Topic: 1975 CB550 carb lean problem

[dilbone]

Just remember that if you change one thing it will affect something else. Everything has to be taken together when you are dealing with carbs. The needle comes into play from about 1/4 throttle & up. You could try going up one main jet size to see if that helps, rather than moving the clip position. Bad carb boots can cause your type of problem.

If you are running with no air filter or the stock air filter housing loose, it will affect the running of the bike and make it run lean.  Also other than stock exhaust will affect the driveability.

Engines are much more senstive on the intake side than the exhaust side.

Check for vaccum leaks in & around the carbs.  Use an unlit propane bottle & pass it around the carbs.  If idle speeds up you've found your leak.

I've checked for vacuum leaks with starter fluid all over the place and have found nothing.  Changing the clip position is kinda my last resort here before I take it in.
I may be way off on this, but if I change the clip one position, wouldn't that kinda give me maybe a 1/2 jet size difference once above 1/4 throttle?

Above 1/4 throttle is exactly where my problem is, changing the clip one position seems less drastic than changing the main jets just yet.
The numbers stamped on the main jet is 68 and on the slow jet is 38...I assume that is stock.

[mlinder]

Just remember that if you change one thing it will affect something else. Everything has to be taken together when you are dealing with carbs. The needle comes into play from about 1/4 throttle & up. You could try going up one main jet size to see if that helps, rather than moving the clip position. Bad carb boots can cause your type of problem.

If you are running with no air filter or the stock air filter housing loose, it will affect the running of the bike and make it run lean.  Also other than stock exhaust will affect the driveability.

Engines are much more senstive on the intake side than the exhaust side.

Check for vaccum leaks in & around the carbs.  Use an unlit propane bottle & pass it around the carbs.  If idle speeds up you've found your leak.

I've checked for vacuum leaks with starter fluid all over the place and have found nothing.  Changing the clip position is kinda my last resort here before I take it in.
I may be way off on this, but if I change the clip one position, wouldn't that kinda give me maybe a 1/2 jet size difference once above 1/4 throttle?

Above 1/4 throttle is exactly where my problem is, changing the clip one position seems less drastic than changing the main jets just yet.
The numbers stamped on the main jet is 68 and on the slow jet is 38...I assume that is stock.

68?
Are you sure? Check again.

[dilbone]

Just remember that if you change one thing it will affect something else. Everything has to be taken together when you are dealing with carbs. The needle comes into play from about 1/4 throttle & up. You could try going up one main jet size to see if that helps, rather than moving the clip position. Bad carb boots can cause your type of problem.

If you are running with no air filter or the stock air filter housing loose, it will affect the running of the bike and make it run lean.  Also other than stock exhaust will affect the driveability.

Engines are much more senstive on the intake side than the exhaust side.

Check for vaccum leaks in & around the carbs.  Use an unlit propane bottle & pass it around the carbs.  If idle speeds up you've found your leak.

I've checked for vacuum leaks with starter fluid all over the place and have found nothing.  Changing the clip position is kinda my last resort here before I take it in.
I may be way off on this, but if I change the clip one position, wouldn't that kinda give me maybe a 1/2 jet size difference once above 1/4 throttle?

Above 1/4 throttle is exactly where my problem is, changing the clip one position seems less drastic than changing the main jets just yet.
The numbers stamped on the main jet is 68 and on the slow jet is 38...I assume that is stock.

68?
Are you sure? Check again.

yes, it is a 68 and after I typed that in I did a search and 98 seems to be typical...I just went out again and triple checked both and yes it is a 68 main and a 38 slow

Is it even possible that these were screwed up at the factory and someone couldnt' read?  That would explain why it's always been lean...
What do I do now?

[mlinder]

Notice the 68 and 98 look very similar. I think stock was 95 though....

If you do, in fact, have 68's in there, purchase and install 95's, put the clip back in stock position on the needle, and have fun riding.

[Cvillechopper]

Didn't the 022A carbs need a 100 main and 40 slow?

http://www.motorcycleproject.com/motorcycle/text/specs.html

http://forums.sohc4.net/index.php?action=dlattach;topic=5410.0;attach=3002;image

[dilbone]

Didn't the 022A carbs need a 100 main and 40 slow?

http://www.motorcycleproject.com/motorcycle/text/specs.html

http://forums.sohc4.net/index.php?action=dlattach;topic=5410.0;attach=3002;image

Not sure exactly what I've got, the air box says it's a CB550F but the carbs say they're 022A which doesn't show on a 1975 CB550F, do I go with the bike model info or the carb info?

At this point whether it's a 98 or a 100 I'm not sure it matters as long as the 68 gets replaced with something close... since the slow has a 38 I'll assume that the 68 in the main was supposed to be a 98 instead.

[Cvillechopper]

You want to start with the correct set up for the carb then make adjustments as necessary to the engine.  I'm running a set of 500 carbs on my 550 now and am going through the same process.  Fun isn't it???

[mlinder]

I could go look it up, I guess, but I though 500 carbs were 100/40 and 550's were 95/38. Or maybe it was 100/42 and 95/40.
I don't remember.

In any case, dilbone, if those are in fact 68's (actually, 67.5's), that's your problem. Grab some 98's or 95's or 100's or wtf ever is stock for those carbs and yer prolly fixed.

[dilbone]

what's the deal with "primary" and "secondary" main jets for these keihin carbs?

Trying to figure out what to order.

[mlinder]

Primary jets is what you need.

[dilbone]

I just looked it up and it says "primary" are 9.4mm long and 4.95mm diameter, they only go up to size #92

"Secondary" are 9.6mm long and 6mm diameter...they go from #68 all the way up to #150 in size...

these are definitely 6mm diameter so I guess the "secondary" main is what fits this bike...why does all this have to be so complicated

[mlinder]

I just looked it up and it says "primary" are 9.4mm long and 4.95mm diameter, they only go up to size #92

"Secondary" are 9.6mm long and 6mm diameter...they go from #68 all the way up to #150 in size...

these are definitely 6mm diameter so I guess the "secondary" main is what fits this bike...why does all this have to be so complicated

Where are you looking this up?

[dilbone]

Where are you looking this up?

I can't find the first place I was looking but found it here too

It's at the bottom of the page

[dilbone]

found a set of 98's for $14 shipped on ebay, I hope to have good news to report by next week

Thanks again to all who have helped me out on this thread, looks like I found a new place to hang out online.

Chris Dilbone

[mlinder]

I can't remember what your carbs are, for the 75, PD's or whatever, but what does your main jet look like?

/edit: nevermind, looks like you'll be fine.

[Aaron Richard]

I know when my bike was stock and I rebuilt my carbs, I installed

#100main jets and #38 idle jets and #3rd notch on needle.

now that I have pod filters, I run

#110 mainjets and #40 idle jets 4th notch on needle.

[Aaron Richard]

found a set of 98's for $14 shipped on ebay, I hope to have good news to report by next week

Thanks again to all who have helped me out on this thread, looks like I found a new place to hang out online.

Chris Dilbone

Make sure you ordered the "press in type"main jets, not the "screw in type". just to double check

[dilbone]

Make sure you ordered the "press in type"main jets, not the "screw in type". just to double check

yeah, he had a nice close up pic of them in the auction, as long as the auction is correct and they are 98's then I should be good.  How on earth a set of 68's got put into this bike is beyond me.

The needles were at the 4th notch so with 98's I should be good with the stock airbox.  Anything will be better than 68's...like trying to drain a swimming pool with a coffee straw...

[mlinder]

Do the '75's use the press in main jets?

[dilbone]

Do the '75's use the press in main jets?

yes, they do...this one does anyway

[Aaron Richard]

yes they do, and they can be a bit of a pain to find in different sizes.. A couple places on ebay sell them. I buy them from this guy in canada that's pretty good. sci consolidated or something like that. about $20 for 4 includes shipping.

[mlinder]

Ah, ok. Like I said, I don't play with those carbs much.

[Aaron Richard]

I do nothing but play with the little buggers. they can be finiky once you start changing air filters and such.

[Aaron Richard]

you may want to buy a set of new o rings that go between the intake and the engine block too. If you suck air in there, it will throw the carbs off as well. I just changed mine and it helped. you can go to any parts store and ask for o rings 1-1/4" by 1/8" thick. You might be able to find them on ebay also. the bike uses the same o rings for the tappet covers as well.

[dilbone]

you may want to buy a set of new o rings that go between the intake and the engine block too. If you suck air in there, it will throw the carbs off as well. I just changed mine and it helped. you can go to any parts store and ask for o rings 1-1/4" by 1/8" thick. You might be able to find them on ebay also. the bike uses the same o rings for the tappet covers as well.

That's good to know, thanks for the heads up I'll check into it.