Gumby Posted August 24, 2007 Share Posted August 24, 2007 Hi folks Ive recently aquired an XJ750 Seca 1982 vintage which has been stood for 8 years so the carbs were well and truly full of varnish. So they have been completely stripped, cleaned and rebuilt with the appropriate Dynojet kit and K & N filter for good measure. My problem is now that it will start without choke, will not idle happily below 1500 rpm and the revs will start to rise and race for no reason. Altering the mixture and balence screws makes no difference nor does putting the standard jets and needles back in. If anything it runs slightly smoother with the Dynojet bits. I have rechecked all the linkages and cleared out all passages carefully many times but still get exactly the same results. Although I have spent many years riding and maintaining motorcycles this is a new one on me ( just been lucky so far I guess ! ) so if anyone out there knows what is wrong or can point me in the right direction I will be very gratefull as the time it is taking me to type this is the only thing stopping me reaching for the big hammer ! Link to comment Share on other sites More sharing options...
fosdyke Posted August 25, 2007 Share Posted August 25, 2007 Hi folks Ive recently aquired an XJ750 Seca 1982 vintage which has been stood for 8 years so the carbs were well and truly full of varnish. So they have been completely stripped, cleaned and rebuilt with the appropriate Dynojet kit and K & N filter for good measure. My problem is now that it will start without choke, will not idle happily below 1500 rpm and the revs will start to rise and race for no reason. Altering the mixture and balence screws makes no difference nor does putting the standard jets and needles back in. If anything it runs slightly smoother with the Dynojet bits. I have rechecked all the linkages and cleared out all passages carefully many times but still get exactly the same results. Although I have spent many years riding and maintaining motorcycles this is a new one on me ( just been lucky so far I guess ! ) so if anyone out there knows what is wrong or can point me in the right direction I will be very gratefull as the time it is taking me to type this is the only thing stopping me reaching for the big hammer ! hi What is the mileage on the bike? Sounds like the carb may be worn giving an over-rich mixture permanently, if you have checked and double-checked the settings then this sounds like the most likely problem. Good luck Link to comment Share on other sites More sharing options...
Gumby Posted August 27, 2007 Author Share Posted August 27, 2007 The bike has done fifty odd thousand miles but was apparently running fine before its long storage. The carbs on my Honda have done twice the mileage and are still all original. Link to comment Share on other sites More sharing options...
yoda Posted August 27, 2007 Share Posted August 27, 2007 If you think that the carbs are OK and you do not have air leaks though the spindle mount holes try checking the carb mounts for leaks. It could be running abnormally rich to compensate for air leakage. All rubber type components should be renewed due to ageing. I assume you have checked and renewed the ignition system parts and got the timing spot on? Are you running fresh fuel from a cleaned tank? If not, you will need to reclean the carbs. Link to comment Share on other sites More sharing options...
Gumby Posted August 27, 2007 Author Share Posted August 27, 2007 Hi Yoda. The timing is still spot on as it is factory electronic and cannot be altered and the fuel I am using for testing purposes is from a clean seperate resevoir I use for all my carb work ( damn tank just gets in the way donchano ! ) as for the spindle seals you refer to I guess you mean the ones on the butterfly valve shafts which on visual inspection look ok but after standing for 8 years who knows ? You are right to say replace all the rubber but as I am finding out here in merry olde England parts seem to be unobtainable for this machine so if you or anyone else knows of a stockist please enlighten this ageing jedi who is starting to stray to the dark side ( use the car more often ! ). Link to comment Share on other sites More sharing options...
yoda Posted August 27, 2007 Share Posted August 27, 2007 If the butterfly spindle holes are sucking air due to wear, then by putting your fingers over any holes will cause the bike to run rich. The carbs should be on flexible mounts (to stop fuel immulsion) and these will leak air after a few years. The only way to find out is to change them. Link to comment Share on other sites More sharing options...
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