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

[Denys]

18 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.  

yes, even if P.O. used colour tune to adjust pilot screws the idle was so rough when I bought the bike. I understood that sometimes pilot screw position shouldn't be the same for all four carbs, but how exactly can I understand how many turnovers should be for each carb to make idle not rough? I was trying a lot of different combinations but never had smooth idle.

Maybe pilot jets are clogged inside differently in each carb that's why I can't make idle smooth? When I was cleaning the carbs I was spraying carb cleaner through pilot jets and blew with compressed air. Maybe it is not enough to make them clean?  I've already ordered new pilot jets and pilot screws to close this question.

[wsn03]

3 minutes ago, Denys said:

yes, even if P.O. used colour tune to adjust pilot screws the idle was so rough when I bought the bike. I understood that sometimes pilot screw position shouldn't be the same for all four carbs, but how exactly can I understand how many turnovers should be for each carb to make idle not rough? I was trying a lot of different combinations but never had smooth idle.

Maybe pilot jets are clogged inside differently in each carb that's why I can't make idle smooth? When I was cleaning the carbs I was spraying carb cleaner through pilot jets and blew with compressed air. Maybe it is not enough to make them clean?  I've already ordered new pilot jets and pilot screws to close this question.

I soak my pilots in thinners every time - obviously taking them out to do it

[Denys]

28 minutes ago, wsn03 said:

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?

1. Yes they are cheap but haven't found any bad reviews about these coils

2. I've tried to disconnect the airbox from carbs and the result was exactly the same - rough idle

3. Maybe it will be enough just to get a new set of pilot screws and pilot jets but not hole carbs sets?

 

[wsn03]

1 minute ago, Denys said:

1. Yes they are cheap but haven't found any bad reviews about these coils

2. I've tried to disconnect the airbox from carbs and the result was exactly the same - rough idle

3. Maybe it will be enough just to get a new set of pilot screws and pilot jets but not hole carbs sets?

 

Did you take pilots out and look through them? You should be able to see right through them against a light

Edited April 8, 2021 by wsn03

[Denys]

1 minute ago, wsn03 said:

Did you take pilots out and look through them? You should be able to see right through them against a light

Yes, I took them out and was able to look through them against a light, but maybe it's not enough just to see light through them?

[wsn03]

30 minutes ago, Denys said:

Yes, I took them out and was able to look through them against a light, but maybe it's not enough just to see light through them?

I find thinners or something as strong is always required, you will be surprised how bigger the hole is after soaking in them. They could be partially blocked. I soak them in thinners overnight

[Denys]

14 minutes ago, wsn03 said:

I find thinners or something as strong is always required, you will be surprised how bigger the hole is after soaking in them. They could be partially blocked. I soak them in thinners overnight

That's exactly what I'm thinking, it is not enough just to have the hole in them but they should be ideally cleaned. Anyway I will try new pilot jets and screws and ignition unit (don't think the unit will somehow change the situation just bought from despair)

[wsn03]

I think what you are doing is right - you have to try all these things. Look at the difference between the new pilots and the old - hopefully the hole is bigger.

Maybe a Gunson colour tune would be a good idea - you can actually see your pilot is set up correctly, and they are quite cheap. Looking at them and reading the reviews I think I might set up my Bandit pilots with them.

[Gixer1460]

1 hour ago, Denys said:

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 

They may be good for older points style ignitions but not for transitorised modern types - I'd complain / send them back as not fit for purpose! 3.0 - 3.5ohms is about spot on although some have run Dyna Grey coils @ 2.2 ohms but not recommended with std electronics!

[TonyGee]

i use one of these, cheap as chips but work really good. i got this one given but they are plentiful on the bay. 

 

[Denys]

3 hours ago, Gixer1460 said:

They may be good for older points style ignitions but not for transitorised modern types - I'd complain / send them back as not fit for purpose! 3.0 - 3.5ohms is about spot on although some have run Dyna Grey coils @ 2.2 ohms but not recommended with std electronics!

How do you think, a little bit higher primary winding resistance could be the reason for rough idle, considering that secondary winding is exactly as it should be according to the manual?

[Denys]

1 hour ago, TonyGee said:

i use one of these, cheap as chips but work really good. i got this one given but they are plentiful on the bay. 

 

But on my gsx 750 inazuma aren't individual coils but two 'double-pin' coils, each for two cylinders, left coil for 1 and 4 cylinders, right for 2 and 3 cylinders.

[TonyGee]

13 minutes ago, Denys said:

But on my gsx 750 inazuma aren't individual coils but two 'double-pin' coils, each for two cylinders, left coil for 1 and 4 cylinders, right for 2 and 3 cylinders.

its not a coil  its an OTOSCOPE !!! 

Edited April 8, 2021 by TonyGee

[Gixer1460]

16 minutes ago, Denys said:

How do you think, a little bit higher primary winding resistance could be the reason for rough idle, considering that secondary winding is exactly as it should be according to the manual?

No Idea! - I've never used coils that far out of spec!

[Gixer1460]

1 hour ago, TonyGee said:

i use one of these, cheap as chips but work really good. i got this one given but they are plentiful on the bay. 

 

Which is - what? Looks like summat a doctor sticks in yer ear!

[wsn03]

1 hour ago, TonyGee said:

i use one of these, cheap as chips but work really good. i got this one given but they are plentiful on the bay. 

 

How does it work? Is it like the Gunsen, or better?

[TonyGee]

5 minutes ago, Gixer1460 said:

Which is - what? Looks like summat a doctor sticks in yer ear!

bang on, its fecking brilliant for looking into small jets and drillings.  

[Denys]

4 hours ago, wsn03 said:

I think what you are doing is right - you have to try all these things. Look at the difference between the new pilots and the old - hopefully the hole is bigger.

Maybe a Gunson colour tune would be a good idea - you can actually see your pilot is set up correctly, and they are quite cheap. Looking at them and reading the reviews I think I might set up my Bandit pilots with them.

Yes I'm ready to buy  Gunson colour but as I remember we have 10 mm spark thread, so I need to buy 10 mm thread adapter, right?

[Denys]

1 minute ago, Denys said:

Yes I'm ready to buy  Gunson colour but as I remember we have 10 mm spark thread, so I need to buy 10 mm thread adapter, right?

or this one should be fine? https://www.gunson.co.uk/product/G4172/Motorcycle-Colortune-Kit-10mm

[wsn03]

5 minutes ago, Denys said:

or this one should be fine? https://www.gunson.co.uk/product/G4172/Motorcycle-Colortune-Kit-10mm

Eblag and Amazon have them at half that price

[wsn03]

49 minutes ago, TonyGee said:

bang on, its fecking brilliant for looking into small jets and drillings.  

I got a jewellers viewing think, brilliant for stuff like jets

[Denys]

1 hour ago, TonyGee said:

its not a coil  its an OTOSCOPE !!! 

got it)

[Buzuki]

9 hours ago, Denys said:

3 full turns backwards

- That`s OK , but even with 1,5-2 full turns backward  your engine have to run at idle very smooth , 

- must admit that I was just once successfully repair those KeiHin CVK32 carbs on one B6  , reason of malfunction was bad float needle valves , those carbs leaking the fuel like crazy , any way just checked original B6 service manual (95-99 model) picture of CVK32 slow system schematic and on that picture tip of the pilot screw is showed flat with round inner surface of the carb throat , so I think maybe before you somebody inserted wrong type of pilots screws ? ,( from my experience by many Mikuni`s carbs from oil-cooled engines pilot screws tips never peek above inner surface of the carbs throat) ,

- further I will check with ohm-meter condition of spark plugs connectors since inside of each high voltage connector is hiding one around 10Kohm resistor ,

- question , did you check condition of O-rings which is hiding between each intake boot and cylinder head ?, since after 32.000Km and 12 years of old engine they can be in very bad condition causing false air to be sucked ruining engine idle ,

- and I guess that you close those four vacuum outlets with suitable rubber caps ? 

 

[Gixer1460]

2 hours ago, Denys said:

Yes I'm ready to buy  Gunson colour but as I remember we have 10 mm spark thread, so I need to buy 10 mm thread adapter, right?

Are you sure they are 10mm - most GSX / GSXR use 12mm plugs?

[Lachie04]

On 4/8/2021 at 9:48 AM, 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.

Measuring header temp is a quick hack to see carbs are set up close.

My dyno guy does it as a quick check prior to a dyno run.

They should all be relatively close

Can be used as a hack to adjust pilots also. I have a cheapo infra red to thermo to do quick checks

Colder temp = richer 

Richer carb settings run better as engine temp increases

Straight up Would seem # 4 is a bit richer or not as sync to the rest.

Pilots are not always set the same so slight differences are normal.

Ensure carbs are clean as and play close attention to syncing carbs first  syncing at 1500 -1800 rpm

Make sure all rubbers are intact including carb to airbox rubbers I once found one which was not sealing after regluing back in was fine I'd been trying to track down the cause for ages.

 

 

 

 

 

Edited April 9, 2021 by Lachie04