engine miss firing

[drpete3]

I got gas at a crappy gas station and the miss started after that. this is Rebuilt engine with less that 10 hrs on it. Ill go along and then the Rpms drop about 2-300 then they will come back up and so on and so on. First thought was bad gas. I still put a bottle of water remover in it and put 15 gal of good gas in it. this jump in rps occurs at any speed. I removed the water seperator and dumped it into a bottle and didnt see any water. Help

[MOBILEMERCMAN]

Careful the ethenol and dry gas absorbs the water so the motor can pass it. It lowers the octane and leans it at the same time. When you looked at the fuel was it clear or cloudy? Cloudy fuel is water laden and bad news. Could you hear it pinging?

[Ratickle]

I just got off the phone with Chris. The filter type you replace. In a pinch, out on the water, you can pull them and slap the crap out of them and about 80% of the water will come out.

But change them if they have water in them when you get back to shore.

The water will not mix in the poly seperator, it will show as little beads/droplets.

Think I got it right.

[Chris]

If I thought I had bad gas, I'd suck every drop of it out of the tank and fuel system. Engines are expensive. Bad gas destroys them.

[Sean Stinson]

I got gas at a crappy gas station and the miss started after that. this is Rebuilt engine with less that 10 hrs on it. Ill go along and then the Rpms drop about 2-300 then they will come back up and so on and so on. First thought was bad gas. I still put a bottle of water remover in it and put 15 gal of good gas in it. this jump in rps occurs at any speed. I removed the water seperator and dumped it into a bottle and didnt see any water. Help

Do yourself a favor drain it and start over with new gas preferably some without ethanol!!!!

[Sean Stinson]

when is the last time you did plugs and wires and such

[Sean Stinson]

pull #1 and #6 plugs and see what they look like on the motor that is missing!!!

[drpete3]

Thanks guys. when i dumped the gas into a empty dry water bottle it was ceal but was more yellow than I expected. Looked like diluted Mt dew. I guess Ive never look at gas in a clear container so that surprised me a little.

This is a new(rebuilt) engine so all the plugs and wires are new.

What should ilook for on the 1 and 6 plug?

No it wasnt pinging. sounds fine to me other than the rpms droping and jumping up. It goes in maybe 10 sec intervals. Normal 10 sec then dropps for about 10 sec over and over.

I was thinking this type of water serarator was just a replacment type.

i only run 87 octane normally (420 Hp 454) and when I filled it after the problem I used 91 from a reputable Marathon station.

any more thoughts?

[MOBILEMERCMAN]

Check your fuel pressure and check for an obstruction or air leak in the fuel supply . Surging like you described can be costly. Don't let it do that. If its surging because its lean it is damaging the motor.

I don't put 87 in anything with a carb.

[Ratickle]

No it wasnt pinging.

i only run 87 octane normally (420 Hp 454) and when I filled it after the problem I used 91 from a reputable Marathon station.

any more thoughts?

Sounds more like fuel starvation than electrical issues.

Unless you know exactly what they did to the engine, assume they may have surfaced the heads and block and your compression was increased so 89 is no longer enough octane.

Float levels possibly guys?
Fuel pressure?
Fuel Filters?

What else?

[drpete3]

Check your fuel pressure and check for an obstruction or air leak in the fuel supply . Surging like you described can be costly. Don't let it do that. If its surging because its lean it is damaging the motor.

I don't put 87 in anything with a carb.

What kind of pressure should it be? I ran the boat fine for the firt 8 hrs or so after the rebuild. then this started. I was going to a differnt lake than normal so as I got close I found a Bp staion in a tiny little town and decided I sould get gas. I ran it for maybe 45 min then we sat for a few hours. I ran it fine for about 10 min on the way back to the dock and then this started. I was about 500 yrd s from the doock and took the boat out. didnt think much of it then. the next day I went out again and ran it maybe a half hour and the problem started right away and never stopped. It seems mild like about 200 rpm even at WOT. ANd when it drops its sounds like its bogging and I can feel the loss of power. actually the feeling is more drmatic than the rpms show.

So I should drain the gas
check fuel pressure
check for fuel obstruction
check for fuel line leak...air entering

I think the first thing I shoudl do is run it again since I ve put dry gas into the system. if the surging is gone then i would assume bad gas. then take appropriate measures to get it out..Right?

[drpete3]

Sounds more like fuel starvation than electrical issues.
Unless you know exactly what they did to the engine, assume they may have surfaced the heads and block and your compression was increased so 89 is no longer enough octane.

Float levels possibly guys?
Fuel pressure?
Fuel Filters?

What else?

I think they wanted to get about 9.25:1 comp

they put in 2.25 and 2" valves
they didnt touch the carb to my knowledge. Quadrajet carb. all new filters

My theory was the the water serarator filled up with water then I started having troubles.

[Ratickle]

Was it almost empty when you put new gas in?

Jim's worried the motor is starving for fuel, running lean, and that will definitely damage a moter.

[drpete3]

its was at about 1/4 tank and I remember putting in 30 gal.

What sdo the plugs look like if its running lean? Why would it run lean? from the gas?

[Ratickle]

its was at about 1/4 tank and I remember putting in 30 gal.

What sdo the plugs look like if its running lean? Why would it run lean? from the gas?

http://www.spark-plugs.co.uk/pages/t.../diagnosis.htm


http://www.gnttype.org/techarea/engine/plugs.html


Detonation/erosion/overheating

[MOBILEMERCMAN]

Any easy first test would be to run it on an outboard tank. Determine whether it is in the supply or the motor. It is also easy to check the float level. The fuel pick up cracking and obstructions in the supply are random misfortune. How many hours is irrelevant. A cracked pick up allows air in the line and only acts up at half tank or less.

[Ratickle]

its was at about 1/4 tank and I remember putting in 30 gal.

What sdo the plugs look like if its running lean? Why would it run lean? from the gas?

How big is your tank?

[drpete3]

http://www.spark-plugs.co.uk/pages/t.../diagnosis.htm


http://www.gnttype.org/techarea/engine/plugs.html


Detonation/erosion/overheating

so do you think Ill see this even if Ive only run it 45 min in this condition?

[drpete3]

Ok i took the boat out now that I added dry gas and still had the problem....prob not bad gas. BTW it was no longer surging it was just plain missing.

So this moring I pulled all the plugs and found one not very tight when taking it out. Put te plugs back in and fired it up on the hose and sounded good again. so I took it down to the lake. Ran strong for about 5 min then started up again. So i figured i either tepmrarily fixxed the problem or this is a warm engin prob. So I pulled all the plugs agian. I broke an insulator on one of the plugs this time. Maybe it was cracked and i didnt notice it before. Put in a new spare plug checked all of the plug wires and boom. the boat ran great all day today. FEWWWWW! i am so relieved that i got it fixxed

[MOBILEMERCMAN]

Nice