6.9 idi doing funny things

[Ethan Smith]

So my idi does this crazy thing. It starts really getting torquey and rips hard right before it runs outta fuel. As if there's a fuel restriction and when the tank starts to pull air its either running proper. (I've got a racor prefilter before the stock filter) or something crazy.
Seriously dudes it's like a drag truck when I'm dipping really low into the tank. I can't figure out why.

 

[Kizer]

She's sucking air instead of fuel.
If it's happening at about 1/4 tank, your "shower head" went ti-ts up.

 

[Clb]

Lean fire issues.
Plus the ip is out of calibration due to air intrusion...
Moral of story...
Fill up

 

[Jesus Freak]

.....ahhhh, air intrusion....... if only we could get these engines to run on air. Maybe if we lived where there was a bunch of smog?...

 

[Ethan Smith]

Alright, no doubt about the air intrusion. But.im telling you guys it runs really well when that air starts intruding. It's running well enough as it is but it's like a drag car when it's running lean. I understand two strokes running lean and rippin about to burn the piston. But with less diesel it autta just big down? I know my timings alright but you guys are saying that as it leans out the timing somehow advances?

 

[Rdnck84_03]

The air in the injection pump messes with the timing inside the pump itself.

James

 

[Jesus Freak]

Alright, no doubt about the air intrusion. But.im telling you guys it runs really well when that air starts intruding. It's running well enough as it is but it's like a drag car when it's running lean. I understand two strokes running lean and rippin about to burn the piston. But with less diesel it autta just big down? I know my timings alright but you guys are saying that as it leans out the timing somehow advances?

Yeah, they run really sweet just before they die.

 

[Brian VT]

...just like a 2-stroke.
Most race drivers have the ability to lean the fuel mix out as needed near the end of the race if needed to win.
If the engine melts down just after the finish line then you know you gave it everything you had. And hopefully you won.

I've burned up some 2-strokes that were going lean and, YES!, they go like hell before they melt down.

 

[Ethan Smith]

It's just crazy to me that diesel does the same thing.

 

[Jesus Freak]

It's just crazy to me that diesel does the same thing.

It's crazy that diesels even work!

 

[XOLATEM]

Yeah, they run really sweet just before they die.

Years ago...I had heard the same thing about chevy small-blocks...

It dawned on me later that it could have been the timing chain loosened up enough to retard the cam timing noticeably and that would make an engine run like a r-a-p-e-d ape just before the chain let go...

'We' don't know anything about timing chains letting go...do we..?

Not naming any names, you know...

 

[Jesus Freak]

Years ago...I had heard the same thing about chevy small-blocks...

It dawned on me later that it could have been the timing chain loosened up enough to retard the cam timing noticeably and that would make an engine run like a r-a-p-e-d ape just before the chain let go...

'We' don't know anything about timing chains letting go...do we..?

Not naming any names, you know...

It didn't let go, it just moved over a few teeth.

 

[XOLATEM]

I've burned up some 2-strokes that were going lean and, YES!, they go like hell before they melt down.

I had a Jawa moped back in the 70's...I took the baffle out of the muffler, ran a hotter sparkplug, bumped up the timing, and put Sears gas in it...(you could get two grades of hi-test from Sears auto back then...IIRC...it was 98 octane for mid-grade and 108 for Super..!)

It ran better for a while...the engine must not have been broken in yet...

but...one night in the summer I was coming home from the other side of town...and I musta been a little lit from some bootleg beer...

I was going down hill and I decided to run 'er wide open and if it was going to fly apart...oh, well...

It was a two-stroke...and you know how they will run ok until it hits a sweet spot...(we used to call it...'getting on the pipe'..)

and then it cut loose and ran up to an RPM that I had never seen or felt before...

Sounded something like this...

(normal accel)..."BBBBRRRRRRRR....MMMMM....

(former top RPM...a 'burble'.." BUDDBBUUDDBBUUDD"

(then scary...like it was winding to the moon...)

"WWWAAAAAAAAAAAAAAAANNNNNNNNNNNN......"

First thing I thought was that it WAS going to fly apart..!!!

BUT...IT DIDN'T....YYEEEEEE....HHAAAAAAA....!!!!

After that night...if I was on level road or a slight down hill...it would do it kinda regularly...

I got the thing to almost do 40 MPH...I loved it...

Was it running lean, guys..?

 

[Rdnck84_03]

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Yup, it can cause some serious carnage. No idea how it was running beforehand though, I bought it in this condition.

The good news is that we don't have to worry about this in an idi.

James

 

[XOLATEM]

Yup, it can cause some serious carnage.

I would suspect a crossfire situation with that broken crank...No#8 firing prematurely...if the plug wires are touching...this can happen...from induction....also winding 'er to the moon and misfiring all the while can break a crank...