idle problems

[alext]

I ride a 1977 XS400D I just rebuilt both carbs. I have not had them synchronized yet. sometimes it idles fine at about 1200 other times when I'm driving and come to a stop it will get stuck at 2500 or 3000 rpm and stay there despite goosing the throttle. other times it will gradually idle down so low that the bike shuts off. the carb kit came with main jets with fewer holes in them so I cleaned and used the original main jets. any body else have that problem or any suggestions?

 

[Fullmetal]

Sounds like a vacuum leak. How do your intake boots look? Are they dry and cracking? My bike was doing the same thing, found the source of the leak were my dryrotted intake boots. You can find some on eBay for pretty cheap.

I'd get those carbs synced asap, too

 

[xschris]

Sync the carbs with a manometer.

 

[alext]

the intake boots are new as well.

 

[alext]

I'm going to try one of those home made bottle jobs with the tubes.
where do you attach it?

 

[xschris]

http://www.xs400.com/forum/showthread.php?t=5685&highlight=sync+carbs&page=2 This is a good thread for syncing carbs.http://www.xs400.com/forum/showthread.php?t=6050&highlight=sync+carbs

 

[alext]

Thanks again. I will build one in the next day or two and post my results.

 

[jonjkim12]

what's the prevention method for keeping the boots, gaiters, and other rubber parts from cracking?

mine new gaiters are already cracking near the bottom where they're stretched, are we supposed to oil these things?

 

[alext]

the quality of the rubber components used in the past I believe is much better than the quality of the rubber components used today for after market parts. that being said all you can do is try to keep them away from heat. tough to do in cali.

 

[xschris]

With anything made of rubber, avoid water, heat and sunlight. I use Meguiar's supreme shine protectant. It seems to work well on the 35 year old rubber bits on my bikes.

 

[spyro235]

At the risk of sounding dumb, I know nothing about the vacuum system on bikes. My motorcycle is doing the same thing, in addition to a few other problems, but one at a time. How do I check for a vacuum leak?

 

[xschris]

Use some carb spray around the boots and carbs and see if the idle changes in any area. If so there is your leak.