Author Topic: Just wont run, white smoke from exhaust?  (Read 3486 times)

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Offline dailydose1

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Just wont run, white smoke from exhaust?
« on: September 17, 2018, 12:43:48 AM »
Hi Everyone,

I have a 1978 xs500 engine. I have adjusted valves to the new specs. I have installed newtronics and used the technique of waiting for spark and seeing where it correlates to the timing. I have good spark on each side. Compression cold with throttle open is about 110 both sides.

Potential probelms:?
-I have new vm34 that I havent rejetted but i assume they could get the bike started with the stock jetting?
-my timing advancer is from a 73 tx500 (not sure if they changed from 73 to 78 and it would make a big difference?)
-I have white smoke coming out of the exhaust when I try to start it, not a ton but I can see it coming out of the exhaust which would make me think it should start?

Anyone have any thoughts?

Online guylr

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Re: Just wont run, white smoke from exhaust?
« Reply #1 on: September 17, 2018, 02:05:31 AM »
Your compression is very low and should be in the 140 -150 psi range. The white smoke is possibly oil mist blowing by the rings. You'll need to correct this first. Confirm the low compression by squirting some oil into each cylinder and retesting. If the compression jumps significantly then your rings are shot. If it doesn't  increase then double check cam timing.

For jetting I'd start with a 35 or 40 pilot jet. And a 130 to 150 main jet. That may be way off but it should start with those.

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline dailydose1

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Re: Just wont run, white smoke from exhaust?
« Reply #2 on: September 17, 2018, 01:03:37 PM »
I have those Jets on the way.
-Will retest compression tonight and do the oil test as well.
-Will also check cam timing if those are all off.

Thank you for your help, if nothing else I have learned a ton working on this bike so far!


Offline dailydose1

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Re: Just wont run, white smoke from exhaust?
« Reply #3 on: September 19, 2018, 12:27:54 PM »
So I rechecked compression and it was 115, about 118-120 with oil in the cylinder. Is that enough to signify the rings are bad?

I had checked the compression before I redid the valve gap so im assuming that is why it jumped up? Still cant get her to run though, the new jets should be here later this week and hoping they help

Online guylr

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Re: Just wont run, white smoke from exhaust?
« Reply #4 on: September 19, 2018, 02:33:52 PM »
The jets are not going to help. If you had the tools a leak down test would point conclusively to rings or valves as the cause of the low compression. Im thinking valves as the compression did not jump up a lot. Either way the top end needs to come off the engine to fix it. Sorry.

Guy
« Last Edit: September 19, 2018, 02:36:09 PM by guylr »
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline dailydose1

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Re: Just wont run, white smoke from exhaust?
« Reply #5 on: September 19, 2018, 03:59:06 PM »
I will take it apart I guess :(

If rings are shot would 0.25 rings over work without a rebore do you know?

Online guylr

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Re: Just wont run, white smoke from exhaust?
« Reply #6 on: September 19, 2018, 07:37:04 PM »
One you take it down have the cylinder bore and piston measured. If on its original bore, still in tolerence with regard to skirt clearance and undamaged then a light hone and new standard rings will work. If it is above standard bore size then spend the money and get it bored for the next oversize with new pistons.

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline dailydose1

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Re: Just wont run, white smoke from exhaust?
« Reply #7 on: September 20, 2018, 01:02:03 AM »
Some pics of the disassemble so far, will update progress and would appreciate help as needed :)

Offline dailydose1

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Re: Just wont run, white smoke from exhaust?
« Reply #8 on: September 20, 2018, 11:45:21 PM »
I have a small circular piece in the oil pump that seems like it is just there? Did it fall out of somewhere or is it just a magnet to collect metal in the oil?

Valves all cleaned, lapping tomorrow.


....caliper comes in tomorrow to measure pistons, etc

Online guylr

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Re: Just wont run, white smoke from exhaust?
« Reply #9 on: September 21, 2018, 02:55:57 AM »
The magnet goes in the sump. A digital caliper is not accurate enough to measure your pistons and cylinder bore. Take your parts to a competent shop that has proper micrometers and bore measuring tools.  It has to be done precisely or your results will not be what you want.

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline dailydose1

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Re: Just wont run, white smoke from exhaust?
« Reply #10 on: September 21, 2018, 03:52:53 PM »
Ill try and get that done today then, the xs500e and the tx500 and earlier xs500 pistons and rings are different than the xs500e right? not seeing much on ebay if im out of spec :(

Offline dailydose1

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Re: Just wont run, white smoke from exhaust?
« Reply #11 on: September 21, 2018, 03:57:52 PM »
Also are the specs for the 500e the same as the tx500 in terms of cleareances?

Online guylr

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Re: Just wont run, white smoke from exhaust?
« Reply #12 on: September 22, 2018, 12:41:56 PM »
I think the rings are interchangable but the E model pistons are higher compression. They will fit the earlier engines just fine if you use a pair of them. Clearance specs are the same.



Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline dailydose1

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Re: Just wont run, white smoke from exhaust?
« Reply #13 on: September 24, 2018, 07:35:52 PM »
So I got it measured, 0.054mm piston to bore clearance....looks to be right on the edge. So my options are this:

-wait for who knows when to find oversized pistons
-get tx500 pistons and rebore (but it wouldn't be the higher compression pistons)
-get new rings and reuse the old pistons

Any thoughts on what would be best?

*Also, does anyone know if the 1978 xs500e advancer is the same as the 73 tx500?*

thank you!

Offline dailydose1

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Re: Just wont run, white smoke from exhaust?
« Reply #14 on: September 24, 2018, 11:23:42 PM »
Some pictures for your viewing pleasure, but please see questions above :)