Good compression, but really bad leak-down test?

[VmaxKen]

Don't feel bad. Not your fault. It's the changing of the times. use to be almost every 'self respecting' high school had 'Auto Shop' classes. My high school's class was considered to be one of the best in all of San Francisco. But 'something happened on the way from that place'. I own and operate the oldest 'Motorcycle Tire, and Modification Center' in California - (if not ((THE)) entire country. In the last few years we have been having problems hiring 'mechanics',
I refuse to use the modern term 'techs'. (I'm old school, and funny that way). I went to my old high school to see if any one there would like to work as a 'mechanic'. I didn't even have to go inside. Driving by, (through the windows)
, I saw all our old automotive equipment, workbenches and 'lifts' had been replaced by desks, with computers on them.

I guess it made sense, as "the times,they are - a- changin", (a 1964 Bob Dylan song) Sure I get that - but we can not find anyone, (man or woman), willing to even get their hands dirty - Let alone knowing the basics of 'internal combustion' engines.

So, no - there is no such thing as a 'stupid question'. And you are not stupid, ignorant, or 'dumb'. We are only products of our our own 'life experiences'.

I do not know what a 'future' world will be like, with millions of 'computer techs', but very few ACTUAL mechanics.

I guess (for some) chang is not always a good thing?

 

[VmaxKen]

Don't feel bad. Not your fault. It's the changing of the times. use to be almost every 'self respecting' high school had 'Auto Shop' classes. My high school's class was considered to be one of the best in all of San Francisco. But 'something happened on the way from that place'. I own and operate the oldest 'Motorcycle Tire, and Modification Center' in California - (if not ((THE)) entire country. In the last few years we have been having problems hiring 'mechanics',
I refuse to use the modern term 'techs'. (I'm old school, and funny that way). I went to my old high school to see if any one there would like to work as a 'mechanic'. I didn't even have to go inside. Driving by, (through the windows)
, I saw all our old automotive equipment, workbenches and 'lifts' had been replaced by desks, with computers on them.

I guess it made sense, as "the times,they are - a- changin", (a 1964 Bob Dylan song) Sure I get that - but we can not find anyone, (man or woman), willing to even get their hands dirty - Let alone knowing the basics of 'internal combustion' engines.

So, no - there is no such thing as a 'stupid question'. And you are not stupid, ignorant, or 'dumb'. We are only products of our our own 'life experiences'.

I do not know what a 'future' world will be like, with millions of 'computer techs', but very few ACTUAL mechanics.

I guess (for some) chang is not always a good thing?

 

[Scrallar]

Now I had time to look a little more at the motorcycle, and it is a happy update.

if sdt354 had not mentioned that i had to do leak-down test in compression stroke (which I have overlooked since this is the first time i try to do leak-down test), then i would probably have ended up separating the engine again to find out of which no fault was

But now I have made a correct leak-down test, and the result is perfect, and about the same on all cylinders.
I had a little trouble getting my equipment 100% sealed around the spark plug hole, but since the result is fine, I didn't bother to do more about it


I also checked timing, and the mark on the flywheel is set correctly, the piston in TDC and the two small marks on the camshaft are correct.
If I rotate the crankshaft 360 degrees and 70 degrees, then the 2 big marks on the camshaft are correctly positioned on cylinder 2-4.


Here I try to start it cold. First I try with ckoker on, then off, and then on when it starts. If the engine is warm then it is not so difficult to start. and if it is warm and has just been turned off, it will start immediately.


Here is a little idle sound. is it normal sound? or should it be a little more smooth? (Don't mind the coolant. The drain plug have a little leakage that I didn't want to look at yet if I anyway had to have engine out again.)


And here are 2 videos where it backfire/spitting through the carburetor. It is worst when it is cold as in the videos here. But it also does a little bit when it's warm and when I drive, but only at low rpm.
And it also does it with air filter assembled, it is only taken off in order to better see it.


https://www.youtube.com/watch?v=rG-y_uJkJjQ&feature=youtu.be

About carbs, then there is some pictures her.
Main jet - I didn't get picture of it, but I have bought brand new mikuni #150 and fitted
Pilot jet - #37,5
Main bleed pipe - 9A
Pilot air jet no.1 - #100
Pilot air jet no.2 - #170 is stamped on it, but when I measure the hole it is 1,85mm
Float level is set correctly.

 

[Fire-medic]

It's still giving you fits? 'Popping' is usually a lean condition. What about the rubber o-rings on the air bleed jets, under the CV diaphragm caps? Are they in good shape?

 

[jedi-]

Are those diaphragm ok ? One looks busted?

 

[Scrallar]

It's still giving you fits? 'Popping' is usually a lean condition. What about the rubber o-rings on the air bleed jets, under the CV diaphragm caps? Are they in good shape?

Do you mean these o-rings in the yellow circle? They are "unfortunately" in good condition

Are those diaphragm ok ? One looks busted?

There are no holes in them and they look fine. But here in Denmark where there are only 32-40℉ at the moment, they are a bit stiff.
Three of them are slightly thicker/stiffer rubber and the fourth is slightly thinner/softer rubber. So I think one has been replaced at some point.
But as soon as they get a little warm, the rubber is soft. but I don't think that's what makes it spitting through the carburetor as they haven't started opening at 1500rpm where it spitting the most.

 

[Scrallar]

What I can find by searching here on the forum, the bike is born with PAJ1 - #90, and PAJ2 - #170

If I measure the hole in my PAJ2, then it is about 1.85mm even though there is stamped 170 on the jet. Does anyone
Are there any who knows if the hole should be 1.70mm when 170 is stamped on the jet?

Maybe I should try to buy new Paj1, and PAJ2 so I'm sure it's the right size.

Are there anyone who knows the item number, or can give me a website for PAJ1, and PAJ2. I probably have to find them in Europe as it will be too expensive to send them from the United States

 

[Fire-medic]

https://www.ronayers.com/oemparts/a/yam/500456a5f8700209bc79313a/carburetor

 

[jedi-]

Sorry, I re-read my post, I meant diaphragm COVERS

 

[Scrallar]

https://www.ronayers.com/oemparts/a/yam/500456a5f8700209bc79313a/carburetor

Thanks.


I found out they are called N102.221. So I will try to order PAJ1 - 90, and PAJ2 170 so I'm sure it's the right one.

I tried to replace PAJ2 with Mikuni 150, but that didn't help. It still spitting through the carburetor and it hesitated in the middle range.

Sorry, I re-read my post, I meant diaphragm COVERS

The covers are in perfect condition. I think it's the light/shade that makes them look weird

 

[speedcostsmoney]

maybe the idle circuit is clogged up try to do the SHOT GUN http://vmax.lvlhead.com/tips/shotgun.htm

 

[VmaxKen]

When I do leak-down, I can clearly feel/hear the air in the intake and exhaust. So my guess is the air passing the valves...
But they should be properly-seated/sealed after the workshop has rebuild them. But maybe they have done a bad job. I just don't understand why there is such good compression then..

Valve clearances was set to
Exhaust 0,29-0,30mm
Intake 0,14-0,15mm

The air screw was set 2,5turns out, and the rubber o-ring looks in good shape.
I did the carbs myself, and they actually looked fine when I separated them (no dirt in them). Jets were not clogged, and the float was set to the right height.
The diaphragms on the sulides has no damage or holes, one has softer rubber than the other three, oo I think one of them has been changed at some point, but it should not mean anything for rough idle..

Next week I will try
Check valve clearance.
Check the chain/timing
Check that the camshaft dont push on the valves when the piston is in TDC.