Suzuki gsx750 inazuma rough/erratic idle. Please help! I've done almost everything

[Denys]

Hi guys, this forum is the last chance to resolve my issue. 

I have 1999 Suzuki gsx750 inazuma with 32k milage (in kilometers), more then half of a year and I can't resolve the problem of rough idle. 

Please take a look on a video:

https://www.dropbox.com/s/xm9ownr9fvlrump/VID_20210402_205138.mp4?dl=0

Here is the list of items which were already done:

Ignition:

• New sparks (NGK CR9EK)
• New original spark cups (9 K-ohms resistance) 
• Checked coils (Primary winding resistance:  left 4.1 Ohms, right-4.3 Ohms; Secondary winding resistance 32.5 K-ohms each.) Even was trying to install new coils they have the same resistanse.
• Checked ingition signal generator/pulse generator coil - 162 Ohms (135-200 in repair manual)
• The spark is on all four cylinders https://www.dropbox.com/s/09jml41y0n9y9dy/0-02-05-9b1b472ffba54a56580ed654e5776009138cabc9409e3322fa73950cf0371f45_97ec7a2_Trim.mp4?dl=0

Carburators Keihin CVK-32:

• Cleaned for two times with full disassembly (all jets and needles including pilot needle), blew with compressed air, 
• Checked float levels - 17 mm all four 
•  Synchronized carburators, also for two times https://www.dropbox.com/s/potyauzmixkk0d9/0-02-0a-804646e05081bcb88ff0a76937abc4ab6f34619a422933f7e15fe55e4424ac2a_4a61209e.mp4?dl=0
• Verified throttle position sensor (all metrics as it should be like in  repair manual)
• Was trying to adjust carbs with idle/pilot screw (was trying 2,2.1,2.5,3,3.5 turnovers) in general behavior was changing but erratic behavior when tachometer gauge arrow jump up and down is still there.
• All 4 diafragms without cracks

Compression

• All 4 cylinders have the same compression level - 11 points on hot engine https://www.dropbox.com/s/pj7rnm5gv90vyv7/hot.png?dl=0

Valve clearance

• Double cheked them, difference between cylinders maximum 0.01 mm
• Intake valves - 0.10mm
• Exhaust valves - 0.18mm

Was looking for air/vacuum leaks with "starter" spray like WD40:

• verified intake boots 
• carburators' vacuum caps and vaccum hose from 4tf carburator to fuel cock
• airbox rubbers (BTW if to spray "starter" liqud into the center line between two parts of the airbox revs started rising, is it normal? https://www.dropbox.com/s/d4f6mte5p0kvdan/2021-04-03_00-51-16.png?dl=0 )
• All fuel hoses are without visible leaks

Miscellaneous:

• Air filter is in stock and new
• Exaust is in stock
• Premium fuel 
• Tank is clean
• No any oil leaks
• New oil and oil filter

The problem is ONLY with idle, all other kinds of acceleration are good, start is good as well. The only one item which I haven't verified yet is the ignition unit.

One more thing, idle roughness depends on engine temperature, when oil tempreture is more than 120 Celsius idle fluttering is +-150revs, from 90 to 110 Celsius idle fluttering is 50-100 revs

PLEASE HELP ME!

Edited April 3, 2021 by Denys

[Captain Chaos]

Hi and welcome to OSS.

To be really sure the carbs are clean, have them ultrasonic cleaned.

 

[Captain Chaos]

and I moved this to oilcooled where it belongs.

[wsn03]

On 4/2/2021 at 11:39 PM, Denys said:

Hi guys, this forum is the last chance to resolve my issue. 

I have 1999 Suzuki gsx750 inazuma with 32k milage (in kilometers), more then half of a year and I can't resolve the problem of rough idle. 

Please take a look on a video:

https://www.dropbox.com/s/xm9ownr9fvlrump/VID_20210402_205138.mp4?dl=0

Here is the list of items which were already done:

Ignition:

• New sparks (NGK CR9EK)
• New original spark cups (9 K-ohms resistance) 
• Checked coils (Primary winding resistance:  left 4.1 Ohms, right-4.3 Ohms; Secondary winding resistance 32.5 K-ohms each.) Even was trying to install new coils they have the same resistanse.
• Checked ingition signal generator/pulse generator coil - 162 Ohms (135-200 in repair manual)
• The spark is on all four cylinders https://www.dropbox.com/s/09jml41y0n9y9dy/0-02-05-9b1b472ffba54a56580ed654e5776009138cabc9409e3322fa73950cf0371f45_97ec7a2_Trim.mp4?dl=0

Carburators Keihin CVK-32:

• Cleaned for two times with full disassembly (all jets and needles including pilot needle), blew with compressed air, 
• Checked float levels - 17 mm all four 
•  Synchronized carburators, also for two times https://www.dropbox.com/s/potyauzmixkk0d9/0-02-0a-804646e05081bcb88ff0a76937abc4ab6f34619a422933f7e15fe55e4424ac2a_4a61209e.mp4?dl=0
• Verified throttle position sensor (all metrics as it should be like in  repair manual)
• Was trying to adjust carbs with idle/pilot screw (was trying 2,2.1,2.5,3,3.5 turnovers) in general behavior was changing but erratic behavior when tachometer gauge arrow jump up and down is still there.
• All 4 diafragms without cracks

Compression

• All 4 cylinders have the same compression level - 11 points on hot engine https://www.dropbox.com/s/pj7rnm5gv90vyv7/hot.png?dl=0

Valve clearance

• Double cheked them, difference between cylinders maximum 0.01 mm
• Intake valves - 0.10mm
• Exhaust valves - 0.18mm

Was looking for air/vacuum leaks with "starter" spray like WD40:

• verified intake boots 
• carburators' vacuum caps and vaccum hose from 4tf carburator to fuel cock
• airbox rubbers (BTW if to spray "starter" liqud into the center line between two parts of the airbox revs started rising, is it normal? https://www.dropbox.com/s/d4f6mte5p0kvdan/2021-04-03_00-51-16.png?dl=0 )
• All fuel hoses are without visible leaks

Miscellaneous:

• Air filter is in stock and new
• Exaust is in stock
• Premium fuel 
• Tank is clean
• No any oil leaks
• New oil and oil filter

The problem is ONLY with idle, all other kinds of acceleration are good, start is good as well. The only one item which I haven't verified yet is the ignition unit.

One more thing, idle roughness depends on engine temperature, when oil tempreture is more than 120 Celsius idle fluttering is +-150revs, from 90 to 110 Celsius idle fluttering is 50-100 revs

PLEASE HELP ME!

It looks to me like you haven't done anything to check the needle float valves - they are a big fail point. They start leaking and over fuel the engine - this will be fine on open throttle, but poor on idle. 

What to do:

Put carbs in a biscuit tin or some sort of metal tray. Connect a remote fuel tank (e.g. from Demon Tweeks), note the level of fuel in the tank (I use masking tape) then turn on tap - leave for a couple of  hours, checking occasionally. If level is the same after that all good, if not you have leaking valves. I have seen new valves not start leaking until after 40 minutes?!? If they are shagged they will start leaking immediately, and petrol will start pissing out.

I buy Mikuni oem only, but some say Wemoto are good. All other aftermarket ones appear to be made of cheese.

Hope this helps - it is the first check I do on any carbs

 

 

[Denys]

On 4/5/2021 at 12:32 PM, wsn03 said:

It looks to me like you haven't done anything to check the needle float valves - they are a big fail point. They start leaking and over fuel the engine - this will be fine on open throttle, but poor on idle. 

What to do:

Put carbs in a biscuit tin or some sort of metal tray. Connect a remote fuel tank (e.g. from Demon Tweeks), note the level of fuel in the tank (I use masking tape) then turn on tap - leave for a couple of  hours, checking occasionally. If level is the same after that all good, if not you have leaking valves. I have seen new valves not start leaking until after 40 minutes?!? If they are shagged they will start leaking immediately, and petrol will start pissing out.

I buy Mikuni oem only, but some say Wemoto are good. All other aftermarket ones appear to be made of cheese.

Hope this helps - it is the first check I do on any carbs

 

 

In my original post is a row: "Checked float levels - 17 mm all four"

 

[wsn03]

2 minutes ago, Denys said:

In my original post is a row: "Checked float levels - 17 mm all four"

 

That's not the same thing I'm talking about - I'm talking about checking the needle float valves for leaks. You have to load them with fuel and make sure they don't flood. The machining on them is microscopic precision, so they wear and then fail, and that's when your problems start. They're also very expensive. 

On by Bandit 1200 they were fooked by about 9000 miles only. I noticed the oem replacements were quite different looking (clearly re-designed)

[Denys]

4 hours ago, wsn03 said:

That's not the same thing I'm talking about - I'm talking about checking the needle float valves for leaks. You have to load them with fuel and make sure they don't flood. The machining on them is microscopic precision, so they wear and then fail, and that's when your problems start. They're also very expensive. 

On by Bandit 1200 they were fooked by about 9000 miles only. I noticed the oem replacements were quite different looking (clearly re-designed)

Sorry, it's my bad, understood now, will do that check asap. How long should they stay with fuel pressure to check them for sure, about an hour or more? 

[wsn03]

30 minutes ago, Denys said:

Sorry, it's my bad, understood now, will do that check asap. How long should they stay with fuel pressure to check them for sure, about an hour or more? 

No worries. In all the ones I've tested the longest I ever found one hold out before leaking was 40 mins, most are pissing fuel out within 10 mins as the fuel fills the bowls then gets past the valve which is supposed to be a cut off. If leaking within 5 minutes this is your idling issue, it is over fueling when on tickover / low or no throttle. If like me you have gravity fuel tap that you forget to switch off, double trouble - diluted oil!!! Scary. I once found an airbox filled with petrol - took the lid off with a lit cigarette in my hand! I'd have lost all my bikes in that inferno, still scares me now. I always have a fire extinguisher since that episode. Plus I don't smoke

For anal retardedness like I suffer I actually go for overnight - I just like to know that gravity fed fuel was held at bay for a long time, even a tiny leak means the valves are on their way out, so no leak overnight means perfect.

Don't put too much fuel in your remote tank, if they are fooked it will make a mess.

This check should always be done on all carbs, these little valves work hard and when they fail they help to destroy engines by filling the crank with petrol - nightmare!

Good luck, hope it goes well

Edited April 6, 2021 by wsn03

[TonyGee]

what are the plugs doing ? are they getting wet or black and sooty ?  a sign of an over rich mixture caused by leaking float valves.  

[Denys]

23 hours ago, wsn03 said:

No worries. In all the ones I've tested the longest I ever found one hold out before leaking was 40 mins, most are pissing fuel out within 10 mins as the fuel fills the bowls then gets past the valve which is supposed to be a cut off. If leaking within 5 minutes this is your idling issue, it is over fueling when on tickover / low or no throttle. If like me you have gravity fuel tap that you forget to switch off, double trouble - diluted oil!!! Scary. I once found an airbox filled with petrol - took the lid off with a lit cigarette in my hand! I'd have lost all my bikes in that inferno, still scares me now. I always have a fire extinguisher since that episode. Plus I don't smoke

For anal retardedness like I suffer I actually go for overnight - I just like to know that gravity fed fuel was held at bay for a long time, even a tiny leak means the valves are on their way out, so no leak overnight means perfect.

Don't put too much fuel in your remote tank, if they are fooked it will make a mess.

This check should always be done on all carbs, these little valves work hard and when they fail they help to destroy engines by filling the crank with petrol - nightmare!

Good luck, hope it goes well

Was trying today to test needle float valves, left carbs under fuel pressure for 3 hours but haven't found any leaks, the level of fuel in the tank remained the same, so unfortunately all 4 valves look good. Another issue that I found out is that the temperature on the header pipes is different for all four cylinders. For instance: 1 - 65°C, 2 - 71°C, 3-86°C, 4-56°C, is it normal behavior? I've already ordered a set of pilot jets and pilot screws. I tried to take macro photos of pilot screws inside of carbs and one of them is a little bit smashed in the end, don't know if it can somehow affect idle revs.

[Denys]

23 hours ago, TonyGee said:

what are the plugs doing ? are they getting wet or black and sooty ?  a sign of an over rich mixture caused by leaking float valves.  

The plugs are doing good, all are dry and not black. In general, each of them looks like a new plug.

[Buzuki]

1 hour ago, Denys said:

Was trying today to test needle float valves, left carbs under fuel pressure for 3 hours but haven't found any leaks, the level of fuel in the tank remained the same, so unfortunately all 4 valves look good. Another issue that I found out is that the temperature on the header pipes is different for all four cylinders. For instance: 1 - 65°C, 2 - 71°C, 3-86°C, 4-56°C, is it normal behavior? I've already ordered a set of pilot jets and pilot screws. I tried to take macro photos of pilot screws inside of carbs and one of them is a little bit smashed in the end, don't know if it can somehow affect idle revs.

Strange picture , since usually tip of the pilot screw don`t peek outside in the carburetor throat ,

question , how many turns backwards you turned each pilot screw from fully closed top position ? 

[Denys]

9 hours ago, Buzuki said:

Strange picture , since usually tip of the pilot screw don`t peek outside in the carburetor throat ,

question , how many turns backwards you turned each pilot screw from fully closed top position ? 

3 full turns backwards

[wsn03]

52 minutes ago, Denys said:

3 full turns backwards

So all screws turned out the same then. I have 2.5 on my 750 F and Bandit 1200. Is 3 too rich or the norm for your model?

Have you checked valve clearances? Critical.

When I had a surging problem it was an airleak, I actually eventually found it was caused by a screw for the scottoiler coming loose (fucktard who put in did it with pliers, idiot).

My other port of call - Coils.

I only have experience of Slabbies - my GSXR 750 F ran like a pig until I fitted aftermarket coils and leads - DYNA in my case, but I hear mixed things about them these days - the slabbie coils are known to fail, is that the same for your model?

Also have you balanced the carbs? That will really affect things, they go out of balance quickly.

I don't know what to make of your photo. My concern is any air getting past the pilot more than allowed by normal?

Sorry I haven't been back through your original post, just trying to go through the obvious.

 

Edited April 8, 2021 by wsn03

[Denys]

28 minutes ago, wsn03 said:

So all screws turned out the same then. I have 2.5 on my 750 F and Bandit 1200. Is 3 too rich or the norm for your model?

Have you checked valve clearances? Critical.

When I had a surging problem it was an airleak, I actually eventually found it was caused by a screw for the scottoiler coming loose (fucktard who put in did it with pliers, idiot).

My other port of call - Coils.

I only have experience of Slabbies - my GSXR 750 F ran like a pig until I fitted aftermarket coils and leads - DYNA in my case, but I hear mixed things about them these days - the slabbie coils are known to fail, is that the same for your model?

Also have you balanced the carbs? That will really affect things, they go out of balance quickly.

I don't know what to make of your photo. My concern is any air getting past the pilot more than allowed by normal?

Sorry I haven't been back through your original post, just trying to go through the obvious.

 

I was trying different variants of pilot screw adjusting - 2,2.1,2.5,3,3.5 turnovers, in any of those pilot position idle erratic behavior, was there. I've checked all those items, if you have a minute please take a look at my original post, thanks.

[wsn03]

You mentioned you were trying to change coils.

Are coils a weak spot on yours? I presume they must be as I guess your bike is pre-GSXR F.

Did you try different coils? 

My concern with the crap coils is they change behaviour as you are riding around on them - that's what happened with me. I presume your readings in that case might not mean a whole lot

[Denys]

11 hours ago, Buzuki said:

Strange picture , since usually tip of the pilot screw don`t peek outside in the carburetor throat ,

question , how many turns backwards you turned each pilot screw from fully closed top position ? 

'since usually tip of the pilot screw don`t peek outside in the carburetor throat' - are you sure about that? Look how pilot screws were peek outside as soon as I took off the carburetors from motorcycle, someone who owned motorcycle before me set pilot screw differently for all 4 carbs: 2.5, 2.1 , 2.5, 2.7 

Edited April 8, 2021 by Denys

[wsn03]

If it was me I'd want a decent set of new coils - DYNA preferably - it cured my erratic idling.

[wsn03]

5 minutes ago, Denys said:

'since usually tip of the pilot screw don`t peek outside in the carburetor throat' - are you sure about that? Look how pilot screws were peek outside as soon as I took off the carburetors from motorcycle, someone who owned motorcycle before me set pilot screw differently for all 4 carbs: 2.5, 2.1 , 2.5, 2.7 

I've always known them to need to be the same

[wsn03]

On 4/2/2021 at 11:39 PM, Denys said:

 

 

• airbox rubbers (BTW if to spray "starter" liqud into the center line between two parts of the airbox revs started rising, is it normal? https://www.dropbox.com/s/d4f6mte5p0kvdan/2021-04-03_00-51-16.png?dl=0 )
•  

Whoaoh! Somethings wrong there. The revs changing. Not good. So that box leaking is causing a surge of air. Can you seal it?

Edited April 8, 2021 by wsn03

[Denys]

10 minutes ago, wsn03 said:

You mentioned you were trying to change coils.

Are coils a weak spot on yours? I presume they must be as I guess your bike is pre-GSXR F.

Did you try different coils? 

My concern with the crap coils is they change behaviour as you are riding around on them - that's what happened with me. I presume your readings in that case might not mean a whole lot

Yes, I was trying new coils, bought them here  https://www.Eblag.com/itm/IGNITION-COIL-FOR-SUZUKI-33410-03F00-33410-19C00-33410-19C01-REPLACEMENT/254520491038 I wasn't riding on them a lot, just did short 100 meters ride and understood they are exactly the same as old coils. BTW old coils and new coils have primary winding resistance a liitle bit more that they should accordingly to manual. For instance in manual resistance of primary winding should be from 2.0 to 4.0 ohms at 20 °C, but my old coils have 4.1/4.3 and new coils even more 4.6/4.7 ohms. Can't understand why new coils don't show resistance from 2.0 to to 4.0 ohms 

[wsn03]

7 minutes ago, Denys said:

Yes, I was trying new coils, bought them here  https://www.Eblag.com/itm/IGNITION-COIL-FOR-SUZUKI-33410-03F00-33410-19C00-33410-19C01-REPLACEMENT/254520491038 I wasn't riding on them a lot, just did short 100 meters ride and understood they are exactly the same as old coils. BTW old coils and new coils have primary winding resistance a liitle bit more that they should accordingly to manual. For instance in manual resistance of primary winding should be from 2.0 to 4.0 ohms at 20 °C, but my old coils have 4.1/4.3 and new coils even more 4.6/4.7 ohms. Can't understand why new coils don't show resistance from 2.0 to to 4.0 ohms 

I know nothing about those coils, the only make I know people recommend is DYNA coils - that is what I have. However they did have some problems when production went to China, don't know if this is ok now. 

[TonyGee]

the coils on the zuma are the same as the bandits, in all my years owning bandits and also working on them ive never had to change a coil !!! they are normally pretty reliable.  sometimes you can feel the tip of the mixture screw poking out into the bore of the carb, also if the screws where all at different settings i wonder if the P.O. used a colour tune ? setting all the screws exactly the same doesn't mean its perfect to each carb.  

[wsn03]

So 3 possible issues:

 

1. Coils - are your aftermarket ones any good? ACTION - try to research reviews on the coils you bought, do seem a bit cheap to me!

2. You have a leaking airbox, not sure why it should cause a change in performance as its before the filter, but it is when you spray it.  Action - To me then that needs sealing before you do anything else

3. There is a question mark over your pilot / damage where it is screwing into. That will cause excess air leak which will mess up everything. Action - Can you get another set of carbs?

[wsn03]

3 minutes ago, TonyGee said:

the coils on the zuma are the same as the bandits, in all my years owning bandits and also working on them ive never had to change a coil !!! they are normally pretty reliable.  sometimes you can feel the tip of the mixture screw poking out into the bore of the carb, also if the screws where all at different settings i wonder if the P.O. used a colour tune ? setting all the screws exactly the same doesn't mean its perfect to each carb.  

I used a colourtune, in the end I set screws the same. Perhaps I should have persisted, got quite tired of the thing to be honest! Your theory makes sense though