September 22nd, 2019, 01:59 PM | #1 |
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Name: Hector
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Trouble re-starting
My bike has developed difficulty re-starting after the engine is warmed up. I believe this to be a new issue. After I shut it off, it doesn't want to start whether I try immediately after or let it sit a few minutes. So bad my battery wore down earlier today.
In my "opinion" it seemed to smell rich so I double checked my air-mix and reset them at 2 1/4 turns (they previously were a tiny bit under 3). I pulled the plugs and the right smelled like fuel but looked normal and was not wet. The left did not smell like fuel and looked to be at about the limit of "normal" but definitely well on the lean side. The bike has less than 600 miles since ducatiman serviced my carbs, new OEM fuel filter, new plugs, new OEM petcock, new OEM air filter, sync and valve adjustment. Runs great but idles subpar (since day one, after I cleaned carbs and after ducatiman serviced them, too) but I've just resolved to ignore it. I'm a bit puzzled on what to look at next, and when (hot or cold). Any ideas?
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September 22nd, 2019, 04:05 PM | #2 |
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Have you done tank-vent mod?
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September 22nd, 2019, 04:38 PM | #3 |
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I removed the California evap system a while ago which includes removing the little screw to vent the top of the tank. Is that what you mean?
I haven't experienced any vapor lock up or "whooshing" when I open the cap.
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September 22nd, 2019, 04:55 PM | #4 |
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Have you checked the valves lately?
Have you checked the carb sync? For now, try opening the throttle as you are cranking. |
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September 22nd, 2019, 06:31 PM | #5 |
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I'd urge to disregard the *number* of turns on the pilot screws and instead urge you to set each cylinder (AFTER a ride, bike fully up to temp) by finding its "sweet spot". The required number turns out on each cylinder will differ.
Beware of burns....a very hot, semi-dangerous job for the more experienced. Gloves on, shop rags or towels draped as necessary over crankcase area to temporarily protect and insulate your hands and forearms from heat....work 1 cylinder at a time...turn the pilot screw inward, at a certain point that cylinder will begin to stumble....turn back outwards a bit at a time till the cylinder recovers, then further as necessary to reach its highest RPM....do overs are fully acceptable till you are confidant you've found the "sweet spot"....I think you'll sense and hear it...then and only then...do same to the other side. A large pedestal type shop fan is very helpful for this type of hot "running in place" procedure. Pretty sure I posted all this before.
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September 23rd, 2019, 06:06 AM | #6 | |
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Name: Hector
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Quote:
I've tried to open the throttle when starting, doesn't have much of an effect. It tends to only re-start when the throttle is left alone.
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September 23rd, 2019, 06:08 AM | #7 | |
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Quote:
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September 23rd, 2019, 06:13 AM | #8 | |
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Quote:
How old is the gas in it now? When things just pop up like that the first thing I think of is a fuel issue. |
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September 23rd, 2019, 06:20 AM | #9 |
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^ valid stuff
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September 23rd, 2019, 07:45 AM | #10 | |
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Quote:
I guess I can dump out the gas, drain the bowls and try again this weekend. Thanks for helping out guys, really appreciate it.
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September 23rd, 2019, 08:16 AM | #11 | |
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Quote:
Gas with ethanol goes bad quickly, and can even be bad when purchased. Easy thing to just check off the list before moving on and taking things apart. |
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September 23rd, 2019, 09:35 AM | #12 |
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Good point, it's simple enough. I'll give it a shot and check back in here. Thanks.
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September 26th, 2019, 11:56 AM | #13 |
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Drained the bowls, emptied out my tank and put in fresh gas. Problem remains the same. Any suggestions? I'm so close to finishing up this project, just a speedometer away.
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October 3rd, 2019, 04:39 PM | #14 |
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Smoke machine test
I hooked up a smoke machine to the airbox (engine off) and pumped in smoke hoping to find a vacuum leak but no smoke escaped. I repeated the same process with the throttle wide open and no apparent leak.
I repeated the above AFTER the engine was run to full temperature since that's when the re-starting failure happens. I was hoping that maybe something like a clamp, boot or hose is expanding with the heat and creating an air leak. Needless to say, no smoke escaped. I'm completely stumped.
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October 3rd, 2019, 09:43 PM | #15 |
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1. Test for vacuum-leak going to and at petcock. You may not be getting fuel because petcock is not opening. When you have hot-start problem, disconnect fuel-hose from carbs and aim into measuring-cup. Crank engine, does petcock flow petrol? You can also measure vacuum in hose going between petcock & carbs. Above certain vacuum number, petcock will open and flow. Below certain vacuum amounts, petcock will not open. Simple if you have numbers to look at.
2. If fuel is getting into carbs, perhaps it's not enough due to vacuum-leaks. These leaks suck in extra air and causes lean difficult-to-fire mixtures. Smoke test doesn't work because with engine off, it needs to be pressurised to escape from leak. Meaning you have to plug exhausts and seal inlet to pump smoke in under pressure. One iffy way to test is run engine and squirt carb-cleaner or propane around all intake joints, hoses and clamps. Leak will suck in carb-cleaner and cause change in idle-speed. But it's very subtle and not easy to catch unless you've been shown the shift before. Best way to find vacuum-leaks is to seal exhaust and intake and pressurise it to 2-3psi with compressor. First, plug exhausts with banana, potatoes, wet-rags, etc. Then use fitting that seals off intake and pressurise with compressor to 2-3psi. For dual-carbs, you can make Y-fitting with two radiator-hoses to use one pressure-inlet. Then spray soapy water around all joints, hoses and clamps. I found leaks that smoke and propane couldn’t. Last futzed with by DannoXYZ; October 4th, 2019 at 11:54 AM. |
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October 3rd, 2019, 09:47 PM | #16 |
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I doubt intake vacuum-leaks would be severe enough to cause no-start condition though. Would also cause problem with cold-starts as well if it was that large. More likely it would only cause unstable idling warm or cold.
1. I suspect petcock or its vacuum supply. Need to measure things to rule that out. 2. Also have you tried starting with gas-cap open? Cap vent-mod isn't removing screw, but entirely removing one-way valves inside gas-cap. 3. Test for spark as well when you have hot-start issue. Last futzed with by DannoXYZ; October 4th, 2019 at 11:55 AM. |
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October 4th, 2019, 05:25 AM | #17 |
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As you've had tuning difficulties going on a year now....something has been overlooked, maladjusted.....or something.
@dodgerdad you had posted a running/starting video in a previous thread, can you repost? It was taken after your valve adjust, IIRC. I'd like to hear that again. Or a new one, your choice. Short of being there, that vid next best thing.
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October 5th, 2019, 09:03 AM | #18 | |
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Quote:
I had already planned to test the coils for spark when hot today. Next step will be to double check valve clearances tomorrow to see if perhaps I left them too tight and they're not opening enough when everything is hot and expanded. Thanks for your suggestions!
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October 5th, 2019, 09:07 AM | #19 | |
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Quote:
As for the video, I'll record a new one this weekend IF necessary. Thanks for the input!
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October 6th, 2019, 02:26 PM | #20 |
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Progress, dare I say?
I warmed up the engine last night and shut if off then it wouldn't start, as expected. I tried re-starting it after opening up the gas cap (heard no squeal or whoosh) and no change. Then I check for spark and both coils produced a nice strong spark.
I began to strip off a few things off to access the valves in the morning and noticed the left airbox boot was not fully seated at the bottom. Coincidentally this is the same cylinder that appeared to be a bit lean when inspecting the plug. I moved the aibox as far forward as I could (not enough for my satisfaction) and re-seated both airbox boots to the carbs. By then my battery was dead. I charged up the battery this morning, warmed up the engine and then shut if off. I re-started 3 times in a row so I think that may have been the problem. That leads me to one more question: What is the carb intake diameter? I want to replace the airbox boot springs with crew-on hose clamps. my boots have become a bit "loose" and the airbox just isn't sitting fore enough despite wrestling it around. I figure tight screw-on hose camps should satisfy me that there is a solid air-tight seal.
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October 6th, 2019, 09:41 PM | #21 |
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I haven't had any issues with the screw type hose clamps. A little fumbly, screwing it all down, sometimes if you have them too loose. No problems with leaks, or backing off, though.
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October 6th, 2019, 10:00 PM | #22 | |
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Quote:
But that doesn't really make any sense. Any pre-carb leaks will not affect fuel-metering or AFR. You can start and run the bike with no air-box even. Sure, it may have some mid-range stumbling issues, but it'll still start. Could there have been leak at rubber manifold in between carb and head? And in process of shoving air-box back on carb, you closed up that other leak as well? |
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October 7th, 2019, 06:28 AM | #23 | |
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I did make a couple small brackets to make sure the airbox stays forward against the carbs: https://www.ninjette.org/forums/show...25#post1257525 |
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October 7th, 2019, 07:32 AM | #24 | |
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October 7th, 2019, 07:34 AM | #25 | |
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