Inliners International Forums General Discussion Engines 292 will not stay running and backfiring

I just got my rebuilt 292 in my military jeep and I cannot get it to idle for more than 15 seconds. Seems to only run for as long as the gas that I primed it with burns. When I do get it to run if I rev it up it backfires through the carb like a gunshot not a pop (if that makes sense). It also does this on start up, but not always. It can also be very hard to start sometimes. I can get it to run longer by pumping the pedal but then it will eventually die no matter how much I pump it. The longest I have had it running for is maybe 45 seconds. I need to get it to run longer so I can properly break in the cam. It is running on a 24 volt system, but I don't think that matters since there is a converter from 24-12 volts to run the coil.

I can't check the timing since I can't get it to run. I did go through everything and recheck it. The firing order is right, the dwell is set right, and the valves are operating correctly (haven't rechecked the adjustment yet). The carb is also getting fuel at 4-7 psi. What should the mixture screws be set at to start out, two turns?

It has an offy intake with a 390 cfm Holley and the 2 1/2" manifold. Stock dizzy. Thanks for any help.

Sounds like you have a vacuum leak.
Double check everything.

MBHD

Chop, I have the same Holley on my 194 cu.in. and depending on the age of the Holley...if you have had multiple "pops" thru the carb...check your power valve in the primary side of the carb. I have had the same thing happen to me and changing the power valve cured it. When you remove the power valve look at the number stamped on it's face. Most likely it is a 6 and a 5 representing 6.5 inches of vacuum. Let me know when you get that out. Here is a link to a Holley Guru that I got on this site 6 months ago http://www.bob2000.com/carb.html from Gordy in Iowa. It has great info on how the Holley carbs really work. A lot of mechs I have spoken to think they know how they work but this link has helped me more and saved me $80-$90 per hour for guesswork. I still get a backfire once and a while and yes I have had repercussions from it but I am still working to tune this carb to match the other performance mods that have been incorporated into my engine. Let us know what you find.
Duce

OOps looks like the link has changed. Go to:

http://www.bob2000.com then scroll down to his topic "Carburetor Tuning the Scientific Way" and click on that. Soory should have looked before I leaped.
Duce

I check the power valve and it is fine. It is in fact a 6.5. I checked it according to that link, great link thanks. I took the plugs out and they are fouled badly. I cleaned them up and tried again, but the same thing. So I am going to go and get some new ones, 46's instead of 44's. It just seems like there is to much gas getting into the carb. I can even see it blowing out the top when I get it started.

Your float is stuck... or really badly out of adjustment.

Chop, The float as EFI sez is a very strong possibility. Don't trust the sight gauge..pull the plug on the side and adjust the float on level ground. What intake manifold are you running. Mine is a Clifford, it was not heated when I bought the car and I was literally pumping raw gass through the tail pipe especially on initial start-up. It would not even run until the temp was above 150 degrees. I had to set the choke and leave it run in excess of 1400 rpm until that point. I then I routed the heater hose line through the water jacket in the intake plenum and wala...90% of my fouling and nasty fumes went away. It still does not like running below 150 degrees though. I bought the Holley "trick kit" $$$$ and have a base line to work with. Now it is time to analyze jets, squirters, power valves, and secondary springs. A lot of people get away from Holleys & Cliffords for this reason but I am determined (stubborn) and frugul (cheap) cause the car came with all this stuff brand new. Keep us posted with your progress...maybe you will be able to help me along the way.
Duce

After playing with it more today, I have come to the conclusion that the carb may be bad, but still not positive. Here is what I have, I changed out the plugs and took the carb apart again and this is when I noticed that the primary float was staying level (to the top) because the spring was stretched out. This is the first time I saw springs on the bottom of the floats . So I figured that the primary was staying closed and all the fuel was going to the secondary bowl and then draining into and overloading the engine. I fixed it so the bowl would actually move like it should. I also cleaned out the needle to get any varnish out.

After I put the carb back on I turned on the power so the electric pump could prime the carb. It started leaking gas from everywhere! It was coming from the bowl screws and the accel pump. Never seen anything like it before. So I figure the carb must be bad or whoever built it last time left something out. So at this point I am just going to forget about the 4 bbl and try and find me a 2 bbl. Anyone have one available?

Chop, I still agree with EFI there is something in the float in the primary that is causing this..don't throw in the towel yet and buy a new carb. Not that a 2bbl is what you need vs a 4bbl. Take the time to use the troubleshooting tools available to truely fiquire out what is happening before you move on to another venture...been there done that and the result has been $$$ vs positive results. Trust me...others in this organization will help you achieve your goals and resolve your problems. Thanks again to senior (experienced) inliners for your help with my delimnas!
Duce

Whatever you decide; Having fuel runing "all over" is a dangerous situation!!

Make sure there is a Halon or CO2 fire extinguisher nearby.

A 'educated guess' would be that the float was not closing to start & now various O-rings are not sealed too.

PLEASE be carefull here!!

Take your Carb. to a Shop & have it overhauled to be safe.

I have,,, & my friends have had the same type of problems w/Hollys.

You put in a fresh needle & seat, set the floats, turn on electric pump & bamm, fuel is every where!

It happens sometimes on the initial filling of the float bowls.
Sometimes you need to tap on the top of the carb to get the needle to seat.

Most of the times it would be caused from debris in the fuel system, make sure you have a good inline fuel filter.

If you have doubts about the carb being good, you could have it looked @ or rebuilt.

Was it a known good working carb?

MBHD

I do have an extinguisher in the Jeep and one in the garage. Safety is something I never take lightly. I have good filters and changed them out recently. They look great with nothing visible. I bought the carb off ebay with the claim "fresh rebuild". It looked very clean and I even opened it up to inspect it. It sat for about 4 months before I put it on and first started the truck. That was 4 months ago. I took it apart 5 times over the last week and made some type of adjustment, from both suggestions here and from friends and neighbors. Still no luck.

6T and EFI, I am not disagreeing with you, but it is one of those times that everything that can be done has pretty much been done, with no luck. I can change out the needle and seat and even the floats but I will never trust this carb. I am very positive that everyone on here can help get this thing fixed, but to me it is just not worth it.

One of the reason I decided to go to a 2 bbl is because I realize that a four will do nothing for me. This is for a '69 M715 that weighs 6700 lbs and it is running 5.87 gears and 38" tires. I will never get above 55 no matter how hard I try, so secondaries are not needed.

Thank you all for your help and suggestions.

Well I put on a brand new 2 bbl holley. Starts better but still runs really rich and will not idle. So it is somewhere else. Back to square one.

Okay; Run a compression test and post readings.

What kind/type of ignition system is it??

I will run a test tomorrow, It will of course be a cold test. I am planning on tearing the front down and checking the timing to make sure the marks line up.

I am running a stock point system. I checked the point gap and it is correct.

Okay; from your posts the ignition (system) is okay, but before you tear anything apart let's see what the readings are.

Also; you can set the Ing. timing with a test light W/O it running.

Has the 'backfiring' stopped along with the fuel leaks??

No the back firing did not stop. I can start it but it will not idle. no matter what I do. I went out and got a fuel pressure regulator just to make sure the pressure was good. Didn't make a difference. So I was thinking valves need to be adjusted. Started to take off the valve cover and water starts coming out of the valve cover bolt holes. So at this point I am thinking head gasket so no reason to do a cylinder check. I tear it down but the head gasket shows no evidence of a leak.

Edit: I changed out the head gasket. I took the valve out and cleaned it up and check the tolerances. It was fine. I hope to have it all back together in the next day or two.

It runs and idles! After changing out the head gasket and then readjusting the valves, of course, it runs. Not sure what fixed it but it idles nicely, just need to pull it out of the garage and let it run to burn off the residual oil and other chemicals on the outside of the engine. Then I can get everything adjusted just right and then take it for a drive. Just wanted to say thanks to everyone for your help.