A couple of years ago I installed a Chinese 34 ADF and had trouble with the secondary stop screw rattling loose causing out of contoll reving. (Ref: http://www.fiatspider.com/f15/viewtopic.php?f=5&t=32043 and http://www.fiatspider.com/f15/viewtopic ... 1&start=30) I screwed it back in with some thread sealer and went on my merry way. There were a bunch of other small problems (air leaks, exhaust manifold, brake booster, etc.) which never let me quite get the carb setup right. I think I have these other issues resolved, so I'm ready to fix the carb setup.
It IS running now, but I can't get the idle stable below about 1800 RPM. Also, running the car generally smells like "old car". (I don't have the nose to say if it's exhaust, a rich mixture, burning oil, or what, but I suspect it's the mix.)
I strongly suspect that I don't have the secondary stop screw set the right amount. My question is: How deep should the screw be set?
Thanks!
secondary stop screw - Chinese 34 ADF
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stuartrubin
- Posts: 273
- Joined: Sun May 24, 2015 11:10 pm
- Your car is a: 1975 Fiat 124 Spider
- Location: 44122
secondary stop screw - Chinese 34 ADF
Stuart
1975 FIAT 124 Spider
Il Mostro di Frankenstein
1975 FIAT 124 Spider
Il Mostro di Frankenstein
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blazingspider
- Posts: 173
- Joined: Mon Jan 28, 2013 8:44 am
- Your car is a: 1977 fiat spider
- Location: Oakridge, Oregon
Re: secondary stop screw - Chinese 34 ADF
FWIW I've always heard that you set the stop screw to a depth that just barely keeps the secondary throttle plate from contacting the secondary throttle bore.
That being said on my refurbed 34 adf even if I screw the stop screw in all the way in it doesn't hit the secondary actuating arm so on my carb that set screw does nothing.
In any case you wouldn't want to set the screw in far enough that you are actually engaging the secondary.
My 2 cents
That being said on my refurbed 34 adf even if I screw the stop screw in all the way in it doesn't hit the secondary actuating arm so on my carb that set screw does nothing.
In any case you wouldn't want to set the screw in far enough that you are actually engaging the secondary.
My 2 cents
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stuartrubin
- Posts: 273
- Joined: Sun May 24, 2015 11:10 pm
- Your car is a: 1975 Fiat 124 Spider
- Location: 44122
Re: secondary stop screw - Chinese 34 ADF
blazingspider thanks for your comments. I can't find any "official" documentation on that dumb screw.
On my old carb (which, granted, was of questionable provenance), that screw doesn't even exist. I'm leery about the whole engineering behind it.
But it all may be a moot point. I went to adjust it to see what I could do and the screw it totally stripped! When I set it last year, I put some thread sealer on it to keep it from rattling. So between the thread sealer, stripped head, and the fact that it's in below the surface, that screw it NOT coming it! (Not without a serious fight...) I'm afraid that if I use some destructive means to get it out, I may not be able to replace it...
Suggestions?
On my old carb (which, granted, was of questionable provenance), that screw doesn't even exist. I'm leery about the whole engineering behind it.
But it all may be a moot point. I went to adjust it to see what I could do and the screw it totally stripped! When I set it last year, I put some thread sealer on it to keep it from rattling. So between the thread sealer, stripped head, and the fact that it's in below the surface, that screw it NOT coming it! (Not without a serious fight...) I'm afraid that if I use some destructive means to get it out, I may not be able to replace it...
Suggestions?
Stuart
1975 FIAT 124 Spider
Il Mostro di Frankenstein
1975 FIAT 124 Spider
Il Mostro di Frankenstein
-
blazingspider
- Posts: 173
- Joined: Mon Jan 28, 2013 8:44 am
- Your car is a: 1977 fiat spider
- Location: Oakridge, Oregon
Re: secondary stop screw - Chinese 34 ADF
Stuart,
Once again this is all hearsay but the supposed engineering theory behind the secondary throttle stop screw is to prevent the throttle plate from sticking in the bore or wearing the edge of the plate and the bore surface. It should be set to prevent contact between the 2 surfaces but not enough to affect your idle speed. My old 32 ADFA had the same set up as well.
If your screw is set deep enough to be affecting your idle speed by keeping the secondary throttle open too much then you should try and get it backed out a bit.
If either the screw or the threaded hole is stripped you could try wiring your throttle all the way open and then get a flat bladed screwdriver underneath the screw end and apply some upward pressure on it while trying to unscrew it at the same time.
One other note, I once fought an erratic idle speed that would vary from 900 to 3500 rpm. Turned out to be a broken primary throttle return spring. Couldn't figure that one out for awhile.
Hope this helps out.
Good luck,
Blaze
Once again this is all hearsay but the supposed engineering theory behind the secondary throttle stop screw is to prevent the throttle plate from sticking in the bore or wearing the edge of the plate and the bore surface. It should be set to prevent contact between the 2 surfaces but not enough to affect your idle speed. My old 32 ADFA had the same set up as well.
If your screw is set deep enough to be affecting your idle speed by keeping the secondary throttle open too much then you should try and get it backed out a bit.
If either the screw or the threaded hole is stripped you could try wiring your throttle all the way open and then get a flat bladed screwdriver underneath the screw end and apply some upward pressure on it while trying to unscrew it at the same time.
One other note, I once fought an erratic idle speed that would vary from 900 to 3500 rpm. Turned out to be a broken primary throttle return spring. Couldn't figure that one out for awhile.
Hope this helps out.
Good luck,
Blaze