Hi.
I have problem with my 88' tenere 3aj. It's struggles on constant speed, over 3700 rpm, on every gear. When I accelerate it's ok. Spark, coil, CDI is OK. Second carb's membrane is new, engine is in good condition. Clutch,side stand cut switches are ok. Underpressure ruber hoses are new.

HELP!

Fuel runs from taps OK ? you have taken both pipes off to see taps are clear of rust & stuff.

I was advised to put them mini fuel filters after the taps ?

Mezo.

Since the problem is related to rpm, it's possible your ignition advance is at fault...

Are you sure its related to RPM and not throttle position.

__________________
Did some trips.
Rode some bikes.
Fix them for a living.
Can't say anymore.

Hi.
I have had fuel starvation issues caused by those mini filters, especially in hot temps.
Might be worth popping the fuel tap out and checking the gauze filter.
Just the usual carb check and air line clean may help you.
All the best. Dave.

hi there the first thing i would do is to give it a service , new plug , clean replace or re oil air filter depending if its paper or foam sorry dont own that modal so dont know, set tappets etc. also drain the carbs to see if you have any water /crap in there do this in to a clean container to catch the fuel. is the bike surging at the top speed or do,s it just refuse to go any faster ? . also is the petrol cap brether hole blocked , you may have fuel starvation, you could try loosing the cap ,but not with a full tank and see if it still do,s it . if you have a fuel pump, some do, check this as per your manual or i think they can be bypassed somebody on here will tell you how again my 43f do,s not have one. also check the carb inlet rubbers are not cracked or leaking at the head joint ,but i would think it would pop and bang on the over run if they were that bad, you can do this by leaving the bike ticking over and spraying wd/40 around the rubber ,if the revs increase you have a air leak and they need replaceing or some guys have managed to stick the rubber back to the metal part , also is the carb clean no blocked jets etc good luck do the service first then try the other bits one at a time . you may also have something electrical braking down ,ignition, kill switch, etc .zigzag

Thanks!
Fuel runs without problems and I haven't fuel filters. CDI, coil was repleced with another well-working ones. Plug, and spark is new. Tappets seted. Carbs clean. Carb inlet rubbers - new. I bought new fuel pomp membrane few days ago by ebay, but I don't have it yet.
Kill switches were checked by by-passes and everything is good.

I supose that some elektrical conection starting to cut impulse from/or to ignition on high rpm vibration, or strange problem with underpressure and secend carb diaphragm.....
Hmmm petrol cap breather - I'll check it.

I want to go to Balkans this may, so please do brainstorm.

Greetings from Poland.
Sorry for poor english...

If it is a spark secondary issue . It might be beneficial to gap plug closer.

But I think you might be describing a lean spot in the jetting?
Removing the carb to is a PITA
but if so inclined I would try to raise the primary needle.

Now if your like me (lazy) I would rather take a ride up to a high elevation and see if it runs better. The higher up in elevation you go the richer it will run.
It may take 5000 feet to note a difference, so that may not be doable.
But if that rough spot is gone or better at altitude then you know.

Good luck and let us know

Carbs were checked in every direction on the start. I have model with "barometer" (?) , it changes something with underpressure (and 2nd. carb membrane) over this 1500m (5000 ft.). It isn't lean spot, when I accelarete engine works without problems, and goes smooth through rpm to the top. But on constant speed (constant rpms, or throtle position) on every gear it starts to struggle.
If isn't a mechanical , or electrical problem, maybe it needs very patient tunning. It's a swiss version with another type of jets... Maybe somebody has swiss tenere....

At steady speed, does the problem occure at every rpm range/throttle position?

It its at the same, it could be the carb. Have you done some tests and "read" the sparkplugcolor?

OK so you have a altitude compensating carburetor. (never knew they had them)

I could go into theory on how it works, but I would block one of the lines that go to this(see pic below)and that will put it into low altitude mode.
if you are operating at altitudes below 5000 ft and the lines are open it will run lean.
It operates on the principle of adding extra bleed air at altitude to lean the mixture.
so when lines are closed it is in low altitude mode (richer)
when open it is in high altitude mode (leaner)
hope that helps? and it is easy to try.
Also check lines in this circuit as a leak can cause leanness at lower altitudes as well,

Problem occurs over 3700 rpm, at constant speed (constant rpms),on every gear. Engine has very short, unregular "pauses" , no back fire, no lose of power after pause. When I accelarete it's ok. Spark color is OK. Maybe second carb is the problem, because starts to work on higer rpms. I'll check "altitudometer".

My first thought reading your description is that your idle mixture screw is set too lean. You have had the carbs off to do the intake rubbers, and to replace the membrane, so you might have set everything back to factory spec.
Come to think of it, my Swiss spec Tenere (3DS code as opposed to 3AJ)came with a idle mixture screw plugged off to avoid tampering. Now, on a new carb the factory setting is ok, but when things start to wear you need to rich up the idle mix. So, remove the plug from there and turn out the idle mix screw 1,5 turn and start from there. You might have to remove the carbs from bike to do this - sorry for that.

For correct setting, see my earlier posts.

The idle mix setting is very important at lower engine loads, running @ 3700 rpm at constant speed the throttle is open only a little bit, just in the region where the idle circuit determines the mix.

One more thing 1 - Check the synchronisation of the second carb - @ 7 mm opening of the primary the butterfly valve of the second carb should start opening. Easiliy checked, with carbs off, by inserting a 7 mm drill into the primary carb.
If the setting is off, which I have seen, where *ssh*l*s has set the second carb at immediate opening, you would have also happening what you describe.

One more thing 2 - there is a very small fuel filter on top of the float needle seat - this gets dirty and blocked with time and will, at higher engine loads, impede fuel flow.

Remark: the altitude compensation device works a treat upto 4000 m - do not believe anybody that says you should remove it!

Good luck!

__________________
Auke
http://aukemarieke.blogspot.com

Thanks!
Carb are clean, every "screw regulation" don't stop the problem. But inter-carbs synchronisation can be the major problem, and cause too lean mixture. Tommorow I'll try to check it with my mechanic.

Have you managed to solve this problem and if so - what was cause for it?

Hi,

sometimes the gap for the clip in the needle wears than you also have problems like yours. Often it works just to put the clip one position up.

regards

Thomas