cylinder not firing...

Discussion in 'General VMax Questions' started by Steven May, Jun 10, 2019.

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  1. Jun 10, 2019 #1

    Steven May

    Steven May

    Steven May

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    Hey guys, after replacing the clutch, adding oil and getting her started I have discovered a cylinder isn't firing. I replaced plugs (Gapped .035") checked for spark (yep) and did a compression test on all 4. I think the configuration designates #2 as the front left? (the offending cylinder). As per the shop manual, compression with the throttle wide open until the gauge steadies out, my readings were #1: 160+, #2: 155, #3: 160+ and #4: 160+. The cylinder with the lowest compression is the one not firing, but the manual says a max of 171 and a minimum of 128 with a normal of about 149...Have I done this correctly? I have fire, apparently have sufficient compression, ...fuel? This is an '85 I bought after sitting up an unknown period of time, with the clutch removed. Kinda apprehensive about removing carburetor assembly as I worry about the synchronization upon replacement, but I guess I will have to acquire the tools/knowledge to figure this out, finding a mechanic around here that works on older bikes has proven difficult so far. Advice would be welcome, thanks.
     
  2. Jun 10, 2019 #2

    maleko89

    maleko89

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    Sounds like a sync and/or pilot circuit issue. Does the cylinder fire at higher rpms?

    Mark
     
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  3. Jun 10, 2019 #3

    Steven May

    Steven May

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    Hey Mark, thanks for the reply, and no it does not fire at higher rpms...no fire at all. Pilot circuit?
     
  4. Jun 10, 2019 #4

    maleko89

    maleko89

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    Pilot circuit of the carbs. If it's not firing at any time, drain the float bowl to see if there's any fuel in there. There's a sticky post in the carbs section showing how to do that.

    Mark
     
  5. Jun 10, 2019 #5

    Steven May

    Steven May

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    OK, I will do that and let you know what I find. Thank you.
     
  6. Jun 10, 2019 #6

    Fire-medic

    Fire-medic

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    Change one thing at a time. Switch spark plugs, see if the non-fire condition goes to the next cylinder. Then same thing for the ignition coil. Unfortunately the coils are tough to remove, but maybe you could work a jumper to make the front cylinders 'switch sides.' Having a spare ignition coil handy is a good reason to do this.

    Did you look at the high-tension lead to see if it's corroded? You usually have enough extra length to trim it back about 1/2 inch and then replace the plug cap. Of course, the high-tension lead and the plug cap are things to try switching one at a time.

    In my experience, the left front cylinder is the one that collects sediment from a not-fully clean gas tank, plugging the pilot jet so it won't fire at idle, though it will fire above the rev range that the cylinder is fed by the pilot jet.
     
  7. Jun 10, 2019 #7

    dannymax

    dannymax

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    I'm guessing a stuck float needle.
     
  8. Jun 10, 2019 #8

    Steven May

    Steven May

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    Thanks guys, I am guessing debris, and also possibly a gunked up carb...First, I have no idea how long it set up. Second, the fuel line was spliced together with a brass union (think of a water hose union, you know the ribbed plastic ones), and there was no fuel filter present. I drained the gas, and put on a glass filter I found at oreilly's, and added clean fresh gas before I ever started the bike. The gas that was in it didn't smell stale but I thought it was prudent to change it. No filter on the line threw up flags for me though. I think the filter I put on is probably smaller than the one thats supposed to be on it, but gas is passing through it pretty well. I should mention that my fuel light stays on, even though the tank is over half full? What is that all about? Anyway, I think it's a little much for me to tackle, so I loaded it up and took it to Killeen, Tx. to a shop that said they would work on it. The rates they quoted me for carburetor repair were reasonable, and having never dealt with multiple carbs on anything I've worked on I feel confident in my decision to leave that problem to the experts. I look forward to their phone call telling me its ready, and I can see what it REALLY sounds/runs like!!
     
  9. Jun 10, 2019 #9

    Steven May

    Steven May

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    I will let you know if you are right dannymax, and fire-medic thanks for the advice, although I didn't understand much of what you said at first. The spark did look weak (thin, yellow) compared to cars I have worked on (thick, blue spark). Could that be an indication of a corroded connection? Well it's out of my hands now but I will let ya'll know what the shop finds.
     
  10. Jun 11, 2019 #10

    Traumahawk

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    Yep it can be a corroded connection. You can clip about 1/4th of an inch off the plug wires to get to good copper) and you can ever take the boots apart and check for corrosion. 1-maximx_plugcap_and_parts.jpg
     
  11. Jun 11, 2019 #11

    Fire-medic

    Fire-medic

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    Sean Morley (one2dmax@aol.com) and dannymax are the carb repair guys here who can clean yours for you, and rebuild what needs to be done. I do my own, but I had an experienced shop owner who took-pity on me, and showed me the ropes (I've owned my first one 26 years). Actually, I think they're easier to work on than a Honda Shadow V-twin. I can get the carbs off from a cold engine in under an hour, taking time for a bathroom/drink break. Once you've done it, they actually are pretty straightforward. I believe the #1 problem is not running the bike enough, leaving it sitting for a month or more, and expecting to go riding is not the best way to go. Also, any rust whatsoever in the tank will definitely end-up in your pilot jets, they have tiny orifices, and what looks like dust at the bottom of a slightly-rusty gas tank is enough to make it hard to start, impossible to establish an even-idle, and generally sour-you on trying to use the bike.

    Putting-on a filter is better than nothing. They come stock w/a filter, but you can find aftermarket filters which fit in the stock location and are less-expensive. Did you get a 5/16" I.D. one? Any rust whatsoever in the tank, you're going to constantly be dealing with problems it causes.

    One way to clean the tank is to use industrial-strength vinegar, which is about twice the dose of food-grade vinegar. You just disconnect and seal-off the gas tank, pour in the vinegar to full, and let it sit for 2-3 days. There is a drain on the bottom of the tank with a hex bolt, but it's difficult to reach with the rear fender spat and rear wheel mounted. You can remove the tank in about an hour, and that may be the best way to spend time cleaning it. Out of the bike. Good results also come from using electrolysis, which can be done with a battery charger. VMax gas tank bottom.jpeg

    You can do a lot on your bike, and learn how to do it, reading here. Use the advanced search first to see what's been posted about your area of interest.
     
  12. Jul 9, 2019 #12

    Steven May

    Steven May

    Steven May

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    Hello again guys, well I put the bike in the shop nearly 3 weeks ago and just found out they have not even touched it. I am picking it up this Saturday, and using some of the money I was willing to pay them on a lift, and other tools I may need to work on my new "hobby" (suggestions?) I am dissapointed they have wasted all this time, but I do understand they are a busy shop and didn't want to spend the "lift-time" on my 35 year old bike. So I am becoming a supporting member, and I expect that someone here(Morley?) is going to be getting my carbs in the mail to repair/rebuild. I will be annoying ya'll on a regular basis I am sure. Thanks in advance.
     

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