Idles with choke open but stalls on acceleration

[110%]

Hi everyone,
I had a problem just before winter with poor running on acceleration, and put it down to a faulty tps as I had the recounter fault showing with the counter flicking between 3 different positions. For about a year it was never caused a problem with the engine but in October with the poor running I decided to buy a second hand one and fit it to the bike. This didn't solve the poor running g on acceleration so I left it over winter and bought a brand new tps as the 2nd hand one also had resistances outside of the Haynes Manuel spec.

Having put the new one in yesterday along with a brand new air filter and new spark plugs, the problem persists. The engine idles with the choke on but when I open the throttle it stalls.

The vacuum of the carbs seems fine as I have a carb sync set, and there doesn't appear to be any leaks in the manifolds.

I think I know where my problem now lies, but I was hoping for some confirmation from people on here if you are kind enough to contribute to my problem solving.

Many thanks in advance.

Dave.

[darrsi]

Sounds like an air leak to me, are your carb rubbers in good nick?

[Fazerider]

Did you get your low voltage issue sorted?
Are you getting decent sparks? It's an easy check so long as you remember to let it jump to the cylinder head rather than the insulated cam cover.
Check the fuel level in the carbs. If none of those show a problem I'd guess it's a case of getting the carbs off for a good clean/blow-though of the jets and passageways.


Edit: does it "get through" the rough running at higher revs? If not, a faulty fuel pump/clogged filter may simply be causing fuel starvation.

[110%]

Carb rubbers are fine. I sprayed some carb cleaner over them with the engine running and there was no sudden rev from the extra fuel of the carb cleaner.

I was also thinking it might be the carbs need a full clean. All 4 cylinders are firing, so it's not the sparks or electrics.

I'll have to try pushing through to the higher revs. As soon as I was putting the throttle on it was instantly stalling.

(Fazerrider: The low voltage problem was solved by a new battery. This be has been expensive to maintain over the past few years!!)

[His Dudeness]

If it dies when you open the throttle but runs on choke it must not be getting enough fuel. I'd be leaning towards blocked jets. There's a pun in there somewhere Have you opened up the carbs and had a look at them yet?

[stevierst]

I'd second that about the carbs need a dig out. Even if it doesn't cure it, it's almost fee to do, and its probably not been done for a while.

[110%]

I've tried hammering on full throttle and it kills the engine completely. I'm guessing the fuel pump and fuel filter would be fine if it idles with the choke open.

I think I need to take the carbs out and see if the jets are blocked as I'm guessing if the idle jet is clear and air gets through with the choke open, but when the throttle opens it stalls, (and the air filter is brand new) it must be the main jets not supplying enough fuel.

Thanks very much for everyone's comments.
Last question before I take the carbs apart - are there any important gaskets/rings etc that need replacing on re-assembly if I'm stripping down the carbs?

[anutz]

About to do mine - never touched carbs before so also cautious - the new gaskets cost a lot - but I think you can salvage the ones that are there....

see my question earlier this week...

http://foc-u.co.uk/index.php/topic,16590.0.html

[darrsi]

I know it sounds daft,  but please check your fuel tap is fully open!

[anutz]

if it is open could a blocked fuel filter cause issues - not sure what would block it up so bad?

[darrsi]

if it is open could a blocked fuel filter cause issues - not sure what would block it up so bad?

If you've ever had water in your tank, via a leak around your petrol cap, then it's possible that rust could eventually clog up the fuel filter, but i would imagine that would cause below average performance rather than cutting out altogether.
Always worth changing though as they're very inexpensive and easy enough to fit.

[Fazerider]

Carb gaskets: I've always been able to re-use the big ones that seal the float bowls.


I have had an O-ring that seals the brass needle valve body fail, which caused a carb to flood. This doesn't sound like your problem, but if you're pulling them out for cleaning and inspection they may not survive re-insertion… it's best to replace. There are complete pattern kits of everything rubber (and the needle valve) for the float bowls available at about £18 per carb (don't bother to look at genuine Yamaha prices), but as the little O-rings are probably all you'll need you can get a universal assortment box for about £5.


Taking them on and off is a bit of a faff so if you've an extra length of petrol hose and a separate petrol reservoir, it's worth checking that the fuel levels are correct while the carbs are on the workbench.

[110%]

Thanks everyone.

The fuel tap is open - it is something I always forget to turn it back on after I take the tank off! I'm going to have a look at the fuel filter first following the comments from Fazerrider Darsi and Anutz.

I'll keep you posted!!!

[110%]

I've now bypassed the fuel filter and fired it up with the same problems. It's quite dirty so I'm going to replace it anyway but it isn't the cause of the problem. The fuel pump also appears to be working fine.

When I took the carbs off though there was some quite salty deposits around the insides of the carb rubbers.

<img src="http://foc-u.co.uk/MGalleryItem.php?id=2534" alt="" />

[darrsi]

I've now bypassed the fuel filter and fired it up with the same problems. It's quite dirty so I'm going to replace it anyway but it isn't the cause of the problem. The fuel pump also appears to be working fine.

When I took the carbs off though there was some quite salty deposits around the insides of the carb rubbers.

<img src="http://foc-u.co.uk/MGalleryItem.php?id=2534" alt="" />

I'd imagine over the years the airbox has breathed in moisture from either wet salty roads in winter, and could have even been owned by someone living by the sea before.
Nothing to worry about anyway.

[110%]

I'm going to give them a good clean but wouldn't have thought it was a major issue.

Top tip: When removing the carbs, it makes it much easier to release the 2 throttle cables at the handlebar end to give yourself even more slack in the cables at the carb end to remove them from the bracket.

[unfazed]

I've now bypassed the fuel filter and fired it up with the same problems. It's quite dirty so I'm going to replace it anyway but it isn't the cause of the problem. The fuel pump also appears to be working fine.

When I took the carbs off though there was some quite salty deposits around the insides of the carb rubbers.

<img src="http://foc-u.co.uk/MGalleryItem.php?id=2534" alt="" />

That is normal enough on a bike in the condition yours appears to be in the picture, clean them out with a vacuum cleaner and wipe them with WD40 which will make putting the carbs back on easier. Wipe the carb inlets the same way. To help putting them back on push back the airbox housing back as far as you can and tighten the 2 bolts. This stops the air box moving around when trying to refit the carbs

There is another inline filter where the petrol hose pipe fits on the centre carbs T piece. Be carefull removing it as the fitting between the carbs is plastic and you don't want to break it. See pic. This filter is usually forgotten, it just needs to be cleaned if it is dirty.
When cleaning the jets do not be tempted to poke steel wire through them, steel is harder then brass and can enlarge the jet, if crud needs to be dislodged use a bristle from a brass wire brush. I have found the cellulose thinners is good to clean the jets, but not for use on hands or rubber O rings. Remember to clean the emulsifier tubes also called the jet holders. On top of the emulsifier tube (jet holder) there is a seat which the needl goes through and is kept in position by the emulsifier tube( jet holder), it is a push fit, be careful it does not fall out with out you realising.

[110%]

Thanks for the reply unfazed. I think I've found my problem. There is a white goo in every float tray that's clogging the jets.

I think once these are all cleaned out it might work again!!

[unfazed]

Thanks for the reply unfazed. I think I've found my problem. There is a white goo in every float tray that's clogging the jets.

I think once these are all cleaned out it might work again!!

Taking the jets out to ensure they are clean will save taking the carbs off again.

Mosty likely a mixture of water and fuel, was the bike out in the weather or under a cover and idle for a while?

[110%]

Yeah I left it over the winter outside with a cover on. As it wasn't running well anyway I wasn't firing it up every few weeks like I normally would just to keep it in tune.

Carb 3/4 now. Ive got carb cleaner to clean all the jet etc and trying to do a decent job cleaning. I might have it sorted before sun down!

[110%]

I've finally got the carbs cleaned out and back on the bike with a new fuel filter for good measure. The carbs were tricky to get back in especially getting the throttle cables fixed again. It's very easy to get the accelerator cable caught around a lower connection on the carbs, so I would always advise to get the accelerator and decelerator cables connected before pushing and fixing the carbs back into the carb rubbers and air box.

On turning the ignition the fuel filter obviously kicked in and took longer than usual to stop pumping and then all it  took was a few cranks of the starter to get the fuel flowing through the system again, but once fired up it was roaring with the throttle open.

I've tried to attach some photos of the white gunk that had built up in the carbs. It was almost like the gelatin from a pork pie but not as tasty!

Details FZS600 clogged carb1

FZS600 clogged carb1

Details FZS600 clogged carb2

FZS600 clogged carb2

Thanks for everyones help and hopefully this post may help someone else in the future from a google search.

[anutz]

nice 

Need to do my carbs now...

[anutz]

Did you have any issues with the seals/gaskets - did you have to replace any?

[110%]

The carb gasgets looked fine and so I didn't need/want to replace them. I simply gave them a bit of a rub down with carb cleaner to get rid of any build ups.

The O-rings to the main jets I also left on as they were. They seemed like they were in good condition so again I didn't bother replacing them and soaked them carb cleaner with the jets.

If you're looking at taking your carbs apart soon, some of the screws were really tricky to remove without tearing the heads off, but a bit of WD40 left to soak and a knock with a hammer did the trick of loosening them.

[110%]

Also, as unfazed mentioned, don't use steel wire to poke gunk out of the holes in the jets. I snipped off some old electrical cable and used a strand of copper which is softer yet still rigid enough and therefore won't damage the jets.