Topic: Bike stutters

[Spanner 1]

I've a sneaking suspicion that your stutter is actually electrical....... the Dyna ign. dropping-out at certain ( low ) rpm., especially as you say the bike runs really good when it's colder weather, at least until the motor gets up to 'normal' temp. What often appears to be a carb related problem can be ignition and visa versa  . Try this, take off the points cover and take the bike  for a run( on a dry day ) and see if the air cooling on the Dyna pick-ups has any effect, easy to try at least  

[Heirborn]

My 1970 is and had been doing the exact same thing.  I'm running pods and open 4 into 2 pipes.

Runs really good when cold, great at highway speeds, it hesitates/stutters a bit when rolling on the throttle but shags fine after that. Cruising around town is a bit gurgly.

I too am really interested in a solve.

[Brown Bomber]

What can cause this bike to stutter and gurgle when I just barely give it gas going down the road? It idles great at about 1100 RPM and has tons of power when you grab a fist full of gas, but cruising at 30-40 miles per hour is miserable. Also, it runs like a dream when cold and about 40 degrees outside...until the engine gets warm.

My 750K2 with stock ignition does the Exact same thing, (I mean Exact) so I think we can rule out Dyna. I use the factory air box and mufflers, I've tried running without the filter, and it still stumbled. I've had the bike since April of '09 and it has done it all along, sometimes worse than others, but always there. I've taken the carbs off and cleaned them thoroughly at least four times and tried putting the needle clips from the second to the first slot, just made it run rich and still stumbled after warm up, so they are back in the second slot now.

[jimbojangles]

Yah, I think Dyna is out. I had this problem before I switched over. I actually hoped the dyna would be the fix. I'm leaning toward a couple different theories that I'll try out this weekend. One is that my advance mechanism needs some attention or my timing isn't perfect. The other is that I just suck at cleaning carbs.

I'm still going to follow up on electrical...I've noticed a couple of shady wiring fixes from the PO. Is it possible that a regulator or rectifier could cause these symptoms? That whole area under the side cover is pretty rough looking and I don't know a whole lot about that part of the system.

[Duke McDukiedook]

If these coils are the same type of Taiwanese coils that partsnmore sells I received a bad new one from them and was running on two cylinders until my Pop set me straight. Don't assume that anything new you buy can't be defective, I made that mistake and it took a while to figure it out.

[jimbojangles]

OK. I did some work this weekend and eliminated some possibilities....Still stutters.

I checked the advance unit and it's performing just fine. I cleaned and lubed it just in case. I also set timing with a light, so it's spot on.

I didn't buy a compressor because I'm waiting for Black Friday sales. However, I bought berryman's in a can and sprayed through the pilot circuit liberally. I then re-synched my carbs. I did notice that what is synced at idle isn't synched at 3,000 RPM. I got things as close as I could without pissing off all the neighbors.

I rode to work today, even though it was 38 degrees outside, and had the same issues. I've got nice color on plugs 1,2 & 3, but 4 is all fouled up. I'm going to try backing the idle screw out to 2 turns out on my drive home. I've tried switching jets around to different carbs, but it's always #4 that is rich.

My question to other people with this problem:  Do you also have just one cylinder that runs rich?? It would help to know if I'm on the right track.

Thanks

 

[Brown Bomber]

I always had a pretty even color on all four plugs.

[Duke McDukiedook]

After I sorted out my bad coil I had a #2 pipe tha would not get as hot as the others- luke warm.
So I deracked the carbs and cleaned them again, thoroughly with compressed air.
Fixed the problem, pipes all even temp, has run great since then.

[Ved]

Just a shot in the dark here, but my Maxim was doing the same exact thing, and after messing with it for weeks it turned out to be that the gas cap vent was clogged. It was definitely a "DOH!" moment for me.

[TwoTired]

However, I bought berryman's in a can and sprayed through the pilot circuit liberally.

Throwing liquid on stuff doesn't always get it clean.  The pilot circuit has four holes going to the carb internal routing.  These holes are at the pilot jet, the pilot air jet, the air screw, and the exit into the carb bore.  With the spray cleaner, you can squirt into each hole and verify the passage is clear by noting the positive flow from each hole to all others.

I then re-synched my carbs. I did notice that what is synced at idle isn't synched at 3,000 RPM.

This makes no sense to me unless the adjusters were loose.

I rode to work today, even though it was 38 degrees outside, and had the same issues. I've got nice color on plugs 1,2 & 3, but 4 is all fouled up. I'm going to try backing the idle screw out to 2 turns out on my drive home. I've tried switching jets around to different carbs, but it's always #4 that is rich.

You need to verify the actual fuel level in each carb bowl.  Sounds like you have it too high in #4 carb.  And, the raw gas getting to the cylinder is making it sputter.

My question to other people with this problem:  Do you also have just one cylinder that runs rich?? It would help to know if I'm on the right track.

It is certainly NOT normal to have one cylinder run richer than the other.

Cheers,

[Spanner 1]

O.K. then, if not an ignition prob., howabout the #4 float fouling on the bowl gasket which is 'bowed' in at the sides and touching the float.... very small clearance there and very easy for the gasket to unseat when your putting the bowl on.....

[Kong]

While you all sort out the carb issue I'll toss in a little sidelight that may prove of great value to you all.  You can buy a portable air pressure tank of about 5~8 gallon capacity for very little money.  They are made for fixing flats in remote areas.  If you unscrew the hose that they put on the things and replace it first with a male nipple and then a length, 4 or 6 feet, of air hose and then a standard female connector you can use it temporarily power air devices.  Of course you can plug a regular air bib into it for blowing up tires, but you can also put a blow nozzle on it to clean carbs.  You just take it to the local gas station and fill it up at their air pump; if you're lucky it will be free, if not it will cost you a hand full of quarters.  I also use mine to power an airbrush, with it will do for about 20 minutes of continuous spraying.  You'd probably have to refill one to do 4 carbs but it would give you compressed air sufficient to blow the passages clean.  I think I paid something less than $25 for my tank.  The hose and fittings probably ran another five bucks.

[Skoti]

Hey Skoti, what do your plugs look like? any problem cylinders?

[/quote]

My plugs are more or all the same colour, sort of light brownish/greyish.

Bike runs really well 'on throttle'.
 
Stutters only when cruising through towns around 30mph.
Change up a gear and load the engine slightly and the stutter disappears.

It seems the stutter maybe created sort of between the transition from slow running jet to main jet fuel supply, would that make sense? 

[jimbojangles]

Thanks guys,

I don't think I'll make it another week before I get a small compressor. Probably something from Harbor freight. I really expect that this is a carb problem. I plan to dip the carbs one more time and go after them with compressed air afterwords. Like other people in this forum...I can tear carbs off a bike in no time now. I just hate it. I have run guitar strings through all of the air passages before, but I think there must still be a bottle neck somewhere.

The sync thing is still confusing, but I read somewhere else when I did a search that this is normal...I still don't think that's right.

I tried riding home with the idle screw on #4 two full turns out and the stutter wasn't nearly as bad as when all idle screws are 1.25 turns. For the first time the plug wasn't solid black. The only problem is that my idle isn't as smooth now.

I'll post my progress after I get a compressor.

I honestly think the people in this forum are the reason so many great sohc 4s are still on the road. I can't imagine putting this bike back together without the information I've gotten from this website.

Thanks.

[jimbojangles]

Well I haven't cured my problem, but thought I would post an update as it may be a while before I do much more work...No garage and I hate winter.

blowing the air passages out helped my bike run a lot better. Way more low end power. I feel like if I dip each carb overnight and then blow them out that the bike will run great. Cleaning carbs without an air compressor was just an exercise in futility. I may drop the needles to the second notch as it still runs a little rich in the midrange.

I did discover one cause for the stutter and likely other poor running problems. One of my sync adjuster nuts will not stay tight. The 10mm nut on carb #3 keeps coming loose. This was causing the bike to quickly fall out of sync. I squirted some liquid gasket on it to keep it in place but as to not permanently lock it in place. Bike is running stronger than ever now.

Thanks for all of the help.
 

[Duke McDukiedook]

Use a low strength loctite or other anaerobic adhesive on that nut.

[jimbojangles]

OK, I promised the people who were having the same problem that I would post my solution. Here it goes:

1. Lose the crappy Emgo replacement air filter! I actually got this idea from an oil thread (who says their useless?) I bought the filter brand new last summer, but it was causing the bike to run rich...pretty much all of the time except at full throttle. I tried calibrating the carbs countless times, before it dawned on me to try a different brand of filter. I replaced it with a K&N replacement filter and the sparkplugs started looking much better. I had to replace one plug that just didn't seem to fire right after running so rich for so long, but now it runs great.

2. Sync your carbs CORRECTLY. The video of the guy syncing his 500? 550? is a great place to start, but a bit misleading. Syncing my carbs are 3-4,000 rpm left me with one cylinder a little rich at idle and some annoyed neighbors. I think the air filter was the root of my problem, but my idle is a lot smoother with a proper carb sync.


I hope this helps someone...

[jimbojangles]

OH yah. Nothing would have helped if I hadn't done a proper carb clean with compressed air! I'd said the carb dip and compressed air got me half way there. The new air filter and proper sync did the rest.

I hope to not clean carbs again for a long long time, but at least now I know how.

[OneWheelDrive]

I have a suggestion.  Try turning off your petcock for a few minutes while cruising around town.  I was having the same issue with my 750K2 and although I thought I had set the floats correctly, they were a couple of mm's too high, causing the rich off idle stumble.  If the stutter goes away in the first couple minutes of being starved of fuel, you know you have to drop the floats a bit. I would definitely check that #4 float though as it definitely sounds like something is off in the carb bank.

I also had the same experience with a cheap EMGO filter choking the motor and have had much better luck with the K&N replacement.

Good luck all!

[Skoti]

I had exactly the same problem with my CB750F1, done all the things listed here and nothing worked.
Just fitted new carb slide needles and needle jets and that's cured the stutter plus | get another 20 miles to the tank full.

[Duke McDukiedook]

Hopefully you replaced them with OEM Keihin needles, the Keyster replacement needles have a spotty record.

[Skoti]

 Replaced with genuine Honda needles and jets.