Topic: When it rains....

[Inkscars]

I freak out and scream at stuff.
So, I've been complaining about this "hiccup" on my motorcycle Elsa, for quite sometime. Tested stuff, adjusted stuff, couldn't ever duplicate it sitting still.
Elsa is a 1977 cb750 k with stock PD carbs.
I run uni filters, kerker 4-1, 125 or 130 main jets(I don't want to pull them off right now) needles
I believe 2nd clip down. 2.5 out on mixes
So, I've had this problem off and on go a season or so, sometimes it's more prominent than others, but there's no rhyme or reason to it.
Spark plugs have been changed, the cylinders always show a remarkably similar reading during a chop.
Vacuum gauge is new and was tested on an electric vacuum pump. Intake boots have been tested for leaks while running. Bike has been timed. Tappets adjusted.
http://youtu.be/9mhVDLl7QnI
I was checking my sync today because of a midrange gurgling and it just started happening. I've never known what cylinder it was.
I am happy to answer questions if you want to help trouble shoot, or maybe you have had something similar happen?
Hopefully that link works.

[Retro Rocket]

If you love screwing round with your bike simply because you love working on it then use pods, if you want a good state of all round tune with fuss free operation, use the airbox. Sorry Amber but pods really suck on these old bikes, especially with the stock carbs, you will always have some sort of compromise when tuning with pods.... Flat spots are very common.... Pods are designed for flat out operation, I have 3 hi horse power engines to build in the near future and i will be using some sort of airbox for all 3, one is even fuel injected and still gets an airbox...Only reason is that i want a consistent state of tune...  If you want to spend a couple of hundred on a filter system with velocity stacks, member Tintop has an aftermarket filter system that works well, the velocity stack design incorporated in the design goes a long way to helping the bike run well....I can link you if interested.....   Sorry if thats not what you wanted to hear.....

[Inkscars]

As much as I love seein your name pop up in my replies retro,
This is not a pod thread
This is not a #$%* on my vacuum gauges thread
This is a help or GTFO thread.
I have never ran a stock air box on this bike because it was toasted. I have deleted the brackets and ridden it for years now.

[Inkscars]

Also, it does not explain why it happens on one cylinder.

[scottly]

Sounds, and looks by the gauge, to be a slight back-fire. My guess is that cylinder is slightly lean.
BTW, that is a very small sneeze, not a hiccup.

[Inkscars]

Ok, so be honest.
Am I #$%*ing knit picking?

[scottly]

If knit picking is the difference between good enough and perfection, then maybe. Honestly, since you have narrowed it down so well to the one cylinder, why not make it perfect? Play with the idle mixture screw on that carb only, and see if you can stifle the sneeze.

[lucky]

This is a help or GTFO thread. LOL ...lol..lol

"I run uni filters, kerker 4-1, 125 or 130 main jets(I don't want to pull them off right now) needles
I believe 2nd clip down."

IF the clip is NOT on the 2nd notch down from the top of the needle it will have a hesitation when trying to give it quick throttle.

1st clip groove down on the 1977 was the stock position.

The 2.5 turns out on the mixture screws sounds excessive. Too lean.
Make them 1.5 turns out and see what you have.

You can get a free small screw driver in the package of 9V Duracell batteries that is good for those mixture screws or one of those eye glass screw drivers works well.

Make sure the pilot screws have the O ring,washer, and spring and that the o ring is not mangled.

One thing you failed to tell us which is critical with your set up is the idle jet SIZE.
You should be running a #42 with pods and 4 into 1 exhaust.

That is WHY you probably have that mixture screw out 2.5 turns.

My recommendation is #42 idle jets and 1 turn out on the mixture screw.


I hope this helps.

[Inkscars]

My idle and WOT work actually work pretty well. Snap to WOT can be precarious but let's say I need to get the hell away from someone or go from 15-60 really fast it's good.
It's like cruising, like 45 or sometimes even 65, just barely needing to turn it when it does the gurgling.
I always pull and clean my pressed slow jets when I'm cleaning, but if they have a number stamped on them I haven't noticed the last couple times.
I read a few threads back in the day when they talked about drilling them out to help with some people's idling issues.
My air mixes have o rings washers and springs I believe.
Again, I tinker at a shop and doing other carbs sometimes throws me on remembering my own.
I am able to get my hand in with one of those little bits that has a flat driver on it pretty easily. I guess it wouldn't hurt anything to check and adjust them tomorrow.

I hate even telling people on the forum that I run the uni filters. It is possible to tune them. Sure it takes practice. Once you've done a set a pd carbs, it takes like no time to do them again. If my bike had ran when I got it, and the box wouldn't have been cracked with spider #$%*s in it, I might have used it.

[Retro Rocket]

As much as I love seein your name pop up in my replies retro,
This is not a pod thread
This is not a #$%* on my vacuum gauges thread
This is a help or GTFO thread.
I have never ran a stock air box on this bike because it was toasted. I have deleted the brackets and ridden it for years now.

Hmmm, a little defensive...     Wasn't intending to fcuk with ya.... 

I hate even telling people on the forum that I run the uni filters. It is possible to tune them. .

My point was that pods will NEVER run as well as a set up including the correct velocity stacks and if possible, still air  {sounds like you already know this}.....   I know , I know, GTFO....

[camelman]

Any chance the plug wire for that cylinder could be arcing/shorting?  Might be good to see if it touches any other wires or the frame. If do, then wrap that short portion of the wire with electrical tape to see if the hiccup stops.

I wouldn't jump to thinking it is a carb problem just yet...

Camelman

[dave500]

if your plug caps are old check them with your multimeter,try switching the cap from that cylinder to another and see if the vacuum jump follows it.

[lrutt]

truly sounds like slide cut away. On the lean side. Problem there is to have a richer slide you would need to add material. Not easy to do. And i'd bet it's doubtful that richer slides are easily available.

this assumes your problem is just with steady state cruising at low to mid speed. If it's in moderate acceleration at htat speed then I'd be double checking the accelerator pump. You may have partial blockage on the one cylinder, or it might just be weak. 

As for your mix screws, if they are past 2 turns out, then you need to adjust your low speed jets.

My K8 has a stock air box and after market 4 into 2's and is ok but it took some work to get the accelerator pump sorted.

[flybox1]

truly sounds like slide cut away. On the lean side. Problem there is to have a richer slide you would need to add material. Not easy to do. And i'd bet it's doubtful that richer slides are easily available.

this assumes your problem is just with steady state cruising at low to mid speed. If it's in moderate acceleration at htat speed then I'd be double checking the accelerator pump. You may have partial blockage on the one cylinder, or it might just be weak. 

As for your mix screws, if they are past 2 turns out, then you need to adjust your low speed jets.

definitely think you are lean, and probably across the board.  IMS screws are only effective up to 2 turns as lrutt mentions.  increasing pilots is a good suggestion. 38's or 40's might do it.  42's are a huge increase, but seemed to have worked for lucky and are his go-to rec.
 what do your plugs look like after an idle chop?

[Magilla]

I think she needs a beer, a hug and a Valium.  All in that order.

[Duke McDukiedook]

When was the last time you cleaned that set of carbs? Those pilot circuits have to be spanking clean to operate properly.
You may just be hitting a flat spot on your setup that you will never be able to address properly.
My VFRs hit a flat spot at 6-7K and they are bone stock except for K&N air filters.

[iron_worker]

Here is something totally different .... sticking intake valve? Getting some slight spit back through the intake tract?

IW

[Duanob]

Here is something totally different .... sticking intake valve? Getting some slight spit back through the intake tract?

IW

That would hiccup on every rpm if it were valves. I'm going eith the plug cap or wire slightly arcing.

And I don't think people ignore this person because she has a box. I think its because you have a crass way of asking for help from respected members.

[jamesbekman]

I wouldn't call it crass.  Just frustrated with internet forum replies.

[bjbuchanan]

Lucky is right about his recommendation, Retro is too rly. Do what makes you happy but consistent state of tune  is the primary issue with pods. that open area there with pressure fluctations can affect your state of tune because carbs are all about vacuum. Now that I said my piece on the airbox, try the larger pilot jets, or if you have press in drill them with the baby drill bits.

That many turns out on your airscrew is a hallmark of a too small pilot screw. Idle would be just fine and WOT would be good if the mainjet is right. Your rpm range is like 1/4 to half throttle max, probably consistent with 4k-6k rpm right? That is where the pilot jet is beginning to take effect. I have the same issue I am working on currently, diff carbs tho and different setup so my tune tweaks right now prob won't help. I'm about the same stage as you but I run an airbox

[lucky]

My idle and WOT work actually work pretty well. Snap to WOT can be precarious but let's say I need to get the hell away from someone or go from 15-60 really fast it's good.....

(shortened)

"I read a few threads back in the day when they talked about drilling them out to help with some people's idling issues."

That info came from the CB750 chopper web site.

But if you drill them to the recommended size they tell you they will be too large.
They will be #45mm and that is too large. You need #42 mm.

I have personally tested both and the #45 (.017thousandths) was too rich with this same intake and exhaust set up.

I have also tested #38,#40 and #42 idle jets and the #42(.016 thousandths) had the best quick throttle response with NO hesitation at all. To me, any hesitation at all is unacceptable.

It was a lot of work to remove the set of carbs completely  to test each idle jet size.

[camelman]

By the way, not being able to duplicate it while sitting still further justifies the shorting possibility. Thinks jiggle around when riding making a short more likely. You might just have wires in the correct place for a short in that video.

[Tugboat]

BTW - 3200 posts, I think she's earned a little crankiness

Go get 'em, champ!

[Inkscars]

Ok so after reading all of these reposts, I thank you for your help trouble shooting.
I don't expect an answer from someone who has had my exact problem. I enjoy when people have.....opinions or ideas that are outside the range that my puny female mind can reach out and grasp.
As far as my reply to retro, he and I have what I would consider some history, and there's never any ill intent with him.
While I'm on my soapbox, granted many many of my 3200 posts are SSDB, but I have build threads and a pretty good voice when others need help, have donated parts for builds gratis, and have even mailed beer and get well soon cards to other members. So, I that doesn't make me a respectable member, oh well.

*steps down*
As for #4, the cap was replaced due to a split in the boot last summer, the wire was trimmed to make sure it was tight and free of corrosion.
The valves were re-adjusted just yesterday by another mechanic at the shop.
The carbs were cleaned when I had the pinstriping done on my tank last so, maybe late February?
Sunday if its raining I will fiddle with the carbs some just to drown the curious cat.

[Retro Rocket]

Gave inky a hug and a Valium, alls good.....