Idle Hesitation/Bog - '78 xs400

[Monowakari]

Tore my carbs apart and cleaned them thoroughly with carb cleaner. Set the timing to be fairly accurate and point gap is perfect. Valve clearances all within spec on the tighter side (quite quiet now, might have read my old posts on the valve train noise, has all but gone away now with valves in spec.!!!).

Reassembled with new carb intake boots in prime condition. Idle mixture screw is out 3.5 turns each side, they are fairly synced, going to build a manometer today or soon (this week).

The only thing I couldn't get out in carb rebuild was the pilot jet due to not having a small enough screw driver to get in there but throughly cleaned with carb cleaner with a tiny spray nozzle and just blasted 'er.

You can hear the pods gurgle in air when I engage the throttle and it hesitates for a fraction like its bogging down then it soars to where it should be and no issue through idle at ~1200rpm to revving to 6-7k rpm (in neutral on center stand). You can even see the vacuum action on the clamp or the rubber deflecting underneath it.

All I can think of is, should have cleaned pilot jet but couldn't get it out...can always go back in.
Perhaps the floats need much more accurate adjustment? [It's like 1.05" float height and just under 1-9/32" fuel max (float extended all the way up so just over an inch and a quarter). - basically 26mm and 32mm, juuuuust off...]
Idle mixture screw in or out a bit?
OR this is how it should sound, question is the slight hesitation when engaging throttle... Revs fine and going to take it for a quick test spin around the block as I'm sure all is in running order...

Cant wait for Pamco with electronic advancer to arrive, will probably help alot, and manometer adjustments.

Anyways, thanks fellas, this is the best forum I've ever been on!

 

[xschris]

Ditch those filters they are the worst style to use with these type carbs. Get the factory H-pipe and use real K&N or uni filters. Also get the correct screw driver to get out the pilot jets so you can clean them the right way and or rejet if need be.

 

[Monowakari]

Went and got a screw driver, I guess I'll have to pull the carbs off again soon. I don't know if that boot would fit with even larger filters. [See pic.] they're almost running into the battery box as is.




They're in line with the battery box so would need to kick out on an angle to clear the battery. I see the h joint does that a bit but am concerned to waste monay... Are there simply better filters than the ones I have as a getaround? Thanks xschris!!

 

[BBS360]

The pod filters you have aren't designed for any particular bike, never mind one with CV carbs. The bike's constant velocity carbs need a smooth, even, and consistent air flow. With the pods mounted directly on the carbs you have no intake tract to smooth the air from the filters. The pleated filter does not pass air uniformly so you're seeing unpredictable pressure differentials inside the carb mouth and more than likely the pods are partially blocking the air ports in the carb mouth too.

If you're keeping the battery box just go with OEM filters on the OEM h-pipe. They're pricey compared to dirt-cheap pods, my new ones were $34 each, but at least you know they were designed for the bike and carbs, and the carbs are meant to work with them.
As is you're clearly not getting any kind of performance increase.
With the battery box still there you're not really improving the bike's appearance as it's mostly designed as a mount for the stock filters.

Keep it stock and be happy with a decently running bike or go all the way with the hot rod mods.
Take out the battery box. Relocate the battery. Hide the electronics. Put on quality filters with a stock or similar intake tract, and maybe even switch to VM/flat-slide carbs.

 

[Monowakari]

The pod filters you have aren't designed for any particular bike, never mind one with CV carbs. The bike's constant velocity carbs need a smooth, even, and consistent air flow. With the pods mounted directly on the carbs you have no intake tract to smooth the air from the filters. The pleated filter does not pass air uniformly so you're seeing unpredictable pressure differentials inside the carb mouth and more than likely the pods are partially blocking the air ports in the carb mouth too.

Thanks for the science, it's so awesome to understand this stuff. PO did some decent mods and some...not so.

If you're keeping the battery box just go with OEM filters on the OEM h-pipe. They're pricey compared to dirt-cheap pods, my new ones were $34 each, but at least you know they were designed for the bike and carbs, and the carbs are meant to work with them.
As is you're clearly not getting any kind of performance increase.
With the battery box still there you're not really improving the bike's appearance as it's mostly designed as a mount for the stock filters.

Keep it stock and be happy with a decently running bike or go all the way with the hot rod mods.
Take out the battery box. Relocate the battery. Hide the electronics. Put on quality filters with a stock or similar intake tract, and maybe even switch to VM/flat-slide carbs.

Yeah I'm not cutting and welding a new battery box around, PO did enough to 'er. I can't find an h-pipe for cheap and might need to source locally if possible... H-pipe and some K&N's would be tight (both in fit and aesthetic). OEM filters are an option, I dont want to use those big ugle boxes however.

I just want the bike running safely and as well as it can until I could afford to do more or trade up for more power.

Anyway, thanks for the info and your advice man.

 

[Wolfe_11B]

If you have don't have the money for the h-pipe and stock airbox, you at least need to make sure those filters aren't ones with the lip as mentioned already. If they do have the lip, get to work on cutting it out. At least the carbs will 'work' if you do that, until you can get something better setup.

I'm pretty sure K&N has a filter size that is flat on one side that will clear the battery box at hook right up to the carbs. Might be worth it.

Regardless, you need to get something other than those Emgo's. With stock CV carbs, H-pipe with quality filters or stock airbox is the only way to go. We've seen it a million times here, and we all know what works by now.

Something I've done with my watercraft before in a pinch- Do you guys have a Lowes/Home Depot type big box store in Victoria? You could have some fun making your own runners for the carbs instead of buying the h-pipe. Just need some PVC of the same diameter as the carb inlet, then use silicon hose or water hose cut down for coupling, and a few worm gear clamps. Even just a few inches of runner length will makes those carbs much happier, you'd seriously be amazed by the difference.

 

[xschris]

http://www.ebay.com/itm/1977-yamaha...ash=item2a461cbe26:g:ccAAAOSwDN1URbwD&vxp=mtr Here is one on ebay. There are many more.

 

[Wolfe_11B]

That's dirt cheap.

 

[lemonhead]

The nice thing about the stock filters is that when they need replacing, you can just peel the old foam off the metal filter frame and hot glue some new uni or other "bulk" filter foam back on it. Makes for really cheap maintenance in the future.

And, yeah, ebay for used parts is a good way to go.