Loss of power slant six
Posted: Wed May 24, 2017 7:52 pm
Hi All,
This past week I have been chasing an odd issue. A few weeks ago I put a MSD BTM6 on my truck as well as a pertronix electric ignition. The issue I was having with that was that the truck would be hard to start, I later found out the timing marks on the crank were not correct. 10 degrees BTC is actually TDC, changed that then the truck ran like a champ.
This past week I noticed that the truck lacked power in gears 2 and 3 or 3 and 4 respectively. In first gear I can get the truck to rev and pull to 4,000 RPM, then in second on a pull she won't rev past 3,000. It feels like the truck surges then eventually will stall if you hold the throttle in. In fourth gear it does it as low as 2,000 Rpm.
I thought it was a carb issue but when I tore down the carb I didn't notice anything out of the ordinary, I readjusted the float height, but I adjusted it too much so it was flooding the truck, I changed the float height and now it runs exactly the same.
Today I pulled the valve cover off and barred the engine over back and fourth to see how much slack was in the chain. There was maybe a quarter inch of movement between the crank and valve train. And when I barred the engine so that cylinder 6 was at the beginning of its exhaust stroke so that cylinder 1 was on its compression stroke allowing me to measure the valve lash. Knowing that the slant six has to have these measurements done with the engine warm, when I took the measurements cold there was a two thousandth difference on both sides ( Intake .010 measured .012, Exhaust .020 measured .022) So I do not think that this issue is a cam or timing issue.
I have ordered a new Holley 2300 to convert it for a blow thru setup.
Does anyone have the slightest idea of what the issue is?
I changed the fuel filter, cleaned the screen in the tank, checked the fuel pump. Checked timing both cam and ignition both were fine. This leads me to believe that the carburetor is the issue here.
This past week I have been chasing an odd issue. A few weeks ago I put a MSD BTM6 on my truck as well as a pertronix electric ignition. The issue I was having with that was that the truck would be hard to start, I later found out the timing marks on the crank were not correct. 10 degrees BTC is actually TDC, changed that then the truck ran like a champ.
This past week I noticed that the truck lacked power in gears 2 and 3 or 3 and 4 respectively. In first gear I can get the truck to rev and pull to 4,000 RPM, then in second on a pull she won't rev past 3,000. It feels like the truck surges then eventually will stall if you hold the throttle in. In fourth gear it does it as low as 2,000 Rpm.
I thought it was a carb issue but when I tore down the carb I didn't notice anything out of the ordinary, I readjusted the float height, but I adjusted it too much so it was flooding the truck, I changed the float height and now it runs exactly the same.
Today I pulled the valve cover off and barred the engine over back and fourth to see how much slack was in the chain. There was maybe a quarter inch of movement between the crank and valve train. And when I barred the engine so that cylinder 6 was at the beginning of its exhaust stroke so that cylinder 1 was on its compression stroke allowing me to measure the valve lash. Knowing that the slant six has to have these measurements done with the engine warm, when I took the measurements cold there was a two thousandth difference on both sides ( Intake .010 measured .012, Exhaust .020 measured .022) So I do not think that this issue is a cam or timing issue.
I have ordered a new Holley 2300 to convert it for a blow thru setup.
Does anyone have the slightest idea of what the issue is?
I changed the fuel filter, cleaned the screen in the tank, checked the fuel pump. Checked timing both cam and ignition both were fine. This leads me to believe that the carburetor is the issue here.