increase in power at all.
The engine is an aluminum 427 FE with alum. tunnelport heads and 2X4 intake. So far I have installed both new carbs from Pony Carburetors, changed out the pertronix unit in the dist. for points and condenser in case the pertronix was fried (it wasn't so I put it back), installed a pertronix flamethrower II coil, disconnected the vacuum hose between both carbs effectively turning it into 2 two barrels, advanced and retarded the timing, replaced the fuel pump, new cap, rotor, wires and plugs, checked float levels in carbs, and probably some other stuff I can't remember.
I was hoping with the vast knowledge base here on this forum someone may have additional suggestions or possibly suggest someone in the Ohio area to take it to. I'm about ready to give up on it. I've heard good things about Paul's Automotive Engineering in Cincinatti, anyone have any experience with them? I need someone good with FE's and multiple carburetion if I can't figure this out myself. Any help greatly appreciated. Thanks.

[rustyBob]

A tooth off on the timing????????maybe.

[Argess]

I have a 2x4 set-up from Pony Carbs. I find that changing to the Holley Blue Accelerator Pump Cams helped a lot with acceleration. Cheap to try. Don't forget to buy 2 kits.

Also, consider setting your initial timing up a bit. Just keep your max timing at 38 or below. I am currently running at 20 deg intial and there's more room to go. With your heavier car, I still would try keeping it up past 18 if you have any kind of performance cam installed. If you are using a vacuum advance, all this is not so critical to acceptable performance.

I dont' think this would cause your issues, but is your linkage progressive and adjusted right? Both carbs should arrive at fully open at the same time, but front carb is open about 30% (more or less) before rear one opens.

Finally, does it belch balck smoke? If a power valve fried, then it will run rich at low rpms and make acceleration difficult.

PS: I just reread your post and see you ahve tried some of the things I mentioned. But, put your vacuum balance tube back on. That shold not be an issue. Rusty Bob is corect about timing being off a tooth causing trouble, but miostly it causes a limit to rpms, not some of the things you are experiencing. Typically, if an engine accelrates fine slowly, but not under ahrd accelration, it is a accelerator pump issue. Try the blue cams in #1 hole first, then perhaps #2 hole if needs be. Tunnel Port....may need a ton of fuel to get it revving into the power band where the main metering takes over.

[d_ford]

I don't think that's it. Initially I set the timing with a light and it was right on, and then timed it by ear when that didn't help. It runs perfectly at idle and normal easy driving so if it was off a tooth it would show up there too.
Thanks for the response though.

[rustyBob]

valves set to tight????????????maybe

[d_ford]

Argess,
The linkage looks like it's adjusted correctly. It does create smoke from the exhaust when I accelerate at all except very easy, that's when it pops and cackles through the exhaust. It seems to do it when the secondaries would be opening but when I disconnected the vacuum hose the should have eliminated the secondaries altogether. I used Jon's advice from Pony Carbs and timed it without using a timing light after I put the new carbs on. The carbs were replaced initally due to this issue and made a huge difference to the better as far as startup, idle and driving as long as I accelerate slowly.
I suppose anything's possible but the carbs were run on an engine and tuned before they were shipped to me and they never backfired after installation so I wouldn't have thought a power valve was out.
The valves were recently readjusted so they should be good to go. I have a new aftermarket distributor and wire set that I'm going to install tomorrow in case the dist. isn't advancing like it should and in case any of the plug wires are bad. I'm just tired of throwing parts at this thing with no results.

[rustyBob]

do you have a pump to check the vacuum module on the dist..

[d_ford]

It's a mechanical advance distributor. Sorry I didn't mention that.

[Argess]

I have the video form Pony Carbs and the part on ignition timing is totally wrong. He says to adjsut the dist for the best idle with vacuum disconnected. I have a mech-only dist, and best idle is up around 38 Deg, but imagine if I stepped on the gas with that much advance? Major detonation.

I helped a friend with his newly re-built boat engine (Chev 350....mercrusier) It was off by 2 teeth. Ran perfectly, but would not rev past about 3000 rpm.

I suspect your timing, now that you mention how you did it. However, if you have "black smoke", you may be getting too much accelerator pump shot. Back to the white cam most likely.

[rustyBob]

ok....try the other dist.......

[d_ford]

Hopefully you're right and tomorrow when I put the new distributor in I'll just start from scratch at TDC on the compression stroke and put the rotor to #1 on the cap. I'll keep my fingers crossed. Thanks guys for your help.

[Argess]

uh.....start at 10 Deg intial and work up....no need to start at zero (TDC). Engine will heat up very fast without enough advance. Find out your total advance and keep things under 38 total. Check advance is working by using timing light and giving it a small amount of throttle from idle. Timing should move smoothly. I don't like going past 2500 rpm with an unloaded engine

[cobred]

I dont think removing the vacuum hose from the carbs will eliminate the secondaries. They are controlled from internal ports. I think the hose only balances the opening so they work together under hard accelleration. There should be a small clip to remove to disconnect the vacuum pod from the rear shaft if you want to bypass the secondaries. I think.

[undy]

It really sounds like you're running extremely lean when your primary butterflies are moving past their fuel transition slots in the venturies, sucking air instead of fuel. You could be compensating for excessive fuel pressure by cranking down on your float bowl float adjustments to compensate for the fuel pressure over-powering the float needle valves?? What's your fuel pressure?

Try one thing.. Mark where your carb bowl fuel level adjuster nuts are at now. Raise the bowl level by turning the adjuster nuts 180 degrees counter clockwise, effectively raising bowl fuel levels. Immediately go take a test drive after you made sure fuel isn't pouring out of your bowl vents. See if that impacts your drivability. If it doesn't at all return your fuel levels to the original "marked" setting. If it does make it run better take a look at your fuel pressure, re-evaluate your bowl level adjustment procedures and fine tune your new fuel levels.

[trularin]

Had a problem like this when I first was setting up mine.

I wasn't delivering enough gas for WOT, hence the engine would pop and fall on its face when I was giving aggressive throttle.

Had to work on the power valve, jets and secondary circuit to increase the amount of gas.

Just a thought.

[Argess]

Back to timing for a moment, as you need to make sure that is OK before experimenting with fuel delivery.

On modified FEs, factory timing is usually out. But one fact remains, max timing is considered as 38 Deg BTDC. Here's how I set mine for first time evaluation (after that, I work on optimizing the initial advance and advance rate):

(Oh....works on points or electronic, but not computer controlled dist)

1/ With engine off, rotate crank CW with a "long" wrench until the timing marks show 38 DEg. Make sure you rotate CW so 40 Deg shows up before you get to 38. If you go past, keep going around again, do not go CCW as you'll get slop in the mechanism plus you could accidenlty loosen the crank bolt.

2/ Locate Cyl #1 ignition wire on the cap and put a small mark on the dist housing directly below cap #1 wire terminal.

3/ Pull the center wire from the cap. Inseert a sparkplug in the end and lay the plug on the engine where it can get a ground. BAsically, you will now have a sparkplug connected to the coil.

4/ Remove dist cap and move out of the way

5/ NOte rotor. It will point either towards the mark you made, or 180 Deg away. Doesn't matter which. Engine could be on compression stroke or exhaust stroke, but it doesn't matter for this procedure.

6/ Loosen dist and rotate dist about 1/2" CCW

7/ Rotate rotor button CCW as far as it will go and hold it there (max mech advance).

8/ With ignition ON, slowly rotate dist housing CW until a spark jumps at the sparkplug connected to the coil.

9/ Let go of the rotor and Double check it points more or less to the mark you made. You don't want to be off by 1 cylinder in sequence.

10/ TIghten down dist and put everything back together.

YOu now have 38 Deg adavnce max advance, but are at the mercy of the intial advance and timing curve whihc will probably be OK, but not necessarily optimized.

You can do all this with a timing light, but I don't like revving the engine to find max advance with no load on it.

Anyway, I suggest doing this timing thing first, then looking at fuel delivery, accel pumps, etc.

[d_ford]

One of my problems on this engine is a lack of timing marks. For whatever reason, it has marks in the aluminum single sheave pulley that bolts to the vibration dampener but no marks that I can see at all on the dampener. One of the marks on the pulley appears to be at TDC but none are marked as to what degree they are. There is a scale of marked degrees on the timing indicator but I don't think they go to 38. I'll look at it again.

[Argess]

Ah, the joy of owning a dial-back timing light. However for the static test posted earlier, you need a mark. You can buy stick on timing tape, but here's how I have done it:

Measure diameter of balancer. Mulitply by 3.14 to find circumference.

Say diameter is 7 inches, then 7 x 3.14 = 21.98 inches

Distance from TDC mark is calcualted as; degrees you want to mark x circumference divided by 360

38 x 21.98 / 360 = 2.32 inches

So, using some white-out or paint, make a mark 2.32 inches CW from the TDC mark.

[d_ford]

I looked at the pulley again and it does have a mark at 40 degrees. Can I use that as a reference point and figure out where 38 is?

[Bobcat]

In looking over your posts , I couldn`t find anything about what your plugs` condition is .... do they read rich , lean , fried or what ?? Also , what are they gapped at ? If too wide , the engine will breakdown under load .
Are you running an MSD ... they are very sensitive to low voltage . You mentioned the PV being new .... doesn`t mean it isn`t bad as I just went through that . You might try replacing them after reading the plugs .

Good luck .
Bob