sputter at wot…

[ghost rider]

my sled now sputters after a ten second WOT run….before i shut down the throttle.
if i turn off the engine and re start it it runs fine until i do the same run again.
installed a BOV and stopped the flooding during throttle shut off…….but what could cause this
durring WOT.?

 

[mbarryracing]

You flogged the cylinders with fuel so many times with not having a BOV, you have probably starting to foul a spark plug. Try new plugs?

 

[ghost rider]

Thanks for the reply Mbarryracing (wicked sled you have), i changed the plugs after i installed the BOV (sorry should have mentioned that)
….plugs are new NGK -cr9's iridium. Could it be electrical -coils? or does my fuel pressure rise too much during boost -not sure how to check that.

ice race this weekend and i want to have a decent showing for what i'm running…...

 

[mbarryracing]

Thanks.
What is your air/fuel ratio when it starts sputtering? If your fuel pressure is out of wack, it will reveal itself by affecting AFR's... but so can a misfire from other causes though. I really don't believe you have a fuel pressure issue.
So lets clear something up first, does it continue to misfire / sputter after you let off the throttle? What do you mean it by if you turn off the engine and re start it, it runs fine?
Does it misfire only during a WOT pull, or once it starts it continues to misfire until you shut it off? Reason I ask is that would be two completely different gremlins...

If it's only during WOT, then what is your spark plug gap set at?
Also could be you have one, or more, carb slides not opening fully (or evenly) at WOT because of leaking diaphrams, leaking carbs, etc. This significantly affects fueling. I've experienced this several times, misleading as something electrical...

 

[ghost rider]

Plug gap at .20
sorry no AFR gauge yet -on my list….fuel pressure was just set at last service a month ago.
durring WOT it runs strong for 6-9 seconds (127 mph)….then sputter and backfire so i slowly pull the throttle back
sometimes the sled will die and stall other times it will bog down until it hits idle rpm and run rough for
about 5 seconds then "clears out" and will run fine again -until another WOT.
other times if i sit the engine off and let it sit for 5-10 seconds it will fire up like nothing happened.
-also just replaced two carb diaphragms…fuel mix screws set at two turns out.
One other oddity is that this only happens after i have been running for 30 minutes or more -fyi it never over heats.
Running at any speed less than WOT it's fine -not tight sounding (revving) but ok…no lack of get up and go
Do the carbs need cleaned?

it's frustrating as hell, thanks for your advise it's very helpful, as you can see i'm stuck for my own answers.

Barry

 

[sebastien]

Maybe your fuel filter. Happen to me on my apex .

 

[ghost rider]

Maybe your fuel filter. Happen to me on my apex .

fuel filter….ill check mine out. Easy fix if it's the problem.
I have never looked at mine let alone changed it in the last six years.
I imagine you fish it out with a coat hanger……

thanks for the help.

Barry

 

[ghost rider]

actually i don't have a filter…..i pulled the hose and it was void of a filter



Barry

 

[mbarryracing]

I recommend you don't run that machine anymore until you have an AFR gage on it. You have no idea if it's rich or lean, and pushing it hard when it's lean will eventually lead to a rebuild due to detonation damage, which will ruin your Birthday...
You say it starts acting up when it's warm and been running a while. You could have a stator going away. Resistance of copper wire goes up with temp...

 

[ghost rider]

Thanks for being honest.... I have to get that AFR ... ASAP
It is cheap insurance and a good guide
Stator is an interesting thought.... I will look into that as I install an AFR.
Sucks having no heat in my garage... But you got to do what needs to be done.
Thanks for all your input !

 

[ghost rider]

ok finally got an aem wideband and it's reading 14.5 at idle……took a few minutes to work as it bounced around
during the initial instal….i assume it has to calibrate?

time to test it with some boost…..

 

[nate007]

Depending on what gauge you got, it may have a calibration procedure that is very important to follow or it wont be reading right. some of them require the sensor to be poqwered up BEFORE it gets installed into the pipe so it knows what afr to read when compared to free air outside the exhaust system. Just be sure to follow the instructions to the letter!
Most gauges use a heated sensor, which is the hot wire you probably had to hook up, and you need to make sure it's to a good source of voltage. If you get any type of error reading, check that first.
That being said, the heated sensor will take up to 30 seconds to warm up and start producing a reading, which is why you're probably seeing the gauge move all over when you first start it. That's normal, just keep from firing it up and hammering it as much as possible to avoid loading the sensor up with raw fuel deposits. It'll kill the sensor faster.

 

[ghost rider]

AEM wide and gauge. Works great.
Idle 14.5 ... Cruise. 12-13. boost @ 10 AFR is 10-11
Still have the pop / shut down / sputter after 10 seconds of wot
So possible electric ? Plugs are new gapped at .18
coils are ten years old -I'm thinking maybe coils?
Very frustrating.....any advise is more than welcome.

Barry