'68 T120 Bonneville Starting Troubles - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 11 (permalink) Old 09-03-2018, 11:21 PM Thread Starter
Minitwins
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'68 T120 Bonneville Starting Troubles

I recently rebuilt the top end of my 68 T120R. I am having trouble getting it started without almost passing out from exhaustion from kicking. It acts as if it wants to fire, it has spark at both plugs, but it just won't go. Anyone have any ideas on what could be preventing it from starting? The battery is fully charged, so I'm guessing it is a air/fuel mixture setting. I haven't messed with adjusting valves or timing and I do have compression. Any help appreciated.

Thanks,
Ethan
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post #2 of 11 (permalink) Old 09-04-2018, 02:50 AM
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Originally Posted by ekaplan1020 View Post
I recently rebuilt the top end of my 68 T120R. I am having trouble getting it started without almost passing out from exhaustion from kicking. It acts as if it wants to fire, it has spark at both plugs, but it just won't go. Anyone have any ideas on what could be preventing it from starting? The battery is fully charged, so I'm guessing it is a air/fuel mixture setting. I haven't messed with adjusting valves or timing and I do have compression. Any help appreciated.

Thanks,
Ethan
I am assuming you reset the tappet clearances?
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post #3 of 11 (permalink) Old 09-04-2018, 01:33 PM Thread Starter
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Would that cause it to not fire up? Is there an easy way to do that? I tried getting feeler gauges in there but could not figure it out.

Thanks,
Ethan

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Originally Posted by ekaplan1020 View Post
I recently rebuilt the top end of my 68 T120R. I am having trouble getting it started without almost passing out from exhaustion from kicking. It acts as if it wants to fire, it has spark at both plugs, but it just won't go. Anyone have any ideas on what could be preventing it from starting? The battery is fully charged, so I'm guessing it is a air/fuel mixture setting. I haven't messed with adjusting valves or timing and I do have compression. Any help appreciated.

Thanks,
Ethan
I am assuming you reset the tappet clearances?
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post #4 of 11 (permalink) Old 09-04-2018, 02:36 PM
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Hi
The tappets definitely need to be adjusted after the rebuild the new parts will nave slightly different tollerances, if a valve is held open even slightly you will find it difficult to start the engine.
You will also need to re adjust them when you re-torque the cylinder head bolts.

On the T120 engine it is a little tricky to set them, but there are some useful tips on this previous thread.

https://www.triumphrat.net/classic-v...g-tappets.html

best of luck
peg

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post #5 of 11 (permalink) Old 09-04-2018, 02:53 PM
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A quick thought here...…...is it timed properly? Double check the points to be sure that they're opening on the proper side of the cam...…….it's an easy mistake to make. You didn't mention it, but are you "tickling" the carbs before attempting to start it?

Just a couple of random thoughts: Jim

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post #6 of 11 (permalink) Old 09-04-2018, 03:03 PM Thread Starter
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A quick thought here...…...is it timed properly? Double check the points to be sure that they're opening on the proper side of the cam...…….it's an easy mistake to make. You didn't mention it, but are you "tickling" the carbs before attempting to start it?

Just a couple of random thoughts: Jim
I am tickling the carbs. As far as the points, it has a Boyer electronic ignition, so I'm not sure if that needs adjusted or what.
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post #7 of 11 (permalink) Old 09-04-2018, 03:59 PM
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I am tickling the carbs. As far as the points, it has a Boyer electronic ignition, so I'm not sure if that needs adjusted or what.
Hi, Eka: Sorry that I couldn't help...……..I'm from the old "points" generation; I know pretty much nothing about electronic ones. Hope that you get is solved soon......and easily.
Jim

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post #8 of 11 (permalink) Old 09-04-2018, 05:26 PM
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If the tappets are adjusted properly, consider a Boyer does need a good battery voltage to start. It also needs a heavy foot on the kickstart. It needs speed on the kick as i have found on my own bike and i have bad knees. Other younger people can just start it first time when i might get lucky first kick but if i am slow, it will not start just for my slow kick.
Have you tried a squirt of engine starter ? there are not many engines that fail to start when inhaling some of this.

Now,where did that bit fall off ?
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post #9 of 11 (permalink) Old 09-04-2018, 05:55 PM
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I'm new to vintage bikes ('74 Commando since Jan. '18)...but I've fitted an electronic Ignition similar to Boyer (Vape Wassell). Before setting it, I needed to check the mechanical timing....crank position mark plate on engine cover for accuracy against the actual piston position. The Boyer & Wassell E.I.'s need 28 degrees BTDC at full advanced RPM (about 5000 rpm on the Commando). To check that, I need to know what mark on the crank gauge to use as 28 Deg BTDC. Marks on my cover's gauge were out 1.5 degrees (I determined this via a degree wheel on crank and a piston stop made out of a hollowed out spark plug with a section of old spoke epoxied through it. So, I set the crank mark to align to 28 BTDC, then lined up the line & marks on the E.I. stator & rotor before nipping up the E.I. rotor to the cam shaft. This gets the EI in the ball park of 28 degrees BTDC (at full advance) good enough for starting/running....then a timing light gun is used to fine tune that rotor/stator alignment while watching the crank mark vs the cover mark for 28 degrees.

Note it is possible to set the timing to 180 degree off quite easily...by using the incorrect stator/rotor marks for your engine or camshaft rotation direction (check the Boyer docs). Also easy to think your at TDC when actually at BDC if you do not use a piston stop or something else to determine piston is up with its valves fully closed). Also, check the ignition system wiring is as per the Boyer docs for your engine (positive or negative ground, 2x6v coils or 12v coils etc.

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Last edited by Tornado99; 09-04-2018 at 05:58 PM.
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post #10 of 11 (permalink) Old 09-04-2018, 06:04 PM
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Tornado, the OP has not altered the timing, just a top end repair. You would not time a Triumph engine to 28 degree so a bit confusing to compare a Commando engine when setting up a Triumph engine.
I am thinking open valves as others have also thought. Or low battery voltage
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Now,where did that bit fall off ?
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