I think you're probably not too far off. They may have thin spots there on the floats or raised areas there from rolling them. The float bowls have a series of raised ribs that run vertically to keep the floats centered. So they rub and bang against those ribs all the time. So they either wear a hole at these cracks or cause stress cracks along these vertical lines of the float

Talked with Bruce, those 16067K1407 floats are $40USD a piece... I'm sticking wine corks in my float bowls...

3 minutes ago, zKars said:

Talked with Bruce, those 16067K1407 floats are $40USD a piece... I'm sticking wine corks in my float bowls...

I don't remember what I paid but I don't think it was that much. Check Courtesy just for a point of reference. I guess one of my thoughts is the float needs a specific bouyancy to work properly. So I didn't want to try to engineer a work around...

On 12/14/2017 at 6:36 AM, zKars said:

Got these beautiful FLAT TOP carbs running on the 510 tonight.  They run SO well.  Took it out for a quick back lane romp and had TOO much fun. 

Here is proof of concept.  Note. The idle is happening with the throttle blades 100% closed.

I swear I'm going to get fake plastic hemi-spherical caps made that you can snap on your flat top bells so you don't have to be embarrassed every time you open your hood...

And no laughing at the roof rack or the mack-tack paint job....

 

 

 

 

 

 

I cant get enough of the sound....
I wouldn't change anything on the flat tops as long as its running smooth I would care less of other peoples' opinions. maybe polish them

I cant wait to get mine to this point

 

Looking at zKars post number 8, I picked up a NOS, what I think is for the 510sss, though I think the same carb was used on the JDM L20 S30Z as well... It looks very much the same, but since this was found in Europe, the set-up is (?) slightly different. I gather this is the rear carb. I would be grateful if someone would confirm and thus there are some nice reference photos. It has HJG38-11 4901H on the side of the fuel bowl.

I have no idea.  Maybe Alan Does...

I must need my glasses checked, as I see a multitude of similarites with zKars images in post no.8.

On further digging, it looks like the HJG38 is for some models in the P510SSS, and the B210 range, though could well just be a needle difference for these two differing cc's as the bodies look the same. According to the Datsun 1200 site, this could be the Nissan Competition set-up, as it is without the advanced idle mixture set-up (IMS) (between the base of the carb dome and the manifold flange it just has a blanking plate, no pipework) and has a banjo fitment bolt for a metal drain tube on the fuel bowl (instead of a barbed fitment for a pipe to go to the air filter housing). It could be that the Nissan Competition (USA) is standard for Europe. I see references to these sometimes being single carbs on some engines, but nothing found to support.... More digging....