Howdy!

Long time lurker, first time poster. Long story short, I bought an R7989 Holley 1945 on ebay to rebuild for my /6 in my truck. (85 D150 a833 lean burn delete with mopar ei) It had an R40159 1945, with all of the fast idle mechanisms removed by the P.O., It idled bad, was hard to start cold, but offered good drivability and adequate performance. It had a 662 jet.

Onto my "new" carb. It has a 642 jet. Float set 1/32 below the bowl surface, idle mixture screw ~5 turns from seated. The truck is now suffering from a low/mid throttle surge, and is gutless. I tried the 662 jet from the original carb, with minimal change. Accelerator pump is in slot 3, as per instructions. Seems to fall on its face off idle when releasing the clutch, but recovers with more skinny pedal. I've played with the timing, Currently sitting at ~11 initial with roughly 31 total.

So ultimately what I'm looking for is a direction to take. Is this 7989 a less than optimal carb to use for this application? Did I miss something? Are there any modifications I can do to get this carb back to where I was? I posted in the FB group about this same situation. Hopefully, I'm posting in the right place. Any advice is very much appreciated.

I suppose I should add, My goal for this vehicle is good drivability first and foremost, second priority is fuel economy. I'm not looking to build a hot rod, just be able to safely merge on the freeway.

Hello and welcome. Thanks for stepping into the light and stopping lurking.

The symptoms you describe could be caused by the carb or the ignition system. Did the problems start only when you installed the eBay carb? Was the non-eBay carb the original carb to the truck?

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Casually looking for a Clifford hyperpak intake for cheap.

Thanks for the welcome!

The poor drivability started after the ebay carb install, as far as I know the carb I removed was original, though I cant say for sure as ive only owned the truck for 5 months or so.

With the original carb idle was rough, but overall drivability was pretty good, and it got 14-18mpg.

OK. By 1985, especially if the truck had lean burn, the original carb would not have had a ported vacuum port for a vacuum advance distributor. Chances are when the lean burn was removed and the standard Mopar igniton was installed the vacuum advance line for the distributor was attached to the port on the carb that has vacuum full time. This means that when the timing was set with the electronic ignition distributor but the original carb the timing would have been very advanced due to the vacuum advance being fully applied.

The first thing I would do if I were you is verify the base timing is correct. The emisions stick/stock timing for the truck would have been something like 16 BTDC when it had the lean burn system. If you have converted to standard electronic ignition, a more reaosnable base timing is something like 8-10 BTDC. Make sure your curb idle timing is aroung 8 BTDC with the vacum advance disconnected.

Once you have the base timing correct, then verify curb idle speed and mixture. If the timing was really out of adjustment then the idle speed and mixture might have been set incorrectly. It could be the overly retarded timing made you turn the curb idle speed scre in so far that the carb was actually operating on the idle transfer slot at idle which would mess up the mixture and give you driveability problems.

Next, verify that the vacuum advance pod on the distributor and the choke vacuum pulloff diaphragms are not ruptured and still hold a vacuum.

If everything hold a vacuum, verify that your timing mark still accurately displays TDC.

Once you do all that, report back what you find.

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Casually looking for a Clifford hyperpak intake for cheap.

Well you're definitely right that the original carb didn't have the right provision for the distributor, I connected the vacuum advance to the small port near the evap inlet, which is a higher ported vacuum location. I never verified if and when it sent a signal from there, as the engine ran quite well the way it was.

I'm afraid I've found something that is likely a factor, if I spray carb cleaner on the corner of the base furthest from any screws between the base and the bowl, it stumbles. The idle was also noticeably worse since I disassembled the first time after rebuilding. Makes me wonder if it was leaking there the whole time, though when I first installed the carb I didn't get any reaction when spraying the same area.

How bad of an idea would it be for me to get another kit and double up the base to bowl gasket? Figure if that solves it, one or the other is warped.

I followed your advice, verified tdc on balancer to be accurate with a piece of rigid metal, and I have thus far tested initial timing 6°, 8°, 10°, 11.5°, 13.5° and 15.5°. @ the latter 2, power was up significantly as was drivability, which would make sense if the carb is suffering from an internal vacuum leak.

I favor filing the base of the carb flat over running two gaskets, but it is up to you. I would also verify that the 1945 you are running has the correct port for the vacuum advance. Stock Chrysler vacuum advance distributors used an unported vacuum source. THis means that the distributor should see NO vacuum advance at idle.

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Casually looking for a Clifford hyperpak intake for cheap.

Upon inspection, I can't find any reason for the lack of sealing at that corner, the surfaces appear true to my somewhat trained eye and straightedge, unless the gasket that came in kit #1 was too thin to get a sufficient seal.

The port I'm using on the new carb for the distributor vacuum signal is the small port, next to the pcv port. It has no vacuum at idle, and a square port inside the throttle body which has a matching relief cut into the throttle plate. Does that sound right?

Thank you for all your assistance so far, this has been a frustrating situation since the beginning.

Update as of this morning: Tried double gasket, same results, spray carb cleaner in that area and the engine runs differently. At this point there are only 2 possibilities I can think of. There is some throttle shaft play, but what is the definition of excessive? any? Or the base gasket isn't perfectly sealing on that side. I took the base apart and sanded it with some 800 on a flat workbench to make sure its true. I'll try a different base to engine gasket later today, and see what happens.

If you can feel or see any throttle haft play, it is too much. You can buy kits for $30-$60 to rebush the throttle shaft.

Your symptoms do sound like a vacuum leak, a problem with the accelerator pump shot, or possibly a problem with the idle transfer circuit on the carb.

I recommend downloading the Holley 1945 carburetor manual and watching the factory training film. Both of those can be found HERE.

I know some of the board members have really gotten into tuning these carbs and have found factory defects such as partially block or incompletely drilled passages. It might serve you well to fully disassemble thie carb and really go over it to make sure all the passages are free from corrosion and other gunk.

_________________
Casually looking for a Clifford hyperpak intake for cheap.

The first thing that caught my eye was "mixture screw at 5 turns out" YIKES! That is wayyyyy too much.
When everything is right on almost any carb system I have worked on, I rarely wind up with that setting at more than 2 turns out. Usually around 1-1/2 ish

7989 was for 1978 passenger car engines Federal emissions. 40159 was for 1985 light-duty trucks manual transmission Federal emissions so was original.

Idle restrictor started in 1977 it may be dirty or too small for today's fuel I would suggest cleaning it really good enlarging it or remove it altogether. At 5 turns out it's the Restriction that setting in your fuel mixture, not the mixture screw.