Carby flooding randomly

[twisties]

Hey mini crew,

Bike: Dhz 160
Engine: z155
Carby: Stock (mikuni 22mm i think)

Problem:
Bike idles and runs fine 90% of the time. If I snap the throttle it seems to flood the carby and not clear itself out.
Example:
Cruising along everything is fine, missed a gear and accidently revved the bike quite high. As a result I could not apply any throttle after this without the bike bogging and dying. It still idles fine but if I try and Rev it at all it dies. I let it sit for a minute, flick the choke on and it will eventually start again and be OK as long as I don't suddenly Rev it hard.
By this I mean if i gently roll the throttle on the whole way it is fine but if I quickly stab the throttle it floods again to the point of fuel coming out of the air filter. The only thing that seems to help is if i put the choke on, it runs slightly better for a moment but eventually floods and dies.

Spark plug looks fine but a tad rich, valves are set at 0.03 and 0.04 as always and before this the bike has run flawlessly for almost 2 years so I believe all the jets etc are fine.

I've cleaned the carb after the first time it happened and replaced the spark plug but I had the same problem the next ride.

Any ideas guys because I am at a loss of what to do next!

 

[my67xr]

When you cleaned the carby/jets did you check the hole at the bottom of the threads where the pilot jet screws into is open?
Can you see light through it into the bore of the carby ?

Have you had the mixture screw out when cleaning the carby ?
It may have something in there blocking the fuel flow
And how many turn's out is the mixture screw?

Pull the carby down and blow some compressed air into the 3 ports on the filter side of the carb,
and check you can feel air coming out in the base of the carby where the jet's screw in.

Also pull the emulsion tube out and check all the hole's across it are open


The Pilot jet in your carby is that a #15 ?
If it is i would recommend fitting a #20, make's starting/warm up a lot better.

And is your air filter oiled too? if not that would be making it run lean in the top end.

 

[gottagetacheaperhobby]

Could you have bent the float arm when you dismantled the carb?

 

[twisties]

Thanks for the quick reply guys! I was hoping it would be something obvious but apparently not..

Gottaget:
It definitely wasn't bent prior to the last time I went riding but I did wonder if that was the problem and adjusted it by about half a mm last night (probably shouldn't have). Unfortunately I haven't had a chance to test it yet.

My67:
- Yes I checked that I could see light through all of the holes where the jets screw in and I could - they're all clean
- I haven't taken out the fuel screw but I should have done that. I'm not sure how many turns out it is but I haven't adjusted it since I set it about 2 years ago and it's always run perfectly up until the last 2 rides
- The ports in the carby are clean - I blasted carb cleaner through them and they weren't blocked
- Not sure on the jet sizes but the emulsion tubes are clean
- Yep the air filter is oiled

I'll have to look tonight and check out the jet sizes and clean the air/fuel screw (I was always scared of removing it in case I put it out of tune but didn't think to count the turns).

As I said I am certain the carb is tuned correctly, I think there must be something funny going on with the floats or something - fuel coming out of the air filter is the reason I say that. I had a fiddle with the float setting last night and tried to adjust it a tiny tiny bit (half a mm). I'll have to give it another look over tonight and see if I've missed anything.

Thanks again guys!

 

[my67xr]

With the fuel coming out the Air Filter, you mentioned above you've done the valve clearance's.
With the clearances tight you do get some fuel blowing back as you kick it over.

Those clearance's you said are wrong, do you mean .003" inlet, and .004" exhaust ?


And you can check the float height by fitting some clear tubing to the drain, hold it up near the top of the carby and open the drain screw
Then measure how far down from the fuel bowl/carby base the fuel level is in the clear tubing.

like this

 

[twisties]

Yep sorry, I meant to say 0.003 and 0.004 - I thought that looked wrong as I was writing it!

Thanks for that My67, I'll measure it tonight and see where it's at. I'm guessing it should be roughly 1 inch below the top of the bowl.

Thanks again! I'll try all of this tonight and see if I can replicate it by giving it a rev in nuetral (can't ride it properly, living in the suburbs).

 

[twisties]

Ok so I checked the jet - it's a 20
Cleaned the air flow screw which is 2 and 1/8th turns out
Checked the float level as shown in the pic attached. Could this be where my problem lies? The fuel seemed to be level with the join across the middle of the carb when the bowl bolts on to the upper half.

Also My67 you mention that my valves were a little tight, could it be worth increasing the gap?

 

[gottagetacheaperhobby]

I reckon your float level is the problem, if its that high explains the fuel out of your air filter.

 

[my67xr]

If your valve clearance's are .003" and .004" then that's perfect.

The carb is a Mikuni 30mm copy, standard jetting is 20 pilot and 100 main.
And yeah, float level is way too high
You need to bend the floats' centre tab up a bit to get the float level down, it need's to be about 25mm

Double check your needle and seat doesn't have dirt in it too, and making it flood.


Once the float level is set, you can readjust the mixture screw to suit, then drop the idle speed down to normal.

 

[twisties]

Big bump for this thread but I never actually fixed this problem.

I started thinking about it again the other day for some reason and remembered that maybe 2 years ago I actually broke the gasket between the bowl of the carb and the top half. I have just been jamming it back in when I open the carb up and this seemed to work fine for a solid year before I started having trouble.

I just realised this is probably what is causing my problem, vacuum leak!!

I'll jump on ebay and get a new gasket. Hopefully I didn't mess things up too badly when I was first trying to fix it!