225 slant six in a 71 Dodge B100 Sportsman that I use sporadically for recreation mostly.
Short block installed in 1983 at 147K miles. Cheaper than re-building the trashed engine when I got the rig back from my ex.
Head re-done in 2004 because of a burnt valve caused by a cracked exhaust manifold caused by horrendous backfiring, caused by a bogus mechanic I was forced to use to do a minor tune-up.
Replacement head is newer [has different spark plugs than the original did] -- had to have been swapped out by head shop, but I have no proof.
Replacement exhaust manifold is newer -- has O2 sensor port.
Had to replace wornout, not re-buildable original 1920 Holly, which had a high-altitude jet -- the rig originally lived at 8000 feet in Colorado as I did.
Now we live at 1620 feet above sea level.
Last summer, we rebuilt the third -- rejected two -- rebuilt 1920 Holly cause it just wasn't right and I'm still not happy with it.

Last time I used the rig, it backfired so bad it blew out the heat-riser bushing opposite the counterweight. The heat riser seems to work fine, so I have left it in. Turned a new bushing and pressed it in.

It backfires during warmup if the fuel pedal is touched at all. Idles too fast and runs too rich. If I cut the air-fuel mix any further, it dies at idle. "Diesels" when switched off at normal run temp.

I feel I've tried everything I know how to do with the carb. Accelerator pump checks out; Float is gauged right -- wish I could get a high-altitude jet

_________________
David Wilkinson
wilki-worker
POB 173
Twisp, WA 98856

David,

I think you have several carburetor problems acting in consort with mechanical engine settings.

Back fire, two major causes: incorrect timing; and running lean in transition from idle circuit to main jet. Hang onto these two ideas for now.

[quote]Diesels when switched off at normal run temp.

Idles too fast and runs too rich.[/quote]

Both of these symptoms were most likely caused by the big fire. Backfire will blow out, or rupture Holley power valves.

If your power valve, which is an enrichment device that only adds fuel during WOT in addition to the main jet’s contribution, is ruptured, it will dump excessive fuel at idle causing an over rich condition. Because of the excess fuel available during idle making a rich condition, the throttle plate has to be adjusted to let in more air, and will not fully close. So when engine is shut down, it will diesel.

Because your engine is running rich at idle, bad power valve, you have to crank open the throttle plates to let in more air which rises idle rpm, and exposes too much of the transition circuit slot, which will make you car bog and backfire under acceleration.

You will need to install the following items:

Backfire prevention kit if available for your unit.

New, [url=http://www.holley.com/TechService/FAQ.asp?category=Carburetor] properly[/url] sized, [url=http://www.holley.com/data/TechService/Technical/power_valves.pdf] power valve[/url], based on your car’s in-gear idle vacuum reading.

Proper low altitude jet, which will be richer than the 8000 foot jet you had, because there is more oxygen available near sea level.

The throttle plates will need to be closed up, using the idle speed adjustment screw, until only about 0.025â€￾ of transmission slot is showing when looking from the under-side of the carburetor.

Interesting reading from Holley can be found [url=http://www.holley.com/data/TechService/Technical/Carburetor%20Tech%20Info.pdf] here[/url] , and [url=http://www.holley.com/TechService/FAQ.asp] here[/url].

Once you get the power valve replaced, proper richer main jet installed, throttle plates closed down, idle circuit adjusted, and all vacuum leaks repaired, your car should run again.

One place to look for a massive vacuum leak is the power brake booster if you have one. Also, check the PVC valve for proper sizing, if it flows too much air because it is for a big V8, that is a vacuum leak as well.

Holley’s how to video section [url=http://www.holleytv.com/featured_landing.php?reset=true] here[/url].

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Thanks for your reply. I appreciate your advice.
First, please note that since the horrendous backfire that cracked the exhaust manifold, the carb has been replaced, the head was redone, and the exhaust manifold replaced.

I note all the references to a "power valve" in the carb, but find no reference to such on any of the parts lists, nor on any of the exploded diagrams or in the manuals I have. Am I missing something?

The carb on the engine now has the jet installed by the rebuilder, not a high-altitude jet -- I was wishing I had a high-altitude jet because the engine ran better and got better mileage with one.

I will check the throttle plates and idle circuit adjustments today if my schedule allows, but believe these are set right.

We have tried so many fixes now, that it seems each added "fix" complicates what should be a simple solution. This is a simple engine with a standard transmission, no power brakes, steering or whatever.

I feel almost like tearing the engine down and starting over from scratch -- at least with the upper engine.

_________________
David Wilkinson
wilki-worker
POB 173
Twisp, WA 98856

Wilkiworks:

Take a look at fig. #8 in this [url=http://u225.torque.net/cars/SL6/docs/Holley_1920_Manual.pdf] Holley 1920 Instruction Manual[/url]. I apologize for the general carburetor discussion. True it dose not have a screw in power valve like some of the other larger Holley units, but has one of a different configuration. I suspect that a malfunctioning PV is still one of your problems.

Make sure the check ball is still installed, rubber diaphragm of PV is not compromised, and all passageway are clear of crud.

If by any chance this unit that you have previously rebuilt was a “Factory Rebuiltâ€￾ off the shelf unit from a big box parts store. There is a good possibility that you will never make it right. Most of them are junk.

Slantsixdan may still have, a nice unmolested, NOS 1920 that he can sell you.

[url=http://www.slantsix.org/forum/viewtopic.php?t=33102]Here [/url]are several more places to look for 1920 info.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

With a 1920, the Power Valve" is called the economiser valve.
Rejetting a 1920 is simple, just pull the float bowl cover and replace the jet. (get a few replacement gaskets, just in case you rip one)
It would be nice to try a known "good" working carb on it. Do you know any fellow "Slanter" in your area that could come by and swap / test carbs on one-another's vehicles?
Don't get carried-away... keep testing / trying different things.
You may want to pull the valve cover and check the valve lash adjustment.
DD

Thanks, Doc
Last evening, I enlisted another friend who is an excellent mechanic. Like me, he grew up on a ranch doing what you gotta do.
We decided to pull the valve cover and check all that, as well as go back to square one with some other stuff. We will be doing this stuff in the next few days if the upcoming family holiday schedule permits.
If this go round doesn't do the trick, we will be pulling the grill, radiator, etc. to check that the timing chain hasn't jumped.
He's gonna help me do some work I haven't been able to -- hate to say so, but getting older and have some vision issues.
Thanks for all the help -- I will keep you all posted.

_________________
David Wilkinson
wilki-worker
POB 173
Twisp, WA 98856

OK - - my rancher friend went back to basics. Really great to have a person with no pre-conceived notions looking at the issues. Bill said, at the start, "Don't tell me what you've done or tried."

I didn't and the engine is running better than it has in more than 5 years.
First he thought that the distributor was installed 180 degrees off, but not so

When Bill brought #1 up to TDC, he discovered that although the engine would idle, run, and accelerate the TDC mark on the harmonic balancer and TDC in #1 cylinder do not match. The timing mark is about 1/8 of a revolution ahead of #1 TDC.

Right now the distributor is recalibrated to match #1 cylinder. Engine idles slower, runs leaner and cleaner with no backfiring. Seems to lack a bit on high-end out on the highway, but I'm driving it a bit where it's at.

Questions: How could this happen?
Timing chain jump?
Could the the balancer be wrong for the short block that was installed? I think I read about different keying between earlier and later engines.

_________________
David Wilkinson
wilki-worker
POB 173
Twisp, WA 98856