454 crusader backfires thru carb at wot

[CTD]

Re: 454 crusader backfires thru carb at wot

The only way to tell if a cam is flat or valves are not opening far enough is to measure it or at least watch the valves move while you crank it. They should all move the same amount, if the cam is going or you have a bent push rod you will be able to see the difference easily. I did see one with a slightly bent push rod once that would let the engine run ok at low power but at higher rpm it would flex enough to not fully open the valve. I only saw it once in 35 years working on cars so it dosn't happen often. I don't know what kind of distributor you are running but I've see quite a few rotors that burnt a hole through the middle and whenever you put the engine under a load it would misfire. Just a couple more things to look at. One more thing you could try is take a spray bottle of water and spray a mist on the dist cap and coil while the engine is running, if you have any weakness in those areas it will show up.

 

[MarineTechStudent]

Re: 454 crusader backfires thru carb at wot

Place your fingers in the carb while running the engine to see if the conditions stops, if it does the float height for that carb may not be right causing a lean condition. You can also spray some fuel into the throat of the carb to see if that stops the problem.

 

[RatFish]

Re: 454 crusader backfires thru carb at wot

Sounds kind of dangerous MarineTechStudent. I not that fond of burns. Hmmm...

 

[dvarnadore]

Re: 454 crusader backfires thru carb at wot

I'm Back with an update<br />pulled and checked the pushrods none bent so I pulled off the heads and took them to our areas best machine shop for marine and preformance.<br />Initial inspection shows no burnt valves but it did show that the head gasket was not the original and that it was also not a marine head gasket. It also showed that it had not seated and that combusted gasses had darkened the areas of the gasket around each cylinder it also appeared that it may have been feeding cylinder to cylinder in one area. I am waiting for a call to see if there were any other attributing factors I'll keep you posted

 

[dvarnadore]

Re: 454 crusader backfires thru carb at wot

update <br />Im a little late with this but better late than never step back to may this year thats when this hell ended<br />the list goes as follows<br />checked the timing ,checked the spark plug wires and the firing order,previous owner had installed electronic ignition a year before I bought the engines,I rebuilt the heads,checked the cam for a worn out lobe ,checked for a bent push rod,replaced the fuel pump ,dist-cap,rotor button,ignition wires,rebuilt the carb, replaced the electronic module in the electronic ignition<br />I did all these things and still had the problem<br />last and finally I replaced the electronic pickup at the center of the "new distributor" and behold problem finally solved<br />I appreciate all the help. just goes to show you that even recently purchased equipment can fail.<br />Beacause I had the mindset that"it's new" or "that was just recently installed that can't be the problem" It caused me to look everywhere else.It cost me a lot of time and money but education is not free and this was a lesson well learned.

 

[barrelman]

Re: 454 crusader backfires thru carb at wot

I'm experiencing the same problem with my 1993 merc 4.3 V6. Popping back through the carb at 2800 RPM and higher. Started as an intermittant , once a day or so to incessant above 2750. This engine has the thunderbolt IV ignition.

 

[Blk-n-Blu]

Re: 454 crusader backfires thru carb at wot

hallan, this thread goes back a ways,you might want to start a new one with your engine specs.

 

[dvarnadore]

Re: 454 crusader backfires thru carb at wot

Originally posted by hallan:<br /> I'm experiencing the same problem with my 1993 merc 4.3 V6. Popping back through the carb at 2800 RPM and higher. Started as an intermittant , once a day or so to incessant above 2750. This engine has the thunderbolt IV ignition.

You might want to check and see if your carb has a small filter in it right where the fuel line enters the carb I just changed mine because of the type of problem your having mine looked clean but try and blow thru it and nothing! it solved the problem.If your engine has been running good and this just started it sounds as if it is fuel starved when you try to open it up<br />good luck!

 

[deputydawg]

Re: 454 crusader backfires thru carb at wot

Some things to add. I have had this problem before. Will it accelerate to that rpm smooth if you snap the throttle open? If so check the float bowl for debris. You may have a plugged jet. Timing off won't cause this problem, check the timing advance to make sure it is advancing as the rpm's go up. Do the leak test on the cylinders, put air pressure to them with a guage. Watch for a while and see if the pressure drops. The cylindars will (on a warm engine) hold pressure for quite a while. Look for any feul filters too. Also make sure to re-check your float level in the carb. It about has to be an early spark at high rpm or feul starved, or a leaking intake valve.<br />If you do a pressure test you will hear an air leak on the bad cylinder. Make sure both valves are closed for this test though.