Topic: Slight Throttle Response Delay

[trism18]

     I have been experiencing some throttle response delay on my CB750 K1.  If you open up the throttle when driving at normal road speeds (45-60), it will hesitate or have slow acceleration for just a moment.  But then it will open up right after that, and the acceleration is fine.  It does not do this all the time, and it seems to be more likely to happen at a cruising speed.  Anybody else experience this or have a solution?  Thanks.

[apormarkos]

i have a similar problem with my 550k.  when off throttle at a red light, it hesitates for a second when i give it gas to get going.  are some of my jets a little clogged?  the bike sat for a year or so, so i'm thinking the carbs might be a bit gummed up...

[TwoTired]

     I have been experiencing some throttle response delay on my CB750 K1.  If you open up the throttle when driving at normal road speeds (45-60), it will hesitate or have slow acceleration for just a moment.  But then it will open up right after that, and the acceleration is fine.  It does not do this all the time, and it seems to be more likely to happen at a cruising speed.  Anybody else experience this or have a solution?  Thanks.

Is your K1 still in stock configuration?  Any changes or additions to the bike?
What is your tuneup history?  And, are you on the Honda recomended maintenence schedule?
Assuming stock and currently maintained, it seems likely your mixture is off at certain throttle positions.
Check your spark plug deposits.  What color is the center electrode insulator?

Try to determine the throttle position where the symptom occurs.  Hold it there, hit the the kill switch, and pull in the clutch.  Stop without allowing the engine to turn and pull all the plugs.  Note the reading on each one and report back along with the throttle position where the problem occurred.
Cheers,

[TwoTired]

i have a similar problem with my 550k.  when off throttle at a red light, it hesitates for a second when i give it gas to get going.  are some of my jets a little clogged?  the bike sat for a year or so, so i'm thinking the carbs might be a bit gummed up...

It would be usefull for diagnosis if you'd state the year model and any changes from stock that have been made to the bike.  History of recent tuneups and general maintenance could also be informative.

Could be, just adjusting the pilot screws on the carbs may help your problem.

Cheers,

[apormarkos]

twotired,
the bike has an unknown (to me) tuneup history, i just bought it 1 1/2 weeks ago.  it's a 76 550k, stock carbs, aftermarket exhaust 4-2, not sure of the brand.  it's not very loud, so i'm guessing it's got some backpressure.  i peeked at the stock filter and it might be the one that it was assembled with- the bike has 12,000 miles. the filter's a little dusty. the biggest issue, however, is an oil leak for which the head has to come off, so i'm leaving tuneup stuff for after.  it responds well to throttle above 4k rpm.  that's about all i know so far... wondering if i should disassemble the carbs, or just run some carb/fuel injector cleaner through with the next fillup.  does that stuff hurt rubber bits?

[TwoTired]

twotired,
the bike has an unknown (to me) tuneup history, i just bought it 1 1/2 weeks ago.  it's a 76 550k, stock carbs, aftermarket exhaust 4-2, not sure of the brand.  it's not very loud, so i'm guessing it's got some backpressure.  i peeked at the stock filter and it might be the one that it was assembled with- the bike has 12,000 miles. the filter's a little dusty. the biggest issue, however, is an oil leak for which the head has to come off, so i'm leaving tuneup stuff for after.  it responds well to throttle above 4k rpm.  that's about all i know so far... wondering if i should disassemble the carbs, or just run some carb/fuel injector cleaner through with the next fillup.  does that stuff hurt rubber bits?

I think the precursor to correcting any performance issue is to have a fresh and complete tuneup done to the engine.  Carburetor adjustments don't drift much with normal use, but tuneup procedures are there for the things that do drift with time and use.  It seems pointless to tune carbs to an ill adjusted engine.

If the stock paper filter is clogged with dust, this will make the plug deposits sooty, and may affect mixtures enough to cause performance issues.  I use the UNI 4055 foam filter in my bikes.  Cheaper, a bit less restriction, and reuseable.  But, I also live in an area where massive dust is not a problem.  I'd want the paper one if lived in that type of area.

Any bike I acquire gets an oil change and complete tuneup to establish a regular maintenence schedule.  It's supposed to be done every 3000 miles, after all.  And what incentive would the PO have to do it before they sold it, and was it done correctly?

I don't take much stock in "miracle" liquids to correct engine maladies, as they usually have a more direct effect on your wallet than beneficial effect to the engine.  Your carbs have orings inside that seal the main jets and the float valve seat.  If you don't know what chemical or chemical blends you are putting in the carbs, how will you know these seals won't be damaged.  I have heard that yamaha carb cleaner is safe for o rings, but I haven't tried it.

Personally, I wouldn't muck with the carbs until I was certain there is a problem there.  Just running fuel through the carbs does a fair bit of cleaning on its own.  If you have jets clogged, the slows clog first as they only have .016 inch orifices. Then you get a cold, dead cylinder at idle, and the head pipes will have evindence of this when felt.
Cheers,

[apormarkos]

twotired,
i'll check the plugs and see, but the filter needs changing regardless, as does the oil.  everything else will have to wait till the major work is done.  thanks for the advice.
apor

[mrbreeze]

OK.Ithink this is probably the post I have been waiting for.I did alot of posting a few months ago about my air fuel probs and would like to jump in here and get some insight on mine and others probs.I have a K5 that just came from Wyoming(5000ft.) to California (89 ft.) last year.I removed stock pipes and went to 4-1 Kerker -- NO BAFFLE. I installed K&N pods.I installed Dyna ignition with Accel coils & wires.I first jetted up from 105 mains to 120's but didn't feel it was enough. Taking CBENS advice, I went up to 137's (Great improvement but....) he said he had an issue with his inline fuel filter and replaced it with a larger unit. Well I just took mine out completely and lo & behold .... More improvement! I must also add that before going to the 137's, I completely dipped, rebuilt and reinstalled carbs. OK!!! Now last week I finally got my Morgan Carb Tune from England.... (Totally love it by the way!) I forgot to mention that when I rebuilt carbs, I set needles in the middle groove.OK.... right before I synched with the Morgan,I pulled the carbs off again and put the clips down a notch(2nd from bottom which raises needle....MORE RICH)................OK(DOKAY!!!) This sucker is soooooo close!!!!......BUTTTTT..... It still has a bit of stutter at low throttle cruise. It idles good-no more popping exhaust,nomore camchain noise.When I start it,it idles low but comes to an acceptable idle when warmed up. It accelerates great but when I am just cruising, it has that stutter #$%* that I just dont care for.Now....my question is...Do I need to pull them doggone carbs for the third time and move those needles up again (TO my last notch) Or... maybe go to 42 slow jets? One more thing I was wonderin'..... The fuel line off of the petcock to the carbs.....It goes under the pod filters so it is below the fuel bowls. Should I route the line up and over the pods so it is above the bowls? I just don't know and I'm probably starting to get the Bob Wessner complex about this whole SOHC fuel thang(HA! HA!) so please help me and some of these other dudes that are having fuel delivery probs. BTW... you guys that post about your fuel probs do need to supply as much info as you can....Year,model stock or aftermarket exhaustcarbs,filters,big bore kits,cams,altitude,temps,lies,fries,flies,etc.etc. Thanks for any imput....MR.BREEZE(damn near there!!!!)

[TwoTired]

It still has a bit of stutter at low throttle cruise. Now....my question is...Do I need to pull them doggone carbs for the third time and move those needles up again (TO my last notch) Or... maybe go to 42 slow jets? One more thing I was wonderin'..... The fuel line off of the petcock to the carbs.....It goes under the pod filters so it is below the fuel bowls. Should I route the line up and over the pods so it is above the bowls?

Some things I'd like to know:
If you mark your twist grip, at about what throttle position do you find the "stutter" problem? 1/3, 1/2, 1/4?
Have you read your plugs to get an idea of the combustion conditions?
What is your spark plug brand an type?
Where is your current air bleed screw setting?

The fuel line loop is okay if you are sure there is no air pocket in the path between tank and carbs.  I'm not sure if the normal fuel flow is enough to bleed that line if there is a high point loop.  I don't know for sure, but it seems like an inline air pocket might make the float level variable.
Cheers,

[mrbreeze]

Hey TOO TIRED,I'm glad that you are the one that jumped on this. You seem to be real knowledgable about these things.I am noticing the probs at low throttle...like maybe an eighth on the throttle (just cruising). I can hit it a little and it picks right up.I can nail it and it gets with the program. It does'nt seem to be like an acceleration prob but more like an off idle kind of thing.I haven't marked my grip or done a plug chop yet (I don't have an ON/Off switch) so it is kind of a hassle to shut er down as I am riding.As far as the plugs,they are stock NGK 8's,...Non resister that I had to get at the Honda dealership.All of the auto houses I went to had resister plugs but I have Accel coils and wires anyhow so I don't think that it's a factor.Your next question about the air screws is one of the reasons I think I may need larger pilot jets. When I bumped my needles up and then synched the carbs, I set my screws to 1 turn out. After a short putt, I turned them in one half turn (which makes it one half turn out from bottom) and the revs picked up a little. I haven't turned them all the way in yet but I read somewhere in here that if the air screws go more than three quarters in or two and a half out,that tthere is still a jetting prob.I think I would rather do the jets some more(A bit of $ but less work) than pull the carbs again and move to my richest needle setting(No $ more work!).....So what do you think? I'm telling ya....I am sooo close! Appriciate the info......MRBREEZE

[TwoTired]

Critical information about whether your current mixture is rich or lean at that throttle setting is important to determine which way the adjustment should go.  The plug condition would relay that over the internet, since I cannot hear what the engine is doing in the problem area.  Spark plug insulator color would be helpful, through not as critical for reading mixtures at such low throttle settings where combustion temps are lowest.
One way to get a clue, would be to see if your annoying symptom goes away with partial application of choke.  If the symptom improves, then you know that the mixture needs to be enriched at the problem throttle setting.

I agree that when the pilot screw is near the closure limit, adjustment gets very critical and you have to think about 1/16 turns as being a significant change.  Closing it off entirely is not a realistic choice as the small emulsion tube on the slow jet will cease to function.  I speculate that 1/4 turn from seated is the pactical (though not desirable) limit for an air bleed setting.  Increasing the slow jet size should improve the 1/8 to 1/4 transition, if indeed your current mixture is too lean for those settings.

Have you seen this chart about what effects mixture per throttle setting?
When the air bleed screws reach their effective limit of adjustment, the slow jet will need to change (bigger for more fuel) or the Air jet (when you are too rich).

Seem like if your carbs are doing well above 1/3 throttle positions, then pulling out the needles would make those setting too rich and you may start fouling plugs, even though it may help your problem area response.  If your required change IS needle centric, it seems likely that a different taper profile would be required.

Can't stress enough about understanding what your current mixture conditions are at various throttle settings in order to minimize adjustments to the proper area of the carb.
Cheers,

[apormarkos]

twotired-
this is not the first time i have seen this chart, but after all this talk of throttle position, i finally understand what it means (i'm about as novice as one can be about carbs).  does this chart apply to many different carbs, all carbs, or just a specific model of carb?  more to the point, does this chart apply to the carbs on my 76 550k?
thanks,
apor

[TwoTired]

I believe the chart applies to Keihin Mechanical slide throttle valve carbs such as those found on the SOHC4. Probably others.  But, if I said all, then we'd see lots of exception cases posted, including CV carb types.

For your carbs, ignore the I.M.S. depiction.

Cheers,

[apormarkos]

twotired,
thanks for the schooling, i will no doubt seek your expertise in the future.
apor