Need help with 225 holly390 never ran right!

I rebuilt my cj3b about six years ago one, of the things I did was install a 225 v6. It was compleatly rebuilt twice actully, but thats a different story. Anyway It ran great, but always had a slight hichup when the throttle was tromped. It has gotten worse over the years and I've had the carb retuned etc. but it never seemed quite right. The main problem is that hesitation when throttle is punched and then it would sort of backfire up the carb. and then it wouldent run right. sort of seemed like it was to rich. Some times it would clear out and run ok.. Now I can start it up and if I don't give it much throttle I can drive around but if I punch it It almost stalls and then runs like crap and backfires etc. I love my jeep and would love to get it running right for once! My specs are 225 board .030 over comp cam grind #cv6252H-10 (mild) Offenhouser intake, Holly 390, Mallory dual poit distributor converted to brakerless points. Does anyone have a 4 barrel that runs right! It also conked out when going up really steep hills. I'd love to not have to go get a new intake etc. but am desprate! Sorry for long post.

 

Your timming could off just a bit or could have a problem with one of the componants in the ignition system. Spark plugs not gapped right. Leak at the intake could cause it to backfire to and not run right. A vacuum leak would also cause it.A freind of mine had a small vacuum hose with a small crack and it would run good some time and sometimes wouldnt. It was a bear to find because it would open during acceleration and close off and run ok but not right when ideling.

 

i had a holly 390 on my cj5 with a holly street dominator aluminium intake.had the same problems you have.at steep angles,such as steep hills at tellico it would flood because the front bowl would overfill and dumpgas from the vents on top down in the carb .also had trouble on rough trails from the float bouncing causing flooding also.the best thing i did was to buy a carb adapter and put the original 2 barrel back on.that cured mine. to me a holly may be fine for the street but not for off roading.

 

Carb backfiring under acceleration is usually a lean indicator. I would take a good look at the accelerator pump. Insure that it is properly adjusted. With the amount of backfiring you describe, a new power valve is probably needed as well. lamar, I too have had poor luck with Holly carbs. i currently run a Q jet and(though it is grossly overcarbed) have had great luck with it. I have also done well with the Holly 450 economaster. Unfortunately, they are no longer made and are scarce on the used side of the house.

 

just fyi....i had the same carb setup on my 70. i spent the xtra cash and picked up one of the holly 450 truck avengers....BIG difference in off road/off camber/bouncy conditions

 

Check your manifold vacumn. Holley's have a power valve that is vacumn operated. That is, it opens and enrichens the fuel mix when your vacumn falls to a certain level. I had about 10 hG of vacumn at my manifold and had the original power valve that opened at 10 hG. Hence I had a stumble because the power valve was always on the verge of opening. You want to have a power valve that opens at a number below your idle vacumn. There are a lot of options available for the Holley. I used a #65 power valve. It opens at 6.5 hG of vacumn. I also exteded the bowl vent with a piece of rubber fuel line. That helps with the extreme uphill flooding. If you really want it to run well offroad you need to address the power valve, install a bowl vent baffle (whistle) put in the spring loaded float valve and properly jet the carburetor for your altitude. I have no complaints with mine. But it took a while to get there.

 

Another thought..not aples to aples but my 318 has a light racing cam in it and I had to change the weights in the distributor to advance the timing faster and also advance the timing setting, now she lauches like a rocket with no hesitation at all from low idle. I'm running a holley 4 barrel.

 

Thanks for the info guys! I thought the holly 450 street avenger would be to big? I bought a rebuild kit and a power valve protector kit from summit racing a little bit ago so I'll probably try once more with 390 then toss it. Posimoto Don't want to sound dumb, but how do/ where do I check vac.? and get/try a different power valve. Carbs are something I never really got a chance to full with. Is it possable to explaine those other mods for off road, or is there a place I can send my carb to get worked on? I don't think I have a vac. leak or manifold leak I've had a bunch of people look at it. Thanks

 

I have a 390 holley on my 231. Don't have any problems, but I do have an HEI dist which might eliminate the timing issues. I have found the best results with about 12hg vacuum. That is using manifold vacuum not carb vacuum. Not sure if that is the right way, but it seems to give me the same baseline. I've never been a carb guy so I just ask a lot of questions.

 

I'm starting to have similar problem with my Holley. Acting like I've got the vac leak blues, but can't seem to find the leak.

No load I can free rev it, instant throttle response, sounds awesome.

1st gear, get a little hiccup, then it takes off like a striped ape

2nd gear, starts to get the bog as load increases

3rd gear, gotta keep it part throttle, but can get up to 50ish mph

OD, can't use the gas at all, whatever mph you're at when you shift is where you hold the throttle to stay. If you slow on a hill, have to down shift to get back up to speed.

Basically, the more load/less vac there is, the less hp it makes, and if I go anywhere near WOT, it acts like it's out of fuel.

Double checked to make sure the choke is opening completely, it's fine.

Poking around today I see what could be evidence of fuel dropped on the intake below the secondary housing. Not conclusive, it's just a discoloration, could just be that I haven't washed it in a long time. If it is fuel, though, how did it get there? I didn't think fuel went into the housing, that the diaphragm just opened a cam. If I've got a fuel drip out of the bottom of the housing, what does that tell me about the secondary?

This problem is progressive, it didn't just start one day, sort of been getting worse slowly, but definitely bad now, undriveable past 60mph

 

I'm assuming you don't have something else wrong in this engine, like a burnt valve or big vacuum leaks or jumped time or something... and that you have set the dwell and timing properly.

Holley sells an accelerator pump cam kit that lets you adjust the volume of the pump shot. You can put the largest cam (biggest shot) on the carb without taking it apart, and try that. At worst it will give you a cloud of black smoke out the tailpipe when you tromp on the acclerator. If that fixes your problem, go to the next size smaller cam until you feel some hesitation, then go back one step.

The power valve can be problematic, but they are a common speed shop item for about $5 and are easy to replace. A backfire can blow out the PV and make a too-rich condition. If you have this problem, you should see black soot if you look at the plugs - what do your plugs look like now? Holley designs their new carbs with a check ball that prevents a backfire from blowing the PV; you can retrofit the older carbs with the check valve.

Holley has instructions for picking the proper PV on their site using a vacuum gauge. However, these carbs work fine with the default PV, which I think is a 6.5? Something like that.

Once you understand them, Holleys are really easy to adjust. All the tuning parts are on the outside of the carb or in the removable fuel bowls, so swapping jets, pump cams, power valves, etc. is easy. I'd suggest you learn a little more about the carb and fiddle with the Holley tuning parts.

 

I thought it was PV at first. I swapped up and down, from 3.5 all the way to 8.5, no joy.

Thought maybe altitude change (just moved from sea level), so have already played with jets. Making a nice tan plug at the midrange/part throttle.

The dist is GM HEI, initial timing is set, tried vac advance connected and disconnected, haven't verified timing chain jumping a tooth, but this problem seemed to develop gradually, so I'm thinking vac leak.

The leak is definitely not massive; I've fogged the propane and don't seem to find any gasket leaks, all ports are either in use or capped.

Really just wondering at this point if a bad secondary diaphragm could cause a fuel drip. There does appear to be evidence of a drip under the housing on the intake, but it is not fresh.

 

I really like the Autolite 4100 series carbs for off road. It will bolt right on to a Holley flange and if you get one from a small V-8 car I think they are only about 400CFM. Right now I am running Holleys truck avenger on my Chevy V-8 and it does very well on the street and off road. Prior to the truck avenger I was running a Quadrajet and I think it is the best over all. One of the things that I have learned about Holleys is that they need to be very clean in the metering blocks. I found that I had to use an ultrasonic cleaner and carb cleaner to get them to meter fuel correctly. It is the only thing I have found that will remove the oxide that sometimes occurs when water has gotten into the carb.
Another thing on off road carbs to remote vent the fuel bowls with tubing. If you look at the Truck avenger you will see how Holley limits the fuel slosh by connecting the vents with a common tube and then drilling some small holes in it for the vent. This more than any other thing they added allows for the off camber capability and fuel control when the Jeep bounces.

 

Hmmm sounds familiar! dead horse I've tried a ton of things and never felt lit it was really right.

 

Plenty.

 

I am always reading these threads on bigger carbs on the 225 and most, not all, but most have complaints.
The holley is always the same have to fool around before it runs right.dead horse
Dont get me wrong I know you can make it work ,
but is it worth it to have all the extra frustration,
I dont know, doesnt sound like it.

I am just going to keep the 2 and call it good.
When I need more I'll just build a bigger engine.

I understand needing to fix what you have but if your thinking about switching....
IMHO dont.

IMHO