Help from the carb gods please! L20B

[280Dan]

This is the first carb I’ve ever dealt with. It’s a Weber 32/36 DGV. It’s backfiring through the carb on any more than light acceleration. It’ll bog, backfire and then go. I smoke tested the best I could and didn’t find any vacuum leaks. I got a hold of a timing light and set it at 12 degrees at around 670rpm according to the timing light. Then I attempted to follow the redline carb tuning instructions. Setting the idle screw out two turns won’t even let me fire it up it just misses and bucks and never runs. If I back it out 3-4 turns it runs and the idle seems high maybe around 1000. Based on the tuning sheet the idle jet is too lean (too small) and it would need a jet change. It’s also dieseling like crazy when I go to turn it off but that seems to be getting worse the hotter the engine is getting which is really hot right now so that may clear up with some Seafoam (?). Any help would be appreciated. This is a kit that I found in the box of spare stuff the PO gave me, other than the gaskets I have no idea what these other parts are. I’m going to try and attach some videos below of what’s going on. Someone told me my accelerator pump could be bad cause it’s only squirting into the passenger side of the carb when I prime it with the ignition on? I thought that was normal…

[280Dan]

Backfire through carb

[datzenmike]

Pull the jets and clean them. I suspect the primary is slightly blocked and not allowing enough fuel through. You probably have a lean backfire.

[280Dan]

Mike when I prime it with the ignition on am I supposed to see fuel squirt into both ports or just the one? 

[280Dan]

That doesn’t look good

[datzenmike]

 

 

 

Ignition on? You have an electric fuel pump? To answer, no fuel will be seen just from having the ignition on or the fuel pump if electric.

 

The pump only supplies fuel to the carburetor nothing more. The carburetor allows fuel in and keeps the fuel bowl filled. The fuel bowl should be filled from the last time the carburetor was used so electric pump isn't really necessary. If engine is running and using fuel then yes the carburetor would at some point need to open and let some in.

 

When running above idle, fuel will be sucked out the primary venturi only till throttle is above about 60% then the secondary begins opening and fuel will be sucked out into it also.

 

Then idling or at low speeds the air flow through the primary is insufficient to produce enough venturi vacuum to get the fuel flowing and a lean bog condition will happen. To transition through this lean portion an accelerator pump manually squirts raw fuel into the primary and secondary.  That you WILL see if you work the throttle and the accelerator pump is working correctly.

 

 

Looks like sediment, Wipe it out then pull those two jets and check they are see through. There shouldn't be any sediment so replace your fuel filter. Should be done every 3-5 years.

[Stoffregen Motorsports]

It's just dirty, but it will probaby need the jets removed and air blown through to clean everything out. There are emulsion tubes under the air jets which can be removed using a thin pick. Just stuff the pick into the top of the emulsion tube and twist slightly to break it free then lift it out. Keep track of what goes where though.

[280Dan]

Removed the jets they were clear. Cleaned everything with carb cleaner and blew it all out with air. Replaced the accelerator pump. Put it all back together and rechecked timing. Idle screw and idle mixture screws adjusted to redline instructions 1 1/2 idle screw and 2 turns on the mixture screw all done while hot. Still runs like shit. Added seafoam to see if that would at least help with the dieseling and it’s still falling on its face and backfiring through the carb with any attempt to accelerate

 

Video

 

[datzenmike]

Take valve cover off and check valve clearances.

 

Set too TDC check both valves #1, intake on #2, exhaust on #3. Turn engine by hand ONE complete turn to TDC again. Check exhaust on #2, intake on #3 and both valves on #4. If there is a tight intake valve it may not be tightly closed. When cylinder fires under load (accelerating) it might slip past into the intake....

 

[Stoffregen Motorsports]

Good call, Tom Clancy.

[banzai510(hainz)]

be honest I dont think nothing wrong with the carb.

move the timing around see if that helps. Most times soemone dropped the oil pump and its off a tooth and they dont tell us expecting us to be Mind Readers. If your in the middle of the timing slop on distributor to get 12 then most likely ok but if the dist is cranked to one side and out of slot then its supect to running out of time when driving or RPMs

 

is the 2ndary opening mechanically? the spring on there to keep it closed till its force open by the cam to open the 2nd barrel.

You see gas squirt in the main barrel? yes only one one side.

 

the dieseling is from the open chamber head and you dont have a idle cutoff selinoid on that weber unless you have the E veriosn which can take the bigger idle jet holder and get a selinoid to cut the gas off/ Later Datsun have a 12volt wire that shuts off with the key to the selinoid.  I myself just push the gas pedal partial down when i sht the key off. or run 91 and above gas might help

 

Look like rust on bottom of float bowl(wipe up with rag).  On truck change out the fuel filter more often or run  2 filters as dirt get past the filler hose and water draines in there and rust the tank

Edited July 23, 2023 by banzai510(hainz)

[builte]

Did you do a vacuum line delete?