Topic: studder at speed

[blantonator]

at mid rpms with slight throttle, i notice the engine tends to sTtudder a little.  What could cause this?  The only recent changes i've made to the bike is a freshly painted tank.

thanks all

[Gordon]

If you want real help you need to supply more information.  We need to know what type of bike it is, as well as any changes that have been made to the bike from stock configuration.

[blantonator]

its a 73 cb350 with aftermarket pipes.  everything has been running fine until recently when i put the freshly painted tank on.

[TwoTired]

Do a plug chop while it is stuttering.

1. What engine size?
2. What year?
3. What model?
4. When was it's last complete tuneup?
5. Does the bike have a stock air filter?
6. Does the bike have stock exhaust?
7. Have you ever adjusted the tappets?
8. Have you ever replaced the filter?
9. Have you ever adjusted the cam chain tension?
10. Have you ever looked and the spark plug tips.
11. What numbers show up on the spark plugs?
12. Have you ever set your points gap?
13. Have you ever set the ignition timing?
14. What setting is the jet needles?
15. What size main jet do you have?
16. Is the air filter clean?
17. Have the carbs been vacuum synched?
18. Have the carb couplers been checked for leaks.
19. Have you ever adjusted the cam chain tension?
20. Do you like playing 20 questions as much as we do?

Hey listers, I'm going to save this list for the next post about fixing a bike with no information.  Hope you like it!

Cheers,

[blantonator]

Do a plug chop while it is stuttering.

1. What engine size? 350
2. What year? 1973
3. What model? CB350G
4. When was it's last complete tuneup? end of last season
5. Does the bike have a stock air filter? probably original filter, seem ok
6. Does the bike have stock exhaust? stock headers with aftermarket pipes
7. Have you ever adjusted the tappets? adjusted end of last season
8. Have you ever replaced the filter? no filter
9. Have you ever adjusted the cam chain tension? no
10. Have you ever looked and the spark plug tips. yes, looked a little wet, but ran good at the time
11. What numbers show up on the spark plugs? dont remember
12. Have you ever set your points gap? yes
13. Have you ever set the ignition timing? was static timed
14. What setting is the jet needles? unknown
15. What size main jet do you have? unknown
16. Is the air filter clean? fairly clean
17. Have the carbs been vacuum synched? previous owner claimed to have done this
18. Have the carb couplers been checked for leaks. not yet
19. Have you ever adjusted the cam chain tension? nope
20. Do you like playing 20 questions as much as we do? *sigh*

Hey listers, I'm going to save this list for the next post about fixing a bike with no information.  Hope you like it!

Cheers,

all filled out!

[TwoTired]

Does it still stutter with the air filter removed?

BTW, Honda procedure is to replace the air filter on a yearly basis.  With 34 years on a paper filter, you've gotten more than your money's worth.
The paper fibers collapse over time, making it progressively more restrictive. This "chokes" the engine.  The running malady symptom I call "burbling".

Further, the bike is supposed to get a complete tune up every 3000 miles this includes cam chain tension and filter renewal, so you have answered several questions wrong.  Have you found everything the Previous owner did to the bike perfect?  Your confidence that the carb sync (part of a general tuneup) is high then?

After-market mufflers *can* also make carb tuning a challenge and different from stock Honda settings, but not always.

I'd focus on the air filter first...

Lastly, this tech forum is for SOHC4 bikes, not twins. So, this thread belongs in "other bikes".  I'll ask the moderator to move it.

Cheers,

[blantonator]

i bought the bike from a 25-year honda mechanic, it was well tuned when i bought it and I've only put 500 miles since.  I'll check the filters and boots for leaks.

[blantonator]

i took the spark plugs out and the left cylinder looks a little wet/oily.  Any ideas?

[Bob Wessner]

Intermittent ignition contact as in bad connection at certain vibration frequency (a reach, that one. ? Hard to check out since it only seems to happen at a certain rpm range.

[TwoTired]

i took the spark plugs out and the left cylinder looks a little wet/oily.  Any ideas?

If it is wet/oily, it may not be firing.  And, then there is the question about why there is an oil build up.

Swap the plug with another to see if the problem follows (or put a new one in its place).  Check to see if it is sparking across the electrodes.

Do a compression check wet and dry.

Verify the tappet adjustment hasn't gone off and is holding open a valve.

Although, you don't seem to want to hear it, but the first thing to do when these bikes don't run quite right is do a tune up on them.  Honda expected them to get regular maintenance for a reason.

[blantonator]

Im fine with regular maintatance, I did a near full tune at the end of last season, and I've only put a few hundred miles on since.   I'll readjust the tappets and will be doing a dynamic timing shortly.  The wet/oily cylinder is definetly firing, but I have noticed a little oil seapage from the head gasket.