Timing for Bonneville

[triman65]

Help.

Does the timing advance or retard as you rev up the engine. I am having trouble sorting it out. I have set it to 38 degrees before TDC but should it be set to 14 degrees before TDC.

At the moment it will start and sometimes backfires, but I cannot get it to tick over.

Mick

[triman65]

 sorry forgot to say it is Boyer ignition.

[L.A.B.]

Does the timing advance or retard as you rev up the engine. I am having trouble sorting it out. I have set it to 38 degrees before TDC but should it be set to 14 degrees before TDC.

The timing advances from idle.

If you are using a strobe then it does give the appearance that the timing mark moves backwards under the strobe light (the rotor mark moves [information edited see my third post belowfrom left to right as engine speed increases)] which could be confusing you?

You need to do the Boyer initial setup with the crank positioned at 38 degrees BTDC.

Either use the 38 degree crank timing slot or the correct alternator rotor timing mark, one mark is 180 degees out, but if you'd used that one then it wouldn't start at all.
Once the crank is set at 38 degrees BTDC the Boyer rotor and pickup is adjusted until the white paint mark on one of the magnets lines up with the lower timing hole (for clockwise rotation) with the pickup plate halfway along its adjustment slots. The Boyer rotor bolt can then be tightened fully and plate screws nipped up.

The engine must then be started and strobed at 5,000 RPM and any adjustment done by moving the pickup plate, as you cannot set it accurately statically.

Disregard any reference to "14 degrees" at that does not apply to a Boyer.     

 

[triman65]

Hello LAB

Where do I find the 38 degree crank timing slot ?

What I have been doing is finding TDC on compression on the righthand cylinder and and turning it back 38 degrees. I will have a look tomorrow at the alternator markings and try that way. The problem is that it will not keep running to try any adjustments. It runs for so long and then it just stops. It has to be the timing as the carbs have new jets and needles.

[L.A.B.]

Where do I find the 38 degree crank timing slot ?

What actual year model "Bonneville" are we dealing with here? As some quite major changes were made to "Bonneville" models between 1959 and 1988?

And is it a T120 or T140 (as production of both models did overlap).

Depending on the year model, you will probably find a 5/8" hexagon plug in the top centre of the crankcase radius behind the cylinders ?
If you remove it you can then insert a Triumph timing tool (type depending on year model) into the hole and the engine rotated until the tool plunger drops into the 38 degree BTDC slot in the crank.
Note that very early unit models have no plug and no slot, slightly later models have a plug and a TDC slot, most year models however have both slots, so don't mistake the TDC slot for the 38 degree slot.

[triman65]

Hello LAB

The bike is a T120r 1972 model. Yes it has the crankcase timing plug to find TDC Which is what I have been using. Are you saying it also has a notch for 38 degrees?.

Mick

[L.A.B.]

The bike is a T120r 1972 model. Yes it has the crankcase timing plug to find TDC Which is what I have been using. Are you saying it also has a notch for 38 degrees?.

Yes, Mick, there should be two crank slots. One for locating TDC and one for 38 deg. BTDC.

Have you strobed it yet? Some Boyer MkIII boxes don't always give very good idling anyway, as they're somewhat "old technology" ignitions. These days there are better systems available.

[L.A.B.]

If you do happen to find your crank has only one slot, then it should be the 38 deg. BTDC one?

With the crank set at 38 deg. BTDC the alternator rotor timing mark should be lined up with the crankcase pointer?

Also note I said previously that under the strobe light, the rotor timing mark will appear to move from left to right as it advances, but that won't be correct for a 1972 model as the timing pointer is in a different position to the later timing mark setup I was thinking of.
So to be more accurate, the rotor timing mark should be seen to move in a clockwise direction, finally lining up with the crankcase pointer (at roughly the 5 o'clock position) at 5,000 RPM when the Boyer is set correctly?

[L.A.B.]

When setting the Boyer statically, OR when checking it with the strobe at 5,000 RPM, this is where the rotor mark should be for a 1972 model as the case pointer is at the 38 degree position and not TDC:

[triman65]

Thanks LAB for all the information. At first I could only find the one slot and I checked the rotor timing mark, it was correct . So I must have been picking up the timing slot and not TDC. The 2 slots are very close and the pistons were very hard to move in small amounts.

I think I will  have to spend more time with the carbs as it soots the plugs up when using the chock. It is still spitting and poping. I am having trouble with the neighbours, about the noise. So will have to leave things a little while

Thanks again for all your help and will keep you posted as how things workout

Mick  Unlucky neighbour to Victor Meldrew  

[L.A.B.]

I think I will  have to spend more time with the carbs as it soots the plugs up when using the chock. It is still spitting and poping.

What plugs are you using?
As the recommended Champion N3 (now N3C) or NGK B8ES can be too cold except high speed running?

Plugs can be bad straight out of the box, so try a nother set.

Is this a new Boyer you have just fitted or has it been with the bike for some while?

99% of Boyer problems turn out to be caused by either a bad battery or bad wiring, connectors or switches. Electronic ignitions do not work well unless the ignition circuit is in good condition, so check and clean ALL the connectors including the coil connections and make sure they are completely sound with NO TAPE JOINTS!
Try connecting the Boyer box directly to the battery with jumper wires as a test to see if that improves things? If it does, then there's obviously a fault in the bike's ignition circuit somewhere.

One thing I would certainly check if the bike has been laid up for some time is the pilot jets (pilot bushes) as they are almost guaranteed to gum up if the carbs are left with fuel in them and the bike not used. Also check the two small mixing chamber drillings are clear as they can also become blocked, see Bushmans link below.
The jets/drillings can usually be cleared by carefully poking them with a piece of fine wire and drastic action such as drilling the carbs as shown in the Bushmans link is only necessary in extreme cases.  

http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html#PILOT

Also check that the float bowl gasket faces are flat, and also check the carb inlet flanges are not warped.  



 

[triman65]

Hello LAB

The plugs I have tried ngk b8es and also ngk b7es. The plugs that were in I cannot lay my hands on but they are the ones with 3 contacts unlike ngk with the single contact. I remember the number was a 6 and was told this was to soft.
Yes it is a new boyer which I changed from the one fitted.
The battery is new it is a GS Motorcycle Battery CB9-B which cost £31 which I thought was a bit dear.
Like you I thought it may have been the jets so I renewed both jets and needles,also washed petrol tank out and renewed all the petrol pipes. When I replaced float bowls with new gaskets, one of the carbs had a weep from floatbowl. The gaskets seemed to be a little hard and showed no sign of depession.
I am sending for new air filters to see if this makes any difference if not may consider new carbs.
Have noticed today that there is an oil leak from the contact breaker so will have to sort this out first and I may as well renew the crankshaft oil seal while I am at it.

Its a good job I am retired

Will keep you informed and thanks again

Mick