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8/15/2017
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Mikey77
8/15/2017 1:42am
8/15/2017 1:42am
Edited Date/Time
4/3/2018 1:24pm
Hi,
My sons kx85 -17, sometimes bogs when he shall make a start at 2:nd gear. It was worse with the Pro Circuit pipe/silencer so I changed back to the HGS exhaust-system and thought I "solved" it because the bike didnt bog anymore when he did the start training.
But now the problem seem to come back.
I run the stock jetting. According to the manual for our current weather (temp + altitude) Stock should be the right setting. And the bike runs very well on the track, it also answers well when twist the throttle with no gear.
I did tried bigger jets but it didnt solve the issue of boging.
I have cleaned the exhaust valve so I dont think that would be the issue either. (bike has about 30h and the piston about 10) It did bog also right after the piston was changed
Sometimes he can make 3-4 starts on 2:nd and it works fine and then for the next starts it bogs right after he let go of the clutch. Maybe the increased engine temperature makes it bog?
When start at 1:st gear there is no issue.
Any ideas?
//Mikael
My sons kx85 -17, sometimes bogs when he shall make a start at 2:nd gear. It was worse with the Pro Circuit pipe/silencer so I changed back to the HGS exhaust-system and thought I "solved" it because the bike didnt bog anymore when he did the start training.
But now the problem seem to come back.
I run the stock jetting. According to the manual for our current weather (temp + altitude) Stock should be the right setting. And the bike runs very well on the track, it also answers well when twist the throttle with no gear.
I did tried bigger jets but it didnt solve the issue of boging.
I have cleaned the exhaust valve so I dont think that would be the issue either. (bike has about 30h and the piston about 10) It did bog also right after the piston was changed
Sometimes he can make 3-4 starts on 2:nd and it works fine and then for the next starts it bogs right after he let go of the clutch. Maybe the increased engine temperature makes it bog?
When start at 1:st gear there is no issue.
Any ideas?
//Mikael
it does not surprise me its worse with a PC pipe, they tend to be more top end than mid range,
I dont recall his last bike kx85 -14 acted in the same way.
The Shop
Kawasaki actualy also provided a additional needle when I bought the bike, I did not check if it is thinner or thicker than stock one.
I personally think it changes the overall gearing more than the handling though, but that's just my limited experience.
(sorry for the bad english )
If everything looks ok the next thing would be the jetting:
Pilot: 42 or 45
Main jet: 142 or 145
Needle: Nape (oem on 13 kx 85 model)
Clip 3rd
Slide (oem from 17 yz85 which is 1 richer)
Air screw: 1.25 to 1.5
Plug: BR9EG with .22 gap
Good Luck!
Is the issue replicatable when doing practice starts or does it only happen behind formal, race gate drops?
80s second gear start is standard and you have to really have the rpms up very high and sorta feather the clutch. Can't just drop it. Takes finesse and technique. But rpms will need to be high.
It happen like this also before the change of piston.
Regarding the Power-valve: When I changed piston I basicly remove the locking clips from the axel and then slide the other "arm" of the axel to the side to get free clearence when remove the cylinder.
Then just opposite when re-assemble all. Do you think the standard position of the axel alligement can be altered in this process?
Im not infront of the bike now but the markers should allign when no throttle is applied, yes?
I see about the plug that I use the stock one, wich is called 105 something, wich I think is 10.5 , so that is maybe to hard then? (get not hot enough)
And regarding the jetting suggestions it all gives more fuel than stock, and basicly for colder weather if look at the chart in the manual. We have about 20-22 degrees celsius now in summer, (68-72 F)
But I did also hear from workshop in sweden that the KX85 in stock is equiped with to small jets so your tips is also similar to what I heared here in sweden.
I think my son may release the clutch to quick, I think he "Chocks" the motor and it have not the power enough to handle the sudden amout of torque wich is applied so quickly.
So more training may actualy get rid of the problem,
Only so i Understand correctly: when you say feather the clutch, it meens release it not to quickly?
Asking a young kid to nail starts perfectly every time is a tall order. It's perfectly reasonable to believe he just needs more practice, especially since you say the bike runs well on the track and he can do 3-4 good starts at times before you have the problem.
He thinks and I observe that it looks like he does similar starts and after 3-4 bikes start to bog,
Neither the -14 kx nor the earlier KTMSX65 -13 acted like this...
I will shortly again change piston and I will try look at all possible mechanical factors to eliminate these as the reason of boging.
Then more practice on the starts and we see where we stand. How about body position? (I think sometimes he climb to much up on the gastank, possibly he is little afraid that the bike will raise out of the gate)
yes is possible, it seems like this both on practis and at the last race as well
//Mikael
The spring on his air screw didn't have enough tension and came loose.
We pulled the spring set the screw 1.5 turn out and the problem was solved.
Pit Row
Or don't dump the clutch let it slip.
Cant test anything this weekend becasue we will be in Uddevalla to watch the MXGP racing. Will be nice for sure.
Some tips above was to use larger jets. Is the plug also telling that? (As I see its darkbrow/almost black)
And Piston ring clearly is done if look at the color under the ring. What about the top of the piston, is that black normal ? I still use the standard plug NGK R6252K-105 (i think is 10,5 hardness) Maybe as suggested above the: BR9EG plug should be to prefer, 9 Hardness get hotter if understand correctly, but why is that better?
To perform a plug chop, warm bike up, find a long straight and run the bike wide open in a tall gear, hit the kill switch without letting off, check plug. Now your plug will give you a decent idea of how your bike is running on the main jet. Black is too rich, White is too lean; shoot for an off white - tan color depending on how hot you want that thing to run. Don't worry if your plug is black before you run this test, it'll clean up at WOT.
Just curious about the top of the piston , I think the blackness (not sure about the english word) is pretty normal, but is quite thick layer , so I was wandering if jetting and/or plug-hardness affect that in any way.
To me, starting line bogs could be caused by jetting, clutch release (rider), track surface and clutch condition.
On our 85s, after we install a fresh clutch, we usually find slight jetting issues that were hiding behind the slipping clutch.
Adding a tooth the rear sprocket also helps and it doesn't affect the rest of the track significantly.
The temperature is slightly dropping day by day in sweden so in a week or two maybe stock jetting is the right setup (that is if its too rich now)
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