Topic: Cranky after Rebuild - UPDATE NEED HELP!

[SOHC4ever]

Thanks again to everyone who helped me through the re-build of the carbs off of a K3. If not for this forum, I wouldn't even have had the nuts to start.

Now, I have the carbs back on the bike. The bike kicks over revs up to 7,000 and 8,000 RPM with no throttle, and doesn't want to come down.

I started with the idle screws 1 turn out, as specified in the FAQ and went to 2 turns out with no change.

Am I missing something obvious?

Additionally, there are 2 hoses that come off of the small nipples on the 2 and 3 carbs (the ones on the top level, not the main fuel lines). When I pulled the carbs off of the bike, I noticed that these lines were connected to nothing! That can't be right, can it?

Much thanks in advance for your help.

[OldSchool_IsCool]

Could something be jamming your throttle open?  Is your idle thumb screw turned WAY in?

[SOHC4ever]

No. The throttle is closed and the idle is backed all the way off. I have the airbox installed if that makes a difference.

[MCRider]

The 2 hoses are float bowl vents and they are open to the atmosphere, not a problem.

The idle is one of many potentials.  I would first go the the A cable. Is it hung open, adjusted too tight? It needs slack in the closed position. With no load on the engine doesn't take much for an overtight A cable to rev it real high. At the twist grip you should have some rotation, 1/16" free before the grip starts to raise the cable.

[gregory1975]

I am by no means an expert on this but I would be checking it in this order.....

1) Is there a visible gap between the thumb screw end and the point where it contacts?
2) Is the throttle cable adjusted to a point where it is holding throttles open?
3) Did you bench sync the carbs?  If they are initally set fairly open I think you could expect an extreme idle.

I have only ever dealt with my 75 k5.  So if the K3 is really very different someone can tell me to shut it 

[Johnie]

You said you started with the "idle screws one turn out".  There is only 1 idle screw unless you are talking about a KO which has 1 for each carb.  Are you talking about the small air screw on each carb?  That K3 carb bank should have 1 idle screw that controls the idle on all 4 carbs together.

The bench sync was my first thought too.  Could be 1 of 3 things.  Throttle cable adjusted to tight, carb slides set to high (sync), or idle screw set to high.
      
From the FAQ:
I need to sync my carbs but have no vaccum meter. How do I bench-sync?
When I rebuild a set of carbs, I always bench sync them before I re-intall them. Basically, I use a 1/8" drill bit as a gage. Here's how you do it: Adjust the idle screw (the main one) until the 1 carb outside of it is open enough to just let the 1/8" drill bit through. Then adjust the _sync_ screws on the other 3 carbs until the drill bit just fits them as well. You'll probably want to close the idle screw before you bolt them back on the bike, 1/8" openeing is pretty big. This isn't a perfect sync, as there are other things that will affect the airflow to a given cylinder, but it will get you pretty close.

[Achmed]

I was having a problem with idle not going below 3000 or so with the throttle cable loose and it turned out a slide on one of the carbs was stuck open-tilted against the bore, I believe.

[WHALEMAN]

I bet you did not have some preload on the main idle adjusting screw when you bench synced. This means they are bench synced high. Look at the top of the carbs where the adjuster nuts are and you should only see maybe 1 or 2 threads on the shaft showing. Dan

[Spanner 1]

+1 on all previous posts !, but could one of your floats be stuck?...an excess of fuel sitting in the carb throat will cause the motor to spontaneously rev, with the slides closed !!! btw
please don't allow your bike to rev to 7 or 8K...really bad for it  ( o.k. when actually underway ) but never on an ' unloaded ' motor IMO..........I never rev my bike past 3k, hot or cold without forward motion !!....remove the airbox and check for fuel, my 2c !
Also, the two tubes you describe are breathers and don't connect to anything..you could check they are clear tho'.

[mlinder]

Possible air leak. Check for that.

[Johnie]

A side note...be sure to put a good fan or 2 on that engine when you are idling and tuning it.  It will thank you for it.

[SOHC4ever]

Thanks to all who have replied.

I checked to make sure, and both throttle cables have slack. I also made sure that all throttle adjust rods are dialed down so that there are only 2 threads showing on top of the lock nut. The thumb screw is dialed all the way back; there is a gap between it and the throttle arm.

As I last fiddled with it, I noticed some problems with my rebuild. Namely, the float needles that came with the carbs don't have a pin at the bottom that opens and closes like the ones that came off of the bike. As I further disassembled the carb that came off the bike, I also discovered that the needle seat in these carbs has a filter attached to one end (see attached pic)- the ones that were re-built do not have this filter .

Having ruled out the throttle cables, idle screw and adjustment rods as problems (I feel as though I've done so, but will gladly listen to a rebuff), I am working on the principal that the float valves not closing are the cause of my rev to oblivion, and I'm ready to replace the float needles with the ones out of my old carbs. My question for the forums is: should I replace the valve seats with the filtered valve seats, or does it matter?

Johnnie: I meant "air screws", not idle screws. Indeed, the big idle screw is all the way out.
A million thanks in advance. Re: the fan - I wish! I plan to write a long diatribe about apartment based mechanics and the s*&t we put ourselves through for our passion... once I get my bike running.

Spanner1: I'm starting to think you're on the right track. Will report back after float needle swap.

Mlinder: I'll check for an air leak, too.

[SOHC4ever]

Alright.

I took the carbs back off, replaced the float needles with a set in better shape. While I had it off I checked all jets and passages again to make sure they were clear, and measured the float height.

Now, I've got it back on and it doesn't want to co-operate. The bastard cranks over ONLY on full choke, (seemingly when it feels like it), runs sluggishly and dies if I drop the throttle. It revvs only begrudgingly.

Can anyone clue me in to what I'm missing?

[Jonesy]

Are the carb slides in backwards?

[SOHC4ever]

Are the carb slides in backwards?

I don't have cause to believe that the slides are in backwards. the cutouts in the slides are on the airbox side... that's right, right?

This has really got me perplexed.

[Spanner 1]

Yes on the slide question.........now it seems like you have low fuel-level in your float bowls !!
with the choke fully applied 90% of engine vacuum is directed to sucking fuel into the motor and it will only run that way??...are you sure your float level is 26mm from bottom of float to carb flange, needle just closed and not pressed by the tab ? Also, is there good and steady fuel delivery from the tank ? Some possibilities......

[SOHC4ever]

My carburetor perplexity now on hold due to intermittent spark. Please stay tuned. (no pun in tended)

[SOHC4ever]

I fiddled with the float height a bit, Spanner, but when I was finished I'm pretty sure that it was the same as when I started.
In any case, the bike runs, but runs rough. It still idles begrudgingly and takes off like a 2 stroke when you roll the throttle, but I think a carb sync will help me out on that one.

I suspect a lean condition, (aforementioned revving problem, white exhaust) and will report back once carbs have been synced and the mixture dialed in.

Requisite sincere "thank you"s to everyone who has helped me out. This is open-source learning at its best (and most fun).

[Johnie]

I fiddled with the float height a bit, Spanner, but when I was finished I'm pretty sure that it was the same as when I started.
In any case, the bike runs, but runs rough. It still idles begrudgingly and takes off like a 2 stroke when you roll the throttle, but I think a carb sync will help me out on that one.

I suspect a lean condition, (aforementioned revving problem, white exhaust) and will report back once carbs have been synced and the mixture dialed in.

Requisite sincere "thank you"s to everyone who has helped me out. This is open-source learning at its best (and most fun).

You already have the carbs back on so it may be a bit to late, but did you bench sync them before installation as discussed a few posts up?  By doing that you can get it dialed in fairly close until you use the vac gauges.

[Fasted]

I had the same problems.  There was a vacuum leak between the carbs and the intake manifolds.  New rubber transition pieces and hose clamps fixed the problem.  You can check for this by spraying WD40 on the rubber transition pieces while it is running.  If the engine revs out, you have a leak.

ED

[SOHC4ever]

You already have the carbs back on so it may be a bit to late, but did you bench sync them before installation as discussed a few posts up?  By doing that you can get it dialed in fairly close until you use the vac gauges.

Hey, Johnnie. Yah. I bench synced them with a small allan key before they went on. Something tells me the mixture screws aren't right.

Hey, while I'm in here: I timed the bike last night and the firing marker doesn't want to line up square with the indicator for either piston set. ie: If I get it lined up for 2 and 3, it will be bang on for one cycle and off for the next. Is this normal? Sounds to me like t-chain tension (thing sure does make a racket), but I've already dialed that in - right after I did the valve clearance. Could the tensioner be hooped?

[OldSchool_IsCool]

Cam chain has nothing to do with ignition timing.  When you are timing your points, are you doing STATIC timing (engine off) or DYNAMIC (running, with timing light)?

[MCRider]

Cam chain has nothing to do with ignition timing.  When you are timing your points, are you doing STATIC timing (engine off) or DYNAMIC (running, with timing light)?

Old School is correct, cam chain is not in this picture.

If the mark is hopping around on a dynamic engine running timing, I suspect the spark advancer is "hooped".   

[SOHC4ever]

Cam chain has nothing to do with ignition timing.  When you are timing your points, are you doing STATIC timing (engine off) or DYNAMIC (running, with timing light)?

Old School is correct, cam chain is not in this picture.

If the mark is hopping around on a dynamic engine running timing, I suspect the spark advancer is "hooped".   

Indeed, I'm using the dynamic method (strobe light). How can I check my spark advancer?

[MCRider]

Cam chain has nothing to do with ignition timing.  When you are timing your points, are you doing STATIC timing (engine off) or DYNAMIC (running, with timing light)?

Old School is correct, cam chain is not in this picture.

If the mark is hopping around on a dynamic engine running timing, I suspect the spark advancer is "hooped".  

Indeed, I'm using the dynamic method (strobe light). How can I check my spark advancer?

Remove the little 10mm nut at the end of the ignition drive bolt. The 17mm nut will fall off. Remove the point plate. Pull on the advancer, it will draw straight out. Be gentle, you can pull the cam out of the advancer. No problem if you do just wiggle it back in. Inspect the springs. they should be uniformly wound, if they have different distances between the soils, indicated they have fatigued. I've heard of respringing them but usually its RR time. The cam should rotate freely on the advancer base. If not it needs to be dressed with a little polish on the base where it rotates and lube there as well. Some white grease, just a tad. Sometimes they just have to be replaced if they are too jumpy. I'm not sure if they are still available. We used to put CB500 advances in on the rumor it would perk things up a tad. No confirm on that.

There are some electronic ignitions that do away with the advancer. I'm not sure, would like to hear what people are doing about them. Just living with it?