VFR750 cutting out

Morning all

I went out for a nice run yesterday on the VFR (93 carbed model), got some nice high speed runs on a private stretch of road. Everything was hunky dory.

A couple of days earlier, I installed a Delkevic stubby exhaust, sealed nicely, no blows etc - sounds great and seems to have freed up a flat spot at 6krpm.

I also know the following:

fuel filter (was) clean (need to check again)
Spark plugs, oil & filter and air filter are new
reg rec looks new, also has a heatsink on top of it. previously revving the bike saw the lights go up and down with revs (I believe this is normal) but didn't test today

Anyway. I started the bike this morning, choke on full as it was freezing. It burped into life, instead of jumping to around 2000-2500rpm as it normally does it sat just around 1500. If I gave it a bit of throttle it didn't do much, just seemed to rev a tiny bit, as though the throttle cable was really slack or something, best way I can describe it!

I let it sit for a few minutes and it eventually went a bit higher up the revs but not massively. I turned the choke off and it idled at around 1000rpm (I have it set to 1200), again the throttle didn't seem to do much.

To make things worse, traffic was awful due to an accident and the bike cut out three times. Once when I was sat at idle and I gave it a bit of throttle to see if it was still lagging (which it wasn't) but as soon as the revs came down it cut out. Fired up fine and carried on. It then cut out again while in gear, idling, with the clutch pulled in. Again it fired up fine. It then did exactly the same thing a few metres down the road.

I got to the indoor carpark and parked up. Gave it a blip and a bit more of a handful and it seemed ok, didn't cut out. I don't know if it's just me but the exhaust sounds a little different to yesterday, not quite as smooth (hope it ain't a misfire).

I'm finishing work at 4pm so I'll see how it fires up.

I'm thinking the following though:

reg/rec is duff? If I buy a voltmeter, how do I actually test the voltage, by simply putting the voltmeter against one of the battery terminals? I believe it should be between 12-15v at idle. Correct me if I'm wrong, some steps to follow would be appreciated. If I put the bike in neutral and turn on the headlights (normal beam) and give it a rev, they should go a bit brighter, if they don't, is that a dead set reg/rec issue?

carb issue? I know the bike was sat for a year or two before I bought it, the guy I bought it off had it serviced and it's always fired up fine (although it's required a smidge of throttle on occasion). So maybe they need a clean (I have a set of ultrasonic cleaned ones coming back to me soon so can swap them over).

Is there anything else I should check? I'm not very mechanically minded with electrics and what not. I'm not shy though and will give it a go.

 

Hmm. Before diving into anything - you need to home in on what is actually causing the bike to stall. Electrical gremlins are such a well know issue with these bikes - my first step would be to check the battery volts. A healthy battery should show up between 12.7 and 13.2 volts. Certainly if its below 12.5 then for now I would discount problems with carbs and focus on running the drill checks as described in post # 9 on the following thread.

http://vfrworld.com/forums/showthread.php/39277-How-to-fix-common-regulator-Stator-failures

Please note you must do those checks TWICE after you have either fully recharged the current battery or fitted a new one! Because faults may not appear until the wiring get's really hot, you need to do the checks first with the bike cold, and again straight after taking it for a good 30 minute ride. The rest of that thread should give you plenty of ideas of what to check depending on the multi-meter results.

Good luck lets us know what you find.



SkiMad

 

Did you buy something off me a while ago? Think it was a street triple Haynes manual, in Deptford? You've got a very similar looking bike and the skimad username seems to tie in with the ski tours the chap talked about!

I've bought a voltmeter and a laser temp gun so I can make sure it's putting out the correct voltage and all four cylinders are at a similar temperature.

 

Yes John the Haynes manual has been well used. You still in that Deptford High Rise? A few years back I was lucky enough to swap a housing estate flat in Brent for this view :smile:..



Brilliant for winters with over 400+ miles of linked ski runs in France and Switzerland and in summer its perfect for motorbikes and mountain bikes.

Good luck with the volt meter.



SkiMad

 

Ah cool, small world!

I know this isn't a comprehensive test but I recorded this video.

https://www.youtube.com/watch?v=7qhU4heMTfA for the regulator. This was after a very spirited 20 minute ride, hence the fan kicking in.

Here's the bike on a cold start. I've only owned one other carbed bike (my other RC36!) which I never ran in winter and it was a none runner very quickly due to carb issues anyway so doesn't count haha. So I don't know if it's meant to lack revs like that from a cold start?

https://www.youtube.com/watch?v=GIjwLEYxZpM - it seems to make a ticking sound at idle as well, can just hear it in the vid.

I'll wait for some comments from clued up types!

 

Just for starters can you give us a bit more info, what is the history on this bike,have you just bought it and you are having these problems, have you had it for some time and been riding it regularly and this problem has just developed, very unlikely exhaust would have anything to do with it

 

No worries, here's a list:

Bought it in January
Guy I bought it off, he purchased it from a chap down the road from him
The bike was sat unused for around four years
The bike was recommissioned in November 2014. New oil, filters, spark plugs, brake pads etc.
RR was changed, I think, in 2008, to an Electrex model.
I've ridden it approximately 10 miles a day 5 days a week.
Had my first long blast out on it yesterday, did around 75 miles, lots of high speed action.

Issues started this morning. Cut out three times on the way to work.
Started fine this evening when leaving work.
Didn't cut out on the way home, rode it like I stole it.
Tested the battery after the ride as per the above videos.

Anything else you need to know?

 

One thing I have never heard mentioned here at VFR World is power supplied to the coils. Supersport boys always say to fit a relay straight from the battery to the coils so you have a genuine 12 volts at the coil, problem is a lot of these bikes are getting age up on them, 30+ on many of them, and your power to the coils is fed through a number of connectors in the harness, ignition switch,kill switch all of which can cause power drops so that by the time the poor coil gets its power it can be down to 8 volts or thereabouts. This can cause all sort of misfiring, difficulty starting and a general overall drop in performance and pulling of carbs looking for answers. Start with pure power to the coils and work back from there

 

99% of bikes like yours have never fitted the coil mod you describe, and they start OK if the battery is really good. If it mostly cuts out at low rpms, i'd guess the carbs' idle jets or circuits are jammed with abominable crud. :disturbed: But first you must verify the charging system output is OK---13.5 -14.5 vdc @ 5000 rpm.

After starting from cold and after about 30 seconds start backing the choke off to 1/4 or zero and use the idle speed adjustment screw to set the idle rpm. Using too much choke for too long can foul plugs and stall the engine.

 

Squirrel, I do find it strange that these problems haven't surfaced here, must be a reason for it. Did the relay mod recently on a mates 84 BMW that would just cut out while riding along. Relay fixed the problem and we didn't find what was causing the problem, but obviously something was breaking down enough to cause it to stop. My CB had a misfire I could hear in the exhaust at 100kph, fine above and below the 100kph, it would cut out at the lights sometimes for no apparent reason, fitted a relay, solved the problems. Just something to keep in mind as these bikes get older and the copper starts to deteriorate at the ends and connections

 

If your bike cuts the lights when it cuts the engine, clean the big red plug between the ignition switch and wiring harness.

Next, tighten both battery terminals and the large black wire to ground.

 

Good info guys. The bike seemed perfectly fine this morning so I'm keeping an eye on it. I'll probably purchase a VFRness and some other bits as a matter of caution as I intend on keeping this bike for many, many years.

 

Hi John

I have just looked at those videos.

That first video showing the "immediately post ride" voltages is very revealing - you definitely seem to have classic VFR electrical gremlins, so I would definitely leave the carbs etc alone for now, at least until you get the charging system working properly.

On that first video - with the ignition turned off, the initial battery volts looked OK, but as soon as the bike was fired up there were several times when the volts dropped down far too low to keep the battery charged. It should be sitting at 14+ volts or at the very least delivering 12+ at idle. On a healthy charging system, whether the lights are on or off should not really result in a significant voltage drop (0.5v) as a properly functioning RR should be plenty capable of keeping up with all the energy demands of a hot engine.

What was very noticeable was that the volts dropped way down to around +7 volts when you were revving the engine. On my VFR the volts stay dead solid at 14.3 pretty much all the time the engine is running, with no substantive change in volts with the engine revved and even with lights and heated grips turned on the volts will settle back at 14.3 within a fraction of a second.

So as the battery volts looked OK, the big question is RR, stator or loom? (It could be more than one!)

Inherently to work out which components are suspect, we now need you to carefully run through the voltage and resistance tests covered in "the drill" and then post up the results. In the meantime welcome to the real VFR owners club - as we have all been there! Having been stranded once in Wales I chose to install an acumen DGV display (plug and play add on behind the instrument binnacle) so I can monitor voltage whenever the bike is running and can now spot problems early.

It would be very informative to see if the engine running volts are higher when the bike is started from cold (ie after being parked up overnight). If a cold start shows a healthy 14+volts then it would indicate the RR is doing its best and is probably working fine whenever it is receiving acceptable AC volts from the stator - but once the stator windings get hot, the insulation on one or more phases of the stator fails starving the RR and - causing the bike to literally drain the battery and eventually run out of electricity and cut-out.



SkiMad

 

Thanks mate, I'll do everything this weekend as it's running ok at the moment (I know this starts intermittently). I'm really not confident with electrics, I've contacted a chap in Croyden called Steve Hallam who I believe is the dogs danglies. I might get him to put me together a copy cat VFRness and so forth. I'm calling him tomorrow to discuss options. Don't mind paying someone else to do it if it solves this long term.

 

No worries. It is astonishing how owning a VFR can help people learn new skills :smile-new:

I guess Steve will have been through the diagnostics routine so many times he won't take too long to track down the fault. In the meantime if you have a bit of spare time it might be worth having a close look at the stator and RR connectors for signs of melting, and checking the obvious - the battery terminals are clean and tight.



SkiMad

 

Dropping to 7 volts I didn't know that, anything dropping below 12 is terminal

 

All you fellas know that VFRs pre-1994 used much different wiring, right ?? Thick, robust, coppery, manly, heavy-duty stuff entirely different from bikes post-1993 or '94. Maybe they saved weight or maybe they saved yen, but after 1993 wires were alot smaller. Whether that is related in any way to more frequent failure modes i'm unqualified to state. But it's a firm "maybe" ! Why did Honda cheap-out suddenly on quality ? Was it all cost-accounting or poor leadership ?

Photo shows pre-'94 heavy-duty wires.

 

To be fair the bike's been faultless since that morning. Not a hint of any issues. I'm keeping an eye on it to see what happens. I'm still going to see Steve anyway so he can give it the once over and confirm whether or not there really is an issue.

Everything on the bike is in near pristine condition. The battery looks brand new, terminals are spotless, the Electrx RR looks ok and seemed to run aroung 20 degrees C while the bike was turned on after a spirited run. So here's hoping it's something of nothing.

 

^ that was a mess Ice-Hunchin :wave: check oot put of stator, three yellow wires, check R/R. Its all in the "good-book" your friend "Man-you-ELL" cheers...

 

Don't get complacent about this because it is working ok now, this is just a warning sign that something is not happy and next time you could end up stranded