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mr mikey

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

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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. LOL

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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

attachment.php?attachmentid=64163&d=1372441058

post-7641-14150824637692_thumb.jpg

Edited by Blue

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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.

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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.

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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 LOL.

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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!

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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.

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

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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.

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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.

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

th_260zdyingissue.jpg

Edited by mr mikey

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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.

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definitely running rich at idle....any chance the SMOG equipment you have installed is causing a lean condition below a certain RPM?

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The smog stuff is actually unhooked at the source, only using blocked tubes to seal off any leaks, I haven't gotten around to making the blockoff plates for everything yet, as this current issue is draining every bit of mental capacity I can put towards the car LOL. I'll get some nipples to cover all the spots, or if you think maybe the parts are internally broken and hemorraghing through to the exterior, like a vac leak thru the housings.

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Seems like something isn't flowing as it should. Here's what I ended up doing temporarily. On the air galley, a black-pipe cap fits perfectly.

post-26781-14150824638157_thumb.jpg

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Have you tried to alter timing-retard it? Does it fire up easy everytime? It seems that the timing might be way advanced.

Linkage-what have you done to eliminate that possibility?

What's the history on the engine? Have you ever heard it run right, or did you buy this and started out this way?

What year car and engine?

What distributor are you running?

I have no answers, just questions:)

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Have you tried to alter timing-retard it? Does it fire up easy everytime? It seems that the timing might be way advanced.

Linkage-what have you done to eliminate that possibility?

What's the history on the engine? Have you ever heard it run right, or did you buy this and started out this way?

What year car and engine?

What distributor are you running?

I have no answers, just questions:)

I thought the same thing about the timing, especially the way it reverse rotates, but it not hard to crank(actually very easy to crank).....my camaro is base timed at 18degrees advanced, so I know how an advanced engine sounds when turning over LOL. The linkage has been checked for slack and worn joints and such, it all seems to be fine. I can spray wd40 around the throttle shafts to check for revving from vac leaks and the idle speed never changes(unless I accidentally overspray into the barrels haha). When I bought it, I was able to drive it the 2hrs to my house, but it chugged and rolled coal when I tried to pull any real hills. Tore the carbs down per the video and found a bunch of crud in the bowls, so I went nuts with a toothbrush and scrubbed all the internal components, and readjusted per the video.....it hasn't been right since. Car is '74 260z, Engine is '74 260z, carbs are '72 240z. Distributor is a "NOS/OEM" electronic ignition distributor listed for a 260z with the GM electronic control module.....it had the Crane(Allison) Fireball 2000 or whatever it's called, but it kept going thru control modules(found later that the setups are finicky when it comes to quality).

I have all the answers, except the one to my question lololol.

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How do you know you are close on timing? You can't check static at 1800rpm, so what advance to you show at your present idle?

Sounds like your effort needs to be somewhere other then carbs at this point.

There was just a 7 page thread with similar issues and it turned out to be timing.

The fact that you know little about this engine, someone could have clocked the dizzy drive wrong.

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Maybe a little off topic, but the one time I ever had reverse rotation and puking smoke out the carbs was when I accidentally clocked my dizzy 180 degrees out like an idiot... then again it wouldn't run at all that way. It seems like it runs pretty well for the first 40 seconds or so of that video, so I'm real curious what the issue is. Do you have a different distributor/ignition-module(points even?) you could try? It might be confirmation bias but whenever I hear about HEI ignition modules there is a problem involved (then again nobody ever complains that their ignition is working perfectly either.)

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How do you know you are close on timing? You can't check static at 1800rpm, so what advance to you show at your present idle?

Sounds like your effort needs to be somewhere other then carbs at this point.

There was just a 7 page thread with similar issues and it turned out to be timing.

The fact that you know little about this engine, someone could have clocked the dizzy drive wrong.

I set it per the instructions for the dizzy. Set the dizzy so the rotor is centered on the #1 plug wire contact, align the dizzy to the 0 mark on baseplate, stab dizzy so baseplate mounts to engine when balancer mark is aligned with 0 mark on timing tab. Then loosen dizzy hold-down and rotate the dizzy so it's pointing at 9 degrees advanced on baseplate, then lock-down dizzy.

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Hardway and I measured the height of the fuel bowl roof from the gasket surface, I think it was 3.4mm so the 23mm down from the edge of the fuel bowl becomes 19.6mm down. We set the fuel level for this and the jets had to be set a little higher to optimize.

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Timing light?

No, not on the base timing setting, it said in the instructions that it wasn't necessary, because the adjustments were fully mechanical. I did use a timing light to check max advance at 3500rpm, and it is sitting on the 36 degree mark on balancer.

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Can you elaborate more about what's blocked off and do you have anymore pictures showing the induction system ?

The smog stuff is actually unhooked at the source, only using blocked tubes to seal off any leaks, I haven't gotten around to making the blockoff plates for everything yet, as this current issue is draining every bit of mental capacity I can put towards the car LOL. I'll get some nipples to cover all the spots, or if you think maybe the parts are internally broken and hemorraghing through to the exterior, like a vac leak thru the housings.

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