leak down test and stumped

[eness76]

I did the leak down test, thanks Awk, and the engine seems really tight. It maybe lost .25lb over a minute +. I'm up to a 350 main jet, and the engine seems lean after it warms up, especially. It seems to rip and carburate great, then it gets a bit of a stumble in the middle when it gets hot. I raised the needle and that seemed to work at first, till it got hot again and it started that again. I've attached the chop, let me know what you guys think. Maybe it's still a bit lean on the main. The smoke ring is almost invisible on the other side.

Heres another weird one, when I redid this bike I am used transparent blue tubing. I've noticed at times it is getting lots of bubbles in the feed line to the carb. That doesn't seem right to me, and maybe it's a coincidence, but it seems to do that when it's not running right. I checked the petcock, it flows perfectly (new petcock and I flushed tank when I rebuilt the bike), I checked the tank cap, took apart the epa cap and it's perfectly clear. I'm stumped. Could it be I'm just still lean?

I'm using a right side bend pipe and silencer, stock bore - wiseco piston, no toil filter with no lid, boyesen power reeds, I ported and polished the exhaust port and raised it 1mm per Ken's youtube vid, I'm currently on a 350main jet and I'm 1 clip position below center, stock pilot and 1.25 turns out on the air screw.

Any suggestions would be great. Thanks guys.

 

[Awk08]

elevation and temps ?
I've run a 330 main at 1800'+ elevation in summer temps w/ a right bend, you may require richer for lower elevations/temps

float height correct @ 20 - 21.5mm ?
you're positive the one way valve in the stock cap is working and the vent tube is allowing air into the tank to prevent vapor lock ?
to check....try cracking the cap loose when it starts acting up

if you completely disassembled the carb for a proper cleaning ?
did you remove the needle jet under the main jet by pushing it up into the carb body, and cleaning the small holes in it ?
part # 11 in this bikebandit link, they're calling it the "main nozzle"..........
http://www.bikebandit.com/oem-parts/2001-yamaha-blaster-200-yfs200n-carburetor/o/m145851sch104690

 

[Awk08]

Dublin Oh. ......Elevations range from 780 feet (238 m) above sea level where the Scioto River leaves the city at Hayden Run Road, while the high point is 1000 feet.

if it's airtight, and plug chops say it wants more fuel..... FEED IT !

 

[eness76]

yes sir, I did push the nozzle out and clean it up when I tore down the carb for the rebuild. The float height looked right on as well, I put a new seat and needle in also. It's apart right now, I can go back and check that.

On the cap, during my ride yesterday I disassembled the cap and took the check balls and the two plates totally out and it still did it. Today while working on the bike I reassembled it and checked it and it flows just fine, regardless of attitude. Even upside down you can still pull air thru it.

I'm at about 800' of elevation and yesterday it was in the upper 70s. I'll go back and check the float height. What is your read on the plug picture? I have a 360 also, I could pop that in there and give it a try next time.

Do you feel there is an acceptable loss rate on the leak test? I've read where some say there should be zero loss, and that vid that mentions no more than 1lb per minute.

 

[tbrooks]

I'm not sure its an acceptable leak. If it drops more than 1 psi in 5 minutes, I'd say it needs to be addressed. On your plug chop its hard to tell, the ring is barely visible, might need to run it a little harder next time

 

[eness76]

That was wfo 1-5. Ran out of room for 6.

 

[Awk08]

What is your read on the plug picture? I have a 360 also, I could pop that in there and give it a try next time.

Do you feel there is an acceptable loss rate on the leak test? I've read where some say there should be zero loss, and that vid that mentions no more than 1lb per minute.

plug looks a little light for my liking, try the 360 and feed that beast

you say it lost .25 over a minute, what did it hold for 5 minutes ?
not that the engine pressurizes or pulls vacuum for 5 minutes straight while running....it does not.

zero pressure loss is ideal, I have one that leaked off from 7 to 5psi over 5 minutes and held that 5psi for 20 minutes.
I still run it like that to this day.
the 7 psi max. is recommended to not blow out the seals, no where is it written in stone it must hold that 7 for any amount of time, if it holds 5 for 5 minutes, thats good enuf for me, has proven to last, and my jetting is right on par with other bikes running similar mods, so that loss of 2 lbs. meant diddly squat.

 

[Awk08]

That was wfo 1-5. Ran out of room for 6.

it's not how far you run or what gear, it's how long you hold it wide open,
at least 20-30 seconds for best coloring of the plug.
use the brakes if you have to, and hold it wide open for as long as you can

 

[eness76]

Awk you must have read my mind, after tbrooks post I hooked it back up and times it for 5 mins and just finished and saw you posted. I charged it to 6psi and after 5 mins is bled off a little less than .8lb. I'm going to put the 360 in as you suggested and leave the clip where it is and see what she does. I just wonder about those bubbles. I've never used transparent tubing before so I have no frame of reference but that doesn't seem right.

 

[eness76]

My float height is 21.5mm with the bowl gasket removed to the gasket surface.

 

[Awk08]

I let the lack of fuel in the upper 1/2 part of the hose drive me nuts before too, as long as there is and remains fuel in the bottom 1/2 of the line, it is getting fuel.

 

[Awk08]

My float height is 21.5mm with the bowl gasket removed to the gasket surface.

thats the upper limit and should have plenty of fuel.
so far everything checks out except the length of time you held it wide open for the plug chop ?
try it again holding it longer, be it in 4th, 5th or 6th, just make it scream for 20-30 seconds
if it's still too light....feed the beast that 360

 

[Blaaster]

Leaning out after warming up!

How does it run before it warms up fully?

In theory it should run richer the warmer it gets.

Could there be a place that could be affected by heat, expanding and then creating an air leak.

I have known carb boots to test leak free, but when the engine gets to temperature the boot leaks.

Is the header pipe leak free to the cylinder?

Do not worry about bubbles in the fuel line, it is quite normal for them to be there.

I worry when there is not a bubble which could mean the needle and seat could have a problem.

 

[eness76]

pipe seems to be sealed up well, I used some copper rtv on the manifold to cylinder, and a new spring on the pipe. There was no evidence of blow-by sprayed anywhere when I took it apart yesterday.

Before it fully warms up it is spot on, super crisp throttle response, no stumbles anywere and pulls hard. After it warms up and a couple of hard wide open runs it develops a stutter in the middle.

When I bought the bike it was totally missing the top end, somebody had apparently disassembled it for a top end rebuild and lost their steam. The bike was abandoned in a storage unit, the guy I bought it from won an auction on the unit so there is no idea how long it sat in that condition. The whole top end is new, my one concern was the main seals, which I didn't replace. They seem to hold pressure fine on the leak down test, but could they be leaking under hot load? The tranny side I don't believe is leaking because the tranny oil level is not changing and the exhaust isn't overly smoky or smell like burning oil.

 

[Blaaster]

What clip is the needle set on?

 

[eness76]

It started at the center position, I experienced the stutter, moved the clip down one position to raise the needle. That seemed to initially fix it but later after many hard runs it returned, perhaps not as bad. I put the 360 main in, and left the clip in this position but I only get to ride on the weekend, so I'll find out this weekend if a little more fuel helps.

 

[Blaaster]

It is possible to plug chop at 1/2 and 3/4 throttle to confirm the needle!