Forum - Briggs & Stratton Racing
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helix

Registered: 08/21/12
Posts: 20
Reply with quote  #1 
This past weekend my son ran a practice and race and the track direction was opposite it usually is. this track has a 2/10th straight that is usually a slight up hill. this weekend was down hill and were we had problems. at the end of the straight is a hard right turn that double backs about 50yds then truns to the left. those two turns he had a dead spot in the engine when he hit the gas coming out of the turn. it would hesitate then spudder a couple times then took off. I though i saw a puff of grey smoke a couple times but wasent totally sure. it would also occasionally do it coming out of other turns in the course. we never had this problem before. i recently adjusted the valve lash and replaced the spark plug. i went back to the old plug but this didnt correct anything. He didnt have an excessive amout of fuel in his catch can either. also it seemed to get worse the longer he went. first couple laps i didnt notice it so much but as the laps increased, the dead spot got worse. any ideas? Also he was running with a few comer class karts which he usually out accelerates bc of the torque, yesterday was not the case. he kept up but didnt pull away as usual. not sure if its related or not.
BriggsRacing1

Registered: 06/22/11
Posts: 188
Reply with quote  #2 
Helix, Thanks for posting your question.  Let me offer you a couple things to check on.  I would lean towards your engine being rich but lean could also give you similar symptoms.  The smoke being the clue towards the rich side of the spectrum. 

A couple things could make this occur:

- A loose metering needle.  Check to make sure that the metering needle clip located on the inside of your carburetor slide is completely seated and holding your metering needle in place.  for whatever reason, maybe while making an adjustment, this might have moved.

- Float level.  We have in our 'latest news' section a carburetor guide and a how to set your float height video to walk you through a proper float level.  Even though you do not have fuel in your catch can, you could still be running slightly rich.  I would check where you are, reset this to our recommendations, and IF you continue having problems I would change the float height in increments of .15" to see if the condition goes away.

- Spark plug.  I would gap your spark plug to .040".  With the strength of a digital ignition system you can open your plug gap up beyond stock.  This will improve your flame front and help reduce any momentary rich conditions (like coming out of the corners slightly rich).

Changes to float height can happen over time or from things that you wouldn't necessarily think about, such as the rough ride to and from the track (kart bouncing in your trailer). 

I think given you were running the track with a downhill configuration that the carburetor slightly loads with fuel and this becomes your hesitation.  If would bet in your normal configuration that this will go away but it is something to be aware of.  Also, the spark plug gap I would do anyways and it is always good to understand how the PZ carburetor float height impacts performance.

Thanks for running a Junior 206!
helix

Registered: 08/21/12
Posts: 20
Reply with quote  #3 
Thanks for the input. i did adjust the float after having issues after the first go around but it didnt seem to improve. ive never adjusted the metering needle before bc it seemed to run just fine but it may be something i need to look at. ill gap the plug as you suggested. what baffles me is why it would get worse as laps increased. will the idle air mix screw affect this? I had to adjust the whole carb set up bc the screws vibrated open. i reset the carb to factory specs but this was a couple races ago and did not have issues
BriggsRacing1

Registered: 06/22/11
Posts: 188
Reply with quote  #4 
Dropping the slide needle (moving the 'c' clip to a higher position) will reduce the surface area of the jet because the needle is tapered (covering more of the main fuel feed).  The idle mixture screw, if you pull it all the way out you can see that it impacts the starting height of the slide, essentially raising or lowering your RPM.  Vibrated out it likely would create an air leak and lower your engine performance as intake manifold pressure would be lost.  On the PZ22 your other adjustment impacts the amount of air fed into the idle circuit.  I would recommend following the instructions on our carburetor tuning guide.  By adjusting it accordingly, it insures that your idle circuit air fuel ratio is in a proper range. 

Daniels father

Registered: 10/05/13
Posts: 3
Reply with quote  #5 
Intake manifolds do break. Fastermotors will confirm this problem. Our motor has a carb support to prevent this from happening AGAIN.

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