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(SFOC) Built Not Bought
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Discussion Starter · #1 ·
hello bike friends,

i call on your help before i torch this bike in a blind rage...

i bought a shed of a gpz500s 1992 to get to work on while i finish the blade project,

i picked it up 500 quid running a little rough, bogging down and not going over 5 grand,

i thought easy fix maybe sparks, coils ...... Oh was i wrong,

so far i have:

1, changes sparks
2, changed coils
3, changes carbs due to the original carbs being cracked,
4, changed fuel filter

and it still persist on misfiring, spluttering the cutting out, its smoking on one cylinder and i cant for the life of me figure out what next apart from a petrol can and matches,

so with the knowledge of you great bike builders out there can you please give me some pointers

:thumbsup:
 

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UnicycleMode
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7,584 Posts
Have you checked the compression with a gauge to see if you have a valve or piston ring not seating proper? I would imagine a washed out cylinder (fuel clears the oil film off the cylinder wall and it wears the bore oval and thus causes a low compression issue) could cause some problems, but it would at least rev. Sounds as though it might have a leaking intake boot between the carb and engine too, a vacuum leak would cause major problems with tuning and the ability for the bike to rev.



I would hold off on having a go at roasting the bike for a moment. Might be something simple. :D
 

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Yea rough running and not reving vacuum leak
 

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(SFOC) Built Not Bought
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566 Posts
Discussion Starter · #4 ·
Ok cool I will try stay away from a kwak BBQ for now then lmao

Ok regarding the leaky boot that's not to hard to look at and figure out didn't think of that so thanks lads will check later today and see if that's the case,

Regarding checking the compression... This is new to me and would normally avoid tech stuff but where would I get the tool and then what would I be looking and when checking?

And much respect for your advice high 5 to all and a massive :shocker::shocker:
 

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UnicycleMode
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7,584 Posts
A compression check involves a compression testing kit, you just remove a spark plug from the cylinder you are intending to check and stick the tube from the gauge down into it and hand tighten the brass fitting on the end into the spark plug hole and give the engine a spin, it should peak after a few revolutions and that would be the reading in PSI on the gauge. Most service manuals list the compression stats and what is still within' service life. As long as both cylinders are within' 15-20psi of each other there shouldn't be any issue.



 

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(SFOC) Built Not Bought
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566 Posts
Discussion Starter · #6 ·
ok thanks ratfighter :thumbsup:

I just took the carbs back off and checked the rubbers from the carbs to the cylinder head and from the air box to the carbs and they look in ok nick no cuts or tears and double checked the carbs for any cracks and checked the seals yesterday and they are ok ....

so I guess its a fleabay job for a compression tool .... shit...

oh lord, when I job turns from simple to a nightmare,

thanks for your help will keep you updates and if there are any other suggestions I can look at while I wait for the kit please try me

:knucks::knucks:
 

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If you can get your thumb over the spark plug hole, the ******* method is to crank the engine with your thumb over the hole. If you've got good compression, you won't be able to "hold" the pressure, it'll push your thumb off. If you can seal the hole with it cranking, it's low.

Did you really go through the new set of carbs, blow out all the passages, check all the little holes in the nozzles and jets? Sounds like classic crapped up carbs to me.

Brownish, whiffy smoke that dissipates fairly quickly is from one cylinder running super rich. White smoke that hangs around a while is burnt oil, either from worn out rings or a shot valve seal. If it smokes more when you chop the throttle shut it's probably valves, if the smoke gets thinner as it warms up it's probably rings.
 

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(SFOC) Built Not Bought
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566 Posts
Discussion Starter · #10 ·
ya for the money I paid for it, it shows promise and plus we are not all flush on the cash and have to make do with what we can afford so ya FU!!!!! if your not going to help fuck off my page

and to be fair fieldarcher I am self taught and I learn a lot off bikes like this so kindly keep your oppinions to your self if you aint going to help and plus at least I can say I try!!!

hopefully you get the hint
 

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(SFOC) Built Not Bought
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566 Posts
Discussion Starter · #11 ·
back to the bike...........

ok I have stripped the new carbs down and gave them a good cleaning and sync'ed them and it sparked into life for a little then died again lmao

then I noticed in the cylinder head where the spark sits its puffing out at the side of the spark plug :glassesf:

I cant seem to see what the exact issue is.... I gather that the cylinder must be cracked or something like that would I be correct??

and anyone else had this issue?

cheers for your help lads
 

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UnicycleMode
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Well shit, sounds like a crack in there, can you get a light in there and see for sure if it has a hair line fracture in it? If so you can easily drop a new head on the engine for pretty cheap. I would imagine it would be worth it as well. Not sure if it would be worth sorting it by pulling the head, having it welded, and then putting the same old head back on it. Might be best off just replacing it completely.


Could inspect the cylinder walls at the same time the head is off, might just have a 250cc boat anchor depending on how bad it is. Sounds as though that poor thing got overheated to the brink of function and finally gave up.
 

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(SFOC) Built Not Bought
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Discussion Starter · #13 ·
YET AGAIN RATFIGHTER THANKYOU!!!!

nice one I was thinking the same its had a really hard life this one lmao rep for you matey as your always coming back to answer my queries,

will be looking on the net now to source another head see if it wants to come back to life watch this space lmao....

rep for everyone for your help on the thread

cheers lads ride safe
 
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