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| '78 yz400 bogging & fork setup https://vintagedirtbikeforums.alp-sys.com/viewtopic.php?f=28&t=4098 |
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| Author: | 2stroker_4_life [ Sat Jun 29, 2013 8:43 pm ] |
| Post subject: | '78 yz400 bogging & fork setup |
Hey all, hoping you can help me with my 400. Bought it off a guy a week ago, he put a new top end in it, used reeds, and restored the bike. The carb kept overflowing because the brass arm on the float that lifts up the needle was gone on the one side. I put a new arm on it, but it seems to still overflow. I took it put for a ride, it starts up first kick, idles good, has good low end, and goes quick, but it feels like it never hits the powerband. I hope you know what I mean. It's like riding a 125, putting it in too high a gear, and opening up the throttle without using the clutch. It still speeds up, but it doesn't hit or spin the tire or anything. Does anyone know what would cause this? I'm running 40:1 mixed with yamalube 2r, and the bike's got a dg silencer. Other than that its stock as far as I know. Now the forks. They feel like they have no dampening, like they're just riding on springs. I tried pumping the forks up to 10 psi but they sont seem any better. I'm wondering whether there's even any oil in them, does anyone know how much oil should be in them? Thanks in advance for any help you may be able to give me. -sean |
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| Author: | Scootern29 [ Wed Jul 03, 2013 9:24 am ] |
| Post subject: | Re: '78 yz400 bogging & fork setup |
Pull the pipe off and look into the exhaust port. He may have put the piston in backwards. |
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| Author: | 2stroker_4_life [ Wed Jul 03, 2013 8:41 pm ] |
| Post subject: | Re: '78 yz400 bogging & fork setup |
Will I be able to see an arrow on the piston that's supposed to be pointing to the exhaust port? That's a good idea, when I get back from Red Bud on Monday I'll check er out and let you know. The carb seems to be overflowing quite a bit, I wonder if it's overflowing faster than it can get gas when I open it up? Thanks for the suggestion! |
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| Author: | Dave [ Fri Jul 05, 2013 3:22 am ] |
| Post subject: | Re: '78 yz400 bogging & fork setup |
on a Yamaha the arrow should face the exhaust port.the only exception to this rule of thumb i know of which is the 73-76 250 Honda two stroke which the arrow faces the intake port on those. |
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| Author: | Scootern29 [ Fri Jul 05, 2013 11:18 am ] |
| Post subject: | Re: '78 yz400 bogging & fork setup |
2stroker_4_life wrote: Will I be able to see an arrow on the piston that's supposed to be pointing to the exhaust port? That's a good idea, when I get back from Red Bud on Monday I'll check er out and let you know. The carb seems to be overflowing quite a bit, I wonder if it's overflowing faster than it can get gas when I open it up? Thanks for the suggestion! By pulling the pipe you won't be able to see the arrow on the piston. If the piston is in backwards there may be windows in the skirt or there could be a kinda half moon cut away. Those should face the reedvalves and carb. If in fact it is in backwards you will have to take the top end off and fix it the proper way. |
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| Author: | 4x4_Welder [ Sun Jul 28, 2013 4:23 pm ] |
| Post subject: | Re: '78 yz400 bogging & fork setup |
If it is still overfuelling, it won't hit the higher rpms. Once you get that sorted out it should do better. IIRC, if that has a reed valve the piston won't fit backwards, the longer skirt will hit the reed cage. |
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| Author: | 2stroker_4_life [ Sun Jul 28, 2013 8:56 pm ] |
| Post subject: | Re: '78 yz400 bogging & fork setup |
Alright, well I took the motor out and took the top end apart. Ring end gap was over 50 thou, and piston clearance was about 7 thou. I'm getting it rebored with the next size up piston as we speak. I hope that this is my problem. I will check the carb out too though once i get the motor done. |
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| Author: | Scootern29 [ Tue Aug 20, 2013 10:43 am ] |
| Post subject: | Re: '78 yz400 bogging & fork setup |
I have a 79 YZ 250 motor sitting on my bench that has the piston in backwards. It will go through the whole stroke. I am sure the piston skirt will not hit the reed cage. From your memory you are probably thinking of the ring locater pin. It more than likely lines up with the opening in the intake port and the ring can pop out and snag. |
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