gas leaking from exhaust pipe

Hello my name is Andrew I am in the process of rebuild a 1983 Yamaha xj 750 that I bought a few months ago the bike sit in a garage for about 4 years I have got it to the point of running and was rideable so far I have managed with some searching to pull the carbs off and replace all the jets on my own fix some of the wiring in the fuse box replaced the oil and a new battery as well as had the front fork seals redone along with the front and rear brakes the issue I'm having now is that I ahd some issues with it not starting a week ago so I did the obvious checks first made sure I hade spark and also did a compression test and checked to verify that the battery was releasing the proper volts I fouind my issue to be the fuel petcock so I checked by filling a clean metal coffee can half ful of gas and stuck the fuel line down in it and hit the starter button and the bike fired up but it sounded ridiculously mean and loud blew out a bunch of white smoke and GAS out of the exhaust pipe I immediately shut it off and 4 1/2 hours later it still smells strongly of raw fuel and still has white smoke in the exhaust pipe

 

Did you set fuel levels in your carbs? Do you have any gas in your oil? You need to know for sure first if you're dumping fuel uncontrollably into the engine, as if fuel ends up in your oil Bad Things Happen.

You said you replaced jets. Was that necessary? What jets did you remove, and which did you replace them with? If you're not having fuel just pour through the carbs into the engine, then your carbs are likely just waaaaaay too rich jetted.

Things to consider, anyways, until someone more experienced offers better advice.

 

Hello Andrew - this site will help you.
Winter's questions are good - and there will be more, we need answers from you before we can truly help.

Raw fuel smell from the coffee can? Best I know the 750 has no fuel pump so how did the fuel get from a coffee can into the float bowls? White smoke is usually moisture, not fuel/oil. How much "gas" came out of the exhaust? Usually letting the bike run for awhile 'burns off' the moisture... don't try that yet until we know more.

When you searched for a resource on removing cleaning carbs did you find this?:
http://xjbikes.com/forums/threads/in-the-church-of-clean.14692/

Did the bike run when you bought it?
When you say it is in a rideable condition; has it really be ridden (for how long) since you bought it?

 

I have rode the bike for a month solid when It comes to the carbs I used k&l carb rebuild kits and I used the exact same jet sizes that was already in it just replaced with new their is no gas in the oil I replaced the main jet, the pilot jet, and the float valve and its not a sweious amount of fuel leaking it seems like the bike loaded it self up and just had way to much fuel in it

 

andrew...please answer stumplifter's questions ?

How did you get the gas from coffee can to float bowls ???

Did you rebuild your carbs with regards to "Church of Clean"

We are trying to help you here

 

Is there fuel leaking out of the carbs into the engine (or into the air box) at all when the engine isn't running?

 

No fuel in air box or on top of the engine

 

No I did not use church of cleans rebuild guide to do it I talked with a guy who runs a motorcycle repair shop here in town and he loaned me a manual and gave me a lot of tips on removal rebuild and re install and as far as getting gas from the coffee can into the carbs I just stuck the gas line from the carb into the coffee can hit the starter switch and it fired up and was sucking the fuel out of the can the only issue was that raw unburned fuel was coming out of the exhaust pipe

 

....

The gas line? Or the vacuum line? The gas line doesn't suck, it's gravity fed. The vacuum line WILL suck, but that'll just dump raw gas into the engine and blow it out the exhaust.

These bikes have vacuum operated petcocks. There's two hoses that go from the carbs to the tank, one carries fuel (but doesn't suck) and one that provides vacuum for the petcock to open (but should not carry fuel).

Definitely sounds like you used the wrong hose.

 

There is no way that fuel can be sucked into the carb float bowls from a coffee can. The fuel has to be gravity fed in order fo the float bowls to fill.

 

ok so upate as to where I am at now in my crisis Wintersdark you was correct I had used the wrong hose I took the bike to a local motorcycle mechanic here in town and his conclusion was that I needed to overhaul the engine said I had worn out piston rings and a serious knock called piston slap he offered to do the job and rebuild with all new gaskets for around $700 but he informed me I could try and tackle the project on my own so I did I now have the engine completely off the frame and am looking for any kind of a guide or tips as to how about going into doing this rebuild on my own

 

Wow,

Most likely your local mechanic doesn't know shit about these bikes.....sorry, but I am just a little passionate about some mechanic making an off the cuff remark about rebuilding and lead you possibly down the wrong road prematurely.

Did you do a compression test to see what the compression psi was across all 4 cylinders......???

You went from from sucking gas thru the vacuum ports to white smoke & gas leaking from your exhaust pipes to now tearing the engine out of the frame.....

So what made you decide to rebuild your engine.......a local mechanic's advise......did he see your bike and decide it needed rebuilding.....

So you went home & ripped it out of the frame.......so you are 100% certain that it needs rebuilding ??? If you are OK with that, then that is fine......

Just don't rush into a rebuild process if you have any doubts.........second opinions are OK too......

 

I'm going to guess here that an engine rebuild is outside of your existing skill set. That doesn't make it impossible, but it certainly is a complex job.

I'd STRONGLY recommend running a compression test yourself first. As fiveofakind says above, that motorcycle mechanic may or may not know anything about these bikes. Do you know him personally and trust him? What exactly did he do with the bike?

While it's not impossible that your engine needs a rebuild, I'd be strongly reluctant to get into a job like that without knowing it needs it. Rebuilding it yourself won't be cheap either, and that's assuming you don't break anything in the process - the gasket kit alone is going to run you around $150-200, and if you do indeed have piston slap or rod knock, you'll need more parts there too, and that's about as major a job as you can have here. Is it knocking hard when cranking?

Doing a compression test yourself is easy and pretty cheap - a basic compression gauge will run you $20-$30, and will answer the question right there.

I'd say, if you DO have a serious knock issue from the pistons/crankshaft, and you're not very experienced with this sort of thing, you'd be better off just finding another motor. However, don't take Random Mechanic's word for that! Take video of it, and post it here so people can give a listen.

This are 35 year old bikes, and even mechanics skilled with bikes of this era(not many these days) may or may not have experience with XJ's in particular.

 

it will siphone into the carbs if his fuel line was full. as soon as the float drops

 

ok so so just to answer to answer a few of the remaining questions i do trust the mechanic ive known him all my life and he has never steered me wrong before i dont know for sure what all he done to check it for me but he did inform me to do the rebuild so i got on this forum and found a post from cds 1984 in regards to removing the engine and splitting it so far the motor is off the frame the valve cover and head is free along with the jug which revealed to me that i have broken piston rings in cylinder 1 and cylinder 4 do i need to finish splitting the engine to get down to the crankshaft or where should my next step from here be i have labled and bagged every nut and bolt that has been removed from the bike and engine up to this point i just do not know how much farther i need to go also all 4 piston have a big gouge in the top of them how could they get their? do i need to replace them as well as rings? where can i order the pistons and the rings from new and not pre used?

 

Hi Andrew, we love you.......

Oh wait.....sorry----I thought I was on my Xj-owners Anonymous forum

 

Ouch. Well, there's that then.

Chacal here has everything you need, and you *know* you'll get the right (both in fitment and quality) parts from him the first time. Click the "xj4ever" pic on the top right of every forum page to get to his catalog, and shoot him a message - he's awesome, and will be able to get you hooked up.

 

Ok so just to clarify what all I do I need to purchase obviously new pistons and rings and the gasket kit is their other little seals or o-rings I need to replace as well I just want to make sure I cover everything in the first shot

 

You'll be better off (financially) buying a used engine.

 

Who knows. Are the piston wrist pins ok? How about the connecting rods?

As k-moe said, you're looking at a point where it'd be a great deal cheaper to just buy a used motor, as you're basically going to be replacing everything but the cases.

With that said, if you really are into a full rebuild... It's gonna cost you about what that mechanic quoted you, if not more. I suspect if the mechanic does it, it's going to cost more than $700.

You'd need pistons, wrist pins, rings, you'd need to at least hone the cylinder sleeves, maybe replace them if they're damaged. You'd need a full gasket kit (there's LOTS of gaskets and such along the way there, but this should include everything you need gasket and o-ring wise)... It's a lot of money.

Pistons, pins and rings alone:

Note: I'm not Chacal, nor am I a skilled parts guy, I just did a quick search there. I don't *believe* there are aftermarket pistons that are cheaper, but obviously talk to Chacal before ordering anything.

I just bring this up as I have a motor I briefly considered fully rebuilding Just Because I Could then I saw just how expensive the parts are and realised there's no way that's happening. After all, you can pick up an old 750 that's not running for a couple hundred dollars and with a little care get a good motor that way... and a whole bike of other parts in the process.


With all the above said, if money is not an option, and you'd love a fully renewed powerplant (or even overbored, as that's an option if you want) and are really into the work, by all means make that old engine new again

 

Did you by chance record your compression numbers?

Posting pictures of the damage (rings and pistons) could be helpful just in case something is being misinterpreted. Maybe some pics of the bike itself also as it may have just become a parts bike and you might be better off finding another to restore.

+1 on getting another motor if the rest of the bike is worth restoring.

 

I had 40 lbs in cylinder 1 and like 36 in cylinder 4 but had 140lbs in cylinders 2 &3 will post pictures here in just a minute

 

considering the prices that you just showed me I think ill just stick with the simple and buy a used motor and have it checked by the mechanic here in town before I go any farther with it and then take a year to rebuild the one that I have and then swap for the new power plant thank you everyone for all of your input and advice will continue using this site

 

Andrew, we really do love you and want to help.

However your mechanic... you need to say goodbye, especially if he allowed/ recommended that you put new jets into your carbs. Unless damaged by the previous owner jets never wear out... just sayin'.

Others have mentioned this and I will be redundant with a message using different words:
Mechanics get paid to fix things, the quicker they can fix your bike the quicker they can move to the next one and keep the benjamins flowing. You want your bike to be safe and reliable, your mechanic wants it to ride out the door. It is in your best interest to read this carefully: http://www.xjbikes.com/forums/threads/the-information-overload-hour.27544/ click on the links within it. Then know that this large community has members that have "been there, done that" and they can offer answers to questions you have while you make your bike safe and reliable.

 

I agree with k-moe......buy a used engine or a parts bike with a good running engine.....going to be real expensive the rebuild way....but if money is no object.....then it is a done deal....

 

I really just want to find another engine I made a thread In a different forum about searching for an engine and now I'm just hoping someone has one laying around from an old parts bike or something