My 61 has 66-type spacer under the 4100 freshly rebuilt carburetor. This spacer has the front 2 holes partially connected and has a vacuum connection which I currently use for my vacuum advance which helps cooling by advancing timing at idle. I have Felpro 60059 4-hole gaskets above and below the spacer. I can find no vacuum leaks. I have a low rpm misfire usually noted when cold that now seems also to be present warm as well. The misfire seems to be reduced by turning in the idle mixture screws, to a point. These are currently at 1 1/4 turns. I noticed that the gasket under the carb is slightly abraided in the center, under the balance tube area, making me wonder if the gasket is interfering with whatever these tubes do. When I took the carb off the engine the carb base gasket was noted to be a homemade single hole affair, which makes me wonder if my 4-hole gasket is incorrect. I note with interest that the base gasket for the 1960 Bird with 352 engine appears to be the single hole type and wondered if perhaps my 61 was cobbled from leftover 1960 parts. FWIW, I also noticed recently when I was adjusting float levels that sometimes the front bowl level would be correct, then not. I can find no vacuum leaks but I have fixed several, beginning with a ruptured vacuum advance. The misfire began about the time the vacuum advance ruptured. I plan to replace the spacer with the correct 61 spacer and experiment with a single hole spacer under the carb. I will also replace the carb needles in case I damaged them in setting float levels. Any advice would be appreciated.
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Bill, it was a pleasure welcoming you to the Forum! I am not qualified to comment on the problem you are troubleshooting, but we have many terrific techies on here who are. Once they start waking up, they should be commenting on the problem you are having. Thanks for the detailed report on what you are experiencing. That certainly helps. If you have not looked at the Advertisements Forum yet, you will find all the major Tbird parts houses listed there. If you need their free catalogs, you can call them or email them to ask for them. They will come in handy when chasing down parts and costs. We also have a pretty good Technical Resource Library (TRL) which link can always be found under my signature and that of John Pizzi ~ jopizz, and in the TRL forum. There is nothing that I can think of regarding the problem you are having in it though.
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Bill,
I'm not sure what kind of spacer you have. A '66 spacer only has a small vacuum tube coming out of the front and is very thin. A 64-65 spacer is thicker and has a coolant port in the front and rear passenger side and a vacuum port for a pcv valve in the rear center. Can you email me a picture of your setup. A Fel-Pro 60059 four hole gasket should work fine above the spacer but in order to use the vacuum port in the rear you need a Fel-Pro 13303. However, you should be using the vacuum port in the carburetor for your vacuum advance and not the spacer. If you don't have the vacuum port in the carb plugged off that's probably why you have a misfire.
JohnJohn Pizzi - Squarebirds Administrator
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Bill,
I'm not sure what kind of spacer you have. A '66 spacer only has a small vacuum tube coming out of the front and is very thin. A 64-65 spacer is thicker and has a coolant port in the front and rear passenger side and a vacuum port for a pcv valve in the rear center. Can you email me a picture of your setup. A Fel-Pro 60059 four hole gasket should work fine above the spacer but in order to use the vacuum port in the rear you need a Fel-Pro 13303. However, you should be using the vacuum port in the carburetor for your vacuum advance and not the spacer. If you don't have the vacuum port in the carb plugged off that's probably why you have a misfire.
John
The 61 and 66 spacers are identical except for the vacuum tube which I had capped for a while until I learned from the FE engine board about how increased timing by using manifold vacuum vs ported vacuum for vacuum advance helps cooling at idle during hot weather. I tried it and it works. A little controversial but it works for me. This has no impact on my misfire as I have tried it both ways. And, I did cap the vacuum port on the carb when I changed. The 61 and 66 spacers are not heated nor is there a PCV fitting. These are much thinner than the 62-65 spacers. Phenolic vs aluminum, too. They also do not have the recessed area under the carb air balance area like the 62-65 do. There is one other difference between the 61 and 66 spacers. The 66 front 2 holes are connected for about 25% of their circumference. I really don't think my issue is the spacer but I'm going to try a 61 just to be sure. That, and a perimeter gasket vs the cloverleaf type as well. Mike of Mike's carburetors insists that the perimeter gasket is the right one. This would remove a partial obstruction in the air balance area and let the chambers "talk" better. Thanks John. I will post how my experiments go.
BillComment
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Your 4100 carburetor uses manifold vacuum also so it doesn't matter whether you use the spacer or carburetor. The vacuum port on the carburetor is below the throttle plates.
JohnJohn Pizzi - Squarebirds Administrator
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jopizz@squarebirds.org 856-779-9695
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Sorry, I must disagree. Maybe I misunderstand.
Bill,
I'm not sure what kind of spacer you have. A '66 spacer only has a small vacuum tube coming out of the front and is very thin. A 64-65 spacer is thicker and has a coolant port in the front and rear passenger side and a vacuum port for a pcv valve in the rear center. Can you email me a picture of your setup. A Fel-Pro 60059 four hole gasket should work fine above the spacer but in order to use the vacuum port in the rear you need a Fel-Pro 13303. However, you should be using the vacuum port in the carburetor for your vacuum advance and not the spacer. If you don't have the vacuum port in the carb plugged off that's probably why you have a misfire.
John
This seems to be confirmed by the difference in timing at idle when I switch from the carb to the spacer for vacuum to the vacuum advance. Timing doesn't change when the carb is the source but advances when the spacer is the source.
Am I mistaken?
Thanks.
BillComment
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If you turn your carburetor upside down and put a wire through the vacuum port you'll see it comes out below the throttle plates. Every 4100 I've worked on has it that way. If yours is different I'd like to see it. I'm not saying you're wrong. I'm just going by my own experience. Every car that I've timed that has a 4100 carburetor I've had to plug the vacuum port.
JohnJohn Pizzi - Squarebirds Administrator
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If you find that your carburetor has ported vacuum I would definitely like to know. That would be an oddity I'd like to make note of. Thanks.
JohnJohn Pizzi - Squarebirds Administrator
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Bill,
I stand corrected. After digging out an old 4100 that I had laying around it appears that the vacuum port is indeed above the throttle plates which is odd because when I changed over to an Edelbrock and had the choice I set it to manifold vacuum because it seemed to me that there was vacuum at idle with the old carb. Maybe the throttle plates just weren't closed all the way. Regardless you are correct about using manifold vacuum. When I set my Edelbrock to ported vacuum the low speed performance seemed terrible. When I changed it to manifold vacuum the car seemed to take off much better.
As to your misfire issue what is the condition of your fuel tank. I've found most misfire problems are due to dirt in the idle passages of the carburetor. If you can make the condition better by adjusting the mixture screws it sounds like it is fuel related. On my '66 I used the standard Fel-Pro four hole gaskets above and below the spacer and it ran fine so I doubt the gaskets or spacer are the problem. Try removing the mixture screws and spray some carb cleaner in the holes. That's worked for me a few times.
JohnJohn Pizzi - Squarebirds Administrator
Thunderbird Registry #36223
jopizz@squarebirds.org 856-779-9695
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Thanks John.
Glad you cleared up the ported vs manifold vacuum question on the 4100. You had me questioning a lot I thought I had learned. Regarding the gas tank, it was new 15 years and less than 10k miles ago, installed by a PO. I replaced all the rubber lines when I got it 2 years ago as well as the fuel filter. I'm still going to replace the carb mounting gaskets and I'll try the carb cleaner in the idle screw holes. Since the first time I noticed the misfire was right after the vacuum advance failed I'm wondering if a bit of the diaphragm may have ended up in the carb. Will do some flushing and blowing while it's off. Thanks for your help.
BillComment
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Bill,
If the car was used regularly a 15 year old tank should be fine. If gas was allowed to sit in it for a long period of time it may have turned to varnish and rust may have started to develop. You might want to pump some gas into a container and check the condition of it. If it's not perfectly clear than you may have debris in the bottom of the tank. There's an access panel in the trunk where you can pull out the sender and look into the tank.
JohnJohn Pizzi - Squarebirds Administrator
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Observations
FWIW...
Noting:
1) The abrasion I have seen in the center of the cloverleaf type gasket where the air balance tubes on the bottom of the carb are located on my 61 with 4100 carb.
2) My 61 came to me with a perimeter gasket under the carb.
3) At least one vendor lists the perimeter type gasket for the 60 TBird with 352 engine which has the same type spacer as the 61.
4) At least one "expert" on another board insists the perimeter gasket is all that is necessary since there is "communication" between chambers (noted by the notches in the barrels on the underside of the 4100 carb).
5) Spacers after 61 are recessed in the center allowing "communication" between barrels.
6) It makes no sense for gaskets to be used without surfaces on both sides to bear on the gaskets. This is particularly weird on the 62 and later spacer with the hot water tube. The cloverleaf gasket in the center is suspended between the air balance chamber above and the recess in the spacer below.
My conclusions are:
1) The gasket between the carb and spacer should be only a perimeter gasket. Similar to Victor Reinz G27104. A cloverleaf type could be used with center removed. I may use a Felpro 1901 because it is thicker than most gaskets and I will remove the center. I may also cut my own from gasket material.
2) The gasket between the spacer and intake can be the perimeter type or cloverleaf type. I will use the cloverleaf type with intact center.
3) The listings by suppliers of the cloverleaf gaskets aren't necessarily wrong, there is just a better solution, for me at least.
BillComment
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Bill,
I've used both the perimeter gasket and the four hole gasket under the carb and I can't honestly say I've noticed any difference. 4100 rebuild kits usually come with one of each type but there's no mention of which one should be used for which application. The Ford Master Parts book only shows the four hole gasket. It doesn't show a perimeter gasket being used for any FE motor. From my experience taking apart original cars a four hole or clover leaf gasket was always used between the spacer and intake. To me a gasket is there to prevent a vacuum leak and nothing more so a thick perimeter gasket under the carburetor should be good enough.
JohnJohn Pizzi - Squarebirds Administrator
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Update
I removed the carburetor, then the venturis, floats, needles, seats, jets and power valve. I flushed and blew out everything, finding nothing visible. I repaired a warped power valve cover and replaced the needles, seats and cover gasket. I previously trued the bottom of the carburetor. I reinstalled the carb with a new 61-type 4-hole spacer with a 4-hole gasket below and a single-hole gasket above, fabricated from 1/16" gasket material. I adjusted the floats. I was hopeful that the warped power valve cover leaking vacuum was the cause of my misfire but the initial trial run revealed minimal improvement, if any. Still a slight misfire, more noticeable when cold, at low rpms. The automatic choke was hanging up a bit during the trial, so I will address that and run it again.
I expect I will be making one more stab at finding this misfire. When I removed the carb for the initial rebuild a year ago, I noticed the rear throttle plates were stuck closed, no adjustment at all. I am wondering if this might not have been done on purpose, perhaps as a way to minimize vacuum leakage past the secondary shaft. I freed it during the overhaul and adjusted the secondaries but I'm wondering now if I recreated the problem. I may try adjusting the secondaries completely closed. If this works, Santa's gonna bring me a new Holley. If not, same result. I'm about done with this carb.
BillComment
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