Hello folks, I’m trying every way possible to troubleshoot and resolve an issue with a Series 1 with triple HD8 SUs.
SYMPTOMS after setting up carbs and ignition by the book:
Engine runs rich and rough at idle: Some black smoke, some burbling and light popping. Jets are set 2.5 turns in, carbs are synced. I I lift the pistons slightly, my idle smooths out and engine vacuum goes from 15 inches to a proper 21 inches.
With engine set to idle as well as possible- Driving down the road under any load, the engine experiences lean backfires. If I engage the choke, the engine smooths out and runs powerful. I stopped several times during test drives to adjust (lower) the jets and the power improved and backfiring was minimized. But… Idle and light cruise suffered horribly. Black smoke, burbling… RICH.
I have checked, adjusted over and over again: Timing, changed plug wires, cap and rotor, (running Pertronix), inspected all floats, inlet needles, piston drop tests, examined jets, needles, vacuum leaks, switched to heavy damper oil, screwed Slow run screws all the way in which helps idle very slightly better.
Any help or insight would be helpul. I work on these cars almost every day and have yet to see one that will not respond to proper tuning.
It should run with a 10% ethanol premium gas just fine on UB or UE needles. Adjust your idle mixture properly and then change needles if needed for anything above idle. With all of the black smoke, your plugs probably need a good cleaning. If you are running real rich at idle and the jets are 2.5 turns down from flush, check to make sure your needles are far enough into the dampers. You could also have a defective set of needles, I have had that before.
I did check the needle depth, and all three were fine. We pulled the plugs, which were sooty once already, and cleaned them. I’ll clean again because it can’t hurt. I’ll do a compression test while I’m at it. The car came to us with the jets flush with the bridge, so someone had been in there already and tried to lean the idle, but the on-load backfiring made the car undriveable.
Thats a very good question. The shop is around 1,700 feet. I don’t think we’re high enough to make the motor run this poorly. We get these regularly and ive never seen one need re-jetting/needles.
I don’t see any wettness at the bowl seam to the body, nor under the bowl either. I was wondering how it would run with torn diaphragms. The jet tolerances are so tight, i wouldnt think enough fuel could be pulled in. Have you experienced this before?
I’ve not seen a torn diaphragm without wet carb bases, but you never know. The tolerances aren’t tight enough to prevent gas leaking past if the diaphragms are leaky. Remove the domes and pistons and observe the fluid level in the jets. Are they all the same? Do you see any puddling? If you turn the key to the on position with the domes off, does the pump stop, and what is the level in the jets at that point?
UE needles run lean with E85. If you’re adjusting the jets extra lean to correct some unrelated condition, they will be much too lean at speed. If you solve the rich at idle problem, the lean at speed problem will sort itself.
Raising the pistons and having the idle change from too rich to normal is weird. It’s almost as if the pistons are sitting too low in the carb, or the needles have been modified. The former would increase the speed of the air over the bridge, increase the depression and more fuel would enter. The jets being as high as they can go suggest an attempt to slow the fuel flow down. What do you know of the history of the car and the carbs. Have the needles been filed on? Do you have another set you can substitute? Are there springs in the bell chamber?
Check the vacuum should be steady
Fuel pressure 3 lb. ( what fuel pump is installed)
Check the compression
Leak down if you can
Are the needles installed in the slides correctly
Correct springs as mentioned……… there are I think 3 different ones
I can lean out the idle by pulling the jets up, but then then the engine leans out on load. Having great vacuum signal is usually a great thing. Needles haven’t been modified. I’m thinking of finding heavier springs. The heavy oil isn’t fixing it.
I have another set of carbs which are pretty rough from ethanol deterioration. We’re building these for another car in the queue, so it might be time to jump on them now even for a reference set.
We don’t know the history of this car. The owner had it for years, but he passed. The rest of the car looks mostly unmolested other than a little body work.
First thing I checked was vacuum. It’s wobbles around 15 inches at idle until I lift pistons a little, then it clears up and comes up to 21, which is perfect.
Don’t know the pump, but it’s definitely worth checking out for over pressure. Good idea.
Leakdown and compression are next just for good measure. Engine seems really healthy otherwise.
Yes, it may come down to rebuilding these carbs. But I’m not convinced they’re that bad. they’re clean, bowls are clean, shafts seem good. But yea… running out of things to point to.
You have some interesting skills, and it’s a pleasure to welcome you to the community! It’s nice to have another knowledgeable voice to discuss rationally these wonderful beasts.
I don’t recall you did a drop test on the slides they are a matched set
And you can run fishing line through carbs to clean out passage ways
Often times these carbs get blamed for tuning problems when actually it’s a tired engine problem related to vacuum
Is there anything to suggest that the springs were modified? Perhaps compare a spring from this car to your reference set.
You can weight the pistons with washers, just find washers that fit around the damper tube. Or large ID washers that fit into the rim of the piston. But if you increase spring strength or weight the pistons, you are restricting airflow at higher speeds, so not really a solution either.
Thank you for your kind words. I work at a shop where we currently have five E-Types on the floor. Every day for me is about troubleshooting, learning discovering and then sharing. These cars are fascinating to me, and are constantly challenging me to be a better mechanic.
need rebuilding