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Landyman |
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Landyman Derestricted Danger
Joined: 20 Feb 2024 Karma :
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Posted: 11:03 - 20 Feb 2024 Post subject: 2002 Suzuki GSX750f acceleration problem |
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Hi.
I need some help and advice with a continuing problem with my 2002 Suzuki GSX750f . I have reset the tappets, renewed the carb diaphragms, replaced the float bowl seals, clean the jets, checked the float settings, reset the pilot to factory, checked the ignition coils resistance and the TPS settings. All of the hoses are leak free, the carbs have been balanced using a Multi-Tune Pro Manometer and the battery is full and happy.
The bike starts on choke and ticks over without a problem, once warm the engine fires up on the button and the rev range is great..... UP TO 5000 RPM after which it starts to die, cough and if I do manage to get it further up the scale, it won't/can't rev beyond 7000 RPM. The motor is sweet as a nut on the low rev range and the individual cylinders test out at 160/170 with a proper compression tester (Snap-On). I have tried all the test fixes such as spraying easy start into the carb mouths when accelerating, pulling on the choke, tightening all hose fixings and clamps, cleaning the timing points, checking and cleaning all electrical connections, replacing the spark plugs with new and checking for leaks on headers and exhaust. ALL TO NO AVAIL!!
I'm a retired engineer (mechanical and on the spanner type) but this has me pulling my hair out, I have had bikes and cars all of my adult life but with this I am struggling, can anyone out there help PLEASE?
Kind Regards. |
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that_impulse_guy |
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that_impulse_guy Scooby Slapper
Joined: 07 Mar 2023 Karma :
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Posted: 11:13 - 20 Feb 2024 Post subject: |
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weirdly enough, a good friend of mine has a 750 teapot that does exactly this. We've been troubleshooting it for ages.
Done what you did+fuel tap. Once its back on the bench, best we could figure out is that it has a k+n so we may go play with some jetting. It seems to go above 7k on smaller throttle opening if you go slowly with the throttle (our one), but wont go there on full throttle ____________________ Gone: Yamaha DT50lc, Suzuki DR500, Suzuki A100, Kawasaki z250ltd, RD350YPVS, Suzuki DR Big, Kawasaki AR125, Kawasaki KMX200, Suzuki GS1000S, Katana 1100, GS550M, Suzuki RGV250
Now: Suzuki GSX400X, Suzuki RF900R, NS400R |
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Nobby the Bastard |
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Nobby the Bastard Harley Gaydar
Joined: 16 Aug 2013 Karma :
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MarJay |
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MarJay But it's British!
Joined: 15 Sep 2003 Karma :
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Landyman |
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Landyman Derestricted Danger
Joined: 20 Feb 2024 Karma :
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MarJay |
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MarJay But it's British!
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Landyman |
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Landyman Derestricted Danger
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Robby |
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Robby Dirty Old Man
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Landyman |
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Landyman Derestricted Danger
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Easy-X |
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Easy-X Super Spammer
Joined: 08 Mar 2019 Karma :
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Posted: 17:03 - 20 Feb 2024 Post subject: |
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Some sort of timing issue? I know on the old bikes I've worked on the points have a spiny-weight system that mechanically advances/retards the timing based on RPMs. Dunno what the equivalent would be on a (relatively) newer bike
I only say this as it vaguely sounds like the wall the 50cc scooter bois try to break through on a regular basis. ____________________ Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter |
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Landyman |
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Landyman Derestricted Danger
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stinkwheel |
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stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
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Posted: 19:46 - 20 Feb 2024 Post subject: |
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Air filter in good order? Just because you didn't mention having checked it.
What you describe sounds exaclty like what happened to a GPZ500 of mine when it ate its own air filter which had been disgustingly manky, I suspect it was the original factory one and the engine finally had enough and sucked all the foam through the mesh and through the engine. (this was a bike sold to me as freshly serviced).
Anyway, that is bye-the bye. New filter fitted and it hit a brick wall at about 6k rpm. You could pull through it eventually and it went suitably batshit if you could get the revs up to 8k. Not ideal for riding because you were either bimbling or thrashing it about flat-out.
The eventual diagnosis was blocked power jets in the carb, they had filter foam lodged in them. These are the little brass jets mounted round the edge of the carb facing back towards the air filter. They bleed more fuel into the system at specific midrage revs before you are fullly onto the main jet and needle. They aren't removable and are jetted internally in the carb. I cleared them by a combination of compressed air applied directly to them and careful poking through with nylon fishing line.
Looks like your carbs have them, may be worth a look. They may even be removable on yours. ____________________ “Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles. |
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Landyman |
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Landyman Derestricted Danger
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stinkwheel |
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stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
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Posted: 21:07 - 20 Feb 2024 Post subject: |
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Mixture screws are for idle. They do nothing at all much above 1/4 throttle.
You are talking midrange which is mostly throttle valve cutaway, needle jet and throttle needle position and taper... If it's a carb problem at all.
If it starts and idles and trundles around a carpark, stop messing with the slow running circuit, it's not that. ____________________ “Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles. |
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Landyman |
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Landyman Derestricted Danger
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MarJay |
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MarJay But it's British!
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Robby Dirty Old Man
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WD Forte World Chat Champion
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MCN Super Spammer
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Landyman Derestricted Danger
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sickpup Old Timer
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Landyman |
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Landyman Derestricted Danger
Joined: 20 Feb 2024 Karma :
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Posted: 09:31 - 25 Feb 2024 Post subject: |
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Hello Again and Thank You for your response.
As Previously posted, the carbs are now totally stripped and have hade the most rigorous cleaning you could imagine. The emulsion tubes, main jets, choke jets, pilot screws and pilot jets have all been removed,soaked in carb cleaner, polished and checked for size. The float chambers have been cleaned and the needles have all been stripped and checked for wear. Following this, everything has been blown through with compressed air and anything brass has been polished. I have ordered new main117.5 jets and a complete set of o-ring seals together with new inlet boot 0-rings. To be further sure, I have constructed a small 'goal-post' gauge with a crossbar hight of 13mm so that I can be assured all of the float levels are set bang on. The exhaust is original, the bike is a UK model and all of the resistances are to spec as issued in Haynes Manual.
I will hopefully have it all back together early in the week,I have changed oil and filter just to ensure that everything that moves is getting the best I can give. As a temp measure I have sprayed all of the HT leads, coils and plug tops with silicon spray to provide a temporary seal against leakage, the next spend, should what I have done fail, will be two new coils and four new plug caps.
Watch this space!!!!!
Kind Regards |
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Landyman |
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Landyman Derestricted Danger
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Landyman |
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Landyman Derestricted Danger
Joined: 20 Feb 2024 Karma :
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Posted: 08:09 - 26 Feb 2024 Post subject: |
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Good Morning
I think that we must have almost exhausted this topic without coming out with a definitive solution that will get me running as should best, here is my latest post to try and explain what is happening and is aimed at the more senior end of the audience. If you remember the days before electronic ignition, computer controls and fuel injection, you will understand what I am trying to say what is happening. In those days the ignition system was a feed through the coil which, via low and high tension leads then fed the distributor which in turn through the action opening and closing points provided the spark to each cylinder, usually in the firing order 1-3-4-2. The whole sequence was kept in balance by a little silver cylinder wired into the points known as the condensor which, when it failed, caused the spark to become erratic, resulting in loss of power under acceleration accompanied by backfiring as unburnt fuel was intermittently fire. The condenser was a quick fix at around £2.00p but, when it went wrong, it stopped the show.
These are the symptoms I am suffering with my bike! By weekend I will have it all back together and will, I would like to think, be able to provide a positive out come however, I'm not holding my breath.
Kind Regards |
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Nobby the Bastard |
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Nobby the Bastard Harley Gaydar
Joined: 16 Aug 2013 Karma :
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