MadManMarsbar Posted May 28, 2015 Share Posted May 28, 2015 Hi Everyone So this problems has stumped alot of people in the past few weeks but if anyoine is gonna know it would be on here So here goes , bare with me on thisSo my dad has had his 4jh since about november , he swapped his triumph trophy 1200 for the FZR as the triumph was too heavy for him , obviously he didnt try to red line in straight away so we didnt find this problem until recently when the weather got nice and he got to know the bike so the Problem : it refuses to rev past 7000 rpm at all , when you get to 7k it will sit there as if it was on the red line , the weird this is tho , it will rev perfectly clean to the red line when its on the side stand the other thing is , when you get to 7k it will pull through it but it takes a very very time to do so wwe have changed the whole ignition system for new yamaha parts and my dad has checked the cards over for bad diaphrams or crap in the carbs but they were all fine an clean , he replaced the main and pilot jets for new ones too we has also checked for restrictors in the inlet ports , you can see straight onto the valves so thats not it , and from what i know the 4jh is 20 years old now and i believe they are too old to have an electronic restriction on them aswellone thing to not is we have change the exhaust for a stubby can my dad was given , but that isnt the issue as it does exactly the same thing with a standard can on it , its just alot quieter Anyone got any advice as to what we could check next ? Link to comment Share on other sites More sharing options...
slice Posted May 28, 2015 Share Posted May 28, 2015 Sounds like a fuel/air mixture problem to me, if it won't max out then your getting to little or to much air or fuel into the system and that will bog down the revs, check your fuel flow from the tank and make sure your fuel filter is clean, that might be restricting it. But just before you do any of that it would be nice if you did an intro in the "new members" section if you would be so kind. thanks. Link to comment Share on other sites More sharing options...
Moderator Cynic Posted May 28, 2015 Moderator Share Posted May 28, 2015 As said by slice, intro's help. Carbs would be where I started looking too, more to if they are opening fully. Could there be a resrictor kit in place. Generally this is in the form of stoppers of some kind in the carb top that stops the carb slide from reaching full throttle. Just that 7000rpm is just over where the party starts, so if it were jets I would expect it to pop and bang or have plugs dripping with fuel. Either way it would not run well under 7k. Just a silly one, tried it with the air filter out? Link to comment Share on other sites More sharing options...
MadManMarsbar Posted May 28, 2015 Author Share Posted May 28, 2015 As said by slice, intro's help. Carbs would be where I started looking too, more to if they are opening fully. Could there be a resrictor kit in place. Generally this is in the form of stoppers of some kind in the carb top that stops the carb slide from reaching full throttle. Just that 7000rpm is just over where the party starts, so if it were jets I would expect it to pop and bang or have plugs dripping with fuel. Either way it would not run well under 7k. Just a silly one, tried it with the air filter out? carbs open fully , that was one of the things we checked , plugs are as they should be in a bike , no petrol left over at all so its burning it all , and yes tried with filter out but same problem Link to comment Share on other sites More sharing options...
blackhat250 Posted May 28, 2015 Share Posted May 28, 2015 An engine will rev to redline in neutral, as it only needs a whiff of fuel, underload is a different story, float level / fuel flow [ from tap] fuel filter . ? Link to comment Share on other sites More sharing options...
MadManMarsbar Posted May 29, 2015 Author Share Posted May 29, 2015 An engine will rev to redline in neutral, as it only needs a whiff of fuel, underload is a different story, float level / fuel flow [ from tap] fuel filter . ? all of that was checked yesterday , all are working as the are , carbs are very clean inside , and bike is completely standard now , we had the original exhaust can fixed , so we could fix the problem without any doubt Link to comment Share on other sites More sharing options...
Moderator Cynic Posted May 29, 2015 Moderator Share Posted May 29, 2015 Not state the obvious but something is off. I have been guilty of missing the obvious same as ANY regular poster on here. If you have the carbs 100%. Same with the ig, ie 100%. If you are certain they are ok then you should be looking to the mechanicals. Compression, valve clearances etc. Still wouldnt discount something carb. 1 Link to comment Share on other sites More sharing options...
slice Posted May 29, 2015 Share Posted May 29, 2015 As above, sounds like fuelling to me but if your sure then it has to be a mechanical/electrical fault, you could be months tracking it down, I do not envy you. I once heard a story of a lady who complained of a strange noise in her car but it never seemed to be constant, at least not till she found her son taking the marbles out of the rear ash tray. 1 Link to comment Share on other sites More sharing options...
Moderator Cynic Posted May 29, 2015 Moderator Share Posted May 29, 2015 Complete truth with my dad at the time. Neighbour called round our house moaning that her car was running badly. When my dad road tested the car (with me) it ran fine. She got back in and then pulled the choke knob (remember them) out to hang her purse. 1 Link to comment Share on other sites More sharing options...
MadManMarsbar Posted May 30, 2015 Author Share Posted May 30, 2015 Not state the obvious but something is off. I have been guilty of missing the obvious same as ANY regular poster on here. If you have the carbs 100%. Same with the ig, ie 100%. If you are certain they are ok then you should be looking to the mechanicals. Compression, valve clearances etc. Still wouldnt discount something carb. As above, sounds like fuelling to me but if your sure then it has to be a mechanical/electrical fault, you could be months tracking it down, I do not envy you. I once heard a story of a lady who complained of a strange noise in her car but it never seemed to be constant, at least not till she found her son taking the marbles out of the rear ash tray. Complete truth with my dad at the time. Neighbour called round our house moaning that her car was running badly. When my dad road tested the car (with me) it ran fine. She got back in and then pulled the choke knob (remember them) out to hang her purse. Yea its always something obvious , has happened a few times with other bikes next step is for the carbs to get ultra sonic'd and then see what happens i want to take the downpipes off and check the exhaust ports but the exhaust studs are about as half as thick as they should be lol Link to comment Share on other sites More sharing options...
pilninggas Posted May 30, 2015 Share Posted May 30, 2015 Perforated diaphrams? When you get this on onw or two carbs the bike feels restricted, but will often pull through eventually. Link to comment Share on other sites More sharing options...
MadManMarsbar Posted May 31, 2015 Author Share Posted May 31, 2015 Perforated diaphrams? When you get this on onw or two carbs the bike feels restricted, but will often pull through eventually. diaphrams have been checked , couldnt see any marks or holes at all Link to comment Share on other sites More sharing options...
Moderator drewpy Posted May 31, 2015 Moderator Share Posted May 31, 2015 mikunis are notorious with their tiny fuel galleries. I hear peeps say they are clean, but all they do is use a tooth brush on the outside. can't believe you haven't sonically cleaned the carbs down as that would be a priority. new jets and gasket kit (from Allens performance) factory setup with standard filter modern fuel id really shite and gums up a carb within 2 weeks if your unlucky I now put premium fuel in my carb'ed bike as there is usually less ethanol content Link to comment Share on other sites More sharing options...
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