68 Tri Carb question 435HP

[Rich G.]

I had the carbs rebuilt and the car runs great and no more fuel smell in the garage, but I have a suspecion that the secondaries are not coming in anymore.

As I understand it, at WOT and 3500-4000 rpm they should come open. Before they were rebuilt, when they came in, I got scared. Now when I floor it and go past 4000 it seems too tame. I don't think I got braver.

I did not install them. They were installed by a friend while I was away. He owns a couple of 67 435's so I assumed he knew what he was doing. I checked the linkage with the engine off, and at WOT the outside carbs are free to move.

Is there a way I can tell if they are working when the engine is running without blowing up the motor? I suspect, if they really are not working it has to be vacuum related and I've been told it could be a gasket issue.

Any thoughts about what to do first?

Thanks

Rich

[Clem Z.]

Re: 68 Tri Carb question 435HP

I had the carbs rebuilt and the car runs great and no more fuel smell in the garage, but I have a suspecion that the secondaries are not coming in anymore.

As I understand it, at WOT and 3500-4000 rpm they should come open. Before they were rebuilt, when they came in, I got scared. Now when I floor it and go past 4000 it seems too tame. I don't think I got braver.

I did not install them. They were installed by a friend while I was away. He owns a couple of 67 435's so I assumed he knew what he was doing. I checked the linkage with the engine off, and at WOT the outside carbs are free to move.

Is there a way I can tell if they are working when the engine is running without blowing up the motor? I suspect, if they really are not working it has to be vacuum related and I've been told it could be a gasket issue.

Any thoughts about what to do first?

Thanks

Rich

without starting the engine have someone hold the throttle wide open and then try and move the linkage that connects the front and rear carbs. if that is free you have a vacuum problem

[Rich G.]

Re: 68 Tri Carb question 435HP

Clem

Thanks. I have done that and they are free. Am I correct in assuming the vacuum comes from the manifold through the base gasket and therefor may be blocked if the gasket is wrong? BTW, I'm not SURE they are not working. It just feels different.

Rich

[Clem Z.]

Re: 68 Tri Carb question 435HP

Clem

Thanks. I have done that and they are free. Am I correct in assuming the vacuum comes from the manifold through the base gasket and therefor may be blocked if the gasket is wrong? BTW, I'm not SURE they are not working. It just feels different.

Rich

the starting vacuum come from the venturi of the center carb and then as the end carbs start to open they create more vacuum to pull them the rest of the way open

[John H.]

Re: 68 Tri Carb question 435HP

Clem

Thanks. I have done that and they are free. Am I correct in assuming the vacuum comes from the manifold through the base gasket and therefor may be blocked if the gasket is wrong? BTW, I'm not SURE they are not working. It just feels different.

Rich

Rich -

No, the vacuum for the diaphragms that open the end carburetors is venturi vacuum (not manifold vacuum), from the port higher up on the center carburetor, next to the choke pull-off diaphragm. Do your rubber vacuum lines look like the photo below? They should.

[Rich P.]

Re: 68 Tri Carb question 435HP

Another thing to chek is what springs were put in the secondary Diaphrams. Too heavy a spring and the secondaries won't kick in till later.

Rich

[Rich G.]

Re: 68 Tri Carb question 435HP

John

Thanks for that picture and the info. I will check tomorrow.

Rich, thanks for the heads up on the diaphams. If my vacuum hoses look right I'll have to check into that.

Rich G

[Rich G.]

Re: 68 Tri Carb question 435HP

The vacuum hoses are connected as shown in John's picture.

Is there any positive way to know if the secondaries are opening in the real world?

[Clem Z.]

Re: 68 Tri Carb question 435HP

The vacuum hoses are connected as shown in John's picture.

Is there any positive way to know if the secondaries are opening in the real world?

on the diaphragm side there is a WOT stop on the linkage where it hit the throttle body base plate so just put a dob of grease at that spot and take it for a full throttle run. if they opened all the way the grease will have a mark in it.

[Rich G.]

Re: 68 Tri Carb question 435HP

Clem

Thanks. I will do that when it stops raining. You fit my definition of a "genius"......You have a simple answer to what could have been a difficult problem. Here I was thinking about how I could put a video camera under the hood

Thanks again

Rich

[Clem Z.]

Re: 68 Tri Carb question 435HP

Clem

Thanks. I will do that when it stops raining. You fit my definition of a "genius"......You have a simple answer to what could have been a difficult problem. Here I was thinking about how I could put a video camera under the hood

Thanks again

Rich

mrs clem may not agree with you about the genius part.

[Tim G.]

Re: 68 Tri Carb question 435HP

You can inhale on the vacuum hose with the engine off and the throttle open to see if the end carbs open. This is easy to do by yourself.
You should be able to open the end carbs easily this way.

[Clem Z.]

Re: 68 Tri Carb question 435HP

You can inhale on the vacuum hose with the engine off and the throttle open to see if the end carbs open. This is easy to do by yourself.
You should be able to open the end carbs easily this way.

you have to hold the center carb wide open because of the return lockout feature

[James N.]

Re: 68 Tri Carb question 435HP

you have to hold the center carb wide open because of the return lockout feature

Are the throttle plates on the secondaries, activated by the diaphrams, supposed to open all the way with the engine off, under WOT at the primary when vacuum is applied to the secondary diaphrams or are they supposed to just crack open a little bit? I'm not able to get the secondaries to open all the way when I apply vacuum to the secondaries with the engine not running at WOT. I can manually open the front and back throttle plates by pulling the linkage forward. The springs do not seem to be overly strong, I get the same results when I disconnect the linkage. And I get the same results when I test the diaphrams individually, again with the linkage detatched. Diaphrams bad?

[Rich G.]

Re: 68 Tri Carb question 435HP

Jim

With all the help here I did determine mine are opening all the way. As I recall, the test you describe did result in the secondaries going open all the way or close to it when I tried it. You're sure your linkage is not restricting the secondaries?

Rich