Posted March 1, 200816 yr after posting in the wrong place here I am again PROBLEM-- deep hole in power at 4000 bike just dies- BLERUGH! then takes off at about 5000 and runs ok the problem is a ongoing one Ihave replaced the emulsion tubes and am running Dyno Jet needles and K&N air filter Ihave checked the ex-up it seems to be ok ANY IDEAS ? OH SHES DONE 45000MILES NICELY RUN IN WHAT?
March 1, 200816 yr Think it might be a advance/retard ignition problem. If you cannot find anything with the fueling then it must be ignition.
March 2, 200816 yr Author Think it might be a advance/retard ignition problem. If you cannot find anything with the fueling then it must be ignition. thats the next step I need to borrow a CDI and I know a man who has one!
March 3, 200816 yr after posting in the wrong place here I am again PROBLEM-- deep hole in power at 4000 bike just dies- BLERUGH! then takes off at about 5000 and runs ok the problem is a ongoing one Ihave replaced the emulsion tubes and am running Dyno Jet needles and K&N air filter Ihave checked the ex-up it seems to be ok ANY IDEAS ? OH SHES DONE 45000MILES NICELY RUN IN WHAT? hi before changing your cdi unit check all your jets are clear and that they are the right size ? and try moving the needle jet up and down one notch from where it is now to see if it makes any difference !
March 4, 200816 yr Author Ive had the carbs apart so many times its driving me mad! If you looked at the emulsion tubes with a magnifying glass you could see they were out of round due to the needles wearing the front edge likewise the needles were also worn on the leading edge, according to everyone I spoke to said this was the problem as the fuel flow was erratic and unmetered as the needles rose in the tubes . So I changed both parts £14 quid each for the emulsion tubes OUCH !!! Plus dyno jet kit. Still no change-runs fine from zero to 4000 ish dies for about 500rpm then pulls away I tried ex-up no change Got fed up with motor hunting while in traffic at around 60mph so changed front sprocket to move the flat spot up the rev range a bit this worked but I just ended up riding like a loon cos it was so much nippier Blew it up ! REBUILT still same flat spot --still puzzled --still need HELP!
March 4, 200816 yr When you took the engine apart, you didn't look at the cams did you? If one is soft and has worn, it might give a clue to what is going on. Have you overhauled the cylinder head? I think you need to look deeper. Ususally I would put this type of problem down to cam timing, that is the lobe action caused by bad engineering design. In this case I doubt that but usually with peaky engines, this cam problem can be overcome using the fuel mapping. Another problem could be the exhaust gas scavenging. If the exhaust is damaged ie partially blocked or is not standard for that engine, this can cause the problem. If this bike has an ex up valve, is it all working? Assuming that you have fully overhauled the carbs, has the fuel system been checked to ensure full flow from the tank at all revs? Does the flat spot happen in all gears at the same revs?
March 5, 200816 yr Author When you took the engine apart, you didn't look at the cams did you? If one is soft and has worn, it might give a clue to what is going on. Have you overhauled the cylinder head? I think you need to look deeper. Ususally I would put this type of problem down to cam timing, that is the lobe action caused by bad engineering design. In this case I doubt that but usually with peaky engines, this cam problem can be overcome using the fuel mapping. Another problem could be the exhaust gas scavenging. If the exhaust is damaged ie partially blocked or is not standard for that engine, this can cause the problem. If this bike has an ex up valve, is it all working? Assuming that you have fully overhauled the carbs, has the fuel system been checked to ensure full flow from the tank at all revs? Does the flat spot happen in all gears at the same revs?
March 5, 200816 yr Author Yoda thanks for the ideas In reply when I rebuilt she had all new shims ,valves re-ground Ididnt notice any probs with cams What Ishould have said was while the rebuild was on I ran another motor and the problem was still there so Im still leaning towards carbs or ignition AS to your question yes the hole in the power is at the same place in all gears but most noticable in higher gears as you tend to run through it in acceleration. Waiting on a ECU to try will post later to let you know how it goes
March 18, 200816 yr don't know if you're sorted but i had very similar fault with my '93 yzf750 tried all the things mentioned in this post & more. I ended up taking mine to the Dyno Centre in Northallerton. Stuart the guy who runs it used to race yzf750's in BSB is very helpful & pretty much knows everything there is to know. I'm sure if you give him a ring he'll be able to help. if it helps when speaking to him my bike was the YZF750 with vance & hines paint job i'm sure he'll remember it.... www.dyno-centre.co.uk Workshop: 01609 760466 Mobile: 07932 493766
March 25, 200816 yr hi try exup valve , they should open at approx 5000, and make shit load of difference if they dont, also these suffer with faulty plug caps , so replace with ngk ones.if all else fails borrow some standard carbs that you know are 100% and see what happens , have you run it on a dyno? to see what happens they couls tell you if fuel or electric related fault.
March 26, 200816 yr Author hi try exup valve , they should open at approx 5000, and make shit load of difference if they dont, also these suffer with faulty plug caps , so replace with ngk ones.if all else fails borrow some standard carbs that you know are 100% and see what happens , have you run it on a dyno? to see what happens they couls tell you if fuel or electric related fault. tried the dyno route at Wilie and Hollands in Wellington after fitting a dyno jet kit , couldn,t make head or tail of anything. went back to standard settings got a air mixture reading of about 12.5 and nice flat line across the rev range but still had flat spot but not as bad . any way talking to a yzf owner today he said that there is a wiring souloution which bypasses the emissions timing and restores the smoothness ANYBODY HEARD OF THIS MOD OR IS IT JUST WISHFUL THINKING?
March 26, 200816 yr i never heard of that mod but i know people used to fit new pulser timing rotors, they used to be about 40 pound, and they alter the ignition timing to give better midrange and pick up,they fit on end of crankshaft on rh side,
March 26, 200816 yr Author i never heard of that mod but i know people used to fit new pulser timing rotors, they used to be about 40 pound, and they alter the ignition timing to give better midrange and pick up,they fit on end of crankshaft on rh side, No I thought it was to good to be true! still Iv,e allways got the xjr to fall back on. its better for my legs anyway,and me back, and me wrists......... OH GOD im getting old HA!
March 28, 200816 yr Author don't know if you're sorted but i had very similar fault with my '93 yzf750 tried all the things mentioned in this post & more. I ended up taking mine to the Dyno Centre in Northallerton. Stuart the guy who runs it used to race yzf750's in BSB is very helpful & pretty much knows everything there is to know. I'm sure if you give him a ring he'll be able to help. if it helps when speaking to him my bike was the YZF750 with vance & hines paint job i'm sure he'll remember it.... www.dyno-centre.co.uk Workshop: 01609 760466 Mobile: 07932 493766 I rang Stuart today what a top man, he rembered your motor- however we could not figure out any one thing that might be the problem. But he did ask if I was Australian as he had a e-mail from a guy in aussie with the same problem how spooky is that?
April 1, 200816 yr I rang Stuart today what a top man, he rembered your motor- however we could not figure out any one thing that might be the problem. But he did ask if I was Australian as he had a e-mail from a guy in aussie with the same problem how spooky is that? That aussie was me, and yeah i have the same problem, only mine sounds a like mine is more affected. I got talking to a fula who had the same thing years ago, turned out to be split and leaky diaphram in the carb, hold em up to the light and chekem, he said they are quite expensive, may be cheaper to get aset of carbs...???My problems been fixed so i no longer have to worry cause some low lifes came along a stole the old girl on sat night from my house so im now wheeless until i finish my old H1 500...
April 21, 200816 yr Sorry to butt in on this thread, but have just seen jimmythehat's post about changing pulser rotors - have you got any more info on this one? Cheers.
April 21, 200816 yr hi im pretty sure harris performance used to do them, poss places like deemon tweeks also, ?? i remember them being about 40 pounds , are you still having no joy with the flat spot?? where do you live? i will have a look at bike for you if you like, lets get it sorted!
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