Engine miss at 3000 rpm for first 20 mins of running XJ650

Hi,

I ride my 1980 XJ650 about every second weekend. In the last couple of months it has a miss starting at 3000rpm. I thought it was the choke stuck on a bit but not that. I haven't yet traced it to a particular cylinder. It is a general engine breakdown like fuel starvation or struggling to breath. It seems to fix itself after 15 or 20 minutes. The bike runs great then. I do live about 300 yards from the beach but bike is in a garage and covered with sheet and bike cover. Has anyone experienced similar?

Thanks.

 

Re: Engine miss at 3000 rpm for first 20 mins of running XJ6

Pull the plugs and replace them.

 

I just noticed this same issue today. When I go to accelerate it feels sluggish, like the clutch is slipping (it isn't) and then the bike picks up.

I'm gonna try the spark plugs.

 

Thanks gents. The plugs have done about 400 kms since new. Maybe I've got a dud one but I haven't determined that it is a particular cylinder yet.

The clutch is fine. It is definitely an engine breakdown at 3,000 rpm and over. It is very obvious to the ear and on the tacho. I thought maybe the damp ocean air might have effect on some electrical contacts somewhere but I have sprayed them all with penetrant. My next thought is maybe CDI breakdown but I don't know what they do when they start to fail.

 

check the floats, it may be a little lean,the float level might be low then as it comes up to temp it works with the leaner mix, are the plugs real white?
open the low speed screws up a little, the width of the screw slot

 

The TCI will give symptoms from a complete loss of ignition to lousy idle and diminished power at speed. I'd be careful of what you spray on your ignition system, if you used penetrant on your coils, you may have introduced your problem. Most penatrants are petroleum based and it doesn't play nice with rubber components, not to mention the possibility of shorting things out. WD 40 is ok but you don't want to drown your parts with it.

 

thanks for the advice guys. I'm sending my tank and bits off for respray this week so will run through those things when I get them (mainly the fuel tank) back. I'll update this post at that time.

Thanks again

 

Could be something easy as mine... Check the robber boot from air box to carb/trottle body. It may be loose and have opened up for extra air to go in. I have a maxim-x and had the same issue you mentioned. I check and the boots have come off completely. I tighten it backup and runs fine again. Could be something this easy...

 

Thanks kvcobra and others. I'm hoping for something simple!