304 not running right, please help

Hi,

I have spent hours on here searching through posts and hours in the garage trying to get my 74 CJ5, 304 going. Rebuilding the carb is the only equipment change I have made so far (Didn't change anything by the way)

Basically, she idles really well, except that there is some black some coming out the pipes, so its running rich. The choke plate is wide open, so its not the choke. You can burn all the gas you want when theres no load on it and it sounds great.

If you take off in it and try to accelerate at all, it will spit and spudder and you have to let off the gas to keep it going. Also, there is a raw gas smell, so yeah, its running rich. If you put it to the floor, it will eventually take off, but then it really smells like gas.

I have checked the voltage from the positive side of the coil and I get 5.5 volts. I also get 5.5 volts off of the left terminal of the starter solenoid (the one nearest the firewall). HOWEVER, after turning the engine over a few times, I got 12V at the coil and 12V at the starter solenoid as well. So I bumped the key sommore and checked again and it went back to 5.5. I don't know what to make of the voltage change. Any ideas?
These measurements were not taken while the engine was cranking.

The distributor cap is new and points appear fine. Plug Wires do not appear old.

I have not taken a vacuum test. The only hose coming out of the carb goes to the distributor. I read somewhere that you could spray wd40 on the carb and if you had a vac leak, the engine would rev up. So I tried that and it didn't do anything except make my carb look shiny.

I checked the primary (negative to positive) resistance on the coil and got 2.4 ohms (Haynes says 1 to 2). I check secondary resistance and got 10,500 which is within spec according to the manual. So i don't think its the coil.

It idles good and revs fine when sitting, so could there be a timing problem?

I'm close to taken this thing to the shop. I like to fix things myself, but it can get frustrating when you get stumped

I appreciate any input that you can offer. I still enjoy taking this thing on test drives even though it runs like crap. I can only imagine how fun it will be when it runs good.

Thanks,

Brad

 

I would take a look down the carb while it is running. Do you see fuel dripping inside? Be careful and wear safety glasses. It sounds to me like maybe the float is set too high or maybe a small piece of dirt got caught somewhere. Pull the vac. line that goes to the distributor while the engine is idleing. Do you have vac. at the port on the carb? If so, either the idle is adjusted too high or you are connected to the wrong port. You should only have vac. going to the distributor when you open the throttle. If you had a vac. leak, it should be running lean instead of rich. Have you checked the point gap? The specs should be in your haynes manual. The timing could be off. Check your manual for specs. Being that it is 74, the factory specs probably say something like 0 degrees (for emissions purposes). If so, I would advance the timing to about 6 degrees BTDC for starters. If the engine starts to kick back against the starter or you get pinging under acceleration then you have too much advance. That shouldn't happen until you get up to around 12-15 degrees at least.

Remember this advice is worth exactly what you paid for it.

Good luck,

Dan

 

A couple of suggestions - first, ditch the Haynes manual and get the factory manual for your year. There's a '72 manual at www.trailforge.com and a '75 manual somewhere on the net, but a '74 manual will provide the very best information available. Very much worth the price of purchase.

Next, you rebuilt the carb yourself? I'd guess you made a mistake, or there's something else wrong with the carburetor. Black smoke indicates a fuel delivery problem. These carbs (Motorcraft 2100) are very susceptible to busted power valves. Take the carb off and look under the power valve cover. If it's dry, make sure the cover is sealing well. If it's wet, the power valve is leaking either because the gasket is not sealing (not likely) or becasue the power valve diaphragm is busted (more common). A bad power valve is a very common problem with these carbs.

Also possible - a problem in the pump circuit. Did you put the pump discharge check ball and weight back? Did you properly install the pump elastomer valve?

hth!

 

Thanks for the replies. I will check the vacuum issues and point gaps, as well as timing. Would an engine idle and rev up well if the timing were off? I did rebuild the carb myself. I thought it went smoothly. The only thing I'm iffy about is the float level. The Instructions said to set the float so that the top of the float was 3/8 from the top of the bowl. I did that dry on the bench and haven't took the top off the carb to see whats happening when its running. I replaced the power valve, but I can take the carb off and check to make sure it is not the problem. I did put the ball and weight back in as specified and I also replaced the elastomer valve.

Thanks guys,

Brad

 

Don't touch your ignition until you get the carb issue sorted out. You didn't touch the ignition before the problem showed up, don't confuse yourself by adding another variable.

The carbs are dirt simple. I've never seen a blown power valve cause the conditions you're describing (black smoke) so I would check the float level first, make sure the inlet seat is tight, make sure you didn't leave out the check ball or weight in the accelerator pump shooter, etc. You're looking for uncontrolled fuel inlet, or something allowing engine vacuum to pull fuel out of the carb.

A blown power valve generally shows up as uncontrollable idle mixture and stumble on light acceleration. It's more of an adjustment than a major cause.

 

ok. I started it up, took off the top of the carb, and adjusted the float (it was close). How touchy is the float level relative to proper carb function? Anyway, I did not take it for a spin, but I still noticed the smoke and the fuel smell. I took a closer look at the pipes (dual exaust off each manifold), and found that the left pipe seemed to be putting out more smoke than the right pipe. So I assume that maybe I didn't quite have the idle mixture screws adjusted to the same opening??? My rebuild kit says to close the screws and then open them up 1.5 turns. I did this but when I installed the carb, it would not idle, so I opened them up til it was ideling around 650. But as I said, my one was off because the left pipe had a good amount of smoke coming out of it. If i had to guess I'd say I had the screws out about 3-4 turns.

As far as vacuum, I took the line off of the carb that goes to the distributor and nothing happened. I wasn't getting any vac there, but I didn't check to see if I had vac when accelerating. I unplugged the big line in the rear of the carb and the engine died. I'll need to get a vac guage to be more precise.


Is it my idle mixture screws making the thing smoke? I looked at the float while the engine was running and no fuel seemed to be leaking . It just maintained the fuel level.

Any thoughts would be helpful

Thanks


Brad

 

I have/had the same issues you have. Only i was running so lean that the engine would die while i was stopping. Me and my buddy adjusted the the idle screws and increased the mixture. According to the tech manual you should be idling at 900 rpm. the black smoke you see can be cause by excessive carbon build up. the fuel smell you have could also be a exhaust manifold leak. You can use the WD40 trick here to find it. I found one of my exhaust welds cracked when I was investigating my fuel smell. And about your sputter and stall, I have the same issue. There is a choke check in the tech manual to press the gas pedal in and release and verify your choke is setting. When I push my gas pedal in my choke sets, but when i watched it when someone else pushed the gas in a second time while the jeep was running the choke plate completely shut and killed the engine. It seems that the choke plate shuts and then opens wide up when you take your foot off the pedal. Maybe this is happening to you.
Hope this helps a little. Just giving you a look at whats happened to me.

 

I am with these other posters that replied to your problem"Carb".
.

The left side exhaust pipe may be shorter than the right side exhaust pipe and may be demonstrating the most smoke between the two sides.I would just stick with the consensus about the carburetor being the problem.
Could be the the diaphram is sealed but not sealed flush all the way around(they are buggers to seal up;its partly a blind feel to get the seal on straight and smooth),float is getting hung up,could be out of adjustment.

I think its set too rich because you've had to in remeding it and so its trying to compensate for a fuel starvation problem somewheres;may be your float is getting stuck(take it apart lightly sand the float rod with fine grit sand paper),may be your fuel filter is clogged partially
(if clogged partially it could idle on park/neutral ok but not when under load when it demands more fuel than your fuel mixtures limits are at or able to deem good and runnin) may be your nozzle collected some new debris dirt/gunk/crud sheit...
Could be one 2 or all of these problems.Change out your fuel filter and I'd take the carb off and make sure its redone top notch.Then put it back on and drive all day

Could be the the diaphram is sealed but not sealed though you may have thought it was"they are tricky to seal up without crinking/rolling.
Good luck and keep patience its just something little as being the main problem

 

Oh and you said that the plug wires look good?
Just a suggestion but at night in the dark start the jeep and open the hood look for any sparking(shorting),look at each plug wire and make sure all of them are not arching.
Also a good idea to pull each plug while turn the engine over but don't start it and make sure each plug is getting spark.

You may also reclean eacj sparkplug with some either/starting fuel if you have not and maybe sand them alittle to clean any carbom buildup if they have any.
You may have done all of this but I am just trying to do my part as are others and help.

 

You shouldn't use the mixture screws to set the idle speed. There's a separate idle adjustment screw just for that purpose.

3-4 turns out sounds way too rich.

Possibly go back to setting the mixture screws to 1 1/2 turns, then set the idle adjustment screw to get your desired idle RPM's.

 

You shouldn't use the mixture screws to set the idle speed. There's a separate idle adjustment screw just for that purpose.

3-4 turns out sounds way too rich.

Possibly go back to setting the mixture screws to 1 1/2 turns, then set the idle adjustment screw to get your desired idle RPM's.

If you disconnected the vacuum hose from the carb, and it was connected to a ported fitting, there won't be much, if any, vacuum at an idle. Only upon acceleration.

If it was connected to a full manifold vacuum port, then there would (or, should) be vacuum at the fitting (not at the disconnected hose going to the distributor), when idling.

 

What carb? I rebuilt a holley and had a wrong PV gasket in the kit. It ran much the way you describe.