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I've been steadily working on my first HD, a '95 Dyna Convertible and I've made great progress except in one area: lower RPMs. No matter how I work on the timing and carb adjustment I can't seem to get the engine to run smoothly from 1800 to 2200 RPM. Starts with a flick of the button, idles great (if a bit lumpy) and accelerates like a scalded goat. Still, it won't run smoothly in that RPM range in any gear.
Here's the setup: Andrews EV-27 cam with Screamin Eagle adjustable pushrods, Keihin CVK 40 carb, 44 pilot, 170 main, Dynojet D146 needle clip on fourth groove from the top , Kuryakyn Hypercharger with K&N filter. I had a 45 pilot, bumped up to a 48, fouled the plugs and started working back down the scale. Same with the needle, moved the clip down a notch to lift the needle and it drank gas and screamed down the road but the low RPMs were unaffected.
As far as I know it still has the stock ignition setup, at least there aren't any after-market labels attached under the covers. And, the timing is as close to dead on as I can get it using that lame clearview plug.
Any good ideas out there?
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Last edited by oldroadie; 07-21-2009 at 08:40 PM.
Reason: I had the needle listed as D148, it's really D146
Location: NC and across the Mississippi every opportunity
Posts: 1,120
First, is this a Harley CV or the jap bike version (CVK)? There is a difference. I'll assume it's an OEM HD for now. Also, some of those kits come with jets that are numbered unlike Kehein, i.e. a 170 Dynojet is a 190 by Keihin measurements. If it is in fact a Keihin 170, that's way lean. An actual 190 is a bit fat, but should be able to tune to that. Is it a Thunderslide, drilled slide or stock slide?
You know what you've tried and I don't so, I'm talking as if I have no clue. Your problem rpms are just at the transition from idle jet, mixture screw and needle initial feed. It's also right where the hypercharger is starting to open a bit... First thing I'd do is prop it open with a cothes pin and plug the vacuum line for checking purposes.
Also, the stated rpms are in a range where the module will almost begin it's advance based on rpms rather than VOES input. I'd check the hoses then the VOES to make sure it was working by pinching the hose at idle and listen for an rpm drop. And again in the 1800-2200 range. (That can take a few seconds for the vacuum to bleed and the rpm drop will be a bit less)
With the 45 jet, I'd go 3 - 3 1/2 on the idle screw as base. 48 about 2 1/2. 3 on the needle is good, regardless of the slide
Next I'd check the float level, critical on these carbs, by removing the air cleaner, remove the overflow hose, connect a clear tubing to that. Using the drain screw, drain the bowl and attach the clear hose next to the bowl (loop it around) so it's sitting vertical. With the bike upright and the carb level (checked with a level) and the drain screw still open, open the petcock with a vacuum pump if necessary and look at the level in the hose. It should be exactly at the bowl flange where it meets the body (+) or (-) 1mm. If it's low, that can cause a problem.
Like most know - bikes all have their unique personalities and sometimes it takes a bit of "socializing" to warm up to them
Thanks for the good response. And, no, I haven't tested the VOES yet, that was next on my list as I was hoping I wouldn't have to shuck out another $70 for parts.
As part of my "let's rebuild this sucker" program all of the vacuum hoses are new and working. It's a Harley badge carb and I can only assume it's a stocker. As far as I can tell it's an undrilled stock slide, but really drilling just changes the throttle response more than steady input, doesn't it? As far as the Hypercharger, once it gets vacuum those gates close and I haven't seen them open back up under any throttle input. Still, with that massive slot in the bottom that shouldn't affect the air intake.
I have no knowledge of the main jet other than the 170 markings but it runs very well at WOT and that's the true test of the main jet, everything in between idle and WOT (for the most part) is the needle taper; at least that's been the case on the many other Keihins I've worked on.
The PO stated it has a Stage 1 jet kit. As you can see from this:
The Previous Owner had the circlip in the third from the top position making the transition even leaner than it is now. That said, the midrange RPM is so much better at the fourth groove I'm reluctant to go back. As for the mix screw, 3 1/2 turns out on the 45 made the throttle really soggy, it got better at 1/2 turn out which is what prompted me to reduce the size to a 44 and it seems to be running well enough at 1 1/2 turns out, again all except for that narrow RPM range.
Location: NC and across the Mississippi every opportunity
Posts: 1,120
Ok. I hesitated to even mention the Hypercharger, as I've never run one so I'll plead ignorance (by definition)
All else you've mentioned sounds familiar...
Correct in that drilling a slide is, by design, intended to increase throttle response. Here's where the ghosts come in - when you do that, it immediately emulates a lean condition during low throttle, mid-range steady running. It'll do it everytime. That's probably why every article/instruction sheet you read tells you to go up one jet size and add up to .050 in shims under the (stock) needle. And, most sheets with the adjustable needle kits tell you to drill the stock slide. That's why I asked...
I almost got away with a 175 once, but it was heat-streaking my cylinders from being too lean. There are at least 3 different "adjustable" needles out there and in fact, there are 7 different OEM needles besides the '88 Sporster needle. 3 different diaphram springs too. I've only played with the springs, stock and drilled slide and Thunderslide, 2 adjustable needles and 2 of the 7 different OEM needles. And of course jets... All that was on one bike (mine) and done one step at a time and the results mentally noted. So, I'm sharing what I've learned. But I never experimented with an adjustable needle on a stock slide so I'll disqualify myself from anywhere near being an expert, but here's what I do know:
It's running rough because it's starving for fuel at steady low throttle position. With that narrow band of "unhappy," I think you're real close. What happens when raising the needle, it changes the fuel delivery rate at a particular slide height. True, richens it up in a portion of the travel, but causes an imbalance otherwise. Fuels a little much at near idle and fools you into thinking it's good at WFO because it's almost rich enough everywhere except actual WO throttle for anytime beyond a short burst. That's what I've found everytime the needle was anywhere other than 3 - the main jet was mis-sized. Also, 1/2 on the screw and the idle jet really isn't doing anything for you at all beyond (and barely) what it needs to actually idle - and that jet (screw-adj) is a necessary part of the overlap from idle to lower midrange - believe me. The needle being "up" trying to compensate for a small main jet is the reason it's soggy when the idle screw is opened up.
I know, with that 170 it'll pull like a mule, even from low rpms and rev up quick under load and make ya grin, but with your cam and other goodies, a jet that small won't work for all 'round riding regardless of the idle setting. And no one is more fuel mileage neurotic than me, but I like my stuff to run decent too.
I have neither the measurements nor the springs with me at the moment and we may need to verify you do not have the shortest (SE 44mm) spring. The CV40s DO NOT like them at all.
Otherwise, here's my take on it... DO check your slide. If a 1/8 or 7/64 drill bit will fit the hole on the outboard side, it's been drilled. Put the needle back to 3 with no shims under it at all. (you can put them on top if you want to keep up with them) Go 180 on the main and turn the screw out 2 1/2 minimum. I'd wager you'll lose a little of the zip, but the jerky feeling from 1800 - 2200 will go away and mileage will be acceptable. I'm sure your cylinders and chambers will like you better on a long hot ride too. And if by chance you hit on something else that works better - do tell! I don't mind getting called-down... all part of the learning curve
And if anyone is wondering when the heck I'll get tired to typing... I'm running a bone stock 80 inch FLT (secret cam, but it's on the mild side) old style SE mufflers, all baffles in place - no fiberglass, stock airbox with baffle removed, KN type cleaner, 34 on the timing, 45 at 3 1/2 turns, 180 main, Thunderslide (slide and spring), needle in 3 and I get 43mpg interstate (anything under 80 and with good fuel) and 50+ on a 45-55mph scenic road. And the oil runs cooler than any Evo I've ever seen....
PS, I'm out of town for a couple, so good luck and have fun...
As usualT150vej is correct, so pay attention to what they man typed (thanks for doing that as you saved me a lot of typing). Now down to the nuts and bolts: When did this problem start and what did you do just before it?? As it is happening right about where the carb is transitioning, have you checked the carb to ensure that no junk got into any of the passages?? Moving the needle up and down only affects 2,500-3,000 RPM's plus, the diameter of the needle affects off idle to about 2,500 RPM's. If the slide is drilled it will give you a higher slide position through all RPM's as it allows the slide to rise easier. Couple that with the lighter spring that most kits give you and you end up with the needle transitioning too soon, this is why most of those kits give you lousy mileage, and the dyno sheets looks like a saw blade from the slide going up and down as the engine goes through the RPM range. Try to find a slide that you know is unmolested and a stock spring, emulsion tube and jets. Put them in along with the sportster needle and you should be very happy with that set-up.
__________________
John Therrien
SPEED COSTS, HOW FAST DO YOU WANT TO GO ????
Marines may guard the gates of heaven
A job they may do well !!
But it takes the 82nd Airborne
To guard the gates of hell !!
When did this problem start and what did you do just before it??
It was this way when I bought the bike. I actually believed the previous owner's "it's a Harley and they all vibrate" crap, for, like, ten minutes...then I started doing my homework and discounting the asshats that kept telling me "they all vibrate". Believe me, after almost 40 years riding I know vibration and I know running rough...different animals.
A real "pro" told me there was an un-usable rpm band on every V-twin and I bought that too, temporarily. I'm an idiot, I'll admit.
Rotten motor mounts seemed the likely culprit at first but they've been replaced and the bike has been "balanced" per the service manual; 5 seconds at idle then tighten all eight bolts to spec. It's sooo much better...it was almost un-rideable when I first got it.
I've cleaned the carb, I checked the jets, I replaced the 45 pilot with a 48 and fouled the plugs, I went back to the 45 then down to a 44 and now it idles really, really good. With the 170 main it hit the rev limiter hard so I left that alone. I'll get a 180, no prob.
I have moved the needle down to the 5th groove and back up to the third and settled at the fourth but I'll take his advice since I'm asking and he's giving. I have not measured the slide hole, I'll do that too.
I already ordered a Sporty needle from my local indy shop but it's slow coming so I haven't done that yet. The shims in the picture were on top of the needle and they're in a baggie on the bench now; don't need shims if you've got an adjustable needle.
Here's a look at the spring, it measures 5" long and the caliper says .02" in diameter:
And a look at the slide, no marks which I take to be stock, with a HUGE hole drilled in the slide: more than 1/8" and less than 5/32" so I'm guessing 9/64s:
All good suggestions from you two and I thank you. I gotta go load a truck In Nashville tomorrow, maybe I'll get back in time to hit the local indy shop and order some new parts. When I get off the road after this weekend's shows I'll give it a go, one step at a time.
Last edited by oldroadie; 07-21-2009 at 07:17 PM.
Reason: added images
With a hole that large the slide will be higher than it should be at all RPM's so you need to replace the slide with an undrilled. Drilling the slide was an old trick that was done on bikes that were going to be rode hard, either on the throttle or off with no/very little regard to part throttle operation. We do not do that or put in the thin weak springs for that reason.
You see that is the beauty of the CV it acts as a "vacum secondary" only allowing the air in as the engine needs it. This keeps the velocity up and that makes more torque which is king on the street. Hope this helps.
__________________
John Therrien
SPEED COSTS, HOW FAST DO YOU WANT TO GO ????
Marines may guard the gates of heaven
A job they may do well !!
But it takes the 82nd Airborne
To guard the gates of hell !!
Location: NC and across the Mississippi every opportunity
Posts: 1,120
I'll try to get a measurement on a spring(s) by Thursday afternoon. Doubtful a dealer would stock one, and it's been a while but 5" sounds like the super short SE 44mm spring. Bad medicine for the CV40.... won't nothing work right except a lean needle and virgin slide and still a pain to dial-in - been there, done that
Seeing the photos you posted, I may have been unclear about the 1/8 hole. It's on the end opposite the diaphram and near the edge of the outboard side, not the actual side of the slide (no holes there). If that's the one you measured as over 1/8" definitely pick up a diaphram (comes with slide) but don't throw that one away just yet. If you measured the wrong hole and the mentioned one is 1/8 or less, you may be able to tune to that ... your call.
For parts, you could email Wally Kerstetter in Sunbury Pa. He used to sell complete kits for CV carbs including, modified & polished slides, springs needles and jets, but don't know if he still sells the kits.
A few years ago I sent Wally an old carb from my '90 Ultra and in a day or two he exchanged it for one of his polished (looked better than new) carb that worked really well. At that time it cost about $125.00. I think I sent it out on a Friday and had the new carb the next Tuesday. It was ironic because I had previously bought an almost new take off from a '06 for $150 that did not look or work as good as the one Wally did. I had more than that invested because I paid both a Harley dealer and an independent shop to set up the old carb before it went to Wally-I even tried buying a new replacement but they were obsoleted. I could have saved several hundred dollars if I had know about Wally sooner.
Rough running at low RPM
