Advice needed for challenging daily commuting.

LewieBike

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Joined
May 21, 2014
Messages
951
I've owned a few 2 stroke dualsport bikes. My Honda MT 250 lightly four stroked at cruise at 60 mph or any time you backed off the throttle on level. Also a Jawa 250 2 stroke single, (old school European Schnerle piston porting..) and they four stroke considerably near WOT until the heavy iron cylinder barrel warms up.

All of my SAAB 2 cycle cars would randomly four stroke among their 3 cylinders at light loads. It's normal for most mildly tuned 2 stroke engines, especially piston ported engines. none of these engines were jetted too rich.
 

FNTPuck

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Joined
Jul 2, 2018
Messages
866
With chinagirls, for a commuter or anything I care about reliability I always aim for light 4stroking when cold, that clears up when warm. Puts you on the safe side.

For a race bike or something that will be rebuilt often anyway, lean is mean (while it lasts). If/when it dies, I will just have to spend a whopping ~$35 on a new top end and I'm good to go again plus get a fresh chance to try new things with porting :ROFLMAO:. You do NOT want to use the same train of thought on an expensive motorcross bike or something.
 

Ralpho

Active Member
Joined
Nov 5, 2019
Messages
189
With mine I run an open header so use a bp7hs ngk with a 70 jet and I'm still afraid.
 

Street Ryderz

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Joined
Oct 14, 2016
Messages
4,160
With chinagirls, for a commuter or anything I care about reliability I always aim for light 4stroking when cold, that clears up when warm. Puts you on the safe side.

For a race bike or something that will be rebuilt often anyway, lean is mean (while it lasts). If/when it dies, I will just have to spend a whopping ~$35 on a new top end and I'm good to go again plus get a fresh chance to try new things with porting :ROFLMAO:. You do NOT want to use the same train of thought on an expensive motorcross bike or something.
This is where the fine line of tuning comes in play,there is full load of weight and gearing the engine sees and the engines own load of just trying to compress the next stroke,if you have your engine load lean then the full load will be too lean as it is normal even for race setup's to four stroke when you lift and take off the loads.Every race bike I've ever ridden is setup this way on purpose for one and most important to help insure you finish the race as wot creates alot of heat and this helps big time to keep it in check,but also because lean in the full load situation as heat builds loses power and starts to feel flat to the rider and lap times grow.
 

SkyArc

New Member
Joined
Dec 21, 2019
Messages
11
Hey all, wow the 4 stroking post here have almost confused me now as both seam to have valid points.

However I thought I would give some feedback on what has taken place on my daily commuter, (I'm not doing the conversation on distance, speed etc for this one)
Quick recap: I'm doing 2 x 31km one way trips a day that take roughly 50 - 60 min drive time with the engine running all the time, clutch pulled in downhills, 3/4 to WOT on straights and WOT on hills (I have many, clime from home to work is 500m above sea level)

It's a basic Chinagirl engine with a CNC performance head, standard NT carb and a 52 tooth sprocket for these hills. She does 50km/h easy on a straight, 40km/h on a decent hill (25°-30°incline) about 35km/h on a steap hill (35°incline) and 22km/h on a 40°plus hill

The bicycle has done 1900km in 2 months 😎
I've clean the head and cylinder 3 times in this time, have had a crazy amount of carbon build up. I've tried BP6HS plug but carbon build up happened really fast, currently using BP8HS, and have had no issues for over 1000km with it.

I've tried Soooo many different oil to fuel mixes and currently using the Castrol racing 2 stroke oil at 45:1 but have been experiencing issues since the swop from the normal Castrol 2 stroke oil. Still getting huge carbon oil build up and more so now. I've tried going leaner but getting a lot of vibration, so today I reverted back to 35:1 with a smother ride.

My biggest issue at present is the loss of power on these long hills (rough 10 - 15km/h less and virtually losing all power on the bigger 40° hills!?
On a straight I still hit 50km/h she does seem a bit slower on throttle reaponce though. The same when revving her with the clutch in, she revs up to full a bit behind the throttle, she takes a few seconds to reach full rpm after I've WOT her.

II checked the ports and had a huge build up of carbon on the exhaust port (1/3 clogged)
The exhaust pipes were just as bad. Cleaned them as best as I could but still having the power loss.

Cylinder and the head are smooth, no scuffing visible, rings look ok but seem a bit loose in comparison to the first time I opened her up to clean them.

I also tried setting the carb pin on notch up for leaner fuel mix but seemed to make no difference, when I moved it one notch down from its original spot I had a real boggy drive and she could hardly reach 30km/h on a straight.
I'm also struggling with the idle, currently have the screw all the way in to maintain the idle.

MMost of these problems started when changing the oil, although having 200km on the new oil I could almost say it's just coincidence.

The engine does feel like it has weight to it or that it's stiffer than it was once started. (the cam shaft turns easily when I've had the engine opened, so I don't think it's a bearing issue)

What could be the cause of this power loss?
Exhaust?
Rings?
Carb?
 

Frogslayer

Well-Known Member
Joined
Jan 20, 2019
Messages
2,535
Your jetted too rich in the carb is what it sounds like. When you add more oil, it leans out the fuel air mixture a little and that's why it's better. Re jet for what ever oil mix you want to run and then run that consistently. I think they all come jetted super rich to run 16:1 used car oil in China. I soldered my jet shut and used a very small drill bit.

P.S. we know you meant to say "crank shaft" instead of cam. 🤪
 

Sidewinder Jerry

Well-Known Member
Joined
Mar 14, 2011
Messages
2,255
Hey all, wow the 4 stroking post here have almost confused me now as both seam to have valid points.

However I thought I would give some feedback on what has taken place on my daily commuter, (I'm not doing the conversation on distance, speed etc for this one)
Quick recap: I'm doing 2 x 31km one way trips a day that take roughly 50 - 60 min drive time with the engine running all the time, clutch pulled in downhills, 3/4 to WOT on straights and WOT on hills (I have many, clime from home to work is 500m above sea level)

It's a basic Chinagirl engine with a CNC performance head, standard NT carb and a 52 tooth sprocket for these hills. She does 50km/h easy on a straight, 40km/h on a decent hill (25°-30°incline) about 35km/h on a steap hill (35°incline) and 22km/h on a 40°plus hill

The bicycle has done 1900km in 2 months 😎
I've clean the head and cylinder 3 times in this time, have had a crazy amount of carbon build up. I've tried BP6HS plug but carbon build up happened really fast, currently using BP8HS, and have had no issues for over 1000km with it.

I've tried Soooo many different oil to fuel mixes and currently using the Castrol racing 2 stroke oil at 45:1 but have been experiencing issues since the swop from the normal Castrol 2 stroke oil. Still getting huge carbon oil build up and more so now. I've tried going leaner but getting a lot of vibration, so today I reverted back to 35:1 with a smother ride.

My biggest issue at present is the loss of power on these long hills (rough 10 - 15km/h less and virtually losing all power on the bigger 40° hills!?
On a straight I still hit 50km/h she does seem a bit slower on throttle reaponce though. The same when revving her with the clutch in, she revs up to full a bit behind the throttle, she takes a few seconds to reach full rpm after I've WOT her.

II checked the ports and had a huge build up of carbon on the exhaust port (1/3 clogged)
The exhaust pipes were just as bad. Cleaned them as best as I could but still having the power loss.

Cylinder and the head are smooth, no scuffing visible, rings look ok but seem a bit loose in comparison to the first time I opened her up to clean them.

I also tried setting the carb pin on notch up for leaner fuel mix but seemed to make no difference, when I moved it one notch down from its original spot I had a real boggy drive and she could hardly reach 30km/h on a straight.
I'm also struggling with the idle, currently have the screw all the way in to maintain the idle.

MMost of these problems started when changing the oil, although having 200km on the new oil I could almost say it's just coincidence.

The engine does feel like it has weight to it or that it's stiffer than it was once started. (the cam shaft turns easily when I've had the engine opened, so I don't think it's a bearing issue)

What could be the cause of this power loss?
Exhaust?
Rings?
Carb?

These hills you're talking about are they paved driveways or dirt hills? The two steepest streets in the world are Canton Ave in Pittsburgh Pennsylvania and Baldwin St in Dunedin New Zealand. They're a 37% grade which converted to degrees is 16.65°.

You may find some private drives that are a 40% grade which is 18°. A hill at 40° would be an 89% grade. It takes specialized motorcycles to climb dirt hills that steep.
 
Last edited:

SkyArc

New Member
Joined
Dec 21, 2019
Messages
11
Mmm, yeah I don't have much to say on the technical side of grade and ° on those hills, other than if those hold the records they clearly haven't been to my side of the world.

These are all roads, even cars struggle to keep 2nd gear and are luck to make it half way up in 3rd if they got enough speed before hitting these hills.

The point I'm trying to make is, she ran ok up most of them with the bigger 52 tooth sprocket and I only needed to pedal assist up some of them to keep her at or above 25km/h. Now not so much, I'm peddling up smaller hills to keep the speed up, and on the larger hills she looses to much speed and stall out while I'm trying to keep going at like 3km/h😂

Frogslayer mentioned the jetting. That sounds like it could have caused it and a easy fix, the problem is that she will still be clogged up, so guess I need to replace rings and exhaust as well.
Any one know of anything I can use to try clean out the exhaust?

And what else could affect compression? The cylinder housing and and piston seem fine, I see no scuffing or scratching on either. I did have alot of issues with the clutch slipping but have managed to sort that out by adjusting the spring on the clutch shaft, after replacing the bucking bar, ball etc.
 

SkyArc

New Member
Joined
Dec 21, 2019
Messages
11
I did take the exhaust cap off and took it for a short run, I'm not sure what to listen for but it's alot louder, it sounds like there is back fire at low and high rmps but relatively quiet and mid rmps and when I let off the accelerator while on straights with the clutch still engaged.

I'll take it for a hill climb in a bit to see if she can do it without dying on me. If it works I guess it's the exhaust that's clogged up.
 

SkyArc

New Member
Joined
Dec 21, 2019
Messages
11
So Wow... That's a crazy amount of torque with the cap off😮😁😎

So she ran without issues, I was heading downhill at 50km/h to a decent hill and flew up half way just to find the morning traffic had to slow down and jump on the tiny pavement and take it gently as it's really like 20cm wide and had not been on it before but she never died she has tremendous torque and acted like it was a straight. If fact she almost wants to lift the front wheel when WOT at very slow pedal speeds.
Not sure how good this will be for her in the long run, as she does seem to struggle hitting top end like this and not sure what that torgue is going to do to my spokes in the long run.

I'm guessing the exhaust is to blame.
Going to try for a smaller jet too.

Any further advice on what I should do and the draw backs I can face with the cap off like this?

Thanks 🙂
 
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