Topic: 750 K2 idle woes

[eenvader]

750 K2 Idle setting Woes...having a tough time setting idle, couple of issues : turning in / out the pilot jet screws on all four carbs don't seem to have an effect on idle but are affecting when you snap throttle and it dies or not...also when I set the main idle stop screw to bring the idle up, i can get it to 3000 rpm and it will sit there, if I push the throttle forward as in negative throttle, the engine will go back down to 900 rpm...setting the main idle stop screw seems to take the engine to 3000 rpm plus but never down lower as in 1000 or 1500, its like full on, and when riding and you let cluch out, the engine drops to 900 or so...if I physically push down on the arms on the carbs that the stop srew is controlling, the idle goes back down to 900, is it my linkage ? its seems very dirty, what to clean with ? or is this some internal carb issue, thanks

[flybox1]

750 K2 Idle setting Woes...having a tough time setting idle, couple of issues : turning in / out the pilot jet screws Idle Mixture Screws (IMS) on all four carbs don't seem to have an effect on idle they wont.....but they do effect air/fuel MIXTURE at idle but are affecting when you snap throttle and it dies or not  Of course...youve changed the mixture either too rich or too lean, so snapping the throttle chokes out the engine ...also when I set the main idle stop screw to bring the idle up, i can get it to 3000 rpm and it will sit there, if I push the throttle forward as in negative throttle, the engine will go back down to 900 rpm...setting the main idle stop screw seems to take the engine to 3000 rpm plus but never down lower as in 1000 or 1500, its like full on, and when riding and you let cluch out, the engine drops to 900 or so...if I physically push down on the arms on the carbs that the stop srew is controlling, the idle goes back down to 900, is it my linkage ? its seems very dirty, what to clean with ? Spray carb cleaner works or is this some internal carb issue, thanks  Turn the main idle set screw to 1200-1400 rpms, AFTER your engine is warmed up....then leave it there.  No real need to adjust it after that.  Choke and throttle are used to get the bike warm from a cold start

So...you have adjusted a few things out of spec.  Lets help you get it set right.
When was the last time you had the carbs off for a good cleaning?
when was the last full tuneup of the bike?
We need to know what intake and exhaust you have on the bike, the model # carbs you have, and what jets you have inside your carbs.

[eenvader]

Hi, original exhaust, original Carbs with the original air box, 110 main jet, 40 idle jet, did a carb sync about 2 months ago...another thing I should mention is the way it starts.....from cold I need full choke for about 5 seconds, then I need to turn choke off and giver throttle for a long time, and it won't idle on its own for at least a 10km run down the highway..it will die on choke quite fast....carbs have never been cleaned by me....I've owned bike for two years

[flybox1]

Great.
First start with an idle plug chop using a set of brand new plugs.
Post pictures of your results

[ekpent]

 Sounds like your carb slides are not dropping back down far enough. Couple of reasons could be mis-adjusted throttle cables or the throttle rod set two high after the synch. Air leaks can mess with an idle also.  When your messing around with it sometime try temporarily removing the push or return throttle cable and see how it behaves.

[Lakelife31]

750 K2 Idle setting Woes...having a tough time setting idle, couple of issues : turning in / out the pilot jet screws on all four carbs don't seem to have an effect on idle but are affecting when you snap throttle and it dies or not...also when I set the main idle stop screw to bring the idle up, i can get it to 3000 rpm and it will sit there, if I push the throttle forward as in negative throttle, the engine will go back down to 900 rpm...setting the main idle stop screw seems to take the engine to 3000 rpm plus but never down lower as in 1000 or 1500, its like full on, and when riding and you let cluch out, the engine drops to 900 or so...if I physically push down on the arms on the carbs that the stop srew is controlling, the idle goes back down to 900, is it my linkage ? its seems very dirty, what to clean with ? or is this some internal carb issue, thanks

Same issue with my 76 550f!! Damn throttle stop screw. I spend half my life on the road twisting that thing.

[eenvader]

Ya after trying to sync the carbs for about 3 hours I managed to barley eek out around 800 rpm idle , also during my extended carb sync session lol, if you adjust  carb one a bit to get the idle up, zoom back to 3000 or 4000 rpm and won't come down....but if you move the idle stop screw up a bit, she jumps to 3000 to 4000 rpm and won't roll back down ... the idle stop screw is essentially not doing a hole bunch.....also she won't stay on choke for more than 10 seconds either when cold...

[eenvader]

checked the cables, there is a tiny tiny bit of slack on the push and the pull cable so I don't think its a cable issue, the linkage looks like its going back down when you release the throttle, gonna check for air leak I guess

[ekpent]

 These early 750's do not run on full choke for long even when cold. The choke is primitive and basically just used to fire the bike off and you tickle it on and off as needed while you hold the throttle open and keep the revs up a little till its warm enough to ride away. Not like modern bikes where you set the choke,walk away and get your gear on.
  Is your large knurled idle adjustment screw working  through its full range to where you can lower the rpm's enough to kill the engine or adjust it up to any rpm from normal to extreme.  Sounds like you had a hard time on the carb synch and if those slide rods are set too high they can make problems. How many threads are showing on that rod above the locknut at the top of the carbs under the rubber boots if you still have them ?

[eenvader]

good to know about the choke, its as you describe so I'll check that box off, I was going to pull the airbox to see into carbs if choke was stuck on, in one or more carbs ? but man I can get it off LOL,,,..... so here is where I'm at, bike will barely idle at 800 or 900 rpm....the big fat "idle stop screw" is barely touching the throttle arm. if I turn it a hair, the idle will start to increase where I want it, but when you giver her throttle and let throttle go, the idle jumps to about 3500 rpm or higher sometimes to 4000, and won't come down , so you end up riding around with bike idling at 3000 at stop lights, if you give her a bit of clutch and release, then the idle settles down to under 1000 again, to remedy this you back off the big idle stop screw a hair, then you are back down to barely idling again....I can set that screw big to not touch the arm and my idle is very low around 500 rpm, ...... as for the carb sync, it was hard to do because I can't get good steady low idle at 1000 to do the sync...when all 4 carbs are close, and you move the slider on carb 1, same thing happends, the idle races to 4000 rpm and won't come back down, if you push down hard on slider on carb 1, it wants to fart out and the idle goes back to almost gone, ....it seems like carb 1 was calling all the shots... . I got lost in the sync, set all my sliders so that there was no thread showing on top, and worked my way back to sync, right now the lock nuts they are about 4 threads down from the top...also I synced at about 1000 rpm with the gauge reading at around 100 KG/CM2 , is that low ? the shop manual says to get a reading of "20 to 22 cmHG" what ever that is ?  its the best that I could do without the idle taking off high, will try and post pics thanks !!!

[flybox1]

good to know about the choke, its as you describe so I'll check that box off, I was going to pull the airbox to see into carbs if choke was stuck on, in one or more carbs ? but man I can get it off LOL,,,..... so here is where I'm at, bike will barely idle at 800 or 900 rpm....the big fat "idle stop screw" is barely touching the throttle arm. if I turn it a hair, the idle will start to increase where I want it, perfect....it should be 1200-1400, set it and dont touch it. but when you giver her throttle and let throttle go, the idle jumps to about 3500 rpm or higher sometimes to 4000, and won't come down , so you end up riding around with bike idling at 3000 at stop lights, if you give her a bit of clutch and release, then the idle settles down to under 1000 again, to remedy this you back off the big idle stop screw a hair, then you are back down to barely idling again....I can set that screw big to not touch the arm and my idle is very low around 500 rpm the bike behaves this way for a few reasons, the main reason being incorrect air/fuel mixture, caused by vacuum leak a the carb boots or incorrect IMS settings , ...... as for the carb sync, it was hard to do because I can't get good steady low idle at 1000 to do the sync 1000 is too low  1200-1400 ...when all 4 carbs are close, and you move the slider on carb 1, same thing happends, the idle races to 4000 rpm and won't come back down, if you push down hard on slider on carb 1, it wants to fart out and the idle goes back to almost gone, ....it seems like carb 1 was calling all the shots... . I got lost in the sync, set all my sliders so that there was no thread showing on top, and worked my way back to sync, right now the lock nuts they are about 4 threads down from the top...also I synced at about 1000 rpm with the gauge reading at around 100 KG/CM2 , is that low ?  actual vacuum value is (somewhat) irrelevant.  just get them all pulling the same  its the best that I could do without the idle taking off high, will try and post pics thanks !!!

forget the vacuum sync for now.   you can revisit it when all other items are sorted.  idle plug chop it, post pictures, and we'll get you headed in the right direction....

[ekpent]

4 threads or more are a little more then ideal normally. You mentioned the airbox and not taking it off. Have you ever had the carbs off yet for a good cleaning ? Whats the history on that.
  Next time you have it running spray some carb or brake cleaner around the carb to head manifolds and see if the rpm's change as you will be looking for air leaks.

[eenvader]

ok need to go to town tonight at get 4 new plugs...just a side note, I pulled one plug out and attached a pic, .......also I sprayed everything (intake boots and around the carbs) with WD40 and nothing changed the idle, so I'm guessing I don't have a vacuum leak.....also at 900 rpm I hearing some popping in the exhaust, does that not indicate lean ? .... .I bought the bike last year, no record of when carbs last serviced. thanks again

[flybox1]

A plug used over many throttle ranges doesn't tell you anything about one particular throttle position....but use it to warm your bike up before throwing in the set of new ones for the idle chop.

[eenvader]

thanks, is this the correct procedure ?


also I have two choices to do the test....1st one being the bike barely idling at 800 to 900 rpm, or, turn the idle stop screw up a hair and have it idling at 3500 rpm....

1) Warm up bike to operating temperature.
2) Let the bike cool down a bit and replace all four plugs with new plugs.
3) Restart bike, let idle back to operating temperature for a minute or two and shutdown.
4) Remove plugs(after cool-down) and "read".

[flybox1]

thanks, is this the correct procedure ?

1) Warm up bike to operating temperature.
2) Let the bike cool down a bit and replace all four plugs with new plugs.  I dont even let it cool, im just careful threading new plugs in..
3) Restart bike, let idle back to operating temperature for a minute or two 4-5 minutes with a fan on the engine case, and shutdown.
4) Remove plugs(after cool-down) and "read".

Once you start it with new plugs, no blipping of the throttle.  just idle.
Put all 4 plugs in a row and take 1 pic.  get a good focused closeup of the tips/insulators.
If tips are all whiter than this plug, adjust each IMS richer till they all match...

[eenvader]

also I have two choices to do the test....1st one being the bike barely idling at 800 to 900 rpm, or, turn the idle stop screw up a hair and have it idling at 3500 rpm....


what is IMS ?


I'd like to know why the idle stop screw is being moved a hair and the idle jumping to 3500 rpm

[flybox1]

also I have two choices to do the test....1st one being the bike barely idling at 800 to 900 rpm, or, turn the idle stop screw up a hair and have it idling at 3500 rpm....  900

what is IMS ?  Idle mixture screw


I'd like to know why the idle stop screw is being moved a hair and the idle jumping to 3500 rpm Probably too much variance between slide heights.  when was it last bench sync/vacuum sync'd?

[eenvader]

Hi. I vacuum synced it yesterday as best as I could, there's no way to get the bike to idle at 1200 rpm, as soon as I move the idle stop screw a hair, the bike revs up to 3500 or 4000 rpm and does not come down again, I can barely get it idling at 900 rpm, it seems that the idle mixture screws have no affect on idle unless you turn them all the way in and the bike dies. I backed them out a half turn, tried to get idle to 1200, backed them out to full turn, then 1.5 turns, then 2 turns, no affect, idle still too low to sync, when I get all 4 carbs reading the same and slightly turn the idle stop screw a hair, it revs again to 3500. if I back it off, the bike is at 900 or 800 rpm, if I move the slider of carb 1, the idle increases a bit then takes off to 3500 again,,,,,I've sprayed the intake boots with WD40 while idling at 900 rpm and it didn't change or rev

[eenvader]

sorry I didn't see your notes on my posts, I thought IMS had affect on idle  ? guess I was wrong, but still can't get the idle stop screw to get idle to 1200, its either 900 or a hair turn to 3500 ugggg, appreciate your help thanks

[flybox1]

Hi. I vacuum synced it yesterday as best as I could, there's no way to get the bike to idle at 1200 rpm, as soon as I move the idle stop screw a hair, the bike revs up to 3500 or 4000 rpm and does not come down again, I can barely get it idling at 900 rpm, it seems that the idle mixture screws have no affect on idle unless you turn them all the way in and the bike dies.  They are not used to control a bikes idle!!!...but they will effect it. I backed them out a half turn, tried to get idle to 1200, backed them out to full turn, then 1.5 turns, then 2 turns, no affect, idle still too low to sync, when I get all 4 carbs reading the same and slightly turn the idle stop screw a hair, it revs again to 3500. if I back it off, the bike is at 900 or 800 rpm, if I move the slider of carb 1, the idle increases a bit then takes off to 3500 again,,,,,I've sprayed the intake boots with WD40 while idling at 900 rpm and it didn't change or rev

Your IMS control AIR.....air allowed into the carb throat, thats all.  if you have the stock carbs for your bike, turning them OUT adds more air (leaner)...turning them IN reduces air (richer) 

the ONLY time you should adjust them, is if a dyno gas analyzer(if you have access to one) or idle plug chops tell you an adjustment is needed.  Do an idle plug chop, look a the deposits on the plug, and make changes as needed.  Simple as that.
if your air/fuel mixture (and vacuum) is right, your bike will idle properly

[flybox1]

Other items you should check....
bowl fuel level - incorrect fuel levels in the bowls can effect idle as well.  the clear tube test can show you if your fuel levels are where they should be.
Carb insulators....old ones may 'look' ok, but off the bike, they can be bent and twisted to show hidden cracks. 
plug caps - if resistance is too high, they can cause a weak, or no spark.  test them with your DMM(digital multimeter), and replace if bad.

vacuum sync again once all check out...

[eenvader]

....in the meantime I sprayed the crap out of a can of carb cleaner all over the boots and carb area, no change in rpm's

[ekpent]

 Actually your plugs don't look all that bad. You need to first fix the issue with the idling and then it racing up to 3000rpm or more before you try and fine tune anything. Sounds like its not really rideable at the moment.

[evinrude7]

would this be helpful?  http://www.hondachopper.com/garage/carb_info/bench_sync/bench_sync.html