In my experience todays gas works fine with our old engines. I have not experienced any problems with cars I work on when properly tuned. Now does ethanol gas cause problems when storing your car? Absolutely! Ethanol attracts water and causes corrosion in fuel system components. But it burns very slow and acts like old 99 octane gas with less power. Yes, our old engines would make more power on the gas blends of yesterday, but they run just fine on todays gas.
Here is a post about todays gas and the is very revealing about how a high performance engines runs on various blends of gas and how much advance the engine can manage.
Wish I could get you car in my shop. I have a List 3795 Holley carb off a 1968 Cougar GT-390 coming my way. I will wet test it on a known GT-390 engine that has no issues. I could do the same for your car, but again you may have other issues not related to the carb.
The other option that I ended up doing was switching carbs entirely.
I went with a 500 cfm Edelbrock AVS2 carb. A larger cfm but otherwise identical one can be had in 650 cfm.
Yes yes yes, I know it’s not original but it’s a good looking carb and it’s a zillion times more street friendly. The previous carb was a Holley that I ended up sending free of charge to another forum member.
These carbs run right out of the box with only minor tweaking required & my gas mileage jumped up from about 9 miles to 13 miles per gallon. My warm up times are essentially half of what I had to do with the previous one.
You might or might not have to add a fuel pressure regulator. I just have the regular old plain Jane fuel pump and no complaints.
Top end horse power is very slightly less but the low end torque is a little bit more. I also added the smaller diameter Edelbrock air filter, makes adjusting much easier.
The main adjustment you need to do is setting the accelerator pump to the longest stroke possible to minimize hesitation.
The only other little gotcha is that you have to block off the hole in the manifold where the hot air choke tube used to go to about a small exhaust leak.
Either JB weld or a tap and die set are your friends.
Noticed today a little puddle of fuel in the front most valley on the drivers side intake manifold. Looks to be leaking from the accelerator pump on the front of the carb. Not sure if it’s the diaphragm or the gasket, but the off idle hesitation it’s doing and possible lean out could be due to this right? Either way the timing is too high and I’m dialing that back to 6 and going from there. What are the best carburetor gaskets to get for one of these? It’s all factory stuff.
Noticed today a little puddle of fuel in the front most valley on the drivers side intake manifold. Looks to be leaking from the accelerator pump on the front of the carb. Not sure if it’s the diaphragm or the gasket, but the off idle hesitation it’s doing and possible lean out could be due to this right? Either way the timing is too high and I’m dialing that back to 6 and going from there. What are the best carburetor gaskets to get for one of these? It’s all factory stuff.
I’ve got a Holley rebuild kit. Are the base gaskets in that sufficient or do I need something else? I think I’m going to spring for the green GFLT accelerator pump diaphragm that’s for alcohol laced fuels this go round. What are the torque specs for the carb to intake bolts?
I’m super confused now. I put the carb back on. Replaced the pump diaphragm with a GLFT ethanol resistant one. Cranked. Felt like it had a dead cylinder but smoothed out. Checked timing. First time I checked it I used the mark someone had put before. Today I crawled under and marked 0,6,8, and 10. Hooked up my dial back timing light and initial timing is around 30. The vacuum advance is pointing straight forward. Something is for sure off here cause there’s no way it would run at 30. Any ideas? Turn right to retard left to advance right?
#4 is the rear one on the passenger side. Just a regular ratchet and a spark plug socket. It’s one of the easiest ones to get to.
#7 is tough, as is #8. I normally remove the master cylinder to change those. Alternative is to reach beneath the master cylinder but the older I get the less nimble I have become.
I wonder if the timing chain has slipped. Sounds like it is getting worse, not better.
I pulled the passenger valve cover. Everything looks good. Cranked it over and all rockers had the same amount of movement. My concern was a wiped cam lobe.
What all needs to come off to get to the plugs? The emissions equipment is in the way but I can’t seem to get that unbolted. Also can’t seem to get the plug wires off the plugs. I at least want to get to number 4 and check it.
If the timing chain jumped is there any way to compensate for that? Since I have the passenger valve cover off I’ll check and see if TDC is truly where it’s supposed to be.
Seems like you are chasing your tail and heading further down the rabbit hole.
You started out seeking advice for an off-idle stumble, run on & a hard warm start issue, right? Seemed like your timing was set out of spec & you had a possible vacuum leak. Not sure you’ve addressed either of these, but now you’ve had the carb apart & are thinking you have a wiped out cam lobe? We’ve also come to learn that the the timing marks you were initially using did not jive with those inscribed on the balancer, do I have that right? If so, that could be an attempt to make it run decent even when the timing chain is off a tooth.
If you want to fix this, you have to get methodical, not take stuff apart & hope you stumble (see what I did there?) on the answer.
PLUGS: With the right combination of universal joints, extensions & an open end wrench (used on the back of your spark plug socket) you can access all the plugs, even with the factory smog equip in place. Heck, I did head gaskets on my R code vert (a show car) in one (painful) day without pulling the motor (full smog & A/C).
Pull the plugs, see what they look like. That will tell you about what is going on in your combustion chambers.
“MISS” on cyl 4 & 7: Hard to diagnose until we know if the crank timing is right, but after I did the above head gasket job, I had a slight miss. Turns out the plug on #7 had the gap closed down. It must have got squashed when I pulled the head. Fixed that, reset the timing & carb & it ran like a bear for the next 15 years. I bet it still runs great.
crank the engine (by hand) to TDC. Make sure it’s true TDC, as close to true TDC as humanly possible.
Look at your damper to see where the timing marks line up relative to the pointer. It should point to where your initial timing is set (6 degrees per the factory spec, for example) per the factory marks. If it’s not, I’d suspect your timing chain either jumped a tooth or wasn’t set up right.
pull the distributor cap & make sure your distributor rotor is pointing to #1 cyl. If not, the distributor might be off a tooth, and you can pull it & put it back in in the right spot.
With the smog in place removing the brake master cylinder gets you all the clearance that you need. Read what I posted it will save time for you and me. You may have to remove the shock tower to cowl brace in order to remove the MC.
The ratchet is a MATCO 3/8s with swiveling head and 20-30 degree angle 2/3s up the long handle, part number BR11SP. It is godsend for doing this job.
The spark plug boot remover is great for on and off and can be had anywhere. It will keep you from damaging the wires and getting the boot to “snap” back on over the plug.
Cranked it over with remote starter switch. Rotor points to #1 damper says 10. Also hits TDC when rotor points to #6. All plugs looked decent except right front. #1. Looks like the plug is too cold for that particular cylinder. Autolite 45s.
