'61 Fuelie Suddenly Running Rough

[John D.]

Re: '61 Fuelie Suddenly Running Rough

HI Larry, I got in on this conversation late.
First of all I recognize the modification on your FI unit. Appears to be typical of John's FI in CA. The altered fuel meter cover that has the bypass line installed is one clue. The line runs under the FI unit to the spider and a small Skinner valve. He taps into the top of the spider with an elbow, etc.
Although not original and not my forte it does typically work OK. Takes a lot of bucks though to undo this modification. New spider, maybe a new fuel meter cover although the hole could be plugged, cranking signal valve, vacuum line and of course the hard to find original Brass T fitting for atop the fuel meter cover. But this is not the issue. This is not what your complaint is.
57 to 61 FI's do NOT have a choke as Jim mentioned. A real deal choke didn't come out until the '62's and was used from 62 to 65.
The earlier units have a cold enrichment. Read all about this in "Corvette Servicing Guide" St12 Manual. Info in the theory section. Great theory for all interested in FI's to read and learn.
Sound like you could have picked up a little bit of dirt or varnish.
When the car is hot put your finger on the "choke" cover Larry. If you burnt your finger then it's working. If not then it died.
But with your nice photos it appears to be working. Look in the theory section again of the manual. You may have a sticking power boost pin or even the smaller enrichment pin. The power boost pin is the fat pin. This would cause the unit to run fat/rich.
A vacuum leak would cause idle flucation. A vacuum leak would make the FI hunt/search for a signal thereby causing erratic idle. Your main diaphragm cover could be warped, that 90 degree fitting could be loose, the rubber hoses could have cracks, the 90 degree rubber hose under the air meter could be loose or cracked. The main diaphragm might have issues. Your small diaphragm which is the enrichment diaphragm appears to be OK from the photos.
Hot ethanol is the pits on our FI's you know. Try some better fuel like 100LL. Open the hood when the engine is hot and see if that helps.
Forgot some elementary info. Spill valve could be sticking. Whew!!!
If you have the original spill valve that Bill Thomas nicknamed the good guy then that could be the problem. I calll those POC valves the bad guy. Replace it with the thumb tack style spill valve. Good luck, John
P.S. Try a little fuel injection cleaner in the gas.
Ethanol is probably boiling away. Your fuel line going from the fuel filter to the engine fuel pump may be too close to the valve cover. Attend to this if it is.

[Larry B.]

Re: '61 Fuelie Suddenly Running Rough

John, You a have a good eye! John's FI did this unit. I will continue checking what I can. There does not appear to be any vacuum leaks, hoses are good and I made sure everything is tight. Some of the things you mentioned need dis-assembly. That is well out of my league. If worse comes to worse, is there a place I could take the car to in So. Cal. to get it looked at? If I send it out would you be able to wet test it? Thanks

[Larry B.]

Re: '61 Fuelie Suddenly Running Rough

Larry, some questions:

From your description of the starting procedure, you must have an electric fuel pump.... true?

The priming circuit is a modification someone has made to your FI unit. Are there any other modifications?

What happens to engine idle if you push the priming button while the engine is running?

How does the engine run once the car is moving? Any hesitation when you step on the accelerator? Any black smoke?

Does the idle mixture screw have any effect? I. E. if you screw it all the way in (closed), does the idle mixture lean out any? Does the engine stall (it should)?


Jim

Jim, The car has a new stock fuel pump. The idle and mixture are are both working and will effect the running if adjusted. I have it adjusted to the best vacuum/idle. I have not tried pressing the primer button when running but I am sure that it would die. The car runs good through the gears and does not hesitate or smoke. It just idles rough. The primer is manual and will only work when the button is pushed and the ignition key is in the on position. As soon as you take your finger off the button the priming should stop.

[Jim L.]

Re: '61 Fuelie Suddenly Running Rough

The idle and mixture are are both working and will effect the running if adjusted. I have it adjusted to the best vacuum/idle.

If you can find a sweet spot for the adjustment of the idle mixture, then the engine is NOT running rich.

I have not tried pressing the primer button when running but I am sure that it would die.

The value of this experiment is in making sure that the engine dies. If it does, then you can justifiably feel confident the primer circuit is working.

The car runs good through the gears and does not hesitate or smoke. It just idles rough.

Based on the evidence thus far, the rough idle isn't due to a rich mixture. Might be a partially plugged nozzle, fouled spark plug, or a sticky/sticking spill valve, like the "Bad Guy" variety John mentioned.

The primer is manual and will only work when the button is pushed and the ignition key is in the on position. As soon as you take your finger off the button the priming should stop.

Now I'm confused. Your engine has a mechanical fuel pump. And, if I understood your starting procedure it's like this:
- turn ignition on
- depress priming button
- release priming button
- turn key to START

If I understand your start procedure, then the priming circuit has no pressure behind it during the time the button is depressed. There should be no fuel to squirt out the nozzles.

What am I missing?

Jim

[Larry B.]

Re: '61 Fuelie Suddenly Running Rough

If you can find a sweet spot for the adjustment of the idle mixture, then the engine is NOT running rich.
The value of this experiment is in making sure that the engine dies. If it does, then you can justifiably feel confident the primer circuit is working.

Based on the evidence thus far, the rough idle isn't due to a rich mixture. Might be a partially plugged nozzle, fouled spark plug, or a sticky/sticking spill valve, like the "Bad Guy" variety John mentioned.

Now I'm confused. Your engine has a mechanical fuel pump. And, if I understood your starting procedure it's like this:
- turn ignition on
- depress priming button
- release priming button
- turn key to START

If I understand your start procedure, then the priming circuit has no pressure behind it during the time the button is depressed. There should be no fuel to squirt out the nozzles.

What am I missing?

Jim

Jim, I assume the primer is somehow tied into the electric and provides enough of a drip when pressed to get it started. After that it has no function. I usually have to press it a few seconds, crank and do over and over to start the car..only when cold and sitting over night. When warm I do not need the primer. It has been running decent up until a few days ago. The FI and engine both have only 10,000 miles if that.

[Larry B.]

Re: '61 Fuelie Suddenly Running Rough

Jim, I assume the primer is somehow tied into the electric and provides enough of a drip when pressed to get it started. After that it has no function. I usually have to press it a few seconds, crank and do over and over to start the car..only when cold and sitting over night. When warm I do not need the primer. It has been running decent up until a few days ago. The FI and engine both have only 10,000 miles if that. Is there any way I can check a spill valve or unclog a nozzle without diss-assembly?

[Jim L.]

Re: '61 Fuelie Suddenly Running Rough

Jim, I assume the primer is somehow tied into the electric and provides enough of a drip when pressed to get it started. After that it has no function. I usually have to press it a few seconds, crank and do over and over to start the car..only when cold and sitting over night.

Larry,

A drip is probably all you are getting with the current procedure.

Try depressing the priming button while you are cranking the engine. You ought to notice a dramatic improvement in cold starting ease.

You've already noted that you don't need the primer when the engine is hot and that shouldn't change.

Is there any way I can check a spill valve or unclog a nozzle without diss-assembly?

Not at all.

The spill valve is embedded deep inside the fuel meter and is accessible only when the unit is off the car and inverted. Removal must be done carefully to minimize the possibility of small parts getting lost inside the fuel meter.

Unclogging nozzles requires removal and disassembly and the internal parts (an orifice disc and a filter screen) are easily lost.

Not to be discouraging, but I don't recommend attempting either of these procedures.

Jim

[Dave S.]

Re: '61 Fuelie Suddenly Running Rough

John, You a have a good eye! John's FI did this unit. I will continue checking what I can. There does not appear to be any vacuum leaks, hoses are good and I made sure everything is tight. Some of the things you mentioned need dis-assembly. That is well out of my league. If worse comes to worse, is there a place I could take the car to in So. Cal. to get it looked at? If I send it out would you be able to wet test it? Thanks

Larry,
No need to bring your car to some unknown FI mechanic. Find a competent FI garu and send the entire unit (minus the baseplate and distributor) to him. It takes all of 15 minutes to remove what you need to send. The good FI guys have test motors and can make your unit run better than new. When you recieve it back you just bolt everything back to the baseplate and adjust the idle.

[Rick G.]

Re: '61 Fuelie Suddenly Running Rough

Larry,

Do your homework if you intend to send your unit out. There are several great FI mechanic's, John is among the best. There are also some who advertise heavily who you should run from. Please understand the great ones are also the busiest and you may have to wait your turn. I also suggest you send both the distributor and base plate with your unit. Most FI mechanics I know of will set your unit up to your distributor and base plate.

[Larry B.]

Re: '61 Fuelie Suddenly Running Rough

I attached some photos of the plugs. The photo's attachments are named left(1st photo) and right(2nd photo). Plugs are in order left to right 2468 and 1357. 6 and 8 eight appear to have the most fuel/rich fouling. Could this be maybe plugged injectors at 6 and 8? Keep in mind that the engine was idling for about 1/2 hour while I was adjusting and trouble shooting. Engine / FI have about 10,000.

[John D.]

Re: '61 Fuelie Suddenly Running Rough

HI Larry, 10K miles on the engine and FI is a decent amount. Spark plugs: What heat range and brand? What ignition coil are you using?
As mentioned by Jim Lockwood be careful if you attempt to clean the nozzles. If one loses a disc/orifice you are in bad shape.
Meanwhile we might be making too much of this situation in that you said it ran OK up until a few days ago. Try some fuel injection cleaner.
Also use a hot coil and a decent spark plug. AC 45 or maybe AC 46. Notice your electrodes seem OK at a glance but the plug is nothing to brag about after that. I don't seen any green rings so must be Autolitle or whatever.
Problem is the AC plugs cost a fortune today.
Change the plugs & dump some X brand fuel injection cleaner (any brand will do) and give it a try. Could be some bad ethanol. On the other hand there isn't any good ethanol. John

[Larry B.]

Re: '61 Fuelie Suddenly Running Rough

John, The plugs are autolite as recommended by Jerry Bramlett in his article. The plugs do not have too many miles on them. I changed out the 45's after reading the article. I have a flamethrower coil and put the stock coil back in with no change. Do you recommend a certain coil other than stock?