Engine hesitation, spits, sputters only when hot - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
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post #1 of 11 (permalink) Old 08-25-2018, 04:21 PM Thread Starter
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Exclamation Engine hesitation, spits, sputters only when hot

03 vstar 650, 27k~ miles. Cobra drag pipes, RAK intake mod with K&N filter. 130 main jets, 2 #4 washers on each needle, mixture screws 3.5 turns out. Symptoms present before and after mod, but has gotten worse as time has gone by. I'll try to be straight and to the point with what I've tried and whats happening.

I can ride for about 30-45 minutes of gentle riding before the engine begins to hesitate, misfire, spit, sputter, backfire/pop- she gets noisy. Or if I'm aggressive with the throttle, it'll happen after about 15 minutes. This starts slow, like I need to switch to reserve, and will progress and become severe and make riding hazardous. Present throughout throttle range. While severe, the bike struggles to idle and might even die. Choking and throttle seems to help at first -slightly-, and briefly.

I've tried removing the fuel cap when this happens and ride for a bit- no change.
Replaced fuel filter. Lots of fuel flow with hose disconnected. Fuel pump seems to be working ok but, but haven't disconnect hose to check for pressure increase.
I've cleaned and synced the carbs. Used propane to search for intake leaks. Found one, and sealed up intake joints with RTV on reassembly. No change.
Pickup coil was out of tolerance- in the 500 ohms or so while cold. Symtoms remind me of last time my pickup coil went out- except symptoms and complete failure occured in the same day. Stator was in tolerance but had one coil that was charred. I replaced both with new OEM parts.
Ignition coils out of tolerance around 17kohms, i think the limit is about 15kohms. I have not replaced these yet.
I do have some excess blow by passed the rings, air and oil will launch out of the crankcase if I take off the oil filler cap while running (not normal, right?) Compression in the mid 120s psi hot, which I know is below factory spec, but I've been told if I'm over 100 dont worry about it.
Charging voltage normal, don't remember the numbers but can do it again if needed.
There is exhaust discoloration mostly on the rear cyl exhaust. Yellowing on the outside cover, blue underneath on the actual exhaust. See pics.
I've fired the bike with the igntion leads disconnected and not grounded in the past, before I knew this can be harmful to the ignition system.
Front carb main jet oring blown out, I can see a small edge of it looking through the main jet. I have new orings, just havent swapped them yet.
Carb heat shield missing- vapor lock?
The bike does take longer to warm up after my mods.
Slight hesitation and pop while shifting gear with aggressive throttle during warm operation- does not seem related to issue when the bike gets hot--- and need to mention, night riding greatly extends my riding duration, even with aggressive throttle. Sometimes night riding I'll have no symptoms. Hot florida afternoon on the other hand- beware how far and where you're riding!

Hopefully thats everything....


Where should I continue from here? Not sure if the mixture is a part of the problem, but I'm suspecting mostly electrical? Just wanted some second opinions before I start swapping parts again (the stator and pickup coil were a chunk of change ) Thanks for any leads
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Last edited by TwoWheels; 08-25-2018 at 05:56 PM.
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post #2 of 11 (permalink) Old 08-25-2018, 06:43 PM
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DO NOT take the oil fill cap off while running!!!!! But really you have checked a lot of the things that comes to mind with the symptoms you describe. It still sounds like a carb problem, or a fuel flow ,but you checked that, the popping on decel and spitting popping ,missing, hesitation on acceleration indicates a lean condition . Maybe do a complete carb clean, a guy on the KLR forum found a clump of green goo in a passage of his carb , removed it and his bike ran great after. Damn ethanol!!!!!!!!
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post #3 of 11 (permalink) Old 08-25-2018, 06:46 PM
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I just reread ,missing heat shield? Vapor lock? The factory does put them on for a reason.
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post #4 of 11 (permalink) Old 08-25-2018, 06:56 PM Thread Starter
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Hmm, I may have to do another carb cleaning. I've been running ethanol free for the last 15k miles or so, only buying regular if I didn't have a choice. Frequent seafoam dosing. Do you guys stick stuff through the passages, like wire? The manual said not to, but online I see a lot of people do. I only sprayed carb cleaner through passages, and compressed air. I've cleaned them several times in the last couple of years.
Also, the heat shield just came in the mail, so I'll put it on and see if it makes a difference.
Another thing I forgot to mention- bike maxes out at about 90mph, then seems like it just bogs down- this is after my intake/exhaust mods though. I suppose the ram air is making it too lean at those speeds.
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post #5 of 11 (permalink) Old 08-25-2018, 07:52 PM
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Its lean and overheating.
Ram air intakes cannot be jetted for 90mph and idle, because of the change in airflow with speed.

27 k miles is too soon for compression to be that low. Was the bike run oil starved?

Missing heat shield will only be a problem when the bike is parked hot, will boil out the float bowls.

Last edited by KCW; 08-25-2018 at 07:54 PM.
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post #6 of 11 (permalink) Old 08-25-2018, 09:05 PM
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You can used the wire from a bread tie to clean jets. Make sure the small holes in the side of pilot jets are 100% clean. KCW is correct, a ram air system can not be tuned from idle to high speed. If you continue to use it pick the most common mph and tune it for that, then the other speeds will be off some. If you are going for performance, do pods. If you like the looks of the ram air, leave it on but non functioning. There have been many threads here on ram air system and are never able to get then tuned for all speeds. Good luck and keep us informed.

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post #7 of 11 (permalink) Old 08-25-2018, 10:11 PM Thread Starter
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Quote:
Originally Posted by KCW View Post
Its lean and overheating.
Ram air intakes cannot be jetted for 90mph and idle, because of the change in airflow with speed.

27 k miles is too soon for compression to be that low. Was the bike run oil starved?

Missing heat shield will only be a problem when the bike is parked hot, will boil out the float bowls.
I should note I'm using a harbor freight compression tester, but I imagine the number is ball park enough. She was neglect by the previous owner:
I bought the bike about 4 years ago with 6k miles. First thing I did was change oil to synthetic and change oil filter. A few weeks later I changed my plugs, air filter and drive shaft fluid- well the air filter was torn wide open, definitely never changed. The guy lived off a long dirt road outside the city. Well, the oil-tainted walls of all the entire intake system were coated with sand. So my motor has been sandblasted . Then, when I drain the drive shaft, it comes out metalic silver. Incredible. It's my first bike and I didn't know what to look for while shopping... I'm stuck with her, so I'll do what I can to keep her on the road!

As far as running lean, should I be increasing jet size, shimming the needle, or adjusting PMS? I'll install the heat shield asap.
I'm hesitant to do another carb cleaning because when I did my mods a couple months ago, I did a cleaning (without using wires to clean). The bike is a weekend warrior as of late, so is ridden at least once a week, with seafoam here and there.

lesblank, next cleaning ill try out the bread wire. I've been leaning towards pods instead of the current setup. It would eliminate a lot of possible leaky joints as well. Right now it's all RTV'ed to seal leaks so its just another reason to avoid taking off the carbs- what a pain
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post #8 of 11 (permalink) Old 08-26-2018, 01:47 PM
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If you think you have the correct jets for the intake and exhaust, Then something is gummed up, or you stiĺl need to adjust the PMscrews. The recommended turns is just the starting point, most people have to tweak them further.

Can't repeat too much, ram air intakes are for racing WFO. without a self adjusting fuel injection system ram air just sucks on a street bike.
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post #9 of 11 (permalink) Old 08-26-2018, 02:09 PM
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theres a rak listed here it seams your jetted for highway speeds and you describe it running rough at around town speed.a rak is not a hypercharger it looks like it uses the stock airbox. pods would fix everythinghttps://650ccnd.com/perf.htmhttps://650ccnd.com/perf.htm sorry link wont work.

Last edited by nick57; 08-26-2018 at 02:13 PM.
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post #10 of 11 (permalink) Old 08-28-2018, 06:15 PM Thread Starter
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Alright, I've ordered the pods and will throw the heat shield back on when I go into to install them. It'll be nice to eliminate all the intake ducting.I'll play around with the mixture and keep you guys updated. Thanks!
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