3YF Crazy idle RPM climb and poor/rich mixture SOLVED

[Stenver3fy]

As I'm new here I would like to greet and take a steep bow to everyone in this forum for these great topics, tips and overall discussions on all things Ténéré.
Thank you!
But now it's my turn to ask for some help and knowledge from you guys. Before starting I have to tell you that I'm not the most tech savvy, I've been doing this bike related mechanical stuff for basically a year with the help of some much smarter friends. To not make this post long and complicated I'll start with the problem which I have now, and what I did prior to the problem and pre-existing problems.

PROBLEM At the moment I have a rich fuel mixture and whilst sitting at idle the engines rpm will increase to 4000-5000 at random. Also I am unable to lower the idle to normal 1300ish. The screw at the bottom of the carburetor doesn't seem to do anything at the moment. Another
phenomenon is that when adding throttle slightly minimally the engine wants to suffocate/choke entirely and when adding lots of throttle quickly it does with a slight delay like suffocating at first but catching it's wind momentarily. I'm not sure if I expressed this understandably.

WHAT I DID PRIOR At the end of last years season I started to have problem with wildly revving engine. Whilst sitting at idle or stopping from driving speed at traffic the engine climbed RPM from idle / held RPM and didn't let it drop, I managed to drive regardless of the problem by depressing the clutch when in gear. I found that I have an air leak, the manifolds between the carburetor and engine were old and crumbling. I bought new ones (not oem). Also I cleaned out the carb, a lot of dirt had gotten in last year. Blew out all the channels and cleared some blockages also. And then I replaced the float needle valve, which in hindsight wasn't necessary. I found an air leak inside the carburetor as well, next to the secondary chambers butterfly valve. I fixed it for the time being with o-rings to eliminate the problem being from that leak. It is safe to assume that that leak had always been there whilst I've owned the bike.

Currently the carburetor should be more airtight than it was last year.

Could the problem be some unadjusted needle that causes my bike to suffocate on its own food?
I read something in another post about a tangled up choke assembly, can it be the cause of random RPM climb? Is it possible that the needle of the choke assembly slightly untangles itself and climbs back up into/ out of the carburetor?

Any tips or advice is much appreciated.

[charliext1vj]

I would be surprised if a constant air leak where you pointed would cause the variable issue - note I am only an amateur sleuth. I would start with the Primary carb - how confident are you with that?
Did you replace

https://www.ebay.co.uk/itm/225425559139 ... R-iyg5H7YQ

the rubber goes very hard over the years.

Also really inspect the inlet manifolds well they have a habit of the rubber detaching from the plate even when new - I had this with brand new ones! To rev that high you must be sucking in a lot of air. Perhaps remove the second filter rubber and put your hand over it. The diaphram only works under load and rarely in my experience when stationary. The second carb doesnt come in idle but as you say could feed the air but that doesnt explain why with the butterflies closed you would get lots of fuel as it should try to lean up if it tries to rev out.

It does sound as if the choke is feeding the engine is my guess but you have air issue as well.

Good luck

[charliext1vj]

If you type in Carb Tutorial in the forum - it sends you out to the googledrive - really good document based on the 3AJ tenere but very relevant to you.
https://drive.google.com/file/d/1t0_nuv ... lEvHj/view

[Stenver3fy]

I would be surprised if a constant air leak where you pointed would cause the variable issue - note I am only an amateur sleuth. I would start with the Primary carb - how confident are you with that?
Did you replace

https://www.ebay.co.uk/itm/225425559139 ... R-iyg5H7YQ

the rubber goes very hard over the years.

Also really inspect the inlet manifolds well they have a habit of the rubber detaching from the plate even when new - I had this with brand new ones! To rev that high you must be sucking in a lot of air. Perhaps remove the second filter rubber and put your hand over it. The diaphram only works under load and rarely in my experience when stationary. The second carb doesnt come in idle but as you say could feed the air but that doesnt explain why with the butterflies closed you would get lots of fuel as it should try to lean up if it tries to rev out.

It does sound as if the choke is feeding the engine is my guess but you have air issue as well.

Good luck

Okay. I'll try the hand trick tomorrow. Will remove the retor to reinspect the manifolds.
Inspect the choke, if possible dismantle. And I think I understand how to adjust the needle now, I believe I have to lower it to get leaner mixture if it runs so rich at the moment.

The thing with the butterfly is that I watched a video prior to coming here, the guy there told that the axis of the butterfly valve might get loose and will start leaking air in resulting in uneven idle. He supposed that it might be the one biggest problem with this carburetor and it's usually compensated with the screw. But now the engine runs so rich that I cant even understand if its running at even idle, even if it's 500rpm above normal.
So while I inspected it found it to be a little loose and then discovered that the seal on the right was not airtight. So I put 3 O-rings in there to see if it would stop the air leak which it did. Also the butterfly valve itself is now real nice and tight.

Will try to keep this thread updated with more posts on progression and maybe pictures.

[Stenver3fy]

UPDATE

* So I took kind charlies advice and dismantled the manifolds, i found that the larger manifolds O-ring had popped out of its groove and was stretched out. I used a heat gun on it for a few minutes at 120C*, at distance ofcourse. Got it to retake its original shape and reattached the manifolds. Both of them were in good conditions meaning the rubber hadn't detached itself from the metal.
* I reattached the retor and tried to run it and it seemed that I got rid of the crazy idle RPM climb. But the idle was still quite rough at 2000rpm or a bit lower. The air box was attached but I opened the side panel of the box to try the palm of my hand on the intakes, to me it seemed that the valves opened at the right moment and the idle evened out a bit when opening the box.
* Took the retor off again, and now I adjusted the needle lower by one groove, it was in the middle setting.
With that test run the box was attached but I had left the crankcase ventilation open (i dont know the correct word).
The test run went well, the idle rpm was at satisfying level of 1500 and below. It held steady but when adding throttle it choked a little before reacting, felt that the mixture was still too rich.
* Dropped the needle by 1 more groove. Now it at the lowest setting.
This test run the throttle reacted really well but the idle went to shit. It was running quite rich. Tried adjusting the bottom idle screw but it had 0 effect on the engine working.
* Took a lil break to figure out if I did something different this time for the idle to get messed up like that and then I remembered that this test run I had all of the intake components attached as they always should've been including the crankcase ventilation hose. But it was late and I called it a night. Been working on that problem for the better part of last 4 days.


* Also I disassembled the choke needle to bits at the start, cleaned it thoroughly and greased it at the end. The knee/bend is quite rusted inside. But the cable moves freely enough to engage/disengage the choke needle at least when not inserted to the carburetor. The rubber cover seems to be only there to annoy me but I'm pretty certain that I have to buy a new choke service set. At this point I just want to know if the choke part of the carburetor works or not because today I believed the cable to be properly attached and working but when pulling the choke handle it had 0 effect.
* My friends 1VJ has the same assembly I believe so maybe hell lend it to me for testing purposes until I finally figure out what are all the things that I need to buy. Besides a new carb which I've cracked as seen on the picture.



And the million dollar questions are: Is the idle messed up because of lack of air? Why does the idle screw not do anything? Does the choke assembly even work at this point? How do I test if choke needle properly closes/opens the channel?
These are the questions that I ask myself today and tomorrow after work, with ideas or without - I'll keep working on the bike once more.

[Stenver3fy]

Did some googling about yesterday before going to sleep and found some symptoms which correlate to mine.
** Poor throttle control at low RPM
** No effect on choke
** The engine may not need the choke at all to start, or it may need it only for a very short time
** Idle mixture screw has no effect

These 4 (maybe more) are associated with too big of a pilot jet. I'm not sure which size I have in right now but I guess its the original 48.
I am going to try to change the jet today to see if it does anything. I am going to add a section of another post (thank you xtzrick) which I found on this forum last night, might be helpful for anyone else battling with this.

[donnybach]

Hi bud. Hope you get it sorted soon. I find the standard settings are mostly bang on. They tested it a lot to start with, so any deviation is probably hiding a fault. You have the carb off, so clean everything with solvent and airline the passages dry. Inspect every component before putting it back in and install to normal settings. This is needles at centre clip position, usually pilot screw 2-3 turns out. Float height is essential. I don’t have the specs for your model but the 1vj is 25-27mm float height, with fuel level 6-8mm below float bowl gasket when carb is level (front of bike raised). Install the choke on its own to see if it can fully close, and test the carb with it fully shut. Don’t buy aftermarket parts for the carb. Choke is about £60. Transformed mine.

[Stenver3fy]

Hi bud. Hope you get it sorted soon. I find the standard settings are mostly bang on. They tested it a lot to start with, so any deviation is probably hiding a fault. You have the carb off, so clean everything with solvent and airline the passages dry. Inspect every component before putting it back in and install to normal settings. This is needles at centre clip position, usually pilot screw 2-3 turns out. Float height is essential. I don’t have the specs for your model but the 1vj is 25-27mm float height, with fuel level 6-8mm below float bowl gasket when carb is level (front of bike raised). Install the choke on its own to see if it can fully close, and test the carb with it fully shut. Don’t buy aftermarket parts for the carb. Choke is about £60. Transformed mine.

I would agree with you on the default settings but taking the fact that the carb is now 26 years old, very beaten and probably been taken apart and tuned before countless times I feel I have to do whatever to get it to run well atleast. And most likely last year it ran with small airleaks from the carburetor itself.

There is a symtom which for some reason I have failed to mention - there is a crazy sucking sound when turning the accelerator slowly to about 1/4 way. I would post a vid but havent gotten to it yet.

The fuel level ar the bowl is at 8mm below gasket and the float itself is 26mm.

The pilot screw doesn't have any effect at the moment but ive had it turned loose by 2.5 revolutions.

About the choke - ive looked up brand new oem parts but will take a week to get them.

Will keep everyone posted!

[Stenver3fy]

phpBB [video]

Here's the video. It was made after readjusting the misplaced orings of the manifold, and prior to changing the needle height. Idk how it sounds on your devices but theres the sucking sound which you can hear even when the box is closed.
https://youtube.com/shorts/yQwu8Q7BzfE?feature=share

[motorang]

Sounds like you should redo the cleaning. Some dirt may block a port to the idle adjustment. Unscrew the idle mixture screw to check if the o-ring is there.

I do not agree that the mixture is too rich in idle, as all the symptoms scream "lean".

On my son-in-laws XTZ660 I had to clean the pilot jet three times before I was clever enough to finally mount a petrol filter just before the carb inlet (I prefer sinter type, as paper filters tend to lose fiber which then clogs up the sieve filter on top of the float valve). There may be some gunk in the system, from vacuum pump or tank.

I would not start messing around with needle position or jet changes - this has to work with stock specs including the correct float height! And run fine after an idle screw adjustment, as the number of turns given by the manual is a starting point only.

Andy