Nothing Special's '71 Bronco

[Nothing Special]

... and on the (sort of).  (edit, sorry, go back a page to see what I just posted about the parking brake pedal)

I pulled it out of the garage, checked all the fluids and called to get insurance back on for the summer, so it was time for a test drive.  It was running like crap.  Wouldn't idle at all, and won't make any power above 2000 rpm without being choked.

I played with the idle screws (Autolite 2100 carb) a bit and found that they were turned WAY out.  I turned them all the way in and backed them out 1 turn.  Then it would idle with some choke.  So I opened them a bit more and got to about 3 turns before choking it didn't help.  So now it will idle (sort of).

I guess it makes sense that it was too rich now.  The big carb change was bushing the throttle shaft to get rid of a HUGE vacuum leak, so it probably needed to be rich to run before and now needed to be corrected.

But that doesn't explain why it seems way to lean on the high speed jets (needed to be choked to run decent).  So I need to figure that out.

And like I said, it only sort of idles now.  We took the obligatory trip to Dairy Queen in it this afternoon (sunny and 70 degrees after highs in the 30s earlier this week, so we even put the top down).  It will sit at idle OK.  But when I try to creep forward in the drive-through lane it will die pretty easily as I try to engage the clutch.  And it will usually die when I come off the gas and hit the clutch and brake to stop.  That definitely needs to be better before taking it 'wheeling in Moab.

[Gary Lewis]

Well, I agree the pedal isn't pretty.  But if it works you can move on to the cables - and won't you need them at Moab?

As for the carb, that's strange.  It does make sense that you had to have the screws out earlier due to the leak, and needed to turn them in now that the leak has been fixed.  But that doesn't explain at all the lean condition at cruise nor stalling at other times.  Good luck!  

[Nothing Special]

I haven't had a working parking brake for several years.  Wanting one is why I switched the rear brakes from disk back to drum a year or so ago.  But having lived without one for the last few 'wheeling trips, a working parking brake definitely doesn't hit the "need" category for me.

Plus, I've rarely had a vehicle with a parking brake that I'd trust to hold the vehicle on the hills I end up on when I'm 'wheeling.  Remember that Jeep that went off Black Bear Road last summer after the driver got out?  I suspect he was trying to use his parking brake to hold it.

Since I wouldn't count on the parking brake I'll always shut off the engine and leave it in gear.  With a final drive ratio of 70.5:1 (4:1 trans, 4.3:1 transfer case, 4.1:1 axles) it ain't goin' nowhere, so I don't NEED a parking brake.


On the carb I'm thinking my next step might be to pull it apart and see if blowing carb cleaner through it might help.  It's running lean when it should be rich, so maybe something's plugged?  That's clearly my priority now.  I don't want it to be stalling on me constantly on hill climbs.  That could get spooky.

[Gary Lewis]

I agree a parking brake isn’t the best thing to hold with on the trail, but I like the idea as another layer of security. Big Blue’s parking brake is binary - on or off. And when on and in 4wd the front wheels are included. Plus with the locker on you have both front wheels locked.

But I agree that it isn’t necessary, so isn’t a “need”. With your gearing it won’t move.

And I think your idea on the carb is good. Just keep the cleaner away from the little umbrella check valve for the accelerator pump. Don’t ask.

[Nothing Special]

So after taking the carb apart and trying to clean it it's definitely better.  But not quite "good".  It's still down on power above 2000 rpm with the choke open.  Choking it a little wakes it up a lot.  So it's still running lean.

And while the idle is MUCH better (set at about 800 rpm according to my questionably accurate tach), when it drops down to idle it overshoots, going to around 400 rpm and stumbling a bit before (usually) recovering.  There were a couple of times it actually died, but I can drive it without setting the idle up to around 1500 rpm like I needed to yesterday.

One other thing that I hadn't checked until today, I still do have a slight vacuum leak on both ends of the throttle shaft.  The idle drops a little when I spray carb cleaner at either end of the throttle shaft.  Last year, before I bushed the throttle shaft it was a HUGE change in idle when I sprayed carb cleaner on it, so it's definitely an improvement.  But it also definitely ain't perfect.  Should I be expecting no change in idle when I spray carb cleaner on the throttle shaft?

[nic55kel]

If it were mine I would be checking:
fuel filter plugging
fuel pump - pressure and volume
float level
inlet needle valve assembly for restriction
Main jet partially blocked (would have put this earlier but you say that you have cleaned the carb).
A vacuum leak  will usually show up as an idle that is too high with less and less effect as the rpm and load go up.

[Nothing Special]

Thanks for the suggestions!  Here are my first thoughts (not intending to dismiss any of the suggestions in any way, just, as I said, my first thoughts).

When I tried to start it after cleaning the carb it didn't take long at all to fill the empty float bowl and get it to fire.  Not a very scientific test, but I seem to have good fuel flow, so I don't think I've got a plugged filter or any issue with the fuel pump.  Might be worth a closer look, but I don't think it's that.

I honestly don't know how to check float level on an Autolite 2100.  Or didn't.  I just Googled it and I'm not loving what I found (it was a lot easier to check and adjust on the Holley I had on my old Jeep!).  I should probably take a closer look at that though.

Again, it filled so fast that I don't think I have any inlet restrictions, but still something to keep in mind.

I'm pretty sure the main jets were partially blocked before I took it apart and cleaned it today.  Well, not the jets themselves, they seemed very clear.  But the passages where the fuel goes after going through the jets didn't allow carb cleaner through very well at first.

The idle isn't too high, but then again, the idle screw is still where it was when I had the really worn throttle shaft bushings giving me a much worse vacuum leak than I have now.  And yeah, it makes sense that whatever smallish vacuum leak I have now shouldn't be affecting me at more open throttle above 2000 rpm now (which is where my biggest issue is).  Mostly I'm just wondering if I still have too much clearance in my throttle shaft bushings.  They seemed pretty snug on the throttle shaft and I don't think I can do much better.  But I'm wondering if I need to.

[nic55kel]

I guess the big question is: Did it run okay before you bushed the butterfly shaft?
I would be surprised if that wear would have had much effect above idle/partial throttle.
If it did have adequate power before installing the bushings, what changed?
I am not familiar with that carburetor but it surely seems like there has to be a restriction somewhere in the circuit feeding the main jet.
Anyway good luck.
BTW the spell check doesn't know how to spell carburetor!!

[Nothing Special]

It ran OK but, the idle was really flaky.  It would idle OK most of the time, but then would suddenly drop a bunch of RPM.  Sometimes it would catch and come back, but frequently it would die.  Spraying carb cleaner at the throttle shaft changed the idle speed a LOT (it would about die).  I don't know if that was also the cause of my flaky idle, but it definitely seemed worth fixing.  And the idle is no where near as flaky now as it was last year (although it's not perfect yet).  So it seems like the two could be related.

I bought a carb rebuild kit as well as a kit to bush the throttle shaft.  So it does have a new float and it's likely that the float level is different than it was with the old one.

Also we had some work done in a bathroom and the contractors were cutting stuff in our garage.  The carb was sitting on my work bench.  I'm guessing it got a bunch of crud in it which is why cleaning it today helped so much.

So I think checking the float level is a good next step.  Trying to clean the carb again/more might also be a good thing to do while I have it off the engine and taken apart to set the float level.

[Gary Lewis]

If the idle speed doesn't change when you spray carb cleaner on the throttle shaft then you don't have enough leak there to be an issue.  I think all carbs leak there to some extent.

On setting the float level, have you looked at our documentation at Documentation/Fuel Systems/Carbs, Chokes, & EFI/Motorcraft 2150?  We have the section from the FSM there.

[Nothing Special]

It does drop a bit now, but no where near as much as it used to.  I think I'll quit worrying about that.

I had not seen that.  It does make a wet check seem a little more doable than what I found before (running the engine with the top off the carb didn't see like something I wanted to do ).

I still think I'll pull the carb, set the float level dry and blow more carb cleaner through next.  But thanks, there's a lot there to help if that doesn't get me where I need to be.

[Gary Lewis]

I’ve rarely run one with the top off, but it works.

If your float level is too high you could be getting spill-over on starts or stops. Too low and it could be sloshing away from the idle circuit. So I’d concentrate on the float level.

And blowing out the passages is a good idea. If you have gunk in there it can cause all sorts of issues.

[Nothing Special]

Gary Lewis wrote

....  On setting the float level, have you looked at our documentation at Documentation/Fuel Systems/Carbs, Chokes, & EFI/Motorcraft 2150?  We have the section from the FSM there.

I found the "Instructions" section under Motorcraft 2150.  And in that I found instructions for how to set the float level, both dry and wet, on page 24-25-11.  But in the otherwise pretty detailed instructions all it says is to set it within the specified limits.  However I can't find anywhere that it specifies those limits.

Am I missing something?

[Nothing Special]

I did find an instruction sheet that I kept the first time I put a carb kit in this carb (I got the carb from a junk yard).  It had float level specs, and gave 7/16" dry for my application (and most others).  I was at about 3/8".  Having the float too high doesn't seem like it would make it run lean.  I'm thinking it would go more the other way.

But I dropped it back to 7/16" anyway.  I also sprayed a bunch of carb cleaner again while I had the opportunity.  The test drive really didn't go any different from yesterday.  It's running pretty good, but it needs some choke to make power at mid- to higher speed, and the engine speed drops a little too far sometimes when going back to idle.

Unfortunately I think the next step is going to be to take it to a carb shop.  I just don't have the time to keep poking at it right now.

[Gary Lewis]

Bob - There's not all that much to go wrong with a 2150, especially to cause those symptoms.  It sounds to me like you still have a vacuum leak that is causing it to be quite lean at cruise.

I expect you are running out of time before the trip, so I'm going to tag Bill in this discussion.  Perhaps he will have some suggestions on what would cause these symptoms?

[ArdWrknTrk]

I would have said massive vacuum leak, given the need for choke.

[Gary Lewis]

Yes, massive.  But seemingly only at speed since the idle screws don't have to be out a long way?  

[Nothing Special]

The idle screws are out 2.5 turns, which seems a little far to me.  But not as far as they were last year before I bushed the throttle shaft.

I can't think of where to look for a vacuum leak that happens only at speed.  It's a pretty simple system.  The only vacuum hoses are going to the PCV valve and to the distributor.

And for what it's worth, I have an Autolite 2100, not a Motorcraft 2150.  I don't think there's a lot of difference, so I don't think any of the advice has been off-track.  But in case anyone's keeping track...

[Gary Lewis]

2 1/2 turns is a bit farther out than I usually find on them, but not bad.  Which is why I'm confused with why you are so lean at cruise.  And, like you, I can't think of anything that would do that.

Have you checked to make sure the orifices in the boosters are clear?  I'd run a strand of copper wire through them.  Seems to me like something is blocked.

[Nothing Special]

I haven't tried running a wire through them, but I've sprayed carb cleaner about everywhere I can think of and nothing seems to be blocked.