tat42 Posted September 6, 2009 Share Posted September 6, 2009 Hi I have xs 750 1979 , it is fitted with kand n style filters , bike runs like a pig when over 4000 rpm , bike had been stood for 15 years , I cleaned carbs out etc , have had ignition timing set but still a pig , any ideas ? Thanks Tat Link to comment Share on other sites More sharing options...
Moderator drewpy Posted September 6, 2009 Moderator Share Posted September 6, 2009 Hi I have xs 750 1979 , it is fitted with kand n style filters , bike runs like a pig when over 4000 rpm , bike had been stood for 15 years , I cleaned carbs out etc , have had ignition timing set but still a pig , any ideas ? Thanks Tat to the forum TAT! did you fit the K&N's your self or were they already fitted drewps and used as such? Link to comment Share on other sites More sharing options...
tat42 Posted September 6, 2009 Author Share Posted September 6, 2009 Hi Yes fitted K and N myself , put 155 main jets in . Thanks Tat Link to comment Share on other sites More sharing options...
Moderator Goff Posted September 6, 2009 Moderator Share Posted September 6, 2009 If its running like shit over 4000rpm its probably not getting enough fuel. If you put individual K & N filters on its getting more air - a rule of thumb guide for main jets is +25% as a rough guideline What are the standard jet sizes for your bike? Have you done a plug chop? The colour of the plugs will indicate whats happening to your bike - i have an inkling its running too lean...... What exhaust you got on there? Link to comment Share on other sites More sharing options...
tat42 Posted September 6, 2009 Author Share Posted September 6, 2009 Hi Thanks for your reply . The main jets are 145 , i fitted 170 , but made no difference , the exhausts are 3 singles I dont know the make , the engine is fitted to a trike I have made ,it has only covered 30 miles sinse the build and the plugs look ok . Thanks again Steve Link to comment Share on other sites More sharing options...
Moderator Goff Posted September 6, 2009 Moderator Share Posted September 6, 2009 Hi Thanks for your reply . The main jets are 145 , i fitted 170 , but made no difference , the exhausts are 3 singles I dont know the make , the engine is fitted to a trike I have made ,it has only covered 30 miles sinse the build and the plugs look ok . Thanks again Steve Any baffles or straight through pipes? Has the trike got a custom tank on it? Sounds very much like fuel starvation?? Have you checked the mixture screw? Just trying to help you narrow it down! Link to comment Share on other sites More sharing options...
tat42 Posted September 6, 2009 Author Share Posted September 6, 2009 Hi It is a custom tank , I had a mechanic set the mixture , the pipes have baffles and are road legall . #Again many thanks all ideas welcome ( scratching my head for a couple of weeks 0 Link to comment Share on other sites More sharing options...
Moderator Goff Posted September 6, 2009 Moderator Share Posted September 6, 2009 Hi It is a custom tank , I had a mechanic set the mixture , the pipes have baffles and are road legall . #Again many thanks all ideas welcome ( scratching my head for a couple of weeks 0 Hmmmmmm... scratching me head also! Although it still sounds like fuel starvation. Have you lifted the needle? Also, as you have a custom tank do you have a big tap on it? Link to comment Share on other sites More sharing options...
tat42 Posted September 6, 2009 Author Share Posted September 6, 2009 Hi I have lifted the needle in each carb to max , the tap fitted is recomended for Harley's so should be big enough for a little 750 , but I can see were you are going with this and I will try coming out of the balance pipes of the tank to get more fuel . Thanks again , if you have any more ideas be very happy to hear them as I am pulling out my hair ( not much there to start with ) Link to comment Share on other sites More sharing options...
Moderator Goff Posted September 6, 2009 Moderator Share Posted September 6, 2009 Hi I have lifted the needle in each carb to max , the tap fitted is recomended for Harley's so should be big enough for a little 750 , but I can see were you are going with this and I will try coming out of the balance pipes of the tank to get more fuel . Thanks again , if you have any more ideas be very happy to hear them as I am pulling out my hair ( not much there to start with ) Ahhhhh... think i might have sussed it. The Harley tap only feeds one carb! It MIGHT be that? What is it actually doing at 4K? Spluttering? Losing power? If you can tell me what its actually doing then i might be able to come up woth somethiing else Link to comment Share on other sites More sharing options...
tat42 Posted September 6, 2009 Author Share Posted September 6, 2009 Hi Thats quick ! At 4000 rpm it is like hitting a wall , it splutters and will not rev beyond that ( a gallon of petrol and a match could sort it ) only joking Thanks Tat Link to comment Share on other sites More sharing options...
Moderator Goff Posted September 6, 2009 Moderator Share Posted September 6, 2009 Ok so it could be the Harley tap as i said in my previous post When you cleaned the carbs did you strip them completley ad rebuild them? I had a similar problem with my VFR we stripped them, cleaned them, then rebuilt them - worked a treat! They were absolutely full of gunk which you couldnt see till we stripped them. Im still of the inkling that its a fuel problem you have. If you are riding it and you pull the choke out does it make any difference? Does it run better? If so pulling the choke is making the mixture richer therefore indicating fuel starvation - so solution would be even bigger jets Link to comment Share on other sites More sharing options...
JimR Posted September 7, 2009 Share Posted September 7, 2009 Hi Yes fitted K and N myself , put 155 main jets in . Thanks Tat I guess you are over jetted !!! I repaired an XS750E back in 1983 suffering the same fault (i.e a misfire over 4k, in fact nearly like running on one) and it was down to oversize main jets Regards Jim Link to comment Share on other sites More sharing options...
tat42 Posted September 7, 2009 Author Share Posted September 7, 2009 Ok so it could be the Harley tap as i said in my previous post When you cleaned the carbs did you strip them completley ad rebuild them? I had a similar problem with my VFR we stripped them, cleaned them, then rebuilt them - worked a treat! They were absolutely full of gunk which you couldnt see till we stripped them. Im still of the inkling that its a fuel problem you have. If you are riding it and you pull the choke out does it make any difference? Does it run better? If so pulling the choke is making the mixture richer therefore indicating fuel starvation - so solution would be even bigger jets Link to comment Share on other sites More sharing options...
tat42 Posted September 7, 2009 Author Share Posted September 7, 2009 Hi Goff Things have moved on a little today . Started by putting more fuel to the carbs via balance pipes , problem still there , on swearing a little , OK a lot , decided to take of exhausts but left the down pipes on , 8500 rpm a lot lot better , seems to be a problem with them , bloody ebay exhausts !!! I am going to tinkle more and hope it will get better . Carbs were totally striped as they had stood for 15 years and were like jelly . Thanks for all your help its nice to know that there are good people out there willing to help . Again thanks Link to comment Share on other sites More sharing options...
tat42 Posted September 7, 2009 Author Share Posted September 7, 2009 I guess you are over jetted !!! I repaired an XS750E back in 1983 suffering the same fault (i.e a misfire over 4k, in fact nearly like running on one) and it was down to oversize main jets Regards Jim Link to comment Share on other sites More sharing options...
tat42 Posted September 7, 2009 Author Share Posted September 7, 2009 Hi Jim Thanks for your comments , I hope I have sorted out problem , it appears to be exhaust , on taking of exhaust but leaving on down pipes biked reved to 8500 , but still a little work to do . Thanks again Tat Link to comment Share on other sites More sharing options...
tat42 Posted September 7, 2009 Author Share Posted September 7, 2009 Hi XS 750 running better without exhausts on , like a pig with them on , has any one heard of balance pipes ?- pipes joining exhausts together , my mate has suggested this ( he has never been right as yet , but he has to be right one day ) Thanks Steve Link to comment Share on other sites More sharing options...
Moderator Goff Posted September 7, 2009 Moderator Share Posted September 7, 2009 Balance pipes - you can try them between the two downpipes into a middle pipe. Triumph triples use them - you never know - it MIGHT make a difference. If its running better with the pipes off try doing a plug chop to see how the motor is running? Have you tried pulling the choke when you are riding it to see what happens? If it picks up its running too lean so its back to messing with main jets. Start from a base setting and see what happens - needle in the middle back to standard main jets and then its a matter of experimenting for the best setting! Jolly good luck!! Link to comment Share on other sites More sharing options...
tat42 Posted September 8, 2009 Author Share Posted September 8, 2009 Hi Goff Very little work done on bike today ( lazy ) been working all day . Did manage to tig up some balance pipes out of 22mm stainless will try and fit tomorrow ( if there is not a beer with my name on it ). I tried pulling out choke when on the move , but not any better , will try plug chop when exhaust back on , I dont think the fuel settings are to far out ( he says hopefully ), weather great for bikes today yet both of mine never see the sun ! Thanks Tat Link to comment Share on other sites More sharing options...
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