no start

[nismospek]

Well i decided to try to refill my su's oil and i had some 10W30 Mobil sythetic around. I read that i could use this weight for the su's but now it tries to start up and then it just dies. ive i go heavy on the throttle it backfires through the carbs and leaves a smoke. Im gonna remove the carb tops and remove all the oil . What oil and how much should i put in there??

[EScanlon]

I'll let others help you with the problems, but my friend Gary (Beandip) was able to obtain 20wt oil from a motorcycle shop. They use it in their front fork suspension.

From what he has told me, it only takes about a teaspoon or so, or just enough to coat the top of the brass barrel on the end of the cap stick.

FWIW

E

[beandip]

Just adding 10w30 to your dampeners will not cause what you are experiencing. There is something else going on. Are these 3 screw or 4 screw SUs? If they are 3 screw carbs there should be two conical shaped plastic things sticking up on the top of the carb body. These are to align the dome of the carb to the body. If they are missing then when you reinstalled the domes they are likely miss aligned. This causes the needle to stick in the nozzle. reach your finger into the intake of the carb and lift the vacuum piston up and let it drop. It should drop with a clunk. If it doesnt or if it sticks at all, the needles are in contact with the nozzle. Unless of course there is dirt on the piston and this will also cause it to stick. To lean of a mixture can cause the engine to backfire through the carbs. To answer the amount of oil, from empty about 3cc , Esnanlon is right you can just use a spoon full. You cannot over fill the dampener. Any excess will drain into the intake and be burned by the engine . Gary

[DeesZ]

I agree with Beandip that there is "something else going on" in there. In addition to the good advice already provided, be careful not to mix the parts up from one carb to the other when reassembling them. In other words, make sure the same dome and piston go on the same carb body that they came off of originally. (A suggestion here would be to do one carb at a time to prevent the possibility of mixing up the parts.) As for damper oil, I have used all of the previously mentioned suggestions at one time or another - MMO even works well in some carbs, straight or mixed with your choice of motor oil. I have pretty much settled in using 3-in-1 oil for years to provide the effect of 20W, and it has worked well for me and my needs for normal driving. It also is readily available in the small quantities that you will need, easy to put in with the tiny little spout it comes with, and easy to safely/cleanly store until needed the next time you need it. Please keep us up to date with your findings.... It is the final resolution to so many problems that often don't get posted here....

[nismospek]

If they are 3 screw carbs there should be two conical shaped plastic things sticking up on the top of the carb body. These are to align the dome of the carb to the body. Gary

I do have 3 screw carbs but they are new from Z therapy. I made sure to not mix up the parts when reinstalling the domes. where are those plastic things located because i don't see them. Have any pictures.

Symtoms : as soon as I stop turning the ignition the car just dies. If i go hard on the ignition it sputters and backfires then dies.

Normally I could baby it, it would backfire some and then then it would idle just fine... now it doesn't even want to idle.

[MikeW]

The caps themselves have a sort of dipstick that lets you know how much oil to use. Like DeesZ I use the 3-in-1 20W oil that's readily available.

I'm surprised that a change in oil would cause the problems you are experiencing. The damper oil really just controls how smooth the throttle opening changes. I wouldn't think that 10W30 would be all that different from 20 weight. At the relatively cold temperatures inside the carbs 10W30 should be be closer to 10 weight.

[nismospek]

yah, i read the tech tip and it recommended 10w30 for newer su's. I don't know what it could be. I ran it a few days ago and it was fine but yesterday it started with the problems. I hope i didn't burn something out...

[nismospek]

found out what the problem was.. mixture was set too lean.. it was about 1 turn out only. surprised i could ever get it to start. now it starts first try and idles strong at about 900.

[beandip]

I do have 3 screw carbs but they are new from Z therapy. I made sure to not mix up the parts when reinstalling the domes. where are those plastic things located because i don't see them. Have any pictures.

NISMO I am glad you have the carbs sorted out. The plastic alignment ''pins'' I mentioned are on the upper rim of the carb body where the dome rests. They are there to align the dome which in turn aligns the main needle to nozzle. The 4 screws have a adjustable nozzle mount that allows you to adjust the nozzle to match the needle position so they do not have them. The 3 screw carbs have a non adjustable mount for the nozzle, and use the plastic ''pins'' for this alignment. If when in the rebuilding process the plastic parts were knocked off the body , then the dome can be tightened down with the needle out of alignment. This is the reason Deesz stated that it is so important to not mix the parts. This alignment was done at the factory when the carbs were made. There is a method of replacing them , but this is another story.

MikeW The dampener actually controls the vacuum piston not the throttle opening. If the vacuum piston rises too quickly from idle it will allow too much air volume to fuel mixture . This can cause a stumble and loss of power due to a lean condition, just for a instant. But never the less a irritating condition. Using to thin of oil will allow this to happen. The factory recommends 20wt , I haven't measured 3in1 vs 20wt with a Delmer cup to compare viscosity but visually is seems thinner. 10w30 is a compromise and will work, ATF which many swear by, is 5wt. If used with a rich setting or a vary rich needle it will function, however unless the engine is used at the higher revs like AutoX or track all the time, the likely hood of oil dilution from unburned fuel in the crankcase is high. Gary

[nismospek]

Thanks for all the great info. I didn't know that those aligners existed. I guess since most of them get removed or something. I'm gonna use the 10w30 until i get ahold of some 20 wieght. Would it be a bad idea to mix the oils?? Or should i just remove the dome and clean everything out before switching to the 20 wt?

[beandip]

No there shouldn't be any problem. The biggest issue is the alignment of the domes. Have you tested this by lifting the vacuum pistons with your finger and seeing if they drop cleanly with a clunk? This is important. If the needle is contacting the side of a nozzle it will wear . These surfaces are both brass and soft. This wear will cause a mixture variation you cannot control , plus it can cause the piston to stick. Rather than removing the dome if all is adjusted correctly , you can draw the oil out with a old turkey baster or a length of plastic hose like used for the windshield fluid. Gary If you know anyone else in your area that has a early Z . Split a bottle of 20w with them. You will each have enough to last you for years. Gary