Secrets to finding vacuum leaks?
Thread Starter
|
Fleet Mechanic
Joined: Apr 2004
Posts: 1,443
Likes: 5
From: Willamette Valley, Oregon
Secrets to finding vacuum leaks?
Yes, I have read the books, but I wonder if anyone has any tricks that work well? I have a 302 in my 56, it idles very poorly, like it has a big cam, and having replaced nearly everything I know to replace, its on to check, once again, for vacuum leaks.. Tricks? Ideas? Thanks!
Posting Guru
Joined: Jul 2001
Posts: 2,119
Likes: 2
From: Southern New Hampshire
Well, the old Ford books say to use a propane (unlit) torch and look for a change in idle BUT I would strongly advise against it.
I use a spray bottle with a bit of dishwashing soap dissolved; the same bottle I use to check for tire leaks.
If there is a vacuum leak it will suck it in and cause a stumble. If it is a pressure leak it will bubble up.
What year 302, carb type or FI?? Did it ever run OK since the swap?
I use a spray bottle with a bit of dishwashing soap dissolved; the same bottle I use to check for tire leaks.
If there is a vacuum leak it will suck it in and cause a stumble. If it is a pressure leak it will bubble up.
What year 302, carb type or FI?? Did it ever run OK since the swap?
Senior User
Joined: Jul 2004
Posts: 362
Likes: 0
From: Minnesota
Propane works fine and it's safe. Just turn on the torch 1/2 way (unlit) and move it around where you think the leaks might be until you hear the idle kick up.
Chuck P
www.oldjeep.com
Chuck P
www.oldjeep.com
Thread Starter
|
Fleet Mechanic
Joined: Apr 2004
Posts: 1,443
Likes: 5
From: Willamette Valley, Oregon
It is a 302 from 73, has a Motorcraft 2300 carb, 2bbl. Never has run right and I am pulling what little is left of my hair trying to figure this out.. I have replaced the carb with a professionall rebuilt, new plugs, wires, changed from points to simple elec ignition, new vac advance, new top end, pistons, rings, heads redone, timing chain, pcv valve, ...still idles vrey poorly, like it is about to die , shakes, like a big cam but I believe it is a stock cam. Automatic choke settings are a mystery to me as well..
Postmaster
Joined: Dec 1999
Posts: 2,813
Likes: 6
From: Connecticut
I agree with 286, I use water. I just feel safer that way. I put plain water in an old fantastik or 409 bottle at spray it around the carb base, intake gaskets, vac ports, throttle shafts, etc to see. If you come across a leak, it will smooth out for a few seconds. Check your vac hoses for any cracks. If you have a vac tree on the back of the intake, check for caps that are dried out and cracked, or popped off. If it's a later smogger 302, check the vac valves that are thermo operated for broken hose ports. Make sure timing, dwell , idle speeds are correct if it's points. If it's carbed, make sure your idle mixture screws are set at 1-1/2 to start. Then adjust them in and out slightly until the idle drops slightly. You will hear it. Then back them out a 1/4 turn so it picks up again. Also the float could be set too low and be starving. But I think you'd see that problem with performance. Is it sooting up the tailpipes? You could also have a blown economizer valve . It's under the front of the fuel bowl. Very common problem, especially after a carb backfire. If you have a spare carb, try that and see how it runs.
Barry
50 F-1
Barry
50 F-1
old and in the way
Joined: Jul 1997
Posts: 5,921
Likes: 1,052
From: Lovely Hueytown Alabama
sooty pipes ??? rich mixture
does it have an "EGR valve" on the rear of the intake manifold....???
many times these will stick and give you a very rough idle.... OR if it has been removed and a plate put in its place... the place can leak or even rust out and give you a vacuum leak big time... I'd look for a leak around the intake manifold somewhere..
john
does it have an "EGR valve" on the rear of the intake manifold....???
many times these will stick and give you a very rough idle.... OR if it has been removed and a plate put in its place... the place can leak or even rust out and give you a vacuum leak big time... I'd look for a leak around the intake manifold somewhere..
john
Trending Topics
Postmaster
Joined: Dec 1999
Posts: 2,813
Likes: 6
From: Connecticut
That means it's running too rich. Try adjusting the 2 mixture screws under the front of the carb. ( I'm assuming it's carbed 302)If it doesn't improve the way it runs, the ecomizer valve may be bad. You have to remove the carb to change it. Turn it upside to drain out any gas. Then, if you have a vise , clamp a dift punch in it and put one of the mounting holes over the punch to hold it. Remove the small screws holding the cover. If you find gas inside, the valve is blown. Take a large wrench and remove and replace it. Put the cover back and you're good to go. But before you go this route, try all the other suggestions as far as for a vac leak. Check your plugs to see how black they might be.
Barry
Barry
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
Thread Starter
|
Fleet Mechanic
Joined: Apr 2004
Posts: 1,443
Likes: 5
From: Willamette Valley, Oregon
Its from a 73, I dont think it has a EGR valve? How can I tell?
There is a fiber(?) plate under the carb with a hose from, if I am remembering correctly, the valve cover. As far as changing the idle screws, I did have a shop that is supposed to be excellent with carbs tune it using exhaust gas analysis (sp?) so I hate to change it at this point, he got it running a bit better, but never a smoothe idle, ever. The carb is rebuilt from National Carb. in FL, still could be something wrong with it, of course.
There is a fiber(?) plate under the carb with a hose from, if I am remembering correctly, the valve cover. As far as changing the idle screws, I did have a shop that is supposed to be excellent with carbs tune it using exhaust gas analysis (sp?) so I hate to change it at this point, he got it running a bit better, but never a smoothe idle, ever. The carb is rebuilt from National Carb. in FL, still could be something wrong with it, of course.
Senior User
Joined: Jul 2004
Posts: 362
Likes: 0
From: Minnesota
Originally Posted by 286merc
Propane works fine and it's safe.
Thats about the dumbest statement Ive read on here in a long time.
One spark or hot spot and BOOOOOM!
Thats about the dumbest statement Ive read on here in a long time.
One spark or hot spot and BOOOOOM!
Postmaster
Joined: Dec 1999
Posts: 2,813
Likes: 6
From: Connecticut
73 was a pre EGR era engine. I'd spray water around that fibre plate and see what happens. The 2 paper gaskets sandwiched in between could be bad. Also check that hose between the carb spacer and the valve cover. That's for the pcv system. They can crack and leak vac. Is this a stock engine? I'd really give the engine a going over for vac leaks, tune up specs, etc...
Barry
50 F-1
Barry
50 F-1
old and in the way
Joined: Jul 1997
Posts: 5,921
Likes: 1,052
From: Lovely Hueytown Alabama
one more guess
since your said it was a rebuilt carb this probably isn't the problem... but another place to look... if the body of the carb was really worn it might be the case...
as carbs are used and age the throttle shaft will wear and also wear the carb body... look for looseness (play or wobble) at the carb shaft where it enters the body of the carb... disconnect the linkage and spring and wiggle the shaft around.... a vac leak there should affect the idle since it's pulling air in that sloppy fit...
just another thought...
If you're afraid of propane... I've also heard of using carb cleaner or WD-40 to spray around gaskets and such... it should have the same effect as the propane... should see an increase in rpm and smoothing out of idle
later
john
as carbs are used and age the throttle shaft will wear and also wear the carb body... look for looseness (play or wobble) at the carb shaft where it enters the body of the carb... disconnect the linkage and spring and wiggle the shaft around.... a vac leak there should affect the idle since it's pulling air in that sloppy fit...
just another thought...
If you're afraid of propane... I've also heard of using carb cleaner or WD-40 to spray around gaskets and such... it should have the same effect as the propane... should see an increase in rpm and smoothing out of idle
later
john