RTH: carb again (1 Viewer)

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I have finally obtained good- almost great- idle characteristics today. But I am confused about a couple of things-duh. It is a late 77 california carb on an 86 2F motor. I have no leaks determined by an 8 round Oklahoma rebuild at around 1800 rpm (slowed and died every time). I have the three vacuum ports for the egr, throttle positioner, and vacuum retard plugged for testing purposes. at first I had the power valve hooked to manifold vacuum, as well as the TP diaphram, and my vacuum gauge. I had good idle, but only about 11 inches and steady on the gauge. When I unplugged the PV and capped its vacuum(from the manifold), I was able to get 17 inches of vacuum at 650 ish revs, somewhere about 7*btdc and smoooooth tail pipe noise. Reved up great, real quiet(quietest EVER in this pig I think). I am 1 turn out(surprised me a bit) from closed on the idle mix screw by means of lean drop method. I very much want to keep it this way as it sounds (and feels) the best I have ever heard it run, But I am curious as to why this worked out in this fashion. Do I need to suspect the idle solenoid or idle ports in the carb? What am I missing? Thanks in advance.
 
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You misunderstand the Oklahoma rebuild. It is just a fast and cheap method to (hopefully) clean out the jets, metering holes and nozzles by pulling fuel out of them at higher than normal vacuum. It doesn't check for leaks.

You need the PV hooked up to manifold vacuum. Otherwise it will run really rich. If you can't get it to idle at 650 RPM and greater than 17 inches of vacuum, then you may have a manifold vacuum leak. Besides the manifold gaskets, check the power brake booster and check for cracks in the intake under the carb. It could be the solenoid, but I doubt that you would get it to run below 750 if it didn't work.
 
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Thank you. I knew the Ok rebuild was intended for clearing jets, I thought it also served as an indicator to manifold leaks, thanks for informing me:cheers:.
It idles great right now w/almost 18" of vacuum at 650ish rpms, just when I hook up the vacuum tube to the power valve port on the air horn the vacuum drops to about 10( the source end IS capped while the PV is disconnected).:confused:. I understand that the power valve opens on low vac and is for enriching the mix, confused that it idles so wonderfully w/o the PV hooked up and getting such good vacuum. The idle quality does not really change much if I hook up the PV, just the vacuum drops...
 
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Usually, the reason that the vacuum drops is that with a manifold leak, you have to open the throttle plate so much so that it runs off fuel from the main nozzles.
 
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Drop ONLY happens when vacuum gets to the power valve port. Is it possible that the leak source is the power valve itself? Idle speed climbs slightly and vacuum holds steady at 11 w/ tube connected to the power valve during last test. W/ the vac tube unplugged from the manifold, vac holds around 5 or 6". Then w/ the tube on the manifold and open at the other end, I get about 9-10". When I plug it into the power valve port, vac goes to 11. If I plug the tube or manifold port TO THE VALVE, vacuum goes to around 18 and idle drops to about 650rpms and is smooth. My idle mix screw is 1 turn out from 0, and the idle speed screw is screwed in only a slight amount, if that helps any. Thank you.
 
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meaning prolly less than 1 turn down from contacting the linkage tab...I have not sprayed around the manifold/carb base yet to see if I get a spike in idle speed(for intake leak), but it seems to be directly related to the power valve- seems being the operative word...
 

FJ40Jim

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The secondary barrel is leaking. Air & fuel are entering through the 2nd barrel, which renders the primary idle speed and idle mix ineffective.
 
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OK. So this is caused by- The linkage out of adjustment? Or is it going to be necessary to rebuild the carb to remedy this situation? Thank you- i am :bang::bang: over this. This is the closest I've ever had it running to great since I've owned it(amazing what I though was good before)
 
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The secondary barrel is leaking. Air & fuel are entering through the 2nd barrel, which renders the primary idle speed and idle mix ineffective.




I DID have some control over idle w/ the mixture and speed screw( i thought). When I first fired it up and started w/ the mix screw (for fastest idle)I found that I had to screw the mix screw IN to about 1 turn out(started by turning it out, and got slower fatter idle)The speed screw is doing something too. It WILL raise and lower the apparent idle speed:bang::bang::bang:Is the fact that it is a dec 77 date code make it a 78? Would that make a difference in diagnosis? Thank you guys again
 
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OK. There was some contact between the secondary shaft link and the throttle relay rod keeping the sec a tiny bit open. Remedied that, verified that the secondary butterfly is closed all the way and not opening till the primary hits almost wot. I still have a steady 10.75" at a speed of 650 w/ PV getting vacuum, choke breaker getting vacuum. Still goes to 18" w/ slight drop in idle speed when I pinch off the vac to the PV. I have pinched off and checked the connections at the PCV, brake booster and base of carb w/ a wet rag and get no change in vaccum, w/ the PV getting vac or not. I also have noted that the carb in question is actually a fed spec made in dec of 77 for the 78 model year NOT the 77 cal spec as I stated I needed when I ordered it last year. grrrrrr!
 
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Next. Went to put a vacuum(suck) on the tube to the PV to see if there was indeed a leak at this place. Due to the overwhelming fumes from the gasoline in the bowl I decided against sucking, and went for the blow instead(thinking that if there was a leak, it would manifest as suction or pressure). There is NO air resistance, even w/ a light amount of pressure(less than blowing bubbles thru a straw into a glass of water) I can hear air rushing out from under/in the air horn. There is a small hole behind the port for the PV inside the air horn next to the main air nozzle in the secondary bore. I get a bit more air resistance when I plug this hole w/ my finger and blow, but I can still hear air coming from under the bowl. At this point, I am thinking hack job on the initial rebuild of the carb before I had ordered it. I am ALSO back to thinking about removing the PV plunger and running w/o the PV. Am I STILL being stupid? (seriously) I am sure that I am reading too much into this, and that there is a more rational explanation/solution to this. Forgive my ignance on these issues. EFI must be another way of saying "I don't get it".
 
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hopfully these can help determine if the power valve port is in the right spot. The third pic shows the hole in the air horn to the 5 o clock position to the air nozzle...
clowns and cruisers 175.jpg
clowns and cruisers 176.jpg
clowns and cruisers 177.jpg
 
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I have read somewhere a post by 65 swb45 stating that the 78 carb had internal vacuum porting for the power valve. And the hole in the air horn DOES go thru the power valve port. I would love to just spend more money and find the right vintage carb, but I cant afford to right now. Any thoughts or ideas on this issue would be great.
 

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That is not the power valve port. That is a breather jet that goes right through the carb. The way it is currently connected, it is a massive vac leak. The HIC should be connected to that fitting.
 
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Thank you,Jim. I kinda came to that conclusion, too. If this were on a 78, I would try to find the HIC and rest of the missing emissions stuff, But it is a 77. The only thing that's not "like the others" is the later carb. Gunna yank it today and verify there is internal porting for the power valve(pretty sure at this point.) I have a may 74 carb I am going to doll up and make this pig run with till I can sort out the external porting to the power valve w/ the existing air horn or find the right carb. What are your thoughts?
 
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I ultimately need to obtain the right cal spec 77 year carb so I can pass smog in Cali. I have all the other gear(long re smog). The VSV for the Cali spec has an external control for the power valve. I really want to get everything dialed in and running well. I would really like the idea of having the RIGHT carb so I don't have to beat my head on the wall every 2 years for emissions testing. They are getting pretty good at making sure everything is in place...Thank you.
 
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I ultimately need to obtain the right cal spec 77 year carb so I can pass smog in Cali. I have all the other gear(long re smog). The VSV for the Cali spec has an external control for the power valve. I really want to get everything dialed in and running well. I would really like the idea of having the RIGHT carb so I don't have to beat my head on the wall every 2 years for emissions testing. They are getting pretty good at making sure everything is in place...Thank you.

You might try PMing John Pardi (Pardion here on mud). He has a lot of carbs from that time frame.
 

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