Datsun Roadster Forum-311s.org

Hey guys,
I have not posted anything in quite some time but now I need help.
I have rebuilt my 67.5 u20 with the original mikuni solex carbs. I believe it is the original B cam however, it had the name Mellisa painted on it which leads me to believe it may not be original.Got the car running but not very well. Took the advice on the forum and ordered the seemingly correct jetting 57:5 pilots 200 airs and 160 fuels. Seemed to idle and run better however still had a miss so did some reading on plug choice. Yesterday I bought a set of b6es and upon firing it up it immediately started burning blue, never did in the past with the bpr6es. Took it for a drive and seemed to run very well with the blue smoke stopping after a short while, suspected it was clearing out the carbon etc from the fouled plugs.
After getting home I pulled the plugs and #1 and 3 were white and #2 and 4 were black. Hmmm...did a small adjustment on the screws put the plugs back in and cranked and cranked , it would not start, noticed after cranking that fuel was pouring out of the stacks. Figured it flooded and left the car overnight. This morning I decreased the float height and tried to start it...seems like it wants to fire but will not start. Did those plugs do some damage ? I will not do anything further until I get the expert advice from all but am inclined to change back to the original plug and try to start again ?
Coronavirus lock down should permit me the time to get this figured!
Thanks in advance..Rob in Kelowna

That is not the correct jetting. Not sure where you got the info but it's not right. However you have other problems, give me a call and think we can work it out.

Dave is an expert at these carbs and should be able to get things sorted. But as an FYI, the plugs didn't cause any problems! Not sure why you're messing with float level as it is a fine tuning aspect of carb jetting and typically is not changed much if any from factory settings. However, based on your plugs you're seeing one carb lean, the other rich. Are they balanced with a balancing tool like a unisyn or "the snail" and not by ear? My engine is very sensitive to even minor balance issues, especially at idle so getting that dialed in and locked down is important and typically requires a flow meter. If you don't have one, get the Snail as its far superior to a unisyn in use.
Now that you've messed with float level, you may need to create a way of measuring the fuel level in the carb. Mikuni had a marked glass tube/straw that you placed in the main jet hole to a consistent depth, put your finger over to hold the liquid in it so you could pull it out and see where it was in the tube based on the marks. You may have to make something, and consider that it will be in fuel for short exposure but that means it must be clear, fuel resistant and have marks that won't rub off. If you have one carb that still has the factory setting then you'll have something to compare to. You can also observe what happens when you adjust the float level (how many screw turns etc) and make them equal. Regardless of method, make them equal in both carbs, then you may have to play with it until it seems right. First things first though, compare the fuel level in the carb that overflows vs the one that doesn't and adjust to make sure the carb is no longer overflowing (assuming that's what caused it and not a stuck float valve). Work with Dave to get the jetting right based on the version of the carbs you have, make sure they are balanced etc. Then if needed go back and adjust the float level. Just so you understand, the fuel level in the carb changes where the fuel sits on the emulsion tube. The emulsion tube has holes in it for airflow at different places in the length of the tube. Changes in the fuel level changes how that tube mixes air with fuel. It's subtle, but way off could cover an air hole with fuel or change the operation of the tube.
If you have a carb manual I suggest studying it carefully so you have a good understanding of what does what... it can get confusing! There are good sources on the Internet. We're here to help!

Hey Greg
Thanks for the reply, I have taken your advice many times from previous forum discussions.thank you for that.I think you may have previously posted some info about the b6es changing the timing somewhat as it does fire differently, this is why I thought maybe changing to this plug advanced the timing so that the plugs were burning white ? Anyways...
I reached out to Dave and he really is “that guy” I will adjust float levels on carbs and go from there,
Will keep you posted

Simple thought, are you sure you have the plug wires in the correct firing order?

Just read my post from yesterday... clearly I have a lot of time on my hands! Regarding the plugs, as I recall the ones I noted caused some differences for my engine were the extended nose versions. Looks like that is the BPR6ES plugs per the NGK site. They feature an extended nose. My engine is high compression and it didn't like that plug, causing it to ping. The stock plug is a BR6ES. The BR6ES-11 is the same plug with a wider gap. That can be useful when running a high output ignition.