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Discussion Starter · #1 ·
Hi

I'm a fairly new driver and until I bought this Saab I'd only driven fuel injection so perhaps this is just a feature of carbs:

If I am holding a steady speed at low-mid rpm, and put my foot down, there is a momentary burst of power followed by almost a second of flatness before the power comes back. Although this isn't a massive problem, I can drive around it, it feels like there is a bit of potential missing.

I replaced the worn out distro cap and rotor arm, didn't seem to make any difference. I've cleaned the carb out by removing the top section, cleaned away any deposits from the parts I could get to with carb cleaner. Carbs are a bit of a mystery to me but I did notice some splits beginning to form in that circular black diaphragm, they don't go right through yet but if somebody tells me what it's called I'll replace it.

Pulled the vacuum pipe from the carb to the dizzy cap and it just broke away in my hand - reattached it ok but presume maybe cracked in other places, will that hurt? Tried sucking and blowing it and the advance/retard diaphragm in the dizzy seems to be working. I couldn't feel much action going on when I covered the hole this pipe goes to on the carb, should that be noticeable?

After all this my diagnostic abilities are just about running out and the flat spot seems to last less long now.

Any advice gratefully received!
 

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Sorry, I haven't played with one of those carbs for so long I've almost forgotten what they look like. I do recall they're pretty easy to pull apart and get running smoothly. It's called a Zenith-Stromberg, and there's plenty of info on the net. The diaphragm is called a diaphragm -- you got it in one. If it's cracking, i would replace it.

Carbs on 900 aren't too common -- you might find out more on the 99 forum.
 

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i had exact same problem on my origanl carb and the cause was a leak from where the spindle goes through the carb body. there is a brass bush which on mine had worn out and if you sprayed brake cleaner in that area the rpm would rise. i just replaced with a second hand carb in the end.

nathan
 

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take the 4 screws out of the top of carb and inside will be the rubber diaphram, if it is complete, it will be something else. if just a small hole that will cause the problem as it works on vacumm, hole = no vacumm, and make sure you line up the little lugs on diaphram when refitting. if not that more than likely the jettings are worn, as i had problems on my first ever 900(now upto 24th) it went ok but found out the timing had been advanced a bit to compensate for the flat spot, not the ideal situation. cost me 85 quid for a carb man to recon it and that was 12 yrs ago. if you do need a diaphram it' is also fitted to the carb volvo and i think it has written on the top, cd 150?, also make sure there is some oil in the dash pot (big black screw in middle) as people used to forget to put oil in which makes the shaft move easier etc, sorry to be speaking a bit egg sucking type, but not sure how much you know about carbs.
 

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Discussion Starter · #5 ·
Thanks for the replies, plenty to be getting on with there! I've just put Zenith-Stromberg into google and the first page I clicked on has some excellent diagrams and detailed info.

I'll try replacing the diaphragm and check for leaks and wear where possible, but I suppose it's time to start looking for a new carb or a refurb then? I don't suppose GSF will stock this stuff.

The dashpot was empty when I bought the car but I filled it on the advice of a mechanically minded relative, so I was one step ahead of you there! There's no danger of insulting me with advice, I'm no mechanic (but learning!)
 

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I worked on Jaguars before SAABs, all the late '60s, early '70s cars had Strombergs.
Step one: install new diaphragm. Even if it has no holes, it can be soft or stiff. Then, make sure the "enrichment device" used instead of a choke, is not stuck, or adjusted so that it won't release. Check for leaks around throttle shaft, as suggested, with carb cleaner. Jaguars had replaceable bushings with O-rings to seal the shafts; the O-rings often deteriorated.
 

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Matt77 said:
I'll try replacing the diaphragm and check for leaks and wear where possible, but I suppose it's time to start looking for a new carb or a refurb then? I don't suppose GSF will stock this stuff.
I can heartily recommend Gower & Lee in Bushey, Herts - http://www.gowerlee.dircon.co.uk/ - they rebuilt a '60s single-choke Solex for me before. An absolutely *top* notch job for about £100.
 

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Matt77 said:
...I suppose it's time to start looking for a new carb or a refurb then?
Don't be in a hurry. They need diaphragms regularly and the "chokes" are often adjusted wrong, but they're durable and easy to repair. Except for rare throttle shaft wear that goes beyond O-rings, they work well and can always be fixed with a handful of cheap parts.
The bane of Strombergs (and S.U.s) is a well-meaning neighbor who adjusts them for you. Adjust them exactly according to the manual's step-by-step instructions, then leave them alone. I've had good luck putting a drop of white touch-up paint on the adjusting screws; that usually deters neighbors.
 

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Jim Mesthene said:
The bane of Strombergs (and S.U.s) is a well-meaning neighbor who adjusts them for you. Adjust them exactly according to the manual's step-by-step instructions, then leave them alone. I've had good luck putting a drop of white touch-up paint on the adjusting screws; that usually deters neighbors.
I agree completely. My MGB had twin SU's and I chewed a fairly large discount out of the price because the car was both cosmetically challenged when I bought it and it ran like crap. Back then (I was 19) my mechanical skills were somewhat limited, but the one thing I could do was carbs. I got ahold of the proper manual and had it running great that afternoon. But it got the purchase price down to $600 for a decent tuned 74 MG.
 
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