Hi,
i need help to set properly my 170 ci slant.
I've put a clifford intake and a new holley 390cfm carb, with stock exhaust manifold. I've got backfiring through the intake when i start the engine. Gloups!!! i don't want to break a valve.
I've read the precedent topic on backfiring, but i've got questions:
-i've closed the full manifold vacuum source because i don't know where it does connect, and if it's necessary.
-i've thinking to the ignition timing of my point ignition. I decided to convert it to electronic pertronix, and i'm now waiting the parts. Or it could be the timing chain ?
-does i need to change the exhaust headers ?
-does i need to change the camshaft ?
-does i need to adjust the valve?

Thanks for the answers, i'm feeling alone with this problem in France.
Prattwithney

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Dodge dart 270 four door sedan with 170 ci slant.
Video post you tube dodge dart 1965

prattwithney,

Had the 170 been in good running order before the swap?

If yes, the cam doesn't have to be changed to make it run.

The Clifford manifold does not fit well with the stock manifold unless you do allot of grinding for clearance to properly fit. If this is not done carefully, I am thinking you may have a vacuum leak causing the back firing.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Hi agressive Ted,

When you says vacuum leak, does it mean that i've got a leak between carb an manifold ? manifold and head ?
or vacuum leak with valves , pistons...
Before upgrading i was just carb problem at low rpm, and stalled when i increased speed.

Prattwithney

_________________
Dodge dart 270 four door sedan with 170 ci slant.
Video post you tube dodge dart 1965

A new Clifford manifold will not fit with stock exhaust. So I am thinking there could be a leak at the head and intake.

Did you do allot of grinding to make the intake fit between the stock exhaust runners?

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

One good backfire throught the carb and you will most likely have blown out your power valve. I had blown out 3 of them before realizing I had a couple intake valves too tight.

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i've just read that on the tecnical library from the holley site :
"There still seems to be a lot of misconception about
Holley carburetors blowing power valves. Nothing
could be further from the truth. Holley performance
carburetors built since 1992 have utilized a power
valve check system that effectively eliminated this
infrequent problem. Consisting of a spring, brass
seat and check ball, the check ball system is 100%
effective protecting the power valve diaphragm
from damage due to engine backfire.
The power valve check ball is designed to be
normally open but quickly seals to close off the
internal vacuum passage when a backfire occurs.
Once closed, the check valve interrupts the pressure
wave generated by the backfire, thus protecting the
power valve diaphragm. There is no way that the
power valve’s diaphragm can rupture due to an
engine backfire!"

My carb is brand new, i hope they are in the truth.

My manifold is a old one, bought on ebay, and i've just had to grind a bit to fit it near the stock exhaust headers. But i'm going to look for a leak between the manifold and head.

_________________
Dodge dart 270 four door sedan with 170 ci slant.
Video post you tube dodge dart 1965

A carbon fiber gasket like the Remflex or Australian made ones are great for sealing manifolds or headers to the cylinder head.

All their 4 barrel carbs made after 1992 have the little 'checkball' style valve installed in the carb base, you should be OK if it's brand new...

- D. Idiot