Miss fire When Wet Or Cold

[bettyswolloks]

Hey all. If I start her up on a normal day, she's fine, choke on, set off, no miss.

If I start her up after it's been raining/really cold, she has a miss. Choke on, set off, miss fire, few miles down the road she evens out on a low steady throttle, but try and rev it, miss fire. I'd say 6/7 miles in and she will behave. Yes I'm slowly taking the choke off. But full choke, no choke or half choke it's the same.

If I set off on a normal day, and get caught in a down pour it's the same, after a few miles it clears up.

Plugs are recent, changing them made no difference. I've been through all the block connectors, checked the plug caps and leads, all good, nice connection between lead and cap. I can leave her running and power wash it and its all good, she doesn't cut out or miss fire, untill I set off, then it's like I've been caught in a down pour again.

To me it like a plugs breaking up under pressure, but then it clears up and can take a good hand full under load in 5th no problem.

Any ideas Folks?

[Oldie]

It certainly makes me think of faulty plug caps. I'd replace them anyway as they're cheap.

[m40man]

Sounds to me like this could be water in the fuel. A blocked fuel tank breather can mean water can make its way into the tank. Especially if the bike is left outside uncovered.

Water is heavier, so sits at the bottom of the tank. After or during rain, the water level is raised such that a little is drawn into the engine with the fuel, causing a misfire. After a while, the level is again low enough that it isn't drawn in anymore & the misfire clears.

So next time the fuel level is quite low, it might be a good idea to drain it into something else & see if there is any water in it.

If leaving the bike outside uncovered, some cling-film over the filler cap will stop any rain making its way in.

[bettyswolloks]

Mar 6, 2018 12:26:02 GMT m40man said:

Sounds to me like this could be water in the fuel. A blocked fuel tank breather can mean water can make its way into the tank. Especially if the bike is left outside uncovered.

Water is heavier, so sits at the bottom of the tank. After or during rain, the water level is raised such that a little is drawn into the engine with the fuel, causing a misfire. After a while, the level is again low enough that it isn't drawn in anymore & the misfire clears.

So next time the fuel level is quite low, it might be a good idea to drain it into something else & see if there is any water in it.

If leaving the bike outside uncovered, some cling-film over the filler cap will stop any rain making its way in.

Now I like the sound of that, I've been looking for a good reason to strip the carbs and looking for water is good enough for me!
And yes she is outside in all weather, if it's really peeing down I'll throw a cover on her but normally she's left to her own devices.

I had another good look at the plug caps, and found one one the new coil I fitted that needed the lead to be cut back a touch to get a better connection.

It's not done it since, but the weather has been ok so......

I'll keep ya posted!

[kevin]

Mar 7, 2018 14:35:23 GMT bettyswolloks said:

Mar 6, 2018 12:26:02 GMT m40man said:

Sounds to me like this could be water in the fuel. A blocked fuel tank breather can mean water can make its way into the tank. Especially if the bike is left outside uncovered.

Water is heavier, so sits at the bottom of the tank. After or during rain, the water level is raised such that a little is drawn into the engine with the fuel, causing a misfire. After a while, the level is again low enough that it isn't drawn in anymore & the misfire clears.

So next time the fuel level is quite low, it might be a good idea to drain it into something else & see if there is any water in it.

If leaving the bike outside uncovered, some cling-film over the filler cap will stop any rain making its way in.

Now I like the sound of that, I've been looking for a good reason to strip the carbs and looking for water is good enough for me!
And yes she is outside in all weather, if it's really peeing down I'll throw a cover on her but normally she's left to her own devices.

I had another good look at the plug caps, and found one one the new coil I fitted that needed the lead to be cut back a touch to get a better connection.

It's not done it since, but the weather has been ok so......

I'll keep ya posted!

[kevin]

I used to get this with Honda it's the rain dripping on spark plugs and shorting out on your knees

[bettyswolloks]

Mar 8, 2018 13:24:56 GMT kevin said:

I used to get this with Honda it's the rain dripping on spark plugs and shorting out on your knees

It has been said that I'm numb from the neck down, but I'm sure if feel that!

[m40man]

Mar 8, 2018 13:32:03 GMT bettyswolloks said:

It has been said that I'm numb from the neck down ...

Maybe you didn't hear them correctly .

[bettyswolloks]

Well I'm about to get up and attack the week, it's been raining all night. I stripped the carbs yesterday, one of the bowls had a very small amount of water in. I fitted a new fuel pump and filter, when I 1st fired her up #2 was coldest for longest, #2 was cold the last time it misfired on Me.
Anyway.....

[bettyswolloks]

And the fuel tank over flow is all clear.

[bettyswolloks]

She started up fine, ran lovely for the 1st 2mils, then began to misfire under load for about half a mile the clears up and ram fine the rest of the way in to work, a 20mile ride.
But as it cleared up, the rain had stopped.

[GAv]

HT lead(s) faulty and getting damp?

[cam7777]

Could be a faulty coil pack

[chris900divvy]

For me the problem was water getting in past the ht leads to the coils. With the way the leads are arranged its easy for water to trickle down to the ends of the leads where they meet the coils. Since I sealed them up with silicone where they meet the coils it no longer does it. I'd start by trying that out as its cheap, but if it doesn't sort it then its probably the coils themselves which are cracked up and arcing in the wet the chinese pattern ones are particularly bad for doing that.

[bettyswolloks]

I've been carrying a spare spark plug to test each lead when it does it again and and it was fine, sparking well on all 4.
But I still think it's electrical, I'll get the silicone out and give that a try.
Thanks Folks, I'll keep you posted!

[Oldie]

Mar 13, 2018 17:10:21 GMT bettyswolloks said:

I've been carrying a spare spark plug to test each lead when it does it again and and it was fine, sparking well on all 4.
But I still think it's electrical, I'll get the silicone out and give that a try.
Thanks Folks, I'll keep you posted!

.................................................................................................

Reasonably priced used coils on ebay.


www.ebay.co.uk/itm/yamaha-xj900-diversion-coils/202259695378?hash=item2f179e0712:g:PHcAAOSwZFdagEsA

[bettyswolloks]

So I've had another look at the coils, they test perfect, and look good as well. Took them off and swapped them round. Took off all the plug caps and snipped the ends to get to new wire then sealed them up with silicone. Pot 3 has always been the last to chime in from cold, after swapping the coils over pot 1 was reluctant, so I swapped the plug caps with a spare and it joined he party straight away. It's supposed to be raining again this weekend so with any luck I'll get to try it out.

The way the rain falls on the bike, it kinda funnles it over the middle plugs, might look at making some kind of cover for them to give them a fighting chance.

[bettyswolloks]

So after a long ride back home from donington over Easter in some biblical ran she didn't miss a beat! I think it was the silicone on the HT lads that fixed the thing, happy days!

[andrewed264]

My 600 is having a similar issue.. i will try this silicone idea.. thanks