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Unread 02-01-2014, 06:14 PM   #1
bldams123
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What did I do wrong carb

I searched and cant really find what my problem is. I got a rebuilt motorcraft 2100 for my 86 cj straight 6. I bought a carb kit from that guy off ebay gronk. He sells a good kit and so far the hardest thing to do was come up with a way to remount the throttle linkage (I felt like i was building an erector set haha) only thing i havnt done is install the manual choke. After i adjusted the idol screw and fuel mixture screws it sounds like its running great and idols well. the only reason i havnt taken it for a test run is that i noticed it is leaking gas from what appears to be either before or after the adapter plate. Is this the carbs problem or user error. does it have anything to do with the gaskets they seemed pretty thin. Thanks for any input

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Unread 02-01-2014, 08:18 PM   #2
Knucklehead
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Remove the carb and take a look at your adapter plate to determine if it is oriented correctly (turned 180*). Also, slap it down on a flat plate to determine if it is warped. If it's like the plate on mine, it is phenolic (plastic) and can be trued up with a little elbow grease using a flat surface and sandpaper. Also, I'd check to see if gas is coming past the throttle shaft bores. If so, worn throttle shaft bores will require boring and install of throttle shaft bushings to fix.
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Unread 02-01-2014, 09:39 PM   #3
GPER
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Make sure you use lots of the rtv to seal everything even the bolt holes on the adapter.
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Unread 02-01-2014, 10:27 PM   #4
SouthernGypsy
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Quote:
Originally Posted by GPER View Post
Make sure you use lots of the rtv to seal everything even the bolt holes on the adapter.
RTV? Are you referring to the carb gasket and bolt holes? I didn't want them to be confusion because your never supposed to use RTV on any carb gasket. You use carb gaskets totally dry without any kind of sealant on them at all.
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Unread 02-02-2014, 12:24 AM   #5
Kastraelie
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Quote:
Originally Posted by SouthernGypsy View Post
RTV? Are you referring to the carb gasket and bolt holes? I didn't want them to be confusion because your never supposed to use RTV on any carb gasket. You use carb gaskets totally dry without any kind of sealant on them at all.
I think he means the adapter plate for the carb to the intake manifold.

I've heard of guys doing this, and others saying to just use the 1/4" thick gasket that comes with the adapter plate.

I personally can't get the adapter plates to seal up with the gaskets they give you.
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Unread 02-02-2014, 12:38 AM   #6
SouthernGypsy
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Originally Posted by Kastraelie View Post
I think he means the adapter plate for the carb to the intake manifold.

I've heard of guys doing this, and others saying to just use the 1/4" thick gasket that comes with the adapter plate.

I personally can't get the adapter plates to seal up with the gaskets they give you.
Yea your supposed to use just the gasket, if that wont seal up then the hold down bolts are not snug enough or something (adapter plate or manifold) may have an uneven surface. Helps sometimes to scuff them up with a scuffy pad in a criss-cross pattern, or even sand the adapter plate lightly with fine grit sandpaper stretched over a flat block that is large enough to reach across the entire plate, again doing a criss-cross pattern. On the manifold you pretty much have to take your carb studs (if your using them with the plate) out to do it. Just be sure to tuck a small rag down in the holes while doing it, then blow off the area to get rid of the dust from the sanding or scuffing before pulling out the rags.

Between the carb and plate it's usually easy to see when you have a good seal, though unfortunately not until after you pull the carb back off, but I always look at the gasket and you should see flattened out impressions on one side that match every feature of the bottom of the carb and impressions that match the plate or space block on the other side. If they are clear and distinct and seem about the same depth across the entire surface then you probably have good surfaces and proper torque on your hold down nuts or bolts.


A fairly easy way to check for leaks on a mounted carb on a running vehicle is to get the vehicle to normal running temp. Then take a spray bottle that has a stream setting, clean it out good, drop just a couple of drops of regular dish washing liquid in it and fill it with hot water from the tap, shake it up. Go out and start the vehicle and at idle spray around the base of the carb and plate. If you hear the idle change then you have a leak. The water should pool up around the lips of the gaskets, the carb base, etc. If you see a spot where the water appears to be getting sucked in, then you've found your leak.


Even if you had to resort to a sealant RTV wouldn't be the one to use, you'd want something like Permatex High Tack Gasket Sealant #98H, Item #80062 or a thin coat of copper coat sprayed on both sides of the gasket. In either one you would put it on both sides of the gasket in a VERY thin layer, and I mean thin, BEFORE you put the gasket on and let them get tacky on both sides of the gasket before putting the gasket on the manifold and then quickly following with the plate and bolting down snug.

Regular RTV silicone is not a good mix with gas and vacuum so should never be used under your carb or carb adapter. Not saying that some people haven't gotten away with it but it's generally regarded as a no-no, there are more appropriate sealants if you are forced to resort to that.
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Unread 02-02-2014, 06:33 AM   #7
Matt1981CJ7
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A lot of guys (with actual experience) use a light coat of white lithium grease on carb gaskets. It's not much help as a sealant, but it will allow you to reuse the gaskets, if you have to pull the carb for any reason.

Matt
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Unread 02-02-2014, 07:01 AM   #8
John Strenk
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Yes grease is what I use but the surfaces have to be flat first.

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Unread 02-02-2014, 12:52 PM   #9
SouthernGypsy
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Quote:
Originally Posted by Matt1981CJ7 View Post
A lot of guys (with actual experience) use a light coat of white lithium grease on carb gaskets. It's not much help as a sealant, but it will allow you to reuse the gaskets, if you have to pull the carb for any reason.

Matt

Yea but that's one of our old racers tricks by those of us like who do have a whole lot of actual experience, learned that the first time from my dad building a drag car when I was a kid but not something we use for DD vehicles. Also used by a friend who owns a speed shop in LR who was a famous Drag racer back in the 1960's when I was building my 2nd '71 'Cuda to race in the Silver State Challenge and then later the Pony Express after they changed the name. But that has always only been a trick for racers who constantly take their carbs on and off where an extremely light coat, like rub just a touch in with your fingertip and then wipe off the excess so it actually looks dry again, but not meant for a normal application. Scott who bought the Laredo just asked the old man here who owns the carb shop about putting anything on carb gaskets and the old man (who also builds carbs for the circle track racers here) said the same thing when he said to keep them dry and Scott said he'd seen his cousin putting something on his race bike, the old man told him that's a different situation for the guys who race, etc. and constantly take their stuff off and on so it doesn't stick, but not something for the average street driver. It does work but your surfaces have to be absolutely flawless and if you don't take your carb on and off a lot like a racer and leave it mounted like a long time like most DD's the grease eventually will 'cook' into the gasket over time actually making it brittle, don't know how long that takes but I have seen it happen on people who had used it on a DD several years before and then just left it mounted.
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Unread 02-02-2014, 01:18 PM   #10
Matt1981CJ7
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Well, I won't go into long-winded name-dropping session to make my point.

What I do know is that every seasoned carb mechanic that I know uses a little lithium grease on their gaskets regardless of the application.

Take it for what it's worth.

Matt
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Unread 02-02-2014, 01:40 PM   #11
SouthernGypsy
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Originally Posted by Matt1981CJ7 View Post
Well, I won't go into long-winded name-dropping session to make my point.

What I do know is that every seasoned carb mechanic that I know uses a little lithium grease on their gaskets regardless of the application.

Take it for what it's worth.

Matt

Odd because I have been all over the country and worked with some of the best well seasoned carb mechanics (since I choose not to rebuild my own carbs I have to) and have never seen any of them use that who wasn't using it on a specialty application like racing, etc.

Maybe it's just something more common in your particular area, I have seen some practices that was done some regions that I'd never seen anywhere else so maybe one of those kinda things... Northern Alaska comes to mind; I seen some things done with vehicles up there like putting grease on wheel studs which is something that no one around here would ever do (and would consider a major no-no) but due to their climate it works ok and I suppose keeps things from freezing to each other.
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Unread 02-02-2014, 02:09 PM   #12
Matt1981CJ7
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The practice of using lithium grease on carb gaskets is well-documented everywhere. Do a search, it's a common practice. Heck, my high-school auto shop teacher even recommended it over 30 years ago. Both the mechanics at my local shop do it on every carb they work on, as do the guys who dyno'd my engine. That's good enough for me.

It not only keeps the gaskets from sticking when you remove the carb, it also prevents them from soaking up fuel, so they last longer.

At this point, I think you'd argue with just about anything I say, so I'm sure you'll keep this one up, too.

Matt
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Unread 02-02-2014, 02:31 PM   #13
SouthernGypsy
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Originally Posted by Matt1981CJ7 View Post
The practice of using lithium grease on carb gaskets is well-documented everywhere. Do a search, it's a common practice. Heck, my high-school auto shop teacher even recommended it over 30 years ago. Both the mechanics at my local shop do it on every carb they work on, as do the guys who dyno'd my engine. That's good enough for me.

It not only keeps the gaskets from sticking when you remove the carb, it also prevents them from soaking up fuel, so they last longer.

At this point, I think you'd argue with just about anything I say, so I'm sure you'll keep this one up, too.

Matt

If you read what I said you'd see that I'm not actually arguing with you (and your the one with the pre-existing reputation as an arguer) and no I wouldn't argue with anything you say, only the things where you assume that you know everything there is to know and that the FSM never made a mistake or omitted something. I actually just agreed with you not 5 mins ago about something in another thread, so stick your ego back in your pocket and get over it and move on.

As for this... I told you I HAVE heard of it, lots in fact, but always in relation to specialty things like racing or the float bowl gasket. Never heard of it for a daily driver. Not saying people don't do it, like I said maybe it's even somewhat of a regional thing like your in Colorado so maybe it's more common there ...high altitude? (actually curious about that possibility)... but in all the places I have been long enough that I ever changed a carb (and I have built numerous performance cars and owned over 400 different vehicles in my lifetime) I've just never once heard of it for the mounting gasket on a daily driver and over the years have heard quite a few carb experts tell people not to use anything on a carb mounting gasket.

Done correctly I don't think it would hurt anything on a daily driver just as it doesn't on race cars, other than over a period of time it cooks into the gasket material and turns the gasket brittle but that takes a long time, and by long time I mean several years on a DD and you'd never know it until you eventually took it back off.


Um, and I'm not sure I would use the high school shop teacher as a reference, I have seen several of those who were in fact idiots and told kids to do things that any experienced real world mechanic would never recommend doing. There are of course really good ones as well but the point is just because someones a HS shop teacher doesn't mean they are actually a good real-world mechanic.



Oh, and I tried your search because I actually am always open to learning new things; Out of the first page of 100 results I got about 50 websites saying not to put anything on a mounting gasket, a dozen or so recommending doing it for things like race cars and race bikes so the gaskets don't stick, several recommending it for the upper float bowl gasket, and indeed a few saying people could try it on their mounting gasket though several of those seemed to be on performance oriented websites so the people may or may not have been referring mainly to people who take their carbs on and off a lot. In almost all of the results that did mention doing it the central theme seemed to be the ability to use the carb gasket more than once, which leaves the question who takes their carbs off and on so much they have to worry about re-using a $1.19 gasket; daily drivers or people tinkering with race cars, etc. As for the OP it may be a viable option while he's getting his carb tuned though I have changed my carb 3 times in 4 months and could have re-used any of my gaskets even without putting anything on them. I never reuse gaskets anyway because risking a vacuum leak is not worth the price of a $1.29 gasket to me and I always prep my surfaces properly beforehand so mine come off clean anyway. But if the OP is still in the 'tinkering' phase it might be a choice to save a few dollars until he gets everything completely lined out.
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Unread 02-02-2014, 03:01 PM   #14
Matt1981CJ7
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Blah blah blah.... The readers can do their own searches and see how common the practice is.

Have you ever heard the term, "the guy who talks the most usually has the least to say"?

I tell you what, you're right, I'm wrong. Feel better, Gypsy?

Matt
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Unread 02-02-2014, 03:19 PM   #15
IMJEFF
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This is my first visit to this forum. I've been turning wrenches for about forty years and have never ran across this snarky of commentary "(with actual experience)" from car/Jeep/Harley guys. I hope this isn't the norm here or I just wasted time registering that I'll never get back. Jeeps are supposed to be happy adventures. For the record (having actual experience), I've never put anything on a carb gasket that wasn't headed to a race track. To answer the actual poster's question...make sure you don't have a leak running down from the fuel inlet. It shouldn't leak fuel at the gasket if it's running well unless there's a crack in the carb housing or a leak at the inlet. The fan can blow the fuel around making the original leak location tough to find. Try shielding the carb while you check it with TP to pinpoint your leak.
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