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Suzuki 800 Intruder Club & Forum

A UK Site Dedicated To The Suzuki C800, VL800, VX800, M800, VZ800, VS800, C50, M50 Model Intruder / Boulevard / Marauder
 
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 VZ800 Compression question

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Bluellew
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PostSubject: VZ800 Compression question   Thu Feb 01, 2018 6:47 am

Hi Guys, i have a peculiar situation and need some advice. I got my bike about 2 thousand km ago and when i changed plugs and oil a while ago i noticed that the front cylinder was burning a bit rich. Or so i thought. Just for reference, i decided to do a compression test on both cylinders and to my horror discovered that the rear was 120psi and the front 60psi!!! That is so far out of spec that i nearly had a seizure.

But here's the thing. The bike doesn't smoke. It seems to run quite well. There's a bit of high pitched rattle which sounds like a cam chain may be a bit old, but nothing really bad. I can still get 140kmph out of her without sweat and she starts first time every time. So i suspected the compression tester. But i use the compression tester on other motors (cars) and there never seems to be any sort of variance. When one has been around for a while, you tend to have a feeling about whether your tools are dodgy or not. I checked the valve clearances immediately when i discovered the low compression and they were fine.

The one thing that did get to me, was that i changed to Iridium plugs shortly after the discovery and within a very short time, the front stopped firing. I put in a fresh one and she's been running fine since. The plug that failed was black, so there's obviously some oil burning there, but why no smoke ? Oil level isn't dropping. Do plugs fail due to burning oil?

The bike supposedly has 30 odd thousand on the clock, so how in God's name can a 2003 motor wear to such a silly point and in such an unequal measure at such low km's?

I feel like i may be missing something here and perhaps someone with real knowledge can offer a pointer or two.

I'd like to take a ride to Namibia from Cape Town in April or May and obviously work will have to be done before i attempt a ride into the desert.
Is it possible to just put in some new rings ? or do i really have to pull the entire F@#%$& motor apart and do big ends and pistons and and and ? Money money money.
Is it possible to pull the barrels off without taking the motor out of the cradle or am i just dreaming ?

I rode CX500's all my life and know them backwards, but this straight v twin is still a new thing to me. I love it. I love this bike and need or want no other. 
So any ideas folks ?
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v-twin
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PostSubject: Re: VZ800 Compression question   Thu Feb 01, 2018 7:22 am

When you did the compression test, I presume you had the throttle wound fully open??
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Bluellew
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PostSubject: Re: VZ800 Compression question   Fri Feb 02, 2018 10:46 am

Thanks very much for the response. I did not have the throttle open at all. Will you be so kind as to tell me how this affects the testing. As smart as i might think i am, i am not aware of this aspect.
 Have i been doing compression readings the wrong way for all these years ? How embarrassing.
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simbo
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PostSubject: Re: VZ800 Compression question   Fri Feb 02, 2018 12:38 pm

 
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v-twin
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PostSubject: Re: VZ800 Compression question   Fri Feb 02, 2018 5:30 pm

When the throttle is wide open as you turn over the engine it will suck air in which will give you an accurate compression reading as its the pressure of the compressed air that you are taking a reading off, if you do not have the throttle open the vacuum from the downward stroke may not be able to pull enough air through the carbs to enable a accurate reading.

This is from the Suzuki Workshop manual for you bike:

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simbo
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PostSubject: Re: VZ800 Compression question   Fri Feb 02, 2018 6:42 pm

Learn sommat new everyday 
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Bluellew
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PostSubject: Re: VZ800 Compression question   Tue Feb 06, 2018 9:42 am

Thanks very much for that. Pardon the delayed response, i seem to get to my pc every few days.
I will re-do those tests in a little while and perhaps and hopefully the results will be better.
I'll post the results anyway.
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Bluellew
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PostSubject: Re: VZ800 Compression question   Sat Feb 17, 2018 9:20 am

Thanks for all the help. Especially to "V-Twin"
I did another compression test today ( throttle wide open ) and the cylinders both read 180psi.
Jump for joy.
The front plug burns a bit black and i am hoping that by turning the mix screw to one and a half, as opposed to two and a quarter, they might burn evenly.
I'd like to post a picture of the pair of plugs for comment, but in the process of trying to upload the image, i lost everything and had to start my missive again. 
Is there a simple way ?

Anyway thanks to everyone who keeps this forum going.
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Bluellew
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PostSubject: Re: VZ800 Compression question   Sat Feb 17, 2018 9:28 am

Here's me trying to upload a picture of my two plugs.





And heaven knows, i seem to have succeeded.
Any comments on mixtures or balancing. Please.

The black plug came out of the front cylinder, which was what made me worry about compression in the first place.
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v-twin
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PostSubject: Re: VZ800 Compression question   Sat Feb 17, 2018 9:05 pm

Balance the carbs before changing any mixtures, for reference I think the rear main jet is slightly bigger than the front on these bikes, just in case someone has been playing Wink
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