Odd Problem

A couple of months ago I obtained a 5th Gen as the basis of my next naked VFR project and which in the meantime a friend could use on our European trip. It's a slightly tatty 1999 with nearly 27,000 miles, but appears well maintained and sound.

I got it as pretty much standard but had to fix a seized choke cable which necessitated removing the airbox and although not originally intending to do anything prior to the Euro trip in the summer, I just couldn't face struggling to re-connect all those pipes and tubes under the airbox, so I removed the 'pair' system and flapper gubbins. The bike then started and ran fine, with several quick tests around the driveway of the house. So today I took it for a longer test.

Set off down the road and all seemed fine, but within 200 yds realised I'd forgotten to do up the zip pockets in my jacket so used both hands to do them up as the bike slowed down and then was able to grab the bars and open the throttle again - at which point it coughed and spluttered with an obvious and massive misfire whenever the throttle was opened. If I kept it almost closed it would keep going at nearly 50, but as soon as I opened the throttle a bit more it would miss, cough, splutter and that just got worse if I opened the throttle any more. Maybe I should turn back...

But with a nice breakfast at the far end of this ride and the fact that the bike did actually keep going, I carried on, puzzling in my head what on earth could cause such a catastrophic misfire. Seemed unlikely my plumbing simplification could have caused it, but what could it be.

About 10 miles later I was on a dual carriageway and able to ease the speed up to 70/75 and held it there for the next 5 miles or so and the realisation began to dawn on me that it seemed to be running rather better, confirmed at the roundabout at the end as the bike was indeed now running apparently perfectly - as it then continued to do for the rest of the day - about 100 miles. This has me baffled.

The only electrics I disturbed was the L Rr cylinder (No. 2 isn't it) spark plug cap which I had pulled off the plug while trying out some CoPs for size. But as far as I know the cap was correctly fitted back onto the plug. No fuel lines were disconnected and the bike had half a tank of fuel the whole time I was working on it.

I'm sure when I first set off, it was fine. I would have noticed the coughing and spluttering as I pulled out of my drive. Then 200 yards later, it can hardly run, but clears itself over the next 10-12 miles. Everything else worked fine the entire time.

Anyone any ideas?

Oh, one problem I did notice. The clutch interlock is not working. I thought at first the clutch switch was disconnected, but it's not. However, I just cannot start it in gear. Unless it's in Neutral, the starter doesn't operate. So the interlock circuit needs looking into, but I can't really see this having anything to do with my massive but apparently temporary misfire problem. Although it now appears well and running perfectly, not knowing the cause is a worry that I'd rather not have when setting off around Europe with a friend on this bike. But right now I cannot think of anything that fits the symptoms. Can anyone else?

Did you go back in again?  I have pulled everything apart before and swore up and down I put it all back.  Three times taking it all about later I found what I missed.

I have not looked at it again no, not yet. But I'm trying to establish what could cause such a major engine malfunction (no FI light at all though so no injection problem) which would then cure itself over the next 10 or so miles. So far I've not been able to think of anything that could do that. Problems like that don't tend to fix themselves while the bike is being ridden.

Was this bike sitting for a long time or was it being ridden prior to your purchase?

Gummed up valve that you cleared up through the old Italian tune-up?

Was this bike sitting for a long time or was it being ridden prior to your purchase?

Prior to purchase, I don't know, but I don't think so. It was sitting here for about 6 weeks, but I had started it and then tried a short ride around on the driveway which indicated no problems whatsoever. Nor I think when I first set off. The problem hit after a couple of hundred yards, then cleared itself with NO intervention from me. I didn't try to rev the nuts off it in order to clear it, just ride with low throttle openings to avoid the stutter. I was using the fuel in the tank when I got it, but I only put more in about 60 miles AFTER it had miraculously cleared, so nothing to do with the actual fuel.

It couldn't have been mechanical. Those sort of problems aren't intermittent like that and self clearing. Bad fuelling also tends to result in just poor running, not stuttering as one or more cylinders cut in and out. I'm sure the problem was electrical, but whether spark or injection related is hard to say and even electrical bad connections tend to not fix themselves.

Where was the cold start switch (choke) during this time? Is it possible it was stuck on and then released itself? 

That would explain a rough run once the engine was warm and then fixing itself later. Running too rich would cause the backfire.

When problems start out of the blue, I always check the last thing I touched :)

Yes, the starter valves could be gummy and not returning to position. It is unclear from your description of the cable repair: Did you clean and lube the valves when you addressed the problem? 

How about a leaky fuel injector?

I thought about that but I've never touched the cold start valves, just removed, cleaned and lubed the cable till it was working ok and replaced it. Anyway 2 things lead me to not suspect this:-

1. The bike was already at normal idle speed when I set off, indicating that the cold start system was already fully 'disengaged'.
2. Unless I'm mistaken the cold start system doesn't alter the mixture. The CS valves simply bleed air past the butterflies which the injection system then matches with more fuel as appropriate to the temperature. So it's exactly the same as if the butterflies were held slightly open. Any richer mixture requirement is handled by the ECU reading the temperature and pressure and setting the appropriate mixture, i.e. how much fuel it flows with that amount of air flow. So when an engine is warm, pulling on the 'choke' will only raise the idle speed but not change the mixture from what the engine requires at that temp. and pressure.

So no, I don't think that's it.

Sounds to me like it could be a little water in the fuel as that would sit at the bottom of the tank ,flowing through until you have straight fuel now .

Except it was running ok at first and during several smaller tests and only started misbehaving after several hundred yards of this test. Also, bike has been parked under cover so no obvious way for water to get in.

Please clarify, where did the backfire occur, intake or exhaust?

Didn't actually backfire. At low throttle it was running almost OK, but as soon as I tried to open the throttle it missed and stuttered badly until I reduced the throttle opening again. It felt like it would backfire if I did that repeatedly, but that's just a feeling.

I've had ignition problems before (not on this bike) that had similar symptoms. A weak system could just about work, but broke down when trying to spark through more 'stuff' in the cylinder. But they never cleared up by themselves and instead required replacement coils and/or plugs. With the symptoms now nonexistent, it's hard to know what I need to be looking at. Maybe it will never re-occur? But if it does...

Sounds like the MAP or TPS sensor was not clean as they determine the EFI input rates, along with the other sensors. or water like previously noted. Wait till its cold then try again, if its gone it was transient if its back its temperature related which could be the starter valves.

Mine will NOT rev under load when cold with all the mods, but is fine once warmed up. Mine has the auto enrichment which seems to cut out to early, as in the EFI circuit temp is good, but the engine temp is not quite up there yet. I've had the same thing on bikes with manual chokes, I assume you still had the choke on ?

Mines faulty temp area is 55-65C on the gauge, below that its fine & around an indicated 55C the autroenrichment stops, but the bike does not run happy until it reaches 65C. I plan to put a restrictor in the coolant circuit to the TB's to slow the heating down to cure this.

Oops yes you said "misfire" and I got ocd mentally stuck with "backfire".

Mohawk's post made me think. Ken have you owned a fifth gen previously?

The instructions for the 5th gen state to run the fast idle for 30 seconds at 2500-3000 then shut it off. The temp will typically be at 100°F, and rise fairly quickly while riding to operating temperature. Also it states above 90°F not to use it at all, which is a hint to what the designers expect from the temperature. The fast idle should not be used while riding.  

The owners manual does warn of cylinder wash from excessive use of the fast idle. Looking at Ken's prior posts I agree that there is no indication that the ECU knows about the starter valves. However, it does know throttle position and it does know airflow. So it may not calculate correctly for the state where the fast idle is on and the throttle is being used.

Ken if you did have the fast idle on while riding I would say that is a possible culprit. I do not think the bike will handle that properly.

I have to assume ECU programming changes were implemented for the idle wax unit which has a mind of its own. 

I was otherwise going to suggest running it in pitch black to look for sparks from the wires. Just because that sounds like fun.  :biggrin:

I'm pretty sure the cold start system does not enrich the mixture. The ECU simply uses the temp and pressure readings to decide how much fuel to squirt in and the built-in maps take care of the fuel ratio requirement at that temp etc. So I don't think having the 'choke' on can have much effect once warm. But, the additional airflow though the cold start valves might cause the bike to not run perfectly if used inappropriately. However, I'm not talking slightly imperfect running, I'm talking major coughing and spluttering, inability to open the throttle wider than allowing it to maintain about 45 mph. This is not some minor fuelling inaccuracy. Something major was going on that was causing either the sparks to fail or the injectors to not squirt.

Also, whatever the 'settings' of the bike (i.e. cold start position etc), it was working perfectly for the first quarter of a mile, then while the throttle was closed as it slowed from probably 50 down to about 30 the problem manifested itself, only to clear again by itself about 12 miles later. This was not a gradual process. At about 10 miles it was still coughing and spluttering. Then by 12 it had cleared and was perfect - never to return (yet).

There's 2 issues here. What could cause the bad running like that, so linked to throttle position and also how/why did it suddenly appear and later disappear all by itself.

I think Mohawk's idea about it being temperature related might be relevant, with it just being a limited temperature range at which it occurs. However, I was out to test ride other bikes and so on more than one occasion during the day the VFR was left to cool down as I rode another bike and although I doubt it ever became completely cold, I would have thought it did drop low enough to be within the range at which I previously experienced the problem. Obviously I will try it again from fully cold and see what happens.

I had this exact problem on my fighter. Jumped the neutral safety switch permanently and it went away forever. It was the strangest thing.

Which exact problem was it you had? Only starting in Neutral or the coughing and spluttering?

What was it you 'jumped'? There's no such thing as a "Neutral Safety Switch". Did you mean the Neutral switch (so the Neutral warning light no longer works) or the clutch switch or the side stand switch, all of which are part of the neutral side stand safety interlock system?