When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have noticed my fast idle is non existent. When doing a cold start, I always give it two pumps, then start and sometimes I need to give one or two more pumps and then the engine will start. However, it does not idle up high as it should, but it doesn't have any issues either. It idles low with no sputters or stalls until it warms and then you can hear a little bit faster idle. Once warm sounds like idle is where it should be. I can also drive off while cold and it will drive fine as well as warm. Carb seems to be working well. Only issue I noted was sight glass level a little higher than the middle part but not full, and the sight glass will drain completely after a week or so of sitting.
I looked at the plates on the carb and the passenger plate when cold is closed but not fully closed, maybe 1-8 inch open. As it warms the plate does open up so I know the vacuum part of the system is working as should. I checked the linkage for the fast idle and it can be moved around freely when I open the throttle. However I was unable to wait for the motor cool back down to see if I could engage the fast idle manually.
The carb is a reman'd unit I installed last summer and was told all the adjustments should be close to the oem settings.
Do you guys think that fast idle screw needs to be adjusted? or is this possibly another issue? What does the fast idle screw do when turned in or out? Would the wrong adjustment on that screw cause the fast idle cam not to engage.
Things that have been replaced, fixed:
New carb
Everything with the fuel system including tank dropped and cleaned.
All new vacuum hoses
EGR was inspected and cleaned- had lots of buildup
Unsure about the BVSV and the thermo switches but so far everything seems to be running good on road test.
The only other issue I know of is the inner side of the vacuum advance on the dizzy is not holding vacuum. When I suck air through the hose, I can keep pulling air. The outside holds vacuum. I have ordered a new dizzy and vacuum advance to correct this, but I don't think it affects the fast idle, right?
The Fast Idle Cam mechanism is affected by both its own spring, as well as the linkage to the automatic choke.
In the center of this pic is the spring for the Fast Idle Cam that is wound around the arm that moves the cam into position:
As the choke's internal heating element cools down, it will act on the linkage to close the Fast Idle Cam. However, the throttle plate, when static, it is holding the cam from moving into position. The small Fast Idle Cam spring it not nearly strong enough to act against the much larger throttle plate spring. When you pump the gas pedal a couple times, now the Fast Idle Cam spring can move the cam into position. Only if the spring is working correctly or is strong enough. Plus the choke plate will close all the way too.
Originally Posted by bhaithc
As it warms the plate does open up so I know the vacuum part of the system is working as should.
I assume you mean that once the bi-metal vacuum switch valve (BVSV) routes vacuum to the choke remover, that then the choke is removed?
I say that because vacuum does not incrementally open the choke plate. Vacuum only removes all the choke circuit. The choke plate will incrementally open via the heating element within the choke housing.
Originally Posted by bhaithc
Do you guys think that fast idle screw needs to be adjusted?
I personally never played around with that screw, so I can't say specifically what will happen. It is obviously an adjustment screw to the cam, but in what way I do not know.
I would first check, on a cold engine, that after you pump the gas pedal, the Fast Idle Cam does engage. You may need a mirror to see under the air filter housing. Or just take it off to get more room.
Thank you for the information. I am going to check that spring tomorrow.
When I did a search for "fast idle spring", I was able to find a lot of information. Mostly posts from you! But I know have full understanding of how this system works. Based on that, I believe the linkage was not set right by the carb re builder because the bi metal thing up top obviously works. Its just pumping the throttle when cold doesn't lock the fast idle cam in the down position. It stays up.
Looks like the spring isnt strong enough to allow the fast idle cam to move down on the notch and lock when I blib the throttle. Couldn't verify if it was installed correctly. I did manually engage it then start the truck, but it still idled really low. Will mess with it tomorrow.
Today I did valve adjustment and new dizzy with new advance and wow what a difference. It has better top end. Last thing i need fixed is that choke
I did manually engage it then start the truck, but it still idled really low. Will mess with it tomorrow.
So even with the cam engaged all the way to the highest step, the idle still did not hold a high RPM?
I don't know if I said it in the other posts you found, but when the cam rotates into position, it mechanically holds open the throttle plate a little bit to obtain a high RPM. If the cam is in place, but no high RPM like your saying, then I'd go ahead and play with that adjustment screw.
Or, the linkages are binding, preventing the cam from closing. That spring is barely strong enough, especially after a couple decades of tension, to rotate the cam.
If you don't know which one is the adjustment screw, let me know in this post. I think I've posted the picture before in other threads, but otherwise I can put it here. There are two screws close to the area of the cam.
So even with the cam engaged all the way to the highest step, the idle still did not hold a high RPM?
I don't know if I said it in the other posts you found, but when the cam rotates into position, it mechanically holds open the throttle plate a little bit to obtain a high RPM. If the cam is in place, but no high RPM like your saying, then I'd go ahead and play with that adjustment screw.
Or, the linkages are binding, preventing the cam from closing. That spring is barely strong enough, especially after a couple decades of tension, to rotate the cam.
If you don't know which one is the adjustment screw, let me know in this post. I think I've posted the picture before in other threads, but otherwise I can put it here. There are two screws close to the area of the cam.
Yea fully engaged it doesn't idle high any. Strange too because the carb and linkage are new, installed last year. I have another new carb that has a grey connector and i hand tested that one and its linkage spring is a lot stronger. Snaps in place and holds the throttle as should. Im guessing the spring they used on the remaned one i bought is weak or not installed correctly.
I have another new carb that has a grey connector and i hand tested that one and its linkage spring is a lot stronger. Snaps in place and holds the throttle as should. Im guessing the spring they used on the remaned one i bought is weak or not installed correctly.
I can't remember when I rebuilt mine if it is possible to wind in an extra turn to get a tighter spring.
I'm gonna pull that carb off and see if I can swap the springs out with the other new one.
I cant believe the company would release it with a crap spring like that. The company I purchased it from is called "Carb-X". They claim to do real engine tuning before releasing to buyers. I'm also noticing the fuel bowl goes empty overnight. Which I am sure will eventually give me problems. As of right now, it runs flawlessly besides the choke issue.
09-12-2015, 02:10 AM
