Don's early carb holders very nice...

[TeeCat]

Don's pieces for early bikes are quality. I have mine on as of today. Now, I'll have no rubber degradation worries.

Unhappily, though, I'm still chasing this high idle when the bike's hot. I have been afraid to touch the valves because the bike runs well at speed and pulls hard through the gears, but when the bike heats up it idles too high; I had to back off on the speed screws to compensate. Been through all the mish mosh about synching carbs, looking for vacuum leaks, setting float levels, praying to a cow...

Off to other areas of the forum to look for some answers. I have no intention of wasting another riding season chasing this phantom, so I might be looking for a good local tuner. I have the bike at about 90 percent after having brought it home stone cold dead in August of '07, but I'm running out of patience.

I'll start a separate thread on this topic if need be, but kudos to Don... at least I know my manifolds are not the problem...

 

[Tech7]

I'd love to find the answer to your high idle. I have a GS450 with BS34's on it that does the same thing. When hot, idle just starts to climb for no apparent reason. No cable problems or vacuum leaks. It's pissing me off. Haven't tried praying to a cow yet....maybe if we both do it at the same time..

 

[TeeCat]

Tech, it drives one insane, doesn't it?! I have a feeling that, in my case - and possibly yours as well - it's some ethereal combination of factors. My problem, in addition to having limited knowledge, is also one of limited time, so my "process of elimination" diagnostic method takes forever. The other puzzlement is that, though my bike should be running lean in theory (pods and stock jets), it seems to be rich. I suppose I should start a dedicated thread, as maybe others have the same issue.

 

[Sundie]

have you checked your advance springs? If they're loose, they'll let the advance creep up at idle, which will let the engine speed up, and then it becomes a feedback. Had the same issue, took one coil out of my advance springs, solved the issue.

 

[grizld1]

Best to remove and lube the ignition advance shaft as well. In really good tune you're going to have a difference of 200-300 rpm between cold and warm idle. If you're seeing more than that (and ignition issues have been eliminated), try richening the pilot mixture screws 1/8 turn or so.

 

[TeeCat]

griz... good to see you!

Sundie and griz: I have a whole new ATU, and serviced the rod last summer with some help. The new springs are stock length, though; I had taken a coil out of the old ones as temporary measure before replacing everything.

But you're saying that the new springs may be a tad weak and I might want to take a coil out of those as well? If it won't degrade performance elsewhere, I'll try it. I noticed that the bike is slow to return to idle when hot, so what you're suggesting seems to track with my symptoms.

Oh... I'm running a Pamco, too.

Mix screws are at 3/4 turn out. Why would I want to richen them... I'm trying to grasp the logic behind that, griz.

Jetting stock with pods, but the bike never feels lean as far as I can tell. I timed the bike with a light and it seems pretty close, again, as far as I can tell.

 

[inxs]

- possibilities ?

1. mechanical advance not working properly...test, springs, lubrication

2. throttle cables holding the slide up a bit...reroute them, or replace if kaput

3. intake leaks can contribute to a high idle

4. normally set the idle while hot, but then it may need choke while warming up...normal


- timing advance mechanism unit

- there is a very easy test for this...with the engine is running at the "too high" RPM, kill it...allow a few seconds for the RPM to drop down to below normal, almost stopped, and then restart...the ignition system will work again, the engine will start firing again and the RPM should go back to normal...if it stays at a normal rpm, then your springs need to be replaced...it may creep up again in a few seconds...if the rpm goes up quickly then I would suspect the carb adjustments
- you could easily have both issues, weak springs and poorly adjusted carbs
- to check, remove the cover and strobe directly on the advance mechanism...as you kill to drop the rpm and then reinstate, watch the weights carefully....they should return to the relaxed "pulled in" position and then go out again with increasing rpm...this shows that the advance is working and the rpm is held up by fuel, not ignition

- carb

- lean mix...idle should be set warm...cold idle should have choke if necassary
- synchro
- vacuum leaks are the biggest problem here...check the boots-both inlet and outlet, vacuum barb plugs, throttle shaft seals
- air filter, sticky choke, sticky slide

 

[TeeCat]

- possibilities ?

1. mechanical advance not working properly...test, springs, lubrication

2. throttle cables holding the slide up a bit...reroute them, or replace if kaput

3. intake leaks can contribute to a high idle

4. normally set the idle while hot, but then it may need choke while warming up...normal


- timing advance mechanism unit

- there is a very easy test for this...with the engine is running at the "too high" RPM, kill it...allow a few seconds for the RPM to drop down to below normal, almost stopped, and then restart...the ignition system will work again, the engine will start firing again and the RPM should go back to normal...if it stays at a normal rpm, then your springs need to be replaced...it may creep up again in a few seconds...if the rpm goes up quickly then I would suspect the carb adjustments
- you could easily have both issues, weak springs and poorly adjusted carbs
- to check, remove the cover and strobe directly on the advance mechanism...as you kill to drop the rpm and then reinstate, watch the weights carefully....they should return to the relaxed "pulled in" position and then go out again with increasing rpm...this shows that the advance is working and the rpm is held up by fuel, not ignition

- carb

- lean mix...idle should be set warm...cold idle should have choke if necassary
- synchro
- vacuum leaks are the biggest problem here...check the boots-both inlet and outlet, vacuum barb plugs, throttle shaft seals
- air filter, sticky choke, sticky slide

inxs, thanks for this detailed post!

With regard to your first four:

The ATU is brand new, as are the cables (properly routed and visually synched), the intakes are new as of yesterday, and I set the idle hot, but might not have been at "operating temp".

I synched my carbs by the dead cylinder method and I think I have them really close. I cannot swear to the integrity of the throttle shaft seals. The choke seems to work fine and the bike does need it when cold; she'll sometimes smoke a little until I shut the choke off, obviously. Air filters are new cone type pods.

Now, I just got back from taking her out for about 45 minutes. 75 and sunny. Today, she did REALLY well... just a touch fussy about going into first sometimes before she's up to temp. But when hot, and with just a touch of tolerable clutch drag, the idle actually could have been bumped up a couple hundred rpm, but I did not let her sit and idle... this was brief traffic idling. But I wish the idle would be consistently like today!

Now the only other thing she seemed a little fussy about was that, when I roll off the throttle, the left exhaust is a steady decel rumble, whereas the right one is more of a "crackle". So maybe there's a slight carb imbalance somewhere, but I'm not sure if that's related to the idle moodiness. I have the muffler joints at the headers as tight as I can safely get them, but the left joint is a tiny bit sooty over time.

The bike pulls scary hard and runs really well at speed, so I'm afraid to booger that by dicking with the valves.

Today, I felt that she did really well, but I'm looking for the "consistency" that will allow me to have the confidence to ride her more and farther.

TC

 

[grizld1]

TC, sorry to be slow answering your question. A pilot mix that's too rich or too lean can cause elevated idle. With a rich mixture the engine will sometimes settle to idle slowly, and blipping the throttle can cause the rpm's to drop as they should. If a lean pilot mix is responsible, the engine won't respond to that. Fill a spray bottle and shoot a little water at the boot joints, throttle shaft ends, etc., and wait a little for response; if rpm's drop, you've hit a vacuum leak.

 

[TeeCat]

griz, thanks... no rush. As I said above, she seemed to do well today, responding to backing off the idle speed screws once hot.

We're supposed to have rain this week, but I'll spray water at the throttle shaft ends. I'll also test rider her again to see how she does. Next, I'll try turning the mix screws out about an 8th turn, but before I backed off the speed screws, blipping the throttle would cause a slow return to idle.

 

[grizld1]

Settling down after a quick tweak of the throttle can indicate a rich mixture, so if you do have a mixture issue you might want to try 1/8 turn in first. You can confirm or eliminate the possibility of the advance mechanism hanging up very easily with a strobe; have the light ready, remove your round alternator cover, go for a ride, and have a fast look at what the ignition's actually doing if the high idle recurs.

 

[bluebikerblan]

Back to the carb holders...thanks for the post Tee Cat. Not only did I find the US sourced fuel resistant holders I was looking for but; also a new source of BS 38 CV carburetor diaphragm replacements. JBM Industries and Donald James innovation rocks!

http://www.jbmindustries.com/Yamaha650.html

Best, Blue

 

[retiredgentleman]

TeeCat:
You said you synced the carbs using the dead cylinder method...............that's not the purpose of the dead cylinder method. This may be why you sometimes have a high idle that doesn't want to come down. Your pilot screws are probably mis-adjusted. They can only be adjusted properly when the butterfly is closing off the 3 by-pass holes.

To do the "dead cylinder method" you must adjust the "idle mixture screw" (pilot screw) as well as the "idle speed screw". You should be able to adjust the engine speed down to around 300 or 400 rpm on 1 cylinder firing. If you can't do that, then you're not doing it right,or you have air leaks etc. You have to adjust both screws to achieve this. As you adjust the pilot screw, keep lowering the idle speed screw to get the rpm down.

The important thing to realize, is that the throttle butterfly must be almost completely shut, in order that the pilot screw can be adjusted. This is because the butterfly must be covering up the 3 by-pass holes in the carb throat. If the butterfly is open even slightly, the mixture coming through the 3 by-pass holes over-rides the pilot screw, and you are unable to adjust it.

If someone has had the butterflys removed from the carbs, they may not have re-installed them correctly. The butterflys need to be self-alined. This is done by leaving the butterfly screws loose, while allowing the shaft and butterfly to fully seat against the side of the carbs.............the screws are then tightened (use thread locker on the screws).

 

[TeeCat]

Blue, you're very welcome... and thanks again to Don!

griz and RG -

When I DC'd the carbs late last season, I did it with the pilot (mixture) screws at 3/4 turns out, which has been describes as a "starting point" for early bikes, and used the idle speed to set each side at about 500 rpm, as I was thinking the whole point was to equalize the idle speed screws while having the mix screws at a known quantity. RG, my butterflies will close all the way as far as I can tell, with the idle screws backed all the way off, but if I understand you correctly, you're saying the mix screws have to be used to get the cylinders running equally with the idle speed screws being backed off all the way. Is that correct? The weather conspires against me this week... might be the weekend or later before I can do any more evaluation.

Yesterday, with manageable clutch drag, the rpms were audibly dropping unimpeded between gears, and the bike seemed to be idling well - maybe even a little low - but I suspect that the carbs are still not quite synched, especially since you seem to be suggesting that the mix screws do NOT have to be the same number of turns out, but need to be adjusted independently of one another.

Maybe that explains the decel crackle on the right side. Ugh.

Thaks for all this help guys... I don't want to waste it so I'm trying to implement it one variable at a time, in a way that makes sense to me.

 

[retiredgentleman]

Teecat;
Each cylinder is tuned independently.............you're not trying to match the 2 cylinders for mixture screw turns or for RPM. On my bike the mixture screws are at different turns. With one cylinder idling down at 400 or 500 rpm, (use the carb speed screw to get the rpm as low as possible without stalling), adjust the mixture screw for the highest smoothest idle.

 

[TeeCat]

Teecat;
With one cylinder idling down at 400 or 500 rpm, (use the carb speed screw to get the rpm as low as possible without stalling), adjust the mixture screw for the highest smoothest idle.

Okay, RG, this part clarifies things a bit. I'll see how the bike does if the weather clears up this weekend. But I'll likely have to get out my little ground plug I made on your recommendation (I have a Pamco) and try the DC method again to see if I can get the idle and right side decal crackle resolved.

Thanks again! You'll likely hear more in this...

 

[tx650]

I had this problem once and the vent in the filler cap was blocked
U can open the cap when it starts to rev up and see if it makes any difference
Also as it has been already mentioned here look at the advance unit springs if equipped.

 

[TeeCat]

I had this problem once and the vent in the filler cap was blocked
U can open the cap when it starts to rev up and see if it makes any difference
Also as it has been already mentioned here look at the advance unit springs if equipped.

You know, that's worth checking. Where is the actual vent located, by the way?

The whole advance unit is new, springs and all. I'm contemplating whether to take a coil out just as a matter of course, as I have read that the new ones can be weak. I like my idle at about 1200 rpm or so to compensate for a little bit of manageable clutch drag when hot, and I'm wondering if that might be putting the timing right on the cusp of wanting to start to advance into the power band and causing the "system" to get "confused", if that makes sense.

 

[tx650]

There should be a tiny hole under the cap
I wouldn't worry too much about swapping the coils as I have found them to be almost bomb proof.The only electrical problems I have ever encountered was the rotor thus not charging the battery.They are relatively cheap to replace or rewire,just depends on how ambitious you are.One thing I have found out is that these bikes absolutely need the full 12 volts for them to start.I have never or don't know anyone who has ever started one of these dam fine machines by push starting?
I was at my local m/cycle wrecker yard one day and saw an RD 350 Yam with coils connected so I asked how much he wants?$5 each and so I took them home and did my own "spark"test.
The difference was incredible,the spark on my original 650s was a yellow colour and the 350s were a bright blue.
The wiring colours and hook up were the same but they were just a bit fatter,maybe that had something to do with it,probably need an old school sparky to explain this.

 

[TeeCat]

Sorry, I didn't make myself clear. I was talking about taking one coil off of each advance spring to keep them from letting the timing advance too early. I have a dual point coil and a Pamco that are perfectly fine, and the charging system is doing its job, according to the voltmeter I have installed on the bike.

I'll have to look for the little vent hole in the cap... still can't quite picture it.