idle, and linkage questions May 20, 2020 9:59:04 GMT -5
Post by squishymonster on May 20, 2020 9:59:04 GMT -5
I am working through issues with my carb, pouring over all kinds of information here and there, and I have a couple of questions that I hadn't found answers to yet.
Mainly I am curious if I should be able to idle with the throttle plate 100% closed, and if I should be able to achieve 600rpm that way. I am able to achieve a very low but stable sounding idle with the plate completely closed, but it's a fragile idle in that any movement of the throttle plate kills it (that is, if I disable the metering rod in order to test / isolate the idle circuit).
It seems to me that the amount of air capable of entering the cylinders strictly through the throttle mixture screw port would be far too small, but that's more (false?) intuition than experience.
In that case, it seems very clear that absolutely any vacuum leak in the throttle body would have major consequences since the idle passages are so small, it wouldn't take much to get that small amount of air elsewhere, and then not draw the fuel mixture.
With that low idle, choke 100% off, I made adjustments to the metering rod so that immediately as the throttle starts opening the metering rod starts providing fuel. That means that as I set the idle screw to achieve 600rpm, both the idle mixture screw, and the main jet are providing fuel for any throttle-slightly-opened idle. What I've read so far seems to indicate that is correct operation. Am I on the right track?
With all of that in place, I was idling well with no choke, and my next step is to get acceleration to work properly. My current issue there is after a quick blip on the throttle and quick release I get a fairly reliable backfire up the carb. But before I start tracking that down I wanted to see if the previous things are moving in the right direction.
Second, I have a couple of loose linkages. The pivot between the metering rod and accelerator pump has two plate-like brackets and they separate quite a lot. I don't see any intended mechanical means to stop that separation. I hoped the choke body would hold everything together, but they still separate close to the point where they wouldn't engaging one another anymore.
The two lower brackets on the motor side of the throttle shaft also have a lot of play, resulting in the throttle plate not being able to fully return to the idle position. But I just found another post here regarding that issue. I think i can repair the pin hole with my welder...