Setting Up and Adjusting Idle

[defiant1]

Made some adjustments:

Drilled out the idle air bypass to .086 from .081.

Installed lighter power piston spring.

Adjusted throttle plates so no more than .040 of the transition slots was showing.

Hooked everything back up. Ran motor to operating temp and kicked it off of the choke. It died. So I attempted to hold the throttle at a steady rpm and adjust the timing at the same time. Could not get it to idle. Wound up turning the throttle screw in 1 1/2 turns.

Idle mixture screws were set 5 turns out from seated.

It ran ok (still shuddered) at 850 rpm/14* BTDC and held 12" Hg for vacuum.

However, do to the fact I adjusted the throttle plates 1 1/2 turns I am sure I am no where near the .040" I originally set it at.

Oh then I leaned over the fender and looked down the carb. It looks like I have nozzle drip as well at idle.

Soooo, do I increase the Idle Air Bypass hole diameter even more? Do I back off the idle mixture screws even more? I am gaining. Vacuum is a little better, motor runs a little more consistent...rough idle but consistent.

How do I rectify the nozzle drip? I am assuming this is happening because the throttle plates are open too far at idle.

If that is the case, how can I get the motor running effectively with throttle plates nearly closed???

d1

[71vette]

It seems like you are getting a lot of good help from others but I thought that I would ask a question and make a couple of observations.  For an engine to jump 4" of vacuum when you removed the PCV valve, that seems like a lot.  Have you checked to make sure your PCV valve is the correct one for the engine?  I ask because I had this issue in the past where the PCV was not calibrated properly for the engine and it was allowing too much air.  If I am correct in that it is allowing too much air, this would explain why your idle screws are not making much of a difference because it is so lean. 

When you plugged the PCV hose, I am going to assume that it idled much better since the vacuum jumped to 15".  Is this correct? 
If you add more bypass air, I think it will only make your issue worse.  The way it is now, you have had to open the throttle plates so that it would get some fuel out of the main system to keep running.  Closing the throttle plates enough to stop the drip reduces the fuel but if the system is as lean as it sounds, then it won't idle.

[defiant1]

I have a new PCV valve coming (just in case).  I just ordered one that is for my motor Olds 350, are there different versions out there that compensate for camshafts, timing, etc.??

It did run better when I plugged the hose, rpm increased almost 500 rpm from where it was at so I guess it was not really at idle at that point.

I have not mentioned this yet, but is my APT screw (I can access it) preventing the idle circuit from working correctly?  It is 4 turns out from seated, so this prevents the power piston from traveling all the way down.  When I had it apart I noticed the metering rods could travel quite a bit farther when the APT was seated.  Or does the jet/primary metering rods not affect the idle circuit??

Thanks for the feedback.  Trying to get this figured out before summer is over.

[defiant1]

Drill out the IAB to .096.  Idle mixture screw 9 1/2 turns out--I started out at 5 and the more I turned it out the less nozzle drip I had.  Decreased my nozzle trip by 2/3.  Before it was gushing out, now it is a drip.  Throttle screw still turned over 1 full rotation to get to run at idle.  I am still assuming the throttle blades are open too far leading to the nozzle drip.

Any other suggestions.  Vacuum is around 12.5"  I am slowly improving this reading with every adjustment I make.

d1

[Cliff Ruggles]

Looking at the engine combination, it's going to need more idle fuel to the mixtures screws, and more idle bypass air.  That's a "hefty" cam in a 350 engine at that compression ratio.  Is the cam ground on a 108 LSA (Lobe Separation Angle), or is ground on a 112LSA and installed at 108 ICL (Intake Center Line)?......Cliff

[defiant1]

Looking at the engine combination, it's going to need more idle fuel to the mixtures screws, and more idle bypass air.  That's a "hefty" cam in a 350 engine at that compression ratio.  Is the cam ground on a 108 LSA (Lobe Separation Angle), or is ground on a 112LSA and installed at 108 ICL (Intake Center Line)?......Cliff

Not sure, let me ask the vendor.  All the data sheet says is 106 ICL @ .050 tappet rise.  LSA: 108+2

Shaun

[omaha]

   yeah, I agree with the PCV issue. the pcv should not drop that much. THat cam is bigger than I expected and yeah, if it has tight lobes like 106 for example, it will idle somewhat rough and need more idle fuel.    LSA  means lobe separation angle, and is how "tight" the intake lobe is in comparison to the exhaust lobe. You must find out how tight the cam is. The installed centerline refers to where the cam is installed by using the lobe center of the intake as a reference.  Tight lobe seperation cam will idle a bit rough due to the increased overlap however, it will retain more cylinder pressure (just comparitivley speaking of course) because of the earlier closing intake valve so it could actually be a good coice for a 350 cube engine where comprerssion is a bit harder to make than a large cube engine.

[defiant1]

Looking at the engine combination, it's going to need more idle fuel to the mixtures screws, and more idle bypass air.  That's a "hefty" cam in a 350 engine at that compression ratio.  Is the cam ground on a 108 LSA (Lobe Separation Angle), or is ground on a 112LSA and installed at 108 ICL (Intake Center Line)?......Cliff

Back from vacation (visited Mt. Rushmore, I highly recommend the Black Hills if you have not been).  At any rate, Cliff, the vendor said the cam was ground based off the 108 LSA and it is installed at 106 ICL.  What other adjustments do I need to make to the carb to get it to idle right.  I got a parade on July 4th and need to have the car up and running before then.

d1

[Cliff Ruggles]

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

[defiant1]

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

Thanks Cliff, I will order the parts from you tomorrow.

Shaun

[defiant1]

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

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]

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.

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