Bike will cough and buck on acceleration (dang near violently). This just recently started and no changes were made prior to that. Jetting at the time was 172 Main, 40 pilot, 3 clip + washer on the needle, and 1.5 on the PMS.

It started on the first cool morning of the year, and I thought maybe it was a jetting problem. I dialed the PMS open a tad and it seemed to run better. A couple of weeks went by with no issues, then it started again.
I've replaced the air & fuel filters, proved the fuel flow to the carb. I know the 172 is a bit large for the 1600, so while I had the carb open I rejetted. 167.5 main, 40 pilot, 4 +washer needle, & 2.5 on the PMS.

It will crank up fine and idle smooth as glass. I can run down the street just fine as long as I don't roll the throttle to hard.

Checked for vacuum leaks but found none. Pulled the plugs; rears look good, fronts maybe a little lean. I will replace the plugs since I have them out.

No odd noises from the engine.

Not sure where to go from here. Sounds almost like an ignition timing thing.

OH, dyna 2000 ignition box.

Pull the choke knob out when you accelerate to see what happens when you get extra fuel past the slide. I'm thinking possible slide not opening properly or maybe acc pump not squirting proper. Pulling the enricher will deliver fuel thru another circuit past the slide.

I would install a new spark plugs in the engine and make one hard pass and then check the color of the plug. With a new plug you can get a good reading on the color of the plug. I do that with cars pretty regularly. I usually just pick an easy cylinder and install one new plug. Your symptoms sort of sound like you are leaning out. (Plug would appear white) You didn't say whether you still have the fuel pump and screen installed. I suspect a clogged screen or weak pump but that's a total guess. If it's lean a new plug will tell you really quickly.

pc_doc wrote:
I would install a new spark plugs in the engine and make one hard pass and then check the color of the plug. With a new plug you can get a good reading on the color of the plug. I do that with cars pretty regularly. I usually just pick an easy cylinder and install one new plug. Your symptoms sort of sound like you are leaning out. (Plug would appear white) You didn't say whether you still have the fuel pump and screen installed. I suspect a clogged screen or weak pump but that's a total guess. If it's lean a new plug will tell you really quickly.


Doing just 1 plug on these bikes won't do a complete air leak check. You can have a air leak at 1 of the intake/head connections. Checking just 1 plug won't tell anything about the other cylinder. You also don't need to install new plugs to do a chop test. Air leaks in this area are very common. I don't think he has a air leak issue. You should also be able to disconnect the Dyna 200 and run on the OEM ignition module. The dyna2000 is an add on unit. If that is the issue it will clear up when disconnected.

Have you drained the carb bowl and tank lately? You may be getting some yuck(watery condensate) collecting in the bowl.
Do you mean Dyna 3000?
Is the buck and snort more noticeable right off idle, like when pulling away from a light, or when opening the throttle from a mostly closed position, and does it only last momentarily?
It's easy to remove the cap over the upper diaphragm, and clean the back of the slide as Dave suggested, and visually make sure the accel pump is working properly. If those check out, and it isn't something like water in the fuel, then I'd be removing the manifold and resealing it(just cuz its tough to find a leak there sometimes). Make sure it isn't something simple like a cracked or missing seal on the AIS port on the manifold, also.

SKWEARpeg wrote:
Have you drained the carb bowl and tank lately? You may be getting some yuck(watery condensate) collecting in the bowl.
Do you mean Dyna 3000?
Is the buck and snort more noticeable right off idle, like when pulling away from a light, or when opening the throttle from a mostly closed position, and does it only last momentarily?
It's easy to remove the cap over the upper diaphragm, and clean the back of the slide as Dave suggested, and visually make sure the accel pump is working properly. If those check out, and it isn't something like water in the fuel, then I'd be removing the manifold and resealing it(just cuz its tough to find a leak there sometimes). Make sure it isn't something simple like a cracked or missing seal on the AIS port on the manifold, also.

Cleaning the edges of the slide is also a good idea while you have the top cover off. The slide edges can get pretty gritty/nasty and keep the slide from sliding properly.

UPDATE:

First, thanks for the comments.

Most of it the carb checks recommended were done prior to posting. float bowl was clean & no probs with the gas.

I pulled the carb back off and adjusted the float level per the RSC tech articles. A close inspection of the diaphragm didn't show any tears or holes. I also pulled the intake manifold since the dealer shop was the last one to touch it. Obviously they don't believe in hylomar or anything, so it got sealed and reinstalled.

The TPS checks good on resistance as well as the pick up coil. And yes, Skwearpeg it's a dyna 2000.

Coil resistance was good on primary & secondary for the front, but the rear secondary was high. Traced it back the the plug cap on the exhaust (rt side) plug. bad connection in the internals but was able to restore.
Has new plugs in it as well.

Was all set to get it back together, but as usually Murphy showed up. Throttle has been a bit stiff for some time and only running with a pull cable. I was successfully able to bust that dude, so now waiting on a new one.

I cranked her up in the shop and she ran great. Manually increased the RPMs (don't have a tach) and had absolutely no issues.

Now here's the question: With the engine unloaded and increased RPMs (say 2000 - 3000) should I see any movement on the carb slide or is there just not enough load?

probably won't see much if any movement with a gradual increase in throttle at that rpm. Give it a quick snap of throttle to see movement.

update #2:

Took the bike out yesterday and it pulled like a champ.

Current jetting is 170 main with clip in the 3rd groove, 40 pilot and 2.5 on the PMS.
Didn't find any smoking guns other than the high resistance on rear exhaust side spark plug and lack of sealer on the intake manifold.

I did adjust the float level up to the bowl mating surface, so maybe it was too low. I dunno.

Put a can of seafoam in so I'll ride it hard this tank and start checking my mileage on the next.

Thanks for all the input.