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Lurching at Steady Speed

36K views 58 replies 13 participants last post by  PugslyCat 
#1 ·
Hey everyone, purchased a 2017 750 last Saturday. My first Harley Davidson and first bike after about 30 years.

When I got it home, I has some issues starting it. Pressing the start button would do nothing. I'd play with it for a bit, in and out of neutral, kickstand up/down, clutch in/out, then it would start. That issue seemed to have went away because it's ok now.

My main issues is it's jerking/bucking while I'm holding the throttle steady doing about 25 MPH or under. I've only been riding in the neighborhood until I get used to the bike so I don't know how it does at higher speeds.

Is this normal during a break in? I tried up and down shifting to different gears but it doesn't help. It just jerks and bucks down the road, unless I'm accelerating, then it's fine.

Any insight is appreciated.
 
#2 ·
This is exactly what has been happening with my bike for months. I can't figure out why mine does it. I just cope with it now because I really don't want to take it to my HD dealer and get screwed with their high prices. My model wasn't a model that had the pump inlet recall either, but it still seems like it has something to do with the fuel system. If you find anything out on it please let me know because more than likely that's the same problem with mine.
 
#4 ·
The only logical thing I can come up with is the lag and leap issue with the xg's... But I looked up my VIN and my 2015 model wasn't one of those that were recalled. The solution would be to replace the fuel pump, but I don't understand why it would be in that "lag and leap" category but my model wasn't one of those that were recalled. I know if I take it into the dealership they will tell me it is because of the modifications I have done to the bike, so I'm kinda at a crossroad.
 
#6 ·
At first I thought it was maybe a fuel starvation issue, but it clears up while accelerating. So if it wasn't getting fuel, it seems like giving it throttle would make it worse.

It's only when trying to keep a steady speed. I'm having someone else take it for a ride tomorrow just to make sure it's not me. And I will call the dealer.
 
#7 ·
Same here man... Everything you are describing is happening with mine. If I want to get up and go in a hurry the bike runs perfect, but if I want to just cruise around town 25-30 mph then it sputters. Does yours do it when cornering too? Like trying to keep a steady speed in a corner and it starts sputtering? Mine does it all of the time whether my tank is full or empty. It seems to me like it runs better without as much sputtering when the weather is warming in like the 70's range, but it may not have anything to do with it... Either way, it still does it and apparently it isn't normal so if you take it to your dealership please tell me what they say is wrong with it.


Thanks!
 
#12 ·
Just a quick update. I had someone else ride my bike tonight just to make sure it wasn't me. He said it felt like a misfire. The RPM's aren't fluctuatig, so the clutch isn't slipping. It really does feel like a misfire until you give it throttle. And now it's popping and back firing at times.

I'm calling tomorrow to make an appointment to bring it in. I love the bike but so far this isn't a great first impression. Although the actually buying experience was awesome.
 
#15 ·
Just a quick update. I had someone else ride my bike tonight just to make sure it wasn't me. He said it felt like a misfire. The RPM's aren't fluctuating, so the clutch isn't slipping. It really does feel like a misfire until you give it throttle. And now it's popping and back firing at times.

I'm calling tomorrow to make an appointment to bring it in. I love the bike but so far this isn't a great first impression. Although the actually buying experience was awesome.
On a 2 cylinder, depending on the severity of that misfire, is going to be make or break on that motor.... You will have no power, no speed, knocking and pinging, a crap ton of issues.... A slight misfire could be causing some of these issues I read you had posted, but the others, sounds like there is more to this than someone is letting on or describing...

The clutch has nothing to do with the RPMs fluctuation at all whatsoever.... if it were slipping it would feel like torque steer or exactly that, a slip and then the power catches.... Its either starving for air or fuel, possibly spark but I doubt it... From the vague descriptions... Decel pop and back firing is common when unburned fuel is not being burned properly, along with the possibility of running too lean/rich, and there is a ton of it happening with factory exhausts, but due to the glass packs, restrictive resonators, baffles etc you can't feel or hear it as with performance/open exhausts... Air/Fuel ratio must be as close to stoich/14:1 as possible, but that is in a utopian society and doesn't exist....

Let me ask this, what modifications have been done to this thing? And was it retuned properly thereafter?
 
#13 ·
My RPM's fluctuate when my bike is at idle, and when I start to ride from a stop I have to roll the throttle about a quarter of the way for my bike to get past the "bogging" sound and then it very quickly switches from bogging to BAM normal and off we go. It's friggin' weird and the fp3 and high air flow filter isn't fixing it... I'm in the process of gathering data for the auto tune.. Maybe that will do some help.
 
#14 ·
Playing with fire kid... About to blow something up past the point of no return... And you will be stuck holding the bill and the pieces... Sounds like the data should have been collected before any parts were thrown at it and needed to be fixed first... When you get a data log link it here so I can try and decipher what is going on...
 
#17 ·
I'm going to check spark plugs tomorrow and see how they look.. If they are bad i'll change them and see if that fixes anything. I was thinking fuel pump too top, how much did your dealer charge you for parts and labor? Just so I can get a general $ amount in my head if I have to resort to getting a new one.
 
#20 ·
Or just ignore my advice yet again.... Top just came in and said his piece, and I have been saying it all along... Starving for air, fuel, or spark, that's it combination thereof... Suck bang press blow or for the techs Intake Compression Power and Exhaust strokes... And every dealer and tech comes up with their own labor/diagnosis rates. Yes there is book hours for labor dealing in values of .1 / 7 mins an hour... They will make sure they get paid regardless... The $$$ you spent on mods instead of fixing what's wrong with it would have saved you tons, not the other way around...

Like I said, you are playing with fire kid... Run lean for one second at high RPMs under a full load and watch the sparks fly.... On a turbo/super charged car it's even worse...
 
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#23 ·
Exactly what Top had said... You need to iterate, explain, and possibly complain that this is not the quality you expected from Harley Davidson.... I am not one to complain only when a denial is given and it is clearly covered by the book they laid out for you to sign, that's when things get going for me... I had 1 issue with a TSB and a Recall being performed at the same time on one of my cars recently, got it all taken care of from the stipulations covered under the factory warranty, let alone my extended warranty... Basically read the fine print and use it against them... Recalls have to be fixed at no cost to the owner of said VIN/Vehicle, but the TSBs are Service bulletins that either change the former diagnosis part or change the parts replaced etc etc.... TSBs the owners are responsible for...
 
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#24 ·
exactly,

i just very politely stated that i brought a brand new Harley Davidson because of their service record and based on the fact that under the warranty issues with the bike not running smoothly would be quickly addressed by trained staff.

Bikes can be dangerous enough to ride without complete confidence that the bike isn't going to lurch when you making a tight turn, or crossing traffic.. or trying to lane split. if that was a feature i would have brought a cage instead.

they took my bike in on a Saturday morning, within 60 mins i was told the fuel pump was bad ( despite not being on the recall list) and i was riding again by the afternoon.

remember, just because the person that answers the phone doesn't agree with you, its the sales managers that get a % when you buy new bikes from them... always escalate up.
 
#25 ·
From one of the previous post I read when your going 25 mph it runs rough. I have over 20,000 miles on my stock 2015 Street 750 and it does the same thing at low speed in second gear at 25 mph. I end up lugging it in 3rd gear. I never had a lurching issue with my bike from day one yet they insisted on changing the fuel pump under recall. I was told the reason it runs rough at a steady speed of 25 mph is the bike is tuned very lean. I run a DQ baffle on my Loose Cannon slip on with a stock air intake cover and the K&N filter. I've changed the spark plugs once and there was no difference in performance. The bike doesn't like starting when sitting up in cold weather in my garage for days and weeks. When I first start it for the first time of the day, I always let the bike run and warm up before taking off. I've been happy with the performance of my Street 750. Having a 70 degree day this past Wednesday in SE Wisconsin reminded me why I like spring summer and fall weather.
 
#26 ·
Spent a few hours back at the dealer today. Their initial diagnosis was spark plugs, and that's what it ended up being. They changed out the plugs and it runs great now. It had 2 miles on it when I bought it last week, so it was probably test ridden after initial delivery. But they think the plugs got messed up from sitting. It's a 2017 so I'm not sure how long it sat, or how that would affect the plugs.

Either way, it's fixed and now I can get back to enjoying the bike (for the first time). Thanks everyone for your input.
 
#27 ·
Plugs go bad for sitting form storage and being turned on once or twice? Wow, that's news to me... Sounds like user install error from the Factory if you ask me.... Never have I heard of that when the bike is less than a week old and had these problems from the start.... Maybe someone gapped them too short of an air gap, that'll cause a direct sever misfire, I would have asked to inspect and see the old parts beforehand...

It wouldn't affect them that's the point, unless someone deliberately or unintentionally did so... They knew better or didn't know better...

Just like when I got my HD from the dealer, the air box bolts were stripped, luckily, I can drill and tap so I did to fix the problem that should have never happened in the first place with 5 miles on the bike... I noticed a rattle and a shake at idle speeds and at higher speeds... Loose airbox...
 
#28 ·
I agree with you about the plugs. I mean, it's such an odd issue for a new bike. I've never heard of plugs going bad from sitting. Also, it takes 10 minutes to swap plugs, and I was there for almost 3 hours. I guess they were running diagnostics to make sure it wasn't something else.
 
#30 ·
I still cannot believe it... I would have asked to see the old parts and what exactly was being done... and for a 15 minute job of lifting the tank and swapping the plugs to be a 3 hour job, come one... Not buying it... Even if the ceramic coating or the center electrode was grounded shut or broken internally, you would have more problems than what you had...
 
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#33 ·
Changed the spark plugs yesterday and they looked pretty gnarly. Changed them to NGK IX Iridium. After installation I just idled the bike and it seemed to start better and idle smoother, but I haven't had a chance to take it for a ride due to weather. I attached a picture of the old spark plugs.



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#35 ·
I installed v&h VO2 high flow filter about 2 weeks ago and I looked at the t-body when I was changing it and it looked shiny clean. I looked for any debris or buildup and there wasn't any, so I knew that wasn't the issue. Hopefully when the weather clears up in a couple of days I will be able to take it out for a ride after changing the plugs to see if it helped any. I was also thinking about changing the plug wires to sumax wires as I have seen other people on this forum do also.
 
#37 ·
How many miles on your 750 #1 and #2 they do have some unburned fuel deposits on the plugs which indicate running rich aka too much fuel, offset by the mods and external software you have installed... Tune it right and properly and I guarantee you will have solved most of the issues at hand you are describing... Test the wires before you actually install them, resistance should be far lower than OEM ones, if not then they are junk out of the box and you need a new set... 150 OHMS or less usually for performance wires... That's why I love Coil on Plug setups, none of that matters anymore...

Plugs don't add horsepower and torque, but they can offer cleaner burns for the combustion process, which leads to the potential of more power, but doesn't mean that it will... And the wires, yes, I agree, change the resistance properties and can ensure a greater spark, but that doesn't mean it will again add all kinds of gains, just makes a cleaner ignition signal and lessens the interference if any, yada yada yada... Dwell time, spark intensity, Higher resistance wires will cause issues and many other things come into play but I won't get involved with that right now.... Different topic, more for engine performance...

Once the rest of my parts get here, those are the first things I am checking and installing before I get to the nitty gritty...
 
#36 ·
Sumax had issues with the Early sets of wires. The problem was the wire for the rear cylinder. Specifically the length. Make sure you measure yours first. I have the set with the Short (16.5") wire for the rear. The new sets I'm told by Sumax are 19.5" Hasn't really been a problem on mine. Both Retainers are missing. From the Rear Cylinder Cover Leaks(Warranty).


Use the FP3 and see what your Idle Speed is.
 
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