Hi, I have an issue with my xz550, firstly its a pig to start, when it does start it only runs on the rear cylinder, any fast throttle at all kills it although if I apply slow throttle it will then rev up to limit, after about five minute of idling with only the rear cylinder firing it will suddenly idly erratically and then the front cylinder starts firing as normal, the starting issue I'm sure is because it is not firing on both cylinders, after this all the time it is warm it will start up firing both cylinders, does anyone have any suggestions as to what may be causing this?
The first thing I would do is put in some Berrymans B12 Carb cleaner at 4 to 5 times normal strength then ride around for 30 minutes. Be sure and maintain at least 6 feet social distance!
I agree. At first glance it would seem fuel related. There are some great products for cleaning deposits from combustion chambers and those same products work REALLY well for cleaning carbs.
BUT, it could be something else. Step 2 on my list would be swapping the coils with each other.
How well does it run after the front fires-up?
Carbs have fairly recently been rebuilt, the bike runs okay after the front cylinder fires up, it does have a flat spot 3-4.5k revs though.
These carbs are pretty hard to get all the tiny passages clean to the point they run well. The carb for the front cyl. probably has the idling circuit passage plugged up pretty good. The jet may be good and clean, but after the jet is the passage. I had very good luck with chevron techron fuel system cleaner. I thought I had done a good job of cleaning the carbs, but found out 2000 miles from home that something had broken loose and plugged something up. Used a strong mixture of the stuff and it starting running good on the way home after it had sat with that mixture in the carbs.Whatever you use you want to get it in the carbs and let them sit so the stuff can do it's work. If all you found when you took the carbs apart was varnish then this will work. Not so sure on corrosion.
I had the same problem on my 1983 and found a very small jet was the culprit.
In the bottom of the bore that is next to the swab there is a brass jet with a very small opening to the fuel in the bowl right next to it. I could not blow it out or solvents did not work. Finally my friend suggested a guitar string to ream it and it worked.
After I put it all back together the bike now fires instantly with about 1/3 choke. Before I had to grind away and nurse the throttle until it got warm and ran on both cylinders.
Cleanliness aside, have you done a carb sync and adjusted your mixtures?
I have adjusted the mixture but not done the sync yet, although last evening I disconnected the blk/yellow wire going into the TDI and this evening the bike fired up straight away and was firing on both cylinders, maybe coincidence or yesterday it may have had some gunk in the carb which has now cleared itself? also a quick question does anyone here have for sale or know where to buy the carburetor emulsion tubes from?
If there is a plugged passageway it won't do much good to set the mixture until it is clean and flowing fuel well. It kind of sounds like the rev limiter may have been your problem. If it keeps on starting well I would attribute that to the problem. The jet being plugged and then being fine doesn't have the odds on it's side for that happening.
You HAVE to sync or it will never run properly.
Do a search on $5 manometer if you can't afford the gauges.
Had a go at syncing the carbs today, used this tool
https://www.ebay.co.uk/itm/2FastMoto-2-Carburetor-Synchronizer-Carb-Vacuum-Gauge-Sync-Tool-Yamaha/202780284110?epid=23005669497&hash=item2f36a594ce:g:fqEAAOSw44BYkQWT
hooked tubes up to the recommended points shown in the Haynes manual and both guage needles where jumping around so much I could not get a sensible reading, any ideas why this is?
Solved the needle gauges jumping around issue, the carb balance kit had a couple of inline 'taps' used those to limit the vacuum on the gauges, I could then get a sensible reading.
How is it starting now?
Half choke and it starts very nicely, just got a few little things to sort out, neutral switch doesn't work, took it out and tested the switch itself and it is buggered, I've got a replacement on order, would like to have another go at getting a really good seal on all the exhaust joints, tried to put the bike through an MOT and they failed it on exhaust leaking from the exhaust stubs at the rear cylinder to the y piece, I did try to rectify it and its better but not perfect, I would like to get hold of a nice condition rear brake pedal, the one on the bike is quite shabby, other than that I think it is pretty well sorted now.
You're welcome.
It's nice when you do something that fixes the problem unexpectedly, and removing the wire was a lot easier than going through the carbs. Kind of weird that the cyl. would cut back in once warmed up.
When I put my Y pipe back on I carefully tapped the copper rings down the pipe a little way using a large socket and they re-sealed very well. The copper o-rings are available if you want to shell out about $25US apiece.