On Board Camera

[jonno]

Short video of my LC that wont run past 7000rpm despite the throttle being wrung out!!!

How does it sound?

[oldelsieboy]

"The video you have requested in not available"

OEB

Edit: Now reads,
"This is a private video. If you have been sent this video, please make sure you accept the sender's friend request."

[jonno]

Should work ok now.

[daveg]

Hi Jonno, seems to me like it sounds OK, are you sure your carbs are actually opening the full way, in the video you only tried to rev it it higher gears what does it do when you wack the throttle open in the lower gears - if it was a powervalve I would say the valves are opening.... so after teh carbs I would check - exhaust blocked, silencers need a decoke, or have you left a rag in the airbox. And then after that I would check if it has been badly tuned.... hase any work been done on it?

[elsie1411]

just watched the video and if i'm correct it will pull to the red line in probably the first 3 gears but 4,5and 6 you hold open the throttle and it wont pull through the sticky spot into the power band, if you back off the throttle a little and just hold it there will it eventually creep into the power band but still feel like it's holding back? the first thing i would check is head gasket mine had the symptons i described and when i lifted the head i had a leak between the bore and a water chamber and the lack of compression on one cylinder only manifested it self when under load in the higher gears.
i assumed that you cleaned the carb emulsion tubes as well.
the other couple of things to look for are leaking crank seals and a twisted crank.
but i would certainly start with the head gasket.

[jonno]

Thanks for the comments guys, this is really doing my head in. LOL.

Since the video was taken i have replaced the fuel tap for a new genuine Yam one and stripped and cleaned the carbs completely again. (Noticed a bead of water in the RH throttle slide)!

Now the bike splutters badly again from about 4500rpm up to a max of 7000rpm. Even on the stand in neutral the engine will not rev past 7000rpm.

I am going to revisit the shed one more time this afternoon and go through everything like a dose of salts and then post my findings on here for your comments.

[Norbo]

What size jets do you have fitted mate . it could be as simple as over jetting .

[jonno]

Standard 220 main jets Norbo.

Right, i took the head off this afternoon and it would appear that water has been getting into the right hand cylinder as there was some creamy looking two stroke oil in the head and the piston has less carbon build up on it. I lapped the cylinder head with some wet and dry on some plate glass and put it back on with a new gasket and torqued it down. Took her for a run and no difference, spluttering and running out of guts at 7000rpm. Then i took the tank off and emptied it out and hung it up to dry in case their is water in the fuel. I will try it again once it has thoroughly dried out to see if it makes any difference.

To re-cap, its a standard 1980 4LO motor rebuilt with new crank, pistons, seals & gaskets with new stock size jets in 4LO 01 carbs and standard exhausts. The engine has run less than two hundred miles since the rebuild so is still running in.

The crank has not twisted and is all good.

The engine is running one 1980 cylinder with the smaller exhaust gaskets and one later cylinder with the larger gaskets. (Both on 0.50 oversize).

I would like to check the deck heights of the cylinders, I asked the machine shop to check them when they did the rebores and they said that they were ok. I seem to remember thinking one cylinder was slightly higher than the other when I originally stripped the motor and thats why I asked the machine shop to check them.

I am thinking that this could be the problem so i shall take the cylinders off again to check, the thing is does anyone know what the correct standard deck height should be? (From bottom cylinder mating surface to the top cylinder mating surface).

Thanks in advance Guys.

[elsie1411]

i think you have answered your own question mate the odd barrels should not work together as the main jetting for the 4l0-00 set up is 160 or 140 to cure the bogging down that the early one suffered with and the 4l0-01 barrel runs with 220 mains. my early 350 ran with 190's with all speeds and k&n filters, reed spacers and boysons reeds and it still ran slightly rich. i did try once with 220 jets in mine as that what was in my mates bikes and the bloody thing just wouldn't run at all. also if i remember the early barrels had a slightly different port set up including a cut out in the exhaust port. in my opinion for what it's worth you would do better to try and get either another early or late barrel to match up.

[jonno]

OK,

I have just got off the phone to Taymar Racing and they have assured me that the combination of one early and one later cylinder is not the problem as they have run many combinations over the years with no trouble at all.

I explained the symptoms to them and they are sure that the Stator is the problem and should be swopped for a good one. It is known to them that a faulty stator will cause one cylinder to run weaker than the other with the cylinder with the weakest spark refusing to fire at all under load. This leaves the good cylinder having to work at driving the dead cylinder which results in the engine not making the red line.

So, as soon as i get back from my holiday i will obtain another stator and see if this finally cures the problem once and for all.