Bike sitting for 10 years, no start just backfire - Honda Shadow Forums : Shadow Motorcycle Forum
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post #1 of 37 (permalink) Old 05-25-2019, 12:44 AM Thread Starter
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Join Date: May 2019
Model: VT 700
Year: 1984
Location: Rockford, IL
Posts: 62
Bike sitting for 10 years, no start just backfire

Ok I did do the search before I asked. All of the suggestions I've tried, only partial exception is battery. Ok so picked up an old 84 VT 700. Its been sitting in a garage for about 10 years, and I was told it was "started" 2 years ago. So first thing I do is pull the carbs, and give them a really good cleaning. They were prob the worst carbs Ive seen so far. But after 4 hours in the ultrasonic they look good as new. I ended up having to replace the diaphragms, and choke cable. So after all of that was done, I wanted to see if I could get it to fire. The bike didn't come with a battery, so I used my charger/booster to start it. Well a bunch of seeds flew out of the exhaust, and after a few more tries it just backfires. Sometimes out of the carb, and sometimes out of the exhaust. I decided to go back to the drawing board. Got fresh gas and new plugs, no seeds this time, but plenty of backfires. I pulled the plugs out again, and verified i had spark, seemed to be pretty strong. I started doing more research, and read these old bigs are sensitive to voltage. They need a strong battery, or they will do what my bike is doing now. I ended up having to order a new battery, so I figured I would try a car battery i had laying around. Put it on the charger for a bit, measured about 12.8 volts and tried that. Same result. I also read issue could be linked to a bad stator. I just checked that it seems to be fine. Continuity is good with all three posts, and no continuity to ground. So battery should be here Tuesday in the mean time I'm trying to rule out any other root causes. They way it acts i think it could be timing related. Good news is i have 150lbs of compression on both cylinders. I'm going to let this car battery sit on my battery tender for a day or so and try it again. Also I totally bypassed the fuel system, and connected a bottle of gas directly to the carbs. I also tried spraying a mist of gas with same result, boom. I knew going into this it would be a challenge to get running again. But I figured I would be alot further by know. Heck I got an old Pontiac Deluxe running again after sitting for about 30 years. All that took was a carb rebuild and points/condenser adjustment. I do have the manual, and hoping it can provide some knowledge.

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post #2 of 37 (permalink) Old 05-25-2019, 01:00 AM
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Model: VT700C
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Are the plug wires from each coil going to the plugs on the same cylinder? I think it's the coil on the left is the rear cylinder and the coil on the right is for the front.
Also if you are using jumper cables to the car battery, they need to be pretty heavy duty, mine did the same on cheap cables, like you said they need lots of juice.
Good luck.



Eventually the light always fails you.
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post #3 of 37 (permalink) Old 05-25-2019, 01:15 AM Thread Starter
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Model: VT 700
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I believe this is correct
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post #4 of 37 (permalink) Old 05-25-2019, 07:07 AM
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I have the same exact bike. Mine sat for 8 years partially taken apart. Took some work to get it going. Your plug wires look right. You cleaned the carbs you said, i found on my mike the floats being off or the float needle in the bowls being worn will cause this issue. Also the air fuel screws being wrong will cause this too. The factory float setting for that bike is 7.5mm and the a/f screws setting is 2 1/2 turns out. Also the rubber boots between your carbs and heads being worn,loose, or cracked will xause it to pop on decell and backfire while starting. I am speaking from personal experience with my own 84 Vt700. Hope it helps. Just for inspiration here's mine before and after.

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Last edited by bigolepit; 05-25-2019 at 07:13 AM.
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post #5 of 37 (permalink) Old 05-25-2019, 11:41 AM Thread Starter
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Model: VT 700
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Originally Posted by bigolepit View Post
I have the same exact bike. Mine sat for 8 years partially taken apart. Took some work to get it going. Your plug wires look right. You cleaned the carbs you said, i found on my mike the floats being off or the float needle in the bowls being worn will cause this issue. Also the air fuel screws being wrong will cause this too. The factory float setting for that bike is 7.5mm and the a/f screws setting is 2 1/2 turns out. Also the rubber boots between your carbs and heads being worn,loose, or cracked will xause it to pop on decell and backfire while starting. I am speaking from personal experience with my own 84 Vt700. Hope it helps. Just for inspiration here's mine before and after.

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Wow never though of white for that bike, but it looks really good!! I did clean carbs, not opposed to doing it again. I have a few old snowmobiles so I know the game. The needle and seat looked to be in good condition, but I can change those. The a/f jet is capped so I know no one has messed with it, and should still be at factory settings. Boots, also plenty of experience these from the sled world, seem to be in good condition surprisingly. I’ve been using marvel mystery oil to help the carbs carefully seat into boots. So hoping a good solid battery will be the fix. Seems odd these bikes not being fuel injected or have a chip are so sensitive. I also had a theory. What if exhaust or if the mice made it that far headers are clogged enough that on the exhaust stroke the pressure is being pushed back into the head since it has less space to expand? Also is there anyway to verify valve timing without removing engine? I noticed I don’t have a lot of clearance at the top of the valve cover. I do have manual just haven’t a chance to study it yet.
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post #6 of 37 (permalink) Old 05-25-2019, 11:48 AM
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If your A/F screws are still capped, i'd remove the caps and screws to insure the passage is clean and clear, then reinstall.

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post #7 of 37 (permalink) Old 05-25-2019, 11:52 AM
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If the car battery is connected you don't have to worry about the charging system at this time. You could take the pipes loose at the heads and see if it can start easier to rule out a plugged exhaust.
The valves are hydraulic so no need to adjust them.

150 # compression is a good sign.

They don't run well with the intake tubing off but should still start and run for testing.

The valve timing should never change enough without being apart or broken somehow.

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post #8 of 37 (permalink) Old 05-25-2019, 01:05 PM
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Only other thing I might suggest is to try starting with full choke. This is not a butterfly choke system, but is actually a set of metering rods that richen the mixture. If this helps, then likely the problem could be the idle circuits are clogged, giving you a very lean mixture.

If it jams, force it. If it breaks it needed replacing anyway.
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post #9 of 37 (permalink) Old 05-25-2019, 05:41 PM Thread Starter
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Model: VT 700
Year: 1984
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Ok yeah i did have intake tubing off when I tried to start it. Not sure if that made a difference.
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post #10 of 37 (permalink) Old 05-25-2019, 05:45 PM Thread Starter
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Model: VT 700
Year: 1984
Location: Rockford, IL
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Could the ignition packs be be bad? I keep leaning towards a timing issue, but from what Im hearing theres not much to really set.

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