TT250 PE28FL jetting + throttle cable too short?

[AgentK]

So I'm getting a bit frustrater with mods, installed the Nibbi PE28FL with K&N cone filter and running the stock exhausts, what jets should I be running at sea level in CA? Seems like folks are running jets all over the place at similar condition, anywhere from 112 to 128 and #35-#40. I've tried 115 and now running 120, tried setting the needle on different levels and I keep having an issue when going full throttle, it will bog down and sometimes stall if I keep the throttle wide open for too long. All these tests done standing still in N due to the next problem, but from my understanding it sounds like it's too lean but the park plug is very black.

Them second problem is - the carb is a little bigger so now the throttle cable might not be long enough or could be because of the angle of the cable between carb and gas tank might be too sharp so when I turn the handlebar to right the throttle is being pulled open so obviously I can't ride like that. Also I bought the ebay exhaust to find out it's probably too loud, doesn't have spark arrestor so might not be good for state parks and leaks gasses from the muffler seals so went back to stock muffler.

Thinking of going back to stock carb, or same size replacement. Any suggestions?

[Megadan]

You are all over the place but let's try to narrow the issues down.

With the jetting Wide open throttle = main jet. Period. Adjusting the needle won't change anything here. Black plug = too rich. Unless you are doing a plug chop at a given throttle position we won't know where it may be too rich at but it sounds like the main for sure.

Jetting numbers are "all over the place" because no two engines are the same in terms of mods. No two people live in identical situations in regards to density altitude.
Typically the jetting on the pe28FL is close to the same on the pilot and one size up on the main when compared to true Keihin jets in a PZ30 carb. For the pilot this will be a 35 or 38 depending on the factors mentioned previously. The main is almost always a full 5 point step up.

Is that air filter a true K&N or a chea copy made with paper fiber? If the latter it is likely causing you problems. You would not be the first person to have these issues and the cause was the cheap filter that was installed. In that last instance the inside of the filter tube necked down so small it was just choking off airflow. I am a personal fan of the double layer foam filters for a variety of reasons. Otherwise making an intake tube and moddinf the stock airbox has worked for others.


As for the fuel tank and throttle cable thing. I had the same issue. There are solutions out there but I gave it a caveman adjustment and dinged my tank to buy it room.

Now that I have said all that let me give you my opinion. You don't need the nibbi for a mostly stock bike. The stock carb on the TT250 is beyond adequate. Even with an exhaust it's more than adequate. The difference in power at your level with a PE28 and a VM26/PZ30 is almost nothing and it gets outweighed by the headaches. Even with a ported head and a cam on my engine I ran a PZ30b for a while and I was more than happy. Yes there was a slight gain in the upper RPM ranges with the PE28FL when I put it back on but my top speed was the same at the end of the day and it still pulled nice and strong. People over sell the carbs.

[AgentK]

Yes it’s a real K&N filter. I just went back to the stock carb with stock jets but with the same KN filter, had to use a rubber spacer to make the filter fit on the stock carb as I can’t reuse the stock air box as I blocked the old intake hose. It seem to run almost fine, still a little bog at WOT but less bog, I never tested it stock so could it be ok?
It also seems like the exhaust is running hot, cylinder head was at 250 which may be fine but I wasn’t running it for too long, maybe 5 mins, but the clutch cable running in front of the engine and near the skid plate was smoking, Isn’t running hit a sign it’s running lean? Because of better airflow due to the air filter?

[Megadan]

Have you adjusted the valves recently?

[AgentK]

No, didn’t touch the valves yet.
I’ve pretty much decided to go back to stock. Wasting too much time fiddling with it instead of riding it.

[Megadan]

Originally Posted by AgentK

No, didn’t touch the valves yet.
I’ve pretty much decided to go back to stock. Wasting too much time fiddling with it instead of riding it.

Adjust the valves. CSC themselves will tell you to do it. It's not a mod, it's basic maintenance. Spec foe the tt250 is .07mm. Set at 0 miles, check after first 500. Then every 2500 after that.

Poor valve adjustment will cause all of the issues you have been having, especially the super hot exhaust system. Over time it can cause burned valves, damaged valve seats, and nuke the catalyst.

[AgentK]

I had none of these issues with the stock carb and still on fairly low miles.