HondaCB650

This is a companion post to "carb woes continue 1981". I have suspected accelerator pump because hard throttle twists produce much hesitation. This may be related to the problem discussed in the other post, but I got a rebuild kit anyway.

Now I have 4 interesting questions:
1. where does the spring go? Clymer manual shows spring between cap and diaphragm. When I disassembled pump from #2 carb, cover came off just fine and spring must have jumped out because I found it laying on table a few inches from where I was working. I then cleaned passages in cover and decided to remove bowl and clean carb body passages, just those you can see from underneath.

I then installed new accordion-shaped boot in carb body, then assembled diaphragm and cover onto bowl, with new spring between cover and diaphragm, being careful to get the diaphragm oriented correctly. I then placed bowl over carb bottom, worked pump rod carefully thru boot, and then discovered that pump rod was tight against throttle tab on carb body.

2. If I have spring in right place, is it correct that I have to press the bowl down over carb bottom against pump spring pressure?

3. since rod is tight against tab with throttle closed, how does one adjust gap?

4. what is gap supposed to be? The Clymer manual says go to Table 1 but Table 1 does not have that measurement.

Any help here would be appreciated. Thanks.

Photos are worth 1000 words. Maybe someone out there can tell me if there is a problem here. Pump spring is between cap and diaphragm, thus putting downward pressure on diaphragm. To tighten down float bowl, I would have to push it against the spring pressure.

Obviously something is wrong with throttle mechanism. Can anyone tell me what needs to be done and what the gap between pump rod and tab should be? Also, shouldn't there be an adjustment (other than bending tab) in throttle mechanism that will set the further away from the fully entended rod end?

The rod will work against the spring when the throttle is twisted. So permanent spring load on the float bowl seems not suspicious.
The rod should move (and press on the diaphragm) when you twist the throttle, does it? If it is already completely pressed in and does nothing more when you twist the throttle, then something is wrong. I could imagine some spring in the throttle mechanism is missing or even the whole thing was assembled in a wrong way.
It think the accelerator pump should work in principle even without correct gaps as long as things look not heavily bended. Bending is only fine adjustment, at least for the piston carbs. But if the rod should be fully entered already now, don't try to free it by bending something but rather check for possible assembly errors. You never know what was done in addition to the choke cam removal.
But again, I don't have CV carbs to verify.

Thanks, Volker. I just needed someone's assurance that the diaphragm won't tear or weaken when I screw the bowl down onto the carb body. The throttle linkage, connections, springs, etc. all look ok. As soon as I get the bowl tightened down, I'll check if pump rod moves when throttle is opened. Carbs are not on bike now, but that can be done by hand. Will get back to you on the next installment of this frustrating saga later today.

With bowl tightened down, the accelerator pump rod moves only 3/64ths of an inch (1.194mm) when the throttle is opened all the way. I don't think that is correct but need someone who knows CVs to help out on this. Volker, can you find out what that measurement should be, and how to correct it? As stated earlier, the linkages look ok, but perhaps I'm missing something. Thanks.

PS -- also see "carb woes continue 1981" for latest on a test drive.

ok the spring goes on top of the diafram you then put the cover on after that so it would be
in order cover, spring , diaphragm with needle, then rubber boot it is called a gasket in the book it goes in side of the bottom hole of the housing like a rubber gasket the rest of the gasket sticks toward the carborator where the accelerator pump assembly rod hits the bkt on the linkage .
the book says to make sure the 2 tabs on the diaphragm align with the notches on the float bowl.

You said you had a clymer manual ? a pic of it is on page 194 and 195
If you need me to I will upload the pages for you my book says only to bend the linkage bkt

I looked in my book And setting was no where to be found
it is 0.4-0.6mm or 0.015-0.023 on the 1980 model

all I know for sure is mine is set to around .060mm
But mine may not be right It should not touch tell you start to give it gas
that is how it works as the throttle is turned the rod is pushed and causes extra fuel to enter the carbs to keep the bike from dying .

are you sure the lengths of the old rod and new rod are the same length
compare the old one next to the new one you may not have the right part
well that is my 1/2 cent worth hope some how it helped you. if not Sorry

You know, arcangel, if I had a brain I'd be dangerous. Shoulda thought of measuring that rod before installing new one. Since I have to take carbs out again to put airbox back in (see my post "carb woes continue for '81"), I'll do just that. It only takes a minute to remove the diaphragm. If new one is too long I'll grind it down.

I did assemble pump exactly as shown on pages 194 & 195, and the 2 tabs are aligned properly. 1980 model did not have CV carbs but clearances should be close. I'll just see that there's some gap in mine. .060 sounds about right.

Will get back to you tomorrow.

I don't beleave mine is set purfect Mine has a slight heasitation when cold
but gets better after warm up I think the .015- .023 is most likely correct
this gives a small amount of play so you can adjust the idle and linkages a small amount with out the acc pump kicking in.

So you think .060 is too much. Ok. I'll start with about .030 to leave room for other adjustments, and once those are ok, I'll cut back on the pump clearance so the carbs get a good shot when I twist. Now I have the #1 carb thing to deal with. That's most important right now. Pump can wait.

I looked at mine and there is very little clearance. maybe.010 my pumps always worked so never took it apart.

Thanks CB 650. Now that all of you have confirmed such close gaps, it would seem wise to just do the .010 or .015 gap now. Then I don't have to take those doggone carbs off again to adjust pump after synching. It takes young brains to help out this old one. Thanks to all you guys, Volker, arcangel, CB650. m

Yeeeeeeee haw! I never had a air cooled 4-cyl Honda before, and now I am not sure I'd ever want to get rid of this one. All the frustration is over. The problem with #1 carb? When I rebuilt carbs, I forgot to tighten #1's main air jet, the one that the slide needle goes into. Doggone thing was loose in the carb body. Luckily it did not fall out of the post it sits in. Probably couldn't have because the bowl likely held it in place.

So I tightened it up, put carbs back in, started her up, warmed it, took a cold ride on a damp day and it ran so great and sounded so fabulous I didn't want to get off it, even thoough I was freezing. The sound at 8K rpm is wonderful, and acceleration was great. And for whatever reason, there is no lack of fuel in #1's bowl anymore. Go figure.

Thanks for all the help guys. I learned something else: tighten everything.

As to the young brains mine is more like middle aged 44
wish it were younger maybe it wouldn't hurt so much when I think.
Like my dad used to say if it hurts to think
quit thinking and it will quit hurting .

ok so maybe that was not quit right but it applies better here.
it was
If it hurts to want quit wanting and it will quit hurting.
and if it don't hurt to want keep on wanting.
my dads answer to many things.
now that is old wisdom. I guess he is around 82 now
now I am rambling so
congrats on the fixed bike.

Thanks, arc. We'll let this thank you go for both of my posts, since you and Volker were a big part of both.

I can't remember where i found the info, but the clearance per honda specs is touching to 0.003 clearance for the accelerator rod to the lever that pushes it down, when the floatbowl is tightened.




l8r