Idle problems

I did alot of searching and reading before I decided to post, but haven't found anything with this specific issue.

My Seca has a hard time idling, it will just bob a little at 500 RPM and eventually die -- this is after I cleaned the carbs. I thought it was the idle adjust, but when I turn the idle adjust screw it doesn't do anything until a point where the engine shoots up to 4k RPM.

If I keep the idle screw where the engine just bobs a little at 500 RPM, I can keep the engine going using the throttle, and it runs rough until I get to 2000 RPM and then it's smooth all the way up to 10K.

I have not synched the carbs yet, but am about to try that next. Think it will help?

Man I wanna ride!

 

Whats the condition of your pilot jets?
Sounds like that might be your problem.
A CV carb iddles off the pilot jet after you rev enough your main jet kicks in. Check that.

 

Synch could be way off, too.

 

Your Idle Mixtures need to be set to where they could sustain rpm's with the Throttles Closed.

That you don't have a smooth transition from Rough Idle to 2,000 indicates the Mixtures require adjustment and the Rack isn't very well synchronized.

 

Thanks guys, I'm rebuilding the carbs with that stuff in mind -- maybe I missed a step in the 'doing it correctly' process.

There are rubber bits from something in two of the pilot jets...didn't see that before because I know I cleaned them out real well, but it's possible it could have gotten plugged up again in the time I had the engine turning. Maybe an o-ring is giving out somewhere.

+ I'll sync this bad boy

 

There are TINY O-rings at the Bottom of each Pilot Mixture Screw Placement.

Sometimes hard to see because they are seated below an equally small flat washer.

 

It should idle at around 1100-1200 rpm like the 550s.

 

Still having no luck.

Re-did the carbs, synched them, checked float levels, no vacuum leaks, fresh 93 octane with some sea foam, new correctly gapped plugs, oil change and filter, new air filter....

...but it still bobbles very roughly at 400-500 and dies. Rev it past 2k and it's fine. This tells me I NEED to mess with the idle mixture screws that you mentioned Rick, but I'm not sure I have the courage to go that route.

 

did you look at the plugs?
If you have a white-ish plug you should tweak out a 1/16th inch or so.

sounds like its starving for gas

 

Yea I'm thinking the same, however I don't even know when my idles screw are -- based on the how-to's around here they're covered by those brass EPA plugs. And the thought of getting a drill bit near my precious carbs is simply terrifying LOL

 

OK...found the idle mixture screws. Turns out someone already took out the plugs. Which means they were messing with the screws and probably messed it up bad lol. I fiddled with the mixture screws, still won't idle. The plugs always end up black no matter where the screws are set.

Does anyone know what this is in the picture below? It's the only thing I haven't messed with when cleaning the carbs. I'm not even sure how to get it out (if you're even supposed to). I've got the idle and main jets out, but that thing...I dunno what it's supposed to do!

 

See the sediment and discoloration on the parts.
That stuff has to go.
You have to get a Toothbrush and Pipe Cleaners and scrub all that stuff away.

If thats what the situation looks like in the Fuel Bowl ... I know you are going to find AIR Passages in the Main Fuel Nozzle clogged right up tight.

You have to remove that Hexed Jet and Washer and gently Drive or Push-out the Center Main Fuel Nozzle (Emulsion Tube) and Clean and Shine them up or you'll never run right.


CLOGGED Nozzle:

 

Thanks Rick, I'll give it another go...fourth times a charm LOL

Does that thing circled in my picture come out at all though? I don't wanna yank on things with pliers if I don't have to.

 

I don't think that comes out.
I don't know.
I've never had a set of those to clean.

I looked at the Yamaha Parts Diagram and couldn't find it.
We're better off leaving it alone until we identify what is is and what it does.

I don't have that Book.
We'll have to wait until I go look at the Factory Book.

 

So after reading and reading and researching I still can't find the purpose of that big ol brass post. It has a pinhole in the end, and when I put compressed air in it, the air comes out from a little hole on the inside of the bowl. Hmm.

I also realized the PO mutilated the petcock, and it was leaking fuel from the turnkey and from the back. Maybe this loss of fuel + pressure contributes to my lack of ability to idle

 

I'm having the exact same issues with my newly acquired Seca. I'll start a new thread for it tho so i don't hijack andrews with different info.

 

So I got a new battery, and it starts right up. It will only stay running at 500rpm if I've got the throttle wide open. Once I let off the throttle the tiniest bit it dies.

I checked the plugs and they're wet. This must mean I'm not getting enough spark?? I'm not sure how that could be since I just got a fresh battery, and it's never done this before. I even charged up the old battery, put it in, and it does the same thing.

UPDATE: Put in new plugs, revs and rides around as it should. So the previous ones were FUBAR. But still doesn't idle -- once I let off the throttle it goes 500 rpm.....three seconds....400 rpm.....three seconds....200 rpm..........*dead*

 

Alright pals, proud to admit that I rode my bike around for the FIRST TIME today....all riding/diagnosing while in the repair phase has been done by my brother up until this point. Finally got some gear, and I'm road worthy....sort of

However, the bike has NO power until 2000 RPM. The thing still won't idle, it take a little gas constantly to keep it from dying. Then when you start to go, there's hardly any power until right at 2k and it kicks in.

I'm completely stumped. The carbs have been cleaned four times, new coils, battery, plugs, plug boots, oil, checked float levels, synched the carbs....stumped! Even adjusted the idle mixture screws and they don't make any change. Any ideas what I could look at next?

 

Could be what skills4lou wrote.
Synch could be way off

I noticed when syncing my carbs that turning the middle screw (last step in sync) will either push balance off center in one direction or (screwed in other direction) push idle past where the idle screw can control it. I thought – this could cause an over rev issue if I leave adjusted past where the idle screw can compensate once the engine gets really warm and idles higher.

The reason idle screws make no difference is it won’t idle as you stated.

What method did you use to bench sync carbs?

 

I used Gamuru's method

http://xjbikes.com/Forums/viewtopic/t=6366.html

I actually did it a couple times to make sure I was doing it right. And it's interesting you say your bike gets wamer and idles higher. I can start mine in the morning, and it will idle fine for about a minute. But on a hot day or after riding it, it will die instantly after letting off the throttle.

 

The likely reason it will run ok when started cold is you have fuel enrichment (choke) engaged. (yes?)
Then when warm and you have disengaged the choke. It will not idle.

 

Nope, haven't even touch the choke. It starts in an instant even without the choke. But come to think of it, maybe the choke is "leaking", or not closing all the way?

 

If your bike starts cold without choke, it is somehow set to permanent rich.

 

That would also explain why the plugs are always black, no matter what!

 

yes it would

 

Look at the forks on top of carbs that pull up the choke, should have free play with choke off.
Your profile states your bike is stock, yet it had a PO. How do you know it has not been rejetted?

 

Good point -- he said it was stock, but he had only owned it for a year and even then told me it would run funny at times. Whoever owned it before him could have messed with the jets. I should yank them jets out and check the numbers.

 

I just acquired a 92 xj600 with under 12k miles and am having the same problem and symptoms. I will add that it runs like a monster with the starter plungers out, but the plugs blacken- not sure if the jets are stock. New plugs, battery is good. With plungers in, it runs great above about 1/4 throttle, but has a hard time within that 1/4 and no idle at all. Have not tried synching yet. I am posting this here in case I stumble upon a solution for you.

I am presently on carb cleaning number two to make sure the pilot channels are truly clean. I had some rust in the tank which I cleaned out and found ever so fine rust dust in the bowls, but other than that, they were clean enough to eat out of. I cleaned rust-goo out of the petcock and it seems to work perfectly. Flows like a river on Pri, no flow on the others without vacuum. Flows like a river with a small vacuum applied. I'm assuming the pump works fine, because there is plenty of fuel available to idle with the starter plungers out (even when fully warm). Did you ever get it idling properly?

The only part of the carbs that have wear are the rubber seals that go on either end of the filler tubes to the bowls. There's a brass tube connecting the outer carbs and a plastic T connecting the inner carbs. All of these seals are cracked and broken a bit. There is no sign of any of it in the bowls or jets at all.

I will try it again after this cleaning with the mixture screws out 2 1/2 turns as they were when I got the bike. I tried taking them out 3 turns earlier and it made no difference. I will post an update when I am done.

 

Ahh a partner in crime! I'm sure we can figure this out.

I've tried just about everything -- well, sort of. Plugs, compression check (although I found a mishap with one of my valves...that's another story lol), voltages, idle mixtures, vacuum synced carbs, float levels (which were out of control, see below), confirmed correct carb parts, jet sizes, ect...

However, two things I overlooked:

#1 Ma booots



Checked to make sure they weren't dry rotted and leaking air -- and oh look, they're dry rotted and leaking air! Inexpensive to replace.

#2 Needle valves



That rubber on the end should come to a fine little pinpoint. Anything other than that and it's going to leak. The engine may be flooding at idle, since it's only got just enough air going through the air pilot to keep the engine idling normal, and way too much gas being forced through since the needle valves aren't closing. Once you start giving it throttle, there's enough air to burn all the fuel coming through. That's my theory!

I've got new needle valves coming in this week. I'll let you know how it goes.

 

Wow, I feel lucky with the bike I just got after seeing those pics of the worn valve tip. Those could definitely be messing it up. Well, after blasting the buhjeeziss outta my pilot channels for a second time, I got it idling this morning. Took it for a good rippin ride and by the end of it was able to keep a nice, stable idle going. I bench synced the carbs, but I think I need to do some of the things you have done like vacuum sync and check float levels. I can tell it is missing some of its power. I didn't even do any mixture adjustments after the ride. I just set them at 2 out last night and slapped the carbs back in this morning. So, my problem was a rusty tank that gunked up the petcock and got fine particles in the pilot channels I must conclude. It took extra cleaning to get it out of those tiny passages. Something else I noticed was during the first cleaning the no. 3 and 4 pilot screws left the o-ring and washer behind when I pulled them out. A little gooey maybe, so that could have easily been affecting any adjustments I was trying to make. After the second cleaning, they could repeatedly come out with the screw just like the no. 1 and 2 screws. This assured me that when I bottom them in then back them out 2 turns, that all four screws are really at the same place. I also forgot to mention that I have disconnected all of my California emissions crap and presently have a closed line connecting the no. 1 and 2 carbs without a connection back to the canister. Also did the "clunk" test with the throttle cylinders as mentioned in the forum and made sure there are no places where vacuum leaks could be. Be sure to check the rubber seals that are on the brass tubes feeding the bowls. My carbs are in excellent shape, but have definite were there, so I put some seal on them to make sure no leakage there. Sorry for so much text. Good luck. I want to hear the good news when you have it!

 

""Once you start giving it throttle, there's enough air to burn all the fuel coming through. That's my theory!""

You're right!
Good guess.

""That rubber on the end should come to a fine little pinpoint. Anything other than that and it's going to leak. The engine may be flooding at idle, since it's only got just enough air going through the air pilot to keep the engine idling normal, and way too much gas being forced through since the needle valves aren't closing.""

Beeeeep!
Not a Match ...
And the Board goes back ...

The Needle Valve shuts-off the flow of the supply of fuel that fills-up the Float Bowls.
Once the Bike is cruising, the float valves keep the JETS submerged in Fuel.
The AIR part happens upstairs with the Pilot Mixture Screw.

 

The PO saying 'it runs funny at times' and mdee's comments reminds me of a CBX750 I was tuning for a friend. Carbs clean, sync'd and fresh fuel and it wouldn't idle, fouls plugs and runs bad until about 4000 rpms. Cruising at 5000 rpm it would suddenly accelerate without input from the throttle.

Weird until I noticed the choke plungers were not fully seated. The PO somehow managed to twist the operating collars so that even if the choke lever was fully 'off', two chokes were still partially 'on'. Cleaning and adjusting did the trick finally.

Worth checking this stuff out on our bikes

 

PROGRESS REPORT

So I happened to acquire a working set of '93 xj600 carbs with half the miles of mine for dirt cheap -- sweet! Finally something to compare parts with.

Turns out I was missing an o-ring and brass washer around the main jet -- critical? I don't know but I swiped them from the new carbs. The new set also had flawless needle valves which I also swiped. I slap my carbs with the new bits on the bike with high hopes annnddd.....same result: Runs rough up to 1800 RPM and if you let off the throttle it dies.

So now I figure there's something wrong with my carbs, like Classic said the choke could be leaking or something of that sort. I transplant every piece into the new carbs, make sure it's clean, adjusted, synched. Slap them on the bike annnddd....same result! Runs horrible until about 1800 - 2000 RPM...past that and it sounds great..let off the throttle, it sounds like it fouls the plugs and then dies.

This tells me it's not the carbs! Tried running it with the airbox off -- same result. Maybe it's electrical? Not enough spark until it gets to 1800 RPM? Not sure how that works.

Stumped!

 

I think the bike would run like that if the floats were set too high.
Sounds like the poor thing is drowning in fuel at idle. Once you get the rpm up, it can then drink the extra fuel. (Same theory as RickCoMatic – previous post).

How did you check / set the float levels? Was it just a dry check? Have you checked wet float level?

I don’t think the issue is electrical. The issue is you are getting too much fuel for some reason.

Have you verified that all 4 carbs have free play between the choke actuating forks and their plunger tops when the choke is in the off position? The choke plungers should spring into the carbs when the choke is put to the off position. It looks like that bike has a push / pull button choke at side of carbs – do you know which position is the off position?

 

I know fighting with Sync and Mixture Issues can be a nightmare.
But, if you get the Carbs clean enough to work right, ... you can win the Fine Tuning fight.

The Key is Idle Mixtures.
Everything else you do relevant to Fine Tuning depends on you getting the Bike to IDLE.

Before you begin you have to have the THROTTLES Closed.
To have the Throttles CLOSED; you have to Bench Sync with a Feeler that is closer to the thickness of a human hair than anything else.

A thin strip of 3X5 Card does the trick.
The Idle Rod and Sync Screws will be adjusted to let the Throttle Butterflys Close tight after you make the adjustment.

Closed Throttles makes you adjust the Pilot Mixture Screws to where you are not adding additional "Turns" to compensate for AIR sneaking-in under partially opened Throttles.

There's NO Choke.
There is NO Mechanical Device limiting the Flow of AIR.
There is NO --> ON and OFF.

The System marked "CHOKE" is a Fuel ENRICHMENT Supply.
The system is not ON or OFF
The Enrichment is REGULATED by how much or little you need to Start.

From Closed to Fully Open ... you have control of the degree of Enrichment supplied to the Combustion Chamber by how you regulate the Choke Lever.

The Enrichment Lever and Plungers are one of the MOST ABUSED Components on the Bike.
If you have an issue related to Mistures, ... examine the Enrichment Plungers.

Frustration in NOT being able the START the Bike will often provoke someone to angrily work the ""Choke Lever"" HARD.
In doing so, the "Top Hat" on the Enrichment Plunger can become BENT-Over and NOT sitting TRUE any more.

BENT-Over Plunger Tops will prevent the Plunger from seating when the Lever is moved to the Closed position.

 

Just to add to rick's point-I had a tiny and very irritating
hunt in the idle-after all other areas checked out I made a
5 deg adj to my #2 pilot and a 3 deg turn to #1. All 4 plugs looked
great and these two barely had a hint of rich in them, the change in
idle and overall smothness was remarkable.
It's hard to believe that such a small change in a plug that has
looks just fine can make-but it does.

 

A fun way to view the term ‘choke’ is, the engine can ‘choke’ on too much fuel if the fuel enrichment mechanism is full on with engine hot at idle.

To me, choke is a word efficient, universally recognized term for a mechanical action that alters the air-fuel mixture to assist the starting of a cold engine. And I found support for my usage at:

http://en.wikipedia.org/wiki/Choke_valve

 

PROGRESS REPORT:

Thank you guys for your invaluable knowledge!

Got it working -- not even 100% sure what did it, but I double checked to make sure the choke/enrichment pull lever was 100% closed by looking underneath each diaphram -- sure enough with the help of some compressed air, nothing would go through the enrichment passage when closed. Then I triple checked the float levels, adjusted them about 4-5mm under the suggested line -- fired it up and it idled!

PROGRESS EDIT:

Once it warms up after riding it for about 15 minutes, it starts to idle real low and run rough -- guess it still needs adjustment, but I'm off to a good start

 

You could be inviting trouble if the Floats are not within the Yellow or Green area of this diagram.

The Floats have too remain submerged while at Full Throttle.

 

So there's a line on bowls where the fuel level is supposed to be, and that's where it's set -- but after 10 mins of riding, it struggles a little and then starts to idle real low, meaning it's still running rich. Should I bring the fuel level down just a bit more till it runs right?

 

The Float Level is not a "Tuning" Adjustment.
The Float Level must be correct. Within the Green or Yellow. Below the Yellow in the Red is unacceptable.

The Floats must fill to those levels.
If the Beenie Screens are fouled and the Fill Rate is too slow ... performance will be affected.

The ADJUSTMENT you make to LEAN the Mixture is at the Mixture Screw.

If it runs for 10 minutes before it Fouls ...
Plug Chop!
Run it and Monitor the Colorization of the Plug's Center Ceramic surrounding the electrode.

Too DARK ... Lean the Mixture a bit.
Make the adjustment in this fashion.
Treat the Adjustment Screw as if it were the Second Hand on a 1-Minute Stopwatch.

Make a 2 -to- 4 Second adjustment.
Not very much of an adjustment is necessary when you are close to having it right.

The FINAL adjustment ... bringing the correct colorization to the Plug may very well be within 3-Seconds or less.

A so-called: ""Tweak""

 

Wow, it's amazing how little you gotta turn those things. Thanks, I'll give a try!

I am SO close to getting this baby perfect