1986 VT1100c Ignition problems -Help! - Honda Shadow Forums : Shadow Motorcycle Forum

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Old 04-07-2012, 08:33 AM   #1 (permalink)
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Default 1986 VT1100c Ignition problems -Help!

Hi - I purchased my 1986 VT1100c a year ago with a duff gearbox (no third!) and various other mechanical & electrical issues. I've been working on it ever since. I've now rebuilt the gearbox (worthy of a 2nd post in itself!), and replaced/reconditioned many, many other components (probably worthy of several more posts!).

Bike now starts and is fully MOT'd. However, it will still only run on its rear cylinder (a problem that pre-dates my ownership) and the solution is still elluding me.

Both cylinders have been pressure tested and have virtually equal & good pressure.

Both coils are good as are all HT leads (excellent sparks from all 4 plugs & internal/external resistances well within spec).

Resistance on all 3 pulse generators is fine (Cam plus both crank) - although I've changed both crank units with known good ones to confirm).

Rectifier has been replaced and is working fine.

I've swapped out (and back) different sets of carbs and the problem remains the same with both (again, one is known good - both are VT1100c specific) - plenty of fuel getting to the plugs.

Timing position has been checked and confirmed OK against timing marks and also by having the front cylinder cover off to check physical valve positioning is correct against this).

Primary (A) CDI unit has been swapped out with known good unit.

Only other symptoms are that rt hand exhaust does occasionally backfire & you get occasional 'flashes/pops' of fuel ignition activity from the front carb - whilst the bike is running.

Bike starts fine from cold.

Any suggestions or inspirational ideas would be more than welcome/appreciated! I can now offer a source of spares, knowledge, advice, empathy, sympathy, etc. to any/all fellow Shadow owners who've experienced problems & needed to demonstrate particular determination to overcome them - and/or several cases of beer or bottles of wine to anyone who can help me over (what I really hope is my last) major hurdle before I can get back on the road!.
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Old 04-07-2012, 09:42 AM   #2 (permalink)
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sounds like you are having fun. ok maybe not
so what i think you are saying is that when it is cold it runs ok? but when it is hot the cyclinder cuts out?
sounds like you have looked into just about everything
have to changed out the coils? i have seen coils cut out when they get hot but work fine when cold.
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Old 04-07-2012, 10:51 AM   #3 (permalink)
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like he said ^^^^ the coil will break down when hot.
swap the front and rear coils with each other to see if the problem moves to the other cylinder.
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Old 04-07-2012, 11:01 AM   #4 (permalink)
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I have an 85vt1100 with a similar problem-Mine runs only on the rear cylinder-The front kicks in only after the engine warms up. Be very interested to see what you find out. My next move is plug wires but I haven't been able to change them yet.
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Old 04-07-2012, 12:02 PM   #5 (permalink)
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Thanks for the replies, gents:

Brooksey222: Many thanks for the suggestions - just to clarify - the front cylinder doesn't run whether the engine is hot or cold; the bike just happily starts - and runs (tho' badly as you'd expect) from the rear cylinder alone. I've swapped over the coils (both when the bike's been run for a while & at cold) and this seems to make no odds; there's still good sparks from all 4 plugs from both coils at all temperatures (from stone cold to 'normal' (midway on temp gauge) engine operating temperature. If it wasn't for fact timing is fixed - I'd instinctively be looking to that!

SnowShadow - sounds like you have a slightly better situation than mine - in that at least your front cylinder comes into life when warm - I don't even get that .

The only thing I really can think of as another possibility that I haven't yet been able to try is swapping out CDI Unit B/2 (the smaller of the 2 that sits hidden under the battery tray). It would be great to know exactly what part of the ignition system this controls to know if this is directly linked to either front coil/front pulse gen functionality?

Thanks again gents.
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Old 04-07-2012, 12:13 PM   #6 (permalink)
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Deroyentz,

I'm in awh at your mechanical knowledge. Transmission fixes are like brain surgery to me.

I would suggest you jumper the fuel pump relay. Search and you will find lots of how-to messages.

This relay loads the front coil. If this relay is shorted,it could cause what is happening. Don't worry, this jumper wont hurt the bike, and the relay is unneeded as long as you keep from crashing! Good luck, Dave

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Last edited by verdeva; 04-07-2012 at 12:51 PM.
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Old 04-07-2012, 01:00 PM   #7 (permalink)
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I'll second the fuel pump or fuel lines.

When I first fired up my 86 VT1100 it ran fine as long as I didn't take too much gas and then it would drop out one cylinder and run on that one till the float bowl on the other was fed. Turns out I had a split in a fuel line. I fixed that and not had a single problem since.
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Old 04-07-2012, 04:43 PM   #8 (permalink)
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Quick question if you remove the plugs after running, do they appear wet and smell of gas.
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Old 04-12-2012, 05:32 PM   #9 (permalink)
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Many thanks for all the advice & suggestions, gents. Ironically, managed to identify/sort the issue last night.......turned out to be timing on the front cylinder and duff instruction in the Haynes manual - I should have learnt over the past year that it's always worth comparing notes between the Clymer & the Haynes as there have been several occasions where the two indicate different approaches & different potential solutions for the same problems. Inverted front cylinder top cam chain sprocket by 180 degrees and, miraculously/surprisingly - front cylinder burst into life and bike is running great (first trip out in over a year along the Cornish coast this PM ).

I'll try and upload a few pics - many thanks all again; it's great to find a forum such as this & to know I'm not alone here in the UK in persevering to keep these bikes on the road! There's one thing for sure, I've now invested so much time, money, sweat, tears, etc. etc. in this project that I can't see me ever parting with it - aside from all else I'd never recoup anywhere near what's been invested in it!
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