air filter foam and jetting.

C

CDNTX650

XS400 Enthusiast
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Hello all.

I have a 1979 2f that runs pretty well. But has had a flat spot at the end of the pilot to needle transition. Now...the p.o used some kind of lighter density foam on the filter cages as he probably saw what oem cost.... bIke has stock exhaust and pamco. I have cleaned many times and made sure air and carb cleaner come out of all passages. Done throttle shaft seals. And confirmed proper float height via clear tube. And synced carbs. I did throw in some 47.5 pilots I had kicking around and it did get slightly better. Needle is on number 4...

Would the less dense foam account for the flat spot? Figured with stock exhaust it shouldn't affect it that much. Bike goes like stink once on the needle and main. Not sure what else to look at except maybe run needle on 5.
 
Put the stock air filters in it. Mikesxs has them yamaha sells them and ebay has them. My 2-f has all stock parts and uses stock jets with no flat spots.
 
I see them from 25$ -35$ each on ebay. These will last a long time if you take good care of them. Remember these DON'T get oil. Blow them out with air every 1k miles or so (depending on type of conditions you ride in). I wash them out with warm soapy water then let them dry every 4-5k miles just to keep them extra clean. I replaced the ones on my 79 about 12k miles ago and they still look new.
 
Got two for about 70 cdn. High flow filtro. I was going to try partsnmore ones but reviews weren't good. Maybe this thing will run the way it's supposed to.
 
I had the same issue. The filter foam let in waaay too much air.

Just ordered the stock Yamaha filters from a local shop on friday. Came to $74 for the pair.
 
Not sure how good the hiflo filters are. They "look" like the stock ones but nothing is better the the real deal:wink2: This also goes for the jets. Real mikuni's are far better that the china rip offs. I compared a set of pilot jets. The 45 china ones where smaller than the 42.5 mikuni:wtf:
 
I'll let ya know. I have used high flow stuff before on my ducati with good results. The emgo stuff is what can really be hit or miss. I run a map cycles external oil filter on my 650 which uses triumph trident filters. The one emgo I did order for it was very poorly made. Only genuine now.

And on the jets...probably explains why 47.5 pilots aren't hugely rich I this thing. They aren't mikuni .
 
Got the new filters. Very nice quality. As good as the oem I'd say. The necks are slightly longer too which is nice if your carb manifolds have shrank back from the heat cycling. Bike runs tons better. But I need to remove the 47.5 China jets and put in my stock pilots to eliminate them as a problem.
 
Alrighty. Got er sorted. Never assume...the bs34s you are used to for the 650 preload the needles from the top with a spring that the 400 is the same. If you put it together like that it will leave the needles way down which means lean. So...see a pic on here..have revelation. Assemble with spring on the bottom and c clip in the middle position on the needle and voila. All your tail chasing is solved.

Also discovered a failing coil. Bike gets hot and cuts out on one pot. Coil was so bloody hot I couldn't touch it. Spare fixed that.

Bike runs perfect. New Hiflo replacement filters are as good as oem I'd say. Time to do some riding this week on the neglected 400 scrambler.

Also run a pamco. Set and forget on the 650 and 400.
 
You got me wondering, so I checked the carb manual for DOHC's, and verified I have been assembling the carbs correctly. Spacer, clip, washer, spring, retainer. Good! I've been doing it right. Strange that the SOHC would be different...
 
I think we just explained it dofferent. But yes they are the same as the dohc as per your description. My 650 puts the springs on top of the needles. So if you do that on the 400 the needles are like 1/8 inch lower. Lean as hell.
 
The 77-79 xs400 carbs are different than the 80-82 sohc and 82-84 dohc needle arrangement. Spring on bottom for the early ones and spring on top for the later. The xs360 BS34 uses no spring at all.
 
Ahh. Gotcha. Well. Now I'm dealing with a plug that's black on the left pot. Float has gas in it.....will it ever end. Luckily I have a spare foamy.
 

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