Timing issue?

[MitchB]

Hi gang, looking for a little help from those with more experience...

I'm getting my 350 running from barn find status. I've done little to the motor as yet. It had good compression so I thought I'd just clean / adjust carbs, inspect oil pump / replace lines, new plugs, new oil , fresh fuel and see how see she does. Started second kick. Runs / idles smooth.
When I finally got to ride it, it runs / revs fine to about 6K RPM, then sorta falls off. Won't pull past 6K. Plugs are a nice brown/tan. My first guess was points and/or timing. Checked the points - they were clean and needed just a little gap adjustment.

When I went to check my continuity light before checking timing, oddly the light is always on. Even when the point gap is clearly open. Am I doing something wrong? If not, my guess is a bad condensor. But both sets do it - that seems unlikely. Ideas?

[disc_valve]

If it were really the case that the continuity light was permanently on, then that means the points are permanently closed and there would be no spark at all. Clearly that is not the case as the engine runs! Try connecting the continuity light to the points spring, and make doubly sure that it isn't also touching the points backplate which would give exactly the symptom you're seeing.

As for your misfire at 6000 rpm, that could indicate that the engine is fouled with oil or an over-rich mixture. What main jets have you got fitted? The factory fit was #140 mains, but they were deliberately set rich for running in a new engine. The standard motor runs better on #130 mains, and these were supposed to be fitted by the dealer when the bike came in for its first post break-in service.

Graham

[BRT-GTR]

Hi Mitch,
             Thought I'd let someone else have first crack at this one (thanks Graham ) as there could be dozens of reasons why your engine won't pull past 6000rpm but you have already covered most of the obvious ones..

 Graham has put his finger on the mains reasons for poor performance when the bikes were new but bare in mind this engine is nearly 50 years old and from what you say is pretty original. My GTR back in 69 had the same problem but the UK importer probably wasn't informed about putting smaller jets in (and didn't stock them anyway) and backing off the oil supply slightly after run-in. Never did get it fully sorted. Richard also makes the comment in an early post that some bikes ran noticeably better than others but never found out why..   BS shortened the barrels by 0.5mm at bike 21S01100 and modified the exhaust ports to 'improve acceleration'.  

       You were lucky to get an engine that still turns over, most have seized pistons through standing due to corrosion between the pistons/rings/barrels. It would pay to remove the heads and barrels to check the chrome bores are OK and the rings are free before trying for 8000rpm. It may help to replace the crankseal on the right side, the one in the disc valve cover. In theory the crank centre seal should never wear as it has no metal to metal contact, so should be OK, unless there is play in the main bearings.
 
    Keep us informed how you go on, it may help others (me :: ) in the future,    Brian.  

[hardy]

Hi Mitch,

I'm guessing you have already checked the exhaust baffles are not blocked? On first start for me I found one baffle to be full of leaves!

Ryan

[CL-100]

Not to change the subject but in attempting to check the timing on a 50 Sport, I have the same issue with my points.  I put a continuity light on them and it stays on, even when I manually separate the points by hand.  I bench tested a new set of points and the light goes off when I separate the points.  Visually, the points in the bike look fine. 

I assumed that my only problem was the coil.  Primary resistance is exactly in spec.  Secondary resistance is over 120K so I'm assuming an open circuit on the secondary side. 

Any thoughts?

[OldSwartout]

It may be that one of the insulating washers is missing or has deteriorated.  A likely suspect is the small one around the bolt inside the hole through the base.  Either that, or the wire is on the wrong side of an insulating washer.  

Secondary resistance on a points/coil system is usually 20K or less in my experience, although if  you are measuring through the plug wire, it's more likely to be the plug wire.

[dcr]

Page 53 of the service manual notes that the ohm meter never reads "0" or the light never goes out entirely because the condenser is grounded.

Dan

[CL-100]

Thanks for the responses.  This is somewhat of a learning experience for me so the tips are a big help.  I have a couple of service/technical manuals that cover the 50 but the way the Clymer manual is laid out, the information about the continuity light not going out completely was listed after a section on the 175 ignition, so I hadn't read it. 

With that in mind, I hooked the light up again and find that it very quickly blinks when the points open.  Actually, it's more like it dims momentarily.  Another article I had read talked about a buzz box that "changes tone" when the points open so I'm assuming that the "event" for the points opening is very quick.  I used my multimeter setting it on continuity with an audible signal that reads ohms at the same time.  As the points open, the audible is briefly interrupted and the ohms drop. 

Looks like the timing is spot on.  Still wondering why the secondary coil resistance reads so high.  The design of the coil doesn't allow for secondary resistance testing at the coil as the plug wire is incorporated into the casing for the coil. 

[MitchB]

Thanks guys.
Part of my re-furbish includes checking cylinder bores, pistons and rings - so I'm removing those today...
After, I'll tackle the points again.
I'll try to find a source for new jets - anyone know a US source?

Baffles were fairly clean, coils are new.

[hardy]

Hi Mitch,

I bought mine from Richard, but I read somewhere that carb-worx also stocks them.

Ry

[OldSwartout]

Sudco also carries nearly anything you'd ever want for a Mikuni.  Richard will probably have  any standard parts, though.

[Colin]

I had trouble a lot of years back on another bike that ran well but would not pull the last 3000 rpm in any gear, it did miss at 5000 revs but shut it back a bit and it ran perfect, this took me a while to nail down but it was a coil 
Colin