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Discussion Starter · #1 ·
Hey all!

I just got an old 1983 XS400R (the Seca version of the XS400) which is loads of fun!

Everything on it is great, but I had just one gripe while riding it home. Whenever I would stop at a light and sit in idle for a while, then try to get going (open the throttle) the bike would kind of sputter and stay at idle speed for a second and then rev up. However, if I just let the engine sit at idle for a few seconds, it would rev just fine.

Any ideas? I was thinking it might be low on oil. Its in a storage garage at the moment so I can't check it, but I can check everything tomorrow morning.

Thanks!
 

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Discussion Starter · #3 ·
Carb cleaning is on the list right behind a full fluid change and replacing the brake pads. I just thought it was strange to see the problem in such a specific incident.
 

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Discussion Starter · #5 · (Edited)
I agree on the old thing, but in comparison to a 71 Mach 3 that I refurbished (and it looked and ran factory fresh when I finished, brag brag) carb problems are...bigger maybe?

Anyways. I have set aside monday for fluid changing, it just got a new battery and cleaning, but one more question. This one is pretty bad (be warned).

I was cleaning it up and I noticed something strange on the bottom of the crankcase. About six inches in front of the gear lever, and a couple inches from the side of the case there is a hole. It just a hole, its smooth, milled, has a lip. I stuck my finger in to see what it might lead to and just ran into some muck (oily dirt and road bits). I suspected that there is something supposed to be in the hole so I referenced my shop manual and some parts drawing, but couldn't find any reference to this mystery hole.

It is not threaded, about an inch in diameter, and in the front left of the crankcase, on the bottom, and has me worried.

Any idea what it is?

EDIT: The oil level is fine, and all the oil filter goodness is there, so its not the filter hole.
 

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Discussion Starter · #6 ·
The hole doesn't seem to go anywhere (just part of the mold I guess) so no worries anymore.

I would like to avoid a complete carb clean this summer (I just don't have a whole day to put into it without being able to get anywhere). So if possible, I would like to tune out the low rpm pull problem.

This is the problem: When opening the throttle after the engine has been idling, the engine is VERY sluggish to respond, but picks up quick afterward.

The problem gets worse as the engine warms up and only occurs after the engine has been idling for 30 seconds or so. Thus I am thinking the idle mixture is rich. The engine accepts full throttle everywhere in the band perfectly. I am a little confused by this one, and very novice to tuning a multi-carb setup like this. Thanks!
 

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Discussion Starter · #11 ·
Just got back from a wedding so I am able to work on it again.

I just changed out the plugs (just part of the checklist) and replaced them with some NGKs (they were NGKs to start with too). Rode the bike around a little and the problem seems to have gone away. Throttle response is still a little sluggish IMO, but I don't know this bike. The throttle does pick up right away from idle, instead of sitting at idle for a second or two like it did before.
 
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