VT700 1986 possible carb failure, rattling sound - Honda Shadow Forums : Shadow Motorcycle Forum
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post #1 of 39 (permalink) Old 11-24-2018, 08:32 PM Thread Starter
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Question VT700 1986 possible carb failure, rattling sound

Hello,

First of all, please excuse my grammar/language... I am from Argentina and my english is little rusty.

I am having this problem since 2 years now and I am almost not riding any more .

I will try to give some background about my bike, the problem detail is down in BOLD

I bought her 10 years ago... first bike and with her I learn to drive (yes its a big bike for first timer, I got my first inguinal hernia (really) when I try to turn the corner like a if it were a bycicle), so... the problem began after taking the engine out for pistons/rings service because it used to consume some oil, about 1 litre oil per 400km, anyway it didnt smoke black out the exausts.

(if I knew all the problems that came after I take it to the service... I would never opened the engine!!! for that f#cking 1 litre oil consumtion, I am regreting this everyday)

So, after taking out the engine, replacing piston rings and some other service the mechanic recommend like hidraulic tappets and cleaning every thing I could in the process like water tubes, etc... we put the engine back.

The carburator had got some problems while the bike was stopped (about a year searching parts), I bought the carburator rebuild kit from a reseller in UK... and change everything I could.

HERE THE PROBLEM

I went for a ride hoping no more oil consumtion but problems began, between 3000/4000 rpm the engine rattled if you accelerate fast... and it sound like "cla-cla-cla- cla" very quickly every time in that rpms, like something skipping. After that the engine accelerates like a beast, no problem at all. If I accelerate slowly, did not feel any problem at all.

The mechanic test it and told me that the new piston rings might need some time to settle... ok, I am no mechanic... so I went for about 1000km ride, trying not to accelerate hard to prevent the rattling, just to becareful with her.

Came back a week later, the problem still continues... the mechanic started to doubt, that it might be something in the carburator. There I bout the carburator rebuild kit and two brand new floats and rubber vacums (not the whole piston vacum, just the rubber diaphragm).

Nothing changed, only the mechanic because mine had no more time and he is specialized with motocross bikes not custom like VT700. So the ratting continued, some time passed with no clue, but problem kind of change... now it is between 2000/4000rpm and sometimes even stopped and idle you hear one random rattle.

After that and a new mechanic specialized in old bikes suggested that it might be in the cross-shaft, that the spring damper (23732-MK7-670) with age it lost hardness.

So now I am completely lost:

The good:

1) I learnt a lot about bikes, carburators, engines
2) I learnt to NOT open your old bike engine unless it is completely necesary... even if it consumes about 3 litres each 400km... take bottles of engine oil in your sidebags

The bad:

1) there is no new spring damper to buy from a reseller (or cant find one)
2) the bike runs like s#it
3) I am starting not to trust mechanics
4) almost 2 years I cant enjoy riding my bike.

Hope anyone can give me some help, recommendations...

Thank you very much!

PS: attached some pictures of my baby now and when the engine at service.


PS2: two links to videos with engine runing from start cold and second when hot... anyway, the rattling did not happen on these video, might be useless but hope it can help some trained ear :-p
(fuel light is on, because I have the tail light disconnected)

First:

Second:


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...dog head out of the car window, me on bike...

Last edited by sebadamus; 11-25-2018 at 10:14 AM. Reason: fixing grammar
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post #2 of 39 (permalink) Old 11-24-2018, 08:52 PM
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Originally Posted by sebadamus View Post
Hope anyone can give me some help, recommendations...
With very little to go on, it almost sounds like pre-ignition or spark knock. Did the mechanic check the spark units or pulse generator.

Where specifically from the engine is the sound coming from. Maybe it's not the engine at all?
Good luck,
Phil



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post #3 of 39 (permalink) Old 11-24-2018, 09:08 PM
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Welcome, I was leaning towards the thought of pre-ignition also. Maybe the mechanic upped your compression for more power but it left you with a pre-ignition problem. I think Phil headed you in a good direction.

Last edited by kesanders; 11-24-2018 at 09:11 PM.
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post #4 of 39 (permalink) Old 11-24-2018, 09:49 PM Thread Starter
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Hi Phil,

I looked the service manual for the parts you told (sorry I am more nerd than mechanic) and I am sure none of the mechanic checked that.

The spark unit (its only one piece on my bike, right? on the left side cover)

And pulse generator/s are inside left engine cover, right? so no way to test from outside?

Can I test them easily?

Thanks!!!

PS: the sound comes from the engine, cylinders I think... but its not easy to explain or make a video while driving (will try to record something tomorrow) also, I have no mufflers so its hard to hear, its more you feel and hear it...
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...dog head out of the car window, me on bike...

Last edited by sebadamus; 11-24-2018 at 10:55 PM. Reason: adding
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post #5 of 39 (permalink) Old 11-24-2018, 09:53 PM Thread Starter
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Thanks Kesanders, will try to look more about the things you both recommend! but I will really want to kill the mechanics if the did not thought about that, I mean you just read what I wrote in my jungle-tarzan-english and you already point me somewhere logic.

...dog head out of the car window, me on bike...
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post #6 of 39 (permalink) Old 11-25-2018, 01:15 AM
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Can you try some premium fuel to rule out the detonation sound? Just as a test.

I doubt it is from the damper spring because if it doesn't do it when accelerating hard at other times it probably is not that.



Can you run it while stopped and accelerate the engine hard from a idle and hear any of the sound and listen to an area that is loudest? A long screwdriver handle up to your ear or a piece of hose or stethoscope can pin point the area.


Does it make more noise hot or cold?


The pulse generators are on the right side . You can find a connector and test resistance. About 450 ohms average. But if both cylinders are firing all the time I doubt they are any problem.

Only a biker knows why a dog sticks his head out of a car window.
1983 750 Shadow
From the past=
1951 Cushman scooter
1962 Honda 305 Dream
1965 Honda 305 Dream
1971 Honda 175 scrambler
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post #7 of 39 (permalink) Old 11-25-2018, 08:56 AM Thread Starter
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Quote:
Originally Posted by swifty2014 View Post
Can you try some premium fuel to rule out the detonation sound? Just as a test.
It is premium fuel.

Quote:
Originally Posted by swifty2014 View Post
Can you run it while stopped and accelerate the engine hard from a idle and hear any of the sound and listen to an area that is loudest? A long screwdriver handle up to your ear or a piece of hose or stethoscope can pin point the area.
Thats a good one , my father used to place a screwdriver to let me hear the engine with my ear.

One thing I might forget to mention, is that the problem really shows when you are between 2000 and 4000rpm aproximatelly AND running, I mean... when I ride it. If it is stopped and idle and you accelerate hard... you dont hear it (update: it happens but very very rarely), so the engine needs to be doing some force to notice the rattling.

One more thing, yesterday I started to notice the failure even stopped and idle, from time to time just one "rattle" (going to try to record a little video)

Quote:
Originally Posted by swifty2014 View Post
Does it make more noise hot or cold?

The pulse generators are on the right side . You can find a connector and test resistance. About 450 ohms average. But if both cylinders are firing all the time I doubt they are any problem.
Hot or cold... the same, I mean if I just start the engine and go for a ride with engine almost cold, you noticed the same.

Thanks! going to test that, I think there is a test procedure in the service manual.

...dog head out of the car window, me on bike...

Last edited by sebadamus; 11-25-2018 at 09:18 AM.
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post #8 of 39 (permalink) Old 11-25-2018, 09:15 AM Thread Starter
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Phil,

To add some more info, my last mechanic suggested it was the "damper spring"... he took out the rear wheel and looked the cross-shaft and he told me there was a shiner zone like if it has been polished because of the failure (I attached a diagram picture where he told me)

He did not take the spring out because he had to get or make an special tool (that would be next thing, but I stopped here first to ask forum first)

He told me that adding some washers would make the spring harder (if I cant find a new spring), just to be sure... what would be the synthom if this spring start to fail?


Thanks,

PS: This was last week, so yesterday I started the engine some minutes and noticed something new, maybe it has something to do with the cross-shaft the mechanic opened and closed... but the rattling sound I mention now happens randomly at idle speed (not riding, i.e. in 5 minutes 1 time), will try to get it on video.
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post #9 of 39 (permalink) Old 11-25-2018, 01:57 PM
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the rattling sound I mention now happens randomly at idle speed (not riding, i.e. in 5 minutes 1 time), will try to get it on video.

A video with sound would help a lot. So at least you know it's probably coming from the engine if it happens when your not even riding.....
Phil


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post #10 of 39 (permalink) Old 11-25-2018, 09:47 PM
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I am still not to keen on the damper idea. If it is weak it would clack-clack-clack anytime you take of in 1st gear under load, and then in 2nd, and in 3rd, etc, any time there is a lot of torque against the damper assembly. But to know where the sound is loudest will tell you which area to diagnose.
The first video sounded like a random noise in the front cylinder area.

When the engine was apart for head gaskets was any other work done to the clutch or something?


My guess on the shiny spot is that is where the small end of the spring rides and when the drive ratchets under load and release, the spring can rotate on that shaft section .

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Only a biker knows why a dog sticks his head out of a car window.
1983 750 Shadow
From the past=
1951 Cushman scooter
1962 Honda 305 Dream
1965 Honda 305 Dream
1971 Honda 175 scrambler
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