GSXR400 not running right?

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Goatfan46
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GSXR400 not running right?

Post by Goatfan46 » Thu Jul 04, 2019 11:50 am

Hi everyone, bought myself my first Gixxer...., as a project. It is a 1988 GSXR400 GK73A model. It starts...., but is reluctant to idle with the choke off, even when warmed up.......also it bogs down and cuts out when you "blip" the throttle......it will only rev up.....if you open the throttle very gently.
The guy I bought it off was honest about this and said the carbs probably needed new "O" rings and setting up again properly?.
I have taken the carbs apart, and from what I can see, the O rings are not stretched/broken, or brittle?.....they seem to be okay?. TELL TALE signs on the screwdriver slots on the jets suggest they have been in and out several times. I was thinking that the logical thing to do first is to put a new set of pilot and main jets in before I re-assemble the carbs and try and run the bike again. Can Anyone tell me what are the correct "stock" jets for this bike. The bike is pretty original and has a stock exhaust system on it....,so I assume it should therefore also need stock carb jets?.
As I am a newbie.......ALL advice and infor gratefully appreciated

mechannibalism
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Re: GSXR400 not running right?

Post by mechannibalism » Thu Jul 04, 2019 5:31 pm

Put new orings in anyway, try Litetek.co . Things you want to check- fuel filter above petcock, - carb to head rubber connectors, cracks are an indicator they are gonners the engine will never idle right when gone.-Crimped fuel hose. Let us know how it goes.

moforockband
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Re: GSXR400 not running right?

Post by moforockband » Thu Jul 04, 2019 10:49 pm

Good advise^^ check the plugs and compression 1st. If the engines below 150 psi it will never idle properly. CR9EK is the plug you want.
Also check the carb balance, and for air leaks as mentioned.
Put the carb pilot screws at 2.5 turns out.

Goatfan46
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Re: GSXR400 not running right?

Post by Goatfan46 » Fri Jul 05, 2019 4:43 pm

Thanks for the replies guys all info really appreciated......can anyone actually tell me what model of carbs are on my bike....may sound daft I know but as I said Im new to the biking world......All I know is that they are Mikuni and have flat slides fitted.....once I know what I'm actually working with, I can maybe start ordering the correct o ring and jet kits etc??? :?:

Goatfan46
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Re: GSXR400 not running right?

Post by Goatfan46 » Fri Jul 05, 2019 4:49 pm

Did you mean the mixture srew?.....or the pilot jet situated in the float bowl?

moforockband
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Re: GSXR400 not running right?

Post by moforockband » Mon Jul 08, 2019 9:57 am

yeah the mixture screw, leave the pilots alone, make sure they are clear though.
It sounds like you may be trying to rev it without the airfilters off, as it will not run unless the airbox is fitted. (Have fun putting that back on :D)

Your carbs are BST32/33 Constant velocity carbs and not flatslide. Although the cv slide itself is flat, we tend to call FCR Keihin race carbs 'Flatslide', and they cost big money.
Ping me a PM if you need help, always happy to assist.

Goatfan46
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Re: GSXR400 not running right?

Post by Goatfan46 » Mon Jul 08, 2019 6:10 pm

Thanks a bunch for you help in all respects ....I cant tel you how grateful I am...........What a dumbo......I thought that as the Diaphram had sort of FLAT winglets on them.....they were flat slides!!!!!......hey.....learning all the time......AND YES.......I WAS trying to run it with the airbox off!!!!!......I will let you know how I get on.....when a few new bits arrive for the carbs........but THANKS AGAIN MATE.
BTW.....next question........I was thinking of doing away with the stock airbox, and maybe putting individual POD filters on each carb???.....IF I do....will it make any difference the the "jetting"?

moforockband
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Re: GSXR400 not running right?

Post by moforockband » Mon Jul 08, 2019 9:48 pm

I'd get it running on the airbox 1st. See my thread on pods. It will make the bike a bit more of a pain on the road, but is great for performance.
You will need bigger (128 dynojet main jets on my bike) , and different main air jets to stop it running too rich at the top end.
Be aware that if you don't use the correct technique and the perfect fitting screwdriver you will damage your carbs getting the air jets out.

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Re: GSXR400 not running right?

Post by Goatfan46 » Wed Jul 31, 2019 8:05 am

Hi once again to everyone who has replied, and given me great advice. I can't thank you enough. OKAY..... since my last post, a fair bit of progress has been made (I think?).....all the service bits arrived.....carbs all stripped...cleaned etc etc...... I ran the bike for the first time yesterday and after a bit of jiggery pokery with some adjustments I have arrived at this point.
When I bought it....it would not idle without bags of choke......and it pretty much cut out when you blipped the throttle.
Now.....It feels pretty responsive the "throttle blip"......but idle is not quite there yet......It doesn't seem to like me taking the last "quarter" of choke off....it dies.....I have tried to strike a balance by trying to increase the "idle speed" adjuster up a bit....but is still doesnt like me taking off that last bit of choke?. I am still rumning stock jets. I have had various suggestion about mixture screw adjustment.....from 1 3/4..... to 2.5 turns out. To strike a happy medium to start off with I set them at 2 turns out......and because it still seems to need choke...I turned them all back in to 1 3/4...whick DID seem to help a bit.
I havent tried to balance the carbs yet....as I don't have any guages at the moment. I think I'm nearly there guys?.....,but can anyone suggest what I might still need to do (or try).....to get that final happy medium, so that it will idle without choke????
Again THANKS for all the help so far guys


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