1971 Weber’s issue

[upwardr]

My 71T had a recent engine rebuild and I’m having trouble getting it to run properly.

I have popping up thri the top of the carbs and so I checked the float levels with the screw glass unit. 3 of the float bowls were in the lines except cyl 5/6 . On 5/6 the level was in the lines and when rev’d up a little the fuel in the bowl went up up up to level with the seam on the carb top. Almost to the very top. Emptied the fuel and tried again and this did not happen, it stayed within the lines.
The float seems okay, very buoyant, and after taking off the top both float bowls were about even.

I removed the valve and blew it it to verify it was working.
How do I proceed to resolve this.

[fizeus]

if it is a valve leak you have to replace it and re-set the height level.

[upwardr]

I took off the valve and blew through it and it did close the air. The spring was functioning it seems.there is only a fibre washer but no shims.

Is it a case of bending the brass small stopper or go with shims?

[BK911]

Popping up through the carbs can be due to non-synchronized throttle valves.
Make sure all the valves close the same, and open the same.
Also get an airflow meter and adjust the airflow into each intake.
Also2 clean out your idle jets.

[frosty2]

2nd the suggestion to clean the idle jets, takes 10 minutes, just remove them one at a time.
Blast them out with brake cleaner and then blow them out with air compressor.
I do it every spring and again mid summer if popping starts.
You can google a how to YouTube video by Benny Obscene.

[upwardr]

Cleaned idle jets

I reassembled the top of the carb and checked the air flow with the linkages disengaged and found the left bank at 5 and the other at 7ish. Both banks were very close front to back.

To balance left and right do I use the air correction screws or the linkage?

[upwardr]

[ed mayo]

Use the throttle stop screws at the throttle lever.

[upwardr]

I cleaned all the idle jets and balanced left to right and have all the cylinders the same with in 1.

I hooked up the linkages and adjusted the geometry of the carbs.
Got some fuel and went for a short drive. The carbs are popping still. They are popping out the tops.

I have not adjusted the mixture screws yet but if the carburetor is popping up does this indicate a rich or lean mix.
Any help would be appreciated, I’m about ready to lose my mind.

[PeteKz]

Backfiring through the carb most often means lean. Under what conditions does it pop? Idling? Accelerating? Off throttle? transitions? Need more info.

[upwardr]

Seems to idle well, starts great, when doing 30mph pops like crazy. Have only driven it about 1/2 mile sounds too bad to drive.

[fizeus]

as Pete suggested it can be a lean condition.
consider that 2800/3200 rpms is the transition zone (are you in this range when driving at 30mph?). if so the transition ports can be clogged. if you are lower than this range you have to enrich lean cylinders... tuning carbs just require some expertise and a lot of patience.

[Dpmulvan]

Originally Posted by upwardr

Seems to idle well, starts great, when doing 30mph pops like crazy. Have only driven it about 1/2 mile sounds too bad to drive.

Send me a pm with your email.

[oldie44]

Check your cam timing.
Way back about 1977 I had the same problem. Checked it out and found one cam was out of spec. Corrected it and the engine ran fine.

[ed mayo]

Originally Posted by upwardr

I cleaned all the idle jets and balanced left to right and have all the cylinders the same with in 1.

I hooked up the linkages and adjusted the geometry of the carbs.
Got some fuel and went for a short drive. The carbs are popping still. They are popping out the tops.

I have not adjusted the mixture screws yet but if the carburetor is popping up does this indicate a rich or lean mix.
Any help would be appreciated, I’m about ready to lose my mind.

You need to do the idle mixture adjustment.

[1QuickS]

If you cannot get each cylinder to respond by closing mixture screws (engine speed drops when mixture screw is closed) then you may have a clogged fuel gallery feeding that idle jet, this is different than a blocked idle jet issue. STE readings at idle will be about 5.5 when mixture screws are set correctly, larger readings imply rich idle mixture screw adjustment. Mixture screw and air flow balance to be performed with throttle linkage disconnected.

[upwardr]

Thanks for the help, I have added new fuel which made it better but appears to be too rich. The carbon on the exhaust is very sooty.
Idles well but sounds like a popcorn machine. When I floor it it seem to have lots of power.
Transition from idle to 2000 to 3000 is terrible.

I removed the plugs and they were pretty much black with soot.

My quest continues.

[1QuickS]

STE readings at 5.5 is typical but can be as low as 4.5. Higher readings indicate rich idling due to Lean Best mixture adjustment is off. Have you adjusted mixture screws to "Lean Best" mixture adjustment?

55 idle jets are what you want in a 2.2 liter engine.

It is not unusual to have a sticking float when float bowls are filled after being empty. There are other issues as well such as the divot on the tab where the needle valve sits can cause a side load on the needle valve resulting in flooding. Float levels are best adjusted with shims.

Check air flow on cylinders #1 and #4 when RPM is set to 1500 using hand throttle. If one side is advancing quicker than the other then this needs resolution.

I assume you have Webers and not Zeniths.

I also assume carbs were working fine before engine rebuild.

Possibly the fuel galleries feeding the idle jets are partially clogged which would allow idling but then unable to supply adequate fuel for driving.

My website has tuning info that may help regarding "Lean Best", throttle crossbar blueprinting and "Hidden Gallery" topics: Performance Oriented