90 kat 750 2000-4000 rpm issues

[hitman13429]

Here is some info on the bike.


Bike:
90 kat 750
jet kit
v&h full exhaust
stock air box
carbs have 120 jets with mixscrews at 2.5 turns out. C clips at number 3 on needle.

Issues:
from 2000-4000 I have to give it plenty of gas for it to move and not die.
5000+ the bike seems really rich.

When I got the bike back from a local shop the mixs crews were at 3.5 turns out which gave good top end power but low end was horrible, almost as bad as it is now. Im going to be takeing the bike apart shortly to try something else and would like some input.

[hitman13429]

Follow up. The petcock has 3 positions. To the LEFT on the plastics it says RES/. as in reserve. Strait up on the petcock it self it says NO and to the right it says PRIME. I tried to run it on RES and it didnt seem to wana run. On NO it ran ok... maybe alittle rich but rpm's over 6000 it jerks and also popping was coming from the exhaust. Up tell this point the bike has always been on PRIME.

[Trackerrrr]

No = on

[coolasice]

vacuum leak on the petcock line perhaps? or clogged petcock

[hitman13429]

I was thinking the NO could be ON because when you sit on it and look down it reads ON lol. ok so run the bike with the petcock to ON. I think I might take out the petcock and check to see if its clean

[akarob]

So I'm guessing you never rebuilt the carbs?

Are all the exhaust pipes getting hot?

Sounds like classic clogged carbs.

[hitman13429]

I cleaned them out before I took the bike to the shop. All pipes are getting hot. Since I got the bike back ive put over 500 miles on the bike even with the low speed problem.

[Kreylyn]

Here is some info on the bike.


Bike:
90 kat 750
jet kit
v&h full exhaust
stock air box
carbs have 120 jets with mixscrews at 2.5 turns out. C clips at number 3 on needle.

Issues:
from 2000-4000 I have to give it plenty of gas Throttle for it to move and not die (give it more air to over come the rich fuel settup).
5000+ the bike seems really rich.

When I got the bike back from a local shop the mixs crews were at 3.5 turns out which gave good top end power but low end was horrible, almost as bad as it is now. Im going to be takeing the bike apart shortly to try something else and would like some input.

Stolen from another website, but the info is accurate...

Dynojets numbers are simply the hole diameter. A 140DJ main has a 1.40mm (0.055") diameter hole in it at the threaded end. A mikuni 140 Mikuni has a 140 cc's of fuel flow per minute. And, I honestly have no idea how Keihins are measured.

Width------Keihin # -- DynoJets # -- Mikuni #
0.0350---- 92.5--------- 92----------- 86.3
0.0360---- 95----------- 94----------- 88.1
0.0370---- 97.5--------- 96----------- 90.0
0.0380---- 100---------- 98----------- 91.9
0.0390---- 102.5------- 100---------- 93.8
0.0400---- 105--------- 102---------- 95.6
0.0410---- 107.5------- 104---------- 97.5
0.0420---- 110--------- 106---------- 99.4
0.0430---- 112.5------- 108--------- 101.3
0.0440---- 115--------- 110--------- 103.1
0.0450---- 117.5------- 112--------- 105.0
0.0460---- 120--------- 114--------- 106.9
0.0470---- 122.5------- 116--------- 108.8
0.0480---- 125--------- 118--------- 110.6
0.0490---- 127.5------- 120--------- 112.5
0.0500---- 130--------- 122--------- 114.4
0.0510---- 132.5------- 124--------- 116.3
0.0520---- 135--------- 126--------- 118.1
0.0530---- 137.5------- 128--------- 120.0
0.0540---- 140--------- 130--------- 121.9
0.0550---- 142.5------- 132--------- 123.8
0.0560---- 145--------- 134--------- 125.6
0.0570---- 147.5------- 136--------- 127.5
0.0580---- 150--------- 138--------- 129.4
0.0590---- 152.5------- 140--------- 131.3
0.0600---- 155--------- 142--------- 133.1
0.0610---- 157.5------- 144--------- 135.0
0.0620---- 160--------- 146--------- 136.9
0.0630---- 162.5------- 148--------- 138.8
0.0640---- 165--------- 150--------- 140.6
0.0650---- 167.5------- 152--------- 142.5
0.0660---- 170--------- 154--------- 144.4
0.0670---- 172.5------- 156--------- 146.3
0.0680---- 175--------- 158--------- 148.1
0.0690---- 177.5------- 160--------- 150.0
0.0700---- 180--------- 162--------- 151.9
0.0710---- 182.5------- 164--------- 153.8
0.0720---- 185--------- 166--------- 155.6
0.0730---- 187.5------- 168--------- 157.5
0.0740---- 190--------- 170--------- 159.4
0.0750---- 192.5------- 172--------- 161.3
0.0760---- 195--------- 174--------- 163.1
0.0770---- 197.5------- 176--------- 165.0
0.0780---- 200--------- 178--------- 166.9
0.0790---- 202.5------- 180--------- 168.8
0.0800---- 205--------- 182--------- 170.6
0.0810---- 207.5------- 184--------- 172.5
0.0820---- 210--------- 186--------- 174.4
0.0830---- 212.5------- 188--------- 176.3
0.0840---- 215--------- 190--------- 178.1
0.0850---- 217.5------- 192--------- 180.0
0.0860---- 220--------- 194--------- 181.9
0.0870---- 222.5------- 196--------- 183.7
0.0880---- 225--------- 198--------- 185.6
0.0890---- 227.5------- 200--------- 187.5


And there's this:


QUOTE
We are often asked for a "cross reference" sheet that compares our main jets to Mikuni or Keihin. The fact is you cannot directly interchange the jets for a given size. Many things affect fuel flow through a jet of the same orifice size. The entry and exit tapers of our main jets differ from those of other companies. Due to this, the fuel flow changes as a function of velocity through the carburetor venture. This means that two jets of equal orifice size will have a different fuel flow curve relative to intake air speed. At a certain speed the two may flow equally, but a change in velocity changes the flow characteristics. The Dynojet main jet hole size is measured in millimeters. For example, a DJ142 has a 1.42mm hole.


Michael Cory
Research & Development
Phone: 800-992-4993 EXT. xxx
[email protected]


This is what Factory Pro says on their website:

Unlike other jet companies (dj, rd, keyster), Factory Pro Replica jets, Keihin and Mikuni, follow the original manufacturer's size scale so the Factory Pro Replica jets are interchangeable with original jets - saving a lot of time and improving accuracy for a good tuner.

If your determined to stick with the Dynojunk kit you have installed, then try the following...

118 DJ jets, 2nd clip on the needles, 3 - 3.5 on the A/F screws.

Or...

Swap in a Factory Pro kit and follow thier default suggestion for the bike to run great...

The problem as you have pointed out, your running too rich on the main jet for the setup you have currently. Tune for the jets and setup in the following order...

Choose main jets for top rpm performance
Choose needle position for 5-8K rpms peformance
Choose float position for 3-5K rpms performance
Choose A/F position for 1-3K rpms performance.

Krey

[hardlydangerous]

The needle jets (emulsion tubes) most likely need to be replaced.

this is a classic problem with the older bikes with more miles on them. The FZ and FZR are the worst but the Katana's are bad for it to. After 30,000 km it will start to be too rich and cause all kinds of running issues up to around 4500 rpm after that the bike screams...

99% of the time starting with fresh emulsion tubes corrects the problem and makes dialing in the jetting so much easier

go onto factory pros website and read about the FZR low end tuning issus.

http://www.factorypro.com/prod_pages/prody02.html#Factory_Pro_Supersport_Carb_Recalibration_Kits

[hitman13429]

Previously the a/f screws were at 3.5 turns out and it still had issues but the top end was fine. What if I just turn the screws to 3 3/4 turns out and try running with it in the ON position? Would this cause it to be to lean? In carbs 101 it states the a/f should be right around 2.5 turns granted all bikes are different.

[hardlydangerous]

3.75 turns out is WAY richer then 2.5

[hitman13429]

gotcha... So now at 2.5 turns the low end is running to lean and thats why the low end sucks so bad and the high end pops and is jerky... I sometimes had this with my nitro rc cars id get the way the needles needing to go mixed up.

[hitman13429]

Follow up with more questions. Took the carbs apart. The emulation tubes were clear and they didn't show any signs that they were worn out. On carb one for the pilot jet where there is saposta be the black rubber knob that just is sitting in the opening its not there. What is the purpose of this and is it forsure needed? All the other 3 are fine and there. Also for the floats I made sure they were all level with the carbs as from what I read in a manual. The thing tho in order to make it level the little clips/springs had no play what so ever like I couldn't make the floats go any more up then just even. Next thing with the petcock in the up position or in other terms ON position with the bike off some of the fuel ran up and into the cylinders and went into the oil. I drained the oil and could smell the gas in it. I think something is wrong with the petcock but cant be forsure. Should the fuel run like that in the up position?

Im not sure if there is a oil pan gasket or not because there is puddy all the way around the pan. Eather way it leaks really bad and im gonna buy a new gasket but at the same time a pro shift kit comes with a gasket. Would it be better to right away just buy the pro shift kit?

[hitman13429]

Anyone??????