idle issues cont

[bean1969]

A bench sync can get you close and running, sometimes plenty good enough. I believe that the pilot circuit is too fat in your case and that the butterflies are not your problem. If the lean best does not do it for you...time to pull and go through the carbs again. Do not forget to use a big fan on the engine while running it and making adjustment.

V

hi gustov didnt get to play with mixture screws to day found another issue cylinder 4 not firing!! checked out leads ,plug cap coil, thjey are good as i swapped them with no 1 cylinder issue didnt move to that cylinder.so yeah gonna pull carbs off again they have been in the bath twice already and i have blown carb cleaner through ports/holes blown it through with comppresed air ,but how do you gauge there completely unblocked and clean unless you have a comparison! im gonna do a compression test on cylinders tommorrow,what is the minimum psi required i think if i remember no 4 was about 100psi not great but ill check tommorow,cheers paul.

[gustovh]

hi gustov didnt get to play with mixture screws to day found another issue cylinder 4 not firing!! checked out leads ,plug cap coil, thjey are good as i swapped them with no 1 cylinder issue didnt move to that cylinder.so yeah gonna pull carbs off again they have been in the bath twice already and i have blown carb cleaner through ports/holes blown it through with comppresed air ,but how do you gauge there completely unblocked and clean unless you have a comparison! im gonna do a compression test on cylinders tommorrow,what is the minimum psi required i think if i remember no 4 was about 100psi not great but ill check tommorow,cheers paul.

I believe 100psi is low service limit. So it looks like you need to go through the whole process starting with a valve adjustment, carb clean and don’t forget to change the “0” rings behind the carb mounts. I would also remove the plug caps and cut about 1/4” off the end of the wires and then screw them back on.

#3 carb is not adjustable so the other carbs are adjusted to it. That said, this is how I bench sync my carbs. Using 2 pins of the same dia. I use 1/8” drills I place the end of 1 drill under the butterfly on #3 and make sure that it is centered, you now have a 1/8” gap. Using the end of the other drill I set the gap in the other 3 carbs, there should be just a tiny bit of resistance to the drill. That should get you very close.

V

[salty_monk]

You can get leaks at the airbox as well as the intake boots. They would bypass the filter. You need to make sure you have a good seal to the carbs, that the doors on both sides are well sealed, that the foam filter is oiled properly & that the filter cage is sealing to the airbox body properly.... if not then time for new airbox boots & get some foam draught excluder to use as a seal material for the cage & doors.

[bean1969]

hi gustov so are you saying that after you finish sync that when your throttle is closed with 1/8" gap that is how you leave it set up for idle!yes were gonna check the valves my dad says their fine but i want to check them other wise i just feel like im going round in circles,i have replaced orings ,set floats cleaned carbs, gonna check the plug gaps too to make sure, like i said previous how do you know for sure every little passageway in carb is completly unblocked but i am going to pull them off again. cheers paul.

[bean1969]

hi salty i will make sure this is the case when i put it back together again! think my dad should of stuck to his old british bikes ,singles and twins twice the issues with four cyl;inders lol,i just want to get it sorted for him hes 80 yrs old, he wanted another project ,oh well hope we get there in the end with it thanks for your help cheers paul.

[tom203]

A good bench sync will get you real close mechanically ...but it won’t tell you if one or more carbs have blocked idle circuit passages. Before you reclean them, try this... got any long downhills nearby? Accelerate down, repeatedly closing throttle to put vacuum on the tiny passages in idle circuits. This might suck out some gunk....sometimes you can get lucky.
P.S. your a good son

[Nessism]

You might want to read through the Newbie Mistakes and carb rebuild tutorials linked in my signature. Short cuts are long cuts when it comes to cleaning carbs and performing all the bikes maintenance. Consider this your warning...

[gustovh]

hi gustov so are you saying that after you finish sync that when your throttle is closed with 1/8" gap that is how you leave it set up for idle!yes were gonna check the valves my dad says their fine but i want to check them other wise i just feel like im going round in circles,i have replaced orings ,set floats cleaned carbs, gonna check the plug gaps too to make sure, like i said previous how do you know for sure every little passageway in carb is completly unblocked but i am going to pull them off again. cheers paul.

once all the butterfly’s are set, you remove the pin from #3 and the flys close. So leave the pin in #3 while adjusting the others. I also agree that short cuts aren’t.

V

[bean1969]

hi tom well went round dads tonight to do compression test as no4 cylinder not firing and ive checked out leads, coil, cap etc they were ok. so not great compression no 4 was 100psi the others were around 90/95 . 123 cylinders are firing, so no4 the one with the most compression isnt,so im thinking it gotta be carb,were going to check valve clearencs too,im a bit concerned,dad reground the valves fitted new stem seals and told me he took a bit off the top off stems with a grinder!! he said when he set the gap he aired on the side of caution so they wouldnt be tight.all being said it starts up fine with choke obviously no 4 not firing but dad reckons it is at higher revs. it would be abit awkward fo me at the moment to take it to a hill, perhaps after a third clean i will try it,thanks for the compliment i try to be and i try not to show my frustration with this bike in front of him as i know he is frustrated himself and i think he regrets taking it on ,im more of a 2 stroke guy myself i race quads trx250rs ,but im being teached a lesson in multi cylinder 4 strokes at the mo lol,cheers paul

[bean1969]

hi nessism yes i have followed the carb tutorial its good but he doesnt show not that i can see anyway,how he cleans the pilot circuits and how to ensure they are completely unblocked i have had carb cleaner coming out the hole in front of the butterflys and out of the 3 little holes just behind the butterflys ,but im going to take them off again and have another go at them,cheers paul

[Grimly]

yes were gonna check the valves my dad says their fine

This is where familiarity with older Brit bikes is of no use. Generally, OBBs would signal the valves need attention by getting noisier - the GS bikes don't. The GS bikes get quieter as the valves need adjusted. This could fool somebody with an ear for older engines to think there's nothing wrong with them.

[gustovh]

All your cylinders are LOW, check valve clearance...no guess work here, check the gap.

V

[bean1969]

hi gustov i checked valves tonight they were o.o5 to 0.08 clearences so that seems to be in spec, i just thought! would i get better results with the slides up,as usually the test is done with throttle open but this is not possible with cv carbs unless you hold slides up.but yes they are low. im gonna take carbs of again and clean them and see if i can get no 4 cylinder to fire at idle, as 123 cylinders do so. cheers paul

[tom203]

“..usually the test is done with throttle open but this is not possible with cv carbs unless you hold slides up”

the slides won’t interfere with testing....just hold the throttle open - then the throttle plates won’t block the intakes

[bean1969]

hi tom well had the carbs off again 3rd time in the bath put them back on bike fired up straight away with choke and idled fine, push choke in it struggles to idle but revs out okay and no hanging revs, revs come down sharply.but open up butterflies via idle screw to get it to idle then blip the throttle revs start to hang,it gets worse the more i increase the idle!is it doing it because im having to open up the butterflies to much to get it to idle!ive replaced orings, checked valves cant find air leak ,what next!!im gonna sync the carbs with gauges see if that helps.