dkraven
Full Access Member
- Joined
- Nov 15, 2022
- Posts
- 72
- Reaction score
- 78
- Location
- Portland, OR
- First Name
- David
- Truck Year
- 1977
- Truck Model
- c25 Sierra Grande
- Engine Size
- 350
Came onto this forum months ago for help because the '77 GMC Sierra Grande my neighbor gifted me last November was dieseling when I shut it off. At that point I was new enough to know nothing about carburetors or distributors or timing. I didn't even know what I was hearing was called dieseling. You all took care of me, explained things multiple times when I didn't get it, suggested possible solutions. I got a roadmap for how to set my timing and tune my carburetor.
Learning to tune the carburetor shifted to learning I needed to rebuild the carburetor, which I did. Twice. The first time the accelerator pump was crap so I got one from Cliff's High Performance that did the trick. Of course I stripped the fuel inlet of the carb and had to send it out to get helicoiled.
Speaking of helicoils, I had to helicoil my crankshaft. In setting the timing I found out my harmonic balancer was shot, and I couldn't trust my timing mark. Went to install the new balancer and the bolt just kept turning, and turning. That helicoil operation went well though, and we cheered when we got the new balancer installed and torqued down.
Those are the major points, there were a hundred little problems and throw the wrench down and walk away moments. But then last week I finally got everything reinstalled and tuned up. I'm in Portland, OR where we have strict emissions standards and that was the final hurdle to pass. The test, if you will, of what I've learned this past year. In order to pass emissions I hobbled my tune. Knocked the timing from the healthy 12 btdc to right on the zero mark. Leaned out the idle mixture screws. Upped the curb idle to just over 1000. Went through emissions and... failed. Hydrocarbons are supposed to be at 500 and I was just over 900!
But you don't pay until you pass, and even though it was getting dark, I had tools in the truck. So I went around the corner and fattened up the air fuel mixture, I had gone too lean for the test, lowered the idle a bit, and with fingers crossed went through again. Hydrocarbons came in at 492, 8 below! I passed and high-fived the woman running the test.
Over the past year there have been multiple times I was at the "screw it just gonna sell this heap" point. But I'm glad I kept at it, and I'm grateful to you all for your help. Now I have a dozen other things to sort out with the truck, but a smooth running engine makes it all seem doable. Here's the truck last week getting a sip of gas at the station instead of from a jerry can in the driveway, and hauling some yard material!
Oh, and the dieseling that initially gave me so much trouble, that was just the curb idle screw being in too far and the transfer slots were dripping gas into the intake.
Learning to tune the carburetor shifted to learning I needed to rebuild the carburetor, which I did. Twice. The first time the accelerator pump was crap so I got one from Cliff's High Performance that did the trick. Of course I stripped the fuel inlet of the carb and had to send it out to get helicoiled.
Speaking of helicoils, I had to helicoil my crankshaft. In setting the timing I found out my harmonic balancer was shot, and I couldn't trust my timing mark. Went to install the new balancer and the bolt just kept turning, and turning. That helicoil operation went well though, and we cheered when we got the new balancer installed and torqued down.
Those are the major points, there were a hundred little problems and throw the wrench down and walk away moments. But then last week I finally got everything reinstalled and tuned up. I'm in Portland, OR where we have strict emissions standards and that was the final hurdle to pass. The test, if you will, of what I've learned this past year. In order to pass emissions I hobbled my tune. Knocked the timing from the healthy 12 btdc to right on the zero mark. Leaned out the idle mixture screws. Upped the curb idle to just over 1000. Went through emissions and... failed. Hydrocarbons are supposed to be at 500 and I was just over 900!
But you don't pay until you pass, and even though it was getting dark, I had tools in the truck. So I went around the corner and fattened up the air fuel mixture, I had gone too lean for the test, lowered the idle a bit, and with fingers crossed went through again. Hydrocarbons came in at 492, 8 below! I passed and high-fived the woman running the test.
Over the past year there have been multiple times I was at the "screw it just gonna sell this heap" point. But I'm glad I kept at it, and I'm grateful to you all for your help. Now I have a dozen other things to sort out with the truck, but a smooth running engine makes it all seem doable. Here's the truck last week getting a sip of gas at the station instead of from a jerry can in the driveway, and hauling some yard material!
Oh, and the dieseling that initially gave me so much trouble, that was just the curb idle screw being in too far and the transfer slots were dripping gas into the intake.
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