Topic: long warm up time, lean running, drastic power loss issue

[hman0217]

The following thread is a continuation from here: http://forums.sohc4.net/index.php/topic,164933.0.html

The old thread got too convoluted and the situation has changed since (for example, I switched out the air pods for the stock air box again.

Originally, the main issue was very high revving once the engine got hot (or an extremely low set idle screw that resulted in the throttle having to be feathered for 15+ minutes until hot) and an abysmal fuel economy (down to 12 mpg at the end)

The plugs were black as night when pulled, not after a chop, but after many miles of riding. However, the smell of the exhaust was enough to confirm the mixture was rich.

Those issues WERE fixed after the following were done:

1. timing adjusted
2. valve clearances adjusted
3. boots to and from carbs checked for air leaks
4. carbs synched
5. air screws set

Also, my current setup is stock airbox, 110 main jets, 4-into-2 mac exhaust. all boots to and from carbs have been replaced within the last six months.

After about 130 glorious miles, during which the high rev issue has vanished completely, some problems have set back in. Actually, since the start, I still have had to feather my throttle for 5-6 minutes when cold starting - far better than before, but not ideal. More alarmingly, two days ago I started the bike up 2.5 hours after shutting it down from riding earlier and it was doing all sorts of subtle popping and then, when I laid into the throttle, it hesitated like crazy. It felt like I was getting a fraction of the power. Interestingly, about 5 miles into my ride (slowish city riding), the problem went away. (This last problem actually occurred last year a handful of times, before I even unwisely tried switching to the air pods.)

I did the plug chop. This was done by changing out the plugs minutes after getting off the hot bike, running the bike for five minutes at idle, and then shutting it off and removing. I am posting those pictures again for continuity. As you can see, they didn't really take on any color.

I also posted the plug pictures after 130 miles of regular riding, and was told they looked very lean. So I'm thinking I am pretty lean right now.

the air screws were 2 turns out on #1, #3 & #4 and 2.5 turns out on #2. The directive I was given was to turn the air screws one full turn in (richer) and repeat the plug chop.

But before I go further, I was also requested to do a clear tube method float level check and I am also posting the results of that test below. the first pic is the bike not he center stand with the tubes taped to the side and the following four pictures show the levels of 1 - 4, in that order.

I do apologize sincerely for not doing this earlier. Clearly, #1 and #3 are low by 2-4 mm. Calj, you were right. I admit I didn't execute this step previously.

Based on this new information...

Should I fix the float levels BEFORE I mess with the IMS screws?

Also, I know it's a matter of bending the tabs. But if there are any pointers you'd like to throw at me before I fix these, please do. Also, could this be the reason for the specific symptoms I've experienced - power loss and the previous high rev issue?

While I'm inside the carbs, is there anything else I should verify?

Again, I am sorry to you all for not following your exact advice on this point and am now placing myself fully at your command!

Thanks again.

(images in following post due to posting issues)

[hman0217]

images from above post for plug chops

[hman0217]

images from post #1 for clear tube float check

[hman0217]

No, setting fuel height doesn't require a re-synch. However, once the carbs are properly tuned (AF, jets, etc...) a final vacuum synch may help if you don't get them running right. Also, remember that your valves need to be adjusted properly before a synch (I think that was an earlier post).

Yes, the insufficient fuel issue will be attributed to ALL your stumbling, lean, loss of power issues. Not the only issue, but a major factor. You now see why setting floats by mechanical measure simply is not suitable enough to be accurate. Its a good start, but unless you're skilled it, have the carbs mounted on a bench and sitting perpendicular, you are bound to get variances.

Noted. I will remove the carbs tonight place them on a bench and tweak until the level is right AND I will send pictures.

And yes, the valve clearances were already adjusted.

[flybox1]

Now we're getting somewhere.
Do the clear tube test on the bench and get them all right before putting those back on the bike.

Also, please verify what PILOT JET size you have.
I dont know why its been omitted.  Its kind of important 

[calj737]

Ha, I actually just looked at the fuel level pictures closely (took your post/confession of improper levels for granted). They're so darn low, your motor must have been running on vapors!!!! Geez, when you actually start pulling fuel that motor will feel like a V8 

[flybox1]

Agreed, calj.  All bowl fuel levels are low, but also the test might have too many variables.  Hard to do on bike, clear tubes positions not fixed, etc.  Should have more accurate results when done on the bench.
IIRC, I think he mentioned he had a #38 pilot in the other thread.  Pretty sure 40s are stock 

[hman0217]

Agreed, calj.  All bowl fuel levels are low, but also the test might have too many variables.  Hard to do on bike, clear tubes positions not fixed, etc.  Should have more accurate results when done on the bench.
IIRC, I think he mentioned he had a #38 pilot in the other thread.  Pretty sure 40s are stock 

I did not change out the pilots but I also don't want to assume they are stock 35s. I will verify when I get into the carbs later.

[mrbreeze]

Is this bike a 750 or a 550? I'm pretty sure all the 750's are 40 slow jets. 35-38's are 550? I don't know much about 550's. What altitude are you at? The altitude also is something to consider when jetting. I'm going to go with the others about your fuel levels being too low. If there isn't enough fuel in the bowl to keep up with demand (when you're into the throttle) it will cut out and act up until the fuel supply is replenished. When the level is where it should be...it won't run out of fuel temporarily. If it gets too much fuel it will flood out.
Fuel level is there to supply the fuel and carb synch is there to make sure to make sure they(the carbs) are all on the same page.
Before I understood the importance of fuel level I thought if the float levels were all set to the specified height they were good to go. When I did the clear tube 1,2,& 4 were even but lower than they should have been. #3 was quite a bit lower than the rest. Setting them all to spec fixed the problem.

[flybox1]

In 77, with PD carbs, pilots went to 35s.....but yeah, 40s should be stock for his carbs (not including the 750A)
If he has 35s, that would explain 95% of the lean-ness at idle 

[hman0217]

Is this bike a 750 or a 550? I'm pretty sure all the 750's are 40 slow jets. 35-38's are 550? I don't know much about 550's. What altitude are you at? The altitude also is something to consider when jetting. I'm going to go with the others about your fuel levels being too low. If there isn't enough fuel in the bowl to keep up with demand (when you're into the throttle) it will cut out and act up until the fuel supply is replenished. When the level is where it should be...it won't run out of fuel temporarily. If it gets too much fuel it will flood out.
Fuel level is there to supply the fuel and carb synch is there to make sure to make sure they(the carbs) are all on the same page.
Before I understood the importance of fuel level I thought if the float levels were all set to the specified height they were good to go. When I did the clear tube 1,2,& 4 were even but lower than they should have been. #3 was quite a bit lower than the rest. Setting them all to spec fixed the problem.

Oops yes it is 40 for stock

I live in New York City so I'm essentially at sea level

[flybox1]

Jet brand matters. 
Are your pilot jets from an aftermarket kit, or do they have the Keihin K logo stamped on them.

With the combination of a stock airbox, accurate bowl fuel levels, and #40 pilot jets...you SHOULD be able to tune out the idle leanness.
Correct the bowl fuel level.
Turn all IMS to 1 turn out and redo the idle chop.
 
If idle plugs stay white even with IMS down to .5 turns out, there is something else going on.
MAC exhaust baffled or gutted?
Other things to check:
While the bike is idling, spray WD40 on the carb boots.  any change in RPMs?
Pilot circuit blockage.  Spray carb cleaner and canned air through all passages.
Pilot jets blocked?  pull and clean them.

[hman0217]

Jet brand matters. 
Are your pilot jets from an aftermarket kit, or do they have the Keihin K logo stamped on them.

With the combination of a stock airbox, accurate bowl fuel levels, and #40 pilot jets...you SHOULD be able to tune out the idle leanness.
Correct the bowl fuel level.
Turn all IMS to 1 turn out and redo the idle chop.
 
If idle plugs stay white even with IMS down to .5 turns out, there is something else going on.
MAC exhaust baffled or gutted?
Other things to check:
While the bike is idling, spray WD40 on the carb boots.  any change in RPMs?
Pilot circuit blockage.  Spray carb cleaner and canned air through all passages.
Pilot jets blocked?  pull and clean them.

Exhaust is baffled.

the good news is that I have an oem rebuild kit so if it's not both a 40 and a keihin I'll just go ahead and swap them out

I'll check these recommendations all off as I go

I was told a .008 guitar wire works well for pilot jet cleaning. So I got one to pass through if need be. Anybody do it that way?

[TwoTired]

Just to reinforce the importance of bowl fuel levels
The fuel must be drawn up from the bowl in order to reach the carb throat and be atomized, fighting gravity in the process.  The force provided is the differential pressure between the carb throat and the outside pressure.  The farther away the fuel is from the carb throat, the leaner the mixtures are provided by all the fuel metering orifices.

Honda did this very thing between 77 and 78 cb550 models where the spec for float height changed from 14mm to 12.5mm, effectively raising the fuel level in the carb bowls and allowing the engine run slightly richer over all.

Also be aware that as the slide moves upward, the maximum vacuum or low pressure point moves away from the more forward pilot circuit exit toward the needle jet exit.  The pilot circuit all but shuts off, due to the vast difference in comparative orifice sizes and the Venturi location.  So, don't expect the pilot adjuster to have very much effect on mixture above 1/8 to 1/4 throttle position.  Above that, Slide needle size and taper are mixture dominant until approaching W.O.T., where the main jet sets maximum fuel delivery.

Cheers,

[hman0217]

okay quick checkin... carbs are on a horizontal plane ready to be adjusted. I pulled out the pilot and YES it has a 40 stamped on it but NO it does not have a "K' for Keihin. Furthermore, the rebuild kit I have is a K&L genuine, not a keihin (but also a 40). Is anyone familiar with this brand? Is it worth swapping out, or is it just trading one unknown for another?

pics attached, both of my makeshift carb bench and the rebuild kit brand package.

more to follow...

[TwoTired]

The orifice size is usually ok.  The shape of the machined emulsion tube, and the body length protruding into bowl is a big deal.  Post pictures of yours and get a pic of Keihin.  Compare.

[hman0217]

The orifice size is usually ok.  The shape of the machined emulsion tube, and the body length protruding into bowl is a big deal.  Post pictures of yours and get a pic of Keihin.  Compare.

the first two pics are the installed jet and the rebuild kit jet, respectively. This is followed by another of the "thin side" of the existing jet and then finally the keihin stock jet. The "fat part" seems identical, while the "thin side" seems rather different.

To your point, though, if the part protruding into the bowl is the important one, then I'm good?

[hman0217]

Man I keep over steering like crazy. But I think 2 and 4 are good. Submitting 2 and 4 float level pics for approval. See attached

For 2, there is both 1 and 2 in the pic. 2 is the one on the right (and I reckon 1 is high)

[TwoTired]

You need to measure the thick body length (protrusion depth into the carb bowl pool.)
You need to measure the emulsion tube length,  count the number of holes, and measure the hole sizes. ( determines how well emulsion is performed)
The Keihin type you posted has threads on the fat part of the body, making it the wrong jet to compare to.

Carbs are unforgiving about the lack of attention to detail. 
You can avoid measurements by getting the proper Keihin jet for your carbs.

Cheers,

[hman0217]

You need to measure the thick body length (protrusion depth into the carb bowl pool.)
You need to measure the emulsion tube length,  count the number of holes, and measure the hole sizes. ( determines how well emulsion is performed)
The Keihin type you posted has threads on the fat part of the body, making it the wrong jet to compare to.

Carbs are unforgiving about the lack of attention to detail. 
You can avoid measurements by getting the proper Keihin jet for your carbs.

Cheers,

You need to measure the thick body length (protrusion depth into the carb bowl pool.)
You need to measure the emulsion tube length,  count the number of holes, and measure the hole sizes. ( determines how well emulsion is performed)
The Keihin type you posted has threads on the fat part of the body, making it the wrong jet to compare to.

Carbs are unforgiving about the lack of attention to detail. 
You can avoid measurements by getting the proper Keihin jet for your carbs.

Cheers,

Well the interesting is that, when I went to bikebandit.com and entered in my bike, it gave me both the series 21 & series 22 option, the former which looks like the one I posted and the latter that looks like the one in my bike.

Is one better than the other? Should I just find a dimension chart for the series 22 and compare with that? (And if anyone has s link... A Google search for keihin turns up a mess of aftermarket stuff with barely any authentic stuff)

[calj737]

Order from here:
http://jetsrus.com/a_jets_by_carburetor_type/a_jet_kits_keihin_selection.htm

These are true Keihin brand brass.

[hman0217]

Heres #1 for approval

UPDATE: I swear this looked fine when I took the picture. But looking at it now, it looks closer to 5 mm than 3-4 mm. What do you all think? Is this out of tolerance?

[hman0217]

And last but not least, here's #3

Not ignoring the pilot jet talk but, in the interest of one-step-at-a-time, I'd love to get your blessing on these float levels first

Thanks

[mrbreeze]

I did my carbs around 2005-2006 (75 750K) round tops. I used the K&L kits that I got from Dennis Kirk. People on this forum told me to steer clear of Keyster kits and to reuse my stock brass parts. I have had no problems with the K&L bowl gaskets or the float valves & seats. I've had the bowls off a few times over the years and have reused those same bowl gaskets. I've heard of problems with distorted or leaking Keyster gaskets. I have various main jet sizes that I bought from Honda so I assume they are Keihins. You don't want to use aftermarket needles because people report they have fits trying to tune with them because of different taper profiles from stock.

[calj737]

HMan I think you're fuel is close enough now. If you wanted to tweak #1 just a touch more, that would be ideal but you'll live at 4-5mm.

The issue with K&L brass is that they differ from the stock brass, not that they don't work. If you use it, you need to tune accordingly and can not rely purely on stock settings. Kind of like swapping to a different induction/exhaust system; all bets are off.