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750T Motoplat ignition timing

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GuzziLancs View Drop Down
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    Posted: 29 May 2016 at 12:23
Hello to all out there. I am looking for some help with getting a 1993 750t running, which I recently bought as a restoration project on the basis that it just needed a 'little bit' of work.
From the work I have done so far I can confirm that I have spark at both plugs, I have compression at both cylinders (170 psi) and I have checked and adjusted the valve rocker arm clearances. In addition I have cleaned out the carbs (striped and rebuilt) and drained and replaced all the old fuel from the tank.
The engine is turning over with the occasional backfire which makes me think the timing is out, but I can not find much in the way of guidance as to statically set it up.
The bike is fitted with an electronic Motoplat ignition system.
I have an old workshop manual which I have read and can confirm that the marks on the pick up plate are aligned with the mark on engine block. 
I have rotated the engine until the TDC mark appears in the inspection hole and the until the 7 degree Static Advance Mark appears but I am unsure if the corresponding rotor arm positions are where they should be.
As the engine isn't running I can't check the timing with a strobe and hence need to know what to do next to get the engine firing.
(I have some photographs showing the various marks etc but unfortunately they are too big to upload)

I hope someone out there has the relevant experience and is willing to help get this old bike running again.

Thanks
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Ken-Guzzibear View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ken-Guzzibear Quote  Post ReplyReply Direct Link To This Post Posted: 29 May 2016 at 15:24
daft but double check the TDC and make sure it is on the compression stroke .... I KNOW it sounds nuts but .....only ever did that once many yrs ago m8 was there saw it right away, .... Make sure the coils are wired correct way around too
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GuzziLancs Quote  Post ReplyReply Direct Link To This Post Posted: 29 May 2016 at 17:02
Thanks for the reply Guzzibear.
Rechecked both cylinders and the corresponding TDC mark appears in the inspection window on the top of compression stroke (thumb over spark plug hole). Rechecked valves clearances at TDC (0.15mm IN & 0.2mm EX). When the 7 degree Static Advance marks are in the inspection Window the rotor is aligned with the pick ups. I also swapped over the CDI unit connections to check if they had got crossed but no difference, engine is still not firing.
This is my first 'Guzzi' experience, so I feel I'm missing something obvious, but struggling to think what it is.
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Brian UK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 29 May 2016 at 19:02
When at TDC, or maybe just before, where is the rotor arm in comparison to the pickup coil? It should be just approaching, though I can't give any more accurate info. Is it not keyed anyway?
Brian.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote GuzziLancs Quote  Post ReplyReply Direct Link To This Post Posted: 29 May 2016 at 19:34
Thanks for the reply Brian.
When the 7 degree Static Advance Mark (just BTDC) is in the inspection window the rotor arm is on the pick up and I assume this is the point at which the spark occurs. If the engine was running I would expect this mark to line up with crankcase reference mark when using a strobe.
When the TDC mark is in the inspection window (i.e. just afterwards), the rotor arm has just passed the pick up.
Any other ideas welcome.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ken-Guzzibear Quote  Post ReplyReply Direct Link To This Post Posted: 29 May 2016 at 22:19
Take a look on the moto guzzi club facebook page ...Tim Hicks is your man he just put a 750 engine into his Monza had a fix for ign timing ....Brian may be able to copy his notes but he knows the small blocks well does Tim
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 29 May 2016 at 22:31
I don't recall him saying how to set it up, but he could get it to run, but not rev. Ignition was too retarded.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GuzziLancs Quote  Post ReplyReply Direct Link To This Post Posted: 30 May 2016 at 07:17
Hi Guys, sorry but I'm not on Facebook so if there is anything relevant then please try to copy and paste if possible.
I'm beginning to wonder if the timing is out be a few degrees even though the mark on the pick up plate is aligned with the mark on the crankcase body.....and the rotor is on the pick ups?
Also is it possible that the rotor arm could have moved or is it keyed on the shaft?
I feel like I'm starting to imagine things that aren't there.
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Mike H View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 30 May 2016 at 14:40
What's the history? Could previous owner not get it to work either so flogged it?

Is TDC actually of the compression stroke? It is possible to get it 180 degrees out of phase, oh yes rotor is passing the pickup OK when the line is in the timing hole, but is at top of exhaust stroke, so 180 degrees out...

Good news, the backfiring does indicate fuel is getting through.

Afterthought, do spark plugs actually spark inside engine? I have had this happen! test in free air, yep OK, screw into head, f*** all. Change to new / different plugs, VROOOM!!

Also are plugs 'normal' ones not fancy iridium tipped or whatever it is or triple electrodes, just bog standard Bosch or NGK...

Also assuming plug caps incorporate resistors, these can go open-circuit with age, so could try new caps. The red or black NGK caps with the rubber seals for both HT lead and plug insulator are good.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote GuzziLancs Quote  Post ReplyReply Direct Link To This Post Posted: 30 May 2016 at 15:04
Hello Mike, thanks for your response. 

Previous owner said he had had the bike for a while and it used to run but not used for the last couple of years. Other than that I have no evidence that it was a runner. He was selling his bikes as he was getting divorced (doh!)

I have checked and double checked that when the rotor is aligned with the pick up position and the Static Advance Mark is in the inspection window (i.e just BTDC) that this is on the compression stroke, so that as it goes to TDC I get pressure with my thumb over the spark plug hole and the top of the piston is visible. Although it won't do any harm to triple check!

Plugs are standard NGK B8ES, which I have gapped at 0.6mm. I will order some fancy plugs and quality leads / caps just in case though.

Note, I have some pictures of the current set up which shows the the relevant positions etc., but I couldn't load them as they were too big.

........Back to the shed.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 30 May 2016 at 15:08
I am not convinced, I would make absolutely sure by taking the rocker covers off so I can see the movement of the rockers and valves, then I could be sure that if both valves are shut on the upstroke, then it MUST be the compression stroke.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote GuzziLancs Quote  Post ReplyReply Direct Link To This Post Posted: 30 May 2016 at 15:16
Hi Mike, I'll check the valves are closed at the same time as aligning the TDC mark and checking the SAMs and pick up positions, although I did check the valve clearances earlier.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 30 May 2016 at 16:53
What is the rotor to pickup air gap?
 
Tim, who was talking about this on Facebook was setting up a Rita system.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 30 May 2016 at 16:56
http://www.uk-motoplat.com/testing.html
You might get some useful information here.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GuzziLancs Quote  Post ReplyReply Direct Link To This Post Posted: 30 May 2016 at 17:08
Hi Mike, Brian, Ken,

Rotor to pick up gap is between 0.2 - 0.3mm

Forgot to say earlier the bike has only done 13K miles.

Rechecked the TDC on compression stroke (both valves closed and pressure on thumb over spark plug hole) and can confirm correct mark in inspection window and rotor is just passed the pick up. Note, the Rotor is at the pick up just BTDC on compression stroke and SAM is in the inspection window.

Looks like the HT leads are integral  to the coil units so I will just replace the plugs and the caps for now.

Regards
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