XS 400, doesn't start, please need advices

[fede]

Hello at all,

I introduce myself because I am new in this forum.
My name is Federico and I live in Italy.

Sorry for my bad english but we will try to explain my problems.

We are working to restore a Yamaha XS 400 1978 (2A2 model), the father's bike. This bike is older then me (I was born in 1979)......!

I tried to start the bike with external battery but the bike doesn't start.
I disassembled the carburetors and I found inside a lot of dirt like glue.....!
I spent 1 day to clean the carburetors, all the parts: needle, pin....and in the end it was all prefect.

I reassembled everything but the bike doesn't start again. The problem is that not get gasoline in the cylinder, because the spark plug was dry.
I tried to put some drops of gasoline inside the cylinder and the bike started for half second, so the problem is the carburetors.

Do you have some advice to resolve this problem?
I don't have used the original gasoline tank to provide the gasoline at the carburetors because was dirt, but I used a bottle.
It may be that if not using the tank with the depression tap there are problems?

Thank you in advance for your advices.

Federico

 

[waycoolsportster]

Check again to make sure thae carbs a totally clean. Are the float bowls filling up??? Also check the petcock in the tank to see if it is flowing fuel...not sure if a 78 has a vacuum line to the petcock or not so set the petcock to prime and see if there is fuel flowing

 

[Shaun Chandler]

Hi Frederico and welcome to the forum

I'm rather new to the xs400 myself but from just the caruretor end I would say make sure its really really clean. If there was varnish (the glue like dirt you metioned). It is likely all through the carbs. You may want to look into ultrasonic cleaning if there is anyone in your are that does it. The varnish will be in all the passages and you really can't see inside of them.

Shaun

 

[waycoolsportster]

these carbs are finicky little things!!! Can be a real pain...make sure you have fuel feeding them and if you do it's time to pullem back apart

 

[cherokeedad]

Yea like the others have said make sure your carbs are spotless I had to take mine apart 4 times to get them right but there clean now and she runs like a top

Posted via Mobile

 

[fede]

Thank you at all for the advices.

In this week end I will dismount the carbs and I will re-clean all the parts.
I will do a picture of the barbs to show you the condition and to have your opinion. I hope to resolve the problem.

It's very strange because I think have done a very good work and I thought the bike departed without problems.

Anyway I will keep you updated.

Thank you in advance!

 

[bcware]

Using a bottle instead of a fuel tank should work just fine.

Did you remove all pieces/jets from the carbs when you cleaned them? Have you used an air compressor on the passages?

Are the float bowls full of fuel after you have tried to start the bike? You can open the drains under the bowls while the carbs are still on. I open them a very small amount, just enough to see fuel leaking.

 

[fede]

Yes, sure I have dismounted all the pieces/jet and I have used air compressed on any components.

Also I have checked that was fuel inside the bowls, unscrewing the nut below the bowls.

The thing that I'm not sure is the float bowl height. I know that should be 30 mm from the edge carbs.
Before remounting all I have not checked this value.
Tomorrow I will disassembly the carbs and I will check also this.

 

[drewpy]

Ciao Federico

benvenute a xs400.com

yep, Carbs. start again!

 

[fede]

Yesterday I have again dismounted the carbs, because I read on the service manual that there is a little jet below the screw brass screw without hole.

This jet communicates with the minimum circuit, so I cleaned this jet and all the passage.

I remounted all and the bike started very well!!!

I'm very happy, now we can start the restoration of the bike.

I have also seen that the air filter was completly destroyed, so was pulverized.
For this reason I started the bike without air filter and the carburation was not good but I think should be very better with new air filter.

Thank you at all for the advices, and sure see you soon for other questions/suggestions!!