Weird dysfunctional SU carb issue, rebuilt and floats reset going on 8 times now.....

[mr mikey]

When setting to idle speed, I can't get the rpms to go below 1550, else the engine will just die and chug smoke out the carbs when it dies(seems to reverse rotate a little when it does that). We've rebuilt the carbs and adjusted the floats going on 8 times now per the directions of the SU carb builder dude with the video, and it STILL does this. I'm at a loss. The car has a new distributor in it with the GM module conversion, and I've both based timed it and checked the 3k rpm mark too, everything there is in order, so not sure what it is. Set valve clearances when I changed the valve cover gasket. It's not putting out the exhaust and the vac readings are stable, so not a burnt valve. Brand new fuel pump installed, new lift pump, filter, etc etc etc. Been dealing with this for a LONG time(over a year) on a constant basis, so anything that could be checked/changed for maintenance has been done. WIT'S END BOYS AND GIRLS!!!

-Mike.

Ps. Thanks ahead of time for any/all suggestions. Before I removed the carbs to clean(lotsa sludge in the bowls), I actually was able to drive this thing the 2hrs home from where I bought it......you just don't know how many times I've watched and rewatched that SU tuning video.

[240260280z]

Are the jets sticking due to the chokes? The cable and grunge can cause problems.

Separate the choke lever from the jet, disconnect the fuel line to the jet, then pull out from the bottom of the carb and clean the jet and orifice where it slides up and down.

Here is a recent clean from an Austin Z

Edited June 28, 2013 by Blue

[mr mikey]

Yes, we have completely disassembled and cleaned every part every time we take them down to check and readjust float levels. These are the round-top SU carbs also, forgot to mention in the original post, off my 72 240z.

[Captain_Zeros]

If you've already checked everything then I'm down to grasping at straws, but what method did you use to adjust your float levels? On my Z I had far more luck adjusting with the sightglass method using a piece of clear tubing than trying to use the "hold the lid outside of the car and blow through a tube and move stuff around with a ruler" method.

It's also possible you have a fat vacuum leak at the carb gaskets or the throttle shaft, I guess.

[mr mikey]

Exactly, nothing is making sense here.....I've been having this exact same problem since I joined the site, surprised my patience lasted this long to be honest. All gaskets on the engine(minus head gasket) have been replaced. I used the method of setting the lids on top of a small pint jar and slowly filling via syphon pump to set float levels. It's a tedious process, but it gets the levels dead-on. The only reason I haven't sent both sets of these carbs off to be redone, is at first I couldn't justify the cost of him doing them(rest of car wasn't in very good shape).....but it grew into the "You cannot defeat me!!!" routine.....now I'm getting close to sending them off .

[Jarvo2]

Are you still running a voltage regulator? I was having similar issues and just upgraded to a ZX internally regulator alternator along with the jumpers required...everything is running much much better now!

[mr mikey]

Yeah I'm running an AD244 alt with a v-belt pulley swap to an external regulator with high amp internals, ampere gauge swapped to high-amp ampere gauge and volt meter combo gauge, and everything seems to be doing right, it peaks at 15.2v with no accessories on, which is still in the green range.

[Gary in NJ]

What is the condition of the Grose Valves? You might have one that doesn't fully close, allowing an over-rich condition.

[mr mikey]

Well we're still using a kit we got a couple years ago that included new valves, we've run the engine with the drain screws removed and the "hollow screw to clear vertical tube" method to make sure the level doesn't go too high and it always stays within a millimeter or 2 of where we adjusted it. So I don't think it's bleeding past, unless it just randomly sticks when we aren't testing the level. The way it dies confuses the heck outta me too, when it dies it stops rotating, then it rotates backwards spewing smoke out the blowback holes in the carbs. I'll take a video in a bit showing what it does when it dies.

[zKars]

Pull the domes and make sure that both jets are flush with the bridge with the adjusters all the way in, or at least both are the same and close to the top. Did you remove the needles from the piston? Back in the right place? You are definitely running rich.

[mr mikey]

Here's how she does when easing off gas, started shaking a little at 1800rpm and fell on it's face at 1700rpm.

Edited June 28, 2013 by mr mikey

[mr mikey]

Pull the domes and make sure that both jets are flush with the bridge with the adjusters all the way in, or at least both are the same and close to the top. Did you remove the needles from the piston? Back in the right place? You are definitely running rich.

The needles are in the same place, but when fully warmed up, it does get a teensy bit of sooty exhaust when you get on it good with no load on engine, so I might play with the height of the needles a little.