Running rich, damaged carb rubbers ?

I'm not too hot with mechanics but have-a-go anyway.
Just fixed a poor running, crap spark problem but in the process decided that it would be good to clean up the carbs. As with my old Skoda I:-
- sprayed carb cleaner in the air intake and
- stuck Redex in the petrol (on a full tank and didn't mix it, so may have gone through a bit neat.)
- used Quick Start spray in the air intake to get her going when problematic.

Oops! Now running very rich (sooty plugs) starts with no choke on cold morning and dies at low revs after she gets warm. This was not the previous problem with rough running and poor spark.
I'm guessing that I've fried some rubber seals in the carbs somewhere with all the solvents and in hindsight this seems very obvious and a bit dumb.
What am I likely to have damaged ?

I've just bought a set of carbs from an 11,000 mile bike off ebay. Worth a £28 risk. How should I go at things from here ?

Thanks
Kevin

 

It took me a year to get my bike running again, so maybe this is the blind leading the blind but... the most likely cause that I can think of are the needles and/or needle seat o-rings (if equipped) have been damaged, and are now letting too much gas into the float bowls. Needles don't seem to last more than a couple of years for me anyway, so a set of new ones is probably a good idea regardless.

 

Take them off the bike and clean them one by one.

 

OK, I bought some carbs off an apparently 11,000 mile bike.
These pour out fuel from the overflows when the engine turns over. I didn't keep it running because of the amount of fuel pouring on the road but sounded like it was going to start.
Maybe sticking float valves due to being stood and then posted ?
Can I get to the floats to unstick them from the bottom of the carbs or do I need to strip down from the top?
Is that the most likely or any other ideas ?

Wow, this is a busy forum! I might start a new thread if no-one gets back to me on this one since it's now a whole 6 days old !!

 

Its always been my feeling with redex and the like is its good for a clean system to keep it that way but if you put it through a quite dirty system it will cause more problems than it cures with the dirt it dislodges.
I think you just need to get the manual, strip and clean the carbs, check the float height (described in manual). You should be able to get to everything you need to clean without splitting the rack. Floats you attack from underneath, but i found easiest way was to remove carbs and totally strip one at a time cleaning everything until your sure you cant get it any cleaner, reasemble then onto the next. One tool i found invaluable when cleaning mine was a foot pump with football adapter and airbed adapter unless you have access to a compressed air line.

What bike have you is it the xj600 pre divi, as posted in yamaha forum.

 

Agreed. And I would still replace the needles and seats.

 

Ok, I've started stripping them ! Apart from the petrol inlet mesh everything is fairly shiney.

A couple of questions.

- I've ended up with a 3mm ball bearing rolling around on the workbench ! I see no mention of it in the Haynes. Maybe it's come out my toolbox on a magnetic screwdriver. Any ideas ?

- It's a Mikuni but not the not the Mikuni that is in the Haynes. This one has the 'enrichment valve/choke's all in a line so only one will come out without splitting the rack, which I really don't want to do. They all feel smooth so should I leave them alone. Also the one I took out has a v-groove in the piston but no o-ring. Is that as it should be ?

-Float levels seem to be 19-22mm from the mating face of the float chambre with the body of the carb. The Haynes suggests 16.5-18.5 for an XJ600 but this would raise the level of petrol which seems to be completely wrong.
Should I be measuring from the mating face or the top of the lip around the body ? Any idea what the correct level is for this carb ?

My current plan is to clean the float chambers and jets, but two of the top hat, diaphragm chamber bits have completely welded shut screws, so leave those two. Leave the float levels as set and check the levels with a tube from the drain hole when re-assembled. Is that all sensible ?
Thanks again, well I'm getting pretty quick at getting them on and off the bike anyway !

 

PS yes also posted on Yamaha forum. Not followed that one so well though.

 

On those early Mikuni's with Enrichment Valves in the horizontal configuration ... you can undo the Valve Body with a Boxed-end (closed-end spanner) wrench and move the Valve Body out of the way sufficiently to spray a Carb Cleaner in the Carb Body.

Leave them open by inserting something to prop open the Base while you flush the passage from the Siphon Tube.

The additive likely turned any varnish or residue into a "Paste-like" substance that will have to be cleaned from all the Jets and Ports on the bottom-end.

In the case of Carbs which have a "Stain" on the surfaces of any of the lower end parts ... dismantling them and separating the bodies to flush-out the drilled passages and small copper tubings connecting the lower end with the top end might very well be the BEST course of action.

Particularly if the Engine was run and the sludge drawn into the tiny ports and passages where it will resist dissolving in Petrol and be to viscous to pass through any of the smallest of metering ports.

 

So flush them with carbs upsidedown. I guess flush with petrol since they have a flat rubber seal at the end, carb cleaner may not help the rubber.

Hmmm, the jets have a brown patina, which I just assumed was age. The Holes in jets still look open and round. One more unknown

It seems to me that blocked jets etc.. would be causing the mixture to become to lean. I can see too high float level or stuck open/leaky enrichment/choke valve as being causes of too rich running but are these the only two options.

Ta

 

in my manual it says Float Height 16.5 - 18.5

Fuel Level
1984-85 3.0 +/- 1.0mm below mixing chamber body line
1989 and later 2.5 to 3.5mm below float chamber line

 

That agrees with the Haynes I have.

Am I right that with the carbs upside down reducing the measurement from mixing body to float will raise the level of fuel in the chamber ?

(I found a spring to go with the washer, I reckon it's from inside the choke. Probably sits in the v-groove on the piston to latch the choke on. Think I'll probably do without it!)

 

The spring is likely the return spring.
It surrounds the shaft of the Plunger and pushes it shut upon release.

 

mis-typed, I meant spring to go with the 3mm ball bearing I found on the work bench. It's much smaller than the piston spring, only about 2mm diameter. The latch mechanism hasn't worked for ages anyway so I'll probably just skip it.

 

ok, eventually managed to rig up the carbs with dummy fuel tank, plastic tubing for fluid height etc...

Level was pretty much level with the body-float chamber join, so bent the tabs and gained about 2mm less fuel height. Numbers in the Haynes for float height seem to make no sense. Also with the meniscus being about 1.5-2mm itself it's hard to make sense of a .5mm tolerance. Anyway the bottom of the meniscus is now about at the top of the screw heads which seems about right.

Running well again, although got side-tracked with electrical light problems so haven't checked the plug colour yet. However idling when warm and puling away at low revs so looking good so far.

Thanks for all the help.

PS still looking for a well priced rear shock in the UK ;-)

 

Your Float Heights are "Spot-On" if they are all at the top of the Fastener that secures the Float Bowl to the Carb Body.

Even at the bottom of the screw head would keep ahead of demand at Full Throttle.