Is my engine too rich or too lean? (pics + vid)

[Chainlube]

Spark plugs come with a heat range rating. In simple terms it is the electrode size/shape that is changed on a model of spark plug to shed heat and operate at a given temperature. The "hotter" the plug, the slower it sheds combustion heat, but the better it is at self cleaning as the engine runs. Too cold and the plug doesn't self clean and will be more prone to fouling. Too hot and there can be a risk of it causing pre-ignition.

I will use NGK as the basis of this comparison since it is easiest to remember. The standard spark plug for most of these 2 stroke engines is an NGK B8HS. The number in the plug code is the heat range, and with NGK plugs, the higher the number, the colder the plug. So if you wanted to go with a "hotter" plug, you would want to lower that number. Many people seem to like running a B5HS or B6HS with good luck. Since these engines really don't run very hot, or have aggressive ignition timing, they can run a hotter plug without issue.

That Z4C plug he's using cross references to a NGK B6HS, it's always a good idea to have a 5 and 7 on hand.

 

[ImpulseRocket]

That Z4C plug he's using cross references to a NGK B6HS, it's always a good idea to have a 5 and 7 on hand.

That's a nice detail to know. Thank you.

 

[noah9988]

Stock jet size is 70. If you have a bofeng carb (will say bofeng on it), you need these jets: https://www.amazon.com/gp/product/B08CNDTMRT/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

They go by 5's unfortunately, and I bet a 65 will be too lean. If that's the case you will need to buy a micro drill bit set and drill out one of the smaller jets.

Or you could buy the speed carb, which in my (and other people's) experience performs worse than the bofeng. Those use 5mm jets and you can buy jets in any size you need.

 

[Greg58]

For those that don’t know the heat range for NGK plugs is the lower the number the hotter the heat range ,typical plugs used are a 5-8 depending on tuning factors such as elevation, temperature etc.

 

[Greg58]

All kits are not assembled the same, I’ve found short thread plugs shipped with kits that are not the correct length for the head.

 

[ImpulseRocket]

Stock jet size is 70. If you have a bofeng carb (will say bofeng on it), you need these jets: https://www.amazon.com/gp/product/B08CNDTMRT/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

They go by 5's unfortunately, and I bet a 65 will be too lean. If that's the case you will need to buy a micro drill bit set and drill out one of the smaller jets.

Or you could buy the speed carb, which in my (and other people's) experience performs worse than the bofeng. Those use 5mm jets and you can buy jets in any size you need.

The Bofeng carb (red filter) uses keihin 99101-124 jets and the come in "2.5" increments. Aka 65, 68, 70, 72, 75, etc.

 

[Chainlube]

That's good to know on the Keihin jets, I've got a couple of those carbs here and they came with the black plastic filter that looks like Zoidberg.

 

[dontworryaboutmyusername]

It is a Bofeng. So if the problem is im too rich (too much fuel) and the default jet is 70 I must decrease the size. I was able to find a number 68 with the brand impulse mentions: https://www.ebay.com/itm/172964021351

1. Think it will work good? If so ill go ahead an order and try it out.

2. Would shrinking the jet size which results in less fuel going to the engine by default limit or bottleneck my max power? Would it not be possible to instead increase (somehow) the airflow to the engine so the ratio would no longer be too gas rich? (Mind you I currently have no air filter on and im four stroking)

3. Would adjusting the jet needle clip position make any difference, or is this simply for throttle response? If I understand correctly, since I am experiencing four stroking at full throttle that wouldn't make a difference as the pin would be completely out the jet

 

[dontworryaboutmyusername]

Took the carb apart. The jet has no identifying numbers on it. It looks like the keihin 99101-124 that was mentioned (I ordered a #68). I would have preferred to buy a kit here for a few bucks more which includes .66 - .70 ( https://www.bikeberry.com/products/...mm-68mm-69mm-70mm?_pos=1&_sid=6efef7e11&_ss=r ) but I have no idea if it will fit and the jets appear different.

Would these bikeberry jets fit or am I better off with the keihin 99101-124 #68? From this video its stated #66 is the best

 

[Nickt919]

You may find a positive difference by just changing the plug from the chinese plug to an NGK plug.