Topic: Perfect idle, dies under any throttle

[rockthehellout]

I'm at a loss, so I'm going to bullet point the usual requisite information.

Rebuilt top end last year, valves, rings etc...ran like a champ for several months.

Got stuck in a rain storm, shorted out some minor electrical, headlight etc., quick and easy fixes...and then chaos.

The bike starts and idles perfectly, every time. However, the slightest twist of the throttle gives me pops, backfires, bogging, and ultimately the bike dies. While riding, I can clutch my way through these lower RPM's, and it begins to pull again around 3,500+.

76 750k: Yes I have cheap pods, and a cyclex 4-1 sidewinder. Stock coils, stock carbs, 42 pilots, 120 mains, needle clip one position down.

My poor bike has been sitting in my garage neglected for a year, and I'm ready to get this thing back on the road. When the problems first started I went through every basic electrical and tuning issue I can think of, but I'm genuinely drawing a blank now and need to start from scratch. I cleaned the carbs out last night, the pilots on 3/4 had some gumming but have been soaked, dried, and cleaned, and the problem persisted.

Where would you start? Is this a tuning issue? Valve? Electrical?

[TwoTired]

Look at spark plug deposits to inform you of combustion conditions.

Cheers,

[evinrude7]

rtho, did you check float height?  even further try the "clear tube test" to see how high the fuel is in the bowls.  flybox is the expert on the clear tube method.  starting with accurate float height makes a world of difference. 

[BomberMann650]

I've dealt with two non-honda's that would fall on their arse when given throttle.

1 little kawi had fouled up main jets.  It would run the paces with the choke but not without.  Put some amsoil quickshot cleaner in the gas and got lucky.

The other was smurfette's xj600.  Problem turned out to be the fuel delivery to the bowls.
Those bikes have a filter before a vacuum operated pump.  Replacing those (in addition to another carb cleaning) got the bike running proper.

I can't remember if your 750k has the accelerator pump or not.  But the issue seems similar to what was happening on that XJ

[jgger]

You said stuck in a rain storm........take a glass jar and drain some fuel into it. Let it set for about 5 to 10 minutes and see if you have water puddles in the bottom of the jar. Also re clean all the main jets real good.

[evinrude7]

You said stuck in a rain storm........take a glass jar and drain some fuel into it. Let it set for about 5 to 10 minutes and see if you have water puddles in the bottom of the jar. Also re clean all the main jets real good.

+1

I can't remember if your 750k has the accelerator pump or not.  But the issue seems similar to what was happening on that XJ

no accel pump on the cb750k6

[rockthehellout]

Plugs, 1-4, bowls 3-4 (didn't take pics of 1/2, but right there in the same line)...have to admit I'm naive, even after reading, about float height and where it's supposed to be...but this seems low to me?

[BomberMann650]

Seems low but I'm used to 550's.

Don't let the dog drink out of that bowl 

[Spanner 1]

4x new NGK spark plug caps please. 2x straight 5K ohm caps ( 2 and 3 ) and 2 x 120deg. 5K ohm caps ( 1 and 4 ). Cut about 1/4 inch off the plug wire ends and screw the new caps on. Start and ride the bike . Report.

[rockthehellout]

4x new NGK spark plug caps please. 2x straight 5K ohm caps ( 2 and 3 ) and 2 x 120deg. 5K ohm caps ( 1 and 4 ). Cut about 1/4 inch off the plug wire ends and screw the new caps on. Start and ride the bike . Report.

Had to call me out on the cheap-o caps!  They were the first thing I had tested when this debacle started...2/3 were a bit low and a buddy had a new set of these in his garage so I threw them on. Just trimmed the wires back as well. Fair point though, I'll get a proper set on and report back.

[rockthehellout]

Here's a quick video

[TwoTired]

The black soot on the spark plug is conducting spark energy away from the spark gap.  Run conditions are iffy with this situation.
While new or cleaned plugs will improve matters, the cause of sooty plugs is more fuel delivery than can be combusted with available oxygen.
Spark capacity is not an issue, or it wouldn't make soot.

Either you are using too much choke, your air filters are too restrictive, or your carbs are adjusted (or defective) to deliver too much fuel in one or more throttle positions.
You have no choice now but to replace or clean the plugs you now have before finding the source of extra fuel delivery.

Cheers,

[ekpent]

 Did you save your stock #40 slow jets and your 105 mains ? May be another good starting point and increase the main if needed. Bad condensers can cause running issues also. The new plugs will help and make for a better tuning read.

[evinrude7]

Did you adjust those floats?

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[ekpent]

Did you adjust those floats?

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They do look low.

[rockthehellout]

Did you adjust those floats?

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They do look low.

I'll be diving in to them tonight.

[flybox1]

1. Correct the low bowl fuel level.  dont measure your floats, just continue to adjust them till your fuel level is correct.
2. idle plug chop with a set of new plugs.  4-5min w a fan on the engine.  no blipping.  then post a picture of their deposits for us to see.

[rockthehellout]

So while I'm waiting on the plug caps to come in, I decided to fart around with the carbs a bit. Cleaned the jets again, adjusted the float levels to spec, and still yielded the same result. That is until I pulled out the can of starter fluid to run the most basic test of them all. When sprayed into the 1/4 carbs, it bogged down and nearly died. When sprayed on 2/3 carbs, I got a slight rev then back to level. Video here:

[AirCanuck]

So while I'm waiting on the plug caps to come in, I decided to fart around with the carbs a bit. Cleaned the jets again, adjusted the float levels to spec, and still yielded the same result. That is until I pulled out the can of starter fluid to run the most basic test of them all. When sprayed into the 1/4 carbs, it bogged down and nearly died. When sprayed on 2/3 carbs, I got a slight rev then back to level. Video here:

Trying to learn from this thread. What's the purpose of the test in this video and the significance of the results?

[rockthehellout]

So while I'm waiting on the plug caps to come in, I decided to fart around with the carbs a bit. Cleaned the jets again, adjusted the float levels to spec, and still yielded the same result. That is until I pulled out the can of starter fluid to run the most basic test of them all. When sprayed into the 1/4 carbs, it bogged down and nearly died. When sprayed on 2/3 carbs, I got a slight rev then back to level. Video here:

Trying to learn from this thread. What's the purpose of the test in this video and the significance of the results?

I'm no expert so perhaps someone a little more well versed could clarify it better than I can...but the way I took that was that it likely wasn't in the carburetor and was more likely to be something electrical. I took a look at the timing and it was insanely far off on 1/4 and surprisingly not much better on 2/3. So onto my next ignorant issue...

I got 1/4 points lined up and firing correctly, the which almost immediately solved my problem. However with 1/4 lines up, 2/3 are too far off...with them completely advanced, I'm only reaching the "t" mark, not the F, let alone the adnavce marks. Does this have to do with the point gaps?

[AirCanuck]

So while I'm waiting on the plug caps to come in, I decided to fart around with the carbs a bit. Cleaned the jets again, adjusted the float levels to spec, and still yielded the same result. That is until I pulled out the can of starter fluid to run the most basic test of them all. When sprayed into the 1/4 carbs, it bogged down and nearly died. When sprayed on 2/3 carbs, I got a slight rev then back to level. Video here:

Trying to learn from this thread. What's the purpose of the test in this video and the significance of the results?

I'm no expert so perhaps someone a little more well versed could clarify it better than I can...but the way I took that was that it likely wasn't in the carburetor and was more likely to be something electrical. I took a look at the timing and it was insanely far off on 1/4 and surprisingly not much better on 2/3. So onto my next ignorant issue...

I got 1/4 points lined up and firing correctly, the which almost immediately solved my problem. However with 1/4 lines up, 2/3 are too far off...with them completely advanced, I'm only reaching the "t" mark, not the F, let alone the adnavce marks. Does this have to do with the point gaps?

It doesn't have kickstart right? Why not switch it to electronic ignition if you're worried about your timing? A friend of mine with far more experience does it with all his - says not only is it easier but he sees an improvement in performance. Pretty cheap to do, too; and I believe relatively easy.

[evinrude7]

So while I'm waiting on the plug caps to come in, I decided to fart around with the carbs a bit. Cleaned the jets again, adjusted the float levels to spec, and still yielded the same result. That is until I pulled out the can of starter fluid to run the most basic test of them all. When sprayed into the 1/4 carbs, it bogged down and nearly died. When sprayed on 2/3 carbs, I got a slight rev then back to level. Video here:

Trying to learn from this thread. What's the purpose of the test in this video and the significance of the results?

I'm no expert so perhaps someone a little more well versed could clarify it better than I can...but the way I took that was that it likely wasn't in the carburetor and was more likely to be something electrical. I took a look at the timing and it was insanely far off on 1/4 and surprisingly not much better on 2/3. So onto my next ignorant issue...

I got 1/4 points lined up and firing correctly, the which almost immediately solved my problem. However with 1/4 lines up, 2/3 are too far off...with them completely advanced, I'm only reaching the "t" mark, not the F, let alone the adnavce marks. Does this have to do with the point gaps?

the short answer is yes and i would shoot for .014" or .015".

rtho, there are various views on how to fix the issue of over extending, running out of rotation room with the points plate.  some will shim the plate against the bosses.  i did not have any success with that.  it does not mean it's the wrong way to go.  what worked for me was to return the plate to the middle and then adjust the gap on 1-4.  return the small 2-3 plate to the middle of it's available movement and set points for those.  then i went ahead and timed it statically, lastly dialing it in with a light.  i'm not as experienced as most of these forum members so try all methods available.  you'll find one that works for you. 

[PeWe]

Ignition is not OK?
F should line up with case mark at idle.
Full advance marks line up with case mark after 2500 rpms.

If full advance happen too early, the advance springs are too sloppy. Springs can be fixed. Remove the springs and cut one side 1/2 wound, shape a new grip with a plier.
Possible to fix one spring to start with. I did both on my bike and it worked and still works fine. I used it with Pamco, then Dyna-s and finally points with Hondaman ign module

Here when and how I did my springs with photos. http://forums.sohc4.net/index.php?topic=131339.0

[scottly]

Have you cleaned or replaced those fouled spark plugs yet? If not, you're pissin in the wind. Best way to un-foul sooty spark plugs, IMHO, is to burn the black off with a propane torch...

[rockthehellout]

Have you cleaned or replaced those fouled spark plugs yet? If not, you're pissin in the wind. Best way to un-foul sooty spark plugs, IMHO, is to burn the black off with a propane torch...

Yeah I got the plugs and caps replaced today. It was 100 percent the timing/points. Guessing some moisture got in there during the rain storm. A new set of points and static timing did the trick. Needs some further tuning now that everything fuel and ignition related has been tinkered with, but it's road worthy again!