Datsun Roadster Forum-311s.org

So after a month with a few evening drives, I was getting some pinging and didn’t want any damage from running too lean. Here’s a photo of the plug from cylinder 4 when The carb jet depth was set to 0.080”. The plug color seems to look fine to me, but I’m going to dial it richer to 0.086” today and I’ll see how this new fuel mixture adjustment does over the next few weeks...By the time I get this dialed in, summer might be over!

I thought that about .043" was as far as you want to go on these. That's with EI. That is super wide a gap but plug looks pretty good albeit just slight rich.

Sorry, My plug photo is a bit deceiving, the 0.086” is referring to the carb jet depth for fuel mixture, not the plug gap. Apologies for the confusion...

Do you actually hear it pinging when driving? Mine always pinged/run on when shutting off and had to kill engine while popping clutch in 1st while braking. Plug color really does look good. Timing smog/no smog ?

The pinging was usually only when accelerating from a stop light. It wasn't really that bad, I'm just a little nervous about potential valve damage. I just had the head done over the winter & it had a burnt & broken exhaust valve. If the new 0.080 setting is too rich, I'll split the difference. I'll do some driving the next few weeks & then pull the plugs & report back my findings. Timing is good & I've been running Brisco's EI for several years now.

What plugs and what gap?
I agree, looks actually slightly rich. Were you running and then shut down? Not idling, I assume.
Maybe try a .083
Linda

I've read everything and watched all of the videos on the subject of carb adjustment. I can't adjust mine. The rear carb seems to be pulling much more air than the front carb. What could be causing this? I can't balance them. Why aren't there more YouTube videos on Datsun carbs?

I would suggest pulling both domes/pistons off then peeking in to see where both butterfly valves are. Back off both carb throttle adjustment screws then turn in both to match opening just short of both butterfly’s closing. Then reassemble pistons/domes and adjust your balance with a unisyn. Are your compression numbers ok? Maybe low on front 2 cylinders? All valve adjustments good?

And leave the carb fuel mixture at 0.087"?

Pinging is about spark advance. Back your timing off a degree or two.

What do you mean by pinging? My original problem was too much air to the rear carb and not being able to balance them.

Not sure if already asked - where is the pinging coming from? Carbs? Valve cover?

If valve cover I would recommend checking your valve lash with a feeler gauge. Typically "ping" is bc of too much play/space. But you also have to be careful of extra tight lash...

If carbs - stick with what others said

Edit: here is a link from the wiki on valve adjustment: http://www.311s.org/pmwiki-311/pmwiki.p ... Adjustment

Another explanation from the WIkI
http://www.311s.org/pmwiki-311/pmwiki.p ... Adjustment
Linda

Two different questions being asked on this thread...
As noted, ping is likely due to a bit more timing than she wants or poor quality fuel. Try a different gas station or brand, and if that doesn't solve it back timing off a degree or two. While a richer mix will help with ping, before I'd start messing with needles I'd try above. The overall mix looks perfect to me, and with SUs it's harder to pick specific spots to adjust.

111jag, balance or airflow is a different deal. As noted, it's likely that there's a linkage issue or something bent or misaligned, or a significant intake leak. First, spend time examining your linkage and understand what each screw does and HOW they interact. You can disconnect the linkage via the dog bone ball and socket connectors (carefully), and remove the balance screw, then you should be able to get the airflow equal in both carbs using their individual throttle plate screws (note that when you're doing this you won't be able to rev the car etc via the linkage, and your only adjustment will be the two individual throttle plate screws... if they are not turned in enough to open the throttle plate(s) SLIGHTLY it won't idle... too open and the rpms will run up). If you can't, then there's something else amiss (intake leak, compression or valve issue, or a bent throttle plate etc... it's a pump, and something is reducing it's ability or the demand to pull air through the carb... an inefficiency caused by a leak). But MORE THAN LIKELY, it's a linkage problem. Once you get them flowing equally (and knowing that you can) look at what happens when you reconnect the dog bones and adjust the balance and idle screws... you'll be able to see what's causing the change and make the adjustments to link the two carbs together in balance.

Re carb adjustment: If you get a chance to watch the Z Therapy video on Sus it has a few tips I have not seen elsewhere. Like bending a certain part of the linkage to change the set up of the carb...Can not recall the details, but I have the DVD which came with the carbs. Just saying there are additional areas to check....at least see if linkeage looks the same.
DVD is long, a little blurry and talks about Z carbs too but is quite comprehensive, 4 hrs ! To be expected from one of the acknowledged gurus in SU rebuilding - www.ztherapy.com. Available for purchase per their website, ZTV09, $25.
Linda