Still need help with 435 problem
At idle. , then floored, the engine almost dies then comes back to life. When going 60 mph, then floored, engine sputters, back fires through the side-pipes, then slowly takes off. I've have 2 sets of carbs on it and both did the same. Car runs fine with the 2 end carbs disconected. I am running non-ethonal gas. Car does not ping or run on.
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Re: Still need help with 435 problem
With your car at idle and looking into the carb with the air cleaner top off have someone press on the gas pedal and see if your carb is injecting fuel from activation of the accelerator pump.
Use caution in viewing in case of a backfire. -
Re: Still need help with 435 problem
Keith,
you say the excat same thing happens with 2 different sets of carbs. Then I'd start by checking a few constants.
Chek to see that your vacuum source for the secondaries is working and properly.
Check your vacuum advance for the distributor (each time you stab the throttle the advance kicks in so it could be advancing the spark to much and there is your back fireing through the exaust).
Check to see what the springs are on both diaphrams for the end carbs. If too light they will come in too early.
Check the jetting on both sets of end carbs. Too big and it will dump too much fuel.
Check the float levels on the end carbs.
Check fuel pump for proper flow (It could supplty enough fuel for the center carb but not enough for the end carbs) Although a lean condition usually tends to send the back fire through the carb not the exaust.but at speed you might not hear a back fire through the carb.
Check fuel lines from tank to pump for partial blockage.
Check adjustment on secondary linkage (the 2 rods from the center carb)
Check the accelerator pump on the center carb (you did not specify if you swapped it out also or just the end carbs)
These are just a few things I'd look at to start to see what's up. I hope one might point you in the right direction I could write 20 more but this should get you going.
RichComment
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Re: Still need help with 435 problem
Try new plugs.Comment
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Re: Still need help with 435 problem
Keith;
I'm no expert by any means, but from what you describe at 60 MPG suggests to me that you are getting raw/unburned gas into your side pipes where the heat therein causes combustion.... but you probably already surmised that.
In addition to what the other guys have called out, I would check ignition. Given your tri-power set up you should be running a TI system. I would be checking the ignition wires, amplifier box, etc... I would also pull a couple of plugs and see what they look like after normal driving. If by chance your amplifier box is original, it could be problematic.. the old ones were negatively impacted by heat.. caused them to be marginal a startup and I would assume at other times as well.
Hope this helps.
JoelComment
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Re: Still need help with 435 problem
I'm not an expert either, but I have to agree with Rich P. above....
Assuming you have already done the 'other' checks/changes......
I'd start checking the Vacuum source/levels.....
DavidComment
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Re: Still need help with 435 problem
Keith, You will get many responses so here's mine. What do some of the plugs look like?? I believe engine is going lean and not proper combustion which is why there is popping in exhaust.
There could be many reasons, both sets of booster carburetors do the same thing so I assume the problem lies else where but don't think it couldn't be carburetor related. A vacuum leak inside one of these carburetors could be the problem, surfaces uneven etc. Don't stick your face over the engine because the engine is not pulling the proper mixture, instead it is pulling more air.
Check the vacuum can to make sure it's not ruptured, I think your car has ported vacuum advance so try to move inital timing to 12-14* BTDC to see if that helps any. How much vacuum at idle?
Process of elimination, just do one thing at a time.
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Re: Still need help with 435 problem
Timothy, is on the right tract. That is the classic symptom of LEAN.
The secondaries on that set up is supposed to be vacuum controlled. First I would check the linkage to see if for some reason it is opening the secondaries mechanically. That would cause the stumble. Beyond that, you are going to have to determine why the enrichment circuit is not working correctly, the secondary opening is too quick, or the engine timing is not correct. A bad or incorrect vacuum advance is a common cause of stumble.Comment
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Re: Still need help with 435 problem
Just a comment on one item that Rich mentioned; the vacuum advance. I don't believe you will get more advance when you "stab it", rather under the low vacuum condition of WOT, the vacuum advance drops out and comes back in as vacuum is restored by a closing throttle position. If the vacuum can was actually causing the problem, it would be due to it hanging up the advance plate (causing it to stick) in the distributor - which is not too likely. This used to be a common problem with the pre 57 distributors, but you don't hear of it much with the post 57 distributors.
Stu FoxComment
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