My '82 Bronco was occasionally going into "bogs" when driving. It would just get loud, lose gobs of power and just generally run poorly every once in a while (also backfired on deceleration a lot during these episodes). Then, for no reason it would come out of the bog and run fine. I also had a large vacuum leak inside the carb. So a couple of weeks ago I rebuilt it.

After that it ran much better, had no vacuum leak and the truck overall was more responsive. Life was good for about a week. Then the bogs started happening again and I could tell it was running a little rich. Well the running rich problem has gotten worse, a lot worse. In fact my eyes are burning while I drive this thing around. It drives ok, isn't putting out all the ponies it should be but the biggest sign of a problem is the drop from 14mpg's to 9mpg.

Now, the only problem I have with the carburetor that I know of is that the fuel/air screw on my Carter YFA doesn't do anything. The engine reads almost 25 lbs of vacuum as it sits, but adjusting that screw doesn't do anything (not vacuum, idle speed, nothing) until it bottoms out in the hole from being tightened or falls out from being loosened.

I did notice while spraying some carb cleaner around looking for vacuum leaks that the distributor responds to spray indicating a leak.

One more hint, over the last couple of weeks the gas tank has become extremely hard to fill up. Even on one click and with the nozzle pulled out so far it's barely hanging in there it goes about $5 before clicking off even when the tank is empty.

So... where should I start with this thing?

Thanks!

 

When ya rebuilt the carb, did you make sure the float level and drop were accurate? My float was GONE when I bought the truck, rebuilt the carb, didnt do the float adjustment right, and the idle air mix did nothing because I was still spilling gas into the engine. My engine RPM would fall off when it would flood then rev back up all of a sudden, causing more fuel to come in, then would flood again, and so on so forth.

Is the vac leak actually around the spark advance? Check your vac hoses for cracks. Also, it may seem crazy, some say I am, and this is prolly not gonna be recommended by ANYBODY else, but if you are desperate enough, buy some vac caps, cap off everything but the dizzy and the PCV, and put new hoses on those. As has been said to me by others on here "the engine can run with NO vac lines plugged to ANYTHING, so long as theyre capped off right".

Then grab some carb cleaner and see if ya missed anything.

Keep us up to date with developments.

 

I set the float according to the rebuild kit instructions, it was pretty close. The metering rod was waaay off from where the instructions said it should be. I don't know my carb terminology but the kit said that the metering rod should bottom out when the (don't know the name of it) other rod that it's attached to bottomed out, so they should hit at the same time. I probably had to put 4 full turns on the metering rod to get it to do that. But again, it ran great for the first week after I rebuilt it. I dunno, I just did what the kit said to do.

I like your idea because it's the easiest way to find the problem by adding one more thing back until there's a problem. The only thing is I have 23-24 on my vacuum gauge right now, isn't that about as good as it's going to get?

 

Something isn't set right in the carb. Just guessing, but it's not running on the idle circuit, (when it should be) and that's why the idle mixture screw doesn't have a positive action.

Make sure your timing is set correctly and use your vacuum gauge to adjust carb after you get the throttle plate adjusted right or whatever it is. Over 20 inches of vacuum is "good" but "too good" - maybe related to the carb being horked, dunno. Should be 19 to 21, say. Tuning with a vacuum gauge is real precise and the idea is to lean out the carb as far as possible (but no more) making adjustments to idle and mixture. As idle speed increases with mixture the throttle stop is backed down, etc. The idle mixture needle will have a definite sweet spot on a well tuned engine. Make sure your linkage is set correctly and throttle plate has proper gap at idle, and is perfectly vertical at full throttle.

http://classicinlines.com/vacuum.asp

Sent from my iPhone using IB AutoGroup

 

Hmm true. I didnt see that part about engine vac. Got ahead of myself. Well, Im going to be honest. Carbs aren't anything I know anything about. I just know what problems I had, and were similar at some points.

What do you have your idle speed screw set at? Theres a spec for it. When you hold the gas pedal at an even height, i.e. steady RPM, does the bog happen, or does it smooth out? If it doesnt, when ya take off the dizzy vac line, then cap it at the intake tree, does it smooth out?

Idk all of what the problem could be. Im not the greatest, and Im young, so not too much experience, just a little classroom learning. But I have learned (thanks guys) that a lot of problems can be fixed simply by eliminating the impossible. Whatever remains, however improbable, must be the truth. (Sherlock)

Also read this thread, I had the same conundrum with my air/fuel mix:
https://www.ford-trucks.com/forums/1...se-help-2.html

 

Get back to the pressure reference on the gas tank. Not being able to fill it properly. I am surmising you think there is pressure keeping it from filling, not an obstruction.
For grins, does it make any difference when you run the engine without a gas cap?
How many lines are coming from the gas tank - one for fuel, a vent line and do you have another going to some sort of canister in the engine compartment.
I am with cstephens, start by simplifying the environment.

 

Is the idle speed higher than normal?

 

Timing was just set after I rebuilt the carb, it's dead on at 10.

I will check the throttle plate and the gas cap off. You are right, i'm wondering if there is pressure in the tank that's affecting life under the hood.

The "bog" is far less predictable than I must have explained it. The only thing I can say is that it usually, but not always, happens when the engine is cold. It goes in to what I think is a mega rich condition. So it goes from ridiculously rich to stupid rich for a bit, sometimes for a couple hundred yards, sometimes for 2 miles before it comes out of the bog. Nothing I can do seems to affect it.

I guess I should have said, my plan was to buy a new carb. I started this thread because I thought maybe there was another explanation that would save me putting on a shiny new carb only to find out that it wasn't the problem.

 

Might try hooking the vac gauge and driving it. You should drop waaaay down when you clip the throttle, if you dont pop back up, that may tell ya something. Try just watching the vac gauge while driving, if it bogs, see what the gauge is doing. The motion of the needle tells a story in itself.

Might take the vac gauge and watch it when ya spray the carb cleaner on the dizzy. If there is a vac leak or something fishy at all, and the throttle plate stays closed while the engine revs, the needle should go up, Im thinking. Again, motion of the needle is important.

Does it fluctuate? Stay steady?

 

Check your carb for plastic needles in the float bowl had a 300 -6 1983 carter one barrel carb the alcohol fuel just keeps eating up all the seals and plastic jets installed a holy 440 CC carb 4 barrel and a new intake the carb was easy to adjust with the clear site glass inserts that come with the carb also ordered it with bras jets no plastic having a good time still works and runs