Runs great except for the idle.

[HappySpottedCow]

I need some help with my carbs on the 1980 xs400. I have cleaned the carbs several times including boiling in lemon juice. They are quite clean, and they smell lemony fresh too. The rubber diaphragms do not appear to have any holes. The inlet rubbers from the carbs to the engine are good. The plugs look good, clean, and not sooty. I have adjusted the valve clearances. The stock air boxes are installed. I replaced the rusted out mufflers with new pipes, one into one, that are less restrictive than the stock ones. I have read that I would have to rejet the carbs. The bike runs well and pulls hard over 3000 rpm. The problem is that the bike will not idle without the choke. When the rpm is below 2000 rpm it is likely to stall. I have adjusted the pilot screw out to 3 turns and the idle adjustment screw is in as far as it will go. When I had the carbs off I did not take down the jet numbers, but I did adjust the float bowl height to 32mm. I have replaced the float valves. I noticed the little rubber plugs that cover the pilot jet are in very bad shape.

My questions are:

1. Do I need to rejet if 3000 rpm or more is running good?
2. Are the little rubber plugs important?
3. Should I be looking at the Starter Jet and maybe replace with a larger jet?

The bike really looks great, but with it stalling at idle I don’t want to take it out in traffic.

 

[Under Dog]

My vote is for dirty carbs. I know you've cleaned them "several times", but not idling without the choke is a strong indication that the pilot jet and associated passage ways are still clogged...

1 - I think you need to get the bike to idle without the choke before you consider rejetting.

2- I think the rubber plugs are important...but I can't remember why. I know mine aren't in great shape, but they still work.

3- I would definitely look at the starter jet and it's associated passage ways... but only to clean them out. I wouldn't replace yet.

 

[Specdog]

Do you have plastic floats? The manual is wrong on the height setting. Go with 22mm.

 

[xschris]

You should have the brass floats for an 80. 24mm-26mm works the best.

 

[Scorpio1963]

On my 82 I have the floats adjusted at 27 so your problem Is most likey floats and you need to to resync the carbs.

 

[HappySpottedCow]

They are brass floats.

 

[HappySpottedCow]

I will have to wait until the weekend before I can get the carbs off. I will readjust the float height and clean everything again. It was idling better at one time, so who knows. Just to be on the safe side I will order those little rubber plugs, new pilot screws, and the jets that have been recommended if things don't get too expensive. Clean carbs seem to be the key though.

Thanks for your comments and help. I appreciate you all taking the time.

 

[HappySpottedCow]

Just a quick followup. I got my parts in, thanks Mike's XS, and installed them today. The bike is running and idling now just great. Not sure what one thing fixed it, but here is what I did to the carbs:

1. Replaced the fuel / air screws. The rubber gasket was missing on one of the carbs.
2. Replaced the pilot jet and upped it one size.
3. Replaced the main jet and upped it one size.
4. Replaced those little rubber plugs, the old ones were like jelly.
5. Adjusted the float level to the correct value.

Not sure if it was one thing, or all of them, but the bike runs great now.

 

[xschris]

Good to hear