a little engine diagnosis?

shawnsadler

shawnsadler

Member
Jan 17, 2008
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Marysville, Ohio
www.sadlerforemanracing.com
Anyone ever had this problem before??? it starts at 2:36 and clears up when i come off track... it wouldn't run hardly at all and if i went WOT it bogged out. held half way it would run but sounded like REALLY bad spark knocking... and finally it cleared out and revved all the way through? got me stumped. i checked for air leaks, jetting, dirt in carb, junk on the petcock filters, found nothing. checked plug and wire.. all looked good..

 
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Had you just filled the tank prior to that run or just turned the petcock on reserve? It sounds like water in the fuel....

The pilot jet sits off the bottom of the carburetor 3/8" or so while the mainjet is right at the bottom of the float bowl. Water will collect at the bottom and the main will pick it up causing the low "BOOOOOGGGGGGGGG" when you try to give it any throttle.
 
At 2:16 did I see you reach down and change over to reserve?

Alright, so watch the video again and think about these series of events.

First two minutes: There's a small bead of water sitting in the tank around the petcock but the stand tube in the "on" position keeps it from being let into the engine.

2:15: the engine stumbles as it's running out of gas, you are JUST entering a hard lefthand turn

2:17 you reach down and change over to reserve but JUST as you do, you start to slide. The "bubble" of water at the bottom of the tank rolls to the right side of the bottom of the tank and gas continues to flow

2:32 you straighten up and the bubble rolls back down to the now open reserve hole in the petcock and falls down the fuel line into the float bowl

2:37 carburetor begins to deliver the water directly into the engine at full throttle and engine starts to bog. Instinctively you chop the throttle but continue to "feather it" lightly to keep the engine running.

2:32 the little bit of water from the float bowl is sucked up and into the engine and gasoline starts to flow behind it. As it does, the engine picks back up and you take off again.

It only takes 5mL of water to shut off an engine....
 
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sicivicdude said:
Had you just filled the tank prior to that run or just turned the petcock on reserve? It sounds like water in the fuel....

The pilot jet sits off the bottom of the carburetor 3/8" or so while the mainjet is right at the bottom of the float bowl. Water will collect at the bottom and the main will pick it up causing the low "BOOOOOGGGGGGGGG" when you try to give it any throttle.
Click to expand...

hmmm....... i am pretty sure i topped this one up before the start. it was FRESH CAM 2 from the pump about 6 hours prior to getting to the track. i mixed it 32:1 AmsOil Dominator and topped up the fuel before the main. i do know it was on reserve because when i slide through the corners it tends to load up on the right side of the tank so i don't use "ON" very often.
 
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sicivicdude said:
Had you just filled the tank prior to that run or just turned the petcock on reserve? It sounds like water in the fuel....

The pilot jet sits off the bottom of the carburetor 3/8" or so while the mainjet is right at the bottom of the float bowl. Water will collect at the bottom and the main will pick it up causing the low "BOOOOOGGGGGGGGG" when you try to give it any throttle.
Click to expand...

Yeah, water or a piece of dirt that actually worked it's way thru or working the throttle the way you were, maybe it was stuck in the main and you poked it out with the needle....hence it clearing up when you pulled off.

Unless your stator is getting weak and it was misfiring to the plug. :-/ That would've caused the plug to flood/foul and it would've needed to clean itself out.
 
The WAY it cleared up is what has me leaning towards water. It would barely maintain speed while he was hitting the throttle all the way until he coasted out and around the track and BAM it cleared up and he hauled ass away like nothing happened. That SCREAMS water bubble.
 
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sicivicdude said:
The WAY it cleared up is what has me leaning towards water. It would barely maintain speed while he was hitting the throttle all the way until he coasted out and around the track and BAM it cleared up and he hauled ass away like nothing happened. That SCREAMS water bubble.
Click to expand...

I completely agree, I was typing and eating ice cream while your conversation was going back and forth. Your explanation of the travel of the water bubble, man, that's some good diagnosing.
 
EZRider76 said:
I completely agree, I was typing and eating ice cream while your conversation was going back and forth. Your explanation of the travel of the water bubble, man, that's some good diagnosing.
Click to expand...

Want to take a wild guess how I know the "sound" of a water bubble in the carburetor and how it acts while the carburetor is sucking down that water? ;) One hint, I'm not a "bubble" of water or a carburetor I:I
 
sicivicdude said:
Want to take a wild guess how I know the "sound" of a water bubble in the carburetor and how it acts while the carburetor is sucking down that water? ;) One hint, I'm not a "bubble" of water or a carburetor I:I
Click to expand...

It's late and I'm tired, all I can imagine is there is a slight suggestion to farting in a pool or something....or there is a suggestion of a beer funnel.
 
I am not familiar with OKO carbs, does it have a plastic slosh baffle in the carb.

Maybe the fuel is sloshing up away from the main, this can happen if the float level is set too low.
 
ok. Thanks guys. I checked the reeds, they are fine, pulled the bowl and checked the float height and it's within spec. gonna completely empty this tank and start with fresh fuel again. plug looked good, a Touch rich but it was warmer than i expected this weekend so i'm happy with it. SI thanks for the explanation and fantastic diagnosis. Thanks to the rest of you guys for helping out as well. if you haven't yet you guys should subscribe to my channel to see all my races as i film EVERY one i go to. :)
 
sounds like the air side of the crankshaft seal is leaking this is what happened to mine
 
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