| Slant Six Forum https://slantsix.org/forum/ |
|
| backfiring to a 390 cfm https://slantsix.org/forum/viewtopic.php?t=28742 |
Page 1 of 1 |
| Author: | prattwithney [ Sun May 04, 2008 6:07 am ] |
| Post subject: | backfiring to a 390 cfm |
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 |
|
| Author: | Aggressive Ted [ Sun May 04, 2008 11:45 am ] |
| Post subject: | |
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. |
|
| Author: | prattwithney [ Mon May 05, 2008 11:23 am ] |
| Post subject: | |
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 |
|
| Author: | Aggressive Ted [ Mon May 05, 2008 5:02 pm ] |
| Post subject: | |
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? |
|
| Author: | 70valiant [ Mon May 05, 2008 6:42 pm ] |
| Post subject: | |
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. |
|
| Author: | prattwithney [ Tue May 06, 2008 2:01 am ] |
| Post subject: | |
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. |
|
| Author: | slantfin [ Tue May 06, 2008 4:45 am ] |
| Post subject: | |
A carbon fiber gasket like the Remflex or Australian made ones are great for sealing manifolds or headers to the cylinder head. |
|
| Author: | DusterIdiot [ Tue May 06, 2008 6:51 am ] |
| Post subject: | Yes |
Quote: My carb is brand new, i hope they are in the truth.
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 |
|
| Page 1 of 1 | All times are UTC-08:00 |
| Powered by phpBB® Forum Software © phpBB Limited https://www.phpbb.com/ |
|