A little popping in the exhuast.

Honestly?

Get a manual and learn to work on it yourself, you're about to go broke...

You need a complete carb service, and probably a valve adjustment.

You can't get a good final sync after servicing the carbs if you've got a tight valve or three.

Trying to take shortcuts is not going to work; "running something through it" is NOT going to fix it, and if you're going to pay someone else to do everything that truly needs to be done to make it run 100% it's gonna cost a pretty penny (if they can even pull it off.)

You've got a plugged carb or two, possibly a few tight valves, and maybe even an air leak somewhere. Keep riding it hoping it will "clear out" and you will eventually damage the motor. Backfiring/popping is a lean condition (or a bad valve) and it will only get worse.

Sorry, but that's the bottom line, and you asked.

 

like fitz says.

pull the carbs off. check all 4 main jets inside the float bowl for plugging. take the caps off and pull all 4 emulsions tubes out to make sure they aren't plugged. take all 4 pilot jets out. inside the float bowl. and take all 4 pilot AIR jets out. located on the rear of the carb where air gets sucked into.

take the floats out so you can access the float seats. pull them out to make sure the screens aren't plugged. if they're still on. put back together and check the float heights. put bowls back on and do a wet fuel test for accuracy.

the last time i had plugged jets. i let boiling water do the trick. good as new.

 

Any idea what the last model year was that Yamaha used this type of carb? I was just wondering how hard it's going to be to order kits.

 

Mine was doing the samething. I did the propane test around the throttle shaft seals and found them leaking. Tore the carbs down again and installed the seals and the popping and backfiring stopped.

 

Once you've torn them apart a few times - how long does it take you now to take them off, clean them up and re install?

 

The shaft seal take alittle longer than the rest. You have to file or grind the screw off on the back side to remove them. the last time it took me about ten minutes to take them off. Then about two hours or so to grind the screws replace the seals and bench sync. ten minutes to put them back on. the first time took them off it took me about 45 minutes then I learned how to do it.

 

Not hard at all: http://www.xjbikes.com/Forums/viewforum/f=23.html XJ4Ever, logo link in site banner or PM member chacal.

 

2008 is still using THAT type of carb.

 

So, like you all said, I took the carb bank off, examined the bowls for dirt, cleaned the jets - which actually looked clean anyway, made sure the pistons 'plopped' down, even switched some jets with a carb that was working good ' just in case'. I redid the compression test with a good quality screw in tester, as opposed to my 40 year old 'push it in hard' type and found the compression was around 150 -160 on all four cylinders. Put it all back together only to have the same cool running cylinder. While I was down in that area, I thought I could hear some huffying coming from the intake manifold. I put my fingers around the connections and low and behold - air leaking like crazy. So the carbs came off again ( I'm getting really good at doing this now that I know you have to pull the rubber throats out of the air box), I pulled the offending manifold to find it only had half of a gasket on it, and the manifold itself had some age cracks on both the inside and outside of the body. I think I've found the problem. My local Yamaha dealer ordered the parts and I should be back on the road again in a couple of days. Thanks to Bigfitz for suggesting I tackle this problem with my manual and not waste any money on shortcuts.

 

My 81 XJ750 dose the same but I get flames, this may be because of the straight pipes its running just a tad rich (195 mains) but im not shore.

 

I did notice that mine was running a bit lean. The plugs were lighter than what I'm used to seeing. The PO put in a K&N filter and a 4-1 exhaust, but I don't know if they rejetted the carbs. I'm not much of a K&N fan, so I'll switch that out soon then see if it makes any difference to the colour the plugs are burning.

 

It will be definitely very lean with will do long trim damage you just need to experiment with jetting and getting it running right.

 

Problem fixed. I installed a new intake manifold gasket and the questionable cylinder heated up the same as the other three. Too bad the yamaha dealer ordered the wrong manifold - so now I'm going to have to take the carb bank off again and put the new manifold on - but I can do that on the next set of rainy days. Thanks guys for all your help