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Discussion Starter · #1 ·
I was working on the ZX7R, and here is the scenario.

Engine turns, no start condition.

° Fuel pump primes, then shuts off when carbs are loaded.
° No Headlights on either side illuminate.
° Spark on all 4 cylinders detected.

Tonight, I changed the fuel pump relay, just in case. I did not suspect the relay, as the fuel pump previously primed before, with the old relay, but since I already had a new one, I thought "why not?" I also pulled the larger harness going into the junction block and inspected both sides for damage or corrosion (there was none), and swapped out the headlight fuse, as well as the one on the relay on the left side of the motorcycle (opposite the fuel pump relay). So I went to start it, and it did something new. Before, it had been turning over, but not firing whatsoever. It did not even hiccup. Tonight, I primed the pumps, then hit the choke, and tried starting it. While it still did not start, it did make a queef noise. It was not a full backfire sound, just a "poof!" Unfortunately, I could not tell if it was in the exhaust or the carburetors.

Any thoughts?
 

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One very important thing is to make sure you have a Battery that has the CCA required for the Bike. I believe it's 180 CCA. Anything less will cause the voltage to drop below required for the ignition system and will have a weak spark..
 

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Discussion Starter · #3 ·
Yes indeed. Even put in a brand new battery, although I had the old one charged and tested okay. Unfortunately, my DVOM is about a 2 hours away, so I cannot check for voltage or amperage right now.

One very important thing is to make sure you have a Battery that has the CCA required for the Bike. I believe it's 180 CCA. Anything less will cause the voltage to drop below required for the ignition system and will have a weak spark..
 

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Discussion Starter · #4 ·
Went to start it just a minute ago, and it turned over for about 30 seconds, then backfired out the exhaust (afterfire). Also, when I went to prime the pump, the pump did not shut off, despite being primed for almost a minute.
 

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If the pump keeps running, the float valves aren’t closing. This means that you are flooding out the cylinder(s) and potentially hydro locking the motor. You may want to pull the plugs to see if they are wet and make sure the chambers are not full of gas. You will need to fix the carb issue before trying to start it. Also recommend changing the oil if it has gas in it.
 

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Discussion Starter · #6 ·
Good info, thank you.
I pulled the plugs the other day, and they all had black (dry) carbon on them. Definitely going to change the oil, as I never trust that the previous owner did this when I buy a used bike. That, and a coolant and brake flush, are cheap insurance. ;-)

I should note that the pump did stop when primed the last few times... just today, it did not shut off.

If the pump keeps running, the float valves aren’t closing. This means that you are flooding out the cylinder(s) and potentially hydro locking the motor. You may want to pull the plugs to see if they are wet and make sure the chambers are not full of gas. You will need to fix the carb issue before trying to start it. Also recommend changing the oil if it has gas in it.
 

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Isn't checking the oil level a good start? If enough fuel has found it's way into the motor to hydraulic lock it, some would have made it's way to the oil and the level will have risen, and itll stink of fuel. You can't get much simpler than checking the oil to start with.
 

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Discussion Starter · #10 ·
Agreed. I don't think the engine is hydro locked, though... it rotated fine off the starter.

Also, I didn't have the pump running for a prolonged period of time. It was running for 45-60 seconds or so, and I had taken the fuel tank off prior (thus no doubt causing some air in the supply line).

Checking for hydro lock is safer and easier by removing plugs. If the combustion chambers are full, you will bend or break something.
 
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