Topic: K2 stutter

[7fifty4]

Hello World -

I placed it in the Australian part of this forum, but hope that all people can see this -
and as a side note - I planned to ride to Phillip Island  - next thursday, 23 Jan '14 - which now I can not, I think, unless
 there is some remedy out there for my 'stutter' problem -

The bike - 1972 Honda CB750 K2, with about 92000KM -

The symptoms - as good as I can describe it:

[ "froffel"  - a noise I describe as: "... like when blowing raspberries ]

I have a slight "froffel" or "stutter" in between 5000 and 6000 RPM in fourth and fifth gear
 and when I fully close the throttle from there and then every so slow open the throttle again, I have
  the same "froffel" or "stutter"

It seems to me as the engine would be starved of fuel and when I increase throttle it "dissapears", i.e. the engine runs fine

It also could have been a timing issue, or "timing jitter" which is a phrase I picked up from reading Hondamans book,
 I checked the shaft though... read below

In that rpm range then it feels like a continous "acceleration/ deccelaration" - fast... slow.... fast... slow... fast... slow..

----

What I have done, - not in this particular order, I might add:
{the relevant stuff I mention here, have done more, but does not add any value here}

Engine apart and did put in New:

 Primary and Timing chain tensioners
 Bearings (all)
 Gaskets and seals (all)
 Coils which have New Spark plug leads
 Spark Plugs - D8EA
 Points
 Airfilter (Standard)

Valves being re-ground
Heads machined and pressure tested

Checked shaft where the advancer unit sits on, for run out - got it running true within 0.08mm

adjusted Valves
set Points gap

set Timing - I tried both ways I know off,

  1 - static, set the 'F' and then check the advance and
  2 - the "just the advance" markings with a timing light - ignore where the 'F' ends up


Carburettor cleaned, (in Ultrasound machine - ensuring all dirt gets out of all little holes too), all new gaskets
#110 main jets
Main needle sits on last ring from the top - (Standard)
Adjusted Float heights to 26mm
Synchronised Carbies

Checked whether the rubber boots between carbies and heads and carbies and airfilter are leaking - they are not leaking

Checked and cleaned venthole in tank - the seal looks a bit sad - have a new one coming
I rode the bike with an open fuel cap - no change

Dissassembled and cleaned petcock - all seems clean there
I rode the bike and switched to "reserve"  - no change

New fuel hoses on carbies - to and from Tank and between carbies

Have 98 Octane fuel in tank


What I have not done: (yet)

No new ignition plate - (the plate where the points sit on)
No new condensers - have fairly old ones - CHASING "TEC" condensers, can not locate any
No new inners in carbies, like needles and other jets - all the old parts are in the carbies - I might put all new stuff I have into them this weekend
No new primary and timing chains - new ones are planned for next time when I have the engine apart

---

I am at the end of "my little wisdom" - any suggestions, remedies, ideas?

Thanks in advance

[mutters]

Hi mate, first off, get a cool beer supply for the conditions ,I'm in Wagga , we get your
today's weather tomorrow. So today I know what you suffered with yesterday.?
Anyway back to the real world, what throttle opening are you having the stutter at?? ,it sounds (reads) like the jet needle may need to lifted up ,that is ,circlip down a notch.
Probably not the simplest thing to try but I think it could be close to the money .

stay cool ,Jeff

[7fifty4]

g'day mate - you might get the weather we had yes - man its a stinker. u need a lot of beer !!
back to the real world - the needles are all at the last notch - I tried to say that - so should I go the reverse ?

cheers buddy

[petercb750]

Mate, I'm no mechanic, but I think it's normal for the clips to be in the middle, or a notch either side of middle. I would have thought with them "at the last notch" it would be too lean or too rich depending on which end they're at.
Peter.

[mutters]

Yep, that’s the thinking here,
top notch on the needle may be a bit on the lean side at that throttle setting .
As you say it runs fine at full throttle ,that’s running on the main jets and the needle is out of play.

And if that’s it  its a cheap fix too!!

cheers mate

[7fifty4]

Well, I'm no mechanic either, but, I keep trying things.
   - I give it a shot, nothing to loose, whats a few hours of tinkering, right?
Bugga though, I wanted to ride to Phillip Island, doesn't look like I m going

thanks for all your help
I keep you posted
cheers

[mutters]

yeah mate keep us posted

and some photo's of the patient ??

[jonda500]

Hi 7fifty4, You'll get more eyes on your problem if you post it in SOHC/4 Bikes in the tech forums section.
Also, when did the problem first start - just after rebuilding the carbs? What exhaust - 4 into 1? What pilot jet size? Idle screws - solid or hollow drilled type & how many turns out? Do you know if they are the original carbs for that bike? How long have you had the bike?
Sorry I'm not much help, I've been having similar problems with my cb550F. I saw a definate improvement by dropping the pilots from 40 to 38 but still have a slight miss when I roll on the throttle very slowly after slowing down... I'd love to see your problem solved and solution posted here - might help me work mine out!

[7fifty4]

thanks jonda500 - I placed a shortcut there now - ignore my Pm - cheers

since midnight last night -  I am running:
110 mains -
40 idles -
Needle clip 3rd from the top
Float 26mm
Air screw 1 1/2 turn out

I forgot to mention it has stock standard exhaust system, not even the baffles removed

I have the bike now for about 3 years ( I think ) - and it was always like that and ( silly me) I thought I fix it when I put new rings
in, boy o boy was I wrong.... the amount of stuff and $$$ and time ... and ripped hair....


anyways, after taking the carbs off again last night and changed to all new (aftermarket) jets, and all the same adjustments otherwise, I did take it for testrun tonite - and... no change - I keep looking

it just seems that it does not get enough petrol -


I will post pictures soon -

cheers

here on the forum I  read somewhere, someone saying, " if you can't fix it with a hammer you have an electrical problem...", hmmm

[Terry in Australia]

Mate, I'm no mechanic

You can say that again............

[petercb750]

Mate, I'm no mechanic

You can say that again............

Mate, I'm no mechanic....

[Terry in Australia]

But you're a good bloke, so that's Ok..........

[jonda500]

something doesn't add up - if you started with "needle sits on last ring from the top" which is the leanest needle pos and went to needle clips in #3 slot, you should have noticed some sort of difference?

[mutters]

All right,  how about an air leak in the inlet manifold rubber bits
I'm not sure how to test for that ,maybe listen for a whistle , spread a bit of Vaseline on the joins and see if the idle improves .
By the way, how is the idle .
I'm really liking the idea of blaming an air leak now
everything you can tick off brings you (us) closer to solving this.

cheers Jeff

[Terry in Australia]

If it's making a "Blowing Rasberries" noise, doesn't that sound like a leaking head gasket? Cheers, Terry.

[7fifty4]

I checked and mentioned this, for an airleak in the inlet manifolds by spraying some of the trusted "Start ya bastard" spray on the outside, which should make the engine revvup for a little bit - at least an amount of time to listen to the increase and nothing.
Perpexing indeed, by hanging the needles in the middle notch, no change , yes you read right. I am not making this up mate, sorry.
I have finally found some new "TEC" condensers, so I hope they will be here next week.
So, NO, I am not riding to Phillip Island this week - bugga. may be next year?
no way is it a head gasket Terry- nice try though 

[kghost]

Have you checked the actual float levels using the clear tube method?

[7fifty4]

no, I have not checked the float levels with the clear tube method, I had no spare screw to do that with, I have now and will prepare the screw and then check the levels that way - thanks very much

[kghost]

Worth a shot.

Sometimes there's a low one

[7fifty4]

Hi - no, haven't created the clear tube attachment, its just sooo hot in the shed, I try to get to make it tonite hopefully when its cooling down... but I received a new petcock I have ordered and made some tests - I attach some pix.

The "1:10" on the pictures means:  1 minute and 10 seconds  - run time, or in other words I opened the tap for that time (dont ask why - long story).
Okay - it was in "normal" open position, not the reserve - I tried the reserve also but I could not measure any difference
The old tap shows a 58mm contents - Img_0886.jpg
The new tap showed 60mm contents - Img_0888.jpg
The new tap and the tank leaned towards showed 61mm contents - Img_890.jpg

Okay - I just went to the shed again and converted the amount measured to about 550ml  - so the results you see in the pictures are equivalent to 550ml in 1 minute and 10 seconds. cheers


Bizarre was that the fuel came out of the two brass connections on the tap in different flow rates and every measurement I took it came out in a different flow form a different connection. Different in a way that one had a strong flow and one was trickeling - that surely can not be right... or is it?

What fuel are you guys here in Oz are using - Unleaded? 91, 95, 98 Octane? any additives ... or not... other ideas?
Some people said they are using 87 Octane but that is not available in Oz, right? Would that be too low?
When I rode in europe there were two choices, either a "Super" at 95 to 100 octane or "Normal" which was 91 Octane. Never had any issues putting the "Super " into any 750s then - only issue was that I could not afford it. So it was usually "Normal" I put it. Are the engines "okay" with unleaded at 91?

the last picture (P1080833.jpg)  is taken in Broadford, (near Melbourne), at the HBBB 2012 - this is my new goal, get to the HBBB 2014 - my old goal to get to Phillip Island on Australia day I did not make *sigh* .


cheers

[Ace]

I run standard unleaded 91 in the K1. It didn't like premium unleaded.

Is the stutter at constant throttle position or only when you wind it on? Mine does have a stutter sometimes if you crack it WOT from 4th or 5th. Drop down a gear to get out of it and go.

Issues I've had with stutters -
1. Carby needle settings and main jets not correct for setup (aftermarket cams etc)
2. Sticking mechanical advance unit (bit or rust on the posts where the arms fit on)
3. Coils breaking down, check plug leads/caps as well
4. Change the timing at the points a few degrees (advance and/or retard the timing)
5. Hairline cracks in carby internals
6. Aftermarket kits for carbys that are slightly different
7. Riding in the incorrect rev range when you give the throttle a twist. Ride in the rev range of the cam for best performance.

If you are confident in what you have already tried, do plug chop to see if it's running rich or lean at various throttle settings. Bugger it, pull them out anyway and have a look.

There are so many things it could be, with probably many people on the forum if they heard the bike, rode it etc would be able to point you in a clearer direction if not solve it. Not sure if any SA members are near you.

Be patient and as mentioned before, one carby change at a time, take your time and post back. Best wishes.

[7fifty4]

Hi Ace  - thanks for your reply -

Interesting that you are running unleaded 91 - thanks for that
I put new coils, lead and plugs i n - when I get the plugs out after a run they always show lean - almost pure white all plugs
I hung the needles up into the middle position and had a look at the plugs - again white - lean, no change.
the stutter-froffel occurs when I get into the 5 to 6k rpm in fourht and fifth - slow approach or fast
if I drop a gear and go - that would mean I am at a constand speed of about 140Km/h
what do you mean by WOT -

patience is hard to come by - if I only knew what it is....

cheers

[Terry in Australia]

Not wanting to rub it in mate, but Phillip  island was great, so get that bike sorted for Broadford, or you'll be pissed off!

91 RON fuel is fine if you're running a stock engine and horrible points ignition, but if you hot up your engine and run higher compression pistons, bigger cam etc, you'll need an electronic ignition, which will give you a much fatter spark and then you'll enjoy the benefits of 98 RON fuel. My 836 pings like buggery when I run 91 RON fuel, and feels much smoother with 98.

Don't bother using 98 with points though, it'll be harder to start (the higher the octane, the higher the resistance to ignition) and it'll run really rich, fouling plugs and generally ruining a day's ride. Cheers, Terry.

[7fifty4]

thanks for not rubbing it in Terry.
Could you do me a favour and measure how much fuel is coming out
of your tank? could it be that either the floats are wrongly set, at 26mm,
or I simply mot getting enough fuel to the carbies?
my measurements come to about 550ml per minute
if you could measure, say for about 10 seconds and measure the output,
please?
If anybody else would be able to do this? and write back here?
I researched the internet and some books I have, but no references as
to how much flow is "required" or "standard".
still have to do the "clear tube test" - just too hot in the shed still

cheers

[Ace]

Haven't heard of measuring the fuel out the tap. I run fuel line that I can see in and filters so I know it's getting fuel.

91 RON, mild cam, hondaman ignition, TEC points and condensers, 836 cc with 10.5 :1 compression which is probably down to about 10 or 9.8. Not an issue with 91 fuel.  Didn't like 95, but that was in the NT. Haven't tried it here. My 895cc engine with high lift cam, 10.5:1 compression went down to 9.8 measured was fine on 91 also. I put some upper cylinder lube in the tank as well.

If your plugs look like new (white) then you have a lean condition that you need to fix quick. Did you ultrasonic clean the carbys yourself of get someone else to do it? Did you clean out the passageways and also remove all the jets, holders etc, completely stripping them?

I've had 2 dyna DS-1 ignition fail. I'd go for something else. WOT = Wide Open Throttle.

Up your mains to 115, needle clip in middle, 3rd position from the top.

Start the bike up and let it idle for about 15 mins and check the plugs. If they are still white then turn your air screws in 1/4 to 1/2 a turn and then do it again and check. There are some good diagrams that show you about which carby circuit impacts pilot, needle, main jet settings. Lots of factors when trying to jet correctly.

Another check you can do it while riding along, put the choke on, if the bike improves then you are lean, if it stutters then you should be rich. Fully on will make it stutter as well so don't go that far.