Gasket Sealing Completely?

Rick Parker · #1 (**permalink**) 09-15-2007, 08:02 PM

I found while adjusting the Webers today that the #4 cylinder was not drawing the same amount of air volume as the others. While using the Unisyn it was appearant that very little air was being pulled and the idle mixture screw had virtualy no effect on idle quality. So I removed the carb to be sure the throttle plates were phased EXACTLY the same. Compression checked at 150#. I am going to adjust the valves tomorrow, but I am thinking that perhaps either an intake manifold gasket has failed or the thick insulating gaskets under the carb aren't properly sealed. What else could it be??

zrayr · #2 (**permalink**) 09-16-2007, 12:26 PM

Quote:

Originally Posted by Rick Parker

I found while adjusting the Webers today that the #4 cylinder was not drawing the same amount of air volume as the others. While using the Unisyn it was appearant that very little air was being pulled and the idle mixture screw had virtualy no effect on idle quality. So I removed the carb to be sure the throttle plates were phased EXACTLY the same. Compression checked at 150#. I am going to adjust the valves tomorrow, but I am thinking that perhaps either an intake manifold gasket has failed or the thick insulating gaskets under the carb aren't properly sealed. What else could it be??

compression sounds a little low for a Hi-Po 289. What are the other cylinders reading. My (stock Hi-Po 289) has compression of 200 +/- 10 lbs. across the board. Maybe a slightly bent valve.

Z. Ray

Rick Parker · #3 (**permalink**) 09-16-2007, 01:22 PM

John Peterson came over with some really hi tech scanners and a smoke generator. We verified that all the gaskets are intact. We were able to lightly pressurize the crancase in an attempt to see if there was any leakage into the #4 inlet tract. I think at this point it is something of a mechanical nature. I hope it is something as simple as a valve adjustment, but that is probably wishful thinking.

ENTDOC · #4 (**permalink**) 09-16-2007, 03:43 PM

Rick ,it might be as simple as the throttle linkage being out of adjustment, that is what mine turned out to be when I had one cylinder out of sorts.

Rick Parker · #5 (**permalink**) 09-16-2007, 05:04 PM

When the single shaft controls 1 carburetor and two cylinders how do you adjust for 1 cylinder?

Rick Parker · #6 (**permalink**) 09-22-2007, 01:03 AM

One of the great aspects of this site is the ability to share and occasionally benefit from the situations and difficulties that we all encounter from time to time. I try to learn from them and apply the remedy if the situation or symptom happens to me. Hopefully others some of you feel the same way. Sometimes it is the small things or somthing that has been mis-diagnosed or even over looked that ends up being the cause. Well... my recent problem turned out to be the throat that was actually flowing the higher volume of air. It turned out that the throttle plate in THAT throat was improperly fit and was allowing excess air to bypass it when closed, While the original one in question was actually sealling correctly. I readjusted the other plate and all seems to be ok now, and I will continue on my journey to find the final jetting package.

Thanks to those that replied.