Idles .. running .. then revs drop and stalls, any ideas ?

[400_Rider]

Howdy guys :)

OK I bought this little GSX-R 400RR SP2 hopin I could turn it into the best bike in the world, and its been nothing but a headache

I spent LOTS and I mean LOTS on the bike so far and its still not running right.

Today I put a stage 3 carb kit in it, set the float heights finally, put new o-rings in the idle valve screws and turned em out to 2.75, gone for the proper main jet (not the very largest one, tried that and slowed down @ 10k rpm).

Problem is ..........

When I go to start bike, I press start button engine cranking and its not firing until I give it say 40% throttle and then it builds and builds and builds more until finally firing into life what could cause this ?

Then the revs are say 3,200rpm so I lower the idle speed until its just under that and its fine and idles ok for a while, then after a bit the revs just drop and the bike stalls

When its revving theres black soot coming outta the exhaust, quite a lot and white smoke to begin with too.

Any ideas on what this could be guys please ?

Cheers.

[wullvfr]

is there any backfiring at all?

i would definately say the problem lies with whatever you have done,on the basis it ran fine before you started fitting the new jet sizes etc?

william

[400_Rider]

Hi mate.

Nah it never ran right before hence me getting the jet kit etc.

I just took bike out 2 mins ago and it only did 115mph felt ok though quite quick actually but I have seen 125mph before so theres more to come yet.

Gets bike home on drive and into neutral and straight away, stalls

Also when at traffic lights if dived down to stall again and I had to hold revs at 3,000rpm, so annoying

[wullvfr]

what size of jets did you fit?and what is the standard size?

what exhaust system are you running,is it standard or aftermarket?


william

[400_Rider]

117.5 is whats in now and its better than the 120's that came in the kit.

I got full stainless system on it.

Airbox is on but only butted up to the carbs as it dont fit anymore, I aint sure if thats effecting anything.

[wullvfr]

you need to define if it is running rich or not.

check the plugs and see what condition they are in....black smoke is an indication of the bike running rich but why?
you say its now running 117.5 jets as before it was running 120(was there black smoke last time round with these jets?)

tha air filter could cause the bike to run more rich if there was a blockage or anything similar.maybe try solving that problem or seat it proprerly and see if it makes any difference.

did you adjust or check the float heights?are these correct?was the internal parts of the float chamber ok?

what about a vacuum leak,could be a possibility for the stalling but i doubt it.maybe worthwhile taking everything back off and going through it all again...making sure you have fitted everything correctly.



william

[Jon]

When you set the float levels did you have the carbies on their back or on their side?, most motorbike needla and seets have a spring in.
You need to make sure that when setting the float level the needle is just touching the seat and needle is not compressed.

Does it idle better with choke on or off?, if it idles better with the choke on your idle is too lean.

When you did the 2.75 turns they were full turns? (not trying to be a smartar$e it is easy to count half a turn as a full turn.)

Have you messed with the carb synchronsing screws at all?

regards
jon

[wullvfr]

if it idles better with the choke on your idle is too lean.

that only makes sense if the bike has already warmed up,if the bike is cold then it probably will not idle too well unless the choke is on!!!!

if warm and the idle is crap and the choke on helps then yes it will be running lean....or if putting the choke on makes it even worse then it's running way rich.

another thing gsxr-400,the idle should be set when the engine is upto running temperature!!!!




william

[Jon]

if it idles better with the choke on your idle is too lean.

that only makes sense if the bike has already warmed up,if the bike is cold then it probably will not idle too well unless the choke is on!!!!

Agree completely, sorry for missing that.


regards
jon

[400_Rider]

Thanks for the input guys, really appreciate it :D

OK I'll try to answer as many q's as I can.

1. It don't backfire at all
2. Bike has never idled correctly, so today I installed a stage 3 factory pro kit hoping it would fix things
3. In the kit were 117.5 and 120 main jets, I tried 120 and 117.5 and the 117.5 were better
4. Float heights have been set to 15mm as per instructions and I had to bend the tangs a lot to get this measurement, the carbs were rested vertical and I made sure the float valve wasnt compressed any but the tang was just resting on it, all 4 set at 15mm, there or there abouts
5. Sometimes the bike will idle and can idle for quite a while, however rev it or go for a blast and then it won't idle anymore and it will want to stall
6. When I turned the idle mixture screws I screwed em all the way in until it stopped dead, then backed off a tiny bit, then did 2.75 FULL 360 degree turns out
7. I have synced the carbs before I installed the jet kit, here is a before and after :

BEFORE

http://uk.youtube.com/watch?v=OS5PcA-07cI

AFTER

http://uk.youtube.com/watch?v=TfOigfrvHR8

If we can tackle this one step at a time, idle is me biggest problem, having read the above any ideas where to start next ? tomorrow I was gonna mess with the idle screws see if that helps any.