Bike is stuttering under a load like it's fuel-starved or rev-limited...

[MidnightRide]

I have a 1600 with carb and hypercharger. The AIS still exists. Fuel pump still installed. Carb jetted properly.

I had the bike put away for a couple of years. Only rode it once last summer, under 200 miles. It's always ran great and gets excellent fuel mileage. I put some Lucas fuel conditioner and carb cleaner in it over the winter and fired it up regularly. Seemed to run fine on fairly old fuel.

So I just did an oil/filter change, new battery, and tires, and ran it out on a couple of short test rides a few weeks back, around 20 mile runs. When I was climbing uphill around a tight right hand corner on the test ride, I noticed the bike crapping out, like it was starving for fuel or hitting the rev limiter.

So I took it out on a longer run a few days back, around 90 miles, and notice when climbing a grade in 4th gear it started crapping out again, down on power. It continued so I pulled over to see if something had come disconnected. Nothing strange. I did pull the choke out momentarily while it was crapping out at speed, just to see if it would change anything. It seemed to run smoother momentarily but then reverted to crapping out.

I kept the motor running while I was stopped to inspect the lines, and then jumped back on toward home, 40 miles away. Seemed to run fine again. I was thinking maybe the float was having issues and when I stopped the bowl was able to fill up again. Still don't know.

But I'm also wondering about the issue with the coils shorting out, as I read in another thread. I was riding in shorts with my leg up against the hypercharger. It seemed like I could feel a slight electrical shock on my skin where it touched the HC, but I couldn't be certain. I'm thinking that if the coils are shorting out then that may be what I was feeling.

But this tank of fuel is the first time I've run 87 octane fuel, after reading it was OK here on the site. I've always run premium. I didn't build the bike so I have no idea if the pistons were upgraded by the guy who installed the HC, but since the AIS is still hooked up I'm thinking he would have removed that if he did the piston upgrade. The bike only had 8k miles on it when I bought it, and now has just over 12K.

This may be a bit premature to post for now; I'm going to add premium fuel and have already added more carb cleaner to what remains in the tank, running it into the carb to soak for a couple of days before my next, longer ride, which will likely be tomorrow (Monday). I want to see if the premium fuel and cleaner will change anything.

In the meantime, does this ring any bells to anyone? I have AAA but my girl is in Hawaii for the week and I don't want to get myself stranded on some secluded mountain road on my next run, should this be a symptom of failing coils or the like. I haven't done ANY investigation, such as pulling the plugs and the like, because I suspect it's a carb or electrical short issue. Both times this started was while going around right-hand corners, making me think a wire may be swaying right to short itself if this might be the problem, though it continued after straightening out on a long stretch of highway. It'll run under lower RPM but crap-out under a load.

I'm thinking the carb may have varnished up a bit over the last couple of years of inactivity, other than the monthly startups while it sat. That's why I want to try the fuel approach before digging deeper.

Thanks in advance for your thoughts.

[Lug Nut]

Don't run premium ever for any reason in your bike. Ever. It is unnecessary and causes issues (carbon buildup). 93 is not better quality than 87 just higher octane.


87 octane only. Use Seafoam gas treatment three full tanks in a row. Use 1/3 can of seafoam for full tank of gas (1 Oz per gallon). Run the bike hard like this to help cleaning.

If this doesn't help and your NOT grounding out coils (doesn't sound like it to me from what you described) I would use Seafoam Deep Creep spray directly into carb while running (30 seconds use throttle to keep it running) then let set and cool down. Pull exhaust off heads and Soak the exhaust ports with Deep Creep (use entire can). Let sit overnight and button it back up. Add 4-5 Oz seafoam gas treatment to the oil and start bike and run it up to temp then run it hard for 15-20 min. Come back and change oil and filter.

This will help get rid of carbon deposits you have from using 93 octane gas.

If all of this doesn't help you may have a weak fuel pump, clogged filter (inline fuel filter, petcock screen/filter, carb inlet screen/filter.... Check and ckean/replace those).

You said jetted properly... What jets exactly do you have and do you have stock needle or adjustable one?

[MidnightRide]

I went through all of the jetting and PMS settings a few years ago when I first bought the bike. Everything was correct and the bike ran terrifically. That's not the issue. Fuel pump maybe, fuel filter maybe. I doubt that 4k miles of premium fuel would create carbon issues. I'm not a fan of 87 octane fuel in a bike, ever. This only started AFTER I put a tank of 87 into it, so we'll see.

Nice to know that it doesn't sound like a shorting issue. I'll have to pull the tank and look deeper underneath if things don't resolve themselves after the next run. I think I replaced the fuel filter when I went into the carb, but I frankly don't remember. I do recall that the filter in the tank was shredded so I removed it altogether when I pulled the petcock back then. Maybe since then something has indeed clogged the fuel filter, and that would make sense considering the current symptoms. I'll have to check it after the next run, assuming things don't clear up.

I'm sold on Lucas products, but have never seen Seafoam on a shelf anywhere. Where might I find some without ordering off of Amazon or the like, or is Amazon as good as any?

[Cazwik]

Glad I read this... I was putting premium in out of habit >_< better get some of that seafoam and clean er out.

[Shores]

Walmart, AutoZone or O'Reilly for sea foam or techron plus concentrate. The road star has a low compression engine and doe not do well on high octane which is made for high compression engines. High octane suppresses combustion which is necessary for high compression engines. Low compression engines will carbon up with it. Doesn't matter what you've always done, the road star is a low compression engine. Get rid of that hypercharger also. It leans out the mixture the faster you go. You didn't say what gear you were in when it crapped out. It does have a rev limiter at 4,750.

[MidnightRide]

I wasn't hitting the rev limiter, though it's not unusual for me to do so. Mine kicks in at 4250, unlike the 1700's 4750. I need to pickup a Dyna 3000 so I can kick it up to 5000.

I'm really happy with the HC and have no reason to get rid of it. I've gotten over 55 MPG with the bike. The plugs read fine after a hard run (all previously posted and discussed on the archived site).

It was crapping out under load, the first time in second gear while climbing a ravine, and the last in fourth and fifth while also climbing a shallower grade. Seemed like fuel starvation.

If it still persists on my next run, the fuel filter is the most likely culprit. The petcock filter has been removed. The bike seemed to run fine again after I pulled over and idled it for a couple of minutes while troubleshooting the problem, making me think the float bowl just had time to fill up again. I'll have to check that filter. Things may have varnished up after being so idle in the past couple of years, particularly during the winter months here in Eastern Washington, and that plugged the filter(s).

We'll see how the Lucas treatment does on the next tank. I'll look for the Seafoam the next time I'm in town, which is an hour away. Amazon carries it as well.

I've done a lot of research online, and industry experts of all kinds disagree on the effects of higher octane fuel on lower compression engines. I also have fuel quality concerns of low octane vs. high octane in some of the areas that I ride. I'll see how things progress; still not sure about whether my pistons have been upgraded by a previous owner. My next ride will tell me more.

Thanks for your input. I'll report back after the next ride!

[Agpilot]

Shores is correct. Use the proper fuel in the bike which is 87. Wasting your money and sure not doing your bike any favors using 91. Hyper charger needs to go. Seafoam is available at almost any parts store or Walmart. Best you can get it works. Your fuel system needs a complete cleaning from gas cap down. drain all fuel change and clean all filters carb is more than likely gummed up. If seafoam does not clean it up take it off and clean it....Check fuel tank vent also. Listen to these guys they know what they are talking about..

[Lug Nut]

It does have a rev limiter at 4,750.

4250 for a 1600.... Many people new to Road Stars hit that 4250 and think bike is missing... Seen it several times

[Lug Nut]

4000 miles of 93 octane absolutely will carbon up the pistons.. ive seen it first hand and after cleaning like I described the tops of pistons were like new... Could read numbers on them via camera down the spark plug hole.

Hopefully just cleaning and changing filters will get it right... And instead of a Dyna 3000 you can plug in a CDI from a 1700 bike and itnwill move Rev limiter up 500 rpm's (great mod)


Don't know how on earth your getting 55 MPG on a 1600 carb Road Star. That means you have a range of 291 miles on a tank of gas. That would be really nice though! I get 185 miles until dry on my 1600 with a 65T pulley (but loaded down with fairing/bags/trunk erc

[Brad_G]

If I recall correctly that is for the '04-'07 1700 models, in '08+ the rev limiter was dropped back to 4250.

[MidnightRide]

Yeah in Vegas, hot weather and 2200+ elevation, we averaged 47 MPG riding 2-up but with bags only. I don't run a windscreen or fairing. On my Idaho solar eclipse run a few years back, riding solo with a light load, my speeds averaged well below 70 MPH on Idaho mountain highways, and my fuel light didn't even come on until I hit 238 miles. I can squeeze 5.75 gallons into my tank with my filler-neck mod, and if I could run it totally dry I could get 316 miles out of a tank of gas! I haven't checked it since being up in Washington but will do so once I get this issue nailed down.

[Duke]

I'm fairly sure that you have a fuel problem by what you are saying. I run 91 octane most of the time, and have never had any problems running that fuel. 91 octane is more stable and helps from getting air locked and pre-ignition from heat. Yes, it can be a waste of money using that fuel if you don't need it, but when the temperatures start rising, it's good insurance to run that fuel. These engines make a lot of noise, and it's hard to tell if the engine is having pre-ignition, "spark knock". I'll use 88 octane during the cooler climates and I usually get better fuel mileage with 88, compared to 91, but during the hot days, I'll go for the insurance.

As what Agpilot said, check to make sure that your tank is venting good, and fuel is free flowing.

As for the RPMs, the 1600 has 1.9 to 1 rocker ratio, and the 1700 has 1.4 to 1 rocker ratio. The 1600 are more susceptible to, "valve float" and this is why the 1600s are governed at a lower RPM.

[Tcontrol]

Simple question…..
have you looked at the plugs?…… old fuel even stabilized fuel loses some of its firing power…. Sometimes if it was treated a little heavy with stabilizer, it will coat the plugs and reduce spark efficiency…. While you have the tank off…. Simple enough to look at them… (and i would still put some tape around the throttle cable around the coils… cheap preventative that just might make a difference)

[MidnightRide]

I agree on the taping of the cables for prevention purposes. My cables are virtually brand new however. I really didn't want to get into tearing down the bike right now. My Jeep is ahead of it. Just want to get some riding in now that the oil's fresh and tires are new. The fuel itself is fresh and new. The tank was nearly dry when I fueled it for my first ride a few weeks ago. We'll see what happens on this next ride!

[MidnightRide]

I'd planned on a four hour 200 mile loop today, but the temp's pushing 100* this afternoon so I'm wussing-out a bit. Supposed to run the same temps all week long. Damn, I feel like I'm back in Vegas! Maybe I'll refine my run and make a shorter loop after the dinner hour when it cools down a bit.

[MidnightRide]

Despite the heat, at around 5 PM I went ahead and jumped on the bike and made a modified run which still ended up clocking 196 miles. Still peeling the bugs off my shirt. Made it home under waning daylight, a good thing since all I had was my heavily tinted face shield for the helmet. Had to dodge both deer and turkey along the way. Lots of turkey up here, and dumb as hell.

I was thinking 'fuel mileage' so I just sauntered along the route which included a low mountain pass. Fun ride. All seemed perfectly normal and the bike ran great. Happy and healthy. Ran 150 miles before reaching the main highway again.

Once I got back onto the main highway home, it was 'fuel mileage be damned', so I crunched it through the gears up to highway speeds. Awesome acceleration, sounded great, bold, and super healthy. Then it hit fifth gear and fell on its face. Totally flattened out. I was assuming it was just running out of fuel, finally, so I tried to ease off the throttle while waiting for the float bowl to fill back up. My 5th gear speed was dropping down to nearly 60, sputtering, and I had traffic behind me, so had thoughts of pulling off the road to see if the carb was going to catch back up.

I had thoughts of downshifting, but figured if it was fuel-starved, that wouldn't work. Tried it anyway, and it caught fire again and ran me right up to 80 in 4th gear. I came up on a small town, putted through, then passed the cars in front which opened up the highway ahead. I ran it up to 90 in 5th and held it for at least five minutes. Not quite as healthy as usual, but held the speed fine.

I pulled off in the next town to clear the bugs from my face shield. Ran it back up to speed, but at that point it wouldn't hold 80 in 5th gear. I finally throttled back a bit and limped home for the last 30 miles while toggling back and forth between 4th and 5th at 70-80, with the motor sputtering in either gear.

It was almost acting like my plugs were bad. But if I run at lower RPM's, the bike runs and sounds absolutely normal.

I pulled it in and shut it down with very little idling because I wanted to pull the plugs to see what they looked like from highway use. It doesn't look like I'm going to be able to avoid some kind of tear-down with this. The bike did seem to be much happier with the higher octane fuel and Lucas gas treatment, but it didn't resolve the issue. I got about 3.3 gallons in before I left, so I still had a couple of gallons of 87 in the tank that mixed with the 91.

I dunno. If it's fuel, why does it run stronger at higher RPM's when it loses most of its power in 5th gear at lower RPM's? Is the carb's Venturi effect at higher revs forcing the fuel through an otherwise plugged filter? Seems like that was what was happening...

[MikeyC]

I had an issue exactly as you just described. Turned out there was crude under my float needle valve. And there is another screen at the fuel intake to the carb

[MidnightRide]

I think you're probably right, that it's a crud issue of some type. I just realized that other than periodic start-ups, the bike has basically been sitting for the past three years. The bike ran fine yesterday, spent most of the ride in 5th gear without issue, and it wasn't until I wound it up under hard acceleration that it went flat. I'll have to pull it apart but just don't know if I can free up the time this week to make that happen. Thanks for your input!

[MikeyC]

If you trailer it to Baker City it will still ride but maybe Thursday eve we can pull the carb and open it up. Got a spare carb bowl gasket just in case?

[MidnightRide]

No spares, but that's a thought. I'll see what I can get done this week.

[Duke]

Have you removed the tank vent rollover valve?

[MidnightRide]

No. Didn't even know it had one, but it was four years ago that I last did any work with the tank or carb. I was thinking it was three years but just checked the archives and that confirmed it's been four. We moved the home and businesses 1000 miles north in late 2018 and that's pretty much consumed us ever since.

[Duke]

If your tank isn't venting good, then your bike can act like your describing.

[Duke]

The rollover valve is located on the down tube part of the frame under the seat. You can access it by removing the left side cover and is clamped to the down tube.

[MidnightRide]

I'm thinking I can loosen the gas cap and run it down the road under a load and that'll quickly sort out whether it's a venting issue. Sounds like a good reason to make a quick run this evening. It's a smoke-haze 98* out right now, with forest fires fueling the smoke.

Seems to me that I remember a rubber tube that connected to an outlet on the bottom of the tank. Like I said, it's been four years! I should have pulled over yesterday and loosened the fuel cap to see if a vacuum had built up. I'd thought about it a few days ago but forgot!

I'm hoping you're right, such a simple fix!

[Duke]

The tank connection for the vent hose is located underneath the speedometer.
The rollover valve is like a double acting check valve and it gums up easily. I've had the tank pressure up from that valve, causing carb puke, so I got rid of it.
The safety feature it was designed for is also dangerous when it get gummed up.

[MidnightRide]

The tank connection for the vent hose is located underneath the speedometer.
The rollover valve is like a double acting check valve and it gums up easily. I've had the tank pressure up from that valve, causing carb puke, so I got rid of it.
The safety feature it was designed for is also dangerous when it get gummed up.

Yeah, I remember that up front as well. Maybe I'm thinking about one of my other bikes as to something under the tank...

I pulled the fuel cap off and ran it out a few miles. Nada, same problem, so breathing isn't the issue. Thanks for the suggestion though. I may remove that valve anyway, just as you did.

My tank petcock screen was disintegrated when I first pulled the tank years back, so I just cleaned and left it off while figuring the inline filter would catch it all. I think I'll just order a new petcock/filter as well as a fuel filter and see where that leaves me. May end up pulling the carb as well, just to check that filter. Might as well get them all.

My boat now occupies my old indoor work area, so now I have kind of a makeshift area elsewhere in the building that I'm not thrilled with. Once I start diving in back there again I'll be fine...

[Lug Nut]

Venting or float level it soudss like... I had similar issue... Pulls hard in 4th to over 90 then in 5th just hovers at 100mph. Had to tinker with the float height.

[Dick M]

I'll take this for $200 Alex. On my old bike Kawasaki vulcan I had a problem with the float valve sticking and not closing and it ran fine at high rpm but in high gear when I backed of the rpms it would flood the engine. Sputtered like a SOB. Eventually it stuck open and when parked it dumped the entire tank of gas down into the cylinders and then into the crank case. I'd say replace the float needle valve and check the float level setting.

[brianmac]

uphill , could it have been right at the reserve level and not pumping gas? cock is on front left. i can tell when im bout to hit R by a litlle sputter a few miles and then blah. back level it will be fine

[BlueRidgeSasquatch]

MidnightRide Have you made any headway on figuring this one out? I'm running into about the same. I just haven't had the time to tear into everything and I need to get the raked triple tree replaced with OEM before I worry about getting up to interstate speeds.

[Duke]

I have a OEM tree.
You should check the fuel system, "tank to float valve", and the venting to the tank.

[Father Pobasturd]

Watcha gonna do with that raked tree?

[Duke]

Exactly what I was thinking Farther!