Balancing carbs and adjusting idle

[Omegasteve]

Hi all!

I'm very happy that I've managed to get the bike actually started and able to run to a degree. Now I've borrowed a CarbTune off of a very nice gent and set about balancing my carbs (GSXF600 1994). I have an issue that I can't seem to resolve though. I can get it to start (not reliably though) and then run but I cant get the idle below 2k rpm without it stalling. Each time it stalls it won't restart at all unless I use a very small spray of easy start.

Once it starts again it will once again happily run and rev, but only with the high idle.

Any tips on where to start?

[wraith]

Pilot jets need a clean or are not set right.

[Omegasteve]

2 hours ago, wraith said:

Pilot jets need a clean or are not set right.

Thanks mate, so I know the jets are as clean as I can get them. And blown through with carb cleaner and pressurised air.

I've set the pilot screws to 1.5 turns out as per the manual settings and have also tried them at 1.75 turns too with no change at all. Should I go more than this? I'm under the assumption it's not getting enough fuel as the easystart works. 

[imago]

With modern fuels and the residues they leave you'll need to get the carbs ultrasonically cleaned in a heated unit. It's the only thing that'll take care of the crap in small drillings, especially the blind ones.

[wraith]

Are all the very small passageway are clear and clean to the pilot jets ? 

Have you set the float height right?

 

[Omegasteve]

1 hour ago, wraith said:

Are all the very small passageway are clear and clean to the pilot jets ? 

Have you set the float height right?

 

Everything has been blown through and I bought a carb cleaning brush set which I have passed through all the passageways to the best of my ability.

Float height are set to 13mm currently (manual states 14mm +/-1mm) and the bowls seem to be filling well.

[davecara]

Have the carbs been through an ultrasonic bath @Omegasteve? 
No amount of carb cleaner or compressed air will clean the pilot circuits properly

[Omegasteve]

43 minutes ago, davecara said:

Have the carbs been through an ultrasonic bath @Omegasteve? 
No amount of carb cleaner or compressed air will clean the pilot circuits properly

No they haven't, I was hoping that maybe they didn't need anything quite like that and it was maybe something a bit more simple that I could maybe try at home first before having to fork out for that on the off chance it works.

[Omegasteve]

I have boiled all the metal parts in a lemon juice/water mix that was recommended on a lot of other forums and that did remove a lot of crud from them though and on reassembly it finally actually started so that definitely worked to a degree.

[davecara]

I’ve got an ultrasonic bath you can use if you need 

[Omegasteve]

8 minutes ago, davecara said:

I’ve got an ultrasonic bath you can use if you need 

That's awesome! Out of curiosity, what are the small black rubber bungs for that sit in the bottom of the pilot jet hole?

[TonyGee]

11 minutes ago, Omegasteve said:

That's awesome! Out of curiosity, what are the small black rubber bungs for that sit in the bottom of the pilot jet hole?

not sure about your carbs but some have the pilot jet tube plugged as the fuel will come up through the main jet tube as their is a drilling that goes from the main jet tube to the pilot jet tube.  it that makes sense to you  

[wraith]

The pilot jet system is a manger pain to clean, before I got my Ultrasonic bath, I've had carbs off 4 or 5 times to give them another clean before I get things working.

[Omegasteve]

7 hours ago, TonyGee said:

not sure about your carbs but some have the pilot jet tube plugged as the fuel will come up through the main jet tube as their is a drilling that goes from the main jet tube to the pilot jet tube.  it that makes sense to you  

Is it worth a try removing the bungs? Would that even work? In case that drilling between the main and pilot is blocked? 

[Lachie04]

The bungs are there as the gsxf carbs have an additional flow path for fuel compared to gxsr carbs the bungs should be there. Not to sure to what effect they will affect the carbs though but limits the fuel uptake through the jet in favor of the additional fuel circuit that enters the jet half way up fromthe main jet side (like he said)

Edited December 11, 2022 by Lachie04

[Omegasteve]

10 minutes ago, Lachie04 said:

The bungs are there as the gsxf carbs have an additional flow path for fuel compared to gxsr carbs the bungs should be there. Not to sure to what effect they will affect the carbs though but limits the fuel uptake through the jet in favor of the additional fuel circuit that enters the jet half way up fromthe main jet side (like he said)

That's mega helpful! From the pictures it looks like those have a hole in the bung? The ones in mine are just solid with no hole or anything. Is that correct?

[Lachie04]

No there is no hole it's just moulded that way only an indent

[Omegasteve]

7 minutes ago, Lachie04 said:

No there is no hole it's just moulded that way only an indent

Okay perfect thank you 

[TonyGee]

3 hours ago, Omegasteve said:

Is it worth a try removing the bungs? Would that even work? In case that drilling between the main and pilot is blocked? 

I wouldn't remove the bung but not sure on the effect if they are removed ?   I have a set of carbs from a 1979 bike and they have a threaded screw instead of a rubber bung, my guess is it would be cheaper to use a rubber bung than a steel screw.  the drilling between the main jet and the pilot jet is easy to get to and clean out if its blocked.  

[Omegasteve]

18 minutes ago, TonyGee said:

I wouldn't remove the bung but not sure on the effect if they are removed ?   I have a set of carbs from a 1979 bike and they have a threaded screw instead of a rubber bung, my guess is it would be cheaper to use a rubber bung than a steel screw.  the drilling between the main jet and the pilot jet is easy to get to and clean out if its blocked.  

Just had the bowls off and the drillings seem clear, I've blown them through and pushed some very thin wire through them too. 

[Dezza]

Boiling the carbs in lemon juice will help with the cleaning but if the juice solution is too concentrated and / or this is done for too long, the citirc acid in the juice (the active ingredient here) will very efficiently remove the zinc plating from the steel parts of the carbs. Citric acid is also a good rust remover, especially from chromed bits and is easly available in powdered form as a food additive (1 teaspoon = juice from 1 lemon).

Soaking carbs in a solution of acetone mixed with cellulose thinners will remove fuel 'varnish' from carbs but it will knacker quickly any rubber or plastic bits left in. As said above though, the recent proliferation of affordable ultrasonic cleaners is a godsend.

[Omegasteve]

Okay, so removing the bungs has made absolutely no difference to its inability to start under its own fuel supply.

[Buzuki]

It is important that those four small rubber bungs (plugs) to stay in the original positions to seal against false fuel flow , but over the years and with those modern fuels they become hard and loose the original seal function , couple years ago I have successfully replaced them with precise machined four small brass plugs and that set of carburetors become again OK ,

for correct operation of your set of carburetors is also very important to check and replace all others rubber parts !, mainly O-rings .

Edited December 11, 2022 by Buzuki

[Omegasteve]

So after some more fucking about I think it's finally time for me to just suck it up and check valve clearances.

I've tried plenty of different approaches and it will not reliably start when cold. Sometimes it will after a lot of cranking, sometimes fuck all until the battery runs dead.

It will ALWAYS start with a quick spray and then it will run with a high idle for ages. 

Once warm I am able to switch it off and on at will, as long as its pretty soon after turning off.

If left off for any period of time between maybe 2 hours to overnight it will then not start again.

My belief here is that when warm the clearances are tighter and allowing it to start, then once it cools and the clearances open again it then refuses to start.

The easy start is bypassing this as it's so flammable it doesn't need the same compression that petrol/air does to ignite.

[coombehouse]

On 12/12/2022 at 3:11 PM, Omegasteve said:

So after some more fucking about I think it's finally time for me to just suck it up and check valve clearances.

I've tried plenty of different approaches and it will not reliably start when cold. Sometimes it will after a lot of cranking, sometimes fuck all until the battery runs dead.

It will ALWAYS start with a quick spray and then it will run with a high idle for ages. 

Once warm I am able to switch it off and on at will, as long as its pretty soon after turning off.

If left off for any period of time between maybe 2 hours to overnight it will then not start again.

My belief here is that when warm the clearances are tighter and allowing it to start, then once it cools and the clearances open again it then refuses to start.

The easy start is bypassing this as it's so flammable it doesn't need the same compression that petrol/air does to ignite.

I can't see valve clearance causing that though I could be wrong. It certainly wouldn't make it idle high. The most likely is still an airleak at the carb rubbers or a blockage internally in the carbs