Separate names with a comma.
Discussion in 'KTM 950/990' started by Billroy, Jan 11, 2006.
I have never seen more than a size or two difference. I run 170/172 right now.
Standard is 155/160
The idea is that front runs cooler therefore likes to be richer on main jet. That's how factory jets them too. Some run the same , some run only 2 sizes down. Without a wideband its all a guessing game. Add to that people trying to explain on the forums with their ass dyno saying it "runs better", "pulls harder"... and we have a shit show of feedbacks.
Its much harder to jets this bike that a single. But once you get it right, its a blast.
That's exactly what I ended up doing. I put the 45 jets in and changed nothing else. It started just a bit better but still not good at all.
Then raised the floats and put new fuel shut of valves in the bowl. I found the Kehien part number for them and got them locally super cheap. Will share it here soon.
Anyway, raised the floats to 3.5mm from 3. And changed the mains to 168/172 from 178/180.( broke the change-one-thing-at-a-time rule). Now I can start it with less effort, but still not good. It takes full chock in a hot humid day to start. That shows it is still too lean right? How come it idles ok then?
IMS is at 2.5 +/- 0.5 (flex jets)
What would you recommend I change next?
It still wants to crank a lot to start. Drained the bloody battery again last time I rode it in the city. I have a lithium booster battery under the seat that is a life saver.
stock needles at 3rd
All air jets are stock.
And remember its a 990.
That's what I figured. Well when I get my pilots in i'm going to put it back together and try my baseline setting.
Trying to jet around 4-5K feet. rot intake with pre filter, CJ 2-1 with a fmf 4.1 with spark arrester. 42 pilots, 165/170 mains, stock needles in the middle. floats are at 3 or 4mm, need a better way to get a reading.
Keener, it really does not make sense to me. Weird.
Have you triple checked carb balance tubes and carb breather hoses?
Ps. I would keep for the time being the larger mains. They leak a lot to the idle circuit.
Probably 45+170=42+180 as far as idle mixture is concerned.
Once warn these engines can idle on very lean mixtures btw.
If it starts better wirth the 45 I think it is a problem with the IMS Flexjets...
I have a similar problem with the stock screws IMS that I change
Some times the tips on different air screws can be a little off. I remember some of those non brass air screws on fcr dirt bike carbs would be so far off people had 3-4 size different pilots than before.
Hmmm conflicting data.
1. Is the hard starting from cold or warm/hot? I thought it was a hot issue still right?
2. Where is your idle setting? My guess here is that it is too low. Turn it up and mark the results (clockwise is up I believe). I still think it is a rich issue if a hot start problem.
The full choke issue is throwing me. I would suggest going back to a baseline and modifying the IMS/Idle singularly. Note what your results are and that data should point to what you need to do.
I've got two issues I was wondering if anyone could shed some light on?
Firstly, I'm getting fuel starvation at high speed (180+). It rips getting up there, but then after a second or two, starts cutting in and out, like it's run out of gas, but at a steady rythm. Throttle for a few seconds and it recovers and goes steady, no problems. I have a fuel filter installed that I think is a bit too small - could this be restricting the flow required and draining the bowls at high speed?
Second problem - cruising around town just off idle, I keep getting backfiring through the carbs. Seems mainly the rear cylinder. I've checked my boots and vent lines and no leaks there.....this is cause by a lean mixture, right?
Current setting are
ITG filter plus thick foam prefilter (both iled)
2-1 exhaust with open pipe.
stock needle 2nd clip
floats just under 4mm
ims both at 2
Have you checked out the needles on 3rd position, all else being the same?
The man himself!
I havent yet - I was under the impression that the consensus was set em on 2nd position and work the float heights, and that 3rd position was likely to bring in its own compromises. It's pulling pretty damn hard as it is and the mileage is brilliant (5.8L/100km) so I haven't tried moving needle clips.
Do you think the carby backfire is from needles being too lean?
Well.....there is the posibility that the transition from needles to mains develops a lean spot, hence problem 1 of your post. Also, raising the needles, will enrichen idle, your problem 2.
Raising the needles is not your solution, is just a pointer to the proper way of action. If both problems diminish to an extent, then you will have to rivisit floats and mains, most likely.
Also, you are running a 2-1 exhaust. This is unchartered territory to me. What kind is it?
Moded stock 2-2 ?
It could be lean floats, mains or needles!
I have no experience with 2-1 systems...it could as well be lean pilots.
Reasonable backfiring is normal though and sought after.
We should define what you mean by Backfiring:
A back fire would be through the carbs NOT decel pops through the exhaust.
What I believe Mousitsas is saying is that DECEL POP through the exhaust is desired NOT Backfiring through to the carbs.
**Most motocrossers use this lean technique as their bikes don't idle for long. Makes the hit hard right off bottom and actually warms the bike up faster. I caution as a lean condition does feel like extra power but will be hard on the valve train/pistons/etc. With a wideband you could achieve your results much better by tuning to an acceptable AFR to avoid any lean damage.
Thats right coolrunnings, i meant to say backfiring on closed throttle during deceleration. Not the exploding stuff, but of the burbling type.
No backfiring= too rich idle
Exploding backfiring= too lean idle
I have checked the vaccum lines I use for syncing multiple times.carb vent hoses are not blocked. Checked everything multiple times.
It backfires (through the carbs) even with a little throttle during the start. It also pops some times super loud like a gun shot through the exhausts if I give it throttle during the start.
Lots of chock helps starting it with the current setup. I'll go back to larger mains and see what happens.
It is shooting in the dark without wideband. I'm looking into that.
I have a second set of flexjets,I'll try them. Yea the tip of one of my flexjets was a little bent which I fixed a while back. I'll try another set and stock ones.
It runs just fine once it starts, arrrrrrrr...
ya that bent one is no good. Just a hair difference make a big deal.
Starting: Generally on a 4 stroke you never touch the throttle during the start. Most manuals state something to this effect. May I suggest if you do, open and shut the throttle prior to hitting the starter. This will "prime" the system if it is lean although fuel dripping down the carb can cause the backfire you are talking about.
IMS - Going back to stock will help to eliminate causes. The o-rings/washer/spring can be culprits if worn.
While you have the carbs out, clean the bowls and **replace** your pilot jets. Even if they look clear they may not be flowing correctly.
Man this is a doozy.
I assume you mean "Lots of choke." I'm almost positive I have read, maybe even in this thread, that when jetted correctly, these bikes should not need more than 1/3 choke to start. If you're giving it full choke, I wonder if you might be flooding the engine. That or your bike is very lean for some reason.
I am NOT an expert, or even a novice, on this stuff. So take my thoughts for what they're worth, i.e. nothing.