Topic: CB550 carb has throttle return issues

[dennco2]

Hi,  I am attempting to restore a 550F that has been sitting around for many years. The throttle cable linkage was locked up and now freed up ... but the throttle return spring on the carb seems to be too strong and requires great effort to twist the throttle grip for power. It seems the throttle twisting effort should be 1/4 of what it is!

Then I removed the 4 carbs from the common mounting plate .... so I could attach new fuel lines to the nipples. When remounting the plate, the return spring and a pin popped off inadvertently and now I am not sure how it reattaches. Does the pivot pin attach between carbs 2 and 3 inside an indent in the casting?

Is there a way to lighten up the return to idle spring by stretching it a bit? Thanks for any help on this.

[Scott S]

Did you replace the throttle cables? Honda cables weren't really designed to be lubed.

 There's also a sort of throttle lock on the grip. Is there a knob on the underside of the RH control? It's not screwed in onto the throttle tube, is it?

[BomberMann650]

Remember, you are opening four carbs.

Not exactly a throttle body butterfly now.

[harisuluv]

There's a dowel about half an inch long that fits between the 2&3 bodies.  One side goes there, the other goes on the linkage.  If you don't remember removing it, it probably is on your garage floor somewhere.

With that being said, it sounds like you have a bunch of other issues.  You should do some research first, cause it's easy to damage your carbs if you don't know what you're doing.

[dennco2]

A previous owner has changed out the handle bar to a straight Cafe racer type. Also, it only has one throttle cable ... not 2. He must have changed out the throttle grip too .... if 2 cables are stock.

I have the steel pin for the return throttle spring and will reinstall it today.

The whole bike was in bad shape when I got it. The front brake system was locked up ... so I had to buy a complete rebuilt system on Ebay. Bike price $20  ..... brake complete rebuilt system  $250 .... battery $35 .... fuel line $10. I had it running 2 days ago ... but not making good power. One possible problem was definitely a kink in one the fuel lines. Inside of the carb bowls looked surprising good and all floats and needles working as it should. Didn't go any further than the bottom end of carbs ..... so far.

[riverfever]

This was my first motorcycle so I wasn't sure how the throttle was supposed to feel but it was also very difficult to keep open because the spring was quite strong. As harisuluv hinted at, you want to make sure that several things are correct on your bike. If the cables were that bound up then it would probably be wise to replace with new. That helped with mine. Then make sure you have the cables routed correctly. Even after this, I still felt like it took a lot of effort to keep that throttle open. I searched around and finally found a spring that would do the job. I must have tried half a dozen different ones. You want one that's just right because it does need to be strong enough to close those carbs quickly. I've only ridden mine on a few short rides since installing the new spring (just to do plug chops and tune) but it's going to be a lot nicer than the stock one. I found mine at an Ace Hardware in the "It's OK You're Still a Man" section.

[dennco2]

On my carb set,  the steel pin inserts to both carb 2 and 3 to provide the bottom mount for the idle return spring.
The return spring is 2.5 " long and stretches to about 3.5" to hold the throttle at idle position. That is a lot of tension on the spring .... even at idle position. I now wonder if this is correct spring for this carb set?

I took a picture of it.  Can someone comment on if this spring is the correct one .... or how to find a longer one with LESS tension?  Thanks.

[riverfever]

That's the right spring dude. If you want a lighter spring, take that one and start hitting the spring section of hardware stores and find one. The one I ended up using is 3.5" long from hook to hook. However, I had to use one that had loops on each end. I snipped them out how I wanted them so they would still hook on like the stock spring.

[Scott S]

 I don't think you need to be thinking about replacing the spring. You have plenty of leverage with the throttle. Make sure your throttle or cable isn't binding. That's where my money's at.
 Either that or you have something assembled incorrectly after removing them from the mounting plate.
 

[dennco2]

Thanks for the tip on Ace hardware springs there Riverfever! 

I bought 2 for testing and the 2nd one worked great with a couple of bending mods. Half the tension at full throttle .... but snaps back to idle quickly and securely. The spring only cost $1.59  and I will post a pic for others if they are interested. It can easily stretch farther than it needs to on the carb.

The throttle action on the carb and the cable all functions good with no extra friction. I'll mount the carbs tomorrow on the bike and hope all goes well.

[Scott S]

 You were talking about how hard it is to open the slides with the carbs off the bike? Then, yes....it's a very stiff spring...but only to do with your fingers.
 When installed, with a good cable and non-binding throttle, it isn't NEARLY as hard as when trying to do it by hand.

[riverfever]

Scott I still think he's talking about the difficulty when ON the bike. Mine was incredibly hard to operate and that was after (because many told me the same thing) a new throttle tube, replacing the single cable with a double, routing the cables correctly, adjusting them correctly, etc. My hand would cramp so badly during a ride of 20 miles. I do think it's just how these older bikes are (significantly different than a modern bike) but having never owned one before, I just wasn't used to it.

[blackbike]

my '74 CB750 is pretty heavy to operate, (single or double cable makes no difference) but keeping the cable and all the exterior moving parts well lubed makes quite a difference....it's all in the return spring....

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[dennco2]

The Ace hardware return spring is slightly too weak to snap the throttle back to the idle stop ..... after connecting up the cable and twist throttle. I am still happy though as all I have to do is roll off the power with my hand and idle speed is easily reached. Beats straining my hand to roll on the throttle to get to and maintain the power.

I think part of the grip twisting strain on my hands may be due to the Cafe racing  or drag bars on this bike. I think the throttle cable had to be routed differently as a result. Any way, the throttle grip feels quite nice now and I am happy.

[riverfever]

Man that throttle needs to close on it's own for safety. I helped a guy in the next town up the mountain from me vacuum sync his carbs yesterday (71 500) and he's using the stock return spring with a push/pull, cables routed the same way and it felt wonderful. Not sure why my spring is so dang strong. Let me look in my boxes of crap and see if I have another one of the springs I used. If I do I'll send it to you. The ACE I go to is a bit far from my house (I'm a school teacher and off for the summer so I don't go down to Colorado Springs all that much) but if I can't find one in the garage I'll pick one up next time I'm down there (likely this weekend while grabbling dinner or shopping for fur coats).

[dennco2]

The perfect spring would have slightly more tension that what is in there now.  It almost returns to idle on it's own and I help it along with the slightest effort.

Does the carb set have to come off to change out the return to idle spring?   

[alacrity]

I followed Hondaman's suggestion here.  See how tightly wound the stock spring is?  It just needs to be a little less tightly wound, and you adjust that one "wind" at a time till it's good.  Remove it. Jam a flat blade screwdriver in the middle of it and twist/ pry apart the spiral there. Create a gap. (Maybe 1/8").  Reinstall, test.  Do it again on the next wind if necessary. Etc.  Mine took only one step of loosening to be great.  Of course this assumes cables are excellent and routed correctly, And there are no other mechanical problems with the carbs blocking or interfering with  throttle function.

[dennco2]

Update on my throttle return/ carb spring issues.

I added a thick foam rubber Shinhopples throttle grip COVER ... to increase the grip diameter and make it easier and smoother to rotate the throttle or even just holding it in a steady throttle position. The grip cover slid on the grip quite easily with a dish washing wet solution and later I had to use a type of contact cement to secure the cover on well for NO slippage.

The other thing I did was slightly relocate the throttle housing on the handlebar inwards .... because it was slightly rubbing on the outside mounted end bar mirror and causing extra rotating friction. Now the Ace coil spring on the carb snaps back to idle quite nicely .... and I now have acceptable rider comfort working and holding the throttle where I want it while riding. The original spring and grip was killing my hand and wrist!

[BomberMann650]

If it works it works.