Nothing Special's '71 Bronco

[Nothing Special]

Separate post because it's a separate angle (edit: and see the last post on the previous page for my findings on float level), but today I also pulled the passenger's side spark plugs.  It's a royal pain getting at the driver's side, so after what I saw on the passenger's side I decide to skip the driver's side.

All 4 passenger's side plugs were very white, looking like it's running lean.  It acts like it's running lean, so I'm thinking it's just running lean.  I did get an e-mail that the jets I ordered have shipped, so hopefully I'll have them early next week.  And hopefully I went big enough!  I have 48s and I ordered 49s and 50s.  So we'll see what we see when they get here.

[Gary Lewis]

Sounds like you are getting it dialed in.  Float level - check.  Plugs - check.  Jets - soon.  Hope that solves the problem.

And I can't think of what else it could be.  But do you have EGR?  

[FuzzFace2]

Gary Lewis wrote

Sounds like you are getting it dialed in.  Float level - check.  Plugs - check.  Jets - soon.  Hope that solves the problem.

And I can't think of what else it could be.  But do you have EGR?

Or power valve?
That would also add more fuel.

On the jets if really white I would of gone with 50's and 51's.
IIRC Holley has you going up or down by 2 numbers till close then 1 to hit the mark.

Do you run a AFR meter?
I dont know if they help or hurt LOL
It did point me to an issue with my Carter YF carb that I might not have known about other wise.
In the cool mornings the AFR is not bad, still a little rich, but when it warms up in the after noon it is a lot richer. Think I am going to see about leaning it out just a little more some day.
Dave ----

[Nothing Special]

Gary Lewis wrote

Sounds like you are getting it dialed in.  Float level - check.  Plugs - check.  Jets - soon.  Hope that solves the problem.

And I can't think of what else it could be.  But do you have EGR?

No EGR.

FuzzFace2 wrote

Or power valve?
That would also add more fuel.

The power valve was new with the rebuild kit I got when I bushed the throttle shaft last winter.  So it's not the same one I was running last year, but it "should" be good.

FuzzFace2 wrote

On the jets if really white I would of gone with 50's and 51's.
IIRC Holley has you going up or down by 2 numbers till close then 1 to hit the mark.

If I'd have looked at the plugs before I ordered the jets I'd have gone a little bigger too.  As it is I'll start with the 50s when they get here and see what I think after that.

FuzzFace2 wrote

Do you run a AFR meter?
I dont know if they help or hurt LOL
It did point me to an issue with my Carter YF carb that I might not have known about other wise.
In the cool mornings the AFR is not bad, still a little rich, but when it warms up in the after noon it is a lot richer. Think I am going to see about leaning it out just a little more some day.
Dave ----

I do not have an AFR yet.  It's on the list, but hasn't been very near the top.  As I said, I got this carb from a junk yard and just ran it.  It's always worked pretty good, but I've never been confident that it was really dialed in.  So some time I would like to do that.  And if I can't get it back to "pretty good" the AFR might move up the list.

[FuzzFace2]

Good on everything but the power valve.
OK so the PV is new and should work but do they make different ones like Holley's to dial it in?
Holley's are marked on them so you know what vacuum it works at. Are the MC ones the same or can you use Holley's?

I knew the jets were different and when I could not get my MC carb to run right on my AMC 304 motor and having the 2300 Holley on the shelf and a box full of tuning parts for the race track I went Holley.

Son just rebuilt a 2300 for his Jeep YJ running a 258 AMC straight six.
I told him to write down the jet size, PV size and the accel pump nozzle size so he knows what he is starting with and we can adjust from there as needed. I think he said before when he was using the Jeep it ran rich?

I just never got into the MC carb to know what parts you can get for them to "dial it in".
Dave ----

[Nothing Special]

FuzzFace2 wrote

Good on everything but the power valve.
OK so the PV is new and should work but do they make different ones like Holley's to dial it in?
Holley's are marked on them so you know what vacuum it works at. Are the MC ones the same or can you use Holley's?....

There are power valves for Motorcraft / Autolite carbs available at 2.5", 3.5", 4.5", 5.5", 6.5", 7.5", 8.5", 9.5" and 10.5" Hg (just what's listed on the same web site where I ordered the jets).  I don't know what I have in it or whether they are interchangeable with Holley power valves (they look very similar, but then again, so do the jets which are actually 1/16" bigger thread).

I've got to admit that I really don't know anything about power valves.  Where in the operating range do they have their impact?  And how do you decide if you have the right one. or which way to move if you don't?

[ArdWrknTrk]

They open at X "hg.
Rule of thumb with Holley's is 1/2 of closed throttle vacuum minus two inches.
So, if I have 18" at idle, a 7 is about right for me.

[nic55kel]

As I understand it the power valve opens to richen the mixture for acceleration and high power demand situations. You don't want it running lean under those conditions on the other hand you don't want a rich mixture in normal cruise or your fuel economy will suffer. Bit of a juggling act to find what vacuum you normally cruise at so the valve is closed unless of course at normal cruise with the 8000lb trailer you need the fuel enrichment for engine longevity.

Bob

[Nothing Special]

Thanks!  So I should probably get a vacuum gauge and figure out what power valve I need (and I should probably figure out what power valve I have).

I'm 95% sure that there was a new power valve in the rebuild kit I bought and that I used it.  But I can't find the old power valve.  So either I'm wrong and there was no new power valve, or else I'm right and I threw the old power valve away.

Going on the 95% chance, I wonder if the old power valve opened sooner than the new one?  If it did, maybe it was opening during cruise and was giving me a "good" mixture even though the jets were too small.  Then now with a power valve that's not opening at cruise I'm running too lean.

Anyway, I may never know.  But for now my plan it to stick the 50 jets in (hopefully tonight, tracking says they're out for delivery).  If it runs good I'm going to run it.  If not, then I'll need to do more diagnosis now.  But if it runs good I may never figure out what power valve it SHOULD have (until/unless I get an AFR and actually try to dial it in).

[nic55kel]

I like your theory on the old power valve or maybe it was leaking, as you say you will probably never know.
Hopefully it runs better for you with the new jets.

Bob

[Nothing Special]

I doubt it was leaking.  This got last several posts back, but when I first started it this spring I could hardly get it to idle.  Turned out (no pun intended) that the idle screws were turned way too far out.  I'm guessing that was to deal with the vacuum leak at the throttle shaft.  Now that I fixed the vacuum leak I needed to lean out the idle mixture to get it to idle.  If the power valve was leaking I'd have gone lean at idle when that was fixed.  And I didn't.

But this is just bench racing.  No way to really determine anything from it.

[Nothing Special]

Well I got the new jets, but the jury's still out.  I didn't get much chance to test drive it last night.  Our city had a 7:00 curfew yesterday so my evening was pretty short and I didn't get a chance to really get it up to operating temperature.  And this morning I drove it to work, but it's pretty cold this morning (low 30s) and the temp gauge never got up to where it normally runs.

That said, it's not a lot different.  Maybe that's because it's not getting warmed all the way up, or maybe it's just not all that different.

Last night it did feel like it was waking up pretty well with just a little more throttle.  That might be accelerator pump, but I was trying to roll in slow enough that there wouldn't be much of that.  So maybe it's that the power valve is about to open?

Anyway, my plan today is to drill out my stock 48 jets to about 0.052" and see if that helps.  But eventually I probably need to get an AFR and a vacuum gauge and really try to dial it in.

[Gary Lewis]

Hard to test w/o getting it fully warm.  But if it felt like it was waking up you are on the right track.

The power valve shouldn't be open at cruise unless you are climbing a pretty significant hill, so you need to get the engine happy with the jets.  An AFR meter will help a lot, but you can do it with a vacuum gauge.  That will let you know when the power valve is open and you can tune the main jets to keep it closed most of the time.

As for drilling jets, that doesn't always work well in my experience.  The jets are tapered to smooth the flow in and out, and if you take the taper out by drilling you may actually lose flow.  But, it is worth a try.  Good luck!

[Nothing Special]

Looking at the 48 jets under a microscope, the output end looks pretty square, with just a simple chamfer on the input end.  So I should be able to get it pretty close.  And my intent is to just get it pretty close, then to order a range of "real' jets around wherever I end up.  (And we'll see how many years it takes me to actually do that if "pretty close" is "good enough" )

[Gary Lewis]

I understand the "good enough".  I have a t-case shift lever that's backwards to the pattern on the knob.  

Anyway, I think I've read that each jet size varies as to the input and output taper.  And that some jets with different numbers have the same orifice size but with different tapers.  I don't know if that is true, but my memory says I read it at Holley's site or in a book on their carbs decades ago.

But if you have a microscope you can see if you have any taper left after drilling.  If not, maybe use the next larger bit to add some?  Or use a Dremel tapered grind stone, by hand, to at least take the edge off?

[ArdWrknTrk]

I don't think you're going to get a dremel stone into a jet.
I have some micro diamond burrs for drilling FR10 PC boards.
Maybe they would be small enough.
But the place in Japan I got them from went out of business after SMD's took over.

The power valve should only open when vacuum drops below it's set point, and older power valves (like came in the 4180's were two-stage.

The best tuning instrument you can get (my opinion) is a vacuum gauge on the dash.
This will tell you more about how you drive, and how your engine responds.

[Gary Lewis]

You are probably right on the stone.  I've not even been out to the shop since getting back, so haven't eyeballed a jet/stone combo.  But hope to get out there in a bit and will do.

And I agree on the vacuum gauge, at least for this application.  Bob knows he's a bit lean given how it perked up with larger jets.  So if he can get it to perform well off the main jets and just dip into the power valve when climbing a big hill or needing to pass, w/o WOT, then I think he'll be "there" on the mains.

Then it is a question of when the PV comes in.  Is there an area of throttle/low vacuum where the engine is "flat" just before the PV comes in?  If so, then go to a PV that opens at a higher level of vacuum.  If not, then it is "good enough" time.  

[Nothing Special]

I checked my 48 jets with plug gages before I drilled them out.  An .047" gage would go through but an .048" gage would not.  So I guess they were running slightly small.

I ran a #55 drill bit through both of them and now an .052" gage goes and an .053" gage does not, so right where I was aiming.

The chamfer in the jets is a lot bigger than the difference in hole size, so I'm not going to touch the chamfer.  I think I have essentially the same lead-in now that these jets had before.

I'll stick these jets in tonight and see what I think.

On the power valve, I'm thinking it's probably pretty close.  If it feels flat at steady cruise and wakes up with just slightly more throttle it seems likely that the power valve is opening just a little above steady cruise.  I could imagine that once I get the jets dialed in that the power valve might be opening just a bit early, and going one step lower in vacuum to open might be better.  But it's probably pretty close.

[Gary Lewis]

I think you are going to be "right on".  I say that because the jets will work out nicely with the taper above the drilling.  And the richer mix is going to increase the vacuum at cruise 'cause you'll have to close the throttle just a bit and you'll be farther away from when the PV opens because of that.  

[ArdWrknTrk]

Gary Lewis wrote

  If not, then it is "good enough" time.  

Who are you????

And what have you done with Gary?