throttle linkage not allowing WOT CARB question

[Wilson_WWSC]

I have a SBC 327 in a 73 240z with a holley 1850 4bbl carb. When I step on the gas pedal, the primary valves open less than halfway. How do I get them to open all the way? The linkage is the original 240z linkage. This is the JTR conversion, it used to be scarab. Is that the problem?>

 

new question:

So in my Holley 1850, I noticed that there was a small round hole in the one of the barrels. I sprayed some compressed air from a can upside down into the hole for the vaccuum secondary and it sprays out of that little hole. It looks like a casting error or it could be that it should be there. I'm thinking that it is an error. Should I plug it up with some JB weld? How does the vaccuum secondary work (ie. where does it get vaccum from?)

Edited March 24, 2010 by Wilson_WWSC

[MONGO510]

Check to see if you have excessive slack in the linkage. You may have to change the lever arm lengths at the carb or at the linkage to increase the travel of the cable.

 

Mongo

[Wilson_WWSC]

Check to see if you have excessive slack in the linkage. You may have to change the lever arm lengths at the carb or at the linkage to increase the travel of the cable.

 

Mongo

 

 

There is no slack, do you know where I can find said parts? I have a Holley 1850 4bbl 600cfm on it.

[grumpyvette]

can you post a couple CLEAR pictures of your carb linkage?

 

there are ways to do it

 

http://www.jegs.com/i/Mr-Gasket/720/1523/10002/-1?parentProductId=743777

 

http://www.jegs.com/i/Competition-Engineering/247/3465/10002/-1?parentProductId=943335

 

http://www.jegs.com/p/Mr-Gasket/Mr-Gasket-Throttle-Pedal-Cable-Kit/743795/10002/-1

[Wilson_WWSC]

Ok, I lied, there is a small amount of slack on the cable, but as you can see by the 4th picture, which demonstrates about how far the throttle is opened when the gas pedal is all the way down, that the slack doesnt really factor into my problem yet. I took the pedal stopper out to see if that would help things, and it doesn't do much.

 

Edited March 22, 2010 by Wilson_WWSC

[specialk]

You have a geometry problem. With X inches of pedal travel, you need Y inches of cable travel. In the post from grumpyvette, the first item he lists (the bellcrank) will almost certainly provide your solution, essentially 'multiplying' X by Z to give you Y.

 

A little hint, replace the roller with the bellcrank, put the cable coming from the pedal in a hole close to the pivot and the cable from the bellcrank to the carb far from the pivot.

[Wilson_WWSC]

that makes sense. So I will be using 2 bell cranks? Thanks everyone.

[jt1]

The cable needs to hook to the carb arm where the spring is attached.

 

You might want to look at the Lokar throttle cable. It's a nice setup with a lot of adjustability.

 

It's a good idea to run a dual return spring.

 

Those are some killer valve covers. You need to spiff those bad boys up some.

 

jt

Edited March 22, 2010 by jt1

[grumpyvette]

if your local to the west palm beach fla area I can CURE that issue in under 30 minutes and get it operating smoothly, but theres a couple routes you can go and all of them will be superior to the current set up

some thread rod,1/4 20 thread heim joints , and a couple bell cranks would cure that easily

 

btw the rollers they use on glass slide doors can be used as a roller pivot and the custom arms brazed to them to make nice smooth pivot points CHEAPLY

Edited March 23, 2010 by grumpyvette

[specialk]

that makes sense. So I will be using 2 bell cranks? Thanks everyone.

 

A total of 2? Yes. But, you already have one. Just replace the roller on the bracket attached to the firewall with a bellcrank, threaded rod from existing bellcrank to new bellcrank (use heim joints), and then threaded rod from new bellcrank to carb (again, using heim joints).

 

See GV's picture.

[Wilson_WWSC]

ok so the local place that would have this kinda stuff was closed last night so I went to home depot and made myself a new throttle cable that works for a grand total of 2.80$ and 1 hour of labor to make and put it in.

 

So in my Holley 1850, I noticed that there was a small round hole in the one of the barrels. I sprayed some compressed air from a can upside down into the hole for the vaccuum secondary and it sprays out of that little hole. It looks like a casting error or it could be that it should be there. I'm thinking that it is an error. Should I plug it up with some JB weld? How does the vaccuum secondary work (ie. where does it get vaccum from?)

[grumpyvette]

because you obviously have above average skill at taking clear pictures a picture of the carb suspected casting (FLAW)with you pointing a pencil at both where you sprayed the air and the flaw would help a GREAT DEAL to answering your question

Edited March 24, 2010 by grumpyvette

[Wilson_WWSC]

Ok, as a warning, the pics that I took are not VERY clear, as I was too close.

 

Here is a picture of the hole that I sprayed stuff in (the one with the cork gasket), except this is the opposite side. I sprayed stuff on the carb. body side of this hole. This is a pic of the vaccum secondary diaphragm housing.

 

The red arrow in this picture indicates wehre the hole is. It is less than .5mm in diameter, and is pretty round. It is right on the seam of the casting.

[John Scott]

I wasn't going to jump in, but...

Someone needs to say it, your linkage is a hodgepodge mess. Looking at the multiple fasteners on the carb is scary, the cable eye fastener will either just pull out of poor crimp or stress and wear out over time, and the slack in the cable and pulley is asking for trouble. The are some great images here on how others have used the stock mechanical linkage with great success. The attachment should be on the vertical plane of the carb linkage with the correct geometry,and some means for the linkage to rotate without friction, a bushing etc. A trip to the parts yard or looking at aftermarket solutions for cable linkage can also provide a clean and trouble free install. I've rushed into getting a carb to open using cables, coat hangers, what ever and finally learned to take my time to get it right. Finding yourself on the side of the road or track with a broken gas pedal is not worth it.

Please get this right, as your long term enjoyment and safety depend on it.

 

 

 

Edited March 24, 2010 by John Scott

[Wilson_WWSC]

looks like I may have to change the location of the throttle bolting onto the carb. I know the original linkage was super ghetto, but it worked for more than 30 years.

[John Scott]

Sorry, I should have just said needs more work.

You'll appreciate the time you spend getting it right.

Again, bending the pedal in my picture above can give you lots more throttle travel. I used a torch and went in small increments until I had full throttle and could still use the factory throttle stop on the floor board. My aftermarket throttle mount (any good supply house, universal chevy) on the manifold also allows for a good deal of adjustment.

Good luck!

[Wilson_WWSC]

I don't think bending the pedal is an option for me because the bellcrank already travels to its maximum limit. I've just started the car with my rebuilt carb and am glad that there were no engine fires. I still need some help on the hole in my carb though as per post 13.

[Wilson_WWSC]

Here's an additional question: Is there supposed to be smoke coming out of the intake plenum up the barrels? This happens after I turn off the car. The smoke is a light grey color and lasts for about 2 mins. Is this exhaust?

[Wilson_WWSC]

Ok, as a warning, the pics that I took are not VERY clear, as I was too close.

 

Here is a picture of the hole that I sprayed stuff in (the one with the cork gasket), except this is the opposite side. I sprayed stuff on the carb. body side of this hole. This is a pic of the vaccum secondary diaphragm housing.

 

The red arrow in this picture indicates wehre the hole is. It is less than .5mm in diameter, and is pretty round. It is right on the seam of the casting.