Duraspark Conversion Issue

[BigMeatyClaws]

Hello all,

Finally did the duraspark conversion. My issue I'm having is the engine will start if I pump the accelerator 5 or so times, run in a loping/missing kind of way, then die after maybe 5 seconds. Sometimes it backfires through the carburetor. If I accelerate while it is running it backfires through the carb with visible flame and then dies.

I've tried:
Cleaning the new carburetor with spray without removing it
Adjustments to distributor timing
Checked plug order

 

[RonD]

Reads like vacuum advance issue

Are you using Ported(above throttle plate) or Regular(below throttle plate) vacuum on the distributors vacuum advance?

Set timing with vacuum advance unplugged and its hose plugged up
Engine warmed up is best
Set at 10-12deg BTDC
Then add vacuum advance back, and it should change to 18-22deg BTDC
If it doesn't change then vacuum advance in distributor is not working
Pull cap and rotor
Put vacuum hose on distributor and suck on it, i.e. pull a vacuum
It should hold vacuum and the arm should move a plate inside distributor

 

[BigMeatyClaws]

I'm using the spark port. Underneath the choke.

 

[RonD]

I added to my previous post on testing vacuum advance

Vacuum advance is there because when you change the air/fuel ratio when engine is under load, richen it, the spark timing must also change from the basic RPM spark timing

When a gasoline engine is cold it needs to be Choked, carb or fuel injected
In a carb a Choke plate is used, to decrease the amount of air flow into the carb which increases the regular vacuum so more fuel is sucked out of the idler Jets
This Richens the air/fuel ratio so enough gasoline Vapor is in the cylinders for spark to ignite it

Spark can only ignite gasoline vapor, not liquid gasoline
Cold gasoline has less vapor, can't smell it as much, as when its warm
Cylinder needs about 30% vapor to fire by spark
So the colder it is the more cold gasoline needs to be sent to the cylinders to get to that 30% minimum
Compression Heats the liquid gasoline to get more vapor, but it still needs to get above the 30% mark for good ignition

Computer does this for fuel injection based on outside temp at startup, it adds more gasoline
But on a carb its a mechanical adjustment of the choke plate based on outside temps, usually choke needs to be adjust twice a year, for winter and summer driving

Having to pump the gas pedal for cold start on a carb engine means there is not enough Choke being applied

 

[19Walt93]

I'm using the spark port. Underneath the choke.

That's where the hose should be. It sounds like either the choke isn't closing all the way or there's a problem with the accelerator pump. With the engine off and the air cleaner removed, watch down the carb when you work the throttle, you should see a good squirt. Once everything is set right it should require one pump to supply a little gas and allow the choke to close.

 

[85_Ranger4x4]

I have had all sorts of cold blooded beasts... backfiring thru the carb when running sounds like timing.

 

[kimcrwbr1]

There is a large vacuum port on the back of the egr spacer it is under the brake booster hose and easy to miss. It goes to the vapor cannister and float bowl vents that were controlled by those two solenoids that dont work if you trashed the computer harness. I just put one of those vacuum restricter so you dont get the fuel vapor from the tank in theengine compartment. Did you put the carb spacer under the new carb felpro #60529 it will solve the vacuum leaks at the carb base. Pull the carb and lightly surface the base. Install the spacer with a new gasket on both sides and do not over tighten it down. Preset your needles out three full turns and bring it up to temp and set base timing at exactly 10 degrees btdc. These little engines like it rich on the idle air and lean with the high speed jets. If you dont know what jets it has get two #42 jets and put them in when you surface the base of the carb.

 

[RonD]

Warm up engine
With Vacuum hose unhooked from distributor and plugged
Set base spark timing, 10-12degBTDC
Plug vacuum hose back on
Should see spark timing change to 18-22BTDC if vacuum advance is working like it should

 

[BigMeatyClaws]

Turns out my timing was just way off. Sorry folks.

 

[RonD]

Thanks for the update