Distributor/Carburator Woes

[dawson357]

I've finally got the Grande up and running after swapping out the FMX for a top loader. However, it's running crappy. It was modified in a speed shop before I got it and was rated at 350hp. My mistake in not getting the rebuild specs. That being said, I installed a new Holley 600 with vacuum secondaries and has a stock Motorcraft 12127 distributor with Pertronix upgrade and Flamethrower coil. Fires right up at 10degrees BTC. No hesitation in acceleration when easing on the pedal but hesitates when jumping on it in each gear. Acceleration rate is terrible. I have stock 2.79 gears, but with 350hp, should light up. I set the accelerator pump as per Holley directions and the float level is correct. Also increased the accelerator pump nozzles to a 35 from a 31. Vacuum at idle is just over 15. The carb power valve is stock at 6.5. Now for the interesting part - the timing is set at 10BTC for #1 cylinder, but the opposing cylinder shows 12BTC. The end play on the distributor shaft I measured at .04 (not positive on what the tolerance should be) with no wobble side to side but I noticed the rotor contact is scraping the top of the cap at each point. I thought the Pertronix magnet might be a tad too thick where the rotor sits but I put a caliper to it and the measurement is OK. Also of note, I have a small fuel pressure gauge screwed into the chrome fuel line to the Holley and it reads 9psi. Seems odd since I have a stock mechanical fuel pump. The plugs are black indicating too rich but all I've read says the hesitation is from being too lean. I'm trying to fit this puzzle together between issues with the distributor, carb and timing. Any ideas?

 

[boilermaster]

dawson357,
Start with the fuel pressure, 9 psi is too high for the Holley 600 vac.
it needs to be 6psi, then recheck and adjust float levels, idle speed and mixture.
then re-evaluate the accelerator pump.
have no clue what you mean by checking timing on the opposing cylinder.
Boilermaster

 

[Zach]

What boiler said, to add on. Make sure your throttle blades are squared off on the transfer slot, instead of having way too much curb idle or too little, can cause a hesitation. Holleys cannot take a lot of fuel pressure so that is #1 priority. Set initial timing to where the engine likes with the squared off throttle blades, make sure you check all in timing so you aren't too high or too low. Also stock fuel pumps are generally rated too high, at least in the world of 70s gm replacement parts, no experience on ford, 9-10 is pretty normal despite a quadrajet (or any other carb) struggling with anything more than 6. You could also peak your head over the venturies and make sure the fuel is atomizing instead of dripping. Also make sure the car is properly warmed up before messing with anything, your location is Florida so prob not as crucial but every little bit helps.

 

[dawson357]

dawson357,
Start with the fuel pressure, 9 psi is too high for the Holley 600 vac.
it needs to be 6psi, then recheck and adjust float levels, idle speed and mixture.
then re-evaluate the accelerator pump.
have no clue what you mean by checking timing on the opposing cylinder.
Boilermaster

I have a pressure reducer that I'm going to install and see what happens. Checking the timing on the opposing cylinder I learned from the directions that came with the timing light. The timing marks will appear at the timing pointer the same as on #1. Supposed to match. If not, it says the distributer is out of whack.

 

[dawson357]

What boiler said, to add on. Make sure your throttle blades are squared off on the transfer slot, instead of having way too much curb idle or too little, can cause a hesitation. Holleys cannot take a lot of fuel pressure so that is #1 priority. Set initial timing to where the engine likes with the squared off throttle blades, make sure you check all in timing so you aren't too high or too low. Also stock fuel pumps are generally rated too high, at least in the world of 70s gm replacement parts, no experience on ford, 9-10 is pretty normal despite a quadrajet (or any other carb) struggling with anything more than 6. You could also peak your head over the venturies and make sure the fuel is atomizing instead of dripping. Also make sure the car is properly warmed up before messing with anything, your location is Florida so prob not as crucial but every little bit helps.

Thanks for the suggestions. I'm going to reduce fuel pressure and play with the timing. Have no idea what it's supposed to be now that the engine has been modified. Kick myself for not asking for the specs from the PO.

 

[Stanglover]

This issue is similar to when I installed a new Holley 670 Street Avenger a few years back. I also was having similar issues with timing and hesitation.
What I found out from a tuning specialist was that Holley's tend to run rich out of the box. While he did not check fuel pressure on the newly installed stock style pump (something I ought to do as well), what he did I thought quite radicle, but it worked for MY engine. He drilled a 3/32" hole in the center of the primary throttle plates in front of the shaft. He then made sure the transfer slots were squared, setting the curb idle, telling me to NOT TOUCH it!! That change pretty much eliminated the over richness, no more black plugs or horrible gas smell. Other than that, I changed the "squirter" from a 31 to a 35 as you did. My engine pulls 17 inches of vacuum at idle, but I'm still using the 6.5 power valve, which I'm going to recheck when the car comes out of hibernation. By the figures, I ought to be using an 8.5 PV.
As for timing, I recurved the Autolite distributor, rebuilding it with a 10L limit slot and different springs and tension. I too use a Pertronix II with matching coil. Timing is currently set at 14 deg. initial on the damper and 34 all in @ 3k rpm mechanical. The typical STOCK distributor on our cars was more likely to have a 15L slot or 30 deg. on the crank, with only 6 degrees initial, giving a total of 36 deg. mechanical. We know that 14 to 16 initial is better for performance, but you can't just go through more initial timing at it without changing the total all in numbers.
It all works together.
Good luck sorting it out.

 

[dawson357]

This issue is similar to when I installed a new Holley 670 Street Avenger a few years back. I also was having similar issues with timing and hesitation.
What I found out from a tuning specialist was that Holley's tend to run rich out of the box. While he did not check fuel pressure on the newly installed stock style pump (something I ought to do as well), what he did I thought quite radicle, but it worked for MY engine. He drilled a 3/32" hole in the center of the primary throttle plates in front of the shaft. He then made sure the transfer slots were squared, setting the curb idle, telling me to NOT TOUCH it!! That change pretty much eliminated the over richness, no more black plugs or horrible gas smell. Other than that, I changed the "squirter" from a 31 to a 35 as you did. My engine pulls 17 inches of vacuum at idle, but I'm still using the 6.5 power valve, which I'm going to recheck when the car comes out of hibernation. By the figures, I ought to be using an 8.5 PV.
As for timing, I recurved the Autolite distributor, rebuilding it with a 10L limit slot and different springs and tension. I too use a Pertronix II with matching coil. Timing is currently set at 14 deg. initial on the damper and 34 all in @ 3k rpm mechanical. The typical STOCK distributor on our cars was more likely to have a 15L slot or 30 deg. on the crank, with only 6 degrees initial, giving a total of 36 deg. mechanical. We know that 14 to 16 initial is better for performance, but you can't just go through more initial timing at it without changing the total all in numbers.
It all works together.
Good luck sorting it out.

Thanks for the input! Sounds like your issues are very close to mine. I'll adjust timing to 14 and up the PV to 7.5. It does indeed all work together. I guess that's part of the fun messing with cars...solving the puzzle.

 

[Stanglover]

Thanks for the input! Sounds like your issues are very close to mine. I'll adjust timing to 14 and up the PV to 7.5. It does indeed all work together. I guess that's part of the fun messing with cars...solving the puzzle.

You can ONLY go to 14 initial if the TOTAL mechanical is set correctly. Check your distributor plate and see what it was set at. IF you find it is a 13L slot, as this one was, then there's a trick that even Ford did and that is to add a small piece of NYLON tube over the post. That will get you close to a 10L equivalent. see my pics. If it is a 15L then just adding to the initial won't work. You'll need to at least change the plate around and that (I think if I remember) means the rotor will be opposite. Rotate 180 deg, before restabbing the dist. (I think!!)

 

[boilermaster]

dawson357,
All these things go hand in hand, the lesser base timing you have the more one tends to move the carb
hardstop, thus more transfer slot is uncovered, the richer you will be at idle and then the more apt you
are to have to resort to tactics like drilling the primary throttle blades.
Simply knowing what your base timing and total timing are will give you a very good idea of how many degrees has.
for example 10 degrees base +14 degrees distributor (20 degrees crankshaft) = 34 degrees total.
as stanglover stated, more than likely you have more than a 10L in your distributor.

 

[dawson357]

I'm still concerned with the distributor shaft having .04" of end play and the rotor striking the top of the cap. I've read where you can shim the shaft but have no idea where they go, what they look like, where to get them, etc. Shop manual indicates a range of .024-.035 when out of the engine.

 

[dawson357]

You can ONLY go to 14 initial if the TOTAL mechanical is set correctly. Check your distributor plate and see what it was set at. IF you find it is a 13L slot, as this one was, then there's a trick that even Ford did and that is to add a small piece of NYLON tube over the post. That will get you close to a 10L equivalent. see my pics. If it is a 15L then just adding to the initial won't work. You'll need to at least change the plate around and that (I think if I remember) means the rotor will be opposite. Rotate 180 deg, before restabbing the dist. (I think!!)

Good point. Will do.

 

[dawson357]

dawson357,
All these things go hand in hand, the lesser base timing you have the more one tends to move the carb
hardstop, thus more transfer slot is uncovered, the richer you will be at idle and then the more apt you
are to have to resort to tactics like drilling the primary throttle blades.
Simply knowing what your base timing and total timing are will give you a very good idea of how many degrees has.
for example 10 degrees base +14 degrees distributor (20 degrees crankshaft) = 34 degrees total.
as stanglover stated, more than likely you have more than a 10L in your distributor.

Will pull the dizzy and have look. All this is good stuff. Thanks

 

[boilermaster]

dawson357,
do Not attempt to shim the distributor at the upper roll pin.
there is an overall length specification from where the distributor meets the engine block to the bottom of the distributor gear when this spec gets too big you ruin a distributor or a camshaft.
.005'' out of spec is not terrible

 

[dawson357]

dawson357,
do Not attempt to shim the distributor at the upper roll pin.
there is an overall length specification from where the distributor meets the engine block to the bottom of the distributor gear when this spec gets too big you ruin a distributor or a camshaft.
.005'' out of spec is not terrible

Another good point. The .035 is the max out of the engine. Mine is .040 in the engine which may be the cause of the rotor scraping the top of the cap. I'm going to remeasure the rotor height without the Pertronix magnet and with it to make sure there is no difference. One thread I read indicated you should use a stock Ford rotor. Some aftermarket brands may be a touch too tall and rest on the magnet. If so, I can sand off a mm or two to take care of that. Man, lots to tweak.