Second Gen Carburetor Flaw Revealed!!!! - Kawasaki KLR 650 Forum
2008+ KLR650 Wrenching & Mod Questions For repair, maintaining or modifying discussions related to the newly updated 2008 and beyond, Generation 2 KLR650 Motorcycle.

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post #1 of 47 Old 08-09-2019, 10:52 PM Thread Starter
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Second Gen Carburetor Flaw Revealed!!!!

Second Gen KLR Jetting / Detonation / Oil burning solved (once oil burning starts it probably wont stop, but it might)

So if you've followed my progress on my bike you've seen the first two plug readings, well here they are again



The one on the left is no shims just 2.5 turn out on the screw. the one on the right is with one shim under the needle and 2.5 turns out on screw. Moved in right direction as the scavenge area has some color albeit gray and white. (doesn't show on the pic very well, they're both too white)

So, i decided to add another shim under the needle


so by this image we are still lean but now we've dirtied up the scavenge area

This didnt make sense ... unless. There used to be an issue where the machine could draw fuel from the needle jet at idle or just off idle , which is way too soon. causing a false rich behavior when it was actually VERY LEAN at low throttle openings. Sure as shit the KLR has this issue. This was an issue back in the late 90's early 2000's on a lot of models.

this is a picture of the needle and slide using a mirror. the at rest position of the slide was too low making the air under the slide move too fast drawing fuel from the needle jet at idle when fuel should not draw from that circuit until much later. This slide if you look to the edges is raised cause i took the photo after the oring was put on.


The solution is easy

A #210 Buna-N o ring stretched over the slide will raise its AT REST height 3mm or so increasing the available volume and consequently lowering the air speed under the slide at idle and just off idle because that area is the butterfly valve, bypass ports and pilot jets job. (this was a Kawasaki directed procedure for many many models.) I remember doing this mod on a klr 250 years ago and many many atv's the cvk38 and 40ls were bad


I put the o ring on and removed one of the two shims and thats it. And ran the bike (stock #40 pilot), it instantly had a Huge lean condition just off idle, it just bogged confirming my theory.

IT Definately needed #42 Pilot now and 1 3/4 turns out on the fuel screw should be about right. And one shim under the needle. 2 was too much.

what this mod does is isolate the needle effectiveness to a higher engine rpm/throttle opening where it is supposed to be so it can't affect idle and just off idle.

here is my redneck lawmower tank for running it without the fuel tank while i was testing. lol


going to run it a bit and will pull plug and post pic. But this problem is the major cause of all those running issues i've been hearing

the coolant temp spikes

the oil burning

premature rod failure.

I'm not done with the jetting now that the carb circuits are operating where they are supposed to i can jet it pretty easy now it could very well be perfect as follows.

i took it for a short rip and again an marked improvement in power and smoothness off idle and in the mid range so drastic improvement from stock.

Might not need any shims under the needle with the o-ring on the slide and the #42 Pilot 1.75 turns out on the mix screw. This is the part i have to check now that the problem is isolated.

Right now i'm running :

#210 Buna-N o ring on the slide (made for petroleum products)
#42 Pilot Jet
1.75 Turns out on the mix screw
1 0.025" shim under the needle (probably not needed)
145 Main Jet
spark plug gap 0.07mm (0.031")

2009 KLR 650 STOCK except for thermo bypass and doohikey, custom 3/4" lowering link
87 Octane fuel
65 deg ambient temp

This works really good, will verify with plug readings but its damn good. (Remember the little hole on the bottom of the slide goes towards the engine)


JdgDReDD
27 years as licensed motorcycle Mechanic
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Last edited by JdgDReDD; 08-09-2019 at 11:50 PM.
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post #2 of 47 Old 08-10-2019, 07:22 AM
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I have already done the.22 cent mod, how does the vent hole size in the diaphragm affect this mod?
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post #3 of 47 Old 08-10-2019, 07:53 AM Thread Starter
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Quote:
Originally Posted by Keith View Post
I have already done the.22 cent mod, how does the vent hole size in the diaphragm affect this mod?
This mod will work no matter if the vent hole size has been increased or not. (i'm not a fan of increasing the vent hole on the slide as it can create problems on smaller engines.)
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post #4 of 47 Old 08-10-2019, 07:57 AM Thread Starter
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If you dont want to spend 10$ on a pilot Jet you can use a #77 drill on the pilot jet

here is a handy chart i got at one of the yearly Kawasaki update seminars. Shows starter and pilot jet values and matching #'d drills. personally i've never drilled a starter jet but hundreds of pilots.



hold the drill bit in a vice grip and put the jet in a drill

Last edited by JdgDReDD; 08-10-2019 at 08:06 AM.
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post #5 of 47 Old 08-10-2019, 08:12 AM
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1. Vacuum port ("vent hole") enlargement. No effect on mixture; theory suggests quicker transfer of "vacuum" (pressure differential) from venturi for faster throttle response (vacuum above diaphragm lifting slide and needle).

2. Plug readings. A most complicated and confusing diagnostic technique, what with ethanol and who knows what additives in the fuel.

That said, even in the "bad old days" of REAL gasoline (and REAL lead), and the absence of deluded eco-Nazis, only a THROTTLE CHOP plug reading was considered valid and consistent. What is a throttle chop plug reading? Bike, at nominal operating temperature, is run at WOT (wide-open throttle), throttle is chopped closed and ignition immediately turned off; bike is coasted to a stop, and only then is a plug reading made.

Reason? Plug reading indicates mixture composition ONLY for the last time engine was running. Throttle chop indicates appropriateness of main jet diameter; maybe such thing as an idle plug reading is valid and consistent.

All this said, air/fuel meter tells a true tale, quantifiable beyond, "Looks about right!"

DISCLAIMER: Above post contains questionable opinion and perhaps flawed memories; contrary comments welcomed!

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post #6 of 47 Old 08-10-2019, 08:25 AM Thread Starter
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Neoprene orings swell and grow when exposed to fuel. must use Buna Nitril oring (Buna-n)

so ppl know i aint bs'n

this is from when i completed apprenticeship in 95



Here is a patch from the first time i went to Fairview College in 1990



Last edited by JdgDReDD; 08-10-2019 at 09:08 AM.
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post #7 of 47 Old 08-10-2019, 09:29 AM Thread Starter
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A good test for someone that wants to verify for themselves is to run the bike without the slide in at all

it should idle and rev slightly before it coughs and dies due to no slide being installed

with a #40 pilot it will cough the second you open the throttle

with a #42 it will have some throttle before it coughs and dies out


MAKE SURE THERE IS NO SPILT FUEL AROUND as backfiring WILL occur lol

its that area JUST off idle that is the issue. The needle is feeding fuel too early causing the bike to need too small of a pilot jet.
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post #8 of 47 Old 08-10-2019, 11:21 AM
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I dig what you're doing here man. I don't have an opinion on whether it's right or not, but it's good to see someone looking at details in the fuel system.

You mention that the condition of being rich on idle and off idle could be the root of several issues that seem to have been pretty well worked as being tied to other things.

Coolant temp spikes (lack of bypass in radiator system; fixed by Thermobob)
Oil burning (high oil pressure at crank with <5K RPMs, addressed by Paul and Tom's oil modifications)
Premature rod failure (not sure about this one)

So my question is, can you give us an idea of how this would be linked to each of these?

Personally, if you've got the machine running smoother that's enough to interest me, regardless of whether this mod can address the above. So I'd be interested to hear about not only the above, but also your progress and observations. Keep it up!

2017 KLR in black
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post #9 of 47 Old 08-10-2019, 03:39 PM Thread Starter
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Quote:
Originally Posted by samuel View Post
I dig what you're doing here man. I don't have an opinion on whether it's right or not, but it's good to see someone looking at details in the fuel system.

You mention that the condition of being rich on idle and off idle could be the root of several issues that seem to have been pretty well worked as being tied to other things.

Coolant temp spikes (lack of bypass in radiator system; fixed by Thermobob)
Oil burning (high oil pressure at crank with <5K RPMs, addressed by Paul and Tom's oil modifications)
Premature rod failure (not sure about this one)

So my question is, can you give us an idea of how this would be linked to each of these?

Personally, if you've got the machine running smoother that's enough to interest me, regardless of whether this mod can address the above. So I'd be interested to hear about not only the above, but also your progress and observations. Keep it up!
Falsely rich, it acts rich when it isn't due to the needle jet feeding fuel at idle . Its actually very lean.
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post #10 of 47 Old 08-10-2019, 03:52 PM Thread Starter
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SO

done some more jetting, here's where i am


this picture has the following jetting
#210 Buna-N oring on the slide
#42 Pilot (mix screw 1 5/8ths out)
3 shims under needle
145 main
Lean Lean Lean, messed up scavenge area and center electrode


this picture ....

#210 oring like the rest
#40 Pilot (mix screw 3.0 turns out)
5 shims under the needle
148 Main Jet
This is getting better, still lean but coming around and now that we are raised up on the needle the pilot had to be dropped to maintain off idle mixture.

Still no danger of the needle coming out of the nozzle


so i went to 7 x 0.025" shims under the needle



you may or may not see from the picture that the taper starts quite a bit up from the shims. That is the reason for so many shims, drawing the taper higher to where we need it. 7 or 8 shims will be max and we'll have to machine the needle to get the taper where we want. But we arent there yet. notice the first three shims are trimmed down to fit inside the first part of the needle holder.

the first shim added made the most difference, and the last two. there is a large flat spot on the needle which the middle 4 shims made nearly no difference. BY this point personally i would have raised the taper by machining the needle, but i wanted to see if i could fix it withouth doing that so anyone can do it.

Jdg

i'll keep you posted.

I've done the mod, and seen more improvement but have as yet to pull the plug

SO i now have
#210 Oring on slide
#40 pilot (3.5 turns out on the mix screw)
7 x 0.025" shims under the needle
#148 Main Jet

Not sure i've ever seen a carb so far out on the needle jet.

Last edited by JdgDReDD; 08-10-2019 at 04:31 PM.
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