Vacuum Question for Dort

[ollinger123]

Hello everyone, I have a 1923 Dort with a 6 cyl. Falls engine.  In order to the engine to run, I have to pull out the choke about a 1/4".  I don't believe there are any vacuum leaks, so my guess is I don't have enough compression to generate the vacuum need to draw in the fuel without a partial choke.   I currently have a vacuum tank between the gas tank and the carb.   Would adding an electric fuel pump help, and if so where would I install it?

 

Thanks, Jon

[JFranklin]

Could the problem be that the carburetor is running too lean? If you think compression is to blame do a compression check.

Edited August 14, 2018 by JFranklin (see edit history)

[Ben Bruce aka First Born]

I would install a vacuum gauge on the intake manifold. THEN I would know.

 

  Ben

[PFitz]

If it starts you have enough compression to pull air/fuel at the carb if the carb is not the problem. Anytime you need to run with the choke out means it's too lean.  So, is it lean because it lacks enough fuel mixing in the right proportion with the air intake, or is it lean because it's leaking air into the intake system somewhere ?

 

In the carburetor, a partially clogged idle fuel feed (very common), or an air leak, will make it too lean, thus needing to use the choke to pull additional fuel from the main fuel jet circuit during idle.

 

If it's too lean during idle and at higher speeds when the main jet kicks in, then very likely the float level is too low can also cause poor fuel pull-over.

 

Adding a fuel pump will not fix what is wrong. That's just treating a symptom, not curing the problem.  And unless you seal or bypass the vac tank the electric pump will make it flood out through the vac tank vent. Plus, pressurizing the fuel line to the carb will change the float level if it is properly set for the low gravity feed pressure of a vac tank.  It may then go from running too lean, to too rich.

 

As said above, you should try hooking up a vacuum gauge to the intake system and do a compression test. Without those numbers it's just a guessing game.  

 

Paul

Edited August 14, 2018 by PFitz (see edit history)

[ollinger123]

Thanks for the feedback, it seems the low speed fuel jet is not working.   I will pull apart the carb to see if anything is blocked.  

[Rusty_OToole]

Some of those old engines take a long time to warm up completely. There is a lot of iron there. Unlike today's light weight aluminum engines that warm up in minutes. One old timer who drove a Willys Knight 4 cylinder on tours in the sixties and seventies, told me it did not stop burning oil until he drove 60 miles. After that it burned no oil for the rest of the day.

[ollinger123]

I finished cleaning the carb.  Works better than it did, but not 100% off choke.   I think it should be good enough for what I need.  Thanks for the tips.

 

[PFitz]

Quote

 

 

Did you also check the float level ?

 

Paul

[Guest]

 

The jets on my Marvel carb are removable and I had to mechanically clean the primary one inside after soaking and blowing it out. When I looked through the jet you could see the crud.  I took one strand from a stranded wire (against all advice to not put anything in a jet) and worked it up and down a few times and then blew back down the jet.  When I checked it was perfectly clean.  Put it back in and have not had any trouble for years.

Maybe you still have some crud in your jet?

[ollinger123]

Thanks for all the advice, it runs on with the choke all the way in now.   Now I just need to figure out what the adjustment is to prevent it from back-firing once it's in 3rd gear...

[Guest]

Is it "back" firing (back through the carb) which indicates a lean mixture or "after" firing in the muffler which indicates a rich mixture.  Lean mixture could either be in the carb adjustment or a vacuum leak.  After firing  would definitely be a carb adjustment.