371 Olds Tripower Backfiring

Well i'm Trying to get my New Engine Running properly in my Truck. I had a thread last year after killing the engine in it
http://www.jalopyjournal.com/forum/showthread.php?t=390012&highlight=f1+almost+finished

Heres some specs on the engine so you guys have an idea what im fighting

-1957 Olds 371 BLock Bored out 70 thou
-Solid Engle Cam 274 running duration, 238 @.050" with Ross Adj. rockers
-Ducoil Distributor(dizzy has not been Put on scope)
-Oem J2 tripower intake with 3 rochesters and vintage speed Tripower kit (alum. secondary bases, 56 jets(too small i think) power valves plugged in outers no idle circuits in outers and no choke on all
-Cam has been Degreed
- electric carter fuel pump 5 psi

We broke in the Cam and everything seems to be good including the oil pressure this time haha. Except for a backfiring/ No power problem. It tends to pop back into the intake when i rap the throttle. i took it for a drive around the block and it has terrible power, Backfiring and ****ping out. so i now know its worse under load. Weve Got the timing as close as possible. 5 Psi Fuel Pressure, Proper Float Height, rocker adjustment has been Triple checked. I Was Told it was Probably too lean due to a Vacuum leak. So i went Removed the outer carbs and Blocked with Plates and monitored with manifold Pressure Gauge. No Difference, and still backfiring, I changed the intake gasket to a paper and sealed very well, Still no difference and Vacuum sitting at around 6.5 psi at idle. Im not quite sure what to do next i think im going to try a stock dizzy with pertronix and see if that makes a difference, Perhaps the advance or a short is throwing in an extra spark Here and there any ideas? Summers disappearing will be gone soon, i really wanna Drive this thing.

 

Pull the distributor & coil out and beg, borrow or steal another. It sounds like an ignition problem? If the next distributor & coil does'nt solve the problem, well you know it's not ignition.

 

Thats really low vacuum. Have you tested for leaks with brake cleaner or propane?
Put plugs on all vacuum ports that are being used, including the vacuum advance and test for leaks.

Atleast try that before moving on to the mechanicals. Maybe the valve timing is off or the distributor is a tooth off?

 

you sure the balancer matches TDC on your timing tab? I know you said it was degree'd ... just sounds like it could be timed wrong. Leave the timing light on the bench and set it "by ear".

 

I ran a DuCoil on a 394 for a short time,
it was tricky to set up but once I finaly got it right it worked very well

I think your idea of putting a stock distributor in
at least to iron out the rest of the bugs is a good one

 

I had a tough time getting mine timed right also- is the balancer a stock unit? they have that rubber im-between the inner and outer and i swear the timming marks are off after they remake them. I could not get it anywhere near running decent trying to do it off the marks. I also eliminated the end carbs from the start just to get the cam set and things on course. It runs really well now but it took a couple of weekends of pulling the distributor and starting from scratch. Pull the plugs, verify the proper stroke and if its poping try going a tooth back even if its away from the marks. Mines way off the marks now but it runs strong and i also have a converted distributor.

Good luck,

 

check for a busted mech advance spring in the dizzy, and verify your TDC. It's a timing problem.

 

Well the Pulley is a 303 pulley, the rotating ***embly was balanced to zero internally. Im going to try the Stock Distributor and we'll see what happens. I'll let you know what happens, thanks for the help guys

 

If you think it needs more jet; stagger your fingers over the center carb to richen it to see if it stops popping and if it is more responsive.

Keep the outboard carbs sealed off untill you get it figured out.

That vacuum reading does not sound good to me....esp when chasing low rpm issues.

 

I agree to use the stock dist for now; make sure to test the advances.

I agree on ignoring the damper mark for now, just use it to see when and how much advance. Set timing by ear and vacuum readings.

Also, what intake manifold; is it made to fit the 371? and do a visual on the gasket crush around the ports, looking for suspect gaps.

EDIT; the reason I asked about the intake; I have a 371 intake that was machined to fit 324/303 a long time ago. I don't have a 371 to try it on but it might cause a port gasket error when used on a 371. That's why I suggested a visual on the composition gaskets.

 

6.5 psi at idle is really low I would be looking for vacuum leaks.

 

Throw some timing into it, it is way retarded.

 

Yep, my vote is for not enough advance. Use a TDC indicator in the #1 spark plug hole to find the true top dead center. Remark the balancer and re-time. Add advance as needed.

Also, be sure you don't have vacuum leaks anywhere on the outboard carburetors.

Good luck!

 

***uming the distributor is in at true tdc and the basics are right, connect up your vacuum gauge and start advancing the timing while watching your gauge, if its increasing in psi then it's timing, if it doesnt increase I'd say vacuum leak.

 

I can advance it till im getting around 10 psi but than it wont start

 

oh and the intake is a stock j2. un machined. its definately sealed.

 

that's how I do it too,
bring the rpm up to about three grand and adjust to ear
then test drive and repeat

I also measure diameter of pulley,
find exact tdc and put my own timing marks on it in five degree increments,
so I know where I'm at,
at idle and full advance

it usually becomes a matter of compromise
between easy start and strong top rpm

seems to me my DuCoil was very sensitive to distributor rotation
very little movement makes a big difference

not to knock them, but I prefer the magneto

 

I don't know what it is, but:

I personally put together a Pontiac engine, and used the wrong timing mark on the timing gear. Had about 6 inches vacuum and it backfired through the carburetor.

Took it back apart. Timing gear had four, that's right, four timing marks! Got a mechanic friend who had used that timing set before to help. End of issue.

Jon.

 

you do have the wires in the correct order on the cap don't you?

(you must if you can get it to not backfire at all..)

the DuCoil is an odd duck
if I remember correctly it should look like this;

 

Im thinking it may be the cam not put in and set up right to the crank at TDC

dont trust marks on a dampner..piston stop is a very good way to be dead sure on T.D.C.

I would first go the path of least resistance..Distributor. if that dont cure it...Cam

 

got it going boys! it Hauls ***! I ripped the ducoil out had the new dizzy in set to 10 degrees, than a friend checked out the hamb on his iphone and saw pauls post we both went holy ****! i ahd no idea it had its own firing order. i cant believe how well it actually ran with the completely wrong firing order only popping once when rapping the throttle. The engine sounds bad *** now, Tripower works great. Great throttle response. Everything is Rad. took it for a spin around the block and im still smilin

 

Great to hear it. That's why we ask the questions on the H.A.M.B. There is expert advise near by.

 

its funny, most people ive talked to, they ask what kinda distributor im running and i told them a ducoil and they were like Ducall? what in the hell is that? (with a southern accent) On here Its the norm

 

Congrats!

 

cool!