Hi guys,

Following a small accident I had recently where I hit a car at low speed, I disassembled the nose, replaced the fairing bracket, and am now at the point where the gauges are refitted and the wiring is done back up. I didn't take apart anything else aside from the nose.

However, since reconnecting everything, I haven't been able to start it. It ran once, for about 3 seconds, and then never again. The starter cranks the engine very well (although after some trouble shooting the battery is now becoming empty and I removed it to charge it). There appears to be fuel judging from the smell and occasional huge backfire (flames from exhaust!). I suspect the ignition is somehow not functioning properly (e.g. sparking when the exhaust valve is open, hence the backfire). I intend to check the ignition by sparking the spark plug socket against the frame first. Update: I have sparks, and there is a voltage on the fuel pump (which doesn't necessarily mean it's turning).

Now I'm baffled as to how this happened, as everything else seems to be working just fine, it ran momentarily and I still do get the occasional backfire. Moreover, I never touched anything else than the nose.

The bike had been standing still for ~1.5 months while waiting for parts, but I started it a week ago before disassembly and although the first 5s were a bit rough, it ran beautifully otherwise.

A last thing to note; I didn't remove the battery leads while disassembling the nose. This shouldn't be a problem as far as I know but just for information.

A next step would be to try all of this (ignition troubleshooting page from the rapair manual):
http://www.motor-forum.nl/download.p...e41194ace07b4b
But getting to the ignition coils is rather cumbersome since I have the bike in my work's garage

I was hoping any of you lads have some suggestions

 

Link doesn't load so can't see what's in there, but my guess is heavily on the tipover sensor. Check that it's not fitted upside down or defective. I've seen it being the case in more than a few similar threads. also check your killswitch on the right handlebar, it sometimes sticks so that even though it appears to be on it's not. Exactly why I never use mine.

 

Link is the ignition troubleshooting guide from the repair manual. I can't find a tipover sensor in the wiring diagram for the F3, are you sure it has one? The kill switch seems fine; I checked the voltage on the fuel pump during starting and it's definitely not zero.

 

Sorry my bad remembered incorrectly. First thing would be as you said to verify do you have spark at all by grounding a plug and cranking. You've surely checked all fuses already?

 

Check all your wiring connections. One may not be making a good connection.

 

Fuses are all fine; as is the kill switch (fuel pump has voltage when starting). In a few hours I will check the sparks and if that doesn't tell me anything go mental with the wiring diagram and multimeter to check all connections

 

Okay an update.

- I have sparks, I tested 3 out of 4 spark plug sockets with a wire close to the engine and they spark just fine and regularly
- Earlier I tested there is a voltage on the fuel pump (note that that doesn't mean it's actually turning..)

In other words I have a turning crank and ignition, and no more reason to assume there are electrical problems. My money is now on the fuel; even though the filter has been replaced and the system cleaned in May last year I may have gotten some bad fuel which has now clogged up the system (perhaps last week it was running on what was left in the hoses?)

This idea is reinforced by the fact that every day when I take an hour to take a look at just after lunch it it seems to have more cylinders igniting on the first try than any other; perhaps some fuel is seeping through which is then used on the first try.

Any guesses as to where to look first?

 

On a F3 the fuel pump only runs when the engine is running, or trying to run as in when you're trying to start it. When the bike has sat for a while, getting fuel back to proper levels in the carbs can be troublesome. So, here is a way (documented in shop manual Chapter 18, pg 18) to bypass the Fuel Cut relay and energize the fuel pump.

On the right side of the bike, behind the side cover is the Fuel Cut relay. It's located in between the ICM and the R/R. It's got a 3 pin connector on it. Disconnect that connector and with some type of jumper wire (a paperclip will suffice, just don't let the paperclip touch the frame) place a jumper/short between the Black wire and the Black/Blue wire. When you turn on the ignition key, you should be able to hear and feel (put your hand on the fuel pump) the fuel pump running. Now, understand that it may not run for long because as soon as the bowls in the carburetors get full, and the Float Valves close, fuel pressure will build up and the pump will stop.

The way you know your carburetors are set and ready to go. Give it a shot and let us know.

 

Good news! I bypassed the relay, turned the key, fuel pump started. Pump started its clicking sound, then slower, then stopped. With the relay bypassed, I started the bike. It ran for a bit, then I stopped and started it again to be sure. What struck me is that the relay was clicking a lot slower than I saw in videos of people replacing pumps, but I suppose this is to be expected due to line pressure felt by the pump as opposed to showing an open pump

I then put the relay back in place, and it started fine again. In other words, it's solved! Thanks heaps!

I do wonder why this fuel cut relay exists in the first place; it seems much more sensible to bring the fuel pressure up to appropriate levels before trying to start in the first place (cars do this as well). Anyone can shed some light on this?

 

Oh no.. After a lot of epoxy and fibreglass, I finished all the bodywork and put the bike back together again. Nearly finished (just a few minor things to do, like mirrors and fixing the upper air hoses), I started it and rode it around the parking lot a bit. I then finished it, tried to start... Nothing. Judging by the smell, there is petrol, and I had a few backfires. However I still suspect a fuel problem. I did re-check the sparks with a wire in the socket against the frame, which are fine.

Since there is the smell of petrol, perhaps the engine is flooded, with the plugs not sparking because they're wet? I'm not sure if this is/can be the case. I suppose the only way to check is to take the tank + air filters off and undo the spark plugs..

I tried:
- Starting with choke off & on.
- Unflooding a bit by fuel off, choke off, full throttle cranking.
- Bypassing the fuel cut relay again. This is where it gets interesting: This time the pump did (and does not still) stop after a few seconds of filling the float chambers. What does this indicate? No pressure/fuel coming through to the float chambers? Faulty/dirty float valve(s)? I'm not sure what causes the pump to stop usually; back pressure or float valve sensors?

I'm quite puzzled because it ran fine less than an hour before..