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84 XV1000 runs fine for 3 seconds then...

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84 XV1000 runs fine for 3 seconds then...

PostAuthor: Jdriskill » Fri Feb 12, 2021 8:36 pm

Hi all,

I have learned so much from this forum about these bikes. Thanks to everyone that posts here.

Having a problem where the bike starts up and runs fine for about 3 seconds then it won't rev up (bogs) and backfires. I have modified the bike quite a bit: ais system is removed, gravity feed for the fuel system, single carb, kick stand switch deleted, etc. I'm certainly aware that it is probably something I did at some point. The bike did run fine for quite some time after all these mods so it wasn't something that happened right away after I installed it wrong or mis-wired it. Also, I had the same problem with the dual Hitachis and I thought I might fix it by going to a single Mikuni, but the problem is still there. I suspect that it is ignition related. I can confirm that I have good strong spark to both cylinders even when the problem is happening. Plugs look a bit on the rich side so it seems to be getting plenty of fuel. I think that it may be timing related. Is there something different about the way the bike determines timing at start up then after 3 seconds? If I shut the bike off and restart it it runs fine for about 3 seconds every time, hot or cold. It idles although it does pop and isn't very smooth, but it bogs and really backfires when I rev it. I know this is an odd problem and I've done quite a bit of digging around but I'm starting to get that hopeless feeling! I need some input from some fresh minds on the problem!

Thanks in advance for your help.

Jeff
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Re: 84 XV1000 runs fine for 3 seconds then...

PostAuthor: chrismalm » Sat Feb 13, 2021 12:39 am

Have you followed the troubleshooting procedures in the FSM ? What's your battery voltage during those 3 seconds ? Did you check the resistance of your pickup coils, ignition coils, ignition wires & boots ? What plugs are you running ?
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Re: 84 XV1000 runs fine for 3 seconds then...

PostAuthor: Jdriskill » Sat Feb 13, 2021 6:39 pm

Thanks Chris,

No harm in double checking the basics!

Coil #1:
Prim: 4.5 ohms
Sec w/ wire: 16.9K ohms (I measured from the coil to the end of the wire and boot)

Coil #2:
Prim: 4.5 ohms
Sec w/ wire: 16.85 ohms

Pickup:
Green to Brown: 147 ohms
Blue to Red: 147 ohms

NGK BPR7ES (It had BP7ES in it with the same results)

Voltage is constant, but high-ish: 15-16 volts at startup and when it starts bogging.
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Re: 84 XV1000 runs fine for 3 seconds then...

PostAuthor: chrismalm » Sat Feb 13, 2021 10:58 pm

Well, there went the easy answers :huh?: Your ignition and charging systems seem to be in spec.
Can you rig up a clear tube to your float bowl drain and check static and running fuel level ?
Maybe something upstream is restricting fuel flow into your bowl (petcock, filter, float needle...)
Other than that, I got nothin' :ider:
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Re: 84 XV1000 runs fine for 3 seconds then...

PostAuthor: mark75 » Sun Feb 14, 2021 4:41 pm

:yup:

ample spark?
check.

ample fuel?
check?

it must be fuel delivery then. either float valve issue, or filter, or pump ...
does the fuel pump run ~5 sec. each time the key is turned on?
does the F.filter allow easy drainage? clogged?

open a carb drain-screw and see how much fuel you get out.
should be ~ 2 oz(?) or = about 1/2 or 1/3 of float bowl


here's a thread with links for doing the clear tube / float thing. >>> viewtopic.php?f=5&t=55517
you may have to sign-in with each link :con:

WOW. I totally missed that you went grav. feed. :doh:
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Re: 84 XV1000 runs fine for 3 seconds then...

PostAuthor: Jake » Mon Feb 15, 2021 7:48 am

It sure sounds fuel related.

Starts and runs for three seconds, how much time between start intervals ?

You converted to gravity feed. What did you do ? What about the evap canister, is the tank properly vented ? Did you coat the inside of the tank with anything ? Internal filter or external filter ?

If you converted to gravity feed and used a petcock, remove the fuel line, add another line to it and direct it into a container. Turn on the petcock, are you getting a good flow ?
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Re: 84 XV1000 runs fine for 3 seconds then...

PostAuthor: Jdriskill » Fri Feb 19, 2021 3:19 pm

Sorry I'm late to respond. Thanks everyone. Seem fuel related from the beginning to me. I'm going to run some tests using a different fuel source and report back.

I did not coat the tank with anything. There is an external petcock and an inline filter. I have checked the flow previously and it seemed fine. I also see some fuel in the filter when it is acting up which I assumed meant the needle was seated, but like I said I'm going to run some tests and report back. Somewhere some assumption I've made is wrong!

Thanks again everyone
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Re: 84 XV1000 runs fine for 3 seconds then...

PostAuthor: Timbox3899 » Sat Feb 20, 2021 9:31 am

I would say fuel as well, now comes the fun part. If you don't know the shape of the tank, if there is old rust fuel or other stuff in there? I don't know what type of filter you have either. Some of the filters will filter out some of the stuff but even the little stuff will get back into the carbs.

If it were me, I would pull the carbs and give them a good look. Make sure the jet at the bottom of the float bowl is not plugged alone with the other jets. If you do pull the carbs and as soon as you remove the float bowl you see rust residue, you will have to treat the gas tank.

To test the gas tank, just let the fuel you currently have in it run into a light colored container. You will be able to see if there is color to it or if there are things floating in it. Do the gas without the filter, this will give you a better reading.

Checking the petcock. Those vacuum petcocks always give me pause of trust. I change them out with fully manual on and off ones. This way when I turn the gas off, I know it is off.

I use Evapo Rust remover, cost about $20 a gallon and works very well. The nice thing about this product is that you can reuse it for other projects in the future.

Hope it all goes well for you, looking forward to your updates.

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Re: 84 XV1000 runs fine for 3 seconds then...

PostAuthor: Jdriskill » Sun Feb 28, 2021 4:49 pm

A long overdue update! It's funny how life just gets in the way sometimes.

I feel confident that I've eliminated the possibility of it being fuel related. I used a gas can placed 2 feet above the carb and ran a clear line straight to it. I could see fuel the whole time in the tube. Seeing as how I had the problem with the old Hitachis and the new Mikuni that covers pretty much covers it! So - back to spark. Maybe the igniter is bad? I've checked all the connections and grounds. So odd. I suppose it could be the pickups too, but it seems unlikely that it would run fine for a bit then start to bog if they were the culprit. I wish I had an igniter to swap in and see if that changes anything.

I'm not sure you'll be able to see this, but here's a little video of the action:

https://photos.app.goo.gl/jxy1ucizoro23T6f6

Thanks guys!
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Re: 84 XV1000 runs fine for 3 seconds then...

PostAuthor: chrismalm » Sun Feb 28, 2021 8:43 pm

That video helped clarify the situation for me. I'll throw another long-distance dart...
It seems to idle fine. I still think it's fuel related.
I think your float needle isn't letting in enough fuel to keep the bowl full when you rev it.
My recommendation is to put the bike on it's centerstand
Attach a clear tube to the bowl drain and route the end other up alongside the bowl
Then open the drain screw and mark the static fuel level on the bowl
Then start the bike and rev it and see if the fuel level in the tube drops
If it does, you'll have to find the bottleneck.
The Hitachi float has a tang that keeps the needle from opening too far.
Your carb's float needle might not be opening far enough.
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Re: 84 XV1000 runs fine for 3 seconds then...

PostAuthor: Flyingdog » Sun Feb 28, 2021 10:59 pm

At first blush, I'd say there's still a fuel delivery problem. What size Mikuni is that? Did you use any base line setting/jetting that's been documented to work or did you just throw it on hope'n it would work as is? JMO: that's a horrible idle and it does not take a lick of throttle off-idle. That would be my first flag.
I'd also check that regulator. While not outta this world if yer rev'n to 5k (actually your numbers would be considered high, when 15v should be the very top output)..it is high for just idle'n. Over charging can cause a host of problems. Specially rough idle-to-off idle wheez'n sneeze'n spitt'n & cough'n like that.
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