Post Number: 1
|Posted on Wednesday, July 30, 2008 - 01:55 pm: ||
I have a 1969 Chrysler Marine 318 with a Carter AFB carburetor in a '69 Correct Craft Barracuda.
The boat has developed a backfiring problem above 2600-2700 rpms. Idle is smooth and even, acceleration is good up to 2400-2500 rpms. Above that there is a constant "pop" and although acceleration is not great, the boat continues to accelerate. The carb has been adjusted at idle and the plugs seem to be burning acceptably (With the exception of # 6 which seems to be gettiong fuel, I can smell gas, but is perfectly clean. The points/condenser has been changed over to a Pertronix electronic ignition recently, the backfiring was worse prior. Plugs are new.
I have tried to power time under load to eliminate the backfiring to no avail. Any suggestions?
Any idea how the By-pass idle air adhustment screw is supposed to be adjusted?
Post Number: 12
|Posted on Wednesday, July 30, 2008 - 03:31 pm: ||
You could be starving for fuel. The AFB's have a "piston" that gets pulled down under vacuum when the secondaries open up. This opens the needle valve more to let in additional fuel. They sometimes get stuck. You can check for freedom of movement by taking off the little covers at the top of the carb.
There are two of them. When you unscrew the retaining screw you will see an aluminum piston with a rod that bends over and points back down. Be careful removing the covers, the piston is spring loaded and will pop up.
Also you may try changing your spark plug wires.
Post Number: 1751
|Posted on Wednesday, July 30, 2008 - 05:20 pm: ||
Broken valve spring will pop like that ?
If you can hear it in the carb its an intake valve spring !
|Posted on Friday, July 29, 2011 - 10:34 am: ||
I have a 318 Chrysler and changed the points. Now my exhaust consistently spews water and I can not get my rpms over 1200. Did I install points
Post Number: 3
|Posted on Friday, July 29, 2011 - 10:06 pm: ||
I would check your dwell angle. Your points may have gone out of adjustment after installation. It happens occasionally. Also, you might consider installing a Pertronix electronic ignition kit. I installed one on my M440B and eliminated my ignition problems.
Post Number: 1
|Posted on Monday, August 15, 2011 - 10:39 am: ||
I have a 1970 Owens with a M440 running rough only under pressure around 2200 RPM when i got it about 4 months ago i change plugs/wires/coil/dist cap/rotor /fuel pump and i was still running rough back fire and all so i had the timing adjusted ones the timing got adjusted. now it bogs down after having it at 2200 rpm for about a minute i can keep it at 2000 and ill run perfect but anything over that it gives me problems any suggestions
Post Number: 10
|Posted on Monday, August 15, 2011 - 10:35 pm: ||
I have discovered the best first step diagnostic tool for situations like these. Put gas in a small squirt bottle, one that has a 1/16" to 1/8" hole and with the engine under load at max. RPM spritz gas directly into the carb. and if the engine picks up RPM you know you have a gas problem and not an ignition or valve problem. Maybe it's as simple as a clogged gas filter. But it is crucial to find the right type of bottle. DO NOT POUR GAS OUT OF A COKE BOTTLE for this test! Hope you find it is just a clogged filter.
|Posted on Saturday, July 14, 2012 - 10:50 am: ||
my 318 chysler turns over but wont start.
Post Number: 299
|Posted on Saturday, July 14, 2012 - 12:43 pm: ||
Did you have any symptoms before this ? Have you done any work to the engine recently ?