VFR400 problems - Craig, Mitzy et al
Discussion
MY friends VFR is not playing ball.
To start it requires full choke, as soon as you touch the throttle it tries to die.
If you give it a healthy handful of throttle it'll completely stall.
If you give it tiny increments in throttle you can "fool" it into revving but its really lumpy and sounds like its on 2 rather than 4 cylinders.
If you take the choke off it also dies, it doesnt idle or anything.
Had plugs off, they're ok - i would say that the spark looked weak whilst cranking but there was a spark and the plug gap was ok.
All 4 plugs gave a spark.
Fuel is coming out of the tap no problems, the vacuum feed to the tap is working fine (pulsing).
I pulled off the vacuum diaphrams off of the rear carbs, they looked ok - the rubber hadn't gone brittle.
There was fuel dripping from the tap overflow, also from the exhaust where the can meets the pipe - sounds like flooding but it needs the choke to run - catch 22!
We were thinking fueling but the more I think about it the more i think it's something to do with the ignition, very weak spark - the fuel in the exhaust makes me think it's not being burnt in a cylinder (or 2) and being ejected out into the exhaust...
Any ideas?
To start it requires full choke, as soon as you touch the throttle it tries to die.
If you give it a healthy handful of throttle it'll completely stall.
If you give it tiny increments in throttle you can "fool" it into revving but its really lumpy and sounds like its on 2 rather than 4 cylinders.
If you take the choke off it also dies, it doesnt idle or anything.
Had plugs off, they're ok - i would say that the spark looked weak whilst cranking but there was a spark and the plug gap was ok.
All 4 plugs gave a spark.
Fuel is coming out of the tap no problems, the vacuum feed to the tap is working fine (pulsing).
I pulled off the vacuum diaphrams off of the rear carbs, they looked ok - the rubber hadn't gone brittle.
There was fuel dripping from the tap overflow, also from the exhaust where the can meets the pipe - sounds like flooding but it needs the choke to run - catch 22!
We were thinking fueling but the more I think about it the more i think it's something to do with the ignition, very weak spark - the fuel in the exhaust makes me think it's not being burnt in a cylinder (or 2) and being ejected out into the exhaust...
Any ideas?
It starts ok, it's just the running.
Good point about continual running.
Good shout on alternator.
The bike hasn't been riden for years but was started once a month and run up warm - the battery went flat, it was changed and since then it's not been too clever.
It's the proper battery, so maybe we'll look at the alternator next.
Good point about continual running.
Good shout on alternator.
The bike hasn't been riden for years but was started once a month and run up warm - the battery went flat, it was changed and since then it's not been too clever.
It's the proper battery, so maybe we'll look at the alternator next.
If only it was that simple 
No choke means it will not start, idle or anything.
Get it running on choke, engine temp gets up to 70°-80°, back choke off - bike dies.
Plugs are not coming out wet - they are the correct colour if not a little darker from running on choke but not rediculous.
I just keep thinking it's ignition and not fuel - I will look into the rectifier thingy.
No choke means it will not start, idle or anything.
Get it running on choke, engine temp gets up to 70°-80°, back choke off - bike dies.
Plugs are not coming out wet - they are the correct colour if not a little darker from running on choke but not rediculous.
I just keep thinking it's ignition and not fuel - I will look into the rectifier thingy.
I think you're on about a multimeter - it checks voltage.
On a car engine it'll show 12v from the battery, once running it's usually 13-14v because the alternator is charging - if not it'll drop as the system runs the battery down, ECU driven engines wont work below a certain voltage but i assume that carb fed engines lose their spark strength - hmmm, maybe i'm answering my own question
I'm hoping the bike runs on the same principal.
This I can do, a job for this weekend coming perhaps.
On a car engine it'll show 12v from the battery, once running it's usually 13-14v because the alternator is charging - if not it'll drop as the system runs the battery down, ECU driven engines wont work below a certain voltage but i assume that carb fed engines lose their spark strength - hmmm, maybe i'm answering my own question
I'm hoping the bike runs on the same principal.
This I can do, a job for this weekend coming perhaps.
Not touched the idle screw - it doesnt point to idle screw as when you take choke off it dies anyway, even when your holding 6000rpm, taking choke off just makes it stall.
It's a brand new battery, the old one died over the winter so my mate replaced it with a high spec one.
We thought it had got varnished up but he used to run once a month and put fresh fuel in.
I'll get a meter on it.
I have suggested getting the carbs off and getting them rebuilt but I wanted to rule out everything else first before taking it to bits.
It's a brand new battery, the old one died over the winter so my mate replaced it with a high spec one.
We thought it had got varnished up but he used to run once a month and put fresh fuel in.
I'll get a meter on it.
I have suggested getting the carbs off and getting them rebuilt but I wanted to rule out everything else first before taking it to bits.
Not at the moment, i'll ask him to take some.
It's the white red and blue version but the wheels have been powder coated gold which he wants to change back to white.
Other than that it's completely standard.
Just google imaged this one which is the same.
It's the white red and blue version but the wheels have been powder coated gold which he wants to change back to white.
Other than that it's completely standard.
Just google imaged this one which is the same.
Edited by Regional on Wednesday 22 April 09:03
Edited by Regional on Wednesday 22 April 09:04
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