Slide height screw (idle)

[Thumper]

This is a photo of the slide height adjustment screw (idle) on a new TBR7. We rejet it (both jets) and shimmed the needle. It starts right up, runs great, and no popping. But the idle adjustment seems too short! There is no spring on it, and it is all the way in. It has no effect on the slide height!

This might be normal for this carburetor, but how do you adjust the idle?

[buzz]

Thats the idle screw works on mine.

[Megadan]

Suggestion. The part that acts on the slide is just an offset pin on the screw. Back it out until the slide ends up at the same place, that will give you more room for adjustment.

[Bruces]

Any chance your throttle cable is adjusted too short ?

[Thumper]

Thanks, all of you. Why didn't I try removing it? It was always all the way in. Yes, there is indeed a spring on it.

Mega, I don't quite understand what you are saying. If the screw is all the way in, the slide is held at highest point the pin can hold, right? How can unscrewing it do anything except drop the slide? The pin is fixed length (one solid piece of brass). Thing is that it doesn't seem to change the slide height.

[Thumper]

Originally Posted by Bruces

Any chance your throttle cable is adjusted too short ?

Thanks... I just checked and in fact there is about 1/3 inch slack before the cable even moves the slide! Removing the adjustment screw did not change that, so the slide appears to be bottomed out WITH or WITHOUT the adjustment screw all the way in!

I need to pull the slide and verify that the place where the pin engages is not damaged. The pin does not seem to do anything to slide height.

I think MegaDan is implying that the screw all the way tightened has not adjustment in that position, which is true! But the idle is NOT elevated at all. On my "Youall" PZ30 carb, I can set the slide height screw to 1500rpm idle! Maybe more. I always twist the throttle when I screw it in, so it isn't grinding the beveled surface it pushes. Then I let it go and back off the screw to desired setting.

[Megadan]

Originally Posted by Thumper

Mega, I don't quite understand what you are saying. If the screw is all the way in, the slide is held at highest point the pin can hold, right? How can unscrewing it do anything except drop the slide? The pin is fixed length (one solid piece of brass). Thing is that it doesn't seem to change the slide height.

Attachment 26774

The slide is raised and lowered by the pin. There are two types. one where the pin has an offset to it and is smaller in diameter than the threads. This means its acts like a cam on the slide, manually raising and lowering it. The other type, which is what appears to be your style, is just a rounded end that "ramps" the slide up and down. Move it in and it lifts the slide with the radius of the rounded end, move it out and it lowers it. With it being screwed all the way in, it's just riding the slide as high as it can go all the time.

In either instance, backing it out still resolves the issue. For the first type I mentioned, since the screw was bottomed out and not allowing for any adjustment, it would move the offset pin back in place, but with a full rotation or two to work with, thus giving it full up and down movement. In the latter, as you discovered with yours, it puts it on the end of the pins rounded edge, putting you back into the area where it actually can affect the slide position and change the idle speed.

[Thumper]

Originally Posted by Megadan

The slide is raised and lowered by the pin. There are two types. one where the pin has an offset to it and is smaller in diameter than the threads. This means its acts like a cam on the slide, manually raising and lowering it. The other type, which is what appears to be your style, is just a rounded end that "ramps" the slide up and down. Move it in and it lifts the slide with the radius of the rounded end, move it out and it lowers it. With it being screwed all the way in, it's just riding the slide as high as it can go all the time.

...

Your description matches my assumption on how it works. Yes, all the way tight should adjust the slide to highest adjustment/position possible-highest idle speed. But the thing is, the idle is like 700-800rpm, not elevated at all! It doesn't seem to lift the slide. It is freezing cold in the garage this morning. I will take another look this afternoon when it is at least in the 50s!

By contrast, on my storm, I can set the idle to practically 2000 rpm with this slide position adjuster.

[JerryHawk250]

Open the throttle a little before turning that screw in. It might be hitting the side of the slide instead of lifting the slide.

[Thumper]

I always twist the throttle a bit and hold it when I tighten the screw (as you suggest), because I don't want it to damaged the slide. Then I drop it back down (unscrew it) to make a final adjustment. I just wonder if it was already damaged when we got the bike.

It is a knurled head on the Storm, so I can easily adjust it anytime. I might file some ridges in this one so it can be easily turned by hand.

this TBR7 has only about 1 mile on it, just up and down the street test drive. We did change the oil, rejet (both jets), shimmed the needle ~1mm, and adjust the valves before starting it. And it starts right up.

[Thumper]

I rolled it out and fired it up. The idle screw has no effect when it is cold, no matter what the choke position is. It just doesn't lift the slide far enough.

After it warms up, it works but can only elevate the idle to about 1000 rpm. I think it needs to be a mm or 2 longer to be useful.

I use that adjustment on my Storm all the time when it is cold. It can lift the slide a lot more, I guess.

[JerryHawk250]

Did you try it without the spring just to see if it will work? You might be able to trim the spring if it does to allow more adjustment turning it in.

[Thumper]

Originally Posted by JerryHawk250

Did you try it without the spring just to see if it will work? You might be able to trim the spring if it does to allow more adjustment turning it in.

The adjustment screw can be tightened all the way (as it is in the first photo above) with the spring in place, so it can't be any farther in, even without the spring.
Maybe the bevel on the slide that the pin sits on is not in the right position for this carb. A longer adjustment screw might be the answer.

This may be an example of mismatched generic parts that we see so often on these bikes, like my kick started on the storm that bruised my calf!

At least it works marginally once warm. We can live with it for now.

[JerryHawk250]

Originally Posted by Thumper

The adjustment screw can be tightened all the way (as it is in the first photo above) with the spring in place, so it can't be any farther in, even without the spring.
Maybe the bevel on the slide that the pin sits on is not in the right position for this carb. A longer adjustment screw might be the answer.

This may be an example of mismatched generic parts that we see so often on these bikes, like my kick started on the storm that bruised my calf!

At least it works marginally once warm. We can live with it for now.

Oh, I see what you are talking about now. I just noticed the screw head was hitting. Try filing or grinding down the case some so it can go in farther. At this point it would hurt to try.

[Thumper]

Originally Posted by JerryHawk250

Oh, I see what you are talking about now. I just noticed the screw head was hitting. Try filing or grinding down the case some so it can go in farther. At this point it would hurt to try.

A replacement carb cost under $40, and I think I can shave a mm or 2 off the body without destroying it. That would allow the screw to get deeper.

It is not that bad, and actually fine once warmed up, but I may try it. Good idea.