My 1991 Yamaha XJ 900f

Hi Guys

My bike is booked in for an MOT on Saturday. I thought I had it all sorted and then started it half an hour ago and fuel is pouring out of the overflow pipes when the engine is running. I am sure I got the float levels right. Do you have any ideas please, I have run the engine before many times and the fuel was not leaking. Thank.

 

how are the float valve seals? Were they replaced in recent history?

 

No I don't think they have been replace dkavanagh. I have had the bike for about a year had lots of problems getting it ready for the road but it is mechanically very good. I stripped the carbs cleaned them and it was running fine and now this has happened.

 

I am going back out to look at bike just now. I will check what you have stated thanks.

 

There are four narrow tubes coming from the carburetors and one larger diameter tube. Petrol is pouring out of the larger tube. I set the float heights as specified in a Haynes manual. Can anyone tell me what the likely cause of the fuel pouring out of the pipe. When I start the engine it runs for about 30 seconds before the fuel starts pouring out.

 

Someone already did.

The float valve needles are not sealing. There are also o-rings the seal the needle seats to the carb body, and they should be replaced as well. Chacal has some lovely brass float needles that people who prefer such things swear by.

 

Yes K-moe the thing is it was not happening at all and only started yesterday, so I will have to check it out tomorrow. I will fit new float valve seals and hopefully that should fix the problem.

 

Rap the float bowls with the handle of a screwdriver. You might be lucky and only have stuck floats. I would be more confident in that answer if the float needles had already been replaced though.

 

You probably meant "tap", didn't you?

 

Nope.

rap1
rap/
verb

1. 1.
   strike (a hard surface) with a series of rapid audible blows, especially in order to attract attention.
   "he stood up and rapped the table"
   synonyms: hit, strike

Multiple-meaning words are context driven

 

Oh, I see !

 

Thanks k-moe I will try that as I don't think all four carburetors are affected and as the bike suddenly had this problem I think a jammed float is the most likely cause. To be honest I don't know if the carbs have had the float valves etc replaced so I will check this out first to see if the flooding stops. The bike has done approximately 34000 miles to date.

 

It's not the miles that matter with rubber parts; it's the years.

 

Yes got the Carbs off now k-moe the fuel is coming out of the pipe which fits into the carb joints on the right hand pair of carbs near the foot brake the other pair of carbs are not leaking at all. I will strip them down tonight. Thanks again.