Flathead Problems -"Poping"??

My friend just finished his AV8 and can't seem to get the flathead to run right. It is an 8BA, Merc crank, elderbroke heads, Sharp three carb intake with 94s on a progresive linkage, mallory duel point, speedway clear wires. The motor makes a poping noise under acceleration. It also seems that one exhaust pipe is cool while the other is hot and carbons up. Some of the plugs look good while the others are carboned up (mixed on both sides of the motor). Could it be the mallory? Are the speedway wires causing grief (they are running in chrome looms)? This is a brand new build on this motor.
Thanks

 

Those nice chrome looms can cause crossfiring. Could be what's happening to your engine.

 

Dump the tree twos, put on a single intake and carb. Get it running properly and get a little time on the engine. Then work out the 3 2's.

 

Try the coil. Mine was jacked up and was making my car pop bad uner accelleration.

 

If only half of the cylinders are firing maybe one points set is not working right or missing. Most older Mallory dual points only have 4 lobes so one set of points is only going to fire 4 times for each revolution of the distributor instead of 8.

 

When I was younger, my friends and I would stay up late "Poping". We'd get all hopped up on wine and crackers and punch each other in the ash mark. The first one to pass out started the first round of "Alter Boy".


sorry, couldn't be helped

 

Sounds like ignition problems as you explain only half the engine runs good . I would use one carb to set up the new engine like " flatjack" said to get it running correctly first . Also check your condensers and points again . Just because they are new doesn't mean they are good . I have had it happen to me before .
I really think it has got to do with the ignition . If it's popping as you up the RPM's it's electrical problems .

 

I'm with flatjack. I've been thru all of this a few times. I ALWAYS bring up a fresh flathead engine with a stock manifold. I've got one right on the shelf just for that purpose. Get some time on the engine, get it timed etc and then put on the multi carb setup. Good luck.

 

Thanks for the info. I passed all the ideas on to my friend and he going to try to trace everything back.

 

Your friends problem may be the intake , are the runners into a common plenum if not you will starve the cylinders at the front & rear of the engine as they only get idle mixture & will run VERY lean. connect all 3 carbs & see what happens it may be way fat but you can always jet it down . Most flathead intakes are not designed for progressive linkage.I had the same on a flathead roadster I built 12 yrs ago, re connected the linkage & it ran killer. Follow the runners, I've got a Sharp intake at the shop I'll look at it in the AM & post again.

 

how can you tell about the plenum? i have and intake on my roadster two carb set up but olny running the front carb how does it effect the motor my seems to run fine but fouling plugs i'm not sure what maifold i have its been ground smooth does it need boyh carbs? billy

 

Hi Mate,

Cast my vote for the single carb on a single carb manifold.

Danny

 

Billy , With the manifold on the car see where the runners go if they are directed towards ports they are individual runners, if the collect into a larger area (plenum ) then your OK with progressive linkage . It's easy with the manifold off, check your plugs if all are firing it is good, I had the end 4 plugs white they were so lean, just from a run to Pomona from Whittier !!!. Plug check is sure fire way to see if all is OK .

 

you get so many differnt answers 1 carb good or no they both have to be hooked up or your going to burn up the rear cylinders ???????

 

If its a new Mallory change the condenser. They are noted for their frequent failures!

 

OK a couple of things, the Sharp intake is a common plenum so progressive linkage is OK just make sure the carbs are synced (balanced ) Yesterday I had a runability problem with a Mallory dual point on an 8BA with a 4 barrel carb, would not keep running, tried condenser, coil, carb changes, all to no avail. I put a petronix unit in the disi , Hey Presto it runs like a charm. I hate to say it but almost always I come across a Mallory distributer there are problems. When they work , they are great , when there is a running problem I find out it's the Mallory disi !!!!.

 

Holy crap. A three-foot high stack of tuning problems and mysteries going on simultaneously.
Recent Mallory: This is a CORE, not a distributor, till you have examined and fixed its likely problems. Discard condenser immediately, examine points for heavy wear even if they have 5 miles on them. Replace with NAPA parts...examinr the loop of wire connecting the points back to wire from switch...you may well find it touching housing and leaving burn marks from shorts!!
After giving it new small parts and curing the possible bad wiring, you will have to check and quite possibly fix the advance curve, but that is a job for later after car is running fairly well.
Next--sounds like carbs are a mystery, and you also cannot de-bug and tune a triple while fighting possibly numerous ignition issues!
Remove all three, disassemble, carefully st and confirm float level at lowes spec (biggest number). See that all jets are the same, power valves actually seal to bottom of bowl with good gasket contact.
Put on stock manifold or totally block both end carbs. Tune it til it runs well as a single, swap carb, repeat til all three are functional as stockers. See with tining light that you have functioning advance with considerable part coming in by 2000...finer tuning of the M can wait for later.
Now, put all three back on...tuning in the triple will be next flog.
You simply cannot diagnose and fix 27 things simultaneously.
By the way, nearly all common flathead manifolds are 180 desicgns with no common plenum. Common plenum requires less carb and tuning changes.

 

Bruce to the rescue!

Danny

 

Check the Mallory for a couple of things, #1 point gap, which out of the box is notoriously bad,#2 total advance of the dist. as the Mallorys have way to much advance out of the bopx, usually 30 + degrees and lastly the condensors on most Mallorys are pretty poor and a simple test is to hang a Ford condensor from a "68 302 on it for a test.

Wit a balast resistor in line to the distributor the points won't fry, with out they will cook rapidly.

These are the generall issues we check when installing Mallory distributors, as we spin them on our Sun Dist. Machine.

Running the center carb alone would issolate the usuall fuel issues.

Good luck Max Sr. @ H & H

 

Ahhhh ..... love it!
Didja flog one another with the palm fronds?

 

Yep..

 

A lot of the Mallory's gap problems are actually rubbing block problems...M points totally wear out their blocks at around-the-block mileage. GE points from NAPA. And condenser. Discard originals immediately. This is a core for a build, not a functional new distributor.