750T Motoplat ignition timing |
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iceni
Senior Member Joined: 16 Sep 2014 Location: Colchester Status: Offline Points: 2480 |
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This probably has nothing to do with it, but I had it on the side stand when it started on one cylinder. As soon as it cut out, I put it on the centre stand and left it while I worked on another bike. Later, I went for a ride, and it ran ok, but before I put it down to "one of those things" I think I need to go for a longer ride and see if the problem returns when the engine is hot
Will post again re progress (or not)!. |
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Brian UK
Moderator Group Joined: 13 May 2014 Location: Surrey Status: Offline Points: 17641 |
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Sorry if I'm stating the obvious, but have you checked the choke plungers are seating correctly? Also the neoprene washer in the bottom of the plungers can become badly worn. Both would cause rich running.
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Brian.
Better 5 minutes late in this world than years early in the next. |
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GuzziLancs
Senior Member Joined: 29 May 2016 Location: Appleton Status: Offline Points: 155 |
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Hi Brian, thanks for the message.
Nothing wrong with stating the obvious sometimes. I've stripped and cleaned out the carbs a couple of times so I hope its not a problem but won't do any harm to recheck the choke. I'm replacing the main jet and atomiser as I think they are not to spec but not sure if this would cause the bike to run excessively rich and one cylinder to cut out. Also do you think the compression readings are high (175/180 psi) and what would cause this? Other thoughts are an intermittent fault in ignition circuit when warmed up giving poor spark? Regards
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Keep calm and carry on fettlin'
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Brian UK
Moderator Group Joined: 13 May 2014 Location: Surrey Status: Offline Points: 17641 |
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If jets are the same both sides, it couldn't cause a problem on one side only. But the choke (enrichener) on that side would if fuel can leak past. Main jet size in any case, only affects the mixture over 3/4 throttle.
Compression, that looks good, not overly high. On the Motoplat system, is there a large capacitor in the circuit? I seem to remember there was. If so then they do break down over time, so maybe that might give a problem with the spark. Just guessing though.
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Brian.
Better 5 minutes late in this world than years early in the next. |
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GuzziLancs
Senior Member Joined: 29 May 2016 Location: Appleton Status: Offline Points: 155 |
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Thanks Brian, both sides are running rich but only the right cuts out when warm.
The condenser you mention is no longer available but not sure of the technical details so difficult to replace with like for like. Corresponding with a guy who sells that stuff says it should run without it but I'd rather replace it and see if it makes a difference. I know what you mean about the main jets but I just thought I'd try and get it back to spec and then see before I think about replacing the more expensive bits. Regards
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Keep calm and carry on fettlin'
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Mike H
Senior Member Joined: 21 May 2014 Location: East Anglia Status: Offline Points: 8733 |
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I agree about getting the jets back to standard, and start from there.
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"Chicken nuggets don't dance on a Tuesday."
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Thetar
Falcone Joined: 10 Aug 2018 Location: Ireland Status: Offline Points: 42 |
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Did you ever get to the bottom of this?
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Simon B
Guzzino Joined: 30 Aug 2019 Location: cheltenham Status: Offline Points: 1 |
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Hi, I have recently come across the same problem with my 91 750t... Did you manage to find the cause for this? The bike pops and bangs but doesn't start!
Thanks
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GuzziLancs
Senior Member Joined: 29 May 2016 Location: Appleton Status: Offline Points: 155 |
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Hi, sorry for delay but I’m on holiday at the moment.
I no longer have the 750T, it was more of a project that I sold about 2 years ago so the details are a little hazy. From what I recall I ended up replacing the ignition system including the coils and I also ended up with bigger jets after trying various sizes, although it still ran a bit rich but it did run better. Good luck and I hopE this is useful.
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Keep calm and carry on fettlin'
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