Bike takes forever to warm up

Hello,

Short time lurker first time writer. Well I have a 1982 xj750j, for the most part the bike runs great. The only problem that I can tell is the idle. When I start the bike up it fires right away and idles up with the choke on. I adjust the choke to get a good rpm and let it warm for a bit then close it, but not all the way if I do that it wants to die, it does not die just wants to. If I run it for 15 to 20 min then I can close the choke all the way and it will idle fine. When I first fire it up I can smell unburnt fuel and when I pull the throttle just a little it does not idle up immediately, but instead it kind of ramps up then reaches the rpm that that the throttle pull should have kida like it's choking then starts running right. If I pull the throttle good it responds great. Also at low throttle it first gear it runs kinda choppy.

The bike runs great except for at low rpms at an idle and in first gear. Does anyone have any suggestions on how this could be fixed?


Thanks,
Qualm

I am pretty new to bikes I have only owned this for a short time and it's my first. So far pretty easy to work on. I am going to attempt to change the rear brake drum soon as I can't stand the squeaking.

 

sounds like one of your cylinders isn't firing. with a cold engine, start it and hold your hands on all the header pipes and see if they're all getting hot at the same time. If this is true you'll have a fuel or air issue on that carb

 

Well it seems that you are correct. I held my hand on all of the pipes and the 3rd one from the left, while sitting on the bike, did not get hot like the rest of the pipes. The other 3 got to hot to hold my hand on, at the top by the engine, for more than a few seconds but the one that I mentioned above did not get hot enough to force me to remove my hand until it began to heat up because of the engine.

What would be my next step?

Hook a hose up to the float bowl and see if it is getting gas?

Thanks
qualm

 

Swap the plug in #3 (the cold one) with #4 and see if it follows the plug - could be gas or could just be a bad plug....

 

Well I tried what was suggested and it appears that I was wrong on my diagnosis. All of the exhaust pipes heat equally. I have checked the exhaust pipes 3 more times and they all heat equally. I believe that I have carb problems. Not really sure what is wrong it just runs like crap at low throttle pull and appears to be missing. The idle is rough and choppy not like it should sound at all.

Maybe a carb rebuild will clean it up?

Thanks

 

was the bike ever running good? tell us the history best you can

 

Carb cleanups that are done properly do wonders for your bike. You're gonna want to set float levels, bench sync the carbs, and set mixture screws to 2.5 turns. Then after installed again after cleaning, you're gonna need to sync and Colortune. That'll be the BEST thing for your bike. She'll really appreciate it too i promise.
I mean, if you havent cleaned the carbs yet this would be a great oppurtunity
-Chris

 

The bike has always been running like this. I bought it from a friend that just drove it for one summer. He bought it from a guy who had it in his garage for who knows how long. I believe that the guy that my friend bought it from wrecked it and then never drove it again. The tank has a dent, left turn signal is duck taped on, and the handle bars are slightly tweaked. When I got it 2 years ago I changed the oil, spark plugs and had an acquaintance go through the carbs to clean them. When it came back from him the bike ran the same no change. This year I pulled apart and cleaned the master cylinder, for the breaks, and replaced the front brake pads. I will do the rear drum soon. Other than that I have just drove the bike. It fires up every time, unless it has been sitting for more than 4 days and in that case I have to turn it over for a bit and wait then repeat till it fires.

 

Sounds like its running lean when cold. Could be some junk in one of the pilot circuits or maybe an air leak around one or all of the carbs. Also check that the air cleaner is seated right in the airbox and that the foam gasket is in place. What do your plugs look like as far as color goes?

 

I had the same problem but it wasn't a major deal. I simply left the choke on enough to keep it idling at 1050 and took off like always. At first it seemed to take about half a mile before I could cut the choke. NOW I can cut it off at the stop sign about 100 yards from my house.

 

Yeh mines a little worse than that and it runs rough. I have to leave the choke on for about 5 miles or so, or 10 min of driving before having the choke open has an effect on my idle.