Carb damping oil? Flow guide valve ?

[sahunt66]

I've finished cleaning my carbs and need to install them. For filling the oil reservoir, I guess 20W oil is what you use? Is there some kind of oil you recommend that's good and maybe has a handy way of putting it in (squirt tip, etc...)?

Also, does the flow guide valve effect the engine runs or is it just for emissions control? I noticed that the hose that goes from it to my air cleaner was cracked. I wonder if that was contributing to my car running badly.

:classic: :classic:

[seerex]

I have been told that 20w castrol if best for the carbs or fork oil , If you are talking about the float lines from the carbs to the air cleaner , it won't affect how it runs it just dumps the extra fuel from the carbs <if any is there> to the air cleaner, if we are talking about the same line. and if you put too much in the carbs its ok if you raise the piston inside the carb it will get rid of the excess and just get burned in the engine <as I was told on ye olde ztherapy video > , good luck:geek:

[Bambikiller240]

Originally posted by sahunt66

Also, does the flow guide valve effect the engine runs or is it just for emissions control? I noticed that the hose that goes from it to my air cleaner was cracked. I wonder if that was contributing to my car running badly.

:classic: :classic:

The Flow Guide Valve is just for emissions control. It routes vapors from the fuel tank to the crankcase if your engine IS NOT running, or to the aircleaner if the engine IS running. The cracked hose will not affect engine performance.

As for carb oil, I use 20 wt oil and I bought a small old fashion "oil pump can", the kind with a trigger and flexible spout to top up my carbs when needed.

[Chino 240Z]

A cracked fuel vent hose may not change the way the motor runs, but a plugged or restricted hose will. The carbs will not operate properly and will even drain out fuel.

For carb oil, we have been using that Marvalous Mistry Oil and have notice good carb response time with it. JM2cents.

[Zedrally]

Carb Oil,

Use ATF.

[Ed]

Originally posted by Zedrally

Carb Oil,

Use ATF.

I was told the same thing by a mechanic at Z-whizz in San Diego. I guess ATF is the same as 20wt (or was it 30wt?).

[Zedrally]

I think with it being a detergent oil it prevents buildup that prevents sticking.

I've used it in both cars for several years now with no adverse effects, can't say performance is any better, but I've always got ATF on hand [cheaper to]!

[sahunt66]

Thanks, I bought some Marvel Mystery oil as suggested above. It was cheaper than ATF and I don't have any cars with automatics to use up the balance from filling the carbs.

:alien: :alien:

[240ZMan]

Sahunt66,

What oil to use in the carb dampers seems to get the widest range of answers possible. I'd suggest you experiment. I found this summer (when I picked up my 73 with 72 carbs) that 20W was the best. But when it got cold (below 30) that I did better with Marvel. The main thing I noticed was how smoothly the engine responded to the throttle starting up from a stop sign. A thinner oil seemed to give a quicker response, but if the carbs weren't rich enough, there was a little stumble as it temporarily leaned out too much. Using a thicker oil in the summer compensated without having to run too rich.

Like I said, I'd experiment. It's no big deal to pop the domes off and pour out the old oil. Try one oil for a week and see what you learn. After all, that's supposed to be part of the fun of owning a 30 year old car:classic:

[beandip]

There seems to be a miss understanding on what the different weight oils do in the carbs . When the piston , and needle , rises it causes encreased air flow thus leaning out the fuel mixture for a secound untill the needle rises to a point that it allows aditional fuel to enter the air streem. When a thin oil is used like ATF or Mistery oil , it allows the piston to rise quickly causing a leaner mixture. Thicker viscosity oil retards the riseing of the dome just a split secound alowing for a richer mixture , just like a accelerater pump on a detroit carb. This eliminates a stumble off the line. It is only when starting from idle at a stop does this make a difference. After the RPMs are up and you are moving , either oil makes no difference. If you are driving in vary cold temp and the engine is not warmed up most likely the choke is in use any way and either way if the engine is cold it shouldent be pushed in any event. At least this is my 2cts . I have used all three and now I only use 20wt. and find that on the street it works the best for me. I have tried to out clever the builders but have found so far Datsun did a damn good job on these engines. other than the flat tops, but they were forced on them . As for cost of the oil . I have the same qt of oil I started using 3 years ago and have given some away and still have 3/4 of a qt. . :classic:

[Zvoiture]

I have been following some of these carb conversations with great interest, as have just bought my first set. Do Mikuni's have this dampening oil mechanism? Just looking at them it doesn't seem like it. Sorry so ignorant, I just never realized SU's had oil in them for this well-but simply-engineered function.

steve