Tenere 1VJ starting issues

[charliext1vj]

1VJ CARB ISSUES

I rebuilt the bike a year ago – complete strip and assembly except the engine. The engine was unknown condition but has had a significant rebuilt in its life. All I did to the engine was to adjust the valve clearances.
The carburettors were completely stripped, cleaned and reassembled and anything adjustable set mid manufacturing specifications. Also, a new fuel pump was fitted and a new Coil

SO…it has never started easily which meant I tended to leave it parked up. However, when it did start it;
- ticked over nicely,
- accelerated smoothly up to mid-range,
- did not smoke.
So today started to do some investigating by removing tank, air box and ducts and fitting new plug – the old plug appeared black and new one had a reasonably strong blue spark. Connected up an auxiliary fuel tank turned on tap and tried starting it a few times until all air out of pipes and carbs were full.

Tried starting it with both choke on and off and fuel tank dropped a little. It eventually started after 5 minutes of trying the electric start in short bursts;
- It fired up and I observed in the low range carb misting/spitting of fuel
- The vacuum carb does not lift at and lifting it by hand (it moves easily) there was no sign of it wanting to lift on its own at large revs.
So, I think I have 2 issues;
- Why the poor starting as it runs fine once started?
- Is the second carb the diaphragm or other and how can I prove it?

Really value all you thoughts here!

[motorang]

Hi,
these bikes are getting old, so the electrickery may be the problem really.
A strong spark outside the engine does not equal a strong spark under compression.
The ignition energy is generated in a coil inside the stator. The insulation may be weak and it may not work well with low revs.
Plus: the ignition timing is put together from two pickups, one for lower revs and one for higher revs. One of them may be weak or cutting out.
Good news is you can measure them.

Unplug the stator loom from the CDI.

Between red and black there should be a reading of 140-200ohm (this is your ignition energy generated in this coil)
red to ground or black to ground: very high resistance in the megaOhm range or no connection at all.

Then there are three wires which are two color striped. If I am not mistaken they should be black-yellow, green-white and blue-yellow.
The three wires share a plug. The middle one (black-yellow) is common between both pickups.
Between two of them there should be the following resistance readings (there were different versions around but this is one of the standards):

black-yellow to green-white: 115 Ohm is for lower revs and starting (12°)
black-yellow to blue-yellow: 115 Ohm is for higher revs (full spark advance 36°)
green-white to blue-yellow: 230 Ohm
None of them should connect to ground (megaohms again)



See also: https://transmic.net/2016/07/14/yamaha/

Also the ignition may have a weak spark from a not so good side stand switch (if the bike has one), kill switch or ignition switch.

With fresh fuel, the Tenere is a really easy starter and should fire up on second kick, or something is wrong.

As for the second carb issue, you will not get that to lift with no load, if the bike is sitting in the driveway and just revving. It has to work. Like riding up a mountain, or at speed. The vaccum from the intake will the suffice to activate the second carb from around 4000 rpm.
You can try to connect a vacuum cleaner to that primary intake to create enough suction to watch the second carb work: engine not running, carb connected to engine, no air filter connection to carbs, second carb flap horizontally (full open).

Andy

[charliext1vj]

Many thanks for the quality reply Motorang it is much appreciated.

I will do exactly what you describe - probably next weekend though and report back.

There is so much good stuff on this forum but was struggling to get a sensible approach to checking out the carb and didn't even think of the electrics so great tip.

Charlie

[charliext1vj]

Measured the pick up coils today and measured in at 115ohm each - also tried another CDI. Compression checks next.

[dzl]

Does the bike fire up easily when engine is warm/ hot? If yes, is the starter fuel circuit in the carb working properly? Does it start ok if aerostart sprayed into airbox?

Is the starter plunger in the carb move in and out freely when the starter lever operated? Could the starter fuel circuit be blocked? I would pull the starter plunger out and spray carb cleaner into orifice and should observe fluid being sprayed into venturi.

Would be hard to get the secondary vac carb plunger to operate with no load, just revving engine I would have thought but have never tried myself. Does the bike lack power and feel like secondary not opening up?

[charliext1vj]

Hi thanks for the questions

It starts easily from hot but not cold
I have tried running on auxiliary fuel tank straight to the carb to illuminate fuel pump - no change. Plug does look a little black once started.
The carb was completely stripped and I thought I did a reasonable job cleaning it.
The valves were checked but in tolerance and engine rebuilt 10000miles ago but has seen a massive tour since.

I have bought another set of carbs will rebuild those and do the compression tests - many thanks for suggestions

[motorang]

You wrote that you did set the valve clearance. Any chance you did that not correctly, eg in the other TDC?

Andy

[charliext1vj]

Hi Andy thanks for the comments - the valves were basically checked and if i remember right it was only one that was towards end of tolerance so just brought it into centre. Hopefully get some time on it soon...normally I pick ypp the issue quickly but this one is set to test me!