Topic: K2 Missing, & misc. questions

[CB925]

My CB750K2 has been running fairly well since i got it going earlier in the year.  I've recently replaced the airbox (to get rid of the pods), after which it still ran ok.

It ran well for awhile afterwards but is now missing.  I dont believe the two are related.  The points and ignition advance have been set, and carbs synched.  We also replaced the main jets (back to 105's) It had jets drilled to somewhere near 120's.  Presumably the legacy of a previous incarnation of the motor which ran an 836 kit.

So Currently it is as follows:

* Stock Bore (or something near it, i.e. not bigbore)
* Stock Carbs, 105 mains (needle position unknown)
* New Carb to Airbox rubbers
* K&N air filter
* 4 into 1 exhaust

My feeling is that it is an electrical issue, as it runs ok cold, and worsens as the bike heats up.  So much so that it is almost unrideable within 15 minutes.

The points have been filed and gapped, and a suspect condensor replaced.  Which leads me to think it may be Leads / caps, or a coil.  2&3 appear to be the affected pots, which is why we initially went looking at the points.  Any ideas?

I think I may just bite the bullet and buy a dyna ignition, which raises a few questions of its own.

1) is dyna the pick of the bunch?
2) should i use dyna coils, or Bold'or unit that have been suggested in numerous places
3) are the Bold'or coils something Bol'dor specific or do other honda roadbikes have them?

I'm definately after something with replaceable leads.

I also have a set of what I believe to be F1 carbs  (PD41BBQA7).  Are these worth trying?  Not necessarily just due to this problem, as I'm leaning away from fuel.  Are there an gains I could get from these?  Or are they EPA carbs that are more trouble than they are worth?

Also... my gauges are repro items, and while they look ok, they are quite innacurate.  I've purchased some original K2 items, but they need rebuilding.  Anyone got any contacts for me to pursue this?  (in Australia)  I'm also chasing a K2 triple clamp.

Cheers.
 

[KingCustomCycles.com]

Sounds like it is very rich and is loading up as it warms up.  Your spark plugs will tell the story.

[CB750F2]

King may well be right. Drop off the float bowls and check the float levels - difficult but it can be done in situ. Also check the plug leads and caps. At night run the motor until it starts missing then have a look in the dark to see if there is any leakage from the coils or leads. Pat - another aussi.

[754]

I am sorta doubting the last 2 posts..

 AS... it ran well before.. so it sounds like something is deteriorating between startup and fully warmed.

 Gut feelicheck coils.ng points to coils, if it has the problem, then sits for 2 hrs and runs fine cold.. then goes away shortly.. I say coils.

Point ingnition is fine for normal use, but some prefer electronic. I run  car points which seem to last much longer with less adjustment.

[andy750]

The points have been filed and gapped, and a suspect condensor replaced.  Which leads me to think it may be Leads / caps, or a coil.  2&3 appear to be the affected pots, which is why we initially went looking at the points.  Any ideas?

I think I may just bite the bullet and buy a dyna ignition, which raises a few questions of its own.

1) is dyna the pick of the bunch?
2) should i use dyna coils, or Bold'or unit that have been suggested in numerous places
3) are the Bold'or coils something Bol'dor specific or do other honda roadbikes have them?

I'm definately after something with replaceable leads.

 

Im with 754 on this...what led you to believe it was a faulty condensor? Sounds like this could still be an issue. However its so easy to check your plugs Id also look at that in case they are fouling. The K2 can have larger or smaller main jets depending on the build time - my K2 uses 120 mains (stock airbox, exhaust etc) and so checking your plugs will tell you current air/fuel mixture - however if you cant run it for more than 15 min then may be hard to get an accurate picture at higher speed.

I have a Dyna S system - cheapest of the Dyna range. Uses stock coils or go for some CB900/CB750 DOHC coils that have replaceable wires (which is what I use). Relatively cheap off Ebay.  This has worked for me for the last 40,000 miles.

Alternatively check out Forum member Hondamans posts in the FAQ or do a search. He makes a custom ignition unit that compliments your points and has advantages over the Dyna systems. Plenty of people on here have used it with success.

good luck
Andy

[speedy gonzalais]

if it had pods then the mixture would have been adjusted for the extra air intake so now its prob running rich with a normal filter

[CB925]

Hi Thanks for your responses,  I cleaned the plugs, refitted the caps (shortened a few leads doing so), adn fired it up again.  I checked it with an IR temp sensor, and no.4 was running way colder than the others, so i binned that plug and that helped some.  However, it just got me back to square one, where it starts and idles ok, then detiorates.

I dont think its jetting, as it ran ok after i changed from the pods back to the airbox setup.

I'll try to do the run, then cool for 2 hours thing over the weekend.

I'm also going to check for manifold vac leaks, as after i got it running i've noticed the pipes are not running evenly temperature wise.  No.2 seems significantly hotter than the others.

Thanks.

[speedy gonzalais]

if the bike was tuned for the pods then the standard filters wont let as much air thru making the mix fuel rich, to start off this would have no affect on the engine until the carbon starts to build up inside then you will start to notice problems.
try swapping the plug from the hot running cylinder to one of the colder ones then check if the heat moves with it.

[CB925]

Replaced coils (2nd hand off an 84 cbx750), new leads, new plug caps .....

same problem ....  seems unlikely to have the same issue with two sets of coils.

Ran it till it played up, sprayed carb cleaner around manifolds, looking for vacuum leaks, it didn't pick up as I was anticipating.

I'm going to check all my alternator connections, tomorrow, and "reseat" anything ignition related.

I've bought some carb kits and will try them as well.

I've tried to keep it at constant revs for as long as possible the other night, possibly 5 to 10 mins, wasnt straight running so its not a real wonderfull indicator, and the plugs were quite black and sooty.

Checked them after a run tonight, varying revs, and general around town running, and they came out pretty much the same. 

Then i pulled the filter out, and went for a quickrun with the bottom of the airbox removed, still ran crappy.


I'd probably say the plugs looked "carbon fouled" as in the following page  http://www.nightrider.com/biketech/spkplghnbook.htm#Today%27s

any other ideas?

[mlinder]

Id be surprised if you are running rich with 105's and a 4 into 1.

Poor spark can appear to be a rich condition, as there isnt enough spark to ignite the all the fuel.

Check your timing again.

What are your pilot screws turned out to, just to be on the safe side of the whole AF thing.

Are 2 and 3 more fouled than 1 and 4? Need more info.

[CB925]

I was hoping to see a difference between 1,4    and 2,3.   .... but, 1,2,4 seem pretty similar and 3 seemed a bit wettish on the last chop.  I'm thinking 3 might be a little oily.  But I'm pretty confident this was already the case prior to this issue.

The mechanic I had tune it is an old hand with honda 4's, so I'm confident he would have synched and timed it properly.  That's why I was favouring the plug / coil issue initially.

[mlinder]

What plugs are you running?

[CB925]

D8EA's.  After the tune I put a set of Iridiums in it, but they suffered the same fate, so back to cheaper D8EA's till I sort it.  I have head that they are a shade too cold, but it was running fine on them before the issue began.

....  I went to a bike show today, and ran into a mate that has spannered on bikes for many years.  I explained my issues to him, and he concurred with the shop that had done the tune / sync.  He suggested that the needles / needle jets are most likely my issue.  Also said to replace needle & seat, check float height etc.

He seemed quite confident and explained it as such.  It will be running rich on the needles, and when cold its happy with the rich mixture, but as it warms up its too rich.  The sooty black plugs would work in with this theory.  The fact that it still idles ok when the problem initially starts, and will rev, but surges at constant revs all seems to add up, given that the clip position and the needle taper are in play in the region it gives me the most grief, up until the plugs must be fouled.

So, I'll go ahead and kit the carbs, and take it back for another sync.

[mlinder]

Let us know how it turns out. I just have trouble believing 105's are rich. KO came stock with 120's, k1 with like 115's or somesuch. I've seen k3's and k4's with 110's that run great.
The K2 was still pretty hot,, 105's seem small to me :/

[HondaMan]

Sounds like a bad 2-3 coil. Typical of them to run when cold, miss when hot, after they get old enough that the insulation breaks down on the windings inside.

[CB925]

Hondaman: I had my money on the coil/s also, but a completely different pair yielded the same result.  Whilst I realise it is possible I replaced one bad set of coils with another, I'm leaning back towards fuel.

MLinder:  I'm talking moreso from 1/4 to 3/4 throttle, the needle taper, and clip position are moreso in control than the main here.  Granted the main will restrict max fuel flow, but that isn't what would be experienced here.  I do agree, that the 105's are probably too small, I imagine I'll end up with 120's back in there once I've got this midrange issue sorted.

I should also go onto explain some of the bikes history prior to my ownership.


1. Bigbore kit (at some stage it had one)

2. Engine blowup (engine was rebuilt back to standard bore (or thereabouts))

3. I purchased bike

4. sat for 2 to 3 years

5. Got it going again, ran ok

6. Removed pods, and put airbox with K&N in it.

7. Had bike tuned.


My feeling is the problem may have been introduced with sych, perhaps the needles wore together, and they synch upset them?  In that, the worn needles (and possible non standard clip position (unkonwn)) could be the culprit.  Presumably the carbs were setup for the bigbore kit, and possibly never jetted back for the standard bore?  I'll kit the carbs, have it synched again, and if that doesn't solve it I might have to fork out for some Dyna coils.

Also, are F1 carbs a good thing?  I have a set of them in my spares collection, are they worth a try or are they in the "EPA" era?
 

[coyotecowboy]

If you're leaning toward a fuel problem, then you really need to find out where your needle clips are set at.  If someone did put them in the 5th position it will definately foul plugs and run like crap in the midrange.  I've got pods and a 4 into 1 on my K2 (1972 here in the states, I'm not sure what Honda was calling a K2 overseas  ) and I run my needles in the 4th position and 125 mains and probably need to go up to 128's or 130's.  It absolutely won't tolerate the needles on the 5th clip.

Probably not what you were wanting to hear, and you'll need to re-sync but it will eliminate one question.

[CB925]

Hi, yeah, k2 is also 72 for the 750's here in Australia.

When I pull them carbs apart I'll be replacing the needles, and putting them in the mid position.

Given that the its standard or close to, with a 4 into 1 and airbox with a K&N I'd imagine the mid position is still the go?

[HondaMan]

Hi, yeah, k2 is also 72 for the 750's here in Australia.

When I pull them carbs apart I'll be replacing the needles, and putting them in the mid position.

Given that the its standard or close to, with a 4 into 1 and airbox with a K&N I'd imagine the mid position is still the go?

Mid-position is a good start.
Something to look for, if it sat so long: the air passage from the air horn to the emulsifier tube. Here in the 'States, the gas had MTBE (and other evils) for about 10 years, which dissolved the protective surface on the pot metal. This led to a white, powdery residue inside many carb passages if the carbs were then exposed to moisture. This particular passage must be ABSOLUTELY clear, because it is quite small, and this powdery stuff would partially block it, leaving the engine with midrange mix woes of all sorts. It can be cleaned with a 24 AWG mechanics' wire, wiggled through from air horn (tiny brass port there) to mainjet mount. It helps to see the wire come through if you remove the emulsifier and the needle jet in the carb body, otherwise you can barely see the end of the wire arrive at the center of the carb. I often find these blocked, now, one bikes that have been sitting. I use spray cleaner and wire, several times, to clean it out. Be careful to not damage the little brass port at the air horn: the size of that hole is pretty important to the mix.
I've got a post with pix around here somewhere, about 'cleaning carbs'. It might be in my "750 hemi' thread.

[coyotecowboy]

If you're like me and live at a fairly low altitude I'd say put your clips at the fourth position.  I still had the stock airbox on when I got my 4 into 1 and tried it with the clips in the mid (3rd) position and unless you rolled into the throttle it would fall on its face until you got into the upper RPMs.  Went back to the fourth position and all was good.  Hondaman is at quite a bit higher altitude than I am so the third position probably works great out there.  Just use your best judgement 

[CB925]

I live at approx 150m altitude (500feet), and some of my riding in local areas will be higher.  For example, next weekend I intend to go for a ride up to a town that is only a couple of hours from here and is at 570meters (1890feet) elevation, and a town I will often ride to is at 830m (1700feet) and is only half an hour away.  Adding to this I'm only a few hours from sea level, so I'm figuring mid position may be the go?

I used to find that my dirtbike ran a little rich, and ran somewhat better at altitude (up to around 1700m (5800feet)), so I left it that way, as thats where most of its riding was done.  The 750 isn't quite as simple a scenario, so I guess time will tell.

I pulled the carbs and cleaned them before registration earlier this year (compressed air and carb cleaner), they were a bit mucky but ran ok after the clean.  It ran ok for over 6 months before I've run into these issues,  having said that, when I kit them I'll make extra sure to check and clean the tubes Hondaman mentioned.

[HondaMan]

I live at approx 150m altitude (500feet), and some of my riding in local areas will be higher.  For example, next weekend I intend to go for a ride up to a town that is only a couple of hours from here and is at 570meters (1890feet) elevation, and a town I will often ride to is at 830m (1700feet) and is only half an hour away.  Adding to this I'm only a few hours from sea level, so I'm figuring mid position may be the go?

I used to find that my dirtbike ran a little rich, and ran somewhat better at altitude (up to around 1700m (5800feet)), so I left it that way, as thats where most of its riding was done.  The 750 isn't quite as simple a scenario, so I guess time will tell.

I pulled the carbs and cleaned them before registration earlier this year (compressed air and carb cleaner), they were a bit mucky but ran ok after the clean.  It ran ok for over 6 months before I've run into these issues,  having said that, when I kit them I'll make extra sure to check and clean the tubes Hondaman mentioned.

The jetting change needed for altitude on the 750 is only about a 5 number on the main jet at 6000 feet. I moved to Colorado with 110 mains, went to 105 after I got here (6000 feet). I've spent lots of time at much higher altitudes with no plug fouling, and have driven to 300 feet altitude on many touring occasions (Texas, New Mexico, Kansas, Missouri) with the 105 mains by using premium fuels at low levels, regular at home. After my recent "hemi" job, I went down to 100 mains, and have the same overall effect.

[CB925]

... an update .....

Well, I pulled the carbs down, and kitted them.  There was very little evidence of "slugde" in them.  No surprises there, as they were cleaned relatively recently.

I did however find that the filters behind the seats were very dirty (the needle & seat were replaced anyhow, although the kit items didnt have the filter)  I didn't even realise they were in there, and last time I had the carbs pulled out i didnt even think to remove the seats.  The needles were in the mid position.  I was a little surprised at this, as I was expecting them to be richened.

I also cleaned the passages that hondaman mentioned.  I did feel some "opposition" to the wire i used to clean them in a couple of the carbs.

While they were apart I spent some time setting the float levels.  No. 2 was a couple of mm low (approx 24mm).  Could this explain why it was running hotter than the others?  The others were ballpark, but i spent quite a bit of time getting them all as close as I could.

Ok, so with the new needles, needle & seat, mains (I went back to 120's), new pilots, a bench synch and a good clean, I got it all back together, fired it, let it idle, and did a plug check after it idled for a few minutes.  The two outside plugs were a bit sooty, but the two inside looked ok.  I was starting to lean towards ignition again, but took it for a ride anyhow.  I found that it ran "ok", but had a big flat spot at around 4000rpm (guessing as i dont trust my tacho), and seemed a little lacklustre.  The surging was gone (nice & smooth now), and it ran for half an hour with now additional issues.  After the ride I pulled it apart again, as there was an obvious (audible) vacuum leak on no.1, which turned out to be a split manifold.  After this was fixed I rode it again, and it seemed a little better, but It was still far from perfect.

Despite my better judgement, I had organised to go for a ride (about an hour away), and when my mate turned up, I shrugged my shoulders and through caution to the wind.  Whilst the fluctuations were gone, it still had the flat spot, and was woefull at WOT (not to mention slow, and sluggish uphills).   If i nailed it (WOT), it just felt sluggish, and as i wound it back off it seemed to kind of catch up.  Also, slowly winding it on yielded slightly better results.  From what I have been reading on here recently It seemed like rich behaviour, so I put a set of 105 jets in that I found in some F1 carbs I have.  The flatspot still seemed to be there, so I was a little dissapointed, however, when i gassed it past this, it really responded, it actually caught me a little by surprise the first time, as it was a little abrupt.  I did a standing start run.  and it ran quite well, and wound out 30 to 40 kilometers an hour faster before I backed off, above the top speed it had earlier in the day.  I'll do some plug chops to find out whether it may need to go a little richer on the mains, but I'm heading in the right direction now.

Any ideas on what the flat spot / hesitation could be?  Could it be that the carbs haven't been properly synched yet?  I did notice the needles (Napco) appeared to have a different taper compared the to ones I pulled out.

Cheers.
 

[mlinder]

When I mentioned jet size, I didn't realise you were at 5k feet.
You sound a little rich to me. I would try 115's.
For the 4k issue (though on carbed motors, it's throttle position, but you may be near same throttle position at 4k each time) try moving the main jet down a notch.

Carb synch is absolutely necessary for a good running sohc4. For any multi cylinder/multi carbed bike.
one notch down may fix the midrange issue.

When I say one notch down, that means move the circlip one notch up on the needle.

[HondaMan]

While they were apart I spent some time setting the float levels.  No. 2 was a couple of mm low (approx 24mm).  Could this explain why it was running hotter than the others?  The others were ballpark, but i spent quite a bit of time getting them all as close as I could.

If just one is running richer, it will run hotter than the others. A 24mm gloat depth is good for WOT running, like racing, but tends to foul plugson teh street in the midrange.

After the ride I pulled it apart again, as there was an obvious (audible) vacuum leak on no.1, which turned out to be a split manifold.  After this was fixed I rode it again, and it seemed a little better, but It was still far from perfect.

Just a thought here: often, if one damaged intake boot is found, others lurk...

Any ideas on what the flat spot / hesitation could be?  Could it be that the carbs haven't been properly synched yet?  I did notice the needles (Napco) appeared to have a different taper compared the to ones I pulled out.

Can you tell if this taper is "faster" than on the stock needles, or "slower"? A side-by-side, stepped-down-the-taper measurement with some calipers will help decide this question. If "faster", then the circlip needs to move up, like toward the top of the needle. Vice-versa if "slower" taper. For example, the non-Honda Keyster parts I've seen are famous for being too small of a diameter overall, in my experience, which makes everything run too rich.

[coyotecowboy]

When I mentioned jet size, I didn't realise you were at 5k feet.

150m = about 500 feet.  I'm at 1700 ft and had to run 120s and the clip at the fourth position on the needle when I still had the stock airbox and 4 into 1.  I tried the needles at the mid position and it ran like crap in the midrange until you got to 5500-6000 rpm then would take off like a raped ape.

ok, simple test.  Get the motor to 4000 rpm (or wherever it feels weak and you need to back off to get it to pick up again.  Hold it there, then reach down and flip the choke up.  Does it smooth out or lay down?  If it runs better, its starving for gas and if it lays down the opposite is true.  Much simpler than reading plugs when you are trying to decide which way to go.  Don't worry about plug chops until you start getting things dialed in closer.

I grew up playing with RC two-stroke stuff and Dad always told me "an engine will live forever a little rich, but they'll only live five minutes too lean"

[mlinder]

Ah crap, I confused this thread with another carb thread that mentionf 5k feet.

Yes, I run 128's at near sea level with pods.