Spitfire Spitfire Running Rich

[Alabama_Hokies]

Need some Stromberg help. At least I think it is a carb problem.

My 76 Spitfire was running quite well. Idle was solid and no smoke.

The gas tank is in bad shape (internal rust). I have been putting a couple of gallons at a time while working on it.

I added two new filters and filled it up. Ran smooth for about 40 miles. Since then the fuel pump went
out and now it is running very rich and there is black smoke.

Replaced the fuel pump, checked the needle, the diaphragm, the floats, the valve adjustment the compression, still runs rich.

Don't know what else to check, any ideas? I would like to figure this out before removing and sealing the tank.

Thanks,

Dave B

 

[dklawson]

Did you remove and clean the float valve when you were checking the other parts of the carb? If any debris managed to get past your filter(s), something could be holding the valve open.

 

[Alabama_Hokies]

Yea, I cleaned the valve and checked the position of the floats.

I really suspect the diaphram, but it loks good.

Dave B

 

[skucera]

John Twist at University Motors has a Zenith-Stromberg troubleshooting articleat https://www.sterlingbritishmotoringsociety.org/files/zenith stromberg tech tips.pdf (he's an MG expert, but Z-S carbs are on both MG's and Triumphs). He writes that one of the causes for rich running can be a clogged vapor recovery system. To troubleshoot it, disconnect the vapor recovery hoses that connect to the carb and drive it around for awhile.

Other causes can include a clogged air filter... test that by briefly running without an air filter and see if things improve. The other cause is a maladjusted water choke, which won't affect you or me because we both have '76's with manual chokes.

A perforated diaphragm usually results in lean running because the piston can't pull the needle up to let more fuel into the carb. Also, because the piston can't rise, you can rarely get going faster than 20-25 MPH with a holed diaphragm, and I can attest to that. That was the reason I had to rebuild my carb last weekend.

Good luck,
Scott

 

[tosoutherncars]

Water choke? They often fail open...

 

[Alabama_Hokies]

Thanks for the article.

One other item on this car. A previous owner removed ALL the emision control systems. No air pump, no charcoal can, nothing.

The only items this has is a misplaced vapor line from the tank to the left side of the carb (I know that ain't right) and the a hose straight from the carb to the valve cover.

Removing the hose to the valve cover does help some.

Like I said earlier, the system ran fine this way before. Change came some miles after a fill up.

I was thinking broke more rust free that got in the system but perhaps not.

I can remove the pipe from the tank to the carb and try that.

Have already run without filter as well (just in the garage).

Sorry for the long message.

ALL help is appreciated!!!!!!!!

Dave B

 

[Alabama_Hokies]

Great thought. Had that happen to an 80 Spitfire I used to own.

This is a manual choke.

Thanks for the suggestion though!

Dave B

 

[skucera]

The manual choke can jiggle away from the wide open (off) position too. Mine used to jiggle slightly closed until I put some tiny return springs on it to push it all the way open. (I used three springs from Bic pens I had lying around the house.)

Scott