'86 250 YPVS Restore

[JonW]

Ask Arrow for his comments on this...

[BRG1200]

Always happy to learn something, hope I haven't caused offence, will look up the previous threads...

[hybrid]

Yes I would have thought it would seep oil if it's letting air in.
Would like to hear arrows comments on where the air is getting in and what type of line it was.

[arrow]

Hi happyrd, welcome to the forum. The issue is caused by the clear pipes. They are not made from the same material as the original pipe which is still available from Yamaha. Running at the back of the cylinders the pipes get pretty hot in use and very soft! As they are under constant vacuum when the engine is running the diameter goes slightly smaller. When they cool down and go back to original size, this shows up by the air space at the carb end. This is bad news for the engine. If the bike were used every day that's nearly six inches of air a month that the engine is getting on start up’s, before oil. Fit the correct spec. black lines and make up a temporary 25mm length of clear on the carb end as a test, and there will be no air observed. Rest assured in this condition the oil pump check valves are working correctly, if not then they would hide the issue. There is no 0 ring in your pump, but two seals.
This is a c&p from my own post on another forum. Unedited, but should still make sense

[JonW]

Thanks Gary!

[arrow]

No worries Jon, the wifi is playing up in here so did not edit the post correctly will look in again tomorrow.

[JonW]

no worries, have a jar for me and the answer to the next quiz question is '42'

[Gavin]

Yay, blue smoke! Quite an achievement considering the condition the old girl was in. Thanks to everyone who chipped in. Had quite a grin when it fired up. Now it starts first kick every time. Amazed.
When I cleaned the carbs waaaay back, I didn't blow out the jets. This time I bought a carb kit off ebay and replaced all the fiddly bits. I also checked the weak servo by pulling it apart. Seems to move fine as did the cables. Will keep an eye on that.
Finally the carb kit had needles that were about 4mm longer than the ones being replaced. Is that an issue or does the barrel just seat earlier?
Now looking for a bodywork mob who weld plastic, prep and spray. Any recommendations? PM me if it's not PC to mention businesses over the air. Will take negative and positive reviews if it's not hearsay.
Ta




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[Gavin]

The show goes on.... So I've dropped the plastics off to get the full treatment. Should have them back in a few months all nice and gleaming. In the meantime back to the engine. It kicks over first or second boot but I've just noticed it's guzzling fuel and the LHS exhaust blows white-ish smoke as the throttle is backed off after revving it. The RHS doesn't do it. I also noticed that there's a slight spluttering from the smokey pipe. It's like it's missing once every say 5 seconds. Not sure if this is related. I've played around with the carbs / air screw but it just messes up the idle speed. I'm expecting user error and not a fault as such, but any hints might speed things up.
I also found the oil leak on the face of the oil pump. It was the remains of a cardboard gasket that I had sprayed over. Now cleaned off and new gasket seals well. The oil is pumping through well as indicated by me holding the wheel open full while it was idling.
I checked the alignment of the pin to the indicators on the wheel and it was about 5deg off. The adjustment at the bottom of the cable was at it's limit so it may either be at the top adjuster or it needs a new cable.
On a slightly separate topic, I'm now about to offload a 31k (85) tank. I don't want to make anything on it and would be happy to let it go to forum members but I just want my money back. If I can't get it, I'll drop it on Ebay. Will post pics later.

[JonW]

Hmm... interesting. White smoke is usually water (steam), oil is blue/black. the fact its missing/spluttering could also be key to that being the issue. Does the header tank bubble and is the water level dropping? defo need to blank off that pipe, if not its sucking air i would think, that would also cause a different amount of smoke, but maybe not white... Maybe try retorquing the head bolts before you run it again? Did you pressure test the motor before running it (I thought you did?) if so maybe its not the head gasket or such, hmm...

[Gavin]

Thanks for the info Jon, I took the exhausts off and tried to de-coke them on the weekend. Tried the caustic soda and heat gun. Neighbours weren't impressed. Once they go back on I'll fire it up again and see if it made any difference. I didn't pressure test, didn't have the sealing kit and pump. I think there's too much oil being pumped in from looking at the plugs and exhaust ports. I'll try and adjust the pump again.
I also need to remove the carbs and check which size jets and needle I put in. I 'should' have Main=155 and pilot=25, is this correct for the 250?

[JonW]

hmm... have you checked the parts book for your bike, 25 sounds big for a 250 and 155 sounds small. I would think 22.5 and 165, but I dont have any basis for that other than its at the back of my mind. the parts books (on rd350lc.net i think) should list the sizes...

you really should pressure test these motors... remember blue smoke is usually oil, white is usually water...

[Gavin]

Checked quite a few sources and seems to be correct. Remember this is a 250. E tube=345 P-2. Main=155, Pilot=25, but the needle is the big question. I removed a 4N10 and replaced it with a bigger 5N12 which seemed wrong but came with the kit I ordered. I might try and straighten the old ones and put them back in. Pick to follow.


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[Gavin]

Old vs new. Not sure what effect this would have on flow from the tube. Is it the taper or length that matters? No smutty answers please, let's keep this rather British. Good show.


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[James W.]

"Straighten the old ones"?

Good luck with that, how the hell do you bend them in the 1st place?

Have a good close look at 'em, if they are worn, or "bent" just replace them..
..chances of getting a decent tune with dodgy needles.. not much.. IMO..

Check the length of your 5's , as they seat, you wouldn't want then to bottom out on the mainjet..