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Discussion Starter #1
My car has about 600 miles on it, since it was built up 10 yrs ago. I know i know.

Anyway, I finally got it back, moved across the coast and want to drive it, but it is running rich, seemingly really rich and I was told to not run it roo much like that or else I risk damage.

I have been searching for a good mustang guy in my area but cant seem to find anyone. Southern coastal Oregon. I have a friend who used to work on these a long time ago who has offered to help, and another guy who is great and helped me with the trans on other car and he could possibly help too.

Here is the question. I was told recently that the best way to do this is to use a 5 gas analyzer to get it proper. Is this truly the case? Is this the only truly correct way to get rhe mixture correct?

I have to go gather my papers and get specs, but from what i remember, 390 bored slightly over, 10:1 compression, holley 750 carb. Not sure what else is needed.

Thanks for opinions.
 

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Bishop, If your car is running that rich, you don't need a Mustang guy, you need a Holley guy. Find a local mechanic or gearhead friend that can make adjustments to the carburetor.
 

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An air/fuel ratio gauge mounted inside the car can tell you all you need in real time.
 

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Running you stang on a chassis dyno, like I did with my 67 390, the computer will tell you your fuel mixture ratio, no guessing. Then tune, mixture or jetting accordingly. Rerun to confirm.
 

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Despite the fact that a 750 cfm is probably too much carb for a mostly stock 390, (stock was a 600 cfm) it can be made to run right for 90% of what you are likely going to use it for, daily driving and cruising.

That being said, start with the basics, make sure that the floats in the float bowls are actually floating and adjusted to the correct level. Next take a look at your main and secondary jets. It's been a while since I messed with them on a 390 but IIRC I ended up running 67 primaries and 76 secondaries and the engine ran quite well and never fouled the plugs. Next, make sure your power valve is the right one for your engine, IIRC 6.5 is stock. At that point, turn your main mixture needles all the way in and then out 1.5 turns each. Start here with fine tuning and troubleshooting vacuum leaks and other carb anomalies such as binding linkage or throttle plates, leaking accelerator pump diaphragm(s), or too much fuel pressure (mostly an electric fuel pump issue). A vacuum gauge is very useful when fine tuning the idle mixture. Holley puts out a basic tuning guide that is very thorough and helpful. Very good resource to have in your library. Hopefully you will find your issue(s) and get back on the road, reliably. Good luck.
 

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My car has about 600 miles on it, since it was built up 10 yrs ago. I know i know.

Anyway, I finally got it back, moved across the coast and want to drive it, but it is running rich, seemingly really rich and I was told to not run it roo much like that or else I risk damage.

I have been searching for a good mustang guy in my area but cant seem to find anyone. Southern coastal Oregon. I have a friend who used to work on these a long time ago who has offered to help, and another guy who is great and helped me with the trans on other car and he could possibly help too.

Here is the question. I was told recently that the best way to do this is to use a 5 gas analyzer to get it proper. Is this truly the case? Is this the only truly correct way to get rhe mixture correct?

I have to go gather my papers and get specs, but from what i remember, 390 bored slightly over, 10:1 compression, holley 750 carb. Not sure what else is needed.

Thanks for opinions.


Hi I was wondering if you would be interested in selling your mustang if so call me anytime on my cell (443)846-1064 my name is Angelo thanks...
 

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Discussion Starter #7
So I have a friend who has worked on these his whole lfe, and he is gonna come help me. But we dont have a sensor.

Does anyone know of a sensor that does not require a bung to be welded and is reasonably priced?

Angelo, thanks for the offer, but it isnt currently for sale.

But I will keep your info in case that changes.

My buddy is gonna come by next week or so and help me out. We are gathering the info and he is doing all the info searching on my model and getting proper gaskets and jets ahead of time. He knows his stuff.

I will keep all posted.

Sorry for delayed responses. My life is hectic. Dealing with some family health issues.
 

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Discussion Starter #8
Ok, so here is an update and some questions.

My friend came by and we worked on some stuff. Right off bat he checked the idle scred adjustments and it was running rich on idle. So we made some adjustments and tested it.

We took the car to a local shop to get it up on a lift and get help with an air drill to drill hole, put on clamp and get afr meter installed. It is cinnected, hooked up and worked right away (finally some good news). So we drove back and monitored it. Here is what we found.

During idle is is slightly rich. Usually running in 11.5 to 12.5 range. When i am running at normal to avg speeds, just cruising at 3000 rpm at 50 or so mph, it is also running in tbe 12 to 13 range.

However. Here is where we havr an issue and I think we know fix. A couole times i pushed the pedal to the floor, and be noticed at first it just doesnt have the pull it should. It feels sluggish and like it isnt pulling. When i really hit the gas hard for 5 to 7 seconds, the afr meter shot uo and held between 15 and 16. So seemingly very lean. I didnt do this much as he said it isnt good. Parked it and we quit for day. If i run it without stepping on it and just light cruise it cruises in the 12 to 13 range.

My friend said it appears to be the secondaries are need to be jetted up to get the numbers better.

Now here is a new problem that just starter after we started to adjust and I could use some help on this.

After we got to the shop, and home snd after we started to adjust, whej i turned the car off, it still fired a couple times and the died. This is new. It have never done this before.

My friend said it could be because it is getting hot when running lean, and getting too hot and then igniting after it shuts off.

I told him I would post up what we did tonight and get some feedback on this from everyone.

We are also going to check the distributor and make sure everything is proper, but this will be this coming sunday most likely.

So I wanted to get some feedback on these snd get some help.

Please let me know what we should also be checking and what thoughts on the firing after key is turned off.

Thanks guys.
 

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Discussion Starter #9
Oh and the afr meter install was fairly easy and worked right away without much hassle.

Finally something went right!!!

So far i am liking the afr meter I ended up going with.
 

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Your "run on" issue is probably caused by throttle plates that are open too far at idle... either on the primary or secondary side. I'd shoot for an idle AFR of around 13.5, light cruise 14.5 and WOT around 12. Going lean immediately upon WOT is typically caused by an insufficient accelerator pump shot, particularly when the AFR starts to return toward "normal" as time progresses. If it starts to go rich and then goes lean and stays there it sounds like a power valve issue.... a leaky accelerator pump or power valve will also contribute to a rich idle. I concur with the suggestion to find a "Holley Guy". While your "guy" may be skilled, generally, there's no substitute for somebody with loads of experience.
 

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Before you get deeply into trying to get this carb to work right, consider simply getting one more compatible with your engine. A stock original would be a good choice, but these days pretty expensive. A more driveable choice would be a Summit carb. Superior to the original 4150, but uses Holley items in the unlikely event it needs to be reconfigured.
 

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Discussion Starter #12
And I want to throw in a reminder however, that the run on issue literally just started. It has never ever done that before, and only started immediately after we started adjusting carb.

Not saying what it is caused by, just trying to give you all the exact facts to help solve the mystery.

And i have driven it for longer periods of time than yesterday, by a lot.

Thanks again.

Very interesting info from you guys. If this forum wasnt around I would be lost.

Thank you all.
 

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Before you get deeply into trying to get this carb to work right, consider simply getting one more compatible with your engine. A stock original would be a good choice, but these days pretty expensive. A more driveable choice would be a Summit carb. Superior to the original 4150, but uses Holley items in the unlikely event it needs to be reconfigured.
I'm his "guy" and this engine is in no way stock. It has a very aggressive camshaft, aftermarket intake manifold, pistons and more with a compression ratio of 11:1. It's got headers too. The 750 cfm 4150 Holley should be a good fit for this engine. A stock carb might not keep with this engine. But I agree there is something to your idea about bolting on a new performance carb that's a good fit for a 400 hp FE 390. Now that we have an AFR gauge, we're going to play with power valves and jets and see if we can find a good range of AFR using this Holley and consider replacing it if we can't achieve what we're trying to do. Thanks.
 

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Your "run on" issue is probably caused by throttle plates that are open too far at idle... either on the primary or secondary side. I'd shoot for an idle AFR of around 13.5, light cruise 14.5 and WOT around 12. Going lean immediately upon WOT is typically caused by an insufficient accelerator pump shot, particularly when the AFR starts to return toward "normal" as time progresses. If it starts to go rich and then goes lean and stays there it sounds like a power valve issue.... a leaky accelerator pump or power valve will also contribute to a rich idle. I concur with the suggestion to find a "Holley Guy". While your "guy" may be skilled, generally, there's no substitute for somebody with loads of experience.
I agree with your target ranges for AFR, and I believe we can achieve them with larger power valve and smaller primary jets. After finding optimal vacuum by adjusting the idle needle jets I adjusted the idle screw on the throttle assembly to find the smoothest idle speed possible with such an aggressive duration cam. The engine lopes pretty hard and at 1000 rpm it was better, but is almost certainly the cause of the run-on. We're going to adjust that down to 750 or so and I'll bet that solves the issue. Thanks for your feedback. Appreciate it. -- his "guy". :cool:
 

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I assume you're running premium fuel? With compression that high, anything less can cause pinging and run on.
Most definitely. Good question though, and the high compression might still be a contributing factor to the run-on, but in all our test runs, there was no pinging whatsoever. Thanks!
 

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Discussion Starter #17
We just finished another day of working on tuning, and finally have it in a much better place and really close to perfect. This is all thanks to my friend (erik) who came by and really did everything. I owe him one for sure.

The kind of detail information we got from this we never would have even come close to getting right without and AFR meter. Using one of these was absolutely necessary.

The run on is resolved, and running idle, mid rpm and WOT all in the very respectable 12 to 13 range, much much better.

The timing was terribly off, which again was easily fixed by my friend. So coupling those issue, now running properly, it was amazing how much better the car drove. It had so much more pull, power, torque, etc. It was incredible.

We may have to do some perfecting, but it is now out if the danger zone of being super lean. Erik can correct me if I am wrong, but we ended up going 7 or 8 jet sizes bigger for secondaries, and 4 or so for primaries. Not to mention the power valve went from the stock 6.5 to 9 5.

It is very clear the car was never tuned properly. Finally getting it done and it drives like a completely different car.

Thanks again to my buddy erik and to everyone helping me on here as well. Will continue to update as changes happen.
 

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Really enjoyed working on your car Bishop!

Oh, and in addition to the much larger power valve, we went from stock 71 primary jets to 78s, and bumped the secondary jets from 80s to 88s. It really took that much of a change to get the AFR into a safe range about 12 to 13. It's really running great now, especially after fixing the timing. We still have a little more work to do to perfect the tune, but the heavy lifting is done and it's safe (and fun) to drive.
 
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