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Problem with Carbs and Fouled plugs

MadMax

MadMax

Diamond Level Sponsor
Good morning!

We have a 1960 Sunbeam Series 1 with 1725 engine and the twin Zeniths. Engine/car in great shape and runs strong. But….

Plugs on the front two cylinders are fouling and it back fires just a bit (when slowing in 2nd gear). I went through and readjusted the carbs (checked all linkage connection—all good length and not binding). Got good idle at 850 but using a carb unisync, found that the front carb pulls lots less air than the back carb. Fooled with air mixture valve to no avail.

I think that is why front two plugs fouling—low air flow with richer mixture?

Help—anyone got good ideas/thoughts?

Thanks

Doug
 
husky drvr

husky drvr

Platinum Level Sponsor
Which twin Zeniths? The twin downdrafts from the original 1500 or the twin side drafts original to the 1725?

Air mixture screw sounds like downdraft. Using it is not the procedure for carb synchronization. What are the numbers stamped into the carbs?

Here is the link for this sites PDF copy of the sII "Owner's Manual." If you have the sI carbs, the procedure is essentially the same, but the carb models are a bit different. The carb adjustment info starts on page 19 of the PDF (page 34 of the manual).


Hope this helps,
 
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Tim R

Tim R

Silver Level Sponsor
Doug,
Sooner or later you will probably get as fed up as I did with trying to get twin carbs to stay in synch long term on an Alpine. They might be okay if your car just does a handful of miles a year but if you actually use it they are a nightmare. When you do get fed up with it look at the twin choke Weber and curved manifold set up that Alpine Innovations sell. You fit it and forget about it and the car is smoother, faster and MUCH more economical. The set up pays for itself surprisingly quickly.
Tim R
 
bernd_st

bernd_st

Bronze Level Sponsor
Before you reach out that far, better to find the issue with your original carb setup. Your problem sounds quite familiar to me. Even you checked the linkages, but sounds as if the front carb throttle butterfly is not opening in sync with the rear one. Check whether the front spindle is tightly connected to the rear one. Sometimes the coupler piece does not provide enough clamping force and is slipping on the front carb throttle axle. This will lead to the problem you described. Ask me how I know ;-)

P.S. I'm talking about the downdraft Zeniths...
 
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Acollin

Acollin

Donation Time
Whether you choose to change to a new fuel delivery system or not, my suggestion would be to figure out whats going on With what you have. It couldn’t hurt and could possibly inform those of us who still have the zenith carbs.
Do you have CD 150s?

The WSM has a pretty good step by step set up and with the help of the wonderfully knowledgeable forum you could be up and running in an afternoon.. There would be little or no expense, could resolve the issue in a few hours of not so heavy work and be driving again and have the car operational until you make the change to another fuel delivery system.
That said, bernd_st, could be on to a quick and easy remedy. I would, however, probably start the set up procedure from the beginning.
Good hunting
Andrew
 
MadMax

MadMax

Diamond Level Sponsor
Tim R said:
Doug,
Sooner or later you will probably get as fed up as I did with trying to get twin carbs to stay in synch long term on an Alpine. They might be okay if your car just does a handful of miles a year but if you actually use it they are a nightmare. When you do get fed up with it look at the twin choke Weber and curved manifold set up that Alpine Innovations sell. You fit it and forget about it and the car is smoother, faster and MUCH more economical. The set up pays for itself surprisingly quickly.
Tim R
Click to expand...
Thanks--I am already leaning that way. I have dual 2 barrel webers on my 69 Porsche 912, and fail amount of gray hair b/c of them
 
MadMax

MadMax

Diamond Level Sponsor
bernd_st said:
Before you reach out that far, better to find the issue with your original carb setup. Your problem sounds quite familiar to me. Even you checked the linkages, but sounds as if the front carb throttle butterfly is not opening in sync with the rear one. Check whether the front spindle is tightly connected to the rear one. Sometimes the coupler piece does not provide enough clamping force and is slipping on the front carb throttle axle. This will lead to the problem you described. Ask me how I know ;-)

P.S. I'm talking about the downdraft Zeniths...
Click to expand...
Great idea! Yeah, I have 36WPI downdrafts
 
MadMax

MadMax

Diamond Level Sponsor
Thanks to everyone! SOCCA always great help. Yes have the 36WPI Zeniths. "unsync'd" butterfly is great thought and will check. So one more thought--should I pull the carbs to make sure both butterflys are actually closing all the way (assuming coupler works)? D
 
bernd_st

bernd_st

Bronze Level Sponsor
MadMax said:
Thanks to everyone! SOCCA always great help. Yes have the 36WPI Zeniths. "unsync'd" butterfly is great thought and will check. So one more thought--should I pull the carbs to make sure both butterflys are actually closing all the way (assuming coupler works)? D
Click to expand...
Ok, then we're on the right track here. It's not about closing of the butterflies, rather than synchronized opening to full throttle. Pls. note that the Zenith carb spindles are working against spring pressue over travel. No need to take them apart just airfilters off and check the butterfly positions whether they are moving synchronously...
 
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B

beamdream

Gold Level Sponsor
Further to bernd info; if you're using the Unysinc, just adjust the idle screws individually until you get a balanced reading.
 
bernd_st

bernd_st

Bronze Level Sponsor
The little aluminium throttle rod connecting piece has very little clamping play. Sometimes it's neccessary to file the slot in order to get more clamping force...
 
DaveSeries1

DaveSeries1

Silver Level Sponsor
Hi there, thought I'd chime in. I have mostly the same problem with my S1. All 4 plugs come out black and sooty. Idles at 850, but rough and shakes. Timing is correct., Went through the set-up procedure in the WSM, all good. Idle adjustment screws seem to make very little difference. Connected to a vacuum gauge, needle shakes and seems to have a lower than wanted reading. Gauge has color range, no numbers so I can't say how many inches of vacuum it's drawing. Any help? Dave
 
bernd_st

bernd_st

Bronze Level Sponsor
Dave, do I see a grey S1 in your Avatar ? That' s great ! Regarding your problem it must be a different one. All 4 plugs black and sooty means over rich mixture. Would suggest you to open a separate thread and post some pictures of carbs please ?
 
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