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  1. #1

    Join Date
    Oct 2016
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    Default Two bikes. Same issue

    So I have two bikes with the same issue.
    Bike 1-- 98 vstar 650. Sat for 2 years I grabbed it for $350. Carbs were locked solid pulled and cleaned carbs, they were so bad I said fuck em and grabbed carbs from a friend that were in better shape. Cleaned those, installed. Cleaned tank and lines, fresh gas and sea foam. Nothing from rear head. Good spark, pushing air out if the exhaust but its cold. Took tank off and ran the bike with a can of carb cleaner, and rear cylinder would get hot. Did I miss something in the carb? Float seat maybe?

    Bike 2- 2000 shadow 750. This was my bike already. Its hardtail and my wife. Never complained but I got something a little more passenger friendly. So it sat since like October, I would start it from time to time and go out for quick solo rips, but the last couple times it was kinda shitty. Last night while fucking with the v-star I figured I'd drop some sea foam and fresh gas and let it run. Same issue, but on front head. I haven't dipped into this one yet, but I'm guessing also a carb issue.

    Both bikes sat, one cylinder fucked. I did a quick Google search but didn't find much. I know the guys here dig into bikes a lot more than most others.

    Thanks in advance
    Last edited by johndoe; 03-03-2019 at 7:08 AM. Reason: I type shitty

  2. #2
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    I say your carb/carbs, gas tank and lines filter are still dirty.........

  3. #3
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    I'm not going to pretend that I have a crystal ball and know what does wrong with your bike over the internet.

    hell, I haven't even worked on one of what you're working on. But, I used to make my living diagnosing why cars didn't run right. I specialized in Hondas, and was working in shops during the years where we saw carburetor and fuel injected cars.

    What I can tell you here, this how I go at diagnosing a problem.

    Alright, here's my advice:

    1. You don't know that you have two bikes with the same problem. What you do know is that you have two bikes with a similar symptom - a non-running cylinder.

    I strongly advise you to keep an open mind while diagnosing each bike, as they may or may not both have the same cause

    2. Gas engines all need the same three things to run: fuel, spark, and air.

    Air is the easy one to figure out. Is air getting into and out of the cylinder? Did someone leave a rag in an air filter? Does the cylinder have compression? Before going any further, I would give both bikes a thorough visual inspection, and do a compression test on both engines. I wouldn't worry about what the numbers are hot, since you've got a hole on each engine that isn't firing at this time. Just get numbers, write them down somewhere.nothing worse than trying to chase a tune, when you eventually find out you don't really have an engine...

    Then, I would check spark. This means a good battery. Good spark starts with a good battery. Unless you have a bike with a magneto. Again, I would pull the plugs out of all the cylinders on the bikes, check all of them. Checked all of them are getting spark, and that the problem holes, are getting as zesty a spark as the good ones.

    Now, I'm not familiar with the bikes you're working on. Don't know anything about their ignition systems. I generally through a timing light on anything I was checking the spark on, because it only took me seconds more to hook that up, and I could rule out either a jumped timing belt, or someone having dicked around with the ignition timing. not that I usually found anything, just that it was cheap and easy to do, and ruled more bullshit out of the way right up front.

    It should not take an hour to have completed the above checks on both bikes.When working in a shop, with all my tools at hand, it would have only taken me a few moments.

    Were they likely to find the problem? Not necessarily. But it's damn good to do things that rule out stuff that'll leave me chasing my tail. My experience has been that attacking things in a sequential, orderly fashion yields faster results more times, than guessing why something doesn't work, and trying to see whether that shit pans out or not.

    So... Fuel. This is the most complicated of all of the three, with the most options.not only do you have to have fuel delivered, it has to be the correct amount.

    A stuck choke, or a bad float on a carb will give too much fuel. A bad vacuum line somewhere, or a cracked carb boot can introduce "false air" - either making an engine run like crap, or not run at all, depending on how bad it is...

    Remember that visual inspection? That's kind of where stuff like this gets found sometimes.

    Since you're able to get each of these engines to start, you can check for leaks by spraying carb cleaner. Go around manifold fittings, carb boots etc on the problem cylinders, see if you get a reaction. Does it sputter? Does it start to run?

    I would not expect to find a vacuum leak big enough to make the cylinder go completely dead, that you wouldn't see a problem if you look things over slowly and carefully. But, my expectations, plus $5, has a street value of exactly $5...

    I'm fond of taking a little propane plumber's torch that I cut the tip off of, and stuck a long rubber hose on, and using that to introduce fuel.

    It's really handy when you've got something that runs poorly, if you start feeding it propane and the engine speeds up, your lean. If it immediately falls on its face, rich.

    In the case of your bike, if that cylinder works when you feed propane in its carb, then you are not getting a sufficient amount of fuel.

    Now, why not? Petcock working? Check the fuel flow - compare it to the good cylinder. If both carbs run off of one petcock, pull the lines off both carbs and make sure that gas comes out both.

    If you're getting fuel TO the carbs, is it getting IN the carbs? Drop the float bowls (if possible) on the carbs for your "problem child" cylinders. Did they have fuel? If not, why? Probably needle and seat. If they were full, but the engine requires you to add extra fuel to get that cylinder to run, why was enough fuel not getting from the bowl into the intake manifold? Did you leave the idle mixture screw screwed in? Is there an obstruction inside the carb body?

    If you've gone step by step, and got to this point, it pretty much points at the carbs.

    Unless of course I'm missing something. Which I may be. But I sincerely hope that all of this writing will help you get a good mindset to go at this, and not get frustrated. Will have to check in again in a few days, as I am busy moving from Seattle to Texas

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    One other thing, the guy who posted above me mentioned dirty tank. If there's crap in there, I would get that sorted before I tried to do anything else...

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    ^^^^^ That's a lot of great advice above in both post...^^^^^^^^^^

    I based my first post on the length of time the bikes have been sitting.........

    Let us know what you find out...........

  6. #6

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    Thanks for the replies. I've got good spark and compression on the yamaha. Probably should have mentioned that.

    I'm going to go though the carbs again and see if I missed something. And while its apart won't hurt to clean the tank and lines again as well.

    After I get that figured out ill fuck with the Honda. I can't beat my head against the wall on two bikes at once. Lol

  7. #7
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    I strongly suggest making a dummy fuel tank for testing! That eliminates whatever trash is in the stock tank. Riding mower tanks and Briggs and Stratton style shutoff valves

    https://www.amazon.com/Briggs-Stratt.../dp/B0038U3JK2

    work very well.

    Hang the tank as you prefer. Need not be large since small is much handier. I don't run bikes on carb cleaner. I run them on fresh fuel, fed from a proper tank. To verify spark, sure. Run attempts? Too short to be useful.

    Were the carbs stripped and dipped? Carb spray doesn't count. The cheap Harbor Freight "ultrasonic" (vibratory really) cleaners work well.

    Working on two bikes at once was silly. Now you know. Work one, come to a stopping point and switch. Take pics and notes.

    KNOW where all your vacuum lines go. Have some plastic golf tees etc to plug open vac lines like those to vacuum fuel valves which will be disconnected with stock tank removed.

    2000 Shadow would be the easy fix since it's known to have been working. Your low speed jets etc are likely varnished. That's normal. Next time drain the fuel system when you store a motorcycle. Strip carbs, dip, reinistall after dumping the fuel tank.

    I agree with everything thecarfarmer said. Propane is used by auto techs because spray is near worthless by comparison.

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    If the bikes sat for that amount of time you will need two NEW float needles. End of story.
    I really hope that you did not throw away this other two carbs!
    The idle jets will need to be cleaned.
    You need to be able you hold them up to sunlight and be able to see through them.
    Last edited by Luky; 03-03-2019 at 12:00 PM.

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    I really hope that you did not throw away this other two carbs!
    The carb supply for non-HD and non-Britbikes will gradually dry up and Jap bikes often use very specific carbs. I should have saved every carb I could get my hands on.

  10. #10

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    Went through the carbs again, new float needles. And we are better. Both cylinders firing. Still need some tinkering, as soon as I unchoke it, it dies. But at least I know I'm moving forward.
    And I can start cutting into it. Lol.

    Haven't fucked with the Honda. Those carbs suck to take off.

  11. #11
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    Quote Originally Posted by johndoe View Post
    Went through the carbs again, new float needles. And we are better. Both cylinders firing. Still need some tinkering, as soon as I unchoke it, it dies. But at least I know I'm moving forward.
    And I can start cutting into it. Lol.

    Haven't fucked with the Honda. Those carbs suck to take off.
    It still sounds like the idle jets are still stopped up.... They are very tiny did you look through them at a light??

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