Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
Setting Up and Adjusting Idle
defiant1:
--- Quote from: Cliff Ruggles on June 21, 2011, 04:08:11 AM ---108LSA is not helping the situation. I'd go bigger on the idle tubes, .038 or even .039", .058" down channel restrictions, and .110" idle bypass air. It needs more idle fuel and some help getting back on the idle curcuit.
Don't rule out timing either, it may need more initial timing to be happy. I just cured idle troubles with a Buick 350 yesterday, by adding idle fuel, and recurving the distrbutor for more timing at idle speed.....Cliff
--- End quote ---
Ok- Idle tubes replaced w/.039 Idle channel opened to .059 and Idle Bypass air was drilled out to .110"
I am still having the same problem. Engine runs great at fast idle (great vacuum, etc.) as soon as I kick it off the choke circuit it starts spurting fuel out of the nozzles. Backing off the mixtures screws again starts to decrease the nozzle drip, but it does not stop it completely.
Need to some more ideas folks. This is insane. I have a lot of time and money in this carb and I am not happy >:(
omaha:
Have you replaced that PCV valve? (I would block that off for now, just plug the hose for now). The reason I am saying is because you said that when you did this before, you had 15 inches of vacuum.
I would also bump the timing up to 15 or 18. You should able to get it to idle with the 15 inches of vacuum. and the timing at 15. Im really thinkin now that this maight be the problem (the pcv). It will idle its just a matter of the timing and the mixture. Those are the only 2 things. Dont forget, that vacuum gauge can be used as a tool to figure out where the initial timing wants to be set at. since the most efficient burn ( timing and mixture again) will cause the highest vacuum reading, this is why the vacuum gauge is one of the best tools for determining where everything needs to be set at because the timing and the mixture quality will both effect the vacuum reading. keep experimenting with the timing and the mixture and watch the vacuum gauge. Of course, you can go too far with the initial timing and cause the engine to not start up easy with the starter and maybe have some pinging while driving, in that case yull need to back off the timing a bit. with the pcv, its possibe that it is not operating correctly with the cam that you have (because of the pulses of the vacuum or not enough vac etc.) You may end up with a higher idle rpm also just to get it to idle but not excessive amount extra I would not think. It shoukd idle with the .039 and the .059 idle system. Dont get too frustrated and do not give up. (my .02)
Cliff Ruggles:
The current set-up should have plenty of idle fuel. Might want to raise the float to 1/4" instead of 5/16". That will add a tad more fuel to the idle system.
From the sounds of things, the engine isn't very happy with that cam in it. I've seen a lot of idle issues with small/low compression engines using tight LSA camshafts.
It wants timing and idle fuel, you are going to have to give it what it wants to be happy at idle speed. If the engine had another point of compression in it, it would be fine with the current settings....IMHO.....Cliff
defiant1:
--- Quote from: omaha on June 26, 2011, 11:02:36 PM ---Have you replaced that PCV valve? (I would block that off for now, just plug the hose for now). The reason I am saying is because you said that when you did this before, you had 15 inches of vacuum.
I would also bump the timing up to 15 or 18. You should able to get it to idle with the 15 inches of vacuum. and the timing at 15. Im really thinkin now that this maight be the problem (the pcv). It will idle its just a matter of the timing and the mixture. Those are the only 2 things. Dont forget, that vacuum gauge can be used as a tool to figure out where the initial timing wants to be set at. You may end up with a higher idle rpm also just to get it to idle but not excessive amount extra I would not think.
--- End quote ---
I did reaplace the PCV valve, but I will try it plugged and see what happens. I changed float height to 15/32" and tried again. Got it to run ok at 880-900 rpm @ 19* BTDC. It is not dripping fuel at a rapid rate like before, it is just barely weeping out, if you weren't using a flashlight you would not be able to see it.
But, if no fuel is suppose to be coming out at all, then not sure what is left. I guess I could open up the idle tubes more??
I will take a look at the vacuum readings next time and see where the best adjustment is. At initia startup while it is on the choke at around 1000 rpm it is pulling 15", but as soon as it it gets off fast idle it drops around 12".
defiant1:
OK- Omaha I think you are on to something. I plugged up the port on the carb that goes to the PCV valve. Ran the motor to operating temp. Timing is 14* at 850 and was pulling 14-15" of vacuum. Motor ran really consistent and was not shuddering (very very minor shuddering if at all).
I hooked up the PCV valve again leaving the timing and RPMs the same and it ran like ass. Shuddered horribly and the vacuum dropped to 11"
Soooooo, since I replaced the PCV valve twice. 1. Why is this happening? 2. Is there another way to achieve crankcase ventilation so I don't hurt the motor? 3. Are there custom PCV valves? 4. Can I install a breather on the oil fill tube, similar to the Olds 425 motor I received recently which does not have any PCV valve or breather on the valve covers, only a vented oil fill cap.
Thanks for sticking with me on this.
d1
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