No Spark VT700 - Honda Shadow Forums : Shadow Motorcycle Forum
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post #1 of 20 (permalink) Old 07-03-2019, 12:25 PM Thread Starter
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Join Date: Jul 2019
Model: VT700
Year: 1984
Location: UK
Posts: 17
No Spark VT700

Iíve been trawling these pages for a while now and found so much helpful information, but now Iím after a bit of advice please if anyone can help? I bought a 1984 VT700 that Iím trying to get back on the road. I didnt have any experience of any of the workings or anything at all before hand, but had been told she needed a new reg/rec and battery and fork seals and thought ĎI can get that doneí - what a prat. Now it turns out, that itís something not quite so straightforward and Ive been trying to track down the fault myself with the help of this forum and the manual and, of course, You Tube.

After going over the wiring for literally months and trying to work stuff out Iíve noticed when checking out the multitude of Earth connections under the seat, that one of these wires changes to a blue wire and goes up to the coils. It looks to me as though the Fuel Cut Relay has been removed and the wires re-routed. Now the black wire from the reg/rec that should have gone to the relay, goes straight to the fuel pump (I understand this bit), but the blue wire that should have gone to that relay, as been attached to the earth wires that go to the frame. This same blue wire goes to the spark units and coils. I just read that the ignition module connects and disconnects the ground to the coil, so does anyone think the earthing of the wire that was supposed to visit the fuel cut relay could be the source of my headaches? In my mind, it messes it up, but thereís so much about the way all this works that Iím still trying to figure out. Iím a secretary (or was anyway), not a mechanic or electrician. Gotta admit Iím loving it though.

Sorry about the lengthy blurb, sheís a VT700, but someone popped a 750 engine in the frame, installed a manual fan switch in place of the thermo switch and completely changed the petcock orientation to put a different filter in. I had the stator rewound as it was burnt out, bought a (used) reg/rec (just incase), new battery and Ive ordered a new clutch diode (ďrectifierĒ) all the coils and pulsor readings check out. Still cant help but think thereís something obvious that Iíve completely missed.

Any advice very, very gratefully received.

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post #2 of 20 (permalink) Old 07-03-2019, 12:39 PM
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Join Date: Oct 2014
Model: Vt750
Year: 1983
Location: Washington State
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Welcome to the forum.

Yes the blue wire was to trigger the fuel pump relay so when the engine stops, in case of accident ,it turns off the fuel pump for safety. If the relay has been bypassed with a solid connection to the pump just unhook that blue wire from ground. It goes to the coil primary and if grounded will stop that one coil from firing.So if you have no spark to one cylinder that is a place to start. Good to hear you are studying the manual. Here is where the good folks here have provided a good Honda manual if you don't have one already.



https://www.hondashadow.net/forum/72...e-manuals.html


Only a biker knows why a dog sticks his head out of a car window.
1983 750 Shadow
From the past=
1951 Cushman scooter
1962 Honda 305 Dream
1965 Honda 305 Dream
1971 Honda 175 scrambler
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post #3 of 20 (permalink) Old 07-03-2019, 01:14 PM Thread Starter
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Join Date: Jul 2019
Model: VT700
Year: 1984
Location: UK
Posts: 17
Thatís fab, thank you. I didnt trust my own opinion on it, as so much has obviously been done to the bike by someone who Ďappearsí to know what theyíre doing. The clutch switch has also been bypassed and that may well be another one of my query points further down the line! At the moment I dream about the wiring diagram, itís taken over my life (in the best way of course!)

Thanks so much for your reply.
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post #4 of 20 (permalink) Old 07-03-2019, 05:37 PM
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Model: VT700
Year: 1985
Location: West Coast Florida
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Welcome to the forum. There's a lot of experience here with guys like @swifty2014 and others that seem to have a knack for unraveling funky setups on used bikes.

If it jams, force it. If it breaks it needed replacing anyway.
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post #5 of 20 (permalink) Old 07-04-2019, 07:43 AM Thread Starter
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Year: 1984
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Thatís great news, as there appears to have been plenty of modifications to the trike over the years. Her history is hazy to say the least and Iím still trying to get my head round the wiring diagram, only to find I have parts missing and re-routed and bypassed which makes my head hurt!
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post #6 of 20 (permalink) Old 07-04-2019, 05:56 PM
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Model: Vt750
Year: 1983
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If you read the earlier discussions you may have seen the idea of taking out the 2nd spark unit as it is called. It is really a 3rd control box the 1984s and if removed it has solved some no spark issues.

Only a biker knows why a dog sticks his head out of a car window.
1983 750 Shadow
From the past=
1951 Cushman scooter
1962 Honda 305 Dream
1965 Honda 305 Dream
1971 Honda 175 scrambler
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post #7 of 20 (permalink) Old 07-05-2019, 11:48 AM Thread Starter
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Join Date: Jul 2019
Model: VT700
Year: 1984
Location: UK
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I have two separate spark units (both under the back seat), but on the wiring diagram, they are referred to as ďSpark Unit 1Ē, spark unit 2 on the plan is not there at all. Iíve read itís somewhere down by the starter motor, but thereís nothing down there, so I was assuming I had already had this part removed? Still leaves me with 2 units, but both are called Ďunit 1í does that sound right?

Thank you so much for the help.
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post #8 of 20 (permalink) Old 07-13-2019, 10:42 AM Thread Starter
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Model: VT700
Year: 1984
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Sheís alive!!

So I cut the blue coil wire that went to earth, rewrapped all the necessary and put everything back together.

My dad and I then tested the four spark plugs (which were a real pig to get out), but when finally they came out and were tested, all four plugs had a spark.

After putting everything back together and charging the battery fully for good measure, this morning I tried to start up and after much spluttering and choking and clanking (all of which was a bit worrying), she finally started (pretty stinky!)

I took her down the road and back a couple of times and was amazed (and a little frightened) at the speed I could get up. As thereís no MOT or anything, I couldnt take it any further and also I was a little worried about the pull on the throttle when I stopped, felt kinda like it was gonna go without me, but this may have been just because the choke was still a little out.

I thought it might be time to ask a mobile mechanic round to look her over for me before I take her for her MOT as Iím not sure I have all my gears but to be honest, I wasnt sure this day would ever come.

Thank you for the sound advice guys.
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post #9 of 20 (permalink) Old 07-13-2019, 10:47 AM Thread Starter
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Model: VT700
Year: 1984
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Update picture

Here is a quick update picture now that I have the tank and front seat back on. Still need some work to make the side panels fit, as I may need to adjust some pipe work to the fuel filter, but hey, itís progress!
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post #10 of 20 (permalink) Old 07-13-2019, 04:38 PM
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Quote:
Originally Posted by Smileyk View Post
Here is a quick update picture now that I have the tank and front seat back on. Still need some work to make the side panels fit, as I may need to adjust some pipe work to the fuel filter, but hey, itís progress!
Gotta say, after reading through the thread I wasn't quite expecting something looking anywhere near that good!

You scored well, and indeed have a worthy project to bring fully back to life!

I've done a LOT of miles on my first VT700 and will do more once I get some engine work finished. Treat your one well (regular oil changes, reasonable quality oil and coolant etc) and she'll treat you really well.

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