richiexj Posted May 16, 2009 Share Posted May 16, 2009 hi new to site need help i have 1981 xj 750 list of things done valves shimed, inlet rubbers, carbs cleaned more than once ,two sets of carbs one stantard one jetted, k&n filters ,straight through pipes, float levels ,carbs snyc on bike with yics tool, new alternater ,plugs and leads and battery . problems it is running off and on #1 cylinder and running rich can any one help Link to comment Share on other sites More sharing options...
JimR Posted May 17, 2009 Share Posted May 17, 2009 hi new to site need help i have 1981 xj 750 list of things done valves shimed, inlet rubbers, carbs cleaned more than once ,two sets of carbs one stantard one jetted, k&n filters ,straight through pipes, float levels ,carbs snyc on bike with yics tool, new alternater ,plugs and leads and battery . problems it is running off and on #1 cylinder and running rich can any one help to the forum Hi Richie, I guess the cylinder 1 running rich is at idle ? if so you need to spend a while playing with the mix screw if not I would guess some engine problems on cyl #1, which may be the case as you indicate the bike is 'running off' (like a pile of poo ?). When you balanced the carbs was the adjustment cyl 1 ~ 2 difficult to do .. did you have to keep altering the idle screw mid point of the balance adjustment & did cyl#1 have a lower reading to cyl#2. Did you make sure that the yics tool was a firm fit & tightend up, if not the balance will just go out the window as the guages will read very simular across all 4 cylinders. let us know how the bike is set up ! Regards Jim Link to comment Share on other sites More sharing options...
richiexj Posted May 18, 2009 Author Share Posted May 18, 2009 to the forum Hi Richie, I guess the cylinder 1 running rich is at idle ? if so you need to spend a while playing with the mix screw if not I would guess some engine problems on cyl #1, which may be the case as you indicate the bike is 'running off' (like a pile of poo ?). When you balanced the carbs was the adjustment cyl 1 ~ 2 difficult to do .. did you have to keep altering the idle screw mid point of the balance adjustment & did cyl#1 have a lower reading to cyl#2. Did you make sure that the yics tool was a firm fit & tightend up, if not the balance will just go out the window as the guages will read very simular across all 4 cylinders. let us know how the bike is set up ! Regards Jim hi got it running on four today did comp test all within 10% think its the float needles as i could not set them as manual left it to rich so levels all over the place to get it to run . it is running on stock carbs with air pods mix screws 2 1/2 turns out but still rich plugs sooted up three and four the worst have three sets of carbs one set of xj 600 and two xj 750 jim cant remember about adjustment on #1 and #2 as i left it for a while due to stress the joy of it all Link to comment Share on other sites More sharing options...
JimR Posted May 20, 2009 Share Posted May 20, 2009 hi got it running on four today did comp test all within 10% think its the float needles as i could not set them as manual left it to rich so levels all over the place to get it to run . it is running on stock carbs with air pods mix screws 2 1/2 turns out but still rich plugs sooted up three and four the worst have three sets of carbs one set of xj 600 and two xj 750 jim cant remember about adjustment on #1 and #2 as i left it for a while due to stress the joy of it all Hi Richie, dont forget on this motor there is no preset position for the mix screws and these should be adjusted with the yics tool installed to the following :- insure that the valve clearences & cam chain tension are correct install the yics tool balance the carbs to a closer point than 10%, 1% is more like the point you need. At this point you may have a knocking noise from the cam area .. this the is time to adjust the mix screws (I must admit this is difficult to write .. easier to say but I'll do what I can) Warmthe engine start at #1 turn the screw fully home (the motor may die or slow) and turn it out until you get the heighest idle speed (re adjust the idle to 1k) and then follow down the other 3 carbs in order untill you get a smooth idle. To double check switch on the light circut, if the idle drops you are running 'off' and the screws need further adjustment. If you have the mix about right the cam knock will dissappear. But to be honest it would be easier to use some web chat (MSN ?) to relay it to you in words ! Regards Jim Link to comment Share on other sites More sharing options...
richiexj Posted May 28, 2009 Author Share Posted May 28, 2009 thanks jim . iwas working away from home for awhile and have just got back have give up on xj750 carbs as i think it was float needles . and my local dealer said yamaha europe has discontinued float needles . so i have put a set of xj600 carbs on that my mate had lying about . it starts fine revs fine but when i drive it holds back when up the revs like its being starved of fuel. i have not re jetted they are mikuni carbs as to hitachi that were on xj750 is it just a matter of trying different jets or is there some way to work it out do ihave to adjust float levels to . oh bike is not running rich with these carbs on . modifications are air pods/filters two pairs of two into one pipes straight through will i always have a flat spot due to pipes should i fit after market baffles cheers richie Link to comment Share on other sites More sharing options...
JimR Posted May 28, 2009 Share Posted May 28, 2009 thanks jim . iwas working away from home for awhile and have just got back have give up on xj750 carbs as i think it was float needles . and my local dealer said yamaha europe has discontinued float needles . so i have put a set of xj600 carbs on that my mate had lying about . it starts fine revs fine but when i drive it holds back when up the revs like its being starved of fuel. i have not re jetted they are mikuni carbs as to hitachi that were on xj750 is it just a matter of trying different jets or is there some way to work it out do ihave to adjust float levels to . oh bike is not running rich with these carbs on . modifications are air pods/filters two pairs of two into one pipes straight through will i always have a flat spot due to pipes should i fit after market baffles cheers richie Hi Richie, go back to the XJ750 carbs..... there is little chance that the smaller XJ600 carbs will ever allow the 750 to run correctly ... the progression holes within the carbs will be wrong so the bike may run weak or rich when the jets need a supplement (the problem you describe, holding back etc ..). But if you try hard you may be able to get the 750 to run well on different carbs but I guess the time factor may be a little long ! Regards Jim Link to comment Share on other sites More sharing options...
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