**** UPDATE **** SD40 Carburetor issues after rebuild (2 Viewers)

[Wadesters]

My 1965 FJ45 LPB (from Arizona) engine was completely rebuilt also the SD40 carburetor. Yesterday was fire up day. It started immediately, ran well and idled. When throttling up it would stall or run rough. Looked at all vacuum points and all good. Determined it must be with SD40. Reason being when choke completely closed it will run better. That tells me something is wrong inside carburetor.

Shop that rebuilt engine and SD40 is sending their lead mechanic here Tuesday (3 hours one way from me). He said that he set up SD40 the way he took it apart. He asked me to put a questionnaire out to the "guru's". What comes to mind is: accelerator pump, jets, needle valves.

Any diagnose help extremely appreciated and I will share with him upon arrival Tuesday.

THANK YOU!

 

[pb4ugo]

If it runs better with the choke generally indicates it's a lean condition. You may have a vacuum leak.

 

[Wadesters]

Yes we think it is running extremely lean. Took vacuum hose off of PCV tube and is getting vacuum there. Also took vacuum hose off of connection coming off manifold to the pipe going to the unit that operates 4wd and getting vacuum there. Those two are the only vacuum lines I know that it has.

 

[Living in the Past]

Should have a vacuum line running to the distributor. Did you block the PCV and 4WD line not just check if they have vacuum? You are looking to see if air is getting in the 4WD system and possible to much blow by in the PCV system. On the PCV would block the line going into the intake manifold just below the carburettor. Then with the engine running see what what kind pressure you get off the hose coming off the oil fill tube. Would also verify level on the glass on the carburettor. Did you use new gasket on the base? Vacuum leaks, fuel delivery and timing are external things to check. All those okay most likely a carburetor issue.

 

[Wadesters]

Thanks! Yes I did block the PCV and 4WD, engine did not run any different. Carburetor level in sight glass is about 1/2 way. I did use a complete new tube and new gaskets on carb base.

 

[pb4ugo]

I reread your intial post. It runs fine at idle without the choke, but starts running ruff at higher rpms? If you close the choke at higher rpms it runs better?

 

[Wadesters]

Yes. I have the choke completely closed now and actually ran it down the street. With out choke no way it will do that

 

[middlecalf]

Your carb guy coming on Tuesday will check this out, but in the mean time what happens when you screw the throttle mixture (not throttle idle) screw in without any choke (count the revolutions so you can return it back to where it is for the carb guy)? It should die before the screw is completely seated. If nothing happens, then you’re not getting <enough> idle fuel flow to step up (transition) to the fast circuit. The SD40 carb’s choke only closes the venturi plate, it doesn’t bump up the idle speed (and slightly close the throttle plate) as well as with some other single barrel carbs (e.g. Carter). So with the venturi plate closed via the choke cable you are effectively increasing the air flow velocity into/through the carb, which then draws/pulls via the increased vacuum more fuel from the high speed network, and the A/F ratio becomes more rich, which finally satisfies the A/F demand the combustion process needs to rev up. Maybe .

Also, do you see a squirt of fuel (with engine off) when looking into the venturi and bumping the throttle?

 

[Casey E]

Did it run fine before he rebuilt the carb ? I guess I’m asking was this a known good running carb.

 

[pb4ugo]

I was asking because i am thinking the same as @middlecalf. Maybe a cloughed port feeding the venturi, accelerator pump etc. When you close the choke it forces/sucks fuel from somewhere else. 1st don't look straight down the carb just in case it might backfire. When at higher rpms do you see a fuel mist coming out the venturi? Do you see fuel squirt from the accelerator pump when you active the throttle?

 

[3_puppies]

does the fuel level stay constant in the sight glass?

 

[Wadesters]

When the mixture screw is screwed all the way in the motor did die. I bought it used knowing it needed rebuilt so I have no knowledge of it running before.

 

[Wadesters]

When you operate the pedal with truck not running it does squirting fuel.

 

[red66toy]

I ran into this with my SD40. I had to have some choke for it to not bog down while giving it gas driving. Idled great. No vacuum leaks. I had to bend this little metering rod arm like 3mm down. I’ll go find the pic. I think it’s also in my thread somewhere.

 

[pb4ugo]

My guess it's something in the metering system or dirt. If you're not familiar with the carb, I'd let the guy who worked on it b4 find the problem. It may have been assembled wrong b4 he took it apart.

 

[Wadesters]

Thanks @red66toy

 

[red66toy]

I found the pic!
I bent this arm down (at the crescent) down like 2-3mm. Solved my bogging down issue. Props to @mattressking for coming up with this fix. He knows his carbs.

 

[Wadesters]

Thank you very much! Another thing to try on Tuesday.

 

[1969FJ]

When you are checking vacuum, are you using a gauge or just listening for changes. A gauge can sometimes find things not thought of.

 

[Wadesters]

Did not try a gauge just manually checking.