Bonneville America Forums Forums Technical Forums General Tech coughing on acceleration

Initially I did not. I placed the new one EXACTLY where the old was mounted using feeler gauges. Bike ran like new. Then I got the manual in the mail, set the pick-up per the manual, and things have gone from bad to worse. It ran fine for the first 80 miles or so, then developed a tiny "hick-up" on acceleration that was barely noticeable. I figured it was just a burp, but it increased in frequency and violence. I rode the bike today, and barely made it home. If I'm completely stopped, and accelerate, the left cylinder coughs, backfires and very nearly kills the engine. But once the RPM's get above say 1,200 and above, she pulls strong and doesn't miss a beat. I pulled over and just let the bike idle and placed my hands behind the mufflers to see if I could feel which cylinder was banging. An orange flame about a foot and a half blasted out of the left muffler, along with the sound that would put a shotgun to shame.
So far it's had a CDI that cost me $214 and a pick-up coil that was $83, and the bike is still un-reliable to ride. I'm still convinced it's ignition, but not sure what to do from here. I still have a brand new CDI that I will install AGAIN tomorrow and see what happens...Still have original pick-up coil too.....Whatever the problem is, it happens under load, being more pronounced from a stop. If your in high gear, it will cough, but not nearly as noticeable. If you simply twist the throttle in neutral, she accelerates normal. Just allowing the bike to sit and idle is very violent... Guess I'll park her and look forward to a new Thunderbird in the spring if things work out....

At this point you might as well replace the wiring harness... there has to be one available on ebay.
Not that it should make a difference at this point, but did you check the o-ring between the manifold and the head? It wouldn't explain the lack of power at the plug wires but it will make a bike run poorly.

At this point, I just feel that it's gonna be one thing after another, as it is with any aging machine. I will continue to tinker with it, but will no longer trust the bike for any significant trip. Gonna be hard to trust it ever again...

Bring the bike to me when you can and I will get it sorted out for you.

Sounds like it is either flooding the cyl. or it is firing speraticlly allowing excess fuel to build up in the exhaust. Take Chy up on his offer, very hard to diagnose things just on a description. I know how I would approach the problem but it would take pages of text to explain what I would do and in what order and the problem could be at any given point in the diagnosis process.

Mark, you stated that you measured the resistance of the coils and both were the same. This is no indication that a coil isn't failing. You might have an ignition coil run poorly when hot but it registers ok when cool. Did you switch the wires on both coils to confirm the problem switches cylinders? You never stated that you did so. This is the acid test to determine if its a coil failing or the CDI going.

One last thing, do you have your throttle position sensor plugged in or disconnected? I'm curious. If it's still plugged in, unplug it to see how the bike runs? I've had a problem in the past with a bum TPS that caused all kinds of poor running problems. FWIW. Unplugging it solved the problem.

Unplugging TPS makes no difference, coils are next

Anyone have a set of good used coils? I'll swap the new PROCOM CDI unit for them....2005 America. If coils don't fix it, off to Chy's it goes....

I have a set, but I won't be home for two more days, in central Wyoming now and need to see a sick friend in North Central Idaho, before hauling myself to home. The coils are off a wrecked 06 America with 8000 miles. In fact you should probably try before you buy. PM me Friday.

Thank You so much Ryk...as of now, the bike wil sit, as this bike has exhausted all of my play money... Over $300 now. I'll pay for shipping and talk if the coils fix it. Thank again for your kindness!

My similar problem turned out to be a spark plug wire that intermittently didn't work. New wires, problem gone. Of course I tried everything else first.

Ryk's coils and plug wires installed. Started engine, running on one cylinder right off the bat. Left cylinder intermittently fired, but the coughing severely. Inspecting underneath carbs in the sunlight showed a healthy spray of gas coming from left carb/cylinder mating surface when cylinder coughed...Not sure if this is the cause, or effect. Engine will not start at all now. Both cylinders showing healthy spark with strobe gun while it WAS running. Ordering $32 worth of O-rings now..probably another 2 weeks...what a PITA.

For $32 for some blanking o-rings, I think I would have explored the inventories of some industrial suppliers first. Holy Cow! These guys sell more than a few flavors and in metric sizes too. web page

Have you done a compression test? Leak down test?

$17, o-rings will be here Friday.

O-rings won't be here until Tuesday... 7 days to ship parts from northern Kentucky to Atlanta. Definitely re-thinking buying a new Triumph this spring. Obtaining parts beyond ridiculous

O-rings arrived and installed, bike runs on 2 cylinders now and idles sweet with no popping. After 10-12 minutes, quick twisting of throttle causes considerable cough/bang in right carburetor. Still not worth a crap. Bike also kills when placed into gear. Side stand switch disconnected or connected, up or down makes no difference. Contemplating parting the bike out....'cause at this point, it will just be one thing after another, seen it too many times before.

Just have to be capable of diagnosis on a motorcycle and fix the issue. I have bikes over 60 years old that run strong. There are guys with bikes like yours that are older with way more miles that run fine. Stabbing at a problem and throwing parts at it is frustrating and often fruitless. My Speedmaster will probably still be running strong when I pass on.

Okay, so I guess the next move would be to remove the entire wiring harness, with the equipment you either buy or borrow to test components, like "diode packs" or whatever, MAYBE find a problem, or not, put it all back together, and STILL have original problem, and if your very lucky, don't induce who knows how many other problems. Guess I'm not a motorcycle mechanic. Overwhelmed and frustrated. Bike not worth dumping $3000 or whatever to have someone else try to try to repair it. Guess I got all winter to figure it out!

I would rent if I had to, a compression tester that fits and see if you have a dead cylinder or not. Good decisions require 1st hand information. If it's just a burnt valve or shot rings/bore, that's not world ending.

Wouldn't cost much to have a shop diagnose it for you. ( not all are competent) Then fix it yourself.

Frustration talking... I'll figure it out....

The fact that the bike would'nt start when placed into gear was the problem the whole time. Disconnected wire coming from neutral safety switch, cut to length to connect directly to battery negative terminal. Bike again runs flawlessly. There was apparantly a high resistance to ground through that switch, or, right on the hairy edge that was causing the ignition system to misfire from time to time,especially under load. Switch finally went open over time. I can tell that the bike is back to original power, as it easily maintains 75 mph uphill. I knew I would figure it out...Moral of the story, If a "safety" switch is seeking a ground, cut the wire and truly ground it...

So the very FIRST step with these symptoms is to disconnect that stupid neutral safety switch and run it to a known good ground. 80 flawless miles now.

Are you keeping the bike now?

Oh yeah.....frustration causes anger, anger causes, ultimatums .

Sounds like you've been through the wringer trying to sort it out, sometimes its one of those simple simple problems that are the hardest to find. You said you're not a motorcycle mechanic but still be proud of the fact you stuck with it as the intermittent problems are the hardest to find, Job well done!!

Decided to ride the bike from the house to Birmingham Alabama, about 100 miles one way, after I thought I could trust it...Got 74 miles out the interstate near Talladega, lost power, off into the emergency lane I go...was able to get the bike off the next exit and fill the tank, which was 3/4 full anyway. Rolled the dice and back on the interstate where I milked it the rest of the way to Birmingham. Coming back I-20 eastbound, was really bad..almost no power, but was again able to milk it to the next exit. Put gas in again, and a bottle of STP gas treatment, bike ran strong the rest of the way home....
Went to ride the bike the next day, it was popping and spitting back so bad it wouldn't even pull....coughing thru BOTH carbs worse than ever.......Screw this. I would take $1000 for the thing right now if someone would offer it.

Too far away or I would be all over that!

Come get it....West Atlanta area (404) 444-6077

Does it run normal after a fill up? How about if you just stop and open the gas cap and then put it back on? ...?

Sold! I'm in for that... clear title?