Major motorcraft carb problems--PLEASE HELP!

[GaryMB]

Fund Raiser Jeep Show

I installed a gm hei and motorcraft carb a couple of days ago in my cj7. I'm pretty sure the timing is good. At first I had trouble with it backfiring, and then after some adjusting of the floats it was doing better...until it lost almost all its power and the manifold started to glow. Today i fired it up, hoping to adjust the carb with the aid of a friend's vacuum gauge, but, alas, the jeep would not idle any lower than 1500 rpm! The throttle plate would not move, even if I pushed on it...it was not resting on the idle screw. To top it off, the vacuum read about 12" the first time i ran it, but after it died and i started it back up the gauge stayed at about 0", regardless of float level/fuel mixture. When giving it gas, the engine would not rev, unless I gave it gas very slowly, and then it still really sucked. Also, the rpm did bounce up and down a couple of times, but not very often as I would expect with a vacuum leak. Oh, and the manifold continued to glow today. PLEASE HELP! I have a big wheeling trip planned for this weekend, the first one in several months that all my wheeling buddies have been able to commit to.

 

[jay79cj7]

RE: tachometer

I am no expert, but it seems like if you are getting a 0" reading when the engine is actually running, then I would have to guess that your gauge is broken or you have a huge vacuum leak such that you don't develop a vacuum. I am really interested to hear how your manifold is getting glowing hot too!

 

[Junkpile]

RE: $$$CHEAP$$$Small Block Chevy 350 V8!!!

Glowing headers or exhaust manifolds are usually blamed on the mixture being too lean. Lean conditions and vacuum leaks can cause the exhaust temps to be excessively high, but the headers are glowing because the fuel mixture is still burning inside the header. The fuel mixture is more than likely either too rich or the timing is too far retarded. The engines resistance to revving might cause me to look at the timing(both initial and advance) again before I retuned the carb. Good luck.

 

[Inspector-Gadget]

Hi-Ya GaryMB,

A total shot in the dark on this one...

I have read several web articles on the Carter BBD to Motorcraft 21XX carb conversion in contemplation of and preparation for doing that mod.

One web article (which, of course, I cannot now locate) mentioned having to slightly relieve the edges of the two holes in the manifold to carb adapter with a grinder so as to allow the carb throttle plates (butterfly valves) to fully cycle.

As I recall, the author found that the MC 21XX carb throttle plates hung-up on the two holes in whichever adapter that he used.

I mention the above only because of this snippet from your beginning post:

GaryMB wrote:

... but, alas, the jeep would not idle any lower than 1500 rpm! The throttle plate would not move, even if I pushed on it...it was not resting on the idle screw.

If I interpret that quote correctly, your throttle does not return all the way back to idle speed.

As I mentioned -- a total shot in the dark, and admittedly a long shot -- but it would take but a few seconds to look down into the carb throat to verify throttle butterfly valve operation.

Regards,

Lepidopterist Gadget

PS: I would put a timing light on that engine pronto!!! If the manifold(s) are glowing, something is seriously amiss.

 

[GaryMB]

Well, I double checked the timing, and it seemed to be right on (1600 rpm, timing advance plugged, 9 degrees btdc?). As for the carburetor, I discovered that the throttle plate does move and rest on the idle screw when the choke is cold. When it heats up, the metal plate on the top of the carb closes almost completely, and does not open much, if at all, even when I gas it. This is when the 1500rpm idle thing kicks in, too. Any ideas? Also, I have no idea how to adjust all those screws on the carb; maybe they are not adjusted correctly?

 

[Junkpile]

RE: Re: RE: Re: Are wheel caps needed?

When it heats up, the metal plate on the top of the carb closes almost completely, and does not open much, if at all, even when I gas it

Are you talking about the choke butterflies? They are supposed to be open after it warms up. Disconnect it and wire it open to see what happens. It makes sense. The butterfly closes, which cuts off the air and produces a rich condition.

 

[derff96963]

If the choke is closed it will also cause the idle to be high. On the motorcraft carb there is a fast idle cam that keeps the idle higher until the engine warms up and the choke opens. This will stop it from hitting the idle speed screw. You need to find out why the choke is not opening. if its an electric choke you need to have an ignition switched power running to it to warm the coil and open the choke. If its manual you need to attach a cable to it and open it and it warms up.

 

[Inspector-Gadget]

RE: Light Problems

Perhaps someone installed the auto-choke coil spring backwards.

Regards,

Gadget

 

[GaryMB]

RE: CPS sensor prolems? Something else?

OK, I reversed the coil inside the choke and adjusted the fuel mixture, and now it seems to run fairly well. It has more power than with the carter, especially above 2,000rpm, and is alot more forgiving when letting out the clutch. Also, it just refuses to die...just what I was after. However, a major problem remains, and that is that the exhaust manifold was still glowing after I took it for a test drive. Any ideas? the choke butterfly is fully open when the choke is heated up, and here is how I adjusted the fuel mixture: I continued to back out the two screws on the front of the carb near the base until the vacuum stopped rising, about 15.5", and then screwed them back in some and then back to where the vacuum just barely read 15.5"; the idle seemed to increase as i backed out the screws (is that ok, or do I need to keep the rpm the same when adjusting the fuel/air mixture?), and i adjusted both screws on the carb at the same time. One more thing to consider is that the engine did not respond very readily to the throttle until the rpm's reached about 2,000.

 

[Inspector-Gadget]

Re: RE: WTF... airing out my dirty laundry

GaryMB wrote:

OK, I reversed the coil inside the choke and adjusted the fuel mixture, and now it seems to run fairly well.

HAHAHA! I wonder how many Jeepz Peepz thought I had totally lost my mind when I suggested that the auto-choke coil spring had been installed backwards?

Anyway...Gary, the 9-degrees, BTDC @ 1600 RPM was the proper ignition timing setting once upon a time when the initial spark advance was controlled by the computer with which your jeep was originally equipped.

On the original setup, full manifold vacuum was also applied to the distributor vacuum advance.

Now that you have switched to the HEI, you might try setting the ignition timing using 9-degrees BTDC, but at a much lower RPM: say, around 700 RPM (distributor vacuum line disconnected and plugged). You should also have switched the HEI distributor vacuum line to a source of "ported" vacuum, as opposed to manifold vacuum.

The "advance curves" (vacuum and centrifugal) of the original distributor and the HEI differ. Consequently, different timing procedures-engine RPM are required.

As I recall, when I did the HEI mod, I had to play with the ignition timing setting a bit to get the timing dialed-in. Unfortunately, I cannot recall the final setting.

If I have time later today, I will check the timing of the Bubbacon and post that setting here.

That info should give you a starting point, but you will likely have to experiment a bit to get your Jeep engine timing dialed-in.

Hoping this helps.

Regards,

Gadget

 

[GaryMB]

I set the timing to 9 degrees btdc at about 700rpm and readjusted the carb. Now, the jeep runs even better than it did yesterday, and the manifold stopped glowing! The vacuum was closer to 18" this time. Thanks everyone! I think the jeep is ready for this weekend. I'll be sure to get some pics up, and maybe even a video.

 

[mud4feet]

Gadget is the MAN!!

 

[Junkpile]

Mothers Day

So, you were running too rich and the timing was retarded too much?

 

[lah2420]

I'm still trying to figure out how to reverse my choke coil!! That sounds like fun!

 

[GaryMB]

RE: yj 4.2 urgent case here!!!

Yeah, i ended up advancing the timing about 8 degrees. Basically the jeep got no air after the choke warmed up, while it got plenty of gas...so yeah, it was running pretty rich. I was able to pull the choke coil out with some pliars after unscrewing it from the carb...it went pretty quickly.

 

[GaryMB]

Re: RE: Re: 95 YJ Hardtop for sale in Boregon and possibly h

Well, i decided to drive the jeep today, and man did have alot more power! It was enough to throw your head back. The only problem is...when challenging a buddy from a red light, my transmission mount problem became alot more apparent.