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Choppy steady speed and idle (sometimes)

teebo

Veteran Member
Joined
Dec 5, 2021
Total Posts
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Location
Oklahoma City
I've been trying to figure this out on my own for a couple weeks. When cruising at a steady speed, it feels slightly choppy sometimes. Occasionally, it feels like it cuts out very briefly. Once fully warm it actually idles worse, and every once in a while, stalls out with the throttle closed and/or at a stop. It doesn't do this very often though. That is, for the first couple minutes after starting it's as I would expect. Then for the next 10 minutes or so the idle is fine (1200-ish), but after that it's common for the idle to be slightly choppy and closer to 1000. Vast majority of the time it never stalls, but it makes me believe it could. In those case, most of the time it will recover after goosing the throttle and letting it idle for a bit. But it never seems to get back to 1200.

While slow acceleration in first gear from a stop is a little chuggy sometimes, if I am more aggressive it takes right off. From there, acceleration is just fine. Through all throttle positions and RPM's (all the way up to redline). Decelerates just fine too.

Checking plugs after idling in this case, the right side is rich (slightly black plug). Left is fine. Have not done any plug chops (I don't have a kill switch).

Battery was at 13.48 immediately after the ride. Timing checked. Valves adjusted. Float is currently set at 26.5 (it was at 26), but I didn't notice a difference. I used a Uni-Syn to sync at idle and with throttle open. Starts up easy in all cases. 1-2 cranks and boom. I did convert my air filters to use the Unifilter foam (the green 65 ppi). Stock jets. New diaphragm (I converted to the thinner 4into1 style that doesn't mangle the slide). Cleaned carbs (again). New-ish B8ES plugs.
 
I would swap electrical connections between coils so the right coil fires the left cylinder and vis versa. Then see if the rich plug condition swaps with that.
 
I would swap electrical connections between coils so the right coil fires the left cylinder and vis versa. Then see if the rich plug condition swaps with that.

A wise man once said "90% of carburetor problems are electrical."

I swapped coil sides. But neglected to do so with condensors. Still fouled slightly on right and I could occasionally feel it miss a beat. Reduced RPM at idle after about a 5 mile run.

I put in a spare set of NOS condensors. Took it for the same distance ride. First time in awhile idle RPM didn't drop. I didn't feel it cut out.

Hard to say at this point about fouling. Still blacker than left. I tied to clean it before the run.

It's fooled me before. I think I'll put in some fresh plugs and take it for a longer ride.
 
Also... I'm getting one of those quick release fittings for the balance fuel line on the tank. There is no good way to remove the tank without spilling some amount of fuel otherwise.

I've put it off because the one I found on Amazon is $50 and I thought "how many times will I remove the gas tank?"

The answer is "more than enough" when chasing these problems.
 
I did take a little longer ride with the new condensors. I didn't experience the occasional cut out. But it did stall near the end of the ride while approaching my house. I actually restarted while the bike was still rolling forward. Started right up. Right plug was still darker than left, but not powdery.

I had intended to anyway so I'd have spares on hand, but I ordered some coils. I don't like lack of spares and always having to wait for shipping to test.

Another question... It could be complete coincidence, but any chance that Unifilter foam just doesn't let enough air in? Several things have changed since, but there was a point where this wasn't happening. The filters are one of the bigger changes. When I got the bike, it had shorties on it. I had rejetted and it seemed to run quite good. Since then, I've replaced the mufflers with longer Emgo's (so not stock), and put the original stock jets (with new o-rings) back in.
 
The stock jets with the Emgo mufflers should be fine.
I've used the Uni foam for filters without an issue but I also ran them dry, no oil. Oiling can be tricky getting the same amount into each filter and letting the drain off. Too much oil restricts air flow.
 
The stock jets with the Emgo mufflers should be fine.
I've used the Uni foam for filters without an issue but I also ran them dry, no oil. Oiling can be tricky getting the same amount into each filter and letting the drain off. Too much oil restricts air flow.

I had the same thought about the oil. When I first oiled them it was too much. Cleaned and oiled lighter. For this latest round, I cleaned and ran dry.
 
Replaced the coils and same.

One thing I notice is that it just idles better without air filters. I can't imagine putting the foam on wrong. Maybe stretching it too tight, but it's not.

With that said...

I note that when I put the filters on, it does put inward pressure on the carb. So with filters off, if I push the filter end of the carb in and spray carb cleaner around the manifold idle will slow. Normally I'd say Aha! However, it's pretty common for the idle to drop all on its own. Clicking away at 1200 and all of a sudden it slows to 1100 briefly then picks back up. Sometimes I can hear it cut out (like it took gulped). Was it the spray or just its odd behavior. Hmmm.

They are newish manifolds. I'll remove, clean, and rest again.

Not sure if it means anything, but I start with the fuel mixture at 3/4 out (3D carbs). But when adjusting both go down to to 1/2 for max RPM.
 
When you remove the insulators surface sand the mount to be sure it's flat. I use Honda Bond on the gasket, both side, to insure a good long lasting seal. Also when you remount them run your finger around the mating point to try to get them centered up, there should be no lip from the insulator into the head but there may be a lip coming back which is ok.
 
I believe I'm back where I started. I don't even have to test drive it.

At this point I'm not even sure I can tell an accurate idle mixture setting because the idle wanders +/- 150 RPM from one moment to the next. Occasionally it will hold a steady idle for a little bit. One session it seems like it might be steady at near 1200. Come back again later and it won't come off 1050 without adjusting idle screws.

I'm going to take a break and research some more. All I'm doing now is spending time and money.
 
I've cleaned carbs again while paying extra attention to the idle circuit and slow jet. Nothing appears to be clogged. This is the second clean so I didn't expect a change.

I also checked the voltage at the hot posts on the points. Both points open. It's reading about half volt less than battery. Battery was at 13.5 (roughly).

Compression is fine. Roughly 170 for each side. Which is down since I got it. Which was 180-ish then. 170 is the same as when I checked it over a month ago.

The intake boots have been cleaned and sealed. I don't have Honda Bond. But I did have some high temperature gasket maker. I can spray around the boot in any quantity and I don't believe there is a leak there. Though, I think I need to ride it for a awhile and try it while it's hot.

Its actually idling worse. Likely to stall without kicking the idle screws up until it warms slightly.

However... Spraying around the felts will cause a stall. Especially on the right. I have ordered some new felts.

Past that? No idea actually.
 
Also... Choke appears to do nothing at all. Except fully closed, at which point it stalls. But between fully closed and wide open, it doesn't seem to change anything.

Normal?
 
Also... I'm getting one of those quick release fittings for the balance fuel line on the tank. There is no good way to remove the tank without spilling some amount of fuel otherwise.

I've put it off because the one I found on Amazon is $50 and I thought "how many times will I remove the gas tank?"

The answer is "more than enough" when chasing these problems.
Can you post what version you purchased….I’ve been thinking of buying one also for my CB77.
 
It's a shame that we have to buy Hondabond in a tube that will eventually let it harden after using the small amount that we typically need, but there is nothing else like Hondabond/Yamabond/Threebond which, for the most part, are apparently all very similar or the same. Hondabond will last better than any other sealer for that situation. I know it isn't cheap and you'll not likely get to use even half the tube but it works really well. I bought a tube when I built my 450 engine 5 years ago and of course it's hard as a brick now, which reminds me I need another tube for the drag bike engine...

Oh, and often these bikes just won't idle well cold, so you should set the idle speed after it's warmed up and just put up with the lack of cold idle if that's how it is.
 
I also checked the voltage at the hot posts on the points. Both points open. It's reading about half volt less than battery. Battery was at 13.5 (roughly).

Measuring open circuit voltage, with the points open, doesn't really tell much about the condition of the wiring and switches. One strand of wire is enough to get a reading on a digital tester even if it won't pass enough current to do anything else. Measure your voltage at the black/white wire connection on the coils, with one set of points closed, and see what you get.
 
Measuring open circuit voltage, with the points open, doesn't really tell much about the condition of the wiring and switches. One strand of wire is enough to get a reading on a digital tester even if it won't pass enough current to do anything else. Measure your voltage at the black/white wire connection on the coils, with one set of points closed, and see what you get.

Good to know. Thanks.

What voltage is acceptable?

Guess I'll be installing that valve on the tank. Actually, pretty excited about that.
 
I'm not sure what is next. Maybe I'm not cut out for this?

I thought my clean and seal of the intake boots worked. But next time it was at full temp spraying around the boot would cause it to near stall.

So I figured WTH and ordered genuine Honda boots and gaskets. And some honda bond HT (not sure if this is correct).

Same darn thing.

How tight do y'all make the clamp? Is there somewhere else it's getting in and it just seems like the boot?
 
If you're still using the factory clamps, they only tighten up so much and will clamp together at some point. With new boots you should be able to tighten them pretty tight before reaching the clamped-together point. With new boots and Hondabond (HT is fine) you should be fine unless one or both of your intake surfaces on the head is not flat. Some part of all that would seem to be not quite right if you can get a reaction while spraying around them.

You're cut out for this, we all go through stuff at some point in our vintage Honda twin ownership. I chased the oil flow problem for a couple months on my 450 before figuring out I was the idiot who put the oil filter valve back together wrong.
 
Thanks AD.

I used a straight edge to check flatness and it was. But I went ahead and did as LDR suggested and used a block to sand it smooth.

With more careful spray direction, it does seem where it meets the engine is OK. But if spray directly at the boot on the carb side it has an impact. Pretty easy to stall it out with a prolonged spray.

I'm using factory clamps. I wasn't sure if there was a point where it would damage the carb from too much pressure.
 
No, the factory clamps can't do damage to the boot or the carb, they "bottom out" at some point where the ends become clamped together and you can no longer tighten them. I had to use automotive worm drive clamps on the Mikuni carbs on my 450 because I was forcing the 36mm carbs into the boots for the 32mm stock carbs and the factory clamps - which I bought new replacements of - wouldn't clamp tight enough to hold them, so you won't cause any damage.
 
May not apply but I noticed that with the 3D carbs there's a casting part line that extends into the recess where the boot seals.
RIMG0634.jpg
Depending on the rubber it's possible that this could cause an air leak, theoretically the clamp will compress the rubber to conform. I filed the part line down to get an even surface.
RIMG0678.jpg
 
Thanks LDR! I had gut feel it is coming in through the bottom of the carb side. Mainly because if I spritz the top it's OK. But if I douse it, it runs down to the bottom.

I'll pull carbs and check. I'm getting quite efficient at pulling carbs.

I'll probably need to replace the screws on my clamps. Even if they aren't JIS. They were slightly cammed over when I got the bike.
 
I also discovered that the clamps were deformed at the bottom. As in, it's like the end of the clamp caught on the rubber and stopped constricting. Which just caused it to bend outward, right at the very bottom of the boot. Imagine a ball with a huge wart bubbling out. I straightened that out, so it could be a matter of tightness and maybe that casting line.
 
Wanna hear something funny?

Maybe it's normal. Seems unlikely.

I don't think it's the boot at all. Or at least not now. I'm convinced it was originally. Or rather the seal on the engine side.

I got it tight. Real tight with a filed clean casting line. Even tried a different style of clamp. A strong blast would impact idle, only on the carb side.

My starter fluid didn't come with one of those red tubes so it was more of a shotgun blast.

Wouldn't you know... Said blast threw quite a bit against the carb body. Specifically up to that diaphragm cap.

Carefully direct spray around just the boot. All good. Even a tiny spritz around the cap. Chug.

I'd like to confirm more. I ran out of anything that sprays though.

Seal that cap?
 
OMG. It works. It's beautiful. Smooth even start from a standstill. Even throughout. And darned if it didn't want to stall when coming to a stop.

I'm using those diaphragms like are found on 4into1. I noticed those are thinner than the other style that mangle the slide to install.

I guess aftermarket diaphragm + cap just wasn't making a seal. I used a very thin layer of honda bond in that channel the diaphragm sits in. Then a very thin layer on the very outer edge. Let it firm up awhile then torqued it down.
 
Well, that's good news and something that wouldn't have even happened if OEM diaphragms were still available (and at a reasonable cost). I never saw or heard of that issue before and I replaced my share of diaphragms while working in the industry. Glad you got it sorted.
 
That is one of the things I changed. Switched to this style of diaphragm a couple months ago.

But maybe the cap comes into play? Rolls up sooner? Isn't totally flat?
 
After all these years and probably quite a few disassemblies, I could easily imagine the top covers might not be perfect anymore. You found the cure, which is all that really matters now. It's like using a slightly longer bolt in a 450 valve cover bolt hole that a PO weakened the threads on by overtightening, it isn't standard but once fixed the solution isn't visible. Since you'll probably have the bike until you can't own anything any longer, it will only matter to the next person who eventually discovers how you fixed it. And they might learn something from it too.
 
After all these years and probably quite a few disassemblies, I could easily imagine the top covers might not be perfect anymore. You found the cure, which is all that really matters now. It's like using a slightly longer bolt in a 450 valve cover bolt hole that a PO weakened the threads on by overtightening, it isn't standard but once fixed the solution isn't visible. Since you'll probably have the bike until you can't own anything any longer, it will only matter to the next person who eventually discovers how you fixed it. And they might learn something from it too.

I'll just have the bike buried with me.

Anyway... Less tinkering more riding. For awhile.

Though next rainy day I'll put the stock size sprockets on.
 
I wasn't expecting it for sure. I've been working on this for weeks. I've searched all over the internet and not a one had this as a problem.

I don't remember where I got the caps. Out of curiosity I may see if I can find better/nos ones just to see. I mean others are using the same diaphragms and I didn't have this issue with the other style of diaphragm.
 
Thanks. I have such a hard time finding things on their site. Have tried before. Ordered some from ebay from them and I'll test. Plus, I've never liked the rivet on top for the ones I have. The Sirius ones have a respectable rivet.

Put 70 miles on it this weekend. Such fun. Some minor issues to attend to but no show stoppers.
 
I installed a cap from Sirius, after removing the sealant I had added earlier. No leaks detected.

I think I see a slight difference between the Sirius caps and the others. Slightly more curve when its going vertical on the originals? In my head?

I suppose it's possible that I didn't have the screws torqued down enough? I don't recall them being loose.

I don't know. Regardless, the Sirius caps are better looking. Better chrome finish, and the rivet on top doesn't look so cheap.

IMG_20220505_195219.jpg

IMG_20220505_195240.jpg

IMG_20220505_195312.jpg
 
I'm sure you wouldn't be surprised to learn this is actually two issues. One is the idle problem. The intake leak definitely fixed the idle issue.

But the other issue is still there. Mostly. I don't notice it at all, or just barely in 3rd or higher going over 40-45.

It's most evident at slower speeds, say 20-40. Mostly just in 2nd. It sputters. Sounds terrible. When it does it, if I increase the throttle a hair, or shift into 3rd it goes away. If I do a rabbit start with plenty of throttle it's smooth throughout.

My initial thought was something with the slow speed circuit. I did try slightly richer idle setting. Also tried changing the #70 jet to #72. Just to see if that made a difference. It sputtered more.

I check my timing with a strobe. Even though it was dead on with a static check, with the timing light left was advanced and right retarded. So I widened the left gap a hair and retimed. Very close to the same now.

What's going on in this slower steady speed? Throttle position would be minimal. So some combo of idle and slow speed circuits? Am I feeling a too rich condition? I keep thinking my idle screws being at 1/2 out (3D carb) is curious. But maybe this isn't abnormal and I should stop thinking about it.
 
He said when he increased the primary main from 70 to 72 it made it worse, maybe it's a tad too rich and 68 would be better
 
What would cause too rich? Aftermarket mufflers or Unifilter foam air? As another test I tried the Unifilter 60/40 ppi layered foam. And sprayed it with oil. Just for easier air flow. I didn't notice a difference with this condition, but both sides took a very slight tweak richer on idle.
 
If the aftermarket mufflers are louder then there's less backpressure so probably not that. I tend to use filters dry, if you aren't taking the bike off-road then the stuff you encounter on the typical highway ride is not damaging enough to the engine to warrant worrying about oiling the filters whether pleated cloth like the K&Ns I'm using or the Unifoam IMO, and oiling causes more intake restriction so it makes a richer condition.
 
If the aftermarket mufflers are louder then there's less backpressure so probably not that. I tend to use filters dry, if you aren't taking the bike off-road then the stuff you encounter on the typical highway ride is not damaging enough to the engine to warrant worrying about oiling the filters whether pleated cloth like the K&Ns I'm using or the Unifoam IMO, and oiling causes more intake restriction so it makes a richer condition.

I was running dry with the green 65ppi. I was a bit concerned. I don't take it offroad, but it does get dusty here during the summer.
 
Float height to 27 made a noticeable difference. Not gone, but much less obnoxious than before.

27.5 now? What is the most?

I ordered some NOS #68 jets. Probably should get some of larger jets the next size down.

But which is better? Jets or float height.

I still don't get why these changes are needed.
 
The float level has a direct correlation to the amount of fuel available thru the emulsion tubes and jets. I would hesitate to go further without knowing that there you may encounter a very lean condition at high rpm. I would opt instead for a 27mm level and 65 main.
 
The float level has a direct correlation to the amount of fuel available thru the emulsion tubes and jets. I would hesitate to go further without knowing that there you may encounter a very lean condition at high rpm. I would opt instead for a 27mm level and 65 main.

Gotcha. Thanks.

Order the #65 and tossed in some #100. Just in case. I already had both a size larger than stock. Building a set of NOS jets. Not sure what I'm ready for, but I'm ready.
 
Got the #68's in. #65's won't be here for a few days.

So close. It ran so nice, just a few little symptoms. I can even hear the difference. It just sounds happier. Happy bike, happy owner.

I would have ridden longer but it's coldish with the wind, and rain is coming. And I'm a wuss.

So #65 and I'm guessing maybe resetting the float. It's almost like you've done this before, LDR.
 
Got the #68's in. #65's won't be here for a few days.

So close. It ran so nice, just a few little symptoms. I can even hear the difference. It just sounds happier. Happy bike, happy owner.

I would have ridden longer but it's coldish with the wind, and rain is coming. And I'm a wuss.

So #65 and I'm guessing maybe resetting the float. It's almost like you've done this before, LDR.
Actually I haven't done this with these carbs but I have worked on a wide variety of carbs and they all work the same basically. Different methods of accomplishing the same results.
I suspect with the 65 installed you will be able to return the float level to spec.
 
#65 with float back to 26mm is pretty much it. I "may" hear an ever so slight sound when cruising at high speeds. It's subtle and periodic.

Probably not worth taking the carbs off to play with float height. But maybe the next time they come off I may try just a nudge higher.

Thanks all. A milestone for me.
 
There is more. Ultimately good news and thought I'd share in case someone else has this issue.

I rode quite a bit since the last posts. There was still an issue in 2nd at 6-7k range. Sometimes it really chugged.

But just sometimes. I feel there was a pattern just not sure what it was. Again, open throttle more, or close it a little, and it would recover. Really take off, and I'd never feel it.

At any rate. Thought maybe the #68 was fine for slow speed, and I was maybe having a rich condition in the intermediate range.

So... Increased to #68, reduced secondary main to #100. Float still at 26.

Problem still there but less.

Thought maybe it was something else. Checked timing (again), voltages, blah, blah. Settled on non-resistor plug caps and iridium plugs. Maybe the extra quality spark would burn things better?

Problem noticeably better.

Float to 26.5.

Problem gone. Or at least it didn't happen during a nearly 20 mile stop and go trip.

I will run with this for awhile and check plugs after some decent number of miles. Really wish i could plug chop.

I'd still like to know why I'm doing this. But I am learning a bit.
 
Of course you're doing it because it's the pursuit of perfection, getting the bike to run as right as it can. Do you not have the room locally to do a plug chop? A 1/4 mile of road is enough if you get it to the problem range pretty quickly.
 
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