Why does everyone hate 4-stroke bikes?

[DieselTech]

Recommended Class:	Super Stock
Target (MAX) RPM:	7500
Spring Pressure (In / Ex):	20 lbs
Valve Lash (In/Ex):	.003"
Ignition Timing:	32 Deg BTDC

​

	Intake	Exhaust
Open:	52.4 BTDC	86.9 BBDC
Close:	89.4 ABDC	51.5 ATDC
Lift:	.265"	.265"
C/L:	108.0 ATDC	108.0 BTDC
DUR @ 50:	236.9 Deg	236.5 Deg

That's the specs for the cam. It's a hisun 196cc shaved and ported head, header pipe with muffler, 22 lbs springs, pvl aluminum flywheel with 4 degree offset key for 32 degree timing. I bought a new stock coil and put an ngk boot on it with an ngk bpr5es plug. One thing that could be off is the coil gap which I set at .060". I have also lapped the valves and set the clearance at .003".

What's your piston to cylinder deck clearance & what thickness of head gasket are your running. Is your valve size 27mm & 25mm? Are you running stock ratio rocker arms? How much was milled off your cylinder head? I'm just trying to get the fine details to give you a recommendation, I think I would set coil air gap at .045" then get a new plug. A autolite AR3910 or a AR3910X. I also think you need heavier valve springs.

 

[noah9988]

What's your piston to cylinder deck clearance & what thickness of head gasket are your running. Is your valve size 27mm & 25mm? Are you running stock ratio rocker arms? How much was milled off your cylinder head? I'm just trying to get the fine details to give you a recommendation, I think I would set coil air gap at .045" then get a new plug. A autolite AR3910 or a AR3910X. I also think you need heavier valve springs.

If by cylinder deck clearance you mean where the piston sits in the bore at tdc it's .020" below. The gasket thickness is about .010". Stock valve size so 25 intake 24 exhaust. Stock ratio rockers. Honestly I don't know how much I milled off because I sanded it down. I'd guess no more than .020", since I was using 80 grit sandpaper I don't think I took too much off.

 

[DieselTech]

If by cylinder deck clearance you mean where the piston sits in the bore at tdc it's .020" below. The gasket thickness is about .010". Stock valve size so 25 intake 24 exhaust. Stock ratio rockers. Honestly I don't know how much I milled off because I sanded it down. I'd guess no more than .020", since I was using 80 grit sandpaper I don't think I took too much off.

Do you know your combustion chamber size on your cylinder head? They have 24cc & 18cc on stock cylinder heads. Think they even offer a 14cc head.

 

[noah9988]

Do you know your combustion chamber size on your cylinder head? They have 24cc & 18cc on stock cylinder heads. Think they even offer a 14cc head.

It says rs bl 20 on it, I don't know the size.

 

[Karl Snarl]

Have you been smoking a 'not so rare earth' type of vegetation this evening Karl???...lol...lol.

You DO realise that the NGK-BR6HS standard plug we pretty much all use here is also a copper core too???...lol...Most of us are NOT using any 'rare earth' plugs...lol.Just saying...lol...lol.

https://www.oreillyauto.com/detail/c/copper-core/ignition---tune-up/spark-plug/b14eb31b13d7/ngk-copper-core-plug-number-br6hs-spark-plug/ngk1/3922

Trust me bro, some engine only like a certain style plug. I had a car that would run like a champ, on 70 cent copper core champion plugs, anything else is would spit and sputter at higher rpms and when romping on the gas. Was weird, but the only engine I had that prefers one brand over another, or a certain style vs anything else. She wants what she wants.

I mainly tried a champion rn9yc and a ngk bpr5es. I also have some various other plugs that don't have enough reach like a br8hs and some e3's though I didn't try them. I'm not sure if it's floating the valves but the cam recommends 20 pound springs. It's currently not running and I have to wait for parts later in the week but that's unrelated. It's a used engine with very little time on it, but it has had water in it. The bore has light rust staining and a ring at the bottom of the bore with pitting. I've since honed it. I also ordered a new vm22 carb. If I still can't figure it out I'll make a separate post about it.

You were saying your cough out at a cruise, valve should be no where near floating speeds at a cruise.

 

[noah9988]

You were saying your cough out at a cruise, valve should be no where near floating speeds at a cruise.

Yeah valve floating wouldn't be an issue at those rpms. It's possible there's two problems causing each symptom or one causing both.

 

[SirLurksAlot]

Indexing..... A plug that is correctly indexed for the engine it's in will generally perform noticeably better than a plug that's not. Indexing here means the plug gap and ground strap are positioned such that the strap doesn't create interfering turbulence causing less of the swirling fuel/air being exposed to the spark - inhibiting ignition to some degree. Poor indexing is largely why champions were the best for mopar, autolite/motorcraft for ford and ac delco for gm... At least, that was the accepted explanation 'back in the day'

 

[darwin]

On modern cars every shop owner that I've read states OEM plugs are best, 1 and done. They're designed for that motor by engineers. I'm a firm believer in that. Plus most plugs are a PIA to change nowadays x4, x6, x8 too. On these small motors I think a quality name brand getser done.

 

[mason_man]

I've had 2 coils, 2 carbs, and 2 cams in various configurations and jetting but never saw more than 6420 rpm I believe. I'm going to make a new thread about it.and not clutter up this one.

Hi!
The Mikuni vm22 is a Big carburetor, vm18 might be better. Anyway looks like you've worked with main jet and pilot. You didn't say much about the throttle slide needle. You have five settings there. From the factory they start from the center one leaving two up and two down. This is where I think your problem lies.
Start by moving one down and then the second one, if the problem gets worse then start from the top side. You just need to play with it until it's balanced,like everything else. .
Keep your head up! You'll get it..
Man and machine...Jesuit and whizzer.... May the force be with you!

Ray

I think it's my turn to defend the 4

 

[noah9988]

Hi!
The Mikuni vm22 is a Big carburetor, vm18 might be better. Anyway looks like you've worked with main jet and pilot. You didn't say much about the throttle slide needle. You have five settings there. From the factory they start from the center one leaving two up and two down. This is where I think your problem lies.
Start by moving one down and then the second one, if the problem gets worse then start from the top side. You just need to play with it until it's balanced,like everything else. .
Keep your head up! You'll get it..
Man and machine...Jesuit and whizzer.... May the force be with you!

Ray

I think it's my turn to defend the 4View attachment 185298View attachment 185299View attachment 185300View attachment 185301

Yeah I forgot to mention I moved the needle around as well. Since my last replies on here I got the parts and engine running again and didn't experience any running issues yet. I honed the cylinder and put a new rod and crank in it so I didn't want to pin it wide open. I'm going to ride it more today and I'll see what happens.