No power!

My bike was out in the elements and unused for three weeks whilst I was stuck in the UK with covid ( I had not planned being away that long!).  On my return I found the battery had died so replaced it and all seemed Ok, the bike starts and idles - but will not rev past idle.  I have drained the tank and changed the fuel thinking it may be contaminated - but no joy.  It was fine when I left it!  It will idle happily indefinitely - but as soon as the throttle is twisted it dies.  Any ideas?

So it starts easily, Idles happily but dies when the revs hit 3000.  If I keep the choke engaged it will rev slightly higher and then die at 4,000 revs, if I release the throttle it goes back to happily idling.... Completely nuts!

Not really , sounds like its not getting enough fuel . Check out fuel pump fix  on forum .

I didn't know my 2004 GS1200S even had a fuel pump. I thought it was simple gravity fed carbs..... Where would the pump be? For what its worth I had the fuel cock off to check the filter - it was as clean as a whistle.

Sorry ,your right 2004 is gravity fed  so rule out fuel pump . Still sounds like fuel . Try draining the four carb bowls . (screws under bowls ) One turn should do . Check the fuel hose isnt pinched or kinked, or kinks as tank is lowered . Sounds like its getting enough fuel to idle but not enough for main jets to kick in .Also check vacume hose to tap .Does it have a prime position on tap . Try running it on Prime .

Thanks Gus,

I tried running it on prime yesterday - no joy.  It does have a much thinner tube attached to the fuel tap - is that the vacuum hose?  How do I check it? I though the fuel only flowed if there was a vacuum or on prime. When I took the tank off, fuel seemed to flow out erratically when in RES or FUEL. If I get home in daylight, I'll have  a look this evening!  The bus to work is so sloooooow.....

This from the drain of Carb#1 may be part of the problem - what is that pink stuff?  Carb#2 had some bits in it and drained continuously - even when the tap was on main.  Carbs#3&4 were all clear.  I spilled some petrol over the starter motor so will wait an hour or so before cranking her up!

Draining the float bowls certainly did the trick. Thanks Gus.  Back to running normally thank goodness and no more buses!

Shenanigans started again this morning.  Got a few minutes from home on the way to work when it dies at traffic lights.  It took a loooong time before it would catch and start up again.  I decided to divert to the mechanic and keep the revs above 3500 the whole way. Almost made it, but had to push the damn thing the last 500m.  That is a lot of bike to push and I was knackered!  Will let you know the diagnosis when I get the call.  It has been many, many years since I have had a bike die on me like that. Idly thinking whether it is time for a change....

Tank filter was clean, so what was that pink stuff & where did ot come from ??.
Fuel tank vent clear?

Got the bike back from the  crew at APW Motorcycles today.  The float bowls were contaminated with rust, cleaned and refitted all jets, replaced  carby #3 float needle which was leaking petrol into the cyclinder head and the oil was contaminated.  All good now!  It sounds like it is running on all four cylinders and less like a lawn mower, so a big improvement !  Goodbye buses!

So now the problem is slowly coming back.  When on choke it runs rough and there is no stable revs, one second its at 1100 rpm the next @ 3000 or it may go to 700 and stall -  and the smallest of choke lever changes flips from 1100 to 2500rpm.  The engine now takes an age to be reliable and choke can be closed off completely. When it eventually does warm up enough (>15 minutes!), it runs and idles perfectly.  So its a bit of a handful at low revs for the first 15 minutes as you don't know how much power you are going to have - I have to pull the clutch when filtering or going around mini roundabouts as I had the damn thing stall on me when filtering the other day which was not a happy moment.  I suspect it may be a vacuum leak  - but how would I know?

'Cos I aint got them! I recall there used to be at least one clear hose running either side of the air box - but now:

You can just see the clear hose and connector down amongst the carbs:






but !



Is this meant to be connected to something ?

Where does the other end of the clear hose go ?
What does APW say re hose & running like it is?

No hoses from the two spigots under the tank either !

So in the above diagram it looks like there is an 'enrichment plunger' at the front of each carb. These would be operated by the sliding bar across the front of the carbs connected to the choke lever cable.  Problem on my bike is only the plunger on carby #1 moves.  It is difficult to see but it looks like all the other three plungers stay depressed and dont move.  If this is the case I would need to remove the carbs to get to them. I dont have a garage and I am not sure the boss will appreciate a motorcycle carcass on her covered front porch.  Is removing the carbs a weekend project  and are there any o rings or similar I will need to replace ? I would want to get them before starting this.  Of course, if there is only one active plunger anyway I am OK.  Does anyone know?

Would be 4 choke/enrichment plungers. Had all 4 stuck on 1 of my bikes, couldn't free them on bike, once off it took only minutes to free them, hours to R& R.
First up leave them on & give them a good spray with degreaser, then have a beer or a coffee. Then try to move them a little bit at a time. Be gentle.
May need a 2nd or 3rd spray & choice of beverage.
WD or similar if they move.
If not, it's bullet biting time. The plunger piston itself is just a snug fit, (Pic does say " do not reuse" $2.15 O ring part 38 in mick honest suzuki parts carby pic).

Thanks for that. As I have the place to myself this weekend (which means I can work inside the house!) I am going to go for it.  I have ordered the O rings Express post from Mick H (just in case) and hopefully they will arrive by Saturday.    I'll take some photos as I progress. What can possibly go wrong?  Whilst I am there I'll probably take the opportunity to replace the missing hoses.  So long as the smell of fuel / solvents / gin is gone from the kitchen by Monday when the boss returns I should be OK.

Remove tank outside, drain bowls outside too.
I know that smell, went remove battery the other day in garage. Unbolted everything, lifted the tank a little- not enough - just little more 🤬🤬 fuel lines pulled off the tank !!!. Lost about 500ml before I got my fingers in position to block the lines & be able to lift tank off bike. Mopped it up with rags but the fumes in the place that night

Odered the O rings over the phone yesterday and they arrived in my post box 25hrs later.  One less thing to worry about.

So I took the plunge and removed the carbs over the weekend. First task take a photo of the cable layout. The carbs came off surprisingly easily, but I found it easier disconnect one of the throttle cables at the handgrip.  



Here is the tank off to make sure all the cables etc go back in same place later..

Here they are, so far so good and thanks GSX for the tip about draining them first! When I took them apart, first thing I noticed before unscrewing anything was that the piston valve was sticking on carb#3 - it really didnt want to move. So I took out the diaphragm and gave everything a good clean using carb cleaner.  The slider valve did appear to have some grit but once cleaned moved as smoothly as al the others. Then I removed each float bowl, all very clean, but the float in carb #2 was noticeably higher than al the others. it is the blurry one in the distance:

reset it, cleaned all the jets (didnt touch the mixture) and re-assembled. All other carbs were cleaned and all heights OK.  Put evertything back together, including replacing the missing vent hoses etc (they are there for some reason, right?).  The trickiest part was reconnecting the throttle cables! Come the moment of truth, to my amazement she started first time and sounded great. Out for  a test drive and all good. The throttle twist grip had too much slack and I had forgotten to replace the tank gauge connector.  Both easy fixes.  Does she sound better? I think so, much more even on idle with none of the random increases and decreases in idle speed.  Phew!

Oh, - and the choke plungers all worked fine! I just couldn't see them without taking the carbs off.  One of the big hose clamps from the airbox was missing and the inlets were a bit cruddy so I wondered whether they were 100% air tight. So I took the opportunity of cleaning them to make a much smoother seal surface for the engine side hose / clamp.