Infuriating carb problems - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
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post #1 of 38 (permalink) Old 03-23-2019, 01:07 PM Thread Starter
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Infuriating carb problems

I have a 2007 VStar 1100 classic. I bought it knowing that it's sat for a while and would need the carbs cleaned out, which is normally not a problem for me.
It's bone stock, it's exhaust was off the bike but I reinstalled it. I cleaned the carbs and try that I started having problems.
It will idle fine, but given more than 1/8 - 1/4 throttle, it will die. So I cleaned the carbs again. Same issue. I discovered a torn air side intake elbow for the left carb, so I replaced it and the engine intake boot o rings for good measure.
Still have the same issue.
Pulled the carbs again, this time I took them entirely apart, ran the Jets and carb bodies in an ultrasonic cleaner off and on for two days, used wire to ensure the passages were free, blew out the passages, verified the jets and needles spacers were correct for stock, drilled out the PMS screw covers, cleaned those, verified they were the stock turns and bench synced the carbs.
Still have the same issue. I sprayed carb cleaner around my intake connections and I can't get a response from the engine. Covering the intake opening some seems to get it to function correctly, so it's like it's not restricted enough. I even played around with the mixture screws to no avail, and even threw a spring in the air cleaner box to ensure its not moving around.
Nothing seems to be working and I'm about ready to throw the carbs and bike off a cliff.
Are these bikes really this sensitive to their intakes in stock form?
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post #2 of 38 (permalink) Old 03-23-2019, 03:10 PM
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did you check or adjust the float bowl levels, the point at which they cut off the fuel?

have you pulled the fuel line off the carbs, turned the key to run and checked the flow out of the fuel pump? People dont realize these bikes have a fuel pump, because the bottom of the gas tank is lower than the carbs. They will sorta run if the tank is full and the fuel pump is bypassed, but if you are only getting a trickle you wont get enough gas for much more than idling.

Also are you riding the bike and seeing it drop out, or only reving it in neutral? It takes a good mile after starting the bike cold with the choke, to ride off, pushing the choke in as you go, till the engine warms up to feel pretty good. A couple more miles till the engine is at operating temperature, so if you are starting it cold, pushing the choke in, and trying to rev it in neutral... that is sketchy on a bike that is running perfectly.

The air intake is necessary on these bikes, you cannot run the carbs with nothing connected on the intake side, and it needs to be more or less intact, not full of bees or wasps, and the air filter needs to be in place and clean (white).

One other possibility, the timing is advanced by a throttle position sensor (a potentiometer) on the throttle plate. As the throttle is open the sensor tells the ecm to advance the spark. if that is not connected or not reading correctly, the bike will run like crap off idle, if it runs at all.

The jets in the carb are progressive, there is an idle air passage, the PMscrews which cover the low range of throttle twist, and the main jets which dont kick in till you are over half throttle. So you can have good idle air, and good or close PM screw settings, and if the main jets are clogged the open throttle side will bog down.

The other thing to consider, since the bike had issues when you got it, its possible someone else had the carbs apart, put the wrong jets in there, left out some O rings or spacers, or put it back together wrong - It would be a good idea to look at the exploded carb view for you bike on a website like bikebandit (OEM parts... carb...) and see if there are things on the drawing that dont match what you saw in there.

Last edited by KCW; 03-23-2019 at 03:14 PM.
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post #3 of 38 (permalink) Old 03-23-2019, 03:11 PM
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edit: regarding the float bowl adjustment, the bowls hold enough gas for the bike to run almost a mile, so if they fill up while you idle, and then you take off, if the floats were not adjusted right, or your fuel pump is weak (or dead) the bike should get at least half a mile down the street, then drop out starving for gas....

I know this because I forgot to turn my petcock on a few times, and I made it about a mile down the street at a steady 40mph...
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Last edited by KCW; 03-23-2019 at 03:31 PM.
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post #4 of 38 (permalink) Old 03-23-2019, 03:19 PM
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If you think you have beat the carbs to death and they cant possibly be the issue, step back: check the plugs, do a compression test.

When I got my Royal star last fall it was running a bit rough, I decided to put new plugs in it, put the socket on the plug... they were all finger tight, all 4 of them.. never know what you will find on a previously enjoyed motorcycle.
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post #5 of 38 (permalink) Old 03-23-2019, 03:36 PM
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My wife's old 650 had a similar issue. Turned out to be an air leak thru the smashed rubber boot, overfilled bowls and carbs were out of sync. Once I replaced the boot (and had to make sure that the carbs seated properly on the boot before tightening the clamp), adjusted floats and synced the carbs it ran like a beast. Before I did all that it needed good 5 minutes of warming up just to get it rolling.
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post #6 of 38 (permalink) Old 03-23-2019, 03:51 PM
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I had same issue a while back. Had a clogged fuel filter.



Replaced with fuel filter from auto parts house. Works great. Issue fixed.

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post #7 of 38 (permalink) Old 03-23-2019, 04:09 PM
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I hate to ask the obvious question after all the work you have done on the carbs: did you drain the tank and put fresh gas in it?

Old gas with 10% ethanol breaks down and part of it jells. If you have old gas in the tank everytime you clean the carbs and start it up, you will pull that goop into your carbs again.
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post #8 of 38 (permalink) Old 03-23-2019, 04:28 PM
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Yep, I had the same issue with a clogged fuel check valve in an old car. Anything in the fuel line restricting it will cause an issue, but it shouldn't cause an instant issue as the float bowl should be full, as KCW noted it took approx a mile.

If your having an instant issue at 1/8 to 1/4 throttle to go higher, it's a main jet/needle issue. The needle could be worn, or the needle seat could be worn, causing the hole to be too large, so when you increase the throttle and get way too much gas, and it bogs out.

I'll have to assume the ultrasonic did a good job, but generally it takes people 2-3 cleanings before they get the whole carb clean, due to all the tiny small passages, one tends to get missed the first pass.

I'm always willing to drive and help someone if it's within a few hours drive, ocala, florida.
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post #9 of 38 (permalink) Old 03-25-2019, 09:00 AM Thread Starter
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All of the testing is done in neutral in the garage, since I don't want to risk the bike stranding me and having to push it back. So it's not only under load.

I didn't verify the float valve height, but there wasn't any reason for me to suspect as much. Tab didn't look bent in any way. Jets are the correct 115 Front and 112.5 Rear for the solenoid carbs. Needles are stock with the spacers in the correct order. Diaphragms are also intact, with no light passing through the membrane. PMS screws were stock since I had to drill out the caps, but are currently set at 2 turns out, and I've played with up to 3 turns out. Based on the internals, It doesn't appear that anyone had gone through and messed with the carb internals. Though I could try running with the exhaust pipes off since they were off when I got the bike.
Tank isn't a problem since I was running an auxiliary fuel bottle with fresh gas directly into the line that feeds the fuel pump. Fuel pump is working because I can hear the clicking and Ive accidentally run it when the lines weren't connected to the carbs. I've also gotten the same results with the tank connected, which was also drain and fresh fuel put in. Needles and seats look good, with the conical rubber looking fine. I get no fuel leaking out the vents or overflow.
I've also eliminated any strangeness with the solenoid passages by removing the o ring on the main jet that seats with the fuel bowl.

I'm not opposed to ruling out the obvious again, since I'm kind of at a loss and it's good to be double checked. At this point I have cleaned the carbs in some manner 3-4 times, once entirely apart with the carb bodies soaking in the ultrasonic cleaner, same with the jets. As mentioned earlier, I check for light passing through the holes and used thin carb cleaner wires to make sure nothing stubborn was in there and blewout all passages with compressed air.

Since I can use an auxiliary fuel bottle, I might try to rule out the fuel filter by disconnecting it entirely.

As for intake leaks, I've run the bike in nearly every intake configuration (because I started to lose my mind): carbs only, intake elbows, air box, air box to cleaner connector, half of the cleaner, cleaner with no filter, cleaner with filter. Obviously things didn't run right, but I was trying to see if anything could be gleaned from doing all of that. Gaskets between the air box and air cleaner halves are still there.

The things I haven't done, based on reading all of this, are checking for float height, ruling out the fuel filter, ruling out the TPS (would need to check that resistances are in spec), and checking compression.
I also had another thought about checking for intake leaks. I've generally used aerosol carb cleaner, but I've read about people using propane gas to test for intake leaks. Would the gas be able to better penetrate thin cracks versus the carb cleaner? The only reason I ask, and one of the things I suspect, are the engine side intake boots. They have cracks on the exterior, but I don't see any cracking on the inside, and spraying carb cleaner at them while the bike is idling doesn't produce a change in the rpms.

I'm in northern Alabama, so I'm a bit far from you patrick, though the offer is immensely appreciated. I'm also going to be out of town for a couple weeks soon, so I won't be able to try much else. Certainly don't have time to throw new parts at it. I would love to find someone who would let me put their known good carb in, since that could rule out that chunk out.
This is the most puzzling carb I've dealt with, and I've worked on quite a few, including an 03 vstar 650. I'm just thankful that it's easier to remove than a v65 sabre's carb
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post #10 of 38 (permalink) Old 03-25-2019, 09:13 AM Thread Starter
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Also, can someone verify the stock needle configuration? I'm seeing conflicting information between the vstar carb jetting wiki and the parts diagrams from bikebandit/partzilla.
The image on the wiki shows (from the bottom up) shim, plastic spacer, clip, spring, needle holder.
The parts diagram shows plastic spacer, slip, shim, spring, needle holder o-ring, needle holder.
The ordering of the shim, spacer, and clips could be my issue. I may also triple check to see if there isn't an extra shim in there that I overlooked in my frustration
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