Vintage Dirt Bike Q & A

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PostPosted: Thu Jul 31, 2008 6:10 am 

Joined: Thu Jul 31, 2008 5:28 am
Posts: 1
I'm putting an old mx back together. Can anyone please tell me the tubing configuaration for the carb on this bike ? I know the largest fitting is the fuel line from the petcock, but I don't know where the three smaller fittings that are on the left, right and bottom center facing the rear run to. Also need to know where the tube fitting above the oil pump runs to. I have a couple of carb schematics with exploded views which were helpful when I disassembled and assembled the carb for cleaning, just not real clear about the tubing. These probably seem like stupid questions, but I'm no mechanic. Any help would be appreciated. Thanks, Jeff

mx 100 00001.jpg
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PostPosted: Thu Oct 16, 2008 11:48 pm 

Joined: Fri Jun 02, 2006 11:12 pm
Posts: 158
Location: Salinas, CA
Hey Jeff, I had one of these from 1978 - my first bike. Well, actually I still have it, but it's been year's since it actually ran. That carb is just like any other, so here's some tube information to get you set up.

The little one of the bottom of the carb is for draining the float bowl. One of the side ones is connected to an overflow so that if the carb gets too much fuel in it, the fuel will go out the tube rather than filling up the engine. I think the other is a vent for the enricher circuit, but I really don't remember. At any rate you can get pretty clear tubing from OSH in that size. Run enough length from each of those three nipples to drop down behind the engine protruding below the frame rails just a bit then trim them off.

I can't for the life of me remember exactly where the autolube system shoots the oil into the motor. I think the oil tank has a rubber oil inlet line that goes to the oil pump, and maybe that is the fitting your working with. Does the oil injection right in the cases the inside of the pump, or is there an outside fitting? All I really should say about this is that you better get this one thing solved properly or you'll fry that little motor in no time. I do remember removing my autolube system and plugging a hole somewhere so I could run premix. Lord knows why kids do such things, but I am sure at the time I thought it would make the bike go much faster.......

PostPosted: Mon Oct 20, 2008 12:47 pm 

Joined: Thu Feb 09, 2006 6:10 pm
Posts: 51
If it were mine, I would definitly kill the auto lube, I burnt one up back in the day and just dont trust them anymore, way to easy to premix the fuel. just my two cents worth,

C Bly

74 CR 250M
74 CRF 175
75 XR 75
77 ProFab Aberg HL500
97 Montesa Cota 315R
2003 CR500 AF
2004 CRF 450

PostPosted: Tue Jan 27, 2009 10:54 pm 

Joined: Tue Jan 27, 2009 8:48 pm
Posts: 4
I think "THINK" that the oil line runs to the right hand side of the reed block from the pump at the front right of the engine. I went the single cable to the carby and blocked the pump off and ran premix fuel so I knew it was getting the right amount of oil, I just jetted it a little more to compensate for oil fuel mix. If you want to keep it original you could do the same as I but just leave it looking like it is still hooked up just remember to tell other users to only run premix

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