Backfiring; float level?

[Scutty]

After a recent rebuild, I have my 68, big bored, solex carbed, 050 distributed car running but cannot get it to idle below 2000 rpm. It pops (backfires) through the #2 and #4 throats every second or so. I have checked and rechecked the points and timing (4deg static advance). The carbs are rebuilt and recently rebushed. I cannot sync them as the rpm won't drop below 2000.
I suspected a float depth problem so I removed the sight plugs and adjusted the screw on the outside of the carb while it's running and backfiring. I could not get fuel to seep from the sight hole. Should I screw it out to deepen the bowl level until fuel drips out, or is that to far? Can't I take the carb off and set the float level on a bench? It would be a much easier adjustment if I could see in the hole and not have the thing backfiring in my face. Any good ideas or similar experiences?

[adot]

Hey Scutty

Yes, out with the level screw will deepen the bowl level. I once screwed mine IN all the way and bent the brass metal plate that the level screw hits. And when I backed the screw all the way out(in my hand out) I still had no gas comming out the sight hole because the float was stuck down. Had to pop the top carb plate and fix(after I thought it was the fuel pump$100, I did this to both carbs).

Try setting all idle screws all the way out , mix 2 out, and go from there with the 2k idle trouble. maybe bad dist?

GoodLuck
Brett

[Scutty]

I've got the 2 idle screws all the way in to hold the butterflies open to keep the rpm up to keep it running. I've got all 4 mix screws open 2.5 full turns from touching. Is this a good place to start?
I don't suspect the distributor. Just before taking the engine out a month ago, I had a timing light on it, and it advanced ok to 30 something at 3000 rpm when starting from a 5deg static advance. What else should I check/recheck?

[adot]

Pull the idle screws out, out, out.
Plates closed all the way

Try 1 1/2 to 2 out on the mix.

My solex, 050, 1720 will run this way

Brett

[WFBowen]

Scutty:
Double check your fuel system, especially the pump for delivery. Can you determine how much fuel is in the bowls? During the rebuild did you do any modifications to the motor (cam, etc.?) Are you absolutely sure your valves were adjusted correctly? Pull the rocker covers and visually confirm that, on tdc firing stroke for that cyl, both valves are closed. Double check all vacuum ports for leaks. I'm assuming you no longer run the smog stuff on your 68 (throttle positioner, air pump, etc.)
Along with what Bret stated, some members posted here a while back concerning the wrong thickness float needle assy. gaskets in recent rebuild kits which threw everything off. After shutting off the motor, you can carefully stick a dry toothpick into the sight holes to see where (&if) the fuel level actually is.
Keep us posted,
Bill.

[adot]

Scutty

After thinKing about it, you have to get the float level RIGHT FIRST !!!

Brett

[Duke]

Have you checked your throttle linkage for possible binding? Also it may be due to the carbs not being in sync. Back off the idle speed screws & remove the linkage from the right carb. Increase the idle speed screw of the left carb to get the engine idling around 700-800rpm & use a syncrometer to balance the two carbs. You may have to adjust the linkage of the right carb to match the left. If it is idling at 2000rpm your idle speed screws are way too high or the dist plate may be sticking. Just a few thoughts.

[Scutty]

Here's what I did. At adot's suggestion I set the 4 mix screws to 1.5 turns out from touching. This allowed the thing to idle at 1000 instead of 2000. (before I could not get the thing to keep running unless I adjusted the idle up to 2000rpm). Then I was able to sync them left to right, and front to back. It sounded nice idling, but still poped back through the carbs every few seconds.

Then I tried to tackle the float level. I took top off the right side carb and found the needle valve assembly (with the 14mm hex) had vibrated loose from the carb top. With that tight, I then tried to adjust the float depth. The left carb was ok with only a little adjustment. The right carb, however, never did drip out of the sight hole even with the adjustment screw taken out. I put it in a few threads to hold it there, tightened the lock nut down, and that's where I left it.

I took it for a test drive, all seems good except I still get the popping through the carbs! It seems to happen only at idle, but then again, I can't hear anything when I put the gas pedal to the floor. What's the most common cause of carb popping?

[Duke]

It usually means a lean mixture.

[adot]

Yes
lean most of the time. Sucking air down the flyplate shafts. Green912 tells why in another thread, but I still dont understand why? . RE brushed you say, try alittle carb cleaner on the shafts and see if that changes your rpm's.

Get the float level RIGHT FIRST


I think ron had the best fix, WEBERS (NEW)


GoodLuck
Brett

[Scutty]

I found that someone had screwed in the float level screw way to tight. This deformed the little bent metal piece that adjusts the pivot point for the float. Fixing that, and an hour of idle mix adjustments, removed 90% of the carb-popping.
I have had no luck removing my remaining small carb-popping problems, and a backfire from the tailpipe in throttle transition (up and down).
I find when I screw #1,2&3 mix screws all the way in, one at a time, the idle speed slows as that throat gets no fuel.
Screwing #4 all the way in, however, has no affect on the 1000rpm idle speed. How can this be?? Where is #4 throat getting fuel? The idle screw is undamaged and the main jet is clear.
Has anyone had a problem like this?

[Duke]

Sounds like your idle passages may be plugged on that carb. Have you taken them off & boiled them out with a carb cleaner? I would try this as well as cleaning all the jets. Use compressed air to blow out all the passageways after cleaning.

[adot]

Pull the plug wire on #4 and see if that does anything. Maybe your only running on 3. Is the front barrel in sync with the back?

Maybe #4 has to be richened up a bit.

someone= NOT ME, but I have. On both carbs

GoodLuck
Brett

[Scutty]

I've had the carb off and tried to clean it all out with compressed air and squirts of carb cleaner. Perhaps that's needed again.

I'm sure I'm running on all 4. I know what 3 out of 4 sounds and feels like. #4 is firing, but not adjustable with the idle mix screw. Would a cloged idle passage fire in that throat at all?

I'll try a "disassemble and clean" on the left carb next weekend. Any more ideas as to the cause, or similar experience would be appreciated.

[Duke]

To properly clean out all the passageways, you must completely disassemble the carb (all jets etc.) & use "Berryman's Chem Dip" carb cleaner. Let the carb soak for 10-15 minutes & then flush it out with water followed by blowing it out with compressed air. You can put your finger over one end of the passageway while blowing it out to see if the air is coming thru. If not boil it out again-sometimes it takes more than once to remove anything that has solidified in the passageway. I have a Dellorto with the same problem on my garage shelf. Nothing has helped so far. Will eventually send it off for a rebuild or possible replacement. In the meantime the rebuilt Solexes are working just fine.

[Green 912]

This might be a little late but as to the original question, there is a way to adjust the float on a Solex without the expensive float tool.

This nice little trick is from one of the “Men in Plaid”

Take a coffee stirrer type straw and cut it to 50MM measure and make a mark at 29MM. This is now your float tool. Put it in the vent hole above the float and adjust up or down so the float rides with the 29MM mark flush with the vent hole. It is important to use a lightweight straw so it will not throw the measurement off.