Dead NC35 - about to loose my s*#t

GarethC · Derestricted Danger Joined: 14 Nov 2015 Karma :

Hi. First time post here. I have relatively good knowledge of engines and have worked for around 50 hours on this problem over the past two weeks. Bike cranks nicely, but will not fire. Push start also not effective.
Bike was running perfectly, parked it over night, would not start again.
I have rebuilt the carbs over 30 times! Here's what I can confirm:
Carbs 100% clear, petrol flows in, bowls fill up, jets are clear, floats at 12.5mm.
New spark plugs, all at 4k ohms. Leads at 4.4k ohms.
Battery 4 months old. Running flat from testing, but using charger to top it up.
Getting a large spark with screwdriver in lead-end to frame.
Good compression although I don't have a gauge to test.
Clean petrol.
Just won't take.
Any advice? TIA. Brick Wall

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1996 Honda RVF400 NC35. First bike.

Ariel Badger · Super Spammer Joined: 02 Dec 2006 Karma :

why a screwdriver and not a spark-plug to test it?
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GarethC · Derestricted Danger Joined: 14 Nov 2015 Karma :

Forgot to add after that, I added the spark plug to the HT lead, grounded the spark plug and observed good spark.
In the last few minutes, I found pretty serious rust on the grounding metal of the rear coil through which the bolt goes (only checked that one so far). Maybe enough to cause the spark to break down when under compression. Will keep you updated.
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1996 Honda RVF400 NC35. First bike.

GarethC · Derestricted Danger Joined: 14 Nov 2015 Karma :

Continuing my investigation....
I am now convinced it is spark-related. Although in previous testing I found spark on all the leads and plugs, I have now discovered that the spark is erratic across all the leads, with some giving no spark at all. The leads are rather old, and incredibly stiff. With the plugs attached to the leads and the plugs grounded on the engine, I found that the leads appear to have breaks. I cannot even get continuity in some of the leads now. Spark plugs are brand new and measure correct resistance, so I am ruling them out. The coils appear to have correct resistance as well. Anyone have tips of building new leads using the old caps? I can get lengths of lead here in Cape Town but now complete leads.
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1996 Honda RVF400 NC35. First bike.

hmmmnz · Super Spammer Joined: 22 Aug 2006 Karma :

id replace the leads and plug caps as a matter of course,
also check the valve clearances, and make sure you have good compression
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Taught2BCauti... · World Chat Champion Joined: 12 Jan 2012 Karma :

Check the plug gaps too (after you have changed the leads and plug caps) as they are rarely correct out of the box.

If you don't know the exact specified gap, 0.025" (0.635mm) is a good starting point.
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GarethC · Derestricted Danger Joined: 14 Nov 2015 Karma :

Thanks so far guys. Still battling.
Plugs are set to 0.68mm (specs say between 0.6 and 0.7).
Gonna try get hold of a set of leads tomorrow. I tried to make one last night by pulling apart an old one and replacing the lead using a new one I had from my Golf and the old NC35 cap. Nothing really changed. Also trying to borrow a compression gauge to get accurate readings. Although not anticipating big problems here as the bike was going beautifully one day and dead the next.
Updates to follow...
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1996 Honda RVF400 NC35. First bike.

GarethC · Derestricted Danger Joined: 14 Nov 2015 Karma :

New plug leads didn't do the trick. Handing over to the mechanics in the next day or two.
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1996 Honda RVF400 NC35. First bike.

Burnzy1989 · Nitrous Nuisance Joined: 06 Apr 2009 Karma :

Might be your coils braking down or posibly your stator or pick up coils it can be a mind field. Have you checked for a bad earth .

Wull · Crazy Courier Joined: 10 Apr 2014 Karma :

Have you tested the coils? Primary and secondary leads?
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Ariel Badger · Super Spammer Joined: 02 Dec 2006 Karma :

You need to apply a little logic to the problem, it is a four cylinder motorcycle so it will be a fault with a component that is common to all four cylinders.
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GarethC · Derestricted Danger Joined: 14 Nov 2015 Karma :

Your're right. The leads were just a last resort.
It's almost like a kill-switch is engaged. But I have eliminated this through confirming that spark is present when the switch is set to run, and dead when set to off. But the problem presents like an engaged kill switch.
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1996 Honda RVF400 NC35. First bike.

Wafer_Thin_Ham · Super Spammer Joined: 18 Nov 2005 Karma :

Sidestand cut off switch working?
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GarethC · Derestricted Danger Joined: 14 Nov 2015 Karma :

It is. I know this because with the stand down, I don't get spark. With the stand up, I do. But it has to be something like that.
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1996 Honda RVF400 NC35. First bike.

Robby · Dirty Old Man Joined: 16 May 2002 Karma :

Assuming this problem looks like it is locked down to sparks, there are a few common points that can fail.

1. Side stand switch. This is the most common cause when a bike works one day and starts cocking around the next. Sidestand switches can suffer intermittent failure. You can get around this by disconnecting/bypassing the whole thing. If this fixes the problem, but you would like to retain the switch as a safety feature, then it is worth stripping and cleaning the switch. They pick up a lot of road crap which causes corrosion and poor/intermittent connections.

2. Main earth strap from engine to frame, or frame to battery. These can corrode or break. Easiest diagnosis is to run a new, additional connection from somewhere on the engine to the negative terminal on the battery using good thick wire.

3. Fuses. Fuses corrode over time. Old type round glass fuses are an absolute arse for this sort of thing, but blade fuses can still give problems. Pull the relevant fuse and clean its legs, or just replace it.

4. Kill switch. These can fail in the same way as a side stand switch, although this is less likely.

GarethC · Derestricted Danger Joined: 14 Nov 2015 Karma :

Thanks for the input Robby.
1) Side stand switch - I have cut the 3 wires and wound them together. Side stand switch eliminated.

2) Main earth strap may need attention. The strop broke off at the tab on the negative terminal. I had to jimmy it to get home, but it looks like there's good contact. Will get a new one today and replace it tonight.

3) Fuses are all brand new and fuse holders have been cleaned. Measured resistance and voltage before and after fuses - all good.

4) Kill switch seems ok. It lives in the 'run' position in case of corrosion build up (I live 20m from the beach). But engaging the kill switch kills the spark (visual confirmation) while in the run position, there is spark.

I like all the ideas guys..... please keep them coming!
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1996 Honda RVF400 NC35. First bike.

Kris · World Chat Champion Joined: 03 Feb 2002 Karma :

There's no alarm / immobiliser on it is there?

Old knackered Datatool alarms have a habit of doing this.
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GarethC · Derestricted Danger Joined: 14 Nov 2015 Karma :

Thanks Kris, but no alarm. Just the most basic mechanics and electronics.
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1996 Honda RVF400 NC35. First bike.

Kris · World Chat Champion Joined: 03 Feb 2002 Karma :

Just out of interest, you say it has recently had a new battery on it.

Why did you change it? Were you having any issues?
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GarethC · Derestricted Danger Joined: 14 Nov 2015 Karma :

The old battery came with the bike, was a good couple of years old, and wouldn't hold a charge.
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1996 Honda RVF400 NC35. First bike.

Robby · Dirty Old Man Joined: 16 May 2002 Karma :

Sort out the main earth strap before looking for more problems. If you have an intermittent connection there you're going to have problems keeping it running, particularly at low engine speed/low electrical load where poor connections have the largest effect.

You mentioned living near the sea. Salt air speeds up corrosion. It is worth checking all of the frame earth points for corrosion and cleaning it up where you find it, then reassembling with a smear of grease to slow future corrosion.

GarethC · Derestricted Danger Joined: 14 Nov 2015 Karma :

In the past two/three days I have detached most of the earth points, sanded the contact surfaces, and tightened down nicely. There are some more to do. And I will definitely replace the ground strop today and maybe run a secondary one as well to the engine block somewhere. Could be why I can see spark when the plugs are out, but perhaps they haven't got the solid connection to fire when under compression.
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1996 Honda RVF400 NC35. First bike.

Carvel · World Chat Champion Joined: 01 Jun 2010 Karma :

The neutral switch failed on my 400 which caused an intermittent starting fault.
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GarethC · Derestricted Danger Joined: 14 Nov 2015 Karma :

Update: I got the bike back. Turns out it was only the carbon build up on the plugs which prevented it from properly firing in the cylinder. Since the plugs were just about brand new, they were taken away for bead blasting and cleaned up nicely. Bike is running, but still needs a little tune-up. Melted the fuse holder on the output from the rectifier, but the fuse didn't short. Research indicated it was poor connection in the fuse holder. Installed up-rated fuse holder last night and slightly thicker negative and positive wires from the rectifier directly to the battery. We'll see how that goes.
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1996 Honda RVF400 NC35. First bike.