5th Gear Top End Engine Sputters? Plz Help

[DustyRJ7]

Guys, hello, hope all of you are having a great day. I apologize if this has been asked but I am new to the Hawk 250/ Cg250 Honda clone engine. I hear it's more like a CG125 clone engine that's up-sized a bit, technically a 239cc engine.


My hawk is performing well with one exception, the very highest end of the top gear (5th gear) is sputtering at the redline when I pin the throttle.

The bike has good acceleration and power through the gears, however, at the very end of the highest gear it seems to actually hick-up and slow down. This is worrying me.

Out of the 3 motorcycles I've owned this motorcycle is the only one to behave like this at the end of the top gear.

I have installed an aftermarket exhaust, and I have a 17/45 sprocket 128L chain on the bike.

I have read that upgrading the carb takes care of sputtering? Can anyone give their input with this? Also, I have not done the valve clearance, I may try today.

Is this common on a hawk or do you suppose something is off about my engine? I have nearly 3k miles on the engine and I changed the oil twice in the past 500 miles because the oil has blackened quickly, meaning the guy who owned it before me was not changing the oil like he should have. I use Shell t4 15w-40 rotella oil.

Any help or similar experiences would be greatly valued, thanks for taking the time to read.

[DustyRJ7]

To make matters worse, I just realized that my engine is not a stock hawk engine, I have no clue what kind of engine this is but after upgrading the sprockets and exhaust I am still only going 60mph. I think I just have to order an entirely new engine.

[XLsior]

try shimming the needle in the carb, or if it has an adjustable clip move it down so the the wide open position is richer...

[TominMO]

And check/adjust the valves.

[ProDigit]

Changing the needle isn't going to help at wot.
The best solution, is to choose a one size smaller main jet, and either add some fuel or increase the pilot jet.

If your bike starts fine without choke when cold, you can also either reduce the fuel with the AF screw, or get a one size smaller pilot.

Your total volume of fuel provided to the engine needs to go down, and that can only be done by reducing one of the jets or adjusting the AF screw.

Doing so will result in slightly more sluggish low end performance and torque, which you can compensate by raising the needle.

Raising or lowering the needle does not affect peak fuel flow to the engine, it just increases or decreases fuel in the lower to mid range of the throttle.

If the bike hesitates occasionally, I would go the route of a a one size leaner pilot jet, and raising the needle.

If it happens frequently, is go with a smaller main jet. To compensate for it, adjust the AF screw, or if that's not enough, increase main jet needle height by one, or increase the idle jet by one (just make sure the bike doesn't idle rich.

[Bruces]

There is a “Search” feature at the top of the page ^^^^ ,I just searched Hawk sputtering ,and a full page of results magically appeared ,no need for yet another thread on setting up a Hawk properly .

[Megadan]

WOT is purely main jet fueling, especially at high rpm. Adjusting the needle, pilot jet size, or idle mixture is NOT the right solution.

The last thing you want to do is go messing with multiple adjustments. Just do one thing at a time.

2 possibilities here.
1. Already covered, a slight adjustment in main jet size. Example: you have a 115 main. Since you don't know for sure if it's rich or lean you will want to be safe and go UP half a step first to a 117.5(118) and see how it affects the engine in those conditions. If it gets worse THEN go down half a step to a 112.5(113) to lean it out a hair and see how it reacts.
2. If you are approaching 8000- 8500rpm in 5th gear, you may be hitting the ignition cut for the rev limiter on the stock cdi. Yes, it does have one on the Hawks. OR, if not, you may be experiencing spark blowout due to a crappy plug, too wide of a plug gap, and/or the ignition coil is past its dwell time limits and it's generating a weak spark.

People get too focused on fueling and ignore the other important things.

It was an issue just like this that made me upgrade to the nibbi coil a few years ago.

[red2003]

There's no need to guess if it's a rich / lean fueling problem. Get the bike up to the place where you are experiencing the problem, and do a plug chop. It'll be obvious if it is lean or rich enough to be causing this issue. If it isn't, then you can look elsewhere.

[XLsior]

Well the needle position did fix my WOT high rpm in 5th gear stumble.



This after i changed all other possible factors, jets, CDI, Plug, Valves etc.


Why?



Because at WOT the needle was the final choke point when its was positioned lean and no bigger main jet would make any difference.


So before you poo poo me for making the simple suggestion that requires very little effort to test...



Try and think about it a little harder please.