4 stroking problem

Henshooter · Mar 14, 2014

Hey guys ,recently had problems with my king horse 2stroke kit and thanks to you all the problem was somewhat solved

Issues were resolved but she runs somewhat unusual now
I have her almost to her original running state but have noticed she occasionally 4 strokes when under throttle , now I've adjusted the pin in the slide and she runs like a pig on all settings except one , I could understand the kit 4stroking whilst being throttled down but she occasionally 4strokes at the high end when throttling up
I've done a chop test and colour is good ,she's not running hot or anything similar but now I'm at a loss as to how to adjust the carby as I've followed all adjustment or carby tuning steps down to a tee
I have recently changes from the syrup of 16:1 down to 32:1 and she accepted the change very well

I do have a .68 jet and was contemplating changing it to .65 ,would this make any difference in the 4 stroking

I've checked all seals and there's no leaks anywhere and as said she is running well , just wondering if this is a common trait of the china girls because my previous builds have never done this

Any help as to what else I can do to either adjust or resolve the issue would be great

Cheers Henshooter

maniac57 · Mar 14, 2014

The easy way to check if your engine wants a leaner mix (smaller jet) is to shut off the fuel flow and ride till it's dry. If it surges a burst of power right before it dies, you might want a smaller jet. This is the easy way to see if it wants jetting.
If your needle is all the way down, and it pulls hard up to point and then four strokes, this is another indication your main jet is still to big. The needle controls mix only up to medium high rpm. Once it's wide open, the jet size determines mix.
Remember to drop the needle back down when swapping to the next smaller jet so as not to jump too far at once. Run it an hour or two before pulling a plug chop as well.

Henshooter · Mar 14, 2014

maniac57 said:
The easy way to check if your engine wants a leaner mix (smaller jet) is to shut off the fuel flow and ride till it's dry. If it surges a burst of power right before it dies, you might want a smaller jet. This is the easy way to see if it wants jetting.
If your needle is all the way down, and it pulls hard up to point and then four strokes, this is another indication your main jet is still to big. The needle controls mix only up to medium high rpm. Once it's wide open, the jet size determines mix.
Remember to drop the needle back down when swapping to the next smaller jet so as not to jump too far at once. Run it an hour or two before pulling a plug chop as well.

My needle is set on the middle notch , does this mean when I change the jet I should drop it to its lowest setting or can I leave it at the current setting ??

I'll take her for a run with the fuel shut off now and post how it goes , thanks for the help maniac

maniac57 · Mar 14, 2014

Go to the last notch on the needle. If it makes no difference or makes it worse, try a smaller jet.
And drop the needle when you swap jets. First notch (highest setting) when going smaller.
If you don't, the jump in amount of change can mess things up. You want small steps when getting close. It only takes seconds for a overly lean mixture to break things.

mapbike · Mar 14, 2014

Sounds like a smaller jet is in order.

Theon · Mar 14, 2014

.65 jet, needle clip second notch from the top.
then adjust needle if necessary, but I think you will find that's what you will want.

Henshooter · Mar 14, 2014

Hmm I'm in two minds here guys , the issue is she runs well until at the top end where she occasionally 4strokes , I did the fuel line tap cut off and she just loses power when empty , no power increase just before , well one tiny bump but that's it , she gets to her normal top end speed of @40 kph so in general she runs at roughly the same speeds and revs well .

Now will jetting her give me better performance and stop this top end 4 stroking , as said she runs well now except the occasional 4 stroking

I'm just wondering if it's best to leave things alone ,or do they perform better when jetted

Cheers again guys Hen

maniac57 · Mar 14, 2014

Raise the needle till it makes a difference and then split the difference for your final setting. You want it a tiny bit rich for good lubrication and better motor life. I like mine set to pull clean up to top rpm and four stroke a bit when not pulling. I find a bit of extra richness goes a long way to reliablility in any pre-mix engine. I run 40:1 BTW.

mapbike · Mar 15, 2014

All mine 4 stroke a little at low rpm and when not under a load, but when under a load all the way from first hitof the throttle to wide open throttle no 4 stroking at all, all mine run excellent on a mix of 100:1 Opti2.

Slow speed no load 4 stroking is normal but it it does it under heavy throttle and at top speed, you have a slightly rich mixture, it seems odd that it would be good until high rpms before it 4 Strokes, im wondering if fuel lever in float bowl may still be a tad high.....

maniac57 · Mar 15, 2014

I find if the main jet is still too big, it will pull clean with 3/4 throttle, but blubber a bit at wfo when the needle is fully out of the jet. This indicates a rich jet. It also seemed weak at the second needle notch with perfect manners and sound, but weak power until full throttle, when it would blubber again.
Going one size smaller fattened the power right back up without losing the better pull, and I find the needle is more effective again in tuning. It just feels happier. Second notch is my sweet spot. Third makes it blubber, first steals power. Runs like a top everywhere idle to full rpm and four strokes a bit at trailing throttle.

Theon · Mar 15, 2014

It will need to be a little richer for hill climbing, the more load, the more fuel.
If your using it on flat ground, leaning it out a little will likely make it go better.
Checking your plug colour will give an indication of it being way over rich, or way lean,
but if it's four stroking in the top end, the jet is to big.
If your needle is on the middle notch and your happy with the mid leave it there.
Try running it with out the air filter (briefly) and if it runs better, she's too rich.
Less oil, means more fuel.
That's why she's started 4 stroking when you have cut your oil ration back.

mapbike · Mar 15, 2014

maniac57 said:
I find if the main jet is still too big, it will pull clean with 3/4 throttle, but blubber a bit at wfo when the needle is fully out of the jet. This indicates a rich jet. It also seemed weak at the second needle notch with perfect manners and sound, but weak power until full throttle, when it would blubber again.
Going one size smaller fattened the power right back up without losing the better pull, and I find the needle is more effective again in tuning. It just feels happier. Second notch is my sweet spot. Third makes it blubber, first steals power. Runs like a top everywhere idle to full rpm and four strokes a bit at trailing throttle.

I agree 100%

Mine acted the same way when they were way rich until I would start up a hill and then they would run great until the extra load went away and then the " blubbering" would come back.

Map

Henshooter · Mar 15, 2014

Ok upon pulling the bowl of and removing the carby I looked at the jet ,surprisingly it's a .65 I was running all along ,I have a set of diameter gauges so stuck in the .65 an it's a perfect fit , swapped the jets up though and it run the same , thought there must be another issue so pulled the carby to bits , was then that I noticed the slide pin was blunt on the end ,yep there was absolutely no campher on it at all , crist I seem to have got the worst pick of the bunch with this motor , although it wasn't the original carby as I had to take back the original as the fuelcock valve was stripped out and constantly leaked .
Anyway I replaced the pin with one that has a good campher on it and low and behold she runs well at all rpm , and has a slight 4stroke under no throttle ,from what I understand 4stroking when throttling back is a good thing as it provides better lubrication to the motor .

I've come to the conclusion the last build i had was a boy , it was oily, dirty but ran like an animal - strong and steady and very dependable but belle this ones definitely a girl ,she is sweet , gentle and the smallest things are what are important to her ,on that hand she can be a powerful bee with an itch if you get my drift .

Happy now she is running well ,few more weeks and I reckon I'm due for another build hehehe ( don't let the wife see this post henshooter) and the next will be fully ported and run like a beast hehehe can't wait

Regards Henshooter dance1

Theon · Mar 15, 2014

Well done Sean.
It's always good to have some spares with these kits.
Looking forward to your next build, Another mountain bike?

mapbike · Mar 15, 2014

Excelllent.... glad you got it running good.... its always the little things we have to figure out...

Henshooter · Mar 15, 2014

Theon said:
Well done Sean.
It's always good to have some spares with these kits.
Looking forward to your next build, Another mountain bike?

Certainly will ,don't get me wrong I love the cruiser it's my favourite ride but a mountain bike just has that feel you can't get from a cruiser and they feel more solid to me

Lookin at an ally frame mtb and may consider fitting a jack shifter kit to it ,I used to race mountain bikes so I feel most comfortable with them for traffic riding , also the one I'm looking at has disk brakes and the cruisers coaster brake just doesn't have the stopping power as disks and I need to apply the brakes quite early for a stop

Another few weeks when the budget is up and I'll be onto the new one ,can't wait

Regards Hen

Theon · Mar 15, 2014

I took the shift kit off my mountain bike , as I missed the compression braking.
But it was great for crawling up steeper bush tracks. I guess it makes running discs a little more straight forward.
I'm hoping with reed valve, hi compression, big bore exhaust and a 39t sprocket, I won't need to worry about a shift kit on my mountain bike. I've ordered a 203mm disc for the back and hope that I will be able to run this beside the 39t (maybe 5mm apart) and have enough room to run a caliper between the stays.
Just waiting on the new discs.
Shift kits are great, but mine were 'lemons'( $99 each) and have taken a lot of effort to get to work right, I think on a 'Bush Bike', better to keep it simple. And invest in getting the motor to produce more grunt.

Henshooter · Mar 15, 2014

I've got a pair of discs on two rims here Theon ,if they are any good for you I'll happily send them ,I'll take pics of them tomorrow if your keen , got the brakes to go with them too

I'll pm you pics of the lot tomorrow mate

Cheers Sean

Theon · Mar 15, 2014

I started ranting, and realized I was getting a little off topic for this thread, I'll PM you.
Cheers.

2door · Mar 16, 2014

Glad you found the problem, Henshooter. It's always satisfying when a discovery turns out to be the problem.
Good luck on that next bike. Keep us informed and show us pictures.

Tom

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