rich plug advice, please.....

Bike fires up first time with very little choke
Idles nicely at 1050
Ride well with good acceleration, hardly any bogging, possibly only at first gear pull away.
Valves in spec and good compression figures.
Carbs have been ultrasonically cleaned, jets have been checked and cleaned and float levels are spot on.
Clunk test done and sorted.
My only problem which is doing my head in is that 1,2,4, plugs are very close to perfect, but 3 is too rich and when I use a colortune I am getting a Bunsen blue but with flashes of yellow/white and no amount of turning the Pilot Mixture Screws make any difference
I have the petcock pipe on 4 so it’s not that.
Swopped the HT leads - no change, change plugs - no change.
Obviously I am getting too much fuel but other that a leaky needle jet, what else should I be looking at ?

 

Is the vacuum line from the petcock connected to #3. Bet the diaphram is leaking fuel through the vacuum line and there is where you are getting extra fuel in that cylinder.

MN

 

Hi MN-Maxims - Nope, it's connected to 4 !

 

The only other thing that could do what you are saying is the float level could be just a tid too high in that carb and making it too rich. Can you clear tube check that carb with it running to see where it is at?

 

Ok that sound like a plan - I will give it a go.

 

The fact that your mixture screw does not make a difference gives a clue the float level may be too high.
I know there is not a lot of room to clear tube the inner carbs but it can be done but it's a pain.

 

Mmm......... not easy but not too high - if anything a fraction low !

Any other ideas ?

 

Vacuum leak on the #3 vacuum plug. I had that problem with mine. Replace ALL the vacuum caps/plugs. Mine all seemed OK but when I replaced with new ones problem went away. The air leak was NOT detectable using propane or ant other method of leak detection.

 

Swooped the caps about - problem stayed on #3

Questions - If I am get too much fuel in the mix, can any passage be blocked / restricted to cause this ?
It would not be a fuel passage, but an air one ?
If this could be the case, which area should I be concentrating on ?
Although, I believe the sync is spot on could extra vacuum on #3 cause this problem, if so could reducing it improve it ?

Cheers

 

The strange thing is you can't control the idle mixture with the mixture screw. The engine has to be pulling fuel from that carb somehow. The needle has the o- ring and washer in place should seal and control. I'm sure you must have checked the air jets to make sure they are the right size and placed properly.
The key here is why won't the mixture screw control the idle mixture? Some how the fuel is getting in around this circuit in that carb............. Could it be possible the washer under the main jet is not sealing and fuel could be coming up around the outside of the emulsion tube, I would not think there would be enough velocity at idle to pull the fuel up that way. I was just looking at the cut away pictures of the carbs that are here in another thread and I'm not sure where else it could be coming from. Is it possible there is a defect in that carb body casting, did you look to see if there are any casing flaws or cracks in the bosses where the jets screw in? It's a stretch but I would take alook any way.

MN

 

More probable:

Float valve SEAT not sealing properly to carb body allowing high (or runaway) float "level"

or

seal in bottom of enrichment plunger is shot (or its "seat" is badly pitted) so it's as though that carb alone still has the "choke" on...

 

The owner says his float level is if anything slightly low , so that should rule out run away float level but, Fitz you may be on to something. He better look at that plunger and it's seat.

MN

 

That's the FLOAT level. If the valve seat isn't sealing to the carb body, then fuel getting past it would be effectively a "runaway" level; as in, no level at all. This condition (leaking past the valve body) might not show up when checking the levels. It may "check" fine.

(or the enrichment plunger isn't shutting off.) I failed to mention to check and be sure the linkage isn't simply holding that one slightly open...

 

^I've experienced this exact problem.

Something is wrong here, though. When it's screwed all the way in, you're telling me it's still black? We don't ever hit a dry carb? Shouldn't the screw cut off idle fuel flow completely when bottomed out?

 

Probably not your problem, but my pilot screw had to be opened 4 1/2 times just to get combustion in one of my cylinders. I could screw it all the way out--about 12 turns and still not get any change. The bike was running very rich even though the other cylinders/pilot screws all were normal. My problem ended up being a leaking intake gasket between the intake boot and the block. That's why I had to open the pilot screw so much just to get enough fuel to ignite. Fixing the gasket fixed the pilot screw problem but I had to re-sync to get everything in balance. So I would at least rule out vacuum leaks.

 

Right pulled the carbs off at work.....

1. Checked enrichment plunger, cleaned and ensured that none of them up when the choke was off.
2. Checked the pilot circuit screw removed and cleaned and set to 3 turns
3. Checked & cleaned valve seat, seems to be working fine and adjusted floats to correct levels.
4. Checked needle jet, and clunk test.

Put them back on, fired up and drove home - still pulling well and got home pull the plugs #1,2,4, fine #3 sooty.

Now I have not sync or adjusted the pilot screw, but I do not think adjustment is going to make much difference.

I wondered if the float is not floating or there is a problem with the body of the carb ?

Anyway, I am not going to worry about for the time being, the bike runs well, I still have to sync and adjust and we have ( hopefully ) a couple of months of good riding weather, and I might see if I can get a cheap set of carbs to clean up and swoop over, I have spent too much time on these babies.