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Old 06-23-2013, 08:49 AM   #1
Dr. Beard OP
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Carb Running Rich, Odd Case

Hey Guys,

I've put many thousands of miles on my '73.5 R75/5 over the last few years and I recently decided to rebuild the carbs (again, I did so when I got the bike 3yrs ago) to attend to an occasional hunting/high idle and the fact that the right side was running a bit rich.

Both carbs were fully disassembled, dipped, and then properly probed with wires & blown out with air. All rubber gaskets etc replaced. Then both were reassembled, reinstalled and I went for a ride. The left side was now a touch lean & the right was now very rich. So I then went about tuning & balancing from scratch. Here a very brief (ie: abridged/undetailed) breakdown of the method I used from my Clymer: (Both slide needles set at factory spec of 3 clicks in.)

-Remove throttle cable.
-Set throttle screw to just touch the butterfly, turn in 1 additional turn.
-Set idle air screw out 1 turn.
-Run bike on 1 cylinder and adjust idle air screw until that cyl idles @ 1000rpms.
-Adjust both idle stop screw equally until bike idles @800-900rpms.

This worked perfectly on the left side (which has since run a perfect tan color).

On the right side however I had a bit of a problem. The right side wouldn't idle at the base settings. I could only get it to idle by either turning the idle air screw almost all the way in or turning the idle stop screw in 1 full turn further in than the left. Even then, this side still is running very rich (would foul out a plug in under a 100mi). (Not to mention that with idle screws off from left to right it felt very unbalanced.)

Does anyone have ANY idea why I can't seem to tune the right side in? I pulled the carb back off & went through every bit of it again and everything looks perfect. I'm at a loss.

(EDIT: I also checked the valves & they were right where they were supposed to be.)
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1972 R75/5 x2, one hacked
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1970-74 CB/CL 350/360/450's. Too many to count.
1974 XL250 Street Tracker
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Old 06-23-2013, 09:47 AM   #2
SOLO LOBO
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Quote:
Originally Posted by Dr. Beard View Post
On the right side however I had a bit of a problem. The right side wouldn't idle at the base settings. I could only get it to idle by either turning the idle air screw almost all the way in or turning the idle stop screw in 1 full turn further in than the left.
Have you checked for sticking chokes and proper free play on the throttle and choke cables?


My G/S just had a similar issue, and I found the mixture wasn't effecting the idle speed on one side because I had the idle screw speed unbalanced between the carbs, meaning the left idle speed was set high much higher than the right.

I'd start over on the carb baseline, meaning setting the idle screws to zero and turning in a few turns to ensure both carbs are actually balanced.
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your bike is suitably dirty. Well done.

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Old 06-23-2013, 10:00 AM   #3
StmbtDave
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Enricher (choke) installed properly?
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Old 06-23-2013, 10:23 AM   #4
Dr. Beard OP
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Quote:
Have you checked for sticking chokes and proper free play on the throttle and choke cables?
Cables are fine & both chokes are set up/working properly. Choke unit on the side that's running rich is actually a new unit; the old one had a damaged shaft from being over tightened by the PO. Choke unit has new gasket on it too.

I have started over & re-set baseline 3 times in an effort to try to bring human (me) error out of the equation.

Is it possible that I have a weak coil and that's presenting itself as a rich condition on that side? That's a total shot in the dark, but I'm out of easy guesses...
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1972 R75/5 x2, one hacked
1973 R75/5 Toaster LWB (Keeper)
1970-74 CB/CL 350/360/450's. Too many to count.
1974 XL250 Street Tracker
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Old 06-23-2013, 10:37 AM   #5
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Doubtful on the plugs, to test just switch the plug wires side to side
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Originally Posted by Stagehand
your bike is suitably dirty. Well done.
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Old 06-23-2013, 10:50 AM   #6
disston
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Sounds like a carb problem so yes check the wires, plug caps and swap coils if still messing with it.

On the Bings in general the enrichner is often the culprit. On the /5's the enrichner can be even more troublesome but the extra hassle is for the earliest Bings with numbers on them that end in 3 & 4. Your carbs should be 64/32/9 & 10.

Did you replace the throttle shaft O-ring? Did you replace enrichner O-ring?
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Old 06-23-2013, 01:26 PM   #7
Tim McKittrick
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Unrelated to your carbs- your hunting occasional high idle may be due to age weakened springs on your mechanical advance mechanism. I had issues with mine until I replaced the springs and polished all of the moving bits and ensured they moved freely and easily.

If the springs are weak or the mechanism is sticky it will sometimes not retract the bob weights, leaving the engine timing advanced, which will raise the idle speed to 1.5-2k rpm.
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Old 06-23-2013, 03:32 PM   #8
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Quote:
Originally Posted by disston View Post
Sounds like a carb problem so yes check the wires, plug caps and swap coils if still messing with it.

On the Bings in general the enrichner is often the culprit. On the /5's the enrichner can be even more troublesome but the extra hassle is for the earliest Bings with numbers on them that end in 3 & 4. Your carbs should be 64/32/9 & 10.

Did you replace the throttle shaft O-ring? Did you replace enrichner O-ring?
Yeah, mine are 64/32/9 & 10. By enricher do you mean choke? Or the idle air screw? I did replace the o-ring on the idle air screw.

And by throttle shaft do you mean the shaft on the butterfly valve?

Thanks!
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1972 R75/5 x2, one hacked
1973 R75/5 Toaster LWB (Keeper)
1970-74 CB/CL 350/360/450's. Too many to count.
1974 XL250 Street Tracker
2002 R1150GS White Whale

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Old 06-23-2013, 03:34 PM   #9
Dr. Beard OP
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Quote:
Originally Posted by Tim McKittrick View Post
Unrelated to your carbs- your hunting occasional high idle may be due to age weakened springs on your mechanical advance mechanism. I had issues with mine until I replaced the springs and polished all of the moving bits and ensured they moved freely and easily.

If the springs are weak or the mechanism is sticky it will sometimes not retract the bob weights, leaving the engine timing advanced, which will raise the idle speed to 1.5-2k rpm.
Yeah, I've lubed & checked the advance mechanism. Even traded it out for advance on the /6 I was restoring. Didn't change anything. I do have s new set of springs for the advance that I haven't put on yet because I got into this carb issue.
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1972 R75/5 x2, one hacked
1973 R75/5 Toaster LWB (Keeper)
1970-74 CB/CL 350/360/450's. Too many to count.
1974 XL250 Street Tracker
2002 R1150GS White Whale
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Old 06-23-2013, 03:55 PM   #10
disston
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Quote:
Originally Posted by Dr. Beard View Post
Yeah, mine are 64/32/9 & 10. By enricher do you mean choke? Or the idle air valve? I did replace the o-ring on the idle air screw.

And by throttle shaft do you mean the shaft on the butterfly valve?

Thanks!
Seems to not always mater but the fact is that these carbs do not have a choke. They have an enrichner. It is the small squarish part on the side, on the inside side, of each carb that has a bowden cable to the lever. You may call it a choke but it does not restrict air flow like a choke. It puts extra gas in the mix and is correctly called an enrichner. You used new gaskets? And it sounds like you put new O-rings in these? There are two things that have to be correct about the enrichners. 1...they are side specific. They must be mounted on the side they belong to. This is verified by the letters L or R on the inside of the brass shaft that the disk is part of. The one with an R goes on the right and the one with an L goes on the left. You can't see these letters with the enrichners mounted. The letters are stamped in the end of the brass shaft on the inside, like I said before. 2...on the outside side of the enrichners, in the brass shaft is stamped a dot. I have a picture of this one;



It can't be seen very easily with the carb mounted but with the carb removed from the bike you can see here a dimple or a dot stamped into the brass shaft. The lever attached to this carb may be a little different than yours. This short lever has a longer side attached to the bowden cable and a shorter side is not being used here (on some models this has a spring on it, ignore it) What's important is the longer part of the lever and the dot is positioned closer to this side of the lever.

If the position of the dot is backwards you get rich mixtures.

We also don't have idle air screws. They are mixture screws and control fuel flow not air. But check the enrichner dot on the side running rich.
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Old 06-24-2013, 09:39 AM   #11
Dr. Beard OP
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Quote:
Originally Posted by disston View Post
Seems to not always mater but the fact is that these carbs do not have a choke. They have an enrichner. It is the small squarish part on the side, on the inside side, of each carb that has a bowden cable to the lever. You may call it a choke but it does not restrict air flow like a choke. It puts extra gas in the mix and is correctly called an enrichner. You used new gaskets? And it sounds like you put new O-rings in these? There are two things that have to be correct about the enrichners. 1...they are side specific. They must be mounted on the side they belong to. This is verified by the letters L or R on the inside of the brass shaft that the disk is part of. The one with an R goes on the right and the one with an L goes on the left. You can't see these letters with the enrichners mounted. The letters are stamped in the end of the brass shaft on the inside, like I said before. 2...on the outside side of the enrichners, in the brass shaft is stamped a dot. I have a picture of this one;

It can't be seen very easily with the carb mounted but with the carb removed from the bike you can see here a dimple or a dot stamped into the brass shaft. The lever attached to this carb may be a little different than yours. This short lever has a longer side attached to the bowden cable and a shorter side is not being used here (on some models this has a spring on it, ignore it) What's important is the longer part of the lever and the dot is positioned closer to this side of the lever.

If the position of the dot is backwards you get rich mixtures.

We also don't have idle air screws. They are mixture screws and control fuel flow not air. But check the enrichner dot on the side running rich.
This is fantastic knowledge. Thanks!

I'll check my "choke" (enricher) on that carb. It's possible that they sent me one for the left side & I didn't notice. Certainly wouldn't be the first time. That would certainly be an easy fix...
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1972 R75/5 x2, one hacked
1973 R75/5 Toaster LWB (Keeper)
1970-74 CB/CL 350/360/450's. Too many to count.
1974 XL250 Street Tracker
2002 R1150GS White Whale

Dr. Beard screwed with this post 06-24-2013 at 09:45 AM
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Old 06-24-2013, 10:49 AM   #12
disston
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Quote:
Originally Posted by Dr. Beard View Post

I'll check my "choke" (enricher) on that carb. It's possible that they sent me one for the left side & I didn't notice. Certainly wouldn't be the first time. That would certainly be an easy fix...
When you rebuilt the carbs all of the enrichner parts were reused I think except for the O-ring if you changed it.



In this diagram, may not be your year/model, but they are similar, the disk #11 is different from side to side. The rest of it can be jumbled up and will work on either side. It is the disk that has a letter on the inside. Either an L or an R.

And the disk can be mounted in two positions, so the dot on the outside.

On some /5 carbs, and I don't know which years so it may be yours, the O-ring #12 is not used. These parts do not have a groove machined for the O-ring. If it looks like the O-ring doesn't belong there it may not. Post a picture if you find this issue.

Other /5 specific issues include a different style of choke cable, the later bikes have a solid cable that works in both directions. the earlier /5 carbs use a braided cable that only pulls and so have to have a spring return the disk to off position.

So far I suspect you have the enrichners on the correct sides but the one on the right is mounted with the dot pointed the wrong way.

Make sure the gaskets are in good condition and use Blue Locktight on the four screws for each enrichner. These screws come loose regularly with out the Locktight but Blue will make them last.

I hope this is it. let us know.
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Old 06-24-2013, 01:07 PM   #13
Bill Harris
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Oops, I thought I answered this this AM. I'll agree with Disston, my first thought is "wrong enrichener disk" (or other enrichener woes). And double-check your float levels.

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Old 06-25-2013, 05:45 PM   #14
Dr. Beard OP
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Finally got a chance to check the enricher on the right side. The shaft is marked in the right place & the disc inside is marked "R" like it should be. As this is a brand new "choke" unit I have to assume that it's ok.

I have not set the float recently so I guess that's the next thing to check unless anyone has any other ideas. Does anyone have a link to the float procedure?

Thanks for all the great info so far!
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1970-74 CB/CL 350/360/450's. Too many to count.
1974 XL250 Street Tracker
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Old 06-25-2013, 05:52 PM   #15
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Well at least you now know how they go together.
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