Author Topic: Head against wall- Midrange problems  (Read 4803 times)

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Offline Matt Chapter

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Re: Head against wall- Midrange problems
« Reply #50 on: November 14, 2013, 08:24:48 AM »
Maybe this is simplistic of me, but it seems like the problem is carb sync.

If you have one plug that is tan, and three that are sooty, my understanding is the three sooty ones are the problem.  Soot means incomplete burn, or too rich.

Have a gander at this handy page provided by the good folks at NGK. http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp You will also find similar information in most after market shop manuals such as Haynes or Clymer.

Go back to the vacuum sync, double check your manual for target vacuum, and get the three to match the one that's running right.
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Offline josuepdx

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Re: Head against wall- Midrange problems
« Reply #51 on: November 14, 2013, 04:22:13 PM »
So one interesting thing that I noticed when syncing the carbs was that cylinder 2 gauge indicated that vacuum was lagging behind the others. It would take longer for carb to drop and then return to the idle vacuum after I blip the throttle.

When I looked this up to try to figure out what it could mean, I found this. This site is suggesting (at the bottom of the page) that I have a choked or clogged muffler, but I already checked my exhaust for any blockage and it was fine. Any other things that it could be?

http://www.gregsengine.com/using-a-vacuum-gauge.html

Offline TwoTired

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Re: Head against wall- Midrange problems
« Reply #52 on: November 14, 2013, 04:37:57 PM »
Does your vacuum gauge set have adjustable dampers?
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Offline josuepdx

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Re: Head against wall- Midrange problems
« Reply #53 on: November 14, 2013, 07:40:23 PM »
Does your vacuum gauge set have adjustable dampers?

Yes, but I have them adjusted so that all the needles wiggle the same amount.

Offline crazypj

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Re: Head against wall- Midrange problems
« Reply #54 on: November 14, 2013, 08:49:31 PM »
So one interesting thing that I noticed when syncing the carbs was that cylinder 2 gauge indicated that vacuum was lagging behind the others. It would take longer for carb to drop and then return to the idle vacuum after I blip the throttle.

When I looked this up to try to figure out what it could mean, I found this. This site is suggesting (at the bottom of the page) that I have a choked or clogged muffler, but I already checked my exhaust for any blockage and it was fine. Any other things that it could be?

http://www.gregsengine.com/using-a-vacuum-gauge.html

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Offline HondaMan

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Re: Head against wall- Midrange problems
« Reply #55 on: November 14, 2013, 08:51:02 PM »
So one interesting thing that I noticed when syncing the carbs was that cylinder 2 gauge indicated that vacuum was lagging behind the others. It would take longer for carb to drop and then return to the idle vacuum after I blip the throttle.


This hints of a leaking exhaust valve. It can be caused by either a pitted face, or a worn guide that lets it tilt when opened, causing it to momentarily close "later" than it should. When the engine is revved up, the compression in the affected cylinder drops a little as compared to the others, which then lets the others drag it along and lean out its fuel mixture, making it pop.

For a sort of simplistic diagnosis, try either opening the air screw on that cylinder only about 1/8 turn more than the others. If you're so inclined, also raise the needle in the slide by a notch for the same mixture change above 4000 RPM.

Sometimes, this symptom can come from a long-term misadjustment of the carb, like a too-high vacuum on the affected cylinder. If you have the patience, over a thousand miles or so these bikes can actually "heal up" a bit if the seats have lost their seal, because the valves do not rotate in these engines. This lets them pack some carbon into the leaky niches of the seats, making them seal again until, typically, a long hiway trip: that will blow out the carbon and repeat the cycle. If you were to take a REAL long hiway trip, holding it steadily at the 5000+ RPM of our 80 MPH interstate today, it will also tend to flatten the higher points of the seats and make them seal again, but I am referring to 500-700 miles per day for maybe a week at a stretch to accomplish this feat. I have done it, more than several times, with these engines, and it works reliably. But, it's a slow process compared to removing the engine and fixing it in a day or two.

The above "fix", however, does require that the valve guides are in good shape, not too loose, and not oval from wear (which happens on "F" & K7/8 engines and engines with high-lift cams). If the guides are in poor shape, it won't "heal itself". The K0-K4 bikes are the best self-healers. ;)

I am a little concerned about a previous post: you mentioned that you have 657A carbs (unusual for the K3) and that they DON'T have tiny holes in the tips of the air screws. Something seems amiss, there: the primary difference between the 657A and 657B carbs was: the "B" lost the air screw holes and their mainjet went down to #105, and the needle clip went down to the 4th (from top) notch in the later K3 and the K4. The size of the hole in the idle venturi also changed, but it's real hard to gage that one.
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Offline crazypj

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Re: Head against wall- Midrange problems
« Reply #56 on: November 14, 2013, 08:55:57 PM »
I'm wondering if you had carbs completely inverted like the picture in service manual?
If so, you will have incorrect float height, they need to be tilted 60~70 degrees from vertical
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Offline HondaMan

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Re: Head against wall- Midrange problems
« Reply #57 on: November 14, 2013, 10:27:54 PM »
HondaMan.... could you explain the Keyster float valve situation a bit more? Is it because the springs are stiffer?

In a word, 'yes'. They have stiffer springs, and often shorter bodies with longer plungers, even smaller diameter bodies, all of which help them lower the float bowl level too much. I have been setting them at 24-25mm instead of 26mm. They don't tend to leak while on the sidestand like the regular OEM valves could, because the stronger spring adds some extra force in those marginal tilted situations.

They also aggravate the problems with the dimple that appears on the float tang: the stiffer spring makes them stick more often, so polish those tangs up to remove that tiny dent. And, make sure the float posts don't have a burr on them from the sharp edges of the float bracket (this is a bigger problem on the 657 and K0 carbs than on the others,)
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

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Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

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Offline josuepdx

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Re: Head against wall- Midrange problems
« Reply #58 on: December 02, 2013, 04:01:31 PM »
After replacing nearly everything on the carb side on cylinder 2, I have noticed that all my plugs are looking the same now. I also did a leak down test and couldn't find anything wrong with cylinder 2.

I did however notice something stupid that I somehow missed. I noticed that I am not getting anywhere near full advance when I throttle up. Even at 4k I'm nowhere near the advance marks on my timing plate. I also noticed that my pamco seems a bit off as far as timing goes. No matter how I adjust the timing, one is always either more advanced or retarded than the other. I can't seem to get them to both fire at the same time. I've read that you can bend the sensor to make the timing a bit more accurate? But what about the advancing problem? Should I try to see if I can loosen up my advance springs?

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Re: Head against wall- Midrange problems
« Reply #59 on: December 02, 2013, 07:56:03 PM »
Ahh, your running a pamco. You need to take a look at:

This regards your advancer.
http://forums.sohc4.net/index.php?topic=113480.0;all

This regards timing jitter and spring tension
http://forums.sohc4.net/index.php?topic=131339.0;all


Check that your advancer is running correctly to full advance at the || marks at say 4000 rpms and let it sit where it will at idle (around 'F' somewhere).

You might need to bend 2.3 sensor to correct the 180 degree timing alignment between 1.4 and 2.3. Talk to Pamcopete about this one if you have doubts. Shouldn't be a drama.

Sounds like your getting close though.

cheers
alex

Offline josuepdx

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Re: Head against wall- Midrange problems
« Reply #60 on: January 29, 2014, 04:22:42 PM »

This hints of a leaking exhaust valve. It can be caused by either a pitted face, or a worn guide that lets it tilt when opened, causing it to momentarily close "later" than it should. When the engine is revved up, the compression in the affected cylinder drops a little as compared to the others, which then lets the others drag it along and lean out its fuel mixture, making it pop.

For a sort of simplistic diagnosis, try either opening the air screw on that cylinder only about 1/8 turn more than the others. If you're so inclined, also raise the needle in the slide by a notch for the same mixture change above 4000 RPM.

Sometimes, this symptom can come from a long-term misadjustment of the carb, like a too-high vacuum on the affected cylinder. If you have the patience, over a thousand miles or so these bikes can actually "heal up" a bit if the seats have lost their seal, because the valves do not rotate in these engines. This lets them pack some carbon into the leaky niches of the seats, making them seal again until, typically, a long hiway trip: that will blow out the carbon and repeat the cycle. If you were to take a REAL long hiway trip, holding it steadily at the 5000+ RPM of our 80 MPH interstate today, it will also tend to flatten the higher points of the seats and make them seal again, but I am referring to 500-700 miles per day for maybe a week at a stretch to accomplish this feat. I have done it, more than several times, with these engines, and it works reliably. But, it's a slow process compared to removing the engine and fixing it in a day or two.

The above "fix", however, does require that the valve guides are in good shape, not too loose, and not oval from wear (which happens on "F" & K7/8 engines and engines with high-lift cams). If the guides are in poor shape, it won't "heal itself". The K0-K4 bikes are the best self-healers. ;)

I am a little concerned about a previous post: you mentioned that you have 657A carbs (unusual for the K3) and that they DON'T have tiny holes in the tips of the air screws. Something seems amiss, there: the primary difference between the 657A and 657B carbs was: the "B" lost the air screw holes and their mainjet went down to #105, and the needle clip went down to the 4th (from top) notch in the later K3 and the K4. The size of the hole in the idle venturi also changed, but it's real hard to gage that one.

Alright guys. I pushed this bad girl to the back of the garage for long enough. I'm thinking I'll bring it back out this weekend and get to work. Do you think that the 657A carbs could be where my problem is? Is there some sort of adjustment I should make so that they work well on a K3, or should I look into 657B carbs? My other route, that I really don't want to take, is opening up the engine and inspecting the valves.

Now, I've rebuilt a few engines, so that's not what I'm worried about. I'm worried about the time commitment and the chance of opening it up and finding nothing wrong with the valves. Then I'll be back to square 1. Those ****ing carbs are probably going to be the death of me. I just know it. 

Offline josuepdx

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Re: Head against wall- Midrange problems
« Reply #61 on: January 29, 2014, 04:26:11 PM »
Ahh, your running a pamco. You need to take a look at:

This regards your advancer.
http://forums.sohc4.net/index.php?topic=113480.0;all

This regards timing jitter and spring tension
http://forums.sohc4.net/index.php?topic=131339.0;all


Check that your advancer is running correctly to full advance at the || marks at say 4000 rpms and let it sit where it will at idle (around 'F' somewhere).

You might need to bend 2.3 sensor to correct the 180 degree timing alignment between 1.4 and 2.3. Talk to Pamcopete about this one if you have doubts. Shouldn't be a drama.

Sounds like your getting close though.

cheers
alex

Thanks Alex. My advance mechanism is working properly at the moment and just needed a little tweaking to get to work properly. Still haven't resolved my issue yet though.