[davidperagallo]

After completely rebuilding the carbs on my 1980 CM400E I am concerned about the looseness of the mixture screw, as seen in the attached video. I tried stretching out the spring to increase pressure on the threads, but it didn’t make a noticeable difference. I thought of putting some low-hold loctite on the threads, but I’m not sure if that’s a good idea considering future adjustability. Thoughts?

https://youtu.be/em3lUyKhi_Q


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[Old Okie]

Do you have the "O" ring and washer on the screw???
The spring goes on first, then the washer and finally the "O" ring.
The "O" ring will be in the bottom of the hole with the washer on top of it,
then the spring and then the screw.

 

[davidperagallo]

Do you have the "O" ring and washer on the screw???
The spring goes on first, then the washer and finally the "O" ring.
The "O" ring will be in the bottom of the hole with the washer on top of it,
then the spring and then the screw.

Yes, I have them both (right and left) assembled in that order, but the both wobble, as in the video.


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[longdistancerider]

Possibly the wrong screw although the cap indicated it's right. Threads worn on the body or the screw would be the other things causing it.

 

[davidperagallo]

Possibly the wrong screw although the cap indicated it's right. Threads worn on the body or the screw would be the other things causing it.

I don’t recall how they felt at disassembly, but I wouldn’t have any reason to believe that they are anything but stock. The screw threads are clean and defined, but I’d have to take the carbs back off to check the body threads.


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[davidperagallo]

A little Teflon tape on the threads seemed to take care of most of the wobble.

I’m still surprised to see how thread is exposed even when the screws are adjusted all the way in. At 2 turns out (CM400 factory settings) there remains only 1-1/2 to 2 turns until the screw falls out. Is this correct?


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[longdistancerider]

No, there should be more threads holding the screw at 1.5 turn out. I suspect that the old O-ring is still in the body.
On a side note the tab on the float bowl can be cut off to allow full turn adjustments.

 

[davidperagallo]

No, there should be more threads holding the screw at 1.5 turn out. I suspect that the old O-ring is still in the body.
On a side note the tab on the float bowl can be cut off to allow full turn adjustments.

I am 100% sure the old o-rings are out, and the screw doesn’t bottom out. In fact, the tab stops it, then it’s backed out 2 turns, which is where you see it pictured. The threads on the carb body don’t appear to be stripped, but the screws turn loosely as you can see in the “wobble video”. I’ll take a photo of the screws and post it here. Maybe someone will be able to know if they are correct, aftermarket or just wrong...


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[davidperagallo]

Note:
The threads without Teflon rape indicate how shallow the screw is threading.

Sad Note:
In taking the screws out, one of the o-rings has fallen into the abyss of my basement floor.


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[longdistancerider]

I just checked 2 junk carbs with the same screw. Both of them allow the screw to turn in almost to where the cap bottoms out on the carb body. Something is preventing your screws from going all the way in. I did try with the screw only @2 turns in and it was wobbly there.

 

[davidperagallo]

I just checked 2 junk carbs with the same screw. Both of them allow the screw to turn in almost to where the cap bottoms out on the carb body. Something is preventing your screws from going all the way in. I did try with the screw only @2 turns in and it was wobbly there.

Thanks for checking. Did the screw threads descend completely into the body before hitting the tab? Does my screw correspond visually to yours?

I think, especially in light of the now missing o-ring, that I might purchase a new screw set or two.


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[longdistancerider]

My screws look identical to yours. Your wording makes it sound like you're trying to install the screws with the float bowls in place and both tabs, screw and float bowl, intact. If so then the float bowl has to be removed to screw it in fully or one of those tabs has to be cut off. I cut the float bowl tab so that I have a visual reference of exactly where the screws are adjusted to.

 

[davidperagallo]

I will could cut the tabs, which would no doubt allow me to bury the screws, but if I have to back them out to factory position according to where the tabs currently make contact. They’ll still be loose. That is to say, there is nothin in the passage pushing back on the screw; it is simply “tabbing out, not allowing me to turn it any further.

Is there a source for purchasing just an o-ring of that size to replace the one that is now lost?


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[longdistancerider]

The tabs are adjustment limiters dictated by the EPA to prevent "tampering". That's their only purpose in live. The factory setting you're referring to is actually only a starting point is setting mixture after the bikes have been in service for a few years. Cut one of the 2 tabs off, run the screw in until it stops (gently) and then back it out @2 turns. There should be plenty of threads left in the body securing the screw against the spring now.

 

[davidperagallo]

The tabs are adjustment limiters dictated by the EPA to prevent "tampering". That's their only purpose in live. The factory setting you're referring to is actually only a starting point is setting mixture after the bikes have been in service for a few years. Cut one of the 2 tabs off, run the screw in until it stops (gently) and then back it out @2 turns. There should be plenty of threads left in the body securing the screw against the spring now.

I’ll do this.

I don’t have any way of measuring the o-ring is that documented anywhere? I hate to spend $15 on a set when I only need an o-ring.


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[longdistancerider]

All I've got are old dried out crushed ones so that's not reliable. Look in the Project logs and see if anyone is doing carbs or maybe has theirs off doing something

 

[80cb400t]

I ordered like 50 of those size for 4$ or so on ebay. I got the sizes off of the site below, I can't compare to the Honda kit but they seem to fit quite tightly onto the screw. I don't want to give you a wrong size though, if you can find another source for that size or if LDR can confirm I'm not 100% on it.
http://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revG.pdf

I could send you a pair while I'm in the states tomorrow picking stuff up for whatever it costs to mail a letter to NH from WA.

 

[davidperagallo]

I could send you a pair while I'm in the states tomorrow picking stuff up for whatever it costs to mail a letter to NH from WA.

Geesh, for $4.25, I get 100 ct. of 003 Nitrile O-rings on Amazon! I that might even be less than postage from you. I am grateful for your offer and thank you for taking the time to write this.

*If you’re reading this and find yourself in need of said o-ring, please feel free to PM me. I’ll have about 90 that I won’t possibly need.*


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[80cb400t]

All i know is WA to WA costs 50 cents per letter, no idea about cross country. Either way no worries and you're welcome. I can confirm that my bike doesn't run any differently after installing them (no difference since the ones I replaced were still pretty flexible).

If anyone in canada or washington needs any let me know

 

[longdistancerider]

I'll keep you in mind for those.
US postage is the same regardless of which state it leaves and arrives.