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Discussion Starter · #1 ·
I'm back, and yes, I have yet another 'Bike stalls under X condition' thread. Maybe this one will be different. Maybe I just don't know how to search the forum. Who knows?

So, quick recap:
Took the engine apart, put it back together. Ran fine-ish for a couple weeks. Started sputtering and surging after about 45 minutes on the highway. Perused the forum a bit; figured it was an ignition problem.

Turns out, I had a dying plug cap. That wasn't the problem, though.

Problem became progressively worse over the next few rides, especially the longer ones. Scrounged the forum for more nuggets of advice. Left a plume of blue smoke one day - Ah-ha! Oil leak!

The inner valve cover gasket was leaking on the left side and oil was creeping down into the cylinder

That wasn't the problem, either, apparently.

Problem got bad, as in 'I was almost stranded' bad. Left a plume of black smoke as I limped home. Searched the forum a bit more. Decided to check the air cut-off valves on the carbs. One was in bad shape, so I ordered a full rebuild kit to head off any more rubber-related problems.

Got the kit, replaced the cut-off valves, floats, accelerator pump, transfer pipe o-rings, and float bowl gaskets.

The bike starts perfectly. Idles like a happy kitten.

Absolutely refuses to get more than 50ft up my driveway. I roll on the throttle, everything is motorcycle heaven for two seconds, and then it chokes and dies. And no, the choke is not engaged.



I am probably missing something very obvious here (again), but patience and frustration are inversely proportional and I have an overabundance of the latter right now. I need ideas from clear heads before I make things worse.

As always, advice and ideas are welcome and appreciated.
Thanks in advance,
Sam
 

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Have you looked for a mouse nest in your air filter? I found the beginnings of one there today.
 

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Discussion Starter · #5 ·
I hope you save all your old brass parts and the float needles. Most after-market stuff is questionable to OEM brass and needles
I come from a family of pack rats, so... I have boxes upon boxes of motorcycle parts both new and old. Carb parts included.
Have you looked for a mouse nest in your air filter? I found the beginnings of one there today.
A mouse nest, no, but I'm expecting to have enough dust to grow tomatoes in there. Dirt roads are fun. I have a spare filter just in case, though.


In other news, I read up a bit on Mike Nixon's site and... learned a few things. I'll get back into the carbs tomorrow and take another look.
 

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fuel level in bowls correct ?
 

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'84 CX650E that is evolving into a GL500
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The inner valve cover gasket was leaking on the left side and oil was creeping down into the cylinder
This is just not possible. The valve cover's rubber seals serve only to keep oil in and dirt & water out of the area under them. A leaking inner seal would allow oil to get out of the engine but from there it would run out of the drain hole on the side of the engine. There is no way oil from a leaking valve cover seal could get into the cylinder unless the spark plug is missing and the oil entered through the hole it should be in.

Blue smoke is almost always a result of oil getting into the cylinder and being burned with the fuel/air mixture and while it could be possible for that to happen at the same time as you discovered the leaking seal the usual way the oil gets into the cylinder is through a leaking valve seal or past a bad (or broken) piston ring.

Black smoke is usually caused by a rich fuel/air mixture. There are several possible causes for this, including incorrect adjustment of the carb and reversed jets.

A dirty air filter can make the engine act as if the choke is always on so if you have a spare it wouldn't hurt to try it if only to eliminate a possibility.
 

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Funky float level. Probably about 18 mm float height. no fuel reserve in bowls.

Clean the OEM keihin ones and shove them back in. They'll go another 40 years.
 

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'84 CX650E that is evolving into a GL500
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Which carb kit did you use?
AFAIK the only one that comes with the o-rings for the crossover tubes is Randakk's Original, which does not include any jets, needles &c because Randakk knew when he designed his kits that they were rarely needed and the best source for them was a Honda dealer.
The aftermarket jets, needles &c supplied with other kits (even well known brands) are often so far out of spec that they cause more problems than they could fix, not to mention the famous float needles with peeling plating.
A float needle that is too short can cause a high float level....

BTW: In case you don't know you can check the level in the bowl by connecting a length of clear tubing to the overflow/drain barb on the bottom of the bowl and holding the open end of it next to the carb while loosening the drain screw (the bike should be on the centre stand for this).
 

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Discussion Starter · #13 ·
This is just not possible. The valve cover's rubber seals serve only to keep oil in and dirt & water out of the area under them. A leaking inner seal would allow oil to get out of the engine but from there it would run out of the drain hole on the side of the engine. There is no way oil from a leaking valve cover seal could get into the cylinder unless the spark plug is missing and the oil entered through the hole it should be in.
Not possible? Be careful saying that. I must not have tightened the spark plug at some point, because there was definitely oil on the spark plug head as well as dripping out of the drain hole.
Which carb kit did you use?
Speaking from recent, personal experience, don't buy this kit. It's mostly garbage.

That aside, I replaced the floats and needles with the OEM pieces, changed the air filter, and then took the bike for a spin. Runs like a Swiss watch now. Or an old Honda, whichever you prefer.

Now, between a faulty plug cap, loose, fouled spark plug, perforated air cutoff diaphragms, garbage aftermarket float needles, and filthy air filter, it's hard to say what exactly the 'cause of death' was. At this point, I just hope I can get a few thousand miles of peace and quiet in the maintenance department.

Owning Being owned by antique vehicles is fun, isn't it?;)

Thank you all for your advice and suggestions. Hopefully I can close this thread without jinxing myself...
Sam
 

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Not possible? Be careful saying that. I must not have tightened the spark plug at some point, because there was definitely oil on the spark plug head as well as dripping out of the drain hole.
True, anything is possible when incompetence is involved!
Just joking, glad you got it sorted. Now you can enjoy the riding season.
 

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'84 CX650E that is evolving into a GL500
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Think about this: In order for oil that is on the outside of the engine (as it would be if it leaked past the valve cover seal) to get into the cylinder there would have to be a direct connection between the inside of the cylinder and the place where that oil is. And if it had such a connection the cylinder wouldn't have compression.

Now, if there was some oil pooling in the spark plug well and you unscrewed the spark plug it would be possible for some of that oil to find its way onto the tip of the plug. But if there wasn't enough of it to foul the plug that would burn off pretty quickly.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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Failing to tighten a spark plug isn't nearly as bad as failing to tighten the primary gear bolt. That lesson only cost a front cover.
Not that I would have first hand experience with such a thing. :cautious:
 
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