Topic: CARBS (again)

[ic455]

Alright, I can't find the link or page or website where I saw a guide to diagnose carb issues.  Don't recall if it was within the forum or elsewhere, but a search here didn't find the article/post/whatever.  Something about what it means if you open throttle from idle quickly then return the throttle, but the engine RPM drops too slowly.  Plus, I can't get the bike to idle lower than about 1200 RPM (unless my tach is inaccurate, new cable though).  I play with mixture screws until the idle is at it's highest, then back down the main idle screw until it isn't even touching anything but the tach just hovers around 1000-1100 RPM and the engine stutters, sometimes dies.  Maybe the tach is just wrong......

specs: 750 K6, rebuilt carbs with 110 mains, jet-needle clip in center groove, factory airbox with Emgo filter, MAC 4-1 exhaust without baffle.  Carbs are bench-synched.  #2 and #3 carbs, when mixture screw is turned IN, cause idle to rise and engine to smooth out, leading me to believe it's too lean.  Outer carbs don't have as noticeable effect on engine idle, though.  All head pipes nice and hot, engine is silky-smooth above 2000 RPM, excellent power.  Everything is great except idle.  Haven't done plug chop yet, that's tomorrow  
Thanks guys!

update: just found the darn info, guess where?  IN THE FAQ!!!!  My symptoms are very close to what is described as lean, but not all symptoms are there.

[kettlesd]

Off-sync will cause the idle to not drop quickly when the throttle is blipped.

Sounds like it could be partially clogged slow jets (most likely) and/or badly deteriorated o-rings in the mixture screws. Both of these conditions will lean the mix and throw off the sync.

[ic455]

carbs freshly rebuilt with new fuel lines and filter.  found the post in the FAQ (by Harry) stating "If you rev the bike and the revs hang up after closing the throttle this = Lean; if the revs dip down then come back up = rich."  This is my problem, revs hanging up. 

Still the issue of not getting the idle down to the manual's stated RPM of 950.

What is everyone setting their idle at on 750s?  Anybody running higher than stated in manual?

Oh yeah, there aren't any o-rings on my mixture screws   originals didn't have any and the ones that came in the K&L kits were too large to fit into the hole in the carb body; the screw would just push through as it was tightened. 

[ic455]

Definitely too lean, duct taped the airbox intakes today and she ran a whole lot better.  now gotta order some bigger jets!

[BobbyR]

I think you will find out that most of these bilkes like to idle around 1200 - 1500. Actually lower than that and you are draining the battery since the alternator doesnlt put out much juice below that.

[ic455]

I think you will find out that most of these bilkes like to idle around 1200 - 1500. Actually lower than that and you are draining the battery since the alternator doesnlt put out much juice below that.

Thanks, I was kinda wanting to keep the idle at 1200 to 1400(seems happy there) just needed to hear that someone else is doing it, too I guess

[gold01ca]

yep, 12-1400 idle, me too.
and you're right, no o-rings on my idle mixture screws either.

cheers!

[ic455]

Well, installed 120 mains yesterday, and was too rich.  Installed 115s today, and WOW!  Woke her up nicely.  Ugly thing is, I noted a distinct intermittent "lope" which turned out to be my #1 plug wire coming out of the plug cap.  Seems the wire is too old to hold the pin inside (I cut it back about a half inch when I first got the bike)  looks like it's time to try installing new wires in these old coils

[Bodi]

If the wires are not made to be disconnected, it is a BUGGER to change them and it makes a real mess of the coils. Get some plug wire splicers - short plastic things with 2 back to back screw on connections like the plug caps have. The cable near the plugs is usually fine, just attach a length of new cable to the old.
Sudco has the NGK J-1 splicer, probably you could order them from any NGK dealer? I've seen other ones without the screw clamp thingies, much cheaper and waterproof with a glob of dielectric grease.

[ic455]

Thought about going that way, Bodi, just don't know about 7.50 each for the NGK splicers   This is about the lowest price I've found so far.

[dusterdude]

or buy later model coils

[mlinder]

I just ordered dyna 3 ohm coils and some plug wires. Shipped was 148 bucks or so.
Just the fact that I'll be able to easily change plug wires when I need to makes it worth it, let alone a fatter spark from them with the dyna-s.

Not to hijack the thread, but are these the jets I need for the stock carbs on my 69 750?
http://www.z1enterprises.com/detail.aspx?ID=1922

[paxtonpony]

From my experience (mostly lack of), old rubber intakes cause lean issues.  I chased my probs for about 3 months before I finally bit the bullet and bought brand new intakes.  They're only about $45-$50 but more than worth it once the bike is running right.

[BobbyR]

From my experience (mostly lack of), old rubber intakes cause lean issues.  I chased my probs for about 3 months before I finally bit the bullet and bought brand new intakes.  They're only about $45-$50 but more than worth it once the bike is running right.

I did the same and it did wonders. The next year I synched the carbs and that helped also. Unless the carbs are totally trashed, it is a game of small imporvements that add up.

[ic455]

I just ordered dyna 3 ohm coils and some plug wires. Shipped was 148 bucks or so.
Just the fact that I'll be able to easily change plug wires when I need to makes it worth it, let alone a fatter spark from them with the dyna-s.

Not to hijack the thread, but are these the jets I need for the stock carbs on my 69 750?
http://www.z1enterprises.com/detail.aspx?ID=1922

Not sure of the size but that's the same jet I got for my K6, except mine were 115s and 120s, and I think they are the same as long as they screw in and aren't the hex heads.  (not even sure it matters if you interchange the hex and round heads)

[ic455]

Solved the plug wire trouble temporarily by swapping the coils/wires from my new 550   Since it will be a winter project I figure it'll be ok to borrow them for awhile so I can get some riding in while it's still nice weather

[ic455]

From my experience (mostly lack of), old rubber intakes cause lean issues.  I chased my probs for about 3 months before I finally bit the bullet and bought brand new intakes.  They're only about $45-$50 but more than worth it once the bike is running right.

checked into that before, sprayed carb cleaner on the boots and waited for any change in engine running (indicating that the cleaner was sucked in through a crack or split) but nothing.  Tried again using water and still nothing.  Will eventually replace them, though, cuz they're hard as rocks.