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Stromberg mixture how-to, once again.

  • Thread starter Thread starter Tinster
  • Start date Start date

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On second thought, maybe I'll pull the carbs off again and start from scratch.

Blarg!! All this trouble because one carb was running rich!

I hate carbs.
 
Dale, you have a major air leak or linkage adjustment problem. Check out the fast idle screws and make sure the have an air space between it and the cam.

Wayne
 
trrdster2000 said:
Dale, you have a major air leak or linkage adjustment problem. Check out the fast idle screws and make sure the have an air space between it and the cam.

Wayne
Click to expand...

Back to square one where I started but I've now got super clean carbs with new needle valves.

Brent called it first. Throttle linkage adjustment, front carb.
Nice smooth idle at 900 RPM, linkage unfastened and carbs balanced.

There is still an almost constant backfire into the exhaust manifold. The timing was 10* advance BEFORE I brought the air valve needles to neutral.

Remember- my front air valve has no large spring washer inside for some reason? Could that make backfires?

Now what?

Thanks all
 
Wonderful!!!! Now drive it a bit to get rid of the carbon build up in the engine and see if it doesn't smooth out. If not we can start looking for something else.

On the washer, just go to the local hardware store and get one to match or at least the same size then drill as needed.

Wayne
 
I'm lost on the the "large air valve spring washer"... never heard of one. Not the diaphragm hold-down piece, I presume?
 
SkinnedKnuckles said:
I'm lost on the the "large air valve spring washer"... never heard of one. Not the diaphragm hold-down piece, I presume?
Click to expand...

Brent: Inside the air valve piston, there is a hollow shaft in the middle that gets filled with oil. The large spring fits over this shaft and rests on a fiber? washer. The washer is installed over the center oil shaft. One of mine is missing.
Kinda red in color.

d
 
There are 2 potential problems: that piece is supposed to hold & seal the diaphragm to the air valve. If it's not sealing well the carb won't function correctly. It will act like there's a big hole in the diaphragm.

The piece has some weight to it as well and I'm sure was considered in the calculations for the proper spring in the carb. That too would effect operation. Time to start searching your garage for that piece.
 
Brent and all, the washer is used to make a flat surface for the spring to ride on. No sealing is involved here, all the sealing and vacuum control are done by the diaphragm, it uses both sides of the diaphragm.
Look down inside the air valve and you will see a couple of casing ridges, not really a good place for a spring to set.

Wayne
 
Oh - thought he was talking about the diaphragm retainer. I don't have any sort of washer inside the air valve piston on any of my carbs.
 
I don't have a washer on either of my carbs; but, that does not mean I don't need them. I just want to learn more about this.
 
Hmmm. Almost makes me wonder if somehow a washer from a damper top got dropped in there.
 
vettedog72 said:
I don't have a washer on either of my carbs; but, that does not mean I don't need them. I just want to learn more about this.
Click to expand...

OK Wayne- Ready for attempted lifeoff.
Timing set at 12* advance
Carb mixture set at 2 turns
Carbs balanced
Warm idle at smooth 900 RPM.
Still a fairly constant backfire

Test drive time!!

Wish me a drive home and not a flat bed.

thanks all

dale
 
Very nice hour+ drive this afternoon. Blew a bunch of carbon out of the engine and things smoothed out greatly. Took it up to 70 mph along the beach highway.
All green lights back at home. Backfire just about gone.

thanks,

dale
 
Dale, very glad all is almost well. Try and back the timing down slightly, if the backfire continues, to 8 degrees before TDC. You said you still have the vacuum retard hooked up, that gives me concern at 12 as I think that was designed for 4 degrees after TDC, but I may be wrong about this, (ANYBODY WANT TO CHIME IN HERE)????

Wayne

PS Check plug color and you can really get the mixture right, as it will tell you to go 1/4 turn rich or lean.
 
trrdster2000 said:
Dale, very glad all is almost well. Try and back the timing down slightly, if the backfire continues, to 8 degrees before TDC. You said you still have the vacuum retard hooked up, that gives me concern at 12 as I think that was designed for 4 degrees after TDC, but I may be wrong about this, (ANYBODY WANT TO CHIME IN HERE)????

Wayne

PS Check plug color and you can really get the mixture right, as it will tell you to go 1/4 turn rich or lean.
Click to expand...

Wayne- I have the twin ear dizzy and I plug the vaccuum lines when I set my timing. You are correct 4 degrees if the lines are connected. 10 degrees or so if lines are plugged.

I'll go check the plugs and post a photo.

Thanks

d
 
Wayne:

The plugs look pretty decent for a first attempt.
The front carb has grey plugs (lean I'm guessing)
The the rear carb has pale brown plugs ( pretty close ?)

plugs2-2.jpg
 
Dale, backfire can be caused by a lean mixture as well as timing too far advanced.

Looks like you are well on your way to driving season.
 
Dale, give the no 2 side a 1/4 turn rich and you are about as close as it gets. Anti clockwise.
Love the look of the other side.

Wayne
 
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