Slow rev decrease
 

Hi,

Bikes all back together but I have a small problem I'm hoping is a small problem. When letting the throttle off the grip snaps back fine but it's slow to drop the revs off below same around 2500 to idle? Also I'm having problems setting the idle, I get it correct for sitting in the drive but when out on the road it's way to high. if I set it lower though it slowly creeps down and the engine cuts out?

Any ideas?

(It's bound to be something I have (or haven't) done since I have the carbs off and in bits)

Re: Slow rev decrease
 

Adjust the idle to when its warm after a ride, and leave the choke on longer when on the drive so it warms up? Mine does the same thing if the idle is in too far.

You haven't messed with you pilot screw by any chance? i think they are sealed on the sv by default?

Re: Slow rev decrease
 

nah, I left that well alone when I took the carbs to bits, it just doesn't feel right though, slow to drop revs? it didn't do that before.

Re: Slow rev decrease
 

Double checked all the rubbers are sealing correctly? and clamps fully tighted. Incidently what had you done? carb clean?

Like i said, mine does the exact same thing once i turn idle up it will drop in stages almost, from 5k then to 2k waits a while then settles back down.

Wait until someone more experienced replies :-)

Re: Slow rev decrease
 

Is it carburetted, your engine?

If so, your choke may be the problem here - it sounds like you had the same problem I had; corrosion in the choke plungers, causing them not to fully shut. I gave my bike to spannerman to get sorted for this, he said the front plunger was the culprit.

If your bike is FI...well, I'm not sure!

Other thingsn to check first are air leaks - are all the seals seated properly and sealing correctly?

Re: Slow rev decrease
 

If it`s FI then it may be the links that control both throttle bodies , sometimes they get a bit dry or gunky and need a lube , I had to shut my throttle forwards rather than let the spring return it to it`s natural position . Lubed it and that sorted that problem out . This may be something similar for you .

Re: Slow rev decrease
 

Classic air leak symptoms. Reseat the carbs and air box.

Re: Slow rev decrease
 

+1 to that I have just had the exact same problem, just pulled the choke plungers out cleaned them with some degreaser and put them back bike now running like a dream.

Re: Slow rev decrease
 

The screws are exposed unless you are a septic.

First have a quick glance, see if the cam is actually returning fully.

If it is, then you may be running a little lean because of an air leak. Are you sure the airbox is connected and seated properly? Spray some WD around and see if the tickover sound changes.

Is there any backfiring or spitting back through the carbs?

Re: Slow rev decrease
 

Ok - went out and sprayed some WD on the air box connector and the manifold? (bit between carb and engine) and no coughs or splutters.

When you say cams do you mean the bits the cables are attached to? If so then I'll double check that tomorrow when I have more light.

Many Thansk

Re: Slow rev decrease
 

Yes that is the throttle cam

Re: Slow rev decrease
 

ok well everything is moving correctly and springing to where it should be. I think I have found the main problem and fixed this with a new diaphragm/jet needle assembly from my spare carbs. Looks like the Muppet mechanic struck again when putting the carbs back together - doh!

So now it runs better on the drive and it seems to drop back better on the throttle although setting the idle at 1500 rpm it stays there for about 10 to 20 seconds and then drops off and stalls

One thing of note is there appears to be a small amount of oil in the airbox and on the black sliding thing on the front cylinder, could this just be a hangover from the first fault that's now fixed? shall I just run it and see how it goes or is there anything else I should try?

http://i132.photobucket.com/albums/q37/5hort5/m.jpg

Re: Slow rev decrease
 

I dont know what you was originally doing to the bike? But was it doing this before? The golden rule is go back to where you just worked as 9/10 times it something you've inadvertently done. It does sound like an airleak. Assuming it is an airleak and until a grown up shows up with some proper advice, this is where I'd start looking.

• Are the carbs definitely seated in the inlet rubbers properly?
• Did the air box rubbers come out of the airbox as these have a locating lug to keep them in the right place and flush. My first SV had the front one on wrong and was letting air in there.
• Airbox on the carbs properly? Its very easy to misalign it o rmaybe that's just me.:D
• Spigot for balancing on the front carb has its rubber sealing grommet on?

• All vacuum pipes to the fuel pump on okay? To eliminate this you could disconnect it for a second and just place your finger on the inlet spigot and give it a quick rev. If its still the same you could at least eliminate that side of things.

Cant think of anything else of hand.

Re: Slow rev decrease
 

well, I think I have fixed the lumpy running and a few other bits with the diaphragm fix but I still have strange reving, so the videos pretty mush say it all.

Rev it and it drops back to 2.5k rpm, turn the idle screwdown a bit down and it drops it 1.5 or a bit lower if I turn it to far. Rev it and it sticks at 2.5k rpm then repeat turn down the ideal screw a touch, etc etc.

The second one is where I thing I have the idles screw to low and it doesn't stick (we'll a bit) but then just drops and dies

Fixing my mess-up made a difference but I still have this problem. I can't find any air leaks so any other iedas from the vids?

Many Thanks

Si

http://www.youtube.com/watch?v=lc5RzFzrK3g

http://www.youtube.com/watch?v=xkGiGddn9SE

HELP - please :-)

Re: Slow rev decrease
 

My clr was doing the exact same thing after i stripped the carb. I kept reading about air leaks but there were none, only thing that cured it was altering the pilot screw a tad, as i forgot to count the amount of turns it was at before removing it. I assumed the compression being low was why it wouln't play ball at the default value hence somene had set it to a different one.


What exactly did you do when you cleaned your carbs, ie what did you strip off them? 100% no air leaks? Is it fully warm in this video? and the choke plungers are free?

Re: Slow rev decrease
 

yep fully warm just come back from a 10 mile run, I cleaned the carbs out by taking them apart but didn't touch the pilot screw

Re: Slow rev decrease
 

hit it with a hammer....

Re: Slow rev decrease
 

try replicate the problem on your spare set

Re: Slow rev decrease
 

My pointy is doing this now , washed her yesterday and heard a Jingle in the bellypan , reach in there and an exhaust clamp came away in my hand , ordered a new one and will put that on this weekend and see if it cures my problem . I am sure it is not the idle as that is fine , only when the bike is hot after a run does it mess me about ............ I suspect my exhaust needs bolting back together properly after the clamp died on it .

Re: Slow rev decrease
 

That's interesting as I have swapped the CCC race can back to the standard can but wouldn't have expected that to cause the issue.

Re: Slow rev decrease
 

Food for thought isn`t it . I have left mine alone on purpose , when I fit the clamp and it cures/doesn`t cure it ...... we`ll know if I`m barking up the wrong tree :)

Re: Slow rev decrease
 

ahhh ha.

The pilot jet is sometimes changed when a more free flowing can is added, maybe your jet is the wrong size now 5short5, check they are all standard sizes.

Re: Slow rev decrease
 

Anyone know what the default number of turns out it is for pilot screws on the carbs? Is it 2.5?

Re: Slow rev decrease
 

ignore that - found it at the front of the chapter in haynes

Re: Slow rev decrease
 

Rarely. I have not heard of anyone changing pilot to anything but 17.5 (mikuni size) which is the stock size for UK bikes. Some US ones get 15 size.

Pilot screws between 2.5-3 turns but these will just do some crazy stuff if you have an air leak :alien:

Re: Slow rev decrease
 

we i had time today to have another look and after taking the carbs off and refitting them they had the same issue so I dusted of the 5 quid fleebay set and stuck them on, interesting they work rather well. I just reset the pilot screws and set the balance screw to the same as the other carbs and it's not perfect but close and a load better than the ones I had so I'll stick with these now :-)