1967 435 tri power carb question

[Keith B.]

I have been working on my carbs because I have been getting a slight backfire through the carb after acceleration. Upon inspection with the air filter lid off and bringing the RPMs up it does not appear that I am getting the end carbs to open upon acceleration. I have done some simple tests with the ignition off and manually applied vacuum by mouth with the center carb opened completely I can get the butterfly to open a quarter inch on both end carbs. They open completely when open I manually maneuver the linkage again with the center carbopened full throttle (engine off) The linkage does not move at all no matter what kind of RPM I produced even in the 5000 to 6000 RPM range it is not having them move at all. I am not sure what to do next. Any suggestions would be helpful.

[Rich G.]

[Keith B.]

[Guest]

Re: 1967 435 tri power carb question

step 1 Check your set up on your center Carb. first , float level , vacuum hose route and remove secondary linkage and set up center carb. air and gas mixture and let it idle at about 850rpm. and see what happens

[Rich G.]

[Guest]

Re: 1967 435 tri power carb question

it all about setup the carbs. properly ,the secondaries have different colour springs for different RPM opening , like i told keith Step 1 set up center carb. first then there about a few more Steps to follow.

[Patrick B.]

[Guest]

Re: 1967 435 tri power carb question

Correct Pat you have to start somewhere first, why fool around with the secondaries it could even be a ignition problem without seeing the car who knows. going by Keith original question keith had 5000-6000 RPM

[Keith B.]

Re: 1967 435 tri power carb question

Car starts without hesitation, vacuum line has correct set up, motor idles at 850 very smooth. Car was still warm from drive so fired right up. Air filter off for this. Idler screws set at 2 turns (almost kills car when all the way in). Floats are right on. By the way this is an unrestored car with 24k miles. I have reproduction wires on it but original everything else. The car has been started and ran periodically over the last 30 years but very rarely has it been driven.

[Rich G.]

Re: 1967 435 tri power carb question

Many years ago I had a bad coil wire that caused similar issues. Can you look at the wires in a dark place and look for arcing? Or hear a lot of static in the AM radio?

[Guest]

Re: 1967 435 tri power carb question

Keith try a set of spark plugs , mine L71 was doing the same i change the plugs work great , also try removing the ignition top shield when doing a road test maybe one of the wire boot is grounding to the top shield i seen that happen before.

[Keith B.]

Re: 1967 435 tri power carb question

This is the second coil wire I have used with the same effect. I also have the ignition cover off right now to assure no arching on the cover

[David M.]

Re: 1967 435 tri power carb question

Good advice start with trouble shooting 101 basics before deep diving and parts replacing.
Slight back fire upon deceleration suggests a rich A/F mixture and or a vac leak.
Here are some basic checks before replacing anything:

1. Read each spark plug. Black, white, brown? Gaps ok?

2, Verify no vacuum leaks.

3. Is this a mechanical tappet cam shafted Rat? Run the valves.

4. Ignition system verification's: Check the points, condenser and dwell setting. Verify the cap, rotor and mechanical advance are all up to snuff. Distributor shaft have any side to side play? I know its a low mile car but Ive seen the shafts go early due to gum/lack of oiling.

5. Check the negative wire that feeds the points. It can break and become intermittent when the breaker plate moves with vibration or vac advance. Verify the vac canister isn't leaking

6. Ohm out the primary/secondary coil windings. Verify infinite resistance on all 3 terminals to ground.

7. Repro (new) wires does not mean they are any good? What brand did you purchase? Ohm them if suspect(one bad/fouled plug).

8. Hook up a vacuum gauge to direct intake manifold vacuum. Is it relatively steady at 850 rpm? Tune the timing and air/fuel mixture screws on the center carb. Do small adjustments to each system to achieve the highest possible vacuum gauge reading at curb idle.

9. How about fuel filters? If it sits a lot the fuel its self and or the fuel delivery system may need some attention. Never use ethanol laced gas. Especially in a car that sits.

Report back if any of this helped.

[Timothy B.]

Re: 1967 435 tri power carb question

Have you disconnected the linkage and went for a ride to see if the center carburetor by itself performs normal as was mentioned above? This is important as it will help isolate weather there is a ignition problem, wires etc. If the engine motors up to 5000+ rpm on the center carburetor consider the following.

Have these carburetors ever been overhauled.

If the center carburetor works good it's very possible the secondary carburetors are opening correctly BUT they have some jelled fuel that's solidified causing the lean condition when the blades open, this lean condition causes backfire through the carburetor.

You may want to try some good spray carburetor cleaner in the air bleeds on the secondary carbs but watch your eyes and the cars paint. The little tube and solution may blow the fuel blockage open so fuel flows freely again. Or, it may be time for a good cleaning of the secondary carbs.

[Keith B.]

Re: 1967 435 tri power carb question

I changed the spark plugs. They were carbon dry at the tip with two having fluid covering. I changed out the 30 year old 43n spark plugs and put in 44n nos set I had laying around. I ran it in the garage for a while and then took it for a quick ride. it has ALL the power of a 435! no back fires and idled at 850 as I pulled it back into the garage. I want to thank everyone for the suggestions. I spent several hours verifiying the fuel floats, vacuum, coil etc. before I fired it back up. The car is absolutely a joy to own and to drive. I appreciate the ability to have the experts help in any troubling situation.