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  #1  
Old 09-23-2007, 06:40 PM
evam350 evam350 is offline
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429 backfire through carb

Hi everybody

I have a 429 with a 4300 carb and when I try to rev it up it backfires through the carb and if I'm driving it and try to get on it, it backfires and loses power

Yesterday I advanced the timing and revved it up and it didn't do it anymore so I took it on a short drive and everything seemed good

Now today it is doing it again, I tried to advance the timing a tad more but it didn't help

I also put in a new accelerator pump but no help

I took the air cleaner off and pumped the throttle lever by hand and it seems like the accelerator pump is only giving one decent squirt and then the next time I pump it, it barely squirts any gas out


Thanks for any help
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  #2  
Old 09-23-2007, 07:14 PM
Troy Bredthauer Troy Bredthauer is offline
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float too low?
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  #3  
Old 05-19-2012, 09:22 AM
der B der B is offline
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I know this is already an old thread but.... I have exactly the same problem with my 429. Well I did not try to adjust the timing 12 BTDC is correct as per the manual...
Hope anyone can help here!
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Old 05-19-2012, 01:45 PM
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Quote:
Originally Posted by der B View Post
I know this is already an old thread but.... I have exactly the same problem with my 429. Well I did not try to adjust the timing 12 BTDC is correct as per the manual...
Hope anyone can help here!
Do you have the exact same issue with the accelerator pump only putting gas down one throat of the carb?

If so...then sounds like you proably got some dirt in the carb plugging things up. The pump pushes fuel through small passages within the carb that can plug up quickly if you have dirt in there.
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Old 05-20-2012, 09:04 AM
der B der B is offline
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Well... maybe my problem is not exactly the same... the accelerator pump is okay!
Nevertheless, the engine has no power on the road, idles fine, starts good... but has this "sneesing" when opening the throttle
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Old 05-20-2012, 09:17 AM
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Originally Posted by der B View Post
Well... maybe my problem is not exactly the same... the accelerator pump is okay!
Nevertheless, the engine has no power on the road, idles fine, starts good... but has this "sneesing" when opening the throttle

Not entirely sure what you mean but lack of power under load can be many things from fuel to valve and/or ignition timing...amont others.

Is it a continuous lack of power or only initially when you try to accelerate?

The fuel system, carb especially, can not function properly for various reasons. The carb needs to be functioning properly on all aspects to realize the total porformance.

Check the basics:
Are you getting a good fuel supply to the carb? Proper flow and pressure. i.e. is there a pump and/or filter issue
Are the float levels adjusted properly to maintain proper bowl level?
Check choke operation to make sure it's opening all the way when the engine is warmed up
Is the carb clean and not plugged anywhere? If you have dirt in there it will block passages including the primary jets.
Check your initial and total ignition timing. If the initial timing is not set properly and not advancing correctly...that can cause an engine to run weak. Make sure your vacuum advance is connected to the proper source. Should be a vacuum source on the carb that only sees vacuum after the throttle is open. sometimes called "spark" or "idle" vacuum.
Check your manifold vacuum at idle...that can tell you a lot on how your engine is running.

btw...what carb do you have?
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  #7  
Old 05-20-2012, 01:18 PM
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Are the #7 & #8 plug wires crossed?
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Old 05-20-2012, 02:23 PM
big vann big vann is offline
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That is also a symptom of a camshaft lobe(intake lobe) going flat.If the carb suggestions don't solve your issue,you might want to pull the valve covers and watch the rockers as someone turns over the engine(without starting it as this can be messy).If a lobe is flat it should be apparent as the culprit will not rise as much as the rest do.I hope it's not the cam but it does happen.
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Old 05-24-2012, 12:58 AM
der B der B is offline
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OMG!

What can I say... yesterday I had 10 minutes and I checked here and there and just before unmounting the carb and the distibutor I checked the firing order ( a third time) again ...

It's hard to say it but ... I messed it up

should be 15426378 was 15423678

Will test the engine today... think thats the issue


Thanks for your help
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  #10  
Old 05-24-2012, 06:08 PM
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That'll do it.
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Old 05-24-2012, 11:44 PM
der B der B is offline
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It does!
Now the engine is running nice and accepting a step on the pedal without any backfire

Thx
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  #12  
Old 05-25-2012, 06:49 AM
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Nice!!! Always good when you find and easy fix And you know you're not the first to do that!!!
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  #13  
Old 05-26-2012, 04:52 AM
der B der B is offline
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True. Moreover many threads end without a "prob solved" post, letting all users know what the solution was finally... So long
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Old 05-26-2012, 04:52 AM
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