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?
Sorry, further to this, if it's not just a starting issue you need to be careful not to run this too much for 'trial and error'. You could do some serious damage to the pistons if it really is running this rich.
I'm not sure what order to do it in. Your carbs could be totally out of sync, but it's unlikely this happened 'suddenly', so unless it's become an increasing problem I would write that off as a first port of call.
I suggest first you check out the alternator, regulator for voltages and see if you can find any issues with the power supply throughout which might be causing issues. If it's not that you realistically should be looking at the leads. However, don't piss around with the engine too long with this, treat this on it's own and try and find out the problem without running it rich constantly.
Next would be your carbs, which could be out of sync. Get something like a Carbtune and sync them all up. I would suspect they will be on though, as I said.
I'm not sure what order to do it in. Your carbs could be totally out of sync, but it's unlikely this happened 'suddenly', so unless it's become an increasing problem I would write that off as a first port of call.
I suggest first you check out the alternator, regulator for voltages and see if you can find any issues with the power supply throughout which might be causing issues. If it's not that you realistically should be looking at the leads. However, don't piss around with the engine too long with this, treat this on it's own and try and find out the problem without running it rich constantly.
Next would be your carbs, which could be out of sync. Get something like a Carbtune and sync them all up. I would suspect they will be on though, as I said.
Edited by untruth on Monday 13th April 15:42
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.
Yeah, the Battery won't do much more than get it started, then it's just a bystander. You know that the rectifiers are famous for going on these? Basically, check out how the alternator is going, if it's buggered, it is likely rectifier related, just the alternator, or both!
The haynes manual for this bike is good, by the way.
The haynes manual for this bike is good, by the way.
You should be starting it with the choke open and no throttle. Once running, close the choke to the point it is idling.
The sparkplugs are sods on these bikes. I assume you cleaned them up when you removed them? You've probably drowned them in fuel. I ended up purchasing new plugs as I was having starting issues myself. Other than that, ensure you have a decent charge in the battery and you should be good to go.
The sparkplugs are sods on these bikes. I assume you cleaned them up when you removed them? You've probably drowned them in fuel. I ended up purchasing new plugs as I was having starting issues myself. Other than that, ensure you have a decent charge in the battery and you should be good to go.
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.
Regional said:
Without having a manual in front of me, where would I find the alternator?
Is it a mechanically driven unit? I only ask as my knowledge is car engines - obviously there is no alternator belt on a bike engine.
You wont its hidden in that tiny frame, check the charge from the battery, cant remember the tool that Trumpet used as it should be a set level once you start the engine.Is it a mechanically driven unit? I only ask as my knowledge is car engines - obviously there is no alternator belt on a bike engine.
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.
Regional said:
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.
Thats the one :-)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.
Yep, if ifs dropping means its not keeping the charge, this happened to mine and needed the altenator fixing (recoiled or something like that).
When he fixed it my bloke at the garage even showed me it had been fixed by popping one of them on it.
Hope you sort it out babe
x
MITZ
Have you put the meter on the battery yet? You should be getting 13.5v + @ 5000RPM. If not, point the finger at the rectifier first. You can troubleshoot that with the help of the Haynes manual and then move on to the alternator. (Which is found on the right hand side of the bike)
If your electrical system is fine, the carbs could be out of balance or just dirty if the bike has been stood. My NC30 would not idle properely due to varnish build up in the carbs. I had these stripped and cleaned and now it starts on the button and actually idles as it should!
(Have you tweaked the idle speed screw yet out of interest?)
If your electrical system is fine, the carbs could be out of balance or just dirty if the bike has been stood. My NC30 would not idle properely due to varnish build up in the carbs. I had these stripped and cleaned and now it starts on the button and actually idles as it should!
(Have you tweaked the idle speed screw yet out of interest?)
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.
Hi, I found I had to start at the fuel source ie the tap and work from there.
some nc30's were converted to 'freeflow' to allow more fuel at higher revs...
1st step is to check that the tap doesnt flow when turned on! If it does and the vacuum pipe has
been connected then your liable to cause flooding.
I would also change the fuel if it has been left standing for sometime.
The fuel pipes do get worn on these older bikes and can draw in air!
Its worth checking the air filter and pre filter to see if you have any signs of fuel in that area.
Thats just a starter and could be a number of things as suggested earlier by others, the rectifier/regulator is a good shout with many people 'upgrading' them as they are prone to failure.
The manual quotes the correct figures for checking the impedence and is quite a useful read.
Hope you get sorted .. keep us posted
Gaz
some nc30's were converted to 'freeflow' to allow more fuel at higher revs...
1st step is to check that the tap doesnt flow when turned on! If it does and the vacuum pipe has
been connected then your liable to cause flooding.
I would also change the fuel if it has been left standing for sometime.
The fuel pipes do get worn on these older bikes and can draw in air!
Its worth checking the air filter and pre filter to see if you have any signs of fuel in that area.
Thats just a starter and could be a number of things as suggested earlier by others, the rectifier/regulator is a good shout with many people 'upgrading' them as they are prone to failure.
The manual quotes the correct figures for checking the impedence and is quite a useful read.
Hope you get sorted .. keep us posted
Gaz
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