Firing on 3 cylinders and haven't a clue why

6 posts / 0 new
Last post
Firing on 3 cylinders and haven't a clue why

Hi all,

I have a 1997 Bandit 600 and last week I started it and it sounded like 3 cylinders, took it out thinking it's just not getting fuel but nope. It fires on all 4 cylinders though when I get to 40-50 mph though top end speed is greatly impacted and for a while now before the 3 cylinder issue it doesn't seem to pull as well as it used to. 

Found a good chunk of plastic missing from number 4 spark plug cap so replaced cap and still same issue. I've tested coils with multimeter and they're fine, all spark plugs are giving a spark though some do look like a yellow spark so maybe not strong enough of a spark? I've ordered new plugs though I also test number 4 spark plug with a multimeter and according to the multimeter it's fine though only getting 4k ohms of resistance should I be getting more? 

Balanced carbs up too still same issue. I'm hoping it's spark plugs and so will see when they arrive but got a feeling that it's more than that and also a fuel issue. That said the number 4 spark plug does come out looking dry and black which is a rich mixture (correct me if I'm wrong). 

I don't get why it fires on all 4's when going at speed just seems to be below 40 mph that it stutters and sounds like 3 cylinders. Anyone got any ideas? Hoping I don't have to strip carbs out but looks like I might have to if new spark plugs don't fix it. 

should just be plug related or a blocked jet

Dry and black doesn't necessarily mean rich mixture - it's probably just the result of the misfire. Is the problem speed (load) related, or speed and revs related? Personally I'd do a compression test.

Think it's rev related as the more I rev it the more it sounds like an inline 4 not a inline 3 or a twin lol. But if I do like 70 mph seems to run okay but top end isn't as good as it used to be by like 20 mph difference.  I doubt it's compression as it runs okay once I get up to speed and isn't smoke coming from exhaust which surely it would do if It was burning oil? Also rules out valves too. Also all the plugs are getting black and dry (sooty) and obviously smell of petrol so makes things even more complicated as things like crap getting in the carbs seem unlikely as it'll surely only be one or two carbs that get crapped up and not all 4 of them?  Coils work fine according to my multimeter and again why would both coils fail? CDI apparently only works or doesn't work but could be wrong on that but seems like only thing to affect all 4 plugs. Just stumped as to what is wrong with it. 

Start at the beginning!! a wet and a dry comp test....get new plugs...see what happens.....Do remember Japs use a different measure for compression ratios...whilst tradition would say it was the space left at TDC relative to the space at BDC...the japs measure it on valve closure, so given atmospheric pressure at 14.7 merely have to get it , say 8 times atmosphere, to get an idea...consistency is what you look for if on the dry test all is not well, and then a wet test reveals all is still not are looking at a valve issue....for example!...further confirmation can be done with a cylinder leakage test....

Low compression will give you poor running at low revs and better running at high revs. It doesn't have to be burning oil.

Log in or register to post comments