Author Topic: Do I have a problem? (Read 1118 times)

jwurbel · « **on:** January 15, 2024, 04:07:33 PM »

1972 k2 with stock configuration on carburetors: 110 mains, 40 slow, clip in middle (3rd position). Floats set with clear tube method. Synced with Morgan Carbtune. Air mixture screws @ 3/4 turn in. Stock air box and filter. Exhaust is no number Yamiya. Bike starts immediately, idles at 1300 rpm’s. Runs strong through all gears with no hesitation or bogging. However the plugs don’t have much color. Gas is Shell 87. Should I be changing anything? Photos attached.

Lucien Harpress · « **Reply #1 on:** January 15, 2024, 04:13:00 PM »

First question I suppose is how many miles do these plugs have?

Second question (more like a statement)- if it rides fine, pulls strong, runs on all four, and doesn't overheat, I don't see what the problem is.

jwurbel · « **Reply #2 on:** January 15, 2024, 04:19:12 PM »

10 miles. They were installed new.

BenelliSEI · « **Reply #3 on:** January 15, 2024, 06:01:48 PM »

Those are awfully clean, cleanest I’ve ever seen. But, if it runs that well, put another 30-40 miles on it and check again.

Deltarider · « **Reply #4 on:** January 16, 2024, 12:10:21 AM »

Plugs that new will not give much info. I've read a lot of nonsense about plugjobs to be carried out with fresh sets plugs in this forum. Where lead used to help in giving a good indication, todays gasoline isn't much help. What you could do, is add a spoonful of castor oil to a tank filling and then ride and read.

newday777 · « **Reply #5 on:** January 16, 2024, 02:05:26 AM »

Quote from: jwurbel on January 15, 2024, 04:19:12 PM

10 miles. They were installed new.

What kind of ride was it?
Is that after parking it with some idling time?

M 750K6 · « **Reply #6 on:** January 16, 2024, 02:14:07 AM »

I have been looking into a rich running problem on my 750. 10 miles would not be enough to get a good reading. I found 100 to 150 miles gave me a sense of what was happening. A couple of really good heat cycles.

If your plugs look similar after that distance, I'd happily swap your carbs for mine

jwurbel · « **Reply #7 on:** January 16, 2024, 03:39:44 AM »

Castor oil? I won’t discount it and appreciate the comment.

No extended idling time. In town riding with occasional WOT when I could get away with it.

Today I am going to take it out for a long ride which will include freeway runs and will get back with the results.

newday777 · « **Reply #8 on:** January 16, 2024, 03:57:21 AM »

Quote from: jwurbel on January 16, 2024, 03:39:44 AM

Castor oil? I won’t discount it and appreciate the comment.

No extended idling time. In town riding with occasional WOT when I could get away with it.

Today I am going to take it out for a long ride which will include freeway runs and will get back with the results.

The way to test the plug colors
http://forums.sohc4.net/index.php?topic=92318.0

Deltarider · « **Reply #9 on:** January 16, 2024, 05:02:05 AM »

Quote from: jwurbel on January 16, 2024, 03:39:44 AM

Castor oil? I won’t discount it and appreciate the comment.

No extended idling time. In town riding with occasional WOT when I could get away with it.

Today I am going to take it out for a long ride which will include freeway runs and will get back with the results.

My advice is - provided air intake is standard - do a ride with used but still good plugs at a maintained speed and rpm where it matters for you and then close throttle and kill the engine simultaneously, roll to where you can park and read the plugs. For the rest just trust what Honda has designed as far as jets, needles, positions etc.

jwurbel · « **Reply #10 on:** January 16, 2024, 02:32:04 PM »

Went for 30 mile ride at various speeds. Didn’t do plug chop yet. Couple things: part way through ride went to increase idle screw and raised choke 1/4. Caught the error about 2 miles later and corrected. Idle seemed to want to drop below set speed, 1300rpms. Not always but it happened more than once. No problems on acceleration.
All air mixture screws were at 3/4 in. Took photo of #2 and it is showing some color. The rest look the same as previous photos. Not sure if I should turn in the other 3 an 1/8th.

Any advice is appreciated. Out of new plugs so have to buy before attempting any type of chop.

scunny · « **Reply #11 on:** January 16, 2024, 10:51:30 PM »

Air mixture screws @ 3/4 turn in
Do you mean out from lightly seated ?

jwurbel · « **Reply #12 on:** January 17, 2024, 03:19:50 AM »

newday777 · « **Reply #13 on:** January 17, 2024, 04:56:50 AM »

Quote from: jwurbel on January 16, 2024, 02:32:04 PM

Went for 30 mile ride at various speeds. Didn’t do plug chop yet. Couple things: part way through ride went to increase idle screw and raised choke 1/4. Caught the error about 2 miles later and corrected. Idle seemed to want to drop below set speed, 1300rpms. Not always but it happened more than once. No problems on acceleration.
All air mixture screws were at 3/4 in. Took photo of #2 and it is showing some color. The rest look the same as previous photos. Not sure if I should turn in the other 3 an 1/8th.

Any advice is appreciated. Out of new plugs so have to buy before attempting any type of chop.

Without a good run on a Plug Chop you won't see any results to know what is going on with your tune.
Did you read through the link I posted above, yesterday?

jwurbel · « **Reply #14 on:** January 17, 2024, 06:52:51 AM »

Yes, but won’t I need fresh plugs or can I just use these?

newday777 · « **Reply #15 on:** January 17, 2024, 06:54:03 AM »

Quote from: jwurbel on January 17, 2024, 06:52:51 AM

Yes, but won’t I need fresh plugs or can I just use these?

Use the ones you have

Stev-o · « **Reply #16 on:** January 17, 2024, 09:09:11 AM »

Run it! Check back after 100 miles....

Lucien Harpress · « **Reply #17 on:** January 17, 2024, 09:16:57 AM »

I agree. Unless it runs so poorly it won't make it I usually put at least a tank of gas through it before I start troubleshooting. Plus you get a ride out of the deal!

jwurbel · « **Reply #18 on:** January 23, 2024, 09:58:29 AM »

Well rode 50 plus miles at all speeds. Plugs still looked like previous pictures. Turned air mixture screws to 1/2 turn out rode again and although they look a bit darker (grey) still appear lean. Note that bike pulls strong through all gears with no hesitation. Can I drop down another 1/8 or 1/4 or should I try bumping pilot from current 40 to 42?

M 750K6 · « **Reply #19 on:** January 23, 2024, 02:54:46 PM »

Is this a 750 K2? If so...

@Hondaman told me something I didn't know: the air fuel mixture is mixed before it gets to the 'air mixture screw'. Turning in the air mixture screw reduces the amount of pre-mixed fuel that goes past the screw and through the carb. In other words, screwing in makes it leaner, screwing out richens. It's counter intuitive and unlike other carbs I've played with. I think he knows his stuff though.

As you're finding the bike runs well, I suggest you set them back to stock, 1 turn out and don't look at them again for a couple hundred miles. The photos of your plugs don't look suspicious to me, especially if you use fuel that has any ethanol mixed in.

Lucien Harpress · « **Reply #20 on:** January 23, 2024, 03:42:44 PM »

K2 mixture screws control the air. In is richer, out is leaner.

Later on a lot of carbs would switch to the opposite, but concerning the CB750 1972 was before this happened.

jwurbel · « **Reply #21 on:** January 23, 2024, 04:20:10 PM »

I am aware of Mark’s position on this. When I tried to follow that, the idle was difficult to maintain. Only when I went in the opposite direction, in richer, did I obtain a satisfactory idle. Since it’s raining here, Phoenix, I’ll give it some more thought. A bit confusing.

jwurbel · « **Reply #22 on:** January 24, 2024, 11:31:02 AM »

I contacted Keihin direct looking for an answer. Chad Thompson, their rep, got back and stated that turning in would richen and out would lean the mixture on a 657 A. That may still not satisfy everyone but it confirms what I was experiencing.

M 750K6 · « **Reply #23 on:** January 24, 2024, 02:30:42 PM »

Well done for checking with Keihin. 👍

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Author Topic: Do I have a problem? (Read 1118 times)