Author Topic: K2 carbs Rich (Read 1903 times)

Rg72chop · « **on:** July 23, 2011, 08:50:45 AM »

72 K2... with pods and 4 to 2 open exhaust. I rebuilt the carbs and installed new plugs (jets are 40 and 125) clip was in the middle position before the rebuild. After I rebuilt and reinstalled the carbs I synced them, it was really rich so I moved the clip up to drop the needle lower and cleaned the plugs. It helped a little, it was no longer oily but still black and covered in soot so I moved it all the way to the top and re synced them, the plugs are still black. Any suggestions?

ekpent · « **Reply #1 on:** July 23, 2011, 09:12:40 AM »

Did you reuse the stock Kehin slow 40 main jet or are they an afermarket. I have seen some aftermarket and replaced them that were WAY large but supposed to be correct. Stock main on those 72's was a #110 I think so you could go smaller than 125 also if needed.Make sure the slows are clean and not plugged.When jetting it seems no two bikes react the same to a certain jetting,depends on engine condition and other factors so fiddling is required.

Rg72chop · « **Reply #2 on:** July 23, 2011, 09:31:00 AM »

I used the jets that came with the rebuilt kit, but i saved the old ones. i was under the impression stock was 40/120 for a 72

Rg72chop · « **Reply #3 on:** July 23, 2011, 01:00:52 PM »

Put tank back on and went for a 15 min ride. Idle and initial throttle feels good then about 1/4 throttle it seems to bog down and have no power, just after that powering through the flat spot it powers right up and is extremely responsive the bike jumps out and wants to take off through 1/2 to full throttle... it has never had power like that as long as i have had it. (plugs still black)[img]

Johnny5 · « **Reply #4 on:** July 23, 2011, 09:03:26 PM »

I think your needle is too lean now, and your idle circuit is rich. Raise the needle a notch and turn in the air screw 1/4 of a turn and work from there.

Rg72chop · « **Reply #5 on:** July 24, 2011, 11:25:05 AM »

I ran the bike at that notch with the fuel air mixture screws 1 turn out and messed around with them to try and get the idle and low end smooth after an 45 min ride it was stalling when i stopped and the plugs were all black. i may drop the to a 120 jet first then go that route if it doesn't work.

Rg72chop · « **Reply #6 on:** July 24, 2011, 02:35:47 PM »

Changed from 125 jets to 120(still at top clip ) went for a 20 min ride still runs well at idle fuel mixture screws 1 1/2 to 2 turns out still no change flat spot in throttle at about 1/4 throttle power through and top end is all power.

Rg72chop · « **Reply #7 on:** July 24, 2011, 03:30:01 PM »

mixture screws are now 3 turns out seems like like the plugs are looking better but there is still a flat spot in the throttle at 1/4 going to raise the needle as suggested and see how that works.

Johnny5 · « **Reply #8 on:** July 24, 2011, 03:52:26 PM »

Are your pods clean? Maybe too much oil?

slowjo · « **Reply #9 on:** July 24, 2011, 04:33:00 PM »

I hope you find out whats wrong. I have the same problem with my K1CB750. 120 mains 40 slow, needle clip moved one notch up. My plugs look the same as yours and I can not figure it out either.

Johnny5 · « **Reply #10 on:** July 24, 2011, 04:36:16 PM »

Might be able to try a hotter spark plug?

Rg72chop · « **Reply #11 on:** July 24, 2011, 05:51:33 PM »

I did clean and oil the pods just after i started this post and it seem to help so i do not think i have to much, the pods are dry but a little tacky. The plugs look better than they have since i have started and in thinking the old mixture screws had a hole in them the new ones do not, so maybe they have to be turned further out them re comended 1 1/2 (I'm at 3 turns out) it is popping a little when i release the throttle allthough.
Can someone tell me what turning the mixture screw out does? (add air... add fuel...) when i screw it out the black smoke wile reving went away

Johnny5 · « **Reply #12 on:** July 24, 2011, 06:24:32 PM »

Turn in the air screw to enrich, turn out adds more air to lean it out.

Spanner 1 · « **Reply #13 on:** July 24, 2011, 06:27:13 PM »

Mixture screws all-the-way in =all fuel and no air

Are you sure your slow and main air bleeds are clear and supplying pre-mix air like they are supposed to ?? You can verify them by squirting carb cleaner into the bleed tubes in the carb throats.
You will have to hold a finger over the main jet and slow jet to do this ( bowl off, block main and slow ) cleaner must squirt up under jet needle = main bleed and thru' slow opening just at the motor end of the slide = slow bleed......... try that .

Rg72chop · « **Reply #14 on:** July 25, 2011, 05:28:13 PM »

Thanks for all the info...I will be at it again this weekend

Rg72chop · « **Reply #15 on:** July 29, 2011, 01:09:56 PM »

Pulled off the carbs again today and under a suggestion from Johnny5, I am going to drop the clip a notch to raise the needle jet. In starting to understand how the carbs work i am thinking the flat spot in the throttle is where the main jet takes over from the slow/idle jet and the mixture screws have been rich and the main jets i made to lean. So i have leaned out the slow jet with the mixture screws and i am dropping the clip a notch to rich en up the main, with any luck this will get me closer to were it should be. Any thoughts?

Also my carbs from the factory ran 120 40 jets they are 7A JF with my pods and 4 to 2 exhaust should i be like 125 or 130 and what for the slow jet can that be part of the flat spot?

Duke McDukiedook · « **Reply #16 on:** July 29, 2011, 01:23:17 PM »

The air screw only affects idle to about 1/8th throttle, then the slow jet picks up from there and the main jet covers from 1/4 on to full throttle if I remember well (there used to be a chart on this somewhere).

Check out the carb faq for more ideas and help, a lot of information is there to be utilised.

Rg72chop · « **Reply #17 on:** July 29, 2011, 01:32:01 PM »

My flat spot is at 1/4 throttle, so according to what you have said that is the point where the main jet takes over for slow jet could it be jetting then??? like the slow is to low or the main is to high and there is a lag point in between?

Duke McDukiedook · « **Reply #18 on:** July 29, 2011, 01:47:15 PM »

There is no magic formula once the stock airbox comes off the bike and podz are put on.
Podz are meant for racing situations where top end is all you are worrying about, people tend to forget this or flat out don't know it- they sure do look cool, though don't they?

You may never solve this flat spot problem, it will take a lot of work and experimentation on your part- I will give you a hint on solving your problem- only adjust one thing at a time and observe- don't change multiple things at once and wonder what went wrong.

The main jet covers the largest portion of the throttle, I do know that for sure.

Rg72chop · « **Reply #19 on:** July 29, 2011, 03:39:32 PM »

thanks that is some good info as this is my first bike and unless its made out of stone and i can use a hammer chisel on it...its all just trial and error for me. This has been a great help thanks to everyone.

Rg72chop · « **Reply #20 on:** July 30, 2011, 06:18:57 PM »

today i read something http://keihincarbs.com/tips/gate.html Thatmade me take a close look at my needle jet. What this site says is that not all needles are the same. The taper of the needle can make serious changes to how your bike runs.

1/4 to 3/4 throttle jet needle: the jet needle (#2 in illus.) is comprised of five major elements.
1. straight diameter section: in keihin carbs either the last two digit or the last letter denote the diameter of the needle. The higher the last two numbers the leaner the needle the lower the letter the richer the needle. By going to a thinner needle there is a larger area between the jet needle and needle jet supplying a richer mixture.

2. length of the straight section: this determines at which point the needle taper will start relative to the clip position. If you have to run your clip in the highest position a needle with a longer straight section will need to be used

3. needle clip position: this works in conjunction with the length of the straight section. If the engine is too rich above a quarter throttle raising the needle clip (#1 in illus.) will lean the mixture.
4. needle taper: a larger taper will result in a leaner mixture in the first half of the taper and a richer mixture in the last half of the needle. For example, a 1.34 taper will be richer in the first half and leaner in the second half of the taper than a 1.45 taper needle.

5. number of tapers: the needle can have one or more tapers. The number of tapers is not usually changed.

Needle jet: the needle jet/nozzle, varies the fuel/air mixture up to 3/4 throttle. How it overlaps with the jet needle depends on the needle jet orifice i.d., air bleed holes, and type of nozzle screen. Most modern japanese carburetors use a fixed needle jet/nozzle assembly which cannot be removed. If your carburetor has a removable needle jet/nozzle please contact the manufacturer in order to decipher the nozzle code. It is also not advisable to calculate how rich or lean a needle jet is using exclusively the nozzle inside diameter to needle outside diameter discharge area.

Wide open throttle (w.o.t.) main jet: the best trackside method to determine the size of the main jet (#7 in illus.) is to fully load the engine on a long straightaway or hill. At the end of the stretch chop the throttle and hit the kill button simultaneously. The plug is then pulled for a "reading". The parts of the plug you should be looking are: the positive electrode and the last 1/4 of the ceramic insulator . Best power will usually result in a very light tan colored insulator tip and dark colored ring around the tip of the electrode. The electrode itself should have fairly sharp edges. For example, if the ceramic insulator has a nice tan coloring but the electrode has a white ring around the tip and the plug is of the correct heat range then you can easily run a size larger main jet.

For my bike i looked at the new needle that came with the kit and the old that was in good shape the was a big difference... so i cleaned it up moved the clip to the middle position and put at all back on my bike. I no longer have a flat spot at 1/4 throttle top end seems good and I'm still playing with the low end it a little rich but allot better than before.

Duke McDukiedook · « **Reply #21 on:** July 30, 2011, 09:10:19 PM »

Sounds like you are on the right track, a plug chop will let you know what is going on at the RPM you keep it at for a decent period of time before you cut the engine.

The most accurate way of figuring out your jetting is to dyno run your bike- you only do that after you have any possible kinks worked out engine-wise and you are only zeroing in on your carb settings.

If you have any changes in jet/needle parts you better make sure they are Keihin, especially the needles. You can get away with Keyster parts for rebuilds, you just want to make sure you do not use their needles.

Rg72chop · « **Reply #22 on:** August 02, 2011, 04:16:16 PM »

Have been on a few long rides since i put the old needles back on and ditched the ones that came with the kit. I have had to play with the adj. screws and keep checking the plugs. It is running a little rough just above idle and i rarely get it past 1/2 throttle but all seems well other then number 4 plug is still black and sooty the other three look good...

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Author Topic: K2 carbs Rich (Read 1903 times)