High idle, idle screw all the way out?

Man, I'm so close with this bike. Today, I finally found a garage that I could sync / colortune. First off, here's a list of everything I've done. I believe I've hit all the obvious pre-reqs:

- adjusted valves
- cleaned carbs
- replaced all relevant parts in carbs (new float needles/seats, new throttle shaft seals, & idle mixture o-rings).
- Wet set fuel levels with a level (didn't use a level the first time--DOH!).
- bench synced (this is my 2nd time, and I believe it was REALLY accurate. Used strips of index card, following the pictorial guide I found on this forum).

So. After replacing throttle shaft seals and bench syncing today, I rode it around to get warmed up. It was a little choppy, but a lot more responsive. Then I did a vac sync with the 2 bottle method. The bottles worked great, but I found that while tweaking sync screws, the idle would bounce around and almost die in some cases, so to counter this I had my hand on the idle knob adjusting the whole time to keep it running (I think this may be my problem, but read on). I synced 3+4 til they were even, 1+2, then 2+3. During this process, it was idling a little high (around 1500), but thought that my idle screws might've been out of whack which was keeping the idle high. I backed the idle screw all the way out too, and it still would drop.

So then I colortuned. Got everything nice and bluish, then started up with new plugs. Again it was still idling high, but not too bad at about 1350. I ran out of time at the garage and had to head home. Within a mile, the bike wouldn't idle down any lower than 2k at a stop light. And after a freeway ride of about 20 miles, it wouldn't idle less than 4k! I let the clutch out a little with the front break on just to get it down to 2k while waiting at a light.

So what did I screw up? My gut says I shouldn't have touched the idle knob while vacuum syncing, and that I messed up my sync by doing so. How do I fix it? 100 points for any suggestions that don't involve taking the carbs off and bench syncing AGAIN.

 

Check your throttle cable, is it binding or hanging up and keeping the throttle open?
Vacuum leaks, got any?
Those are the first two things I would check. Next things involve carb removal.

 

+ 1 mlew, the manifold clamp bolts can be the culprit.

 

I just checked - the throttle is fine. I DID put a new vacuum hose on, because the old one was 30 years old it appeared. The little caps over the other 3 ports looked solid to me, but then they just have these little clips, nothing you can tighten. I was going to pick up 2 new clamps at the hardware store for the vacuum hose, maybe I should get 3 more to be sure all the vacuum ports are sealed? Or is there some other way I can check that?

 

Replace those caps if they are hard, just a bit of air in there & the slides lift & away goes the revs.

 

I am just at the same stage as you, zhalbert.

I had to re-bench sync cos I 'over adjusted' past the point of no return, so to speak, when vacuum synching, and trying to get the idle down (when at machine operating temperature)

The idle wouldnt come down from @1500-2000rpm, so I kept screwing adjustment screws down, then up etc. til I threw it all out of synch!!
This time, when I bench-synched, I used a lesser guage base measure (33% less), to make the gaps in the butterflies smaller when the throttle is fully 'closed' in the form of a guitar string at bottom dead centre.

Since learned that your method is better (some form of business card, or even better, 35mm film cos it is finer) ie working under the theory that, the smaller you can get the gaps, when closed, the lower the idle you can possibly attain(?)

I havent managed to vacuum sync yet, cos its raining heavily here, at the moment and I havent got cover - but I did start it up yesterday, and without any other 'tweaking' of the synch screws as yet, and after letting it get up to operating temperature (about 6 minutes on the RJSECA) running to the local garage to get some more fuel (it went fine - but can hear it needs synching cos the rhythm is a little 'out') and returning home, the idling was steady at 1250rpm - still a little 'high', but I'm hoping I can get it down a bit more when I vacuum synch, perhaps. If not, the carbs are coming off again, and I will rebench sync, with even lower guage!

I have sealed all possible vacuum leaks by the way.
New shaft seals and fuel line o rings.
It sounds like you may have vacuum leak somewhere (because of the nature of the very high rpm at idling, once it gets warm)?

:?: Did you check your rubber manifold carb to inlets, for cracks? - do a spray test with carb cleaner or wd40 ALL- ROUND these, while the engine is AT OPERATING TEMP and static idling - the rubber expands slightly with heat, and opens up the microscopic cracks, - if rpms increase while youre spraying (or immediatley after) for a short period - you need to find cracks in them, and seal them....? (there are threads on this site that deals with this issue....)
Also spray at the inlets to cylinder head (check manifold gaskets not leaking)

Make sure you didnt 'trap', a throttle shaft seal when installing, and it is seated properly...I did!

:?: Did you examine, and install new carb fuel pipe o-rings (mine were 50% worn) You dont say if you have examined these, and replaced them - they could be the cause of your vacuum leak, and high idling.......?

Regs.

 

PS. My idle aduster screw, is also off (all the way out anti-clockwise) BTW.

 

PS. My idle aduster screw, is also off (all the way out anti-clockwise) BTW.

 

PS. My idle aduster screw, is also off (all the way out anti-clockwise) BTW.

 

To IDLE Hugh, ... the Plant needs AIR.
Search for a source if AIR sneaking-in.

The best way to eliminate AIR from being the culprit is to Bench Sync the Throttles CLOSED.
Use the Thinnest Feeler to set the Throttles evenly.
Strips of:
3X5 Card, 35mm Film, Playing Card, Resume' Paper ...

Make the Bike IDLE using the Pilot Mixture Screws and as little IDLE Rod as Necessary.

Slack the Throttle Cable.

If the IDLE remains High, ... Use Propane or Carb Cleaner and Test for Air Leaks.

 

Thanks for the pointers. I have a trip coming up in a few days, so I'm going to do the best I can to bandaid this thing until I can take the time to take it apart.

My fuel pipe o-rings looked okay, but they probably could stand to be replaced. They made it onto my "next" list.

The little rubber caps were hard. Since I don't have time to wait for new ones, I'm going to try cinching them down with screw-tight clamps to see if that's the issue. If I have time, I will re-bench sync. I ended the bench sync last time by adjusting the idle screw until it had a sliver of light (per the bench sync guide here). I wasn't sure exactly what a sliver is, so I guessed. Maybe it was too far open?

Good luck pauldale! I'll post my progress here.

 

Sorry about me keep double/treble posting....I think I know what causes it now, (trying to return to site, and having to 'go back' seems to cause it(?) after Ive just posted a message....

Anyway, Ive just got a chink in the rain clouds, so Ive attempted to vacuum synch my carbs. - posted on my other thread....ongoing.

 

(replied in your other thread...)

 

You can find Vacuum Port Press-fit Plugs at the Auto Parts Store.

A Blister Pack of a Dozen is $3.79

 

I'll look for that, Rick. Wish I'd seen your post earlier. After work today and went and got a screw down clamp for each of the vacuum ports and both ends of the vacuum hose. Turns out, it's not a vacuum leak as far as I can tell. The WD40 did reduce the idle for a couple seconds (only once when it was just warming up, I couldn't reproduce it), so I'll look for something to seal that. I can see a barely visible crack. It seems too small to have much effect.

So I just decided to pull the carbs and do my bench sync again. I didn't do a great job the first time, because even with the idle screw all the way out, I could still see just a sliver of light under a couple of the carbs. Either that or my sync job just set things way out of whack. In any case, I was a nutcase about making each butterfly have the same feel when pulling out the index card, so I'm going to install and give the running sync another shot tomorrow. That bench sync is as perfect as I can get it.

So my question is (maybe you answered already, Rick), should I colortune first, or running sync first? From your earlier post, I think that I should get it running smooth with idle mixture screws first, then vac sync. Is that right? Will I need to go back and colortune again after that? At this point I'm looking for something that will get me running smooth for a trip I have coming up in a couple days--I will have time later to get it perfect.

 

You should ColorTune, first.

Get the Bike to IDLE on-its-own.
Use the ColorTune to "Zero-in" on the Ideal IDLE Mixture.
Find "Blue".
Blue is ideal IDLE Mixture.
IDLE.
You need MORE than IDLE (Blue).
The correct Mixture is at the RICH-side of Blue.
Blue --> Plus!
Go for The Rich-end of Blue ... PLUS some Supplemental Richness.

The Supplemental Richness is needed too sustain combustion(s) right at "Off Idle."
When the Throttles open and let AIR rush-in that isn't fueled yet.
There's about 6 or 8 rabid eye-blinks of fresh air heading-in that needs the juice.
No juice ... Hesitation getting out of the hole.
Too much juice ... bogging-out.

Once you get her Idling strong, ... Vacuum Sync.

Then, once you have it Synced and NOT Hesitating ... TWEAK.

Tweaking is where you Adjust the Mixture Screw about the width of a Nickel or a Dime, ... smoothing-it-out and Colorizing the Plugs just right.

 

Here's an update: After putting my carbs back on (after my OCD bench sync), I colortuned until mixture was good at idle and 2500-3000 RPMs. I ran out of time for the bench sync, but it idles great at 1050. I notice it slightly less smooth at high RPMs than usual, but will touch up my vacuum sync when I have time.

So is it possible (theoretically) to bench sync so well that you don't need to do a running sync? I just don't know how it works exactly, but it seems like if all the butterflies were perfectly the same, that the running sync would be unecessary. T/F?

 

It IS theoretically possible; just like it's theoretically possible to "dry-set" float levels and get them right. (Theoretically; in practice-- rarely.)

But the only true way to get them in sync is to adjust to a running motor, because the "characteristics" of each cylinder are slightly different.

However, as you've discovered, a good, accurate bench sync will get you real close.

 

Yes, copy that fitz

:lol: And thank-you again, bye the way!

I noticed when I began to vacuum synch, when idling at temp. - 3 and 4 cylinders were lower on the 'dials', and not altogether reading the same (ie say, 5.5 and 7.0, respectively), and required a 'tweak' on synch screw, to bring them level.

1 and 2 however, where almost bang on, and when I tweaked and got them the same, all four dials were showing same readings. (well, +/- negligible)
Proves your point about the cylinders being slightly different characteristically, and the need to vacuum synch, after bench synch to get more precise synchronisation.........THEN colourtune....(?)

As I have said in my thread....(you have already done yours, zhalbert, with colortune (?)), I have sent for colortune plug, and I imagine this will be the final operation before attaining maximum fine-tuning.....?
I thought you had to wait until you had vacuum-synched, before you attempted colortuning.....?
:wink: I will find out then if my pilot mixture screws are fully operational, and dont need o-rings, washers etc........

Regs.

 

@pauldale -- I wasn't sure either, but Rick's post (here on this thread) says you colortune first. A really good bench sync + colortune and it's pretty damned close. Of course I can't stop now until it's perfect...

I will say that I took the same approach (wait to see if my pilot screws are good rather than pulling them out and LOOKING at the o-rings). Because my bike has really low miles (<6500) I thought they were probably fine. Man was I wrong. 2-4 were pretty good actually and probably didn't need anything but a clean. But #1 (incidentally the cylinder I was having problems with), the o-ring was somehow FOLDED up on itself and the washer was bent to hell. It had the same amount of drag as the other screws, which was what made me think it was fine. I figure PO during his "carb clean" pulled the screw out, but didn't make sure the washer / o-ring were seated on the screw before jamming it back in there. FWIW

 

A common practice is to assemble the Pilot Mixture parts and insert the whole works into the Port.
This often allows the O-ring and Flat Washer to 'Tumble' off the Screw and become misplaced or malformed.

Use a long Darning Needle and 'Seat' the O-ring and Flat Washer.
The Needle will fit the Orifice and allow you to Center and align the O-ring and Washer below the Spring and Screw.

 

Yes, zhalbert,
Ricks advice, I will adhere to also.....

:? Even tho' I have a nice steady idle, it seems colortuning itself will be necessary because there seems a kind of 'erratic' idling, like a subtle 'rushing', and then 'slowing down', intermittently, when listening to it....?

:roll: Also got an enigmatic 'puff' or 'pop' or backfire, whatever it is, emanating from the #3 or #4 carb/manifold area, every now and again, which temporarily, (shows on vacuum dials) seems to drop vac pressure...then it catches up again.......

Doesnt affect performance, as such, its just a niggly thing, (one of the pilot mix screw seals?) that could possibly get worse, if I dont sort it.....?..........still got some sort of vac leak.........? (sprayed all around, and no apparent increase in rpm's?

:?: Anyone had this symptom before, after bench/vac syncing......??

Regs.

 

Your "pop" or "puff" could very well be ignition-related; be sure to check the resistor cores inside each plug cap to ensure none have worked loose. You could also unscrew each cap from its wire, lop off a CM or so, and screw the cap back on, giving the threaded spike a new bite into the center of the wire.

Colortuning comes after the initial vacuum sync; then any significant changes to the mixtures will require going back and touching up the vac sync.

If you didn't have the pilot screws out your carbs aren't fully clean though. You may have problems trying to get good results Colortuning if you've not attended to the pilots (screws, o-rings and passages.)

 

:wink: I did have the pilot screws out, and inspected, and cleaned the components thoroughly. Also blew carb cleaner down the apertures...
when I reinstalled them, I did so - o-ring, then washer, spring on screw, then spring on screw together......

:roll: Noticed the o rings, and screws and washers looked 'ok' (altho' I cant compare with new again....!!) except for one washer, which looked very slightly 'bent' (?)

If I have to replace parts in the pilot mix screws, can you remove them, without having to take the carbs off the bike again......?

If I have any issues colortuning, it'll probably mean removing the screw(s) responsible, and attending to them (as you've just said)

The pop or puff, has been sorted....in my other thread.....

Regs.