Cleaning carbs

Scuzi · 25 Apr 2015 at 22:01

My XTZ750 has been bogging at low RPM, backfiring and generally running poor. It has been drinking petrol too. All typical symptoms of the emulsion tubes in the carburettors being worn - a known fault with the bike.

I bought a couple of carb rebuild kits contains new jets and rubbers and pulled the carbs off today.

They're not too bad on the inside. Some varnishing and crud left in the bowls. The outsides are absolutely caked in crap.

What is the best way to DIY (read cheap) clean them? I've heard of people submersing them in coke for 24hrs. Is this a thing? Do I need to take a toothbrush to them?

Any hints and tips appreciated!

Scuzi · 26 Apr 2015 at 20:36

Thanks for the tips. Found an old bottle of Gunk which I used to get all the crap off the exterior and a tin of brake cleaner for the inside. Seemed to do a fairly decent job. Not spotless but good enough!

I got the carbs back on the bike and tried to start it with the choke. It wouldn't fire but eventually did when I pushed the choke back in. It was idling high at about 1700-2000rpm (normal is just under 1000). When I revved it, he revs would hold high at 3-4k then slowly come down to the high idle.

I was expecting to have to do a bit of adjusting but any ideas on where I should begin? Is it just a case of playing with the idle adjust screw?

It's a real pain because the petrol tank has to come off to do any tinkering. I might have to knock up a small tank out of a bottle for this purpose.

Scuzi · 26 Apr 2015 at 20:50

I had the whole lot out! Replaced all the rubbers and jets too. The needle jets should be set right. I screwed the old one to the stop, counted the turns and did the same with the new one.

If I rig up a bottle to hold some petrol I'll be able to tinker while the bike is running. If not, it'll be a tank off - tinker - tank on a million times job.

I was thinking half way through the job - who the hell got the idea for a carburettor? Where did they begin? They're crazy complicated.

Scuzi · 26 Apr 2015 at 20:55

VoG said:
A manual would be a good place to start, failing that get the engine hot so it's idling happily then back the idle adjuster off till you get the idle speed you want, also check both carbs are idling at the same speed as a slow drop to idle speed can be an indication of one carb having a slightly higher idle speed than the other.

The Haynes manual is vague when it comes to this. It shows how to dismantle and assemble but that's about it. This is my first time playing with carbs on anything other than single cylinder 2 stokes so it is a steep learning curve.

I guess it is possible they're out of sync. I'll try the idle adjust but if that doesn't work I'll look at the sync.