Another Carb question

[railroad]

Sounds like your floats may be too high. I would check them with the sight plugs. If you have an electric fuel pump you can get real close with the engine off. I did not see what power valve you installed. By the number, your cam seems mild, I would think your idle vacuum would be a little higher, although 10 gauges will you give you 10 different readings. If it has not been back firing, look down into the carb while idling. You should not see any fuel dripping from the boosters or pump nozzles.

 

[Keeper]

I will give them a look. Though I am pretty sure they (the floats) are correct.

Here are the specs:

cam - Compcams xe262
sbc 355
9:1 compression
stock 882 heads
timing set at 8
holley 600 vacuum secondary - manual choke
66 primary
67 secondary
6.5 power valve

I think that covers it.

 

[Wild Mango]

You mentioned in your initial vacuum gauge hookup the needle "was bouncing around". Suggests to me you were connected to ported vaccum. At idle there should be no signal on ported vacuum. Perhaps the butterflies aren't shut quite enough and the transfer circuits are coming into play, which would explain your black smoke and seemingly very lean idle screw settings.
See an earlier post talking about introducing a little extra air by drilling the butterflies, which allows the tuner to close them enough to stop the transfer circuits being part of the deal. Screamin' likes to notch file them, so there's more than one good way to skin that cat.......................

 

[Keeper]

No it was bouncing because I had it resting on the engine. Once I picked it up the needle was steady.

 

[2old2fast]

How far open are your sec. flaps ? If they are to far open, then the sec idle will supply too much idle emulsion to accurately set your primary idle.

dave

 

[Differen T]

As stated above it is critical that the throttle plates do not expose any of the transfer slots at idle. With your Com 262 cam and 700R4 is 800 RPM idle in gear? If so it is very likely that you are exposing the transfer slots and the best way to check this is to remove the carb and look at the slots from the bottom. If so then you need to provide more air at idle and this is done by drilling the same size small hole in each of the primary throttle plates. Unless you have a complete set of lettered and numbered drill bits it is easy to drill the holes too large using fractional drill bits. Start at 1/16 inch and gradually increase the size until the throttle plates no longer expose the transfer slots. Unfortunately this requires a lot of on and off for the carb and a readjustment of the idle mixture and idle set set screws with every increase in hole size. When done correctly the results will be a smooth transition from idle to power and a pleasant driver. When you determine this setting you will also need to check the adjustment of the accelerator pump cam as it should begin to feed fuel as soon as the throttle plates begin to move. When the pump cam is in the proper position then set the clearance on the accelerator pump actuating lever.

Al

 

[Differen T]

I should also add that generally the power valve should be at least 3" less than the idle vacuum. (10 inches of vacuum, 6.5 is 3.5 inches less than idle vacuum)

Al

 

[Wild Mango]

How far open are your sec. flaps ? If they are to far open, then the sec idle will supply too much idle emulsion to accurately set your primary idle.

dave

What Dave said!! Secondary butterflies need to be shut at idle. All the intake air needs to be going through the primaries at idle and during transfer off idle.

 

[Screaming Metal]

And if after all this your still running rich @ 1/2 turn out, time to change the jets. When setting up a carb, Mike will tell you nothing is set in stone, all motors will take their carbs a little different! Also, make sure your off you pump cam at idle, also double check your powervalve.

 

[Screaming Metal]

Also, what altitude are at there?

 

[RPM]

1 st thing I would do is bump that timing way up off of 8 degrees. It will like 14-18 a lot better.

 

[Keeper]

The timing was set at 8 to break in the cam. I have not played with it since then. It does have a vacuum advance.

First bump timing up a few degrees - will start at 12.

Then I will check the floats.
Make sure I am not leaking fuel into the bowls at idle.
Make sure the secondaries are closed.
Check to make sure the pump cam is not engaged.

Got it. Hopefully I will be able to report back tonight.

 

[2old2fast]

Something that needs to be addressed here are some common misconceptions about carbs, the idle ",mixture screws" do not change the fuel/air ratio entering the engine, only the amount of mixture, main jets have almost no bearing on idle or transition fuel mixture. The idle air bleeds & idle feed restrictions are what controls air/fuel ratio & circuit timing . Their are seperate primary & secondary idle circuits. You gus need to know "what " you're "changing/adjusting"

dave

 

[Keeper]

Oh yeah altitude is 104 meters.

 

[railroad]

I am running the same carb on my stock Ford Mustang 302 GT motor. I think I am running 61 or 62 mains also the 6.5 power valve.
I still have the metering plate on the secondary. I am sure it is stock. After dry setting the floats on mine, I had to lower the level some to get below the site plug. Now I have to shake the roadster to get a little fuel slosh. Nothing major going on with yours, I am sure, like drilling throttle plates. I did put a vacuum gauge on mine to check it. I am pulling about 19". My carb is sitting on a single 4V tunnelram intake, don't know if that makes any diff on mine, but the carb is stock, just like holley shipped it. After adj the floats and idle mixture, it is cruising time.

 

[iajjpop]

On my GM 305 [bored .030 over and a R.V. cam] . I run a #8004 model 4160 , 600 cfm & manual choke, for about 5+ years, and got fed up with it. So last winter I bought a new Holley #080457s , 600cfm with a electric choke $260 + tax. put it on and love it. No more hand choking or flooding it. and boy does it run good.........I placed a ad on craig's list with 2- 4 bbl's--$30 each or 2 for $ 50.In less then 2 hours, sold 2 for $ 50.[one was #8004 from above] & other one was 1 had laying around for years. Helps make new one cheaper.

 

[Keeper]

I learned a couple lessons today.

1. When your "car guy" neighbor helps you set the timing, check to make sure he knows what doing. 8 degrees AFTER, is not the correct 8......
2. Sometimes you just have to suck it up and buy new. After resetting the timing, I started on the adjustments again. Once I screwed the idle screws all the way in and the car still ran, I knew it was time for a new carb.

So now I have a brand new 1850 going on. I will update again once things are up.

Also picked up a timing tape so I can check initial and total timings.

 

[2old2fast]

Hope the new carb works for you . I've never solved any problems by "throwing" money at it ! My .02 worth


dave

 

[Keeper]

Yeah that was the problem with the old one. I rebuilt it, threw more money at it to make it run, then realized it might be to far gone to salvage, like the loose throttle shaft that I somehow missed when rebiulding.

At least this way I know the carb is good and I can teardown the old one, make sure everything is fixed and use it on the next project!

 

[Keeper]

Let me expand on this a bit.

The carb in question was purchased at a swap meet as a "it was running when I took it off" sort of deal. If I would have known it was a working carb with no issues I would not have replaced it and continued to troubleshoot.

I will tear it apart, find what was causing issues, such as the loose shafts, and repair it for the next project. I HATE spending money I do not have to, but sometimes you just have to do it.

As for the new carb, once installed the car fired right up, idled smooth. By then it was 830 and I am sure the neighbors were tired of hearing the car. I will do the adjustments tonight.

Thanks for all the help and troubleshooting. Once I tear down the old one I will post my findings here.