Bike fires, has spark and decent compression but wont run

Hey guys, ive had this bike for about 6 months now. its an xj550 maxim, ive basically just been choppin up the frame and strippin off useless plastics and parts. now im at the stage where im trying to get the engine running decent. i bought new carb boots, plugs, and rebuilt the bottom end of the carbs due to a stuck float and some rotted out o-rings. with the choke on, the bike will fire forever and ever but it will not start. i pulled the plugs and it seems like its not getting gas. i assume there's a vaccum leak somewhere? i just don't know where to start. i know the diaphragms in the top end of the carbs are probably dry rotted because the bike has been sitting for about 10 years. however, i have no idea where to get the parts for the top end of the carbs. Does anyone know a solution to my problem, where to get parts, or anyone that will do a good job rebuilding the carbs? Any input at all would be greatly appreciated.

 

Check out our resident supplier Chacal, click on the XJforever logo at the top of the page on the right, he may be able to help you.

OR You could always wait until our resident XJ550 guru, Bigfitz also known by some people as the duck. He should be able to help you, as, what he doesn't know about the 550 could probably be written on a postage stamp.

You also need to fill in your location in your profile and also put what bike you have in your sig, it helps us all know where you are (there could be half a dozen members within spitting distance of you, who may offer to come and help in person).

I know you've just told us that it's the xj550, but you still need to put the info in your sig.

 

You also NEED to check your back brakes for delamination (click on the link for bigfitz's delamination post in my post),

Also you need to check your valves are in spec too, as it's pointless trying to get your carbs sorted until you've made sure your valves are in spec.

 

Little trick I learned from an old bike mechanic, get some starter fluid and spray it where you think you may have a vacuum leak. If the engine revs a little higher at any point, theres a pretty good chance theres a leak in that area. Of course, smurf is right, definitely want to check valve clearances first. If one of your exhaust valves is off, it could burn quickly, and if severe enough, ruin your engine. When bigfitz comments on your post, he's going to post that over and over until you do it. (I know because he did it on my topic!) And so will pretty much everyone else. Apparently, its pretty darn important.

 

Thanks for the tips, i'll work on my prof asap. As far as the valves go, do you know where i can find all of the specs for this particular bike? the manual was not with it when i got the bike

 

This may sound like a stupid question but i am not entirely familiar with these engines, but when you say check the valves, do you mean check the clearances between the cam lobes and the tappets? if so all i should need for this is a feeler gauge correct?

 

Yes. If adjustment is required, you'll need to swap to a thinner shim, usually just one size down.

All "airheads" are the same. Intake .11mm~.15mm; exhaust .16mm~.20mm. Use a metric feeler if possible, not an American one with metric equivalents; the math will drive you crazy.

The entire procedure is covered in depth, with pics, here: http://xjbikes.com/Forums/viewtopic/t=14827.html

And Part Deux: http://xjbikes.com/Forums/viewtopic/t=29209.html

Plus you will find all sorts of other good stuff in "XJ FAQ Suggestions."

Let me give you a bit of advice in regard to the 550s: Yamaha went to a lot of work to balance the intake and exhaust with the YICS system to create a bike that was quite a little rocket in its day. In stock tune, the 550 is still quite a quick bike, even by today's standards. The more you modify the intake and exhaust, the more of its performance you will give away. That collector box is a major part of the magic; keep that and the stock airbox and the motor will be a joy, regardless of muffler choice. Put pods and a pipe on it and ya' on ya' own.

 

Thanks a ton! i wish i woulda known that air box bit a little sooner, i already bought pods, scrapped the airbox and modified the exhaust. Probably gonna be kicking myself in the ass for that for weeks to come. So my best option for performance and functionality is to run the stock intake and exhaust systems? Thats what i get for being impulsive i guess but i'm bound and determined to get it running decent by summer.

 

If it's popping and you know you are getting fuel, spark and compression, look under the fuel tank and make sure you have the correct leads going to the correct spark plug coils. If anyone has messed with this it's somewhat easy to get them mixed up when you put them back together. I forget which is to the #1 and 4 coil if it's the orange or gray lead. Just something to check. Look for a wire diagram or Fitz might know.

 

okay, i checked the clearances and they are all withing specs, it is firing in the right order, and the carbs have been gone through numerous times and new parts have been installed however it still seems as though no fuel is reaching the cylinders. the bike pops with the choke on but thats it. i'm starting to think its my intake/exhaust system. there are pod filters on the carbs and the exhaust consists of nothing but the 4 individual pipes at the moment. Is that the cause of my problems?

 

Define "gone through" in relation to the carbs.

Did you wet-set the float levels on each individual carb?

Bench sync? Idle mixture screws 3 turns out to start?

Are you sure the enrichment wells (located IN the float bowls) are clean?

What jets are currently installed? Installing pod filters will require rejetting for them, an open exhaust also adds to the equation. But the engine should at least be able to run. However, because of the pods and the open exhaust, everything else has to right first.

 

By gone through i basically mean cleaned, they have been bench synched, but i have not wet set the floats as i am not sure how to do this. I have soaked the bowls in a parts washer and cleaned them out with carb cleaner but i suppose i cannot be 100% sure that they are clean. Could you give me some directions as to how you wet set the floats? i will clean the enrichment wells again and hopefully correctly set the floats and get back to you with the results. thanks again


The stock jets are still installed, because as you stated i was assuming the engine would at least start with this set up

 

I just read the post again and you stated that you had dry plugs when you pulled them. Are you sure it's getting gas? Open up the #4 carb drain screw first, then put the fuel petcock on PRI. DO NOT SMOKE WHEN DOING THe next step and do it outside. If you have no fuel coming out then you have a problem with your petcock. If fuel starts as a trickle then comes gushing out you probably have a vacuum leak coming from the intake manifold to the petcock.
One nice thing about having pods is that you can remove the carbs in just a few minutes to rejet them

Sean

 

Dinoracer: there is gas flowing from the bowls when the drains are opened, but the plugs remain dry, which leads me to believe its either a bad vacuum leak (but from where i have no idea) or still a carb issue. i think am going to strip the carbs down completely and thouroughly clean them, re-synch them and set the floats. hopefully that'll do the trick.

 

do a forum search on "clear tube method" for the float height tolerances; or look in the service manual (factory and aftermarket books cover it.)

Member schmuckaholic did a PDF of it; look in the list here: http://xjbikes.com/Forums/viewtopic/t=34781.html While it's done on Hitachis, check your book, the Mikuni specs are similar. PM me with your email address if you need the page from the factory book that covers it.

Float levels are CRITICAL; they need to be set accurately and on each carb or you'll have no hope of it running. The Mikunis on the 550s are overly sensitive, I learned this the hard way.

Getting this thing to run right on pods and open pipes is going to be a challenge; the 550s especially don't respond well to massive changes in infrastructure. Not to say it can't be done; but it can't be done sloppily or hastily. Unfortunately it's never going to have the "750 sting" (Cycle Magazine, February '81) of the stock bike.

There's a chart of recommended jetting changes for pods/pipes in XJ4Ever's "church of clean" toward the end of the article.

You said it yourself: THOROUGH. Needs to be your new mantra; and do some research.

 

When you take the diaphragms off next time you pull the carbs, take each one and hold them up to a light. If you get light to shine through at any place on them, there is your hole and you will need to replace them. Were the diagphragms stuck and did you clean and polish them per Ricks write up? Your not getting fuel into the engine for some reason?? Doesn't make sense since you are getting fuel into the carb bowls. When you cleaned the carbs did you pull the jets out? Did you clean the emulsion tubes? How many turns from bottom are the idle mixture screws?
Also check here
http://xjbikes.com/Forums/viewtopic/t=8918.html
Rick's guide for cleaning carbs
http://xjbikes.com/Forums/viewtopic/t=1961.html
hope those help
Sean

 

ITS ALIVE! I got it to start and ran it for about five minutes this afternoon after pulling the carbs cleaning them thoroughly, setting the floats and re-synching. It runs but it runs like shit as you all have mentioned and i expected, however, i would like to think some proper re-jetting will fix the problem. However i may decide to put a set of stock pipes back on the bike because i may not be able to stand riding it as is. The set up on there now is fairly obnoxious and requires the use of ear plugs. I really appreciate all the help guys!

 

Coongrats on overcoming your first hurdle!