Carb Guru Honors, Jawa Division

Howdy -

I'm a Moped Newby and the proud new owner of a '93 Jawa 210 (thanks, Chad). When I first got the bike it would only start and idle with the choke full on. Since then I've torn down and cleaned the carb and the exhaust, replaced the sparkplug, cleaned the wimpy filter on the air box, and replaced all of the missing and/or burned out bulbs and lamps.

Still, the motor would bog out as soon as I cranked the throttle far enough to pop the choke off, and would sputter to a halt. The only way I got the Jawa to run AND roll forward was to partially block the air intake. I found that if I applied a strip of duct tape (100MPH GI stuff) across 1/2 to 2/3 of the intake, I got RPMS when I turned the throttle. I could actually run on both flat surfaces AND modest inclines, with a top speed of 30mph. The carb is getting plenty of gas, based on the wet interior of the airbox cover when I pull that off...

Still, I don't much like the "band-aid" approach, and don't really consider it fixed. What adjustments can I try to make the motor breath right? There are only two adjustment screws on the carb, and I can't find them explained properly in available documentation. Can anybody give me starting points to set these at?

Any other wisdom you can pass along would also be appreciated.

Thanks in advance,

Zeke

Re: Carb Guru Honors, Jawa Division

Zeke,

I looked at that bike about two months ago, at Chad's place. Are you in the twin cities area?

If you can get the machine up to 30mph, that would tend to indicate that the carb was not plugged up. It is still delivering enough fuel to produce useful power.

Sounds like the problem is too much air.. Do you have any vacuum leaks, at the joints on the intake maifold, or at the base gasket? Do you have a complete (and working) original air filter / filter housing?

If everything else is good, start thinking about the crank seals. They could be doing this.

Re: Carb Guru Honors, Jawa Division

It sounds o me like your crankshaft oil seals are leaking air into the crankcase. To keep up with the raw air leak you have to artificially choke the carb adding extra gas to whatever is sucked into the crankcase thru the carb.

Has the bike been sitting a long time? Dried out oil seals are a typical result of sitting a long time.

Re: Carb Guru Honors, Jawa Division

Yes, it does sound like crank seals.. but here's another potential clue:

Search the buy/sell forum for a post from Chad, about two weeks back. He was looking for a replacement black-box for the transistorized ignition on the Jawa 210. Unless he owns another that I did not see, I assume he was seeking one for this same machine. Now, this could be a total red herring, but it's worth looking into.

Here's another thought: Go do another of your choke-on 30mph runs.. a mile or so. Then pull the plug and check it out. If the plug color is something reasonable (light tan to a chocolate brown), that would tend to indicate that the choked carb is providing a reasonable air/fuel ratio. If this is the case, you need to have the crank seals tested. Any shop that works on dirt bikes, or ATVs has the tools for the test.

If the seals are bad, you're in for some interesting times.

Re: Carb Guru Honors, Jawa Division

Jon Zetterlund /

Legendre -

This is the same Jawa you looked over - I bought it the next weekend. As for having sat for a long time, I'm sure it did. I'm just not sure when. I thought that Chad had been able to run it the year before, but am probably mistaken. He thought it was a two speed, and would go 40mph, but that's not the case. The speedo goes to 40...

Regarding transmissions - the tranny case was cast and marked for the 2-speed, but never machined for the fill/drain holes. Is there a gearcase and lube involved with a single speed set-up? If so, I can't find any evidence of them.

I don't think I have any front-side air leaks. The airbox pulls air up through a rectangular tube mounted to the upshaft of the frame, through the mease-ly scotchbrite-looking filter, into a chamber in the frame itself (!), out through a bit of rubber hose and into the plastic airbox cover on the front of the carb. Everything is sound and in place - I even fashioned a gasket for where the airbox cover meets the carb, to eliminate air leaks there.

Anyway, since I am unable to check for leaking crank seals, it sounds as though a trip to ScoBroMoCo/BlueCat may be the best route...

Thanks for all the input!

Zeke

Re: Carb Guru Honors, Jawa Division

Zeke,

Not sure if Ryan@BlueCat has the equipment for a crank seal test - but he might. Tom Manley (Manley Cycle) also might, but I'm sure that Hitching Post, Towsley, etc will have it.

Ryan told me recently that BlueCat is going for the bigtime - full service shop with paint & body work, performace tuning etc. I might have the opportunity to do some work with him - which is something I really miss doing. Can't do hard/heavy stuff anymore, but I'd be fine doing electrical work, carbs, engines or other bench work.

You can probably test the magneto-side seal yourself. If you can get the bike running with the magneto cover off, try to get a shot of carb cleaner in behind the stator plate, in the area where the crankshaft comes thorugh - that is the seal area.

If a spray of carb cleaner onto this area has any effect on engine RPM (other than the cleaner fouling the points..) that seal is sucking in air. There may also be evidence of gas/oil mix around the bottom of the mag/stator plate. Either of these are a dead giveaway. You may even be able to hear it.. put a piece of tubing almost into your ear, and place it near the edge of the stator plate. Listen for the Sounds of Sucklence.

Re: Carb Guru Honors, Jawa Division

Jon Zetterlund /

Thanks for the info.

One last question - what are the consequences of leaving things as they are, and including duct tape as new standard equipment? Will things blow up eventually?

Just wondering...

Zeke

Re: Carb Guru Honors, Jawa Division

Jon Zetterlund /

What?

Too gruesome to go into detail?

Re: Carb Guru Honors, Jawa Division

You need to find & fix the issue, no matter what.

It might run OK for now with the tape, but you are just masking (...) the problem. The carb is still not working correctly, and the bike will eventually suffer for that, one way or another.

Too lean, and you could seize - too rich, and you will foul plugs and build carbon.

Are you absolutely sure that the entire stock air filter/airbox is intact? I don't recall, it was a few months ago when I checked that bike out.

Re: Carb Guru Honors, Jawa Division

BTW - if it really gets down to the ugly, I might be willing to have a poke at the motor / carb. If you're still in town, that is.

Never worked on a Jawa before, but I'm pretty decent at not breaking things.

Re: Carb Guru Honors, Jawa Division

Jon Zetterlund /

Legendre -

I'm in Stillwater, and I'll keep you and your wrenches in mind if I get in too deep.

Thanks!

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