Last week, I got myself a 92 600 Diversion which starts no problem and has plenty of power.

The problem is, when its idling, it backfires every few seconds. Also, when I rev it beyond 5k, it belches black smoke out.

I took the plugs out and they are black and sooty which to me says way too rich. The haynes manual however states that you cannot alter the mixture screws. as they are set at the factory.

Any suggestions would be greatly appreciated.

New air filter ?

Checked the air filter and it looks like it has just been replaced

Haynes manual will say you shouldn't but you will be able to , it should tell you how many turns out they should be . You can turn all the way in ( clockwise ), just until you feel resistance count & remember how many so you can always return to this setting . Then back out the same number. To weaken the mix turn in a quarter of a turn at a time ,it should be done with engine hot & let it settle.

This may sound like a silly question but will all 4 carbs have mixture screws or is there just the 1 and where can I find it? The Haynes manual doesn't even tell you where it is.

Hi look at the carb on here I think this is yours if it'll show you where they are ok. http://www.cmsnl.com/yamaha-xj600sfc-1994_model10128/partslist/B-03.html

Hi look at the carb on here I think this is yours if it'll show you where they are ok. http://www.cmsnl.com/yamaha-xj600sfc-1994_model10128/partslist/B-03.html

Thanks root. But its the same exploded diagramme thats in the Haynes with no reference to a mixture adjustment screw

Its the pilot mixture screw , number 5 on that diagram , 29 on this .

I kept putting it off but it got worse, in that when the engine got hot, it wouldnt pull away from road junctions etc unless I revved it up to about 6000rpm.

I replaced the full exhaust system as it was blowing in 3 places, but that hasn't made any difference.

To adjust the mixture screws, the carbs would have to come off as they are hidden and can't be reached with the carbs in place. That makes it impossible to do it with the engine hot. The Haynes manual doesnt even tell you how many turns out it should be. Being that hard to reach, I doubt very much that they have been tampered with at all.

I thought maybe the choke was sticking on, but there is nothing in the Haynes that tells you how to check it. Typical!

Its begining to look like the carbs are just completley goosed and I might as well buy a full set off Ebay!

I wouldn't be that hasty Dennis, you can alter the mix screws with the carbs intact on the bike-its tight but can be done, I dont think thats your problem anyway-they''re factory set and if they did 'go out' it would only be by a tiny amount, have you checked your TPS setting ?

My local bike breakers had a mint set of carbs, so I thought sod it.

I took the old carbs off and what a mess! Choke only working on 2 carbs, red sealant over everything, chewed up screws and badly chewed up mixture screws.

Put the new ones on in a jiffy, connected everything back up, pressed the button and it wont start. Flattened the battery trying! Whipped the plugs out, bone dry and no smell of petrol. I heard it somewhere that if you run out of petrol on a divvie, it can be a nightmare to get it going again. The battery will go flat before its sucked enough juice through to the carbs to start it again. I need to find out if thats correct before I rip everything off again.

Battery now on charge so will try again in an hour...

Whats a TPS setting?

Ok,

step 1-charge the battery

step 2-turn the petrol tap to 'purge' (ON, RESERVE and PURGE are the 3 settings on the divvy)

step 3-after the battery is charged-try it, then come back on and tell us whats happening

On, reserve and purge! I know there are 3 positions but I have no idea which position is which. I just run the bike with the tap in the up position, then top up with petrol when I get down to about quarter of a tank.

When I took the tank off today, I had to turn the tap to the down position to stop the fuel flow. I just assumed that was the off position.

TPS = Throttle Position Sensor. I just googled it and found out my bike hasnt got one. According to what I have just read, its a black cylindrical object with a connector coming out of it on the left side of the carbs. Nothing like that on mine, on either set of carbs.

I was actually thinking of trying the old trick of some neat petrol down a couple of the plug holes to see if I can coax it into life when the battery is charged up

This is the TPS

Definitly no TPS on mine.

Right, battery charged and now trying to figure out which is the purge postition

With the fuel pipe off the tap-when its on PURGE the fuel will piss out

Success, it finally managed to suck some petrol through and it started. Apart from having to adjust the idle speed, all seems fine. The backfiring has stopped and the engine runs a lot smoother. Its still blowing some black smoke out, so I'll take it for a run tomorrow and check the plugs to see if they have sooted up again.

Thanks a lot Barkwindjammer for all the advice

Give it a good high revving thrash-check oil level before you go out ! ! ! , and keep us posted

Oh and treat yourself to one of these as a kind of personal reward

A good high revving thrash. I would love nothing more, but I live in Bradford.. The land of potholes, speed humps, speed cameras and blind taxi drivers

There is one thing I have noticed however after putting on these carbs. The clutch death rattle stands out even more. Oh well, you cant have everything!