Bike only runs when SUPER rich

[Farthom]

Been battling some issues recently with my engines mixture. For whatever reason, the bike will only idle when the fuel mixture is retardedly rich. I bought a bunch of the same kit, and 3 others went together with the carb at stock settings and ran great, just slap on and go. This bike would not idle at all. In order to make it run, I had to take the jet out of a differnt carb (from a grubee engine, which seems to have a larger jet) and set the C clip to the richest setting. This makes the bike run. I did some testing, and moving the clip even one notch leaner would make it stop running. So while it runs well, it has the following problems:

- When I took a look in the piston chamber, the whole thing was 100% caked with black soot and crap. The spark plug is completely fouled, and I can't see it lasting very long.

- The bike runs really jerky..... whenever the throttle isnt wide open the bike jerks pretty violently, even at reasonably high speeds.

- The bike has some issues settling down to a low idle. If I go quick, then pull the clutch, it likes to keep running at a high rpm, until I let the clutch go slightly to give it some resistance. This makes it settle down.

When I had the ORIGINAL jet, and STOCK mixture setting (one from the top) the bike could run, if I were to pedal it REALLY fast and start it with throttle wide open, it would start, and have power only on the top end. As soon as you slowed down for anything, it would die. With this, the problem is definitely entirely on the low end. The bike would idle ONLY when the choke was fully on.

Things I have tried so far:

- I have tried 3 different stock carbs, all exhibit the same problem, so I don't think anything is wrong with the carb itself.

- Tried swapping literally every part of the engine. (Coil, exhaust pipe, spark plug, etc) and nothing improved the situation.


My suspicion.... air leak on the carb intake. I've got an O-ring in there, but it doesn't seem to help much. If I spray it with some chain lube while its running, the idle does rev up a little bit, but not by much. Could a tiny air like this cause such a significant problem? One of the other bikes had a carb come off completely (was still on the intake manifold, but was completely loose) and the bike still ran. We didnt even notice until we returned home from a ride. I will be going to the store tomorrow to grab some of this "Seal-All" stuff people keep talking about. I somehow doubt it will work so I'm tossing all this info up here to see if anyone else has some other suggestions.

Thank you in advance! Everyone on this forum has been super helpful troubleshooting in the past.

Matt

 

[DuctTapedGoat]

There's an air leak somewhere, I totally agree with you - that's what I was thinking before I opened this post. You could have a blown seal too.

Sounds like you've done most of your homework already.

You could have a shoddy intake - do you have any you can test out? What carb are you running? If it is in fact the CNS, you can try the MM intake and solve your problems there.

 

[Farthom]

Blown seal? you mean the little gasket between the intake and the cylinder body?

I tried using the intake from a different engine, and it seemed to make no difference, although it was from a grubee kit and didn't seem to fit right. If sealant doesnt fix it, I will try getting an identical intake off an identical engine. By "shoddy" do you mean, the intake may have a crack or a hole in its weld? some crap like that?

I'm not sure which type of carb I have. It came with my flying horse kit, and has a black plastic cover over the air filter. It kind of looks like a black skull.

 

[DuctTapedGoat]

The engine seals are behind the magnet and behind the drive gear in the clutch cover. A test for air leaks there will let you know quickly.

The intake could be split at a weld, but if you've tried different ones, it is unlikely.

Your carb is an NT carb, so that eliminates many issues.

 

[Farthom]

Ohh, those seals. Yeah, thanks for that suggestion, I never even thought to check those. I sprayed some carp cleaner behind the magneto while it was running and sure enough... there was a leak. Did the same for the gear side, behind the small gear, and it seems to be fine.

So in the end, it looks like I have a dual air leak! Crappity crap. I dont even know how to get that seal out without taking the whole engine apart. I suppose I wont need it afterwards so I could go at it with a small screwdriver.

 

[DuctTapedGoat]

I pulled my dead seal with a hooked safety pin.

Well, that seal is easy to get to. Just remove the magnet and it's right there.

I'm glad you've at least got a proper diagnosis now.

 

[Farthom]

This explains how previous engines with known air leaks would run, while this one didnt. Having two, is what made the problem so severe. Sad I have to wait to receive seals. Shipping is a pain.

Unless, are these seals some kind of standard equipment? Something I could get from a local distributer? Is there a formal title for them that I could ask for?

 

[Farthom]

Well, I got the magneto seal patched up, and I found another thread which suggested snipping a strip of aluminum from a popcan and using that on the intake to seal it. The popcan idea works PERFECTLY! I could spray that intake all day and the idle never changes! The magneto seal still leaks a bit though, I suspect its because of how the new seal went in.... It was a bit difficult, and I ended up pushing one side in a bit too far.

In any case, the bike runs on its proper jet size now! It still doesn't run well however. It will decent with the carb on the richest setting, and while it idles on the stock setting, it doesnt have any power and tries very hard to die out. (Unless you open the throttle wide) On the richest setting its a bit boggy, sputters for a moment before delivering power when you open the throttle quick. The engine no longer jerks at slow speeds also! Any suggestions for getting it to run again on the stock setting where it should be?

Tomorrow I will be:
- Trying again on the magneto seal.
- Test other places on the engine for leaks. (All around the case gasket)
- After a bit of riding on the rich setting, checking the spark plug to see if its still blackened with crud!

 

[rustycase]

You could pack a bit of wheel bearing grease around that crank seal to help it out while it seats...

These are standard seals... it would be possible to get them from a local supplier. Telephone a few places with the number off the seal, or the dimensions and see if they are stocking... You'll pay more than an ebay special, but probably get a better quality product for your money.
...my 2cents...
rc

 

[Farthom]

I got the seals for 2 bucks a shot, so no big deal.