PDA

View Full Version : 258 I6 Carburetor tuning


caionneach
11-20-2003, 11:10 AM
HI FSJers!

I am new to the Full Size Jeep community as I have recently acquired a 1982 2 dr Jeep Cherokee.

The vehicle hardly runs, and has two or three large holes in the driver's side floor pan that need patching.

I recently rebuilt the carburetor and replaced the fuel pump, but the engine continues to idle very high and then quit after a few moments. So it is not idling properly, and I likely need to adjust the idling further, but it frequently dies before I can get out of the vehicle to adjust the idle screws.

Replacing the fuel pump seemed to help, and if I use canned starting fluid or gas down the carb's gullett then it fires off fine. If I force it to idle high with the accelerator, it will usually keep running.

This carburetor is missing the flange which goes in the float bowl assembly, so my problem is probably a float adjustment of some kind. I have not replaced the fuel filter because of the way the accelerator responds.

Any ideas? I have rebuilt carburetors before, but this one is missing the flange.

Kenneth Smith
Monroe, LA

Stuka
11-20-2003, 11:37 AM
Hey welcome to the board smile.gif

It will idle fast when you first start it up until it gets warmed up, this is called high idle.

turn the idle adjustment screw about 1.5 full turns, then lower the idle while its running. You have a carter BBD carb, this is one of the worst carbs in history (which is why i got rid fo mine for a weber). Whats worse is yours is a computer controlled version. The most common problem is the idle jets not working correctly, instead of them misting fuel, they drip it. This makes for a very ruff idle and you have to set the idle to about 1500 to get it to run.

That flange may be making it semi-flood the engine. As I doubt your idle jets are plugged with it being a fresh rebuild. www.carbs.net (http://www.carbs.net) should have this part for you.

caionneach
11-21-2003, 10:15 AM
Many thanks for the advice.

This weekend I will do some basic idling adjustments, and I probably need to adjust the choke assembly as well. I didn't need to adjust the Carter's choke on my '85 CJ-7, so this will be new for me. I have a Chilton manual for this model Cherokee, so that and diligence will help me fix this!

Your link to carbs.net was a God-send, and thanks again.

Cordially,

Kenneth

Originally posted by Stuka:
Hey welcome to the board smile.gif

It will idle fast when you first start it up until it gets warmed up, this is called high idle.

turn the idle adjustment screw about 1.5 full turns, then lower the idle while its running. You have a carter BBD carb, this is one of the worst carbs in history (which is why i got rid fo mine for a weber). Whats worse is yours is a computer controlled version. The most common problem is the idle jets not working correctly, instead of them misting fuel, they drip it. This makes for a very ruff idle and you have to set the idle to about 1500 to get it to run.

That flange may be making it semi-flood the engine. As I doubt your idle jets are plugged with it being a fresh rebuild. www.carbs.net (http://www.carbs.net) should have this part for you.

caionneach
11-21-2003, 10:17 AM
Also, the exhaust is quite smoky while this beast is running, but it doesn't seem to be burning oil. Is this also a consequence of a carb that is flooding?

Kenneth

Stuka
11-21-2003, 10:43 AM
if its black smoke thats unburned fuel, meaning your basically dumbping raw fuel down the carb, make sure the adjustment screws are set to around 1.5 turns out or so (fine adjust after this). But if they are like 2.5 turns your flooding it, which is bad for the engine, washes the oil off the cylinder walls.

joe
11-21-2003, 12:11 PM
Kenneth, here's a couple links worth reading. I can't remember if 82 or 83 was the first year of the computer controled BBD, 83 I think so if yours isn't ignore the first link.

http://www.off-road.com/jeep/jnutter1.htm

http://www.off-road.com/jeep/tech/engine/carter.html

http://www.jeepz.com/modules.php?op=modload&name=Howto&file=engine_carbfix

mtn goat
11-21-2003, 01:37 PM
Nope, 82 came with the infamous computer controlled bbd carb...You should read the first one closley!! tongue.gif

caionneach
11-22-2003, 02:56 AM
My wiring harness has the plug-in that attaches to the stepper motor on the back of the carburetor, but the carb does not have the stepper motor. I don't know if this is standard for the 82 Cherokee or not, but my guess is that one of the owners prior to yours truly swapped out the carb for an earlier model. My 85 CJ-7 had the stepper motor of course, and the plug fit on the backside.

Just wondering.

Kenneth

caionneach
12-01-2003, 07:34 AM
Unfortunately www.carbs.net (http://www.carbs.net) does not have the flange (or "baffle") that goes in the fuel bowl assembly above the float retaining pin. Just called them, and that is the one part for the Carter that they don't have!!

A local auto parts store has the float for purchase, but not the flange! Off to the junk yard I go!

Kenneth Smith
Monroe, LA

caionneach
12-26-2003, 05:30 AM
I was advised to begin my idling adjustment by turning out the idling screws 1 and 1/2 turns on each of the two idle adjustment screws. Something must be wrong with that, because the engine is probably idling at between 3000 and 4000 RPMs!

Any advice?

Ralph
12-26-2003, 06:07 AM
Firstly, without a vacuum guage, you're just playing a guessing game when it comes to trouble-shooting a carb.

Secondly, forget those internet articles that refer to clogged idle tubes as the source of all woes. I have seen a number of BBD's with perfect idle tubes that won't sustain engine idle due to air and even fuel leaks at the throttle shaft.

The throttle body (bottom section) of the carb is made of soft aluminum. Both the rotating friction of the throttle shaft and the pulling motion of the throttle linkage cause the hole to wear out of round, thereby increasing the clearance around the throttle shaft.

Spray a little carb cleaner or starting fluid around the base of the carb. A vacuum leak will draw in the fluid and the engine will noticeably rev up.

The best way to fix it is to have a carb repair shop machine the throttle body and install brass bushings. Costs $60 to $70.

I've had reasonably good success using 24-hour JB Weld to build up the worn section on the throttle shaft, then sand it smooth and reinstall. Have one carb that survived about 20k miles in my Waggy and now 2k or so miles in grimgaunt's J10 without any problems, but I don't know how long-term the JB Weld fix will be. Also, don't use the lesser JB Weld, which cures in an hour or two and isn't very easy to sand smooth.

caionneach
12-26-2003, 07:42 AM
This carb has over 156K miles on it, so I will look for vacuum leaks after I idle it down!!

Ralph
12-27-2003, 04:04 AM
I assume that your rebuild involved no more than a gasket kit and cleaning everything when you had the carb apart. If that's so, with 156k miles on it, I'd be looking at the throttle shaft for sure.

If you don't want to take the carb off and disassemble it, you can at least try jiggling the throttle shaft to see if there's a significant amount of play there.

caionneach
12-29-2003, 12:58 AM
Is it possible that closing off the two front idle screws will still allow the vehicle to idle if there are vacuum problems with the carb? This engine is still idling rather high, and I have closed off (or nearly so) the idle jets on the carb's front. My goal, of course, is to set the curb idle at 600 rpm or so, and I am still above 3000 rpm!!

caionneach
12-29-2003, 12:59 AM
BTW, there doesn't seem to be a significant amount of play in the throttle shaft.

caionneach
01-02-2004, 09:47 AM
OK, it doesn't die anymore. I did the flush the venturi procedures in the above links, and I think I will eventually upgrade the carburetor to a Weber 32/36 or 38 and dispense with the Carter, but I would really rather save my money and buy a rebuilt 360 or 401 V8.

My new problem is high idle. After getting this vehicle keeping it idling was a problem. Not anymore. My choke seems to be the problem, and it seems stuck in the open position and will not idle down. I even screwed inward on the idle screws until I could go no further thinking that would choke off the idle. It didn't affect it a bit! Still idles way high, sounds like 3500 rpm!

Help!

SpeedBump
01-02-2004, 11:43 AM
I had this problem on my 258 and my cure was to find a pre-selenoid bbd with a tight butterfly shaft to casting fit. Then pay close attention to http://www.off-road.com/jeep/tech/engine/carter.html ,,,especialy the part about ....To avoid repeated clogged idle tubes, drill out the idle tubes to 0.032". This will greatly reduce the frequency of clogging and it is a procedure that was actually recommended by Jeep for a while.

Then test different jets/needle combo's, mine finaly ran smoothly after I installed the smallest jets/largest needles I had on hand. To size your jets/needles properly install a set, and go for a highway speed run for a couple of miles. Shut it down and drift to the side of the road without getting into your idle circuit. Pull a couple of plugs and look for a nice carmel brown coloring. Too dark (or sooty) your burning too much gas, too white or speckled with deposits your running too lean.

SpeedBump
01-02-2004, 11:58 AM
If you screwed the idlestop screw(s) clear out and its still racing there are two culprits left..some smog era bbd's had a high idle selenoid that kept the butterfly open momentarily during deceleration, this can fail. You can take it off without repercussion to the rest of the system, some bbd's used this selenoid to set the idle you'll need to drill and tap a setscrew for your idlestop in that case. The other option is missaligned butterfly plates that simply wont close tightly.

SpeedBump
01-02-2004, 12:11 PM
The two idle mixture screws on the front of the base casting dont affect high rpm, they simply adjust the ratio of fuel to air at IDLE if your butterfly's are open more than a quarter inch you are running off your main venturi system, no matter how far the idle mixture screw are in or out the engine wont run without air, and the quantity of air that passes the butterfly plates determines engine speed. Ergo if the plates are closed, the motor will starve and die in the absence of vacuum leaks. The idlestop screw (on the side, beneath the accelerator linkage) holds the butterflys open just enough to pass enough air to permit idle (about 700 rpm)usually less than an eighth of an inch gap.

caionneach
01-06-2004, 02:34 AM
SpeedBump, your posting blasted some common sense into my thick skull! I had mistakenly tightened the fast idle screw too far when I had the carb off last time to clean the venturi and make sure the jets were clear (they were not). So I have successfully idled it down now, but the choke is still a problem.

The problem, of course, is probably moi. I had it apart in the rebuild, but I didn't take the spring out, so the black plastic cover with the spring is probably mated to the assembly wrong where the spring attaches.

Kenneth
Monroe, LA

1982 Cherokee restoration in progress

caionneach
01-13-2004, 10:36 AM
OK, choke seems to be working, but idle is rough. Apparently I need to drill out the jets to 0.032" like the links suggest.

caionneach
01-20-2004, 10:17 AM
Ok---what is the best way to drill out the jets? Hand held drill? Drill press? Drill press at machine shop? How did some of you drill out the jets?

Kenneth

tgreese
01-20-2004, 10:20 AM
Pin vise. Get one at a hobby shop - used for drilling veeerrrryyy small holes in your brass HO locomotive or whatever. http://www.zonatool.com/pinvises.html

Either that, or take the chuck off your drill and turn the drill by hand.

[ January 20, 2004, 05:26 PM: Message edited by: tgreese ]

Ralph
01-21-2004, 05:06 AM
If the idle tubes are clogged, you will be able to see fuel dripping out of them by simply looking into the carb while the engine is trying to idle.

I would still recommend that you check for vacuum leaks, by spraying mists of starter fluid around the carburetor, carb base where it mounts to the intake manifold, and intake manifold gaskets. If the engine revs up when you spray the starter fluid, you will have located a vacuum leak.

caionneach
01-21-2004, 06:35 AM
It has been idling rough, but enriching the mixture a little with the front screws at the base of the carb has improved the idle greatly.

It's still rough, so I will get the pin vise as suggested. Great stuff! Thanks.

On a slightly different note, some of the hoses on the stock air cleaner housing are disconnected from their fittings, and my Chilton's manual does not seem to contain information on how everything hooks up. So the recommendations about vacuum are duly noted, and I will do the carb/throttle body vacuum check when I crank it again.

Right now, however I am fighting the dynamic undercoating option installed by the original owner. This option requires a leaky oil pan gasket and lots of spray. It is ingenious in that if you didn't have the vehicle undercoated at the dealer when you bought it, this option would gradually install the undercoating as you drove the vehicle. You had to put up with low oil pressure, but it would gradually install undercoating. Maybe that was the original intent AMC had for these 258 engines after all!

Kenneth
Monroe, LA

LRRH
01-21-2004, 07:12 AM
but it would gradually install undercoating. Maybe that was the original intent AMC had for these 258 engines after all!Just think of it as FACTORY rustproofing. I mean...most front clips on running AMC cars with a 258 have zero rust. They must be on to something....

mojolounge
01-21-2004, 02:19 PM
If you are going to keep the Chero, Look at doing a 4.0 head swap along with the fuel injection from the donor vehicle. I got away with doing mine for $400.

caionneach
01-22-2004, 12:50 AM
The 4.0 head/Stroker option is interesting, but my question is this: will not the stroker damage the Borg Warner T-5 transmission just like a V8?

If so, then a transmission swap is inevitable anyway. It will still be cheaper and less trouble to install a stroker and a V8 capable transmission.

If I go the stroker route, will I not need all fuel and ignition components from the donor vehicle? Isn't fuel injection computer driven or does someone provide a kit, like Clifford?

tgreese
01-22-2004, 01:01 AM
Originally posted by caionneach:
The 4.0 head/Stroker option is interesting, but my question is this: will not the stroker damage the Borg Warner T-5 transmission just like a V8?

If so, then a transmission swap is inevitable anyway. It will still be cheaper and less trouble to install a stroker and a V8 capable transmission.

If I go the stroker route, will I not need all fuel and ignition components from the donor vehicle? Isn't fuel injection computer driven or does someone provide a kit, like Clifford?Yes, doesn't matter if you hot rod the I6 or swap a V8, the T5 will be stressed.

A stroker doesn't require FI. The stroker is basically a 258 crank in a 4.0L block. The 4.0L head is a separate upgrade that can be applied with or without building a stroker.

You can get a kit for FI, but it's cheaper to take all the FI bits from the donor car, and you need to know more about what you're doing. There is a Mopar FI kit (Hesco?) that can be added to any AMC I6, about $1500 as I recall. It's basically what you would get with a 4.0L FI engine, except it has a crank sensor on the harmonic balancer instead of on the bellhousing. Doesn't require a change of flywheel or flex plate.

[ January 22, 2004, 08:06 AM: Message edited by: tgreese ]

mtn goat
01-22-2004, 04:04 AM
Originally posted by mojolounge:
If you are going to keep the Chero, Look at doing a 4.0 head swap along with the fuel injection from the donor vehicle. I got away with doing mine for $400.How did you get away with clearing the break booster. I have read that the stock 4.0 EFI manifold will not fit on FSJ's

mojolounge
01-22-2004, 04:30 AM
How did you get away with clearing the break booster. I have read that the stock 4.0 EFI manifold will not fit on FSJ's

You use a borla or Banks header. But i know others who have used the stock EFI manifold. As well you guys are right the t-5 would be way stressed with the stroker. But I like the idea of using the fuel injection on the stroker you just have to get some better flowing injectors.

caionneach
02-03-2004, 04:52 AM
Anyone with a diagram of how the stock air cleaner and its assorted hoses connect?