SU's got me stumped

[steve91tt]

If there's such a misalignment, I wonder whether it happens only when the piston is forced in the direction of air flow. Perhaps you could find the problem by sliding the piston up and down while gently applying sideways pressure to it with your finger through the carb's throat.

Great thought! I took your advice and tried side loading up the slide (towards the engine) as much as possible while letting it drop. The front slide produces a metal on metal sound when I do this where the rear does not. I adjusted the dome to minimize the sound but I can't get the front one to drop as smoothly when loaded as the rear. It's not bad enough that I can get the front slide to hang but there is a difference between the front and rear carbs.

[olzed]

Silly question I guess, have you got damping oil in the little cylinder, and the correct grade. Could there be gunge in the damping oil. Unlikely, given the carbs are newly rebuilt.

Brian.

[FastWoman]

Sounds like something's out of tolerance. Maybe there's too much wear on the piston? If I were you, I'd send the entire carb back for replacement.

[Zforce]

I don"t think anyone has mentioned it but have you oiled the tube that holds the damper oil where it contacts the dome ? Lack of lubrication in this area will cause the suction piston to stick.

[tlorber]

Steve,

Is your fuel filter clean? Also make sure you check the screens in the banjo bolts (just before the fuel enters the float bowl). The ones on my Z were fairly clean, but my roadster's had all kinds of crap in them.

[steve91tt]

Thanks for all the great suggestions guys. I will be going down the list and making sure that I address each one of them until the problem is solved.

I spoke to Steve at Z Therapy this afternoon. He told me that I was doing the dome alignment procedure incorrectly. I had been aligning the domes with the nozzle in it's normal position. Steve told me that it is more accurate to align the dome with the nozzle all the way up. In other words, align the slides after screwing the mixture nut all the way in. Doing it this way centers the needle better and minimizes the chance of the needle hanging when the dimensions/tolerances of the carb change as it heats up.

I did this and found that with the nozzle all the way up my front slide would hang as I had it adjusted. Fortunately, I found that at the limit of the dome adjustment there was a spot where there is no rubbing at all.

I reset the mixture back to where it started and took the car for a ride. It seems to run nicely but only time will tell if my intermittent sticking slide problem returns.

Thanks again for the feedback guys! I will keep you informed if this latest fix did the trick.

[Bruce Palmer]

Reminds me of a deal we had not long ago with a customer who bought our carbs, took his car to the local NISSAN dealer to have them installed by an old lind DATSUN mechanic. Turns out that guy was taking money under false pretenses from the dealer cus he didn't know his from a hot rock. Being the service oriented piece of work we are the customer was invited to trailer his car over here on a Saturday and Steve would make it all better.

About 20 minutes of fiddling and the carbs were dialed in. Engine ran well at the two "set carb" RPMS. Nothing would do (while we're here) but to set the timing and check advance curve etc....... It had some kind of ersats electronic non NISSAN module lashup in the distributor from the PO and by golly, rev the engine and timing would jump quite a number of degress and not consistently either. Obviously with advance all over the map the engine didn't run well and he was sent home to confer with his real mechanic. Steve said touching the unit would alter the timing. He also said it could be nothing more than a loose wire.

Bottom line --- customer got his distributor done, i think by the guys I've mentioned in Portland and at last report, he is happier than a dead pig in the sunshine. You guys drifting toward the electronic gremlin thing just got me to thinking.

[Bruce Palmer]

As a little follow up to the UP positioning of the nozzle. The ID of the nozzle is .100" (spot on guaranteed) that's the way we have them made. Base OD on most needles is like .098" .0985" .099" depending on the needle one has, so it makes sense that if you center where the free space ID to OD is minimum, any place above that when the piston moves up, CLEARANCES WILL ONLY INCREASE, right? There should be no way for a needle to rub on anything say in the half way up position without having done so on the way up.

Okay, to maybe put too fine a point on it, I got time, If say you have a needle that is straight and it's rubbing the inside of the nozzle half way up, I'd advance the theory that in the down position the needle would be wedged so tight (cuz remember the needle is fatter the farther toward the dome it gets) you couldn't get the piston to move with out a major reposition of the dome.....

I certainly must have a life around here somewhere......

[steve91tt]

It all makes sence when you think about it. I'm a little embarrassed that I didn't think of adjusting the domes with the nozzles fully up myself. I guess I need to watch your DVD a 5th time!

[Bruce Palmer]

That still doesn't explain the intermittent thing. Unless you can feel interference when you lift the piston (of which you are now on set two) I'd rule out "piston hang" and evaluate the distributor angle. The one we had experience with was a Fireball electronic something or other that was junk.

[steve91tt]

That still doesn't explain the intermittent thing. Unless you can feel interference when you lift the piston (of which you are now on set two) I'd rule out "piston hang" and evaluate the distributor angle. The one we had experience with was a Fireball electronic something or other that was junk.

I went through the ignition system last night and didn't find anything amiss. A timing light shows a steady, consistent spark that advances as it should and the car pull smoothly to 6000 RPM (I don't want to take it any higher until I get a few more miles on the fresh bottom end). I have new plugs, wires, roter and cap. I ran a higher capacity ground to the MSD box just for good measure but it did not seem to make a difference in the way the car runs.

I guess it is possible that there is something in the ignition that is causing a fault that occurs intermittently at idle.

Unfortunately, the only time I have been able to get the hood up while the car was acting up the issue was a stuck slide on the front carb. But that was with the old dome. Hopefully I can safely pull over in time to do some more detective work next time things go south.

[Bruce Palmer]

Steve,

Take the hood off and have someone else drive the car while you ride on the fender hunkered over the motor. I'm sure it wont help solve the issue, I'm just curious what the ticket will read like..... "Well, your honor, this dimwit out in Oregon said that if I were to ......... " :stupid: