CJ8 weber conversion timing/backfire problem

Which carb did you have?

Was it the electric one or no computer?

If the computer is still in the system, it can act strange, so can a big vacuum leak somewhere or EGR messing up...

And No, you can't plug off all the vacuum lines....

The Charcoal canister still needs to be working as does the EGR valve and if you live anywhere near freezing, the air filter hot air flaps. The EGR actually uses a thermostat in the air filter along with the CTO.

Check this site for info on the computer and on the vacuum lines needed for a 'basic' good runner.

Check his index at the bottom too!

I run my 86, well, 78 engine at 9 deg with the ported vacuum, (vacuum when the throttle gets punched), no computer, running 91 octane 'gas' and it just rocks!

I have 3:31 gears and pulling out onto a 40 mph road, if I give it too fast it will light up my 33x9.5 BFG muds and squawk off and will wrap the spedo in 4th, forget 5th...

I tried the stock manifold vacuum and found a dead spot. I tried no EGR and found a dead spot.

No backfires, that is something else.

Loose plug wire?

Major leak at the intake or exhaust manifold?

The carb came loose? (They like to do that at the base plate once they get warmed up the first couple times, , seen that a lot over the years)

One port on the carb still open?

A line to the CTO that opens to nothing?

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Michael Pomeroy wrote:

And I left out one very important detail -- it BACKFIRES THROUGH THE CARBURATOR!

Not the exhaust.

Help please ......

----- Michael Pomeroy snipped-for-privacy@yahoo.com

Are you disconnecting the vacuum advance when you time it? __ Steve .

For starters, check to make sure the carb isn't leaking at the base. You can spray some carb cleaner around the base while it is running to see if the idle changes. While there, give the intake manifold a spray along where it bolts to the head. If the idle changes even slightly, you have found a leak.

Vacuum....

Ok, you have two types of vacuum. One is 'ported', the other is 'manifold'.

A 'ported' vacuum only sucks when the throttle is open. Manifold vacuum sucks the most when the throttle is closed.

I do not know which nipple on your carb is which.... You think the carb only has one nipple plus the manifold vacuum for the PCV valve? That could be, but I suspect there is another you are missing hidden under there somewhere, if so, that can be the backfiring.

How were you firing up the CTO 'timing' advance in your first post below? It sure sounded like you had a manifold vacuum on it if the timing was full advanced at idle, then dipped right away under throttle and slowly advanced after that.

To fire up the EGR and charcoal canister, you need a ported vacuum. This can be 'T' fitted with the timing advance line if you are using the ported timing.

One side of the CTO valve will be a switch that only allows air flow when the engine is hot and shuts off the flow when the engine is cold.

The other side or other nipple on the CTO can, if you have the multi CTO with 3 or more nipples, only allow air flow when the engine is cold.

You can find this by blowing through a hose attached to one of the nipples. Once you locate the two nipples that only flow hot, you run a ported vacuum to one of them. From the other side of it, you run a line and T it to the EGR and charcoal canister purge valve so they only turn on when the engine is hot and you are at speed via the ported vacuum.

Any unused nipples on the CTO should be blocked. An inch of hose with a bolt in it works as a plug for them.

This 'could' give you a little bit of hesitation on a medium warmed up engine because you are missing the air filter thermostat, but once fully warmed up it will go away.

Oh and just in case... when you set the timing, the vacuum line needs to be off the distributor and the line plugged with a bolt or pencil or something.

Hope this gets you somewhere...

Mike

Michael Pomeroy wrote:

On Mon, 15 Sep 2003 10:12:53 -0400 in rec.autos.makers.jeep+willys, Mike Romain was alleged to have written:

Golf tee.

On Sun, 14 Sep 2003 23:33:49 GMT in rec.autos.makers.jeep+willys, Michael Pomeroy was alleged to have written:

Re-check that all your spark plug wires are connected right.

Just a note to let those who have offered suggestions know that I have read and considered them all.

I think the problem is probably directly related to a greater lack of knowledge and understanding than I thought.

So today I bought enough vacuum tubing to replace all the old stuff (it is an '82, so this can't but help), but the earliest I can get back to working on the Jeep is this coming weekend.

In the meantime I will be studying and thinking and working through all the suggestions in my mind. Then I plan to thorougly document where each hose currently runs (in case all else fails I can put them back like they are now) and then try to make it right.

When I do I'll let everybody know how it goes -- or have more questions to ask.

Thanks .....

Mike

----- Michael Pomeroy snipped-for-privacy@yahoo.com

If I can be of assistance, feel free to ask.

I see more of those 80's engines with vacuum lines running incorrectly than I see set up properly.

Lots of 'mechanics' out there even get lost in that maze, so don't feel too bad.... ;-)

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Michael Pomeroy wrote:

Other than being loud and startling, does backfiring hurt anything? Mine backfires occasionally, esp. when the engine is hot and has been running all day, but it is infrequent enough that I haven't worried about it.

Just my 2 cents worth on this. My '76 CJ had the original Carter POS carb, and the even worse Prestolite breakerless ign. I really wanted to keep the thing stock but after too many months of the cold running stumbles, farts & backfires from the carb, and endless stalling episodes caused by the ignition & its bundle-of-snakes wiring, I tossed the entire setup. I replaced the carb with a Weber 551 kit (installed on a 2 barrel manifold from a 258) and installed a DUI ignition kit. PRESTO, now the thing runs like a top, no stalling, better performance & mileage.

What kind of "sabbatical" do you call that? Why are you still trolling here?

Mixture too lean / too rich / throttle cable adjusted incorrectly.

If you tell us when it happens more precisely, should be able to narrow it down for you. (e.g. at idle / when accelerating / when lifting off )

Worst case scenario - backfiring can set fire to your engine bay (blow back in the carb), blow your exhaust apart or even crack piston rings. You want to fix it.

Dave.

Joshua Nels> Other than being loud and startling, does backfiring hurt anything?

I thought several days off, including a weekend, would be long enough to get you to calm down and act like an adult. Alas, apparently not. Back to the killfile you go!

Under heavy acceleration at higher RPMs when the engine is hot. e.g., I have been driving on the freeway in hot weather for an hour and pull off to an exit ramp and sit at a stop light. The light turns green, I hit the gas hard to get back up to speed quickly, and I let it rev fairly high in gear before up-shifting (so that I can accelerate more quickly.) This is typically the point at which I hear a backfire.

Ouch, no kidding. If I drive it like granny (no quick acceleration/high RPMs) I seem to avoid backfiring so I can do that until I figure out the bigger problem... but that's just not a fun way to drive. :-)

That sounds like an air leak.

You could have a leaky exhaust manifold or a bad EGR valve. My first bet is the exhaust.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Joshua Nels>

Could also be running too lean (intake leak or badly set up carb). Exhaust runs extra hot as a result and any unburned fuel in the exhaust goes bang. You can see the flames flickering out the back of decelerating touring cars as a rather extreme example.

for people to forget how much of a troll and liar you are?

Thanks Mike & Dave. It's fuel injected so it's probably not a carb problem. :-) I will see about getting the exhaust looked at.

touring cars