eightOsix
Member
The truck I am working on is a ’65 d1100 4x4. T98 tranny with a np202 tc, Dana 44’s front and rear. The engine is a 72ish 345 with the “e” stuff deleted. I believe it originally came with a 304.
Carburation is a stock holly 2300 which I have completely rebuilt, jetted at #48 mains – I am at 9000 feet elevation. Air screws are set about two turns out where it seems to run well and I get the highest vacuum reading, which is about 13 and steady at 750-800rpm. Last time I checked I had a good pump shot.
The stock holly points dizzy is set at 8* btdc, although I believe the truck runs better at 12-15*. Dwell is 25. Within the last couple years I have installed all new points, plugs, wires, cap. Oil pressure will start up at around 50 psi, and then drop off to around 5 at warm idle. Pressure will come up with increased rpm.
This truck has an easy life - just drive around the valley, no highway driving, no wheeling. Last spring I noticed that I was getting a popping noise from the carb on acceleration, but only when the engine hot.
I did a number of checks to try and cure the problem. Checked for exhaust leaks – ok. Checked for vacuum leaks all around the carb – ok. Steady vacuum confirmed this. Checked the timing and dwell and set as above.
I checked all my spark plug wires, checked routing and confirmed firing order. Installed some new wire separators. Checked the motor in the dark and could not see any arcing.
The problem persisted. With the air cleaner off, hot engine, the popping is more of a backfire, and appears to come from the passenger side venturi. Sometime there is also a knock, again only with hot engine, that seems to be associated with the backfiring. Here is a link to a video Where you can hear the knock and see the vacuum gauge drop about 1 mm with each knock.
So I started to believe that I was having an issue with a sticking intake valve. The truck sat all summer while I dealt with other commitments, but last week I jumped back in.
I removed the pass side valve cover with a warm engine and confirmed that all the valves were moving, push rods were rotating. Didn’t look to me like there was a lot of oil moving around, but I’m not sure how much there is supposed to be. There was oil drooling at several of the valve stems but I couldn’t confirm oil at all of them. I pulled the valve train and disassembled per instruction on this site. I had to tap the stands off the shaft, and I had significant wear at several rocker locations. However, the top of the head was relatively clean and the spit holes were all open. The rocker oil passages were clear. I cleaned the inside of the shaft, which had some grunge but was by no means clogged. See attached photos.
I removed the dizzy, fabbed up a tool and rotated the engine while turning the oil pump. Pressure went right up to 50 at the gauge, and when I got to where oil would flow out of the supply hole there seemed to be an adequate amount. The drainback is slow, but it does eventually drain. Without taking the driver side valve train off I verified that there was oil flow to the rocker shaft with the drill. Even so, I took the drivers side valve train off and did the cleaning routine. This shaft also had wear at two rocker stations. With each I lightly buffed the damaged areas with emery cloth. I know that out of spec shaft/rockers (clearance at the worst spot is around .011) will make the engine not perform as well as it could, but I am hoping that with adequate oil the engine will run reasonably well. So, my first question: would the worn rocker shaft cause the backfiring at the carb?
All of the pushrods and rockers appeared to have similar wear, with the pushrods having a slight flat spot. The assemblies were reinstalled and torqued to 12#. Spinning the drill confirms rapid and profuse oiling at the stands. I couldn’t run the drill long enough to verify oil at each rocker because of the messy overflow.
Got the dizzy restabbed and the motor running. Reset the timing to 8*. Let the engine warm up and burn off all the spilt oil. After the engine got hot the backfire on acceleration was still there. Didn’t hear the knock.
So that’s where I am right now, about the same place as I was last spring, except I know that the valve train is clean and the valve covers look great with some new paint. Not really sure of what the problem is. I was thinking of doing a wet and dry compression test and maybe a leak down test. I also should visually check the valve train with a hot engine. I was also thinking of going back to 50 main jets.
Any suggestions or comments are appreciated.
Carburation is a stock holly 2300 which I have completely rebuilt, jetted at #48 mains – I am at 9000 feet elevation. Air screws are set about two turns out where it seems to run well and I get the highest vacuum reading, which is about 13 and steady at 750-800rpm. Last time I checked I had a good pump shot.
The stock holly points dizzy is set at 8* btdc, although I believe the truck runs better at 12-15*. Dwell is 25. Within the last couple years I have installed all new points, plugs, wires, cap. Oil pressure will start up at around 50 psi, and then drop off to around 5 at warm idle. Pressure will come up with increased rpm.
This truck has an easy life - just drive around the valley, no highway driving, no wheeling. Last spring I noticed that I was getting a popping noise from the carb on acceleration, but only when the engine hot.
I did a number of checks to try and cure the problem. Checked for exhaust leaks – ok. Checked for vacuum leaks all around the carb – ok. Steady vacuum confirmed this. Checked the timing and dwell and set as above.
I checked all my spark plug wires, checked routing and confirmed firing order. Installed some new wire separators. Checked the motor in the dark and could not see any arcing.
The problem persisted. With the air cleaner off, hot engine, the popping is more of a backfire, and appears to come from the passenger side venturi. Sometime there is also a knock, again only with hot engine, that seems to be associated with the backfiring. Here is a link to a video Where you can hear the knock and see the vacuum gauge drop about 1 mm with each knock.
So I started to believe that I was having an issue with a sticking intake valve. The truck sat all summer while I dealt with other commitments, but last week I jumped back in.
I removed the pass side valve cover with a warm engine and confirmed that all the valves were moving, push rods were rotating. Didn’t look to me like there was a lot of oil moving around, but I’m not sure how much there is supposed to be. There was oil drooling at several of the valve stems but I couldn’t confirm oil at all of them. I pulled the valve train and disassembled per instruction on this site. I had to tap the stands off the shaft, and I had significant wear at several rocker locations. However, the top of the head was relatively clean and the spit holes were all open. The rocker oil passages were clear. I cleaned the inside of the shaft, which had some grunge but was by no means clogged. See attached photos.
I removed the dizzy, fabbed up a tool and rotated the engine while turning the oil pump. Pressure went right up to 50 at the gauge, and when I got to where oil would flow out of the supply hole there seemed to be an adequate amount. The drainback is slow, but it does eventually drain. Without taking the driver side valve train off I verified that there was oil flow to the rocker shaft with the drill. Even so, I took the drivers side valve train off and did the cleaning routine. This shaft also had wear at two rocker stations. With each I lightly buffed the damaged areas with emery cloth. I know that out of spec shaft/rockers (clearance at the worst spot is around .011) will make the engine not perform as well as it could, but I am hoping that with adequate oil the engine will run reasonably well. So, my first question: would the worn rocker shaft cause the backfiring at the carb?
All of the pushrods and rockers appeared to have similar wear, with the pushrods having a slight flat spot. The assemblies were reinstalled and torqued to 12#. Spinning the drill confirms rapid and profuse oiling at the stands. I couldn’t run the drill long enough to verify oil at each rocker because of the messy overflow.
Got the dizzy restabbed and the motor running. Reset the timing to 8*. Let the engine warm up and burn off all the spilt oil. After the engine got hot the backfire on acceleration was still there. Didn’t hear the knock.
So that’s where I am right now, about the same place as I was last spring, except I know that the valve train is clean and the valve covers look great with some new paint. Not really sure of what the problem is. I was thinking of doing a wet and dry compression test and maybe a leak down test. I also should visually check the valve train with a hot engine. I was also thinking of going back to 50 main jets.
Any suggestions or comments are appreciated.
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I guess that’s possible. Been in there for almost two years, believe it came with the Holley #37-1343 kit, but I could be mis-remembering. I just ordered a new kit and a 4.5 power valve.
