back to the carb again Help!

[fisherking101]

Ok, i recently bought a 91 kat 750. when i got it it would only idel at 4-5 grand when cold. ride it till it warms up, and then it wont idle at all and it wont start at all almost like it is air starved, or to rich. got it home tore it apart and followed the thread here on carbs. it has dynojet 120's in it, k&n filter kit, vance and hines full 4 -1 hedder, no power pack. dynojet recomends 2.5 out on the jets, and all were out like dobble of recomendations. so after i tore them down, cleaned, inspected all parts, " had to replace some rubber rings", and reassembled every thing this is what happened.
cold idle was like silk, but if i rev it the r's hang around 4-5 then drop to idle. also after i run it " and it runs like a raped ape mid to top end!" and it gets warmed up the idle drops right out of her. and the same thing happens. it will not start unless i let it sit for 20 min or so like its rich or air starved. and i can not get it to idle at all it just drops off and stalls.
any sugjestions or help please. btw i also took it to a shop and they cleaned and checked everything also " carbs off, bike not present" i reinstalled carbs, same problem as before. they are telling me to try to run with out the box and air cleaner to see what happens. dont like this idea cause if it runs ok i still dont know what is wrong adjustment wise.

[jtaghansen]

Get rid of the K&N put stock back on
I won't be the only one to tell you this I'm sure

[Cheriff]

the hanging idle sounds like it could be a vacuum leak,,,, or maybe a lean condition. Can anyone correct me on the second one?

When you are riding in the low end, try adding a LITTLE choke and see if it gets better or worse. Oh, and put the stock filter back on first. Checking spark plugs may also help diagnose lean or rich to give you a starting point.

[Tmod]

A vacuum leak would cause a lean condition so yes check for that.

If it idles good cold but takes a crap when warm it sounds as though you are running a little fat. Don't take the Dynojet settings as gospel. Tinker a little and try some different settings.

If you have to wait 20 minutes before it will start again it sounds like you are getting excess fuel and you have to wait for it to vaporize a bit.

Tmod

[Cheriff]

Also check for fuel in the airbox.

[fisherking101]

ok so last night when i started her i did relize that there was a vacume line sucking on the right side of number 4. and this morning i saw cheriff and tmod's post, thanks also Future Kat Rider, and i saw the vacum pic's so now i know where that vacume line goes. there wasn't one on it when i bought her. so tonight i will try running one. nNow on the jets, how do i tweek them with out having to pull it all apart A, and how do i know which ones to tweek and in which direction B. also why dose every one say to go back to stock, shouldn't the k&n help her breath.

Thanks guys!

[Cheriff]

I can't give a solid answer on the K&N, but I know that it is often the cause of problem for these bikes. I have heard of more success on pre 98 models though. Some people have successfully jetted to make them work, but usually after significant effort (and probably little gain). The best kit for the 98+ models is the Ivan kit, and even he states that it must be used with the stock filter.

Changing jets, you have to take the carbs out. It isn't too bad. I did it for the first time a few months back. Never touched a carb before that. If you are looking at changing needle settings, that can be done by removing the black caps on the top of the carbs. Still need to remove the tank, but this part is pretty easy.

If you do try to change the mains, you will need some needle nosed vice grips and maybe an impact driver. The bowl screws will be a pain in the arse to get out. You will want to replace them with some socket head cap screws. I don't know the correct size but others here will. If you skimp on this step you will regret it.

[Tmod]

Yep you will have to remove the carbs as Cheriff stated to make any main jet changes.

My guess on the K&N problem is yes they do flow more than a paper element but I am guessing that this engine requires some vacuum in the airbox for the carbs to work properly.

Stock calibration is always the best starting point when you don't know what exactly was done before, That will give you a fixed point to start troubleshooting from. After you get that squared away then start your tweaking.

On the note that Cheriff stated about the float bowl screws, I would suggest using a pair of wire cutters (decent pair) and approaching the screws from the vertical position just center the wire cutters as best you can then squeeze and twist and they should pop loose. When I was doing this I tried several things before settling on the wire cutters.

Tmod

[Cheriff]

My guess on the K&N problem is yes they do flow more than a paper element but I am guessing that this engine requires some vacuum in the airbox for the carbs to work properly.


Tmod

It could be related to the fact that they are CV carbs. Or I just pulled that out of my arse.

[Tmod]

It could be related to the fact that they are CV carbs. Or I just pulled that out of my arse.

Well I would normally go along with that but the K&N's work on other bikes with cv carbs without any issues. I have one on my 85 Honda and it works fine. I also had them on a few other bikes and worked well.

Tmod

[Cheriff]

Damn... Thought I could make one from half court.

[fisherking101]

ok vacum leak and hanging rev's fixed. ran a vacume line from #4 to the tank petcock where it goes and now the r's dont stick like they were. on the next thought i have the stock airbox installed with a single k&n inside of it. it still wants to stall/ idle drops out once she is warm, oh and she is still rich, i can smell it when she runs and if i get on it when im tinkering the exust is a little dark, not black like burnt oil dark like rich and unburnt fule. im thinking this is ether re-adjusting on the jets maybe go to 2:20 on the setting insted of 2.5 out. wiht that said my next thought is this. play with jetting to see if i can lean her out some but not too much. the time for syncing. question is this if i adjust the jets, and how do i know if they all need to be a little diffrent ie 2:20 for one 2.5 for one 2:10 for anothe and so on. and once ive done that what is syncing going to do for me? basicly isnt that what im doing when trying to set the jets per jug? or rather carb per cylinder?

[Cheriff]

I would strongly urge you to pick up a stock filter and see how many of those symptoms go away. I would hate to have you buy a filter that may not fix everything, but jetting around K&N's on these bikes can be frustrating unless you get lucky. If it were me this is what I would do next, perhaps others have different ideas.

[III]

I had been going thru some similar issues with my recently purchased 93 600. It had been modded by the previous owner (Dyno kit 134, K&N pods). Ran very sluggish when I first got it. Had to crank the throttle and give tons of throttle to get it started. Seemed to get flooded out mid ride and weak power at low throttle. TERRIBLE GAS MILEAGE.
Found KR.com and started off reading up on carbs. This is where it's led to:
- I've taken off my carbs somewhere in the neighborhood of 15 times now to clean, re-clean, adjust, re-adjust, and double-check. (It's my first bike and part of the reason I bought it to work on it and learn). I must be getting better because I notice improvements each time for the most part.
- Installed, re-checked, and re-installed new NGK spark plugs.
- New battery
- Wangled my way into getting a carb synchronizer, about an hour of tinkering, and a few gas spills later, finally learned how to do it.
- Purchased a factory air box. (results below)
- Oil change

At this point, the bike is riding better than it ever has since I've had, and I'm guessing for a while. I am happy with it's performance, but seem to always be looking for more, which could end up in a wild goose chase simply due to the age of the bike. Unless there's been other restoration, or obsessive upkeep, I'm thinking a 15 y.o. + bike is still, and will run like a 15 y.o. bike.

With that said, here's what I've learned (mostly what the other's have said).
- I would get the carbs synched first. I couldn't believe how much of a difference it makes with the overall performance.
- Float height
- Choke plungers and plate (mine were sticking)
- Cable routing
- Older bike, more chances for leaks. Make sure all seals, clamps, and screws are socked TIGHT.
- I'm still using the pods, until I can re-jet (which apparently is not an option for pres unless its another Dyno kit), and or spend more time tinkering to get those adjustments right with the airbox. I've just been trying to get it run decent and get some time in on it before I spend the time that's going to take. My mains are huge and the airbox must not allow enough flow. (a/f screws are at 2.75...more air, needs backed out) The more I read, the more I'm noticing that the Dyno/K&N setup is more common than I first realized. It's not factory, and it's not recommended, but there's something about the combination that a huge majority of riders and mx dealers must prefer. Therein lies the problem, and the reason for my post. I'm learning that it's pretty much gotta be one way or the other. Get everything back to factory and go from there..., or keep the DJ/K&N setup and get it on the Dynotuner. Either way, it's going to be money, time and effort (factory route), or money, time, and patience (if your Dyno dealer is anything like mine and takes ages for an appt.). I guess it all depends on how much you paid for the bike, how long much you want to spend, and how long you plan on keeping it. It becomes addictive. Either way, these guys at KR will be here to help you out.

[arsenic]

no, you can get a Factory Pro jet kit, which is WAY better then DJ