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Discussion Starter · #1 ·
Hi. Love this forum. I have been lurking for bout 3 weeks.

I am new to the world of motorcycles in general. I've had a Suzuki Burgman (400cc scooter) for the past 2 months and I just completed the MSF Course about 1 month ago.

After looking all over the place for a classic Shadow...one in good condition, but not so nice as to where the owner thinks it's a classic car with a "classic" pricetag... anyway, I found it and brought it home this weekend...a 1986 VT500C with almost 10k on it. In pretty good condition...will post pics as soon as I get it detailed.

The bike runs pretty well. I went through it today making the cable adjustments, brake adjustments, etc... I fixed 3 electrical issues too. There is only 1 remaining problem. The throttle itself does not stick...when I rev it while stopped, it comes back to idle (not too fast but I think about normal). However, when I am riding, and I let off the throttle to pull in the clutch lever to shift gears, the RPM's do not come down quick at all. In fact sometimes they don't come down at all or increase. So needless to say my shifts are rather jerky. Yes, I am letting off the throttle completely.

The only way I can shift smoothly is to pull in the clutch, then hold it until about 2 seconds after shifting up (at which time the RPMS finally start to drop), then easing out through the friction zone. Can you say SLOW shifts!.

Anyway, how should I even start to trouble shoot this? If it were a basic throttle cable adjustment needed, wouldn't I have an issue with the throttle while sitting still? And if it is not that, could it be a carb related issue (out of sync?). I have not done a tune up on the bike yet. But the air filter isnt very dirty. I have not pulled the plugs yet (next week). The bike is cold blooded but idles fine at 1000rpm after its warm when sitting still. However, while riding and come to a stop sign, it idles at 1500... One other possible problem or symptom is that when I start the bike cold with half or more choke, the RPMS's will shoot up to 5000 and I have to move the choke lever quickly back down to about 1/4 to get it down.

Any thoughts? Also, is there an inline fuel filter on this bike? I know about the fuel screen in the fuel shut-off valve...

Sorry for all the questions.
 

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Discussion Starter · #6 ·
Thanks for the welcomes and the advice.

I love the bike. I have already done over half of the entire recommended maintenance procedures in the Clymer manual.

I took out the air filter yesterday and thought it was clean. Then today, it hit me...these filters are not like car air filters. Motorcycle air filters get dirty from the inside/out. So I looked inside the filter and found 2 things. First, an 11/16" socket. Somebody must have dropped that when working on the bike and it went in the intake and into the filter. Second, the inside of the filter is filthy. I have one on order.

The throttle cables are not hanging up and the throttle itself is lubed as are the cables (Did that just today). They were not sticking beofre I did it though.

Could the filthy air cleaner have caused my issue? I noticed while sitting on the bike with the seat removed, if i put my hands over the intake tubes, the RPM's shot up. So I am guessing the bike was starving for air... when I was in gear about 3500 RPM's and went to shift, the bike was not getting enough air and the dirty filter was acting as a choke... I have no way to tell if it is fixed until I get my air cleaner.

I also bought some Seafoam and put that in the gas tank today. If the Air Filter does not do the trick, is it possible that the seafoam will help unstick the slides? I will also check for a pinched breather hose. If none of thagt works, do I have to remove the carbs to R&R the sliders? I am decent mechanically, but know nothing about carburetors...

THANKS
 

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Discussion Starter · #10 ·
Kermitdafrog said:
Then today, it hit me...these filters are not like car air filters. Motorcycle air filters get dirty from the inside/out.
Huh? You lost me on that one.

Rick
I used to race stock cars. The air cleaners on the old carbureted engines surrounded the carb and got dirty from the outside/in. With a motorcycle, especially the 86 Shadow, the air inlet goes directy to the inside of the filter, the air travels from the inside/out to the engine...
 

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Discussion Starter · #11 ·
Kermitdafrog said:
Then today, it hit me...these filters are not like car air filters. Motorcycle air filters get dirty from the inside/out.
Huh? You lost me on that one.

Rick
I used to race stock cars. The air cleaners on the old carbureted engines surrounded the carb and got dirty from the outside/in. With a motorcycle, especially the 86 Shadow, the air inlet goes directy to the inside of the filter, the air travels from the inside/out to the engine...
 

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Discussion Starter · #16 ·
slickster said:
Remove the throttle cables and see if the throttle plates are hanging up, a dirty air cleaner won't cause your problem, neither will a sticking carb slide, it'll just make it run very rich, the throttle plates control rpm....check for vacuum leaks, you said that you held your hands over the intakes and the rpm's shot up, vacuum leak.....typically, sticking throttles are caused by bad cables more often than not.....if you have a bad vacuum leak and someone tried to compensate by cranking up the idle speed....it'll do that...also, if the idle circuits in the carbs are plugged and the idle was cranked up to compensate....it'll do that.....start with something simple, like old, nasty cables and go from there....good luck, Mick
I actually did check this when I took the throttle cables apart to lubricate them. Other than being slightly out of adjustment,they were not sticking. Besides, when the bike is sitting and you rev the engine, the throttle does not stick. Once the bike is warm and the choke is off, the rpm's comes back down to 1000 and hold every time, even if I let off the throttle really gently. The problem with the "sticky" throttle only happens when actually riding the bike and letting off the throttle to shift gears. Especially if you shift at 3500 or more RPM. Sometimes when you roll off and squeeze in the clutch lever, the RPM's hang for a second or two, or they shoot up to 4500, then come down....
 

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Discussion Starter · #17 ·
litnin said:
slickster said:
a dirty air cleaner won't cause your problem, neither will a sticking carb slide, it'll just make it run very rich, the throttle plates control rpm....
Actually, a sticking slide will cause RPM to increase.

When you choke the bike, the RPM increase and the throttle blades don't move.
A sticking slide will do the same thing as a open en-richening valve.

The throttle plates do not control the RPM solely, either.
Throttle plates control the air flow or more correctly, venturi pressure.
The slides control fuel flow and they both work together to regulate RPM.
This certainly sounds to me (like I know anything) like it is plausible. Since the bike has only 10k miles and I don't know the maintenance history, the carbs probably are gummed up to some extent. I figured I would change out the air cleaner, adjust the valves, replace the plugs, clean the fuel screen and replace the fuel filter, and run some seafoam in the gas (already put that in yesterday). Then if the problem still exists, it HAS to be the carbs (I'm guessing) or a vacuum leak. As far as the carb slides...how do you check them to see if they are sticking? Can I do this with the tank off and the carbs still on the bike or do I have to remove them? If they have to be removed, I will probably clean them and replace all the seals while I am at it...but would rather not if I can solve my problem without removing them. Any chance the seafoam will help unstick them?

If I have to remove them, should I sync them too? I do not have a mamometer (sp?)...can I take them off and take them to a shop for that?

Are there any common areas to look for vacuum leaks?

THANKS everyone for all the help and opinions!!
 

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Discussion Starter · #20 ·
litnin - Yeah I am doing basically every maintenance procedure and tune-up item listed in the Clymer manual...I gotten about 3/4 of the way through the non-tune up items.

Thanks for your description of how to check the slides. I will still have to do some reading because I don't even know what the slides look like.

I probably will go ahead and replace all vacuum hoses. I am also going to replace all the fuel lines. But before I do that, I am going to do the tune-up items including the air filter and ride the bike again to see if I still have the problem. Just for curiosity sake I want to know what exactly was causing the problem, and if I change out too many things without testing in between, I'll never know.

THANKS for all the help everybody...I really appreciate it...
 

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Discussion Starter · #22 ·
Re: your fast idle question

rjohnson1969 said:
Q1) Say, did you ever fix that fast idle problem? I have the same symptom, the bike idles really high (~3000) when it is hot.

BTW, good point about the air filter. I never thought of it being inside out. May I say, mine looks brand new from the carb side, and I never looked at the intake side!

Also, here's my trick for the spark plug removals(front left and rear right): My 18mm Cobalt deep dish had no retention provision at all, and I was totally paranoid about dropping it in the hole.
* loosen them, but don't remove
* poke the fuel line in there and cram it down onto the plug
* turn it out the rest of the way with the fuel line, remove carefully
* I threaded the new ones back in with the fuel line
* tightened with the wrench.
Yeah it is fixed. It was a combonation of the carb slides sticking and other gunk in the carb. The carbs are rebuilt, spark plugs changed, tank cleaned out, every fluid is replaced and it runs like a champ. After the rebuild, I had a problem where the bike would run too lean about 55mph or so. But at slow sppeds it was so smooth and quiet. I ended up messing with the air/fuel deal under the cap on the carb. Now it does not run lean at higher speeds, but it runs a little bit rich at slower speeds (not quite as smooth or quiet at idle as before I messed with it. I would say it runs as good as an 86 VT500 is ever going to run.
 

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Discussion Starter · #24 ·
No filter. Just the screen that is on the petcock. The fuel line is hard enough to wrestle on there without having to deal with a filter. I have a Can of Seafoam that I will run through the gas avery couple of months to keep it is clean as possible.
 
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