Wet weather missfire

My st1100 was sitting for 12-18mths befor i got it, it as been fine up till now, a little bit of wet stuff and it`s quite ropey between 1k and 2k
I was thinking carbs need a clean but at 0450 this morning fired on all 4 and was fine.

So where to look first? i`m going to whip the plugs out next week, look and replace the plug leads, should i disable the sidestand cutout switch?

I`m also going to have a close look at the plug caps and possibly use a bit of silicone grease around these points


any more ideas?
Ta
Ray

I would suspect dirty carbs and the plug caps, too. Not so much the leads, tho. But it's easy and cheap to replace the leads to rule them out as the problem. I bought the yellow 7mm silicon spark plug solid core wire by the foot at my local auto parts store.

Check the cap resistance. Should be about 5K ohms. There is a tiny 5K resistor inside the caps. And also run some Sea Foam or other strong carb/injector cleaner through a few tanks of gas.

If you find a cap that measures really high resistance and the small resistor measures OK, check this post :

Rebuilding high resistance spark plug caps : https://www.st-owners.com/forums/showthread.php?145015-Repairing-High-Resistance-Spark-Plug-Caps&highlight=spar+plug+caps

Plug wires have been mentioned already, but the ST1100 has some history with carburetor icing in cool, damp weather. It's most likely to happen when cruising at light throttle settings. Does the problem clear up for a while if you pull over and stop for a bit?

Thanks for the suggestions, last week I was off work on a/l. I checked the plugs, no 3 was a bit darker than the rest so I swapped the plug caps round and gave them a spray of silicone grease and refitted, I also found a crack in one downpipe, no1 had broken clean through so I bodged it with gun gum and a hose clip, it was a straight break so the hose clip has covered and supported the area, i will try and slip a stainless coller on and braze it one day.
I think the carbs may need to come off for a clean, but my last tank of 10-12 mile 30-90 mph commute was just over 45mpg

Down pipe?

If you are getting good mileage and you feel it is bit off why not make some DIY seafoam and see it that clears the carbs? This LINK looks like it does the research right to get you close...

wjbertrand said:

Down pipe?

Click to expand...

The bit down from the exhaust port before the two into one join, the break is about 10mm before the join

Mark said:

If you are getting good mileage and you feel it is bit off why not make some DIY seafoam and see it that clears the carbs? This LINK looks like it does the research right to get you close...

Click to expand...

Thanks for the link
Ray

ssray said:

Thanks for the link
Ray

Click to expand...

You are most welcome!

My nephew bought a big RV which had been sitting and used over a gallon of DIY seafoam in the tank that brought the RV back to his home.
He reported that the engine was rough when he started home and was running smoothly when he got home.

Hope it cleans yours as well as it did his!

Mark

I have made some `seafoam` , today I changed the oil, filters and fitted iridim plugs, will report after xmas when more fuel should be required
Ray