Loud backfire

fjbiker84 · December 04, 2016, 06:09:36 PM

Was near the end of my usual leisure Sunday ride when the FJ started running a little rough. Since I was so low on gas that the fuel light came on when going up hills I figured the bottom of the gas tank may be a little contaminated or has a little water in it (it's happened before). So I emptied the remaining gas from the tank, went to the gas station and got a couple gallons, put that in and tried to start it up. This bike always starts instantly but this time after a lot of cranking - nothing. Then suddenly it backfired so loudly that a neighbor came over from across the street to see if I was OK. It sounded like a gun going off. Anyway, I took off the tank and pod filters to see if there was any damage to the carbs but no visible problems. Put the bike in the garage and gave up. So the question is: Did this do any damage to the engine? Is it an indication that something more serious is wrong? Or should I just put the tank back on and try again tomorrow?

Mike 86 in San Dimas · December 04, 2016, 06:26:10 PM

I would try it again today (after the Raider game). Dont know for sure why that happened but if all was normal before, for now I would chalk it off to an unusaul condition of empty fuel system or maybe it was flooded.

FJmonkey · December 04, 2016, 06:27:44 PM

I doubt you did any damage to the engine as backfires happen outside of the engine. If the pods were ok then the backfire was out the tail pipe. If you have not had this issue before then I would not stress over it. If it happens again then post up with more information on what happened. Draining the tank may have allowed some water into the carbs. This may have allowed a rich fuel situation to build up resulting in the backfire. I would drain all 4 carbs to make sure any water is also drained out. Check the fuel that drains out to see if water is sitting on the bottom of the collection cup.

fjbiker84 · December 04, 2016, 06:51:43 PM

Thanks for the advice! Nice to know it shouldn't have done any damage. I'm going to buy some new spark plugs tomorrow before putting the tank back on - about time anyway. Will also try draining fuel from the carbs and checking for contamination. Then try starting it up again. Will update this afterward. Oh, and how bout them Raiders.

Mike 86 in San Dimas · December 04, 2016, 08:48:47 PM

Raider are real contenders again. feels good, dont count them out this year. Another come from behind win today!

Oh and yeah good to have tamper proof screwdriver set.

fjbiker84 · December 05, 2016, 06:40:01 PM

Drained the carbs and checked for contamination. Went to the auto parts store and bought a new vacuum hose for the fuel petcock because the old one looked a little weak. Put a safety wire around the petcock fuel outlet as has been mentioned on another post. Put more oil on the air pods because they looked a little dry. Then realized I had reversed both sides of the spark plug wires while taking out and cleaning the plugs!!! #2 wire running to #1 cylinder, #1 wire running to #2 cylinder, #3 running to #4 cylinder, etc. Put it all back together and it started right up - ran fine - so there was no damage done. To quote another great Alabamian, "Stupid is as stupid does."

FJmonkey · December 05, 2016, 06:59:48 PM

Awesome, happy to hear you found the issue and she runs well again.

Pat Conlon · December 05, 2016, 08:45:45 PM

Good for you!

As a side note, you if you have foam UniPods, don't oil them, oil is no good on foam, use foam filter spray.
If you have the pleated paper filters (K&N) throw those away and get the foam UniPods.
The fuel vapor from the carbs wash the oil off the paper filters and thus you lose filtering ability.

fjbiker84 · December 05, 2016, 09:01:32 PM

Oh, thanks for that. I'll have to order the right stuff from RPM. I replaced my old K&N filter pods with the RPM duel pod filters but have some K&N oil so used that. They appeared to be completely clean of the oil after just 500 miles or so. Life is like a box of chocolates, you never know what you're going to get.

balky1 · December 06, 2016, 01:25:01 AM

Quote from: Pat Conlon on December 05, 2016, 08:45:45 PM
Good for you!

As a side note, you if you have foam UniPods, don't oil them, oil is no good on foam, use foam filter spray.
If you have the pleated paper filters (K&N) throw those away and get the foam UniPods.
The fuel vapor from the carbs wash the oil off the paper filters and thus you lose filtering ability.

A hijack: do I need to oil HiFlo paper filter? It wasn't mentioned anywhere on it, it is stated as OEM direct replacement. Was original paper filter oiled?

PS: Ah, I found what I wanted to know. Apparently air filters are not oiled, only foam ones as K&N states.

ribbert · December 06, 2016, 04:17:13 AM

Quote from: Pat Conlon on December 05, 2016, 08:45:45 PM
Good for you!

As a side note, you if you have foam UniPods, don't oil them, oil is no good on foam, use foam filter spray.

OK, so what's in the can? I always thought it was just filter oil in a spray can for easier application.

Noel

FJmonkey · December 06, 2016, 08:39:53 AM

Quote from: ribbert on December 06, 2016, 04:17:13 AM
OK, so what's in the can? I always thought it was just filter oil in a spray can for easier application.

Noel

I think what Pat was saying is that oil like motor oil is not what should be used. The UNI oil gets real sticky and traps the dirt better.

Pat Conlon · December 06, 2016, 10:00:02 AM

Correct. Oil for paper filters. Foam filter spray for foam filters. You can use UNI or PJ1, etc, most motorcycle shops carry foam filter spray.
Very popular for dirt bikes.

FJ1100mjk · December 06, 2016, 12:28:29 PM

UNI Part Number: UFF-100, Description: 5.5 oz. aero - Oil

Pat Conlon · December 06, 2016, 03:52:41 PM

Yes Marty, paper oil vs foam oil, they are both oils, but for different applications.

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Loud backfire