Hello everyone,
Recently i have done some major work on my K100... the bike has been transformed into a Cafe Racer, had to switch a lot of parts.
managed to start the bike but as soon as the engine warms up the throttle starts to rev up on its own, can someone tell me if they had this issue before and how can it be solved....
Thank you

Sounds like an air/fuel mixture issue.
The FICU sets the fuel on the rich side on startup. As she warms the fuel is leaned till it reaches the correct mix at operating temp so the revs will pick up. You would normally use the 'idle throttle' (choke) to start but as she warms revs should settle at around 950rpm with the choke off. If you think its revving too much there are a few things you could check/adjust.

The Idle Throttle may need adjusting.
The throttle cable may need adjusting at the grip.
The throttle bodies (TB) may need balancing. This is the air bypass screw (BBS) on each TB.
TBs may not be closing at idle.
Your throttle position switch may be physically interfering with the TB shaft.
Air bypass screw on the MAF may need adjusting.

I think before you start you need to outline what engine modifications you've done, if any, so that advice is relevant.

Cheers

To add to Hollister's list...

If you've had the airbox and air intakes off and used Jubilee clips (worms drives) in place of the OEM clips, chances are that the worm drive on no.3 intake is fouling the throttle linkage bar.

Thank you all, 
I havent done any modifications on engine, just replaced fuel injectors....can also fuel pump be the problem??

I had a similar problem on my LT.

Dai has mentioned it, my LT had Jubilee [worm drive] clips that were fouling the throttle linkage, throttle couldn't return to proper idle position.

If you have not done anything at all to the engine (and by that, I mean taken nothing off except the fuel injectors), then check the throttle cable routing. Is there any slack in the cable at the twistgrip? The twistgrip should move backwards and forwards by 2-3mm before it starts pulling the cable.

I has this issue once. Cause: I'd inadvertently rotated the TPS so that it was holding the throttle open a bit. (I think it happened when I was putting the plenum back on after I'd replaced the TB boots.)

eman-nyc wrote:Thank you all, 
I havent done any modifications on engine, just replaced fuel injectors....can also fuel pump be the problem??

What fuel injectors did you install? There's a number on the side of the plastic part at the top which will look like this 0280150###

I doubt it will be the fuel pump.

What revs is it getting up to with no throttle?

The first thing to determine is if its revving because it's running a little lean OR the throttle is slightly engaged due to poor adjustment or something fouling it.
Take a look at all 4 spark plugs. Keep them in the order they came out and post a pic if you're not sure what you're looking at. If they are whitish/grey your engine is running lean.
What colour is your exhaust?

Take a look at the throttle stop on the TBs at the bottom of the cable. Is it coming to rest on the stop or short of the stop, leaving a gap? Also, as mentioned, the adjustment at the grip should be a tad loose.

Holister wrote:

eman-nyc wrote:Thank you all, 
I havent done any modifications on engine, just replaced fuel injectors....can also fuel pump be the problem??

What fuel injectors did you install? There's a number on the side of the plastic part at the top which will look like this 0280150###

I doubt it will be the fuel pump.

What revs is it getting up to with no throttle?

The first thing to determine is if its revving because it's running a little lean OR the throttle is slightly engaged due to poor adjustment or something fouling it.
Take a look at all 4 spark plugs. Keep them in the order they came out and post a pic if you're not sure what you're looking at. If they are whitish/grey your engine is running lean.
What colour is your exhaust?

Take a look at the throttle stop on the TBs at the bottom of the cable. Is it coming to rest on the stop or short of the stop, leaving a gap? Also, as mentioned, the adjustment at the grip should be a tad loose.

Spark plugs are brand new.....I am guessing it needs adjustment since the bike was completely disassembled then put back together.. however a friend/mechanic will be looking at it.... as soon as i get something i will keep ypu guys updated
thank you all for the feedback

I did a vacum test and calibrated the throttle bodies..
 

but.. it seems that the intake manifolds are the problem....once the engine heats up it starts leaking air...... is there anything I can do before deciding to replace them (they are costly)....
maybe use gasket sealant...
or anybody has any other suggestions

Many thanks,
E

I believe there is an o-ring at the base of the inlet manifold that may be hardened. 

Cheaper to replace than the manifold.

You can test for air leaks while idling by:

1 - Spritz some water mist around the manifolds. If the RPMs go down then they're leaking.

2 - Spray some starter fluid or propane around the manifolds. If the RPMs go up then they're leaking.
(Use proper fire precautions if doing it this way.)

(I usually use starter the starter fluid method.)

If they are cracked or leaking then you should replace them.

Point-Seven-five wrote:I believe there is an o-ring at the base of the inlet manifold that may be hardened. 

Cheaper to replace than the manifold.

The O-ring on 2V bike is built into the manifold and is not a separate part.

The 4V bikes have a separate O-ring there.