Nothing Special's '71 Bronco

[Nothing Special]

Today I checked the float level wet, without spraying too much gas over the engine. The first time I tried (a few days ago) the fuel was pretty low in the bowl when I started the engine, so the needle valve was pretty far open. That gave a pretty impression of an arterial bleed with a geyser of fuel on each fuel pump stroke.

This time I dumped a little gas in the bowl to make sure the needle valve was closed when I started the engine. Once I saw fuel start squirting again I shut off the engine and measured the fuel level. With the needle valve not open very far it didn't geyser so bad, but it still didn't all stay in the bowl. Like I said before, that method of setting a float level sucks!

I don't have an official spec for the fuel level, for some reason the spec sheet that I have doesn't have that one listed. But I found a bulletin board thread that said it should be 7/8". And then I saw another thread that said it should be .8". So I don't know exactly what it should be, but after setting the dry level correctly at 7/16" the wet level is .81".

A lower number means a higher float level, so it seems like if anything my float is still a little high. But since my issues could possibly be caused by a low float and if anything my float is high, I'm thinking I'll leave it where it is.

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]

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.

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]

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]

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.

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.

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.

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]

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.

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.

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.

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.

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]

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]

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?

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]

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.

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]

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

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]

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).

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