Rough or Wont start, backfires through exhaust

[ralt962 11]

I have an odd one.  Looking for suggestions  

• 351 Windsor
• Ran great when I put it away last fall.  Stabil in the fuel, ran it through
• Pulled plugs to spin the engine for oil pressure.  Gaped and reinstalled plugs
• Try to start it now, same fuel, when first trying it would miss and stumble but had to keep it high RPM and it was starting catch, ran rough but had to keep my foot in it.
• All of a sudden it smoothed out ran/idled (didnt take it on road) sounded good.  Like something all of a sudden changed.
• After idling about 10 minutes, it started running really rough again, died
• Checked the carb (600 Holley - new a year ago) float level good, jets clean
• Cranked again will try to start but sounds flooded.  kicks over if I dribble gas in the carb.   backfires through the exhaust and dies.
• Plugs wet.
• Thought maybe the mechanical advance weights were stuck.  They seem fine  I have a 15L and 10L   G3 and G2 weights
• Fuel getting to the carb ok.
• Not sure what next??  Crud in the carb?  Power valve?
• Nothing else changed.

Would love any suggestions.  I know there are a lot of good engine guys out there.

thanks,

[1969_Mach1 333]

Possibly an idle restrictor in the metering block is plugged.  Might also have plugged air bleeds.  Accelerator pump no longer working for a variety of reasons.  Small leaks in the metering block gasket.  If it were mine I'd freshen the carb.  Not good to let them sit for prolonged periods without running the motor once in a while.  Many people with Holley carbs will freshen them once a year just as a preventative type of maintenance.

[ralt962 11]

43 minutes ago, 1969_Mach1 said:

Possibly an idle restrictor in the metering block is plugged.  Might also have plugged air bleeds.  Accelerator pump no longer working for a variety of reasons.  Small leaks in the metering block gasket.  If it were mine I'd freshen the carb.  Not good to let them sit for prolonged periods without running the motor once in a while.  Many people with Holley carbs will freshen them once a year just as a preventative type of maintenance.

Thanks.  Looks like I'll go through the whole carb.  Does sound like something in the idle circuit is plugged or stuck.   I didnt go deep enough when I pulled the bowl off to check the jets.  

Appreciate the ideas.  I'll like you know how this goes.  

[bigmal 225]

Sounds very similar to the issues I had when I fitted an electric fuel pump. I also have a 600 Holley. It was pushing fuel past the needle/seat and intermittently flooding it. A regulator fixed my issue. I'm assuming that you still have a mechanical pump, and note you said the float levels were fine. Just wondering if the needle/seats are intermittently allowing excess fuel in either primary or secondary bowl. Just a thought.

[ralt962 11]

I had that same issue early on during my build.  I was using a Carter pump.  Mechanical.  It was putting out about 15 psi, when its supposed to be 6-7psi.  I had fuel coming out the vent tube.

I switched to an Edlebrock and did check.  You are right it was acting very similar.  I'm going to tear down the carb and also check on the fuel pressure.  But the float level seemed right on. when checked.  

Thanks for the idea.  certainly will check that out.

[dream car 12]

I had similar issue few month ago.  car just started sputtering on the road like run out of gas  manage to get home, wont start anymore. install fuel pressure meter to confirm pressure in line, which is good.  Check and reset the float level. Checked all the wiring to the coil and is good. for two weeks try to figure out whats the problem. No spark to the spark plug.  The final solution, I purchased and installed a Petronix ignition system along with a recommended coil.  The car started right up without even cranking (normally need two or three try)  Not only it run good , it rise the RPM to about 1200 idling., had to readjust the carb to bring down the idle speed. The engine run like  new now..

[ralt962 11]

I've been thinking about the Petronix.  But occasionally I read where the system has died after a year or so of limited use.  

I tore down the carb.  Made sure all of it was cleaned out.  Checked the power valve, idle jets, seats, main jets.  Not sure if I blew something out. 

Changed the condenser,  checked all the electrical connections to the coil and starter.  

It fired right up.  I'm not sure what I fixed.  Buts now running great.  Did a short road trip since it was a great day here.  

Thanks for all the suggestions.  Somewhere in there I must have changed something in the carb or it was the condenser.  But I'm back on the road.  

[unilec 57]

Good idea to switch to the pertronix system, just put the old points and condenser in a plastic bag and chuck them in the glovebox, nothing worse than being far from home and you have ignition porblems.

[RPM 1,190]

I carry a spare ignition set up for this reason. 

[ralt962 11]

Great idea.  I think I'll switch but carry the back up.  Easy enough to pop in the points.