Quick engine cutout in high-G turn - potential causes?

Digitalfiend

New member
So today I let my kid run a gold slide with her Cadet kart. Besides being hilariously quick (for Briggs anyhow), on the 2nd session with the gold slide, she noted that the engine cutout in two relatively high-G corners (one fast tight sweeper and the main hairpin); the engine continued to run fine as soon as she exited the corner. She didn't experience this issue during the first 15 min session of practice. I suspect it was just fuel starvation but I can't explain why. Carb is set to ~.875-.880 float height and 1.080 float drop; needle clip 2nd position, idle mixture set to 2 turns and 1900-2000rpm idle. During the two sessions I didn't hear any breakup or backfiring so I don't think it was too rich or too lean. The following session she was back on her red slide and we didn't experience any cutouts. The first time she noticed it she was probably have been around 5500rpm and the 2nd time it happened, probably 4000rpm or so. I need to review the video again.

Any thoughts as to what may have caused this or what to look for? I thoroughly cleaned the carb for tomorrow's race, so I think we should be fine.

Thanks!
 

flattop1

Dawg 89
Fuel level , fuel supply .
As said float height and or drop .
Also venting both in the tank and carb .
Possibly could readjust carb angle .
Debris in tank or pinching / moving fuel lines
 

Brianf60

Member
We experienced this even changing slides as well. Going to a smaller float height was the cure but to be honest in our case we were running a more aggressive float height.
 

btjones65

Site Supporter
if the carb settings don’t work, take a look at your kill switch wire. Well used motors will wear through the insulation and ground out in hard turns.
 

Mac_49

Site Supporter
Also check how much oil is in the crank. If you're putting in to much that can cause cutouts as well.
 

steve baker

Moderator
Also check how much oil is in the crank. If you're putting in to much that can cause cutouts as well.
Interesting, can you elaborate on this phenomena please. I haven’t heard of this or understand how oil can cause high g turn cutting out.
 

Mac_49

Site Supporter
Interesting, can you elaborate on this phenomena please. I haven’t heard of this or understand how oil can cause high g turn cutting out.
Scientifically I'm not sure but it happened to us where we were running 7,500+ on the straights but once we hit the turns the motor would cut out completely until we found straights again.
We checked everything at the track and found no issues with any clearances whatsoever. One of the mechanics close to us suggest changing oil to see how much we had in the crank. Turns out, someone double filled the motor with oil leaving it with about 28oz inside. We couldn't believe it even ran and were more surprised the pressure didn't blow the motor at those rpm's. So we drained it, filled it with 14 and had absolutely no issues after that.
I'm assuming with that much in the crank it was tossing it up past the valves into the head and fowling out the plug. Reason I say that is the motor smoked drastically in the turns when it'd cut out and cleaned out once we were on the straights. We also noticed a bunch of oil in the valve cover when we were checking clearances. Way more than normal.
 

steve baker

Moderator
Scientifically I'm not sure but it happened to us where we were running 7,500+ on the straights but once we hit the turns the motor would cut out completely until we found straights again.
We checked everything at the track and found no issues with any clearances whatsoever. One of the mechanics close to us suggest changing oil to see how much we had in the crank. Turns out, someone double filled the motor with oil leaving it with about 28oz inside. We couldn't believe it even ran and were more surprised the pressure didn't blow the motor at those rpm's. So we drained it, filled it with 14 and had absolutely no issues after that.
I'm assuming with that much in the crank it was tossing it up past the valves into the head and fowling out the plug. Reason I say that is the motor smoked drastically in the turns when it'd cut out and cleaned out once we were on the straights. We also noticed a bunch of oil in the valve cover when we were checking clearances. Way more than normal.
28 oz …. Holy Moly! Probably what was happening is the oil was blocking the fuel pump pulse fitting not allowing the fuel pump to operate correctly…..🤷‍♂️
But maybe your right the engine was getting into a no burn combustion chamber issue during hi g turns.
 

Mac_49

Site Supporter
28 oz …. Holy Moly! Probably what was happening is the oil was blocking the fuel pump pulse fitting not allowing the fuel pump to operate correctly…..🤷‍♂️
But maybe your right the engine was getting into a no burn combustion chamber issue during hi g turns.
It definitely raised our eyebrows haha.
So technically this is a very one off scenario, always worth checking to make sure. Simple oil change! Can't hurt anyways lol
 

Mac_49

Site Supporter
Also check the flywheel and magneto spacing...there's a small bit of flex on the motor that if they're to close together and touch it grounds out.
Had that also happen to us another time haha. We saw rubbing marks on the flywheel and when we set the spacing again never had an issue after that.
 

Digitalfiend

New member
We experienced a bit more corner exit bogging during this weekend's championship races. The team tech suggested that it might be because the float height was set to .860 (slide needle clip at 2nd position) and coupled with being on a red slide restrictor and geared higher for the rain (meaning we spent more time above 5000rpm). He suggested that perhaps when my daughter let off for the tighter corners to brake, when she got back on the gas, the a/f mixture was too rich and caused the engine to stumble. For the final we changed the float height to .900 (same needle clip position). Does that explanation make any sense?

I checked the valve lash at home after the race and confirmed that the lash (cold) is .001 exhaust / ~0.002 intake (very light drag with a 0.002 feeler but 0.003 wouldn't fit).

I've only been at this for a year but carb / lash tuning is one area I still feel I have so much to learn about. :)
 

fatboy1dh

Member
We experienced a bit more corner exit bogging during this weekend's championship races. The team tech suggested that it might be because the float height was set to .860 (slide needle clip at 2nd position) and coupled with being on a red slide restrictor and geared higher for the rain (meaning we spent more time above 5000rpm). He suggested that perhaps when my daughter let off for the tighter corners to brake, when she got back on the gas, the a/f mixture was too rich and caused the engine to stumble. For the final we changed the float height to .900 (same needle clip position). Does that explanation make any sense?

I checked the valve lash at home after the race and confirmed that the lash (cold) is .001 exhaust / ~0.002 intake (very light drag with a 0.002 feeler but 0.003 wouldn't fit).

I've only been at this for a year but carb / lash tuning is one area I still feel I have so much to learn about. :)

Was it just in the rain? If so, try it again on a dry track before you change anything. In the rain, you get water splashing, air filter cover moving around, driver not controlling throttle the same, lots of goofy stuff. Verify your dry set up before changing anything based on how it performed in the rain.
 
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