'82 XJ750 Maxim, Horrible Idle, Popping on acceleration

Hello All:

I have a 1982 Maxim 750 that starts like a dream, no choke instant cold start, or hot for that matter.

But... It doesn't like to idle very well and when I drive it, it pops and misses on heavy acceleration or cruising, but not on moderate steady acceleration.

About the bike: Stock "original" mufflers, mini pods replacing the air box (done by PO).

It also drinks gas like its going out of style, I haven't driven it much since I got it (3 days ago), but I've already put 3 tanks of gas in it.

Any help would be much appreciated.

***Edit, this shows bike without mufflers, but they are on in now, PO had removed them, I put them back on.

 

Odds are that the bike was not rejetted for the pods or was done incorrectly. PODs are a curse for these bikes as they don't work. They change the airflow into the system far too dramatically and they throw the air-fuel mixture ratio way off. *IF* you somehow manage to get them working okay, the best you can hope for is "normal" performance with a flew flat spots in the acceleration. Search the forum for discussions on PODs, specifically the XJ Mods forum. Read up on the experiences of others.

Your best be by far is to a) replace the OEM airbox (you will need new airbox to carb boots and clamps) and take apart the carbs in order to a) clean them the right way and completely(search "Church of Clean") and b) to check the sizes of the jets and if changed, replace with stock.

My guess is that it is so messed up that fuel is just pouring through (possible stuck/mispositioned float valve?) and that is why you are using so much fuel. Gas only burns when it is atomized in the air, when a vapor. Liquid gas does not burn. So it is probably going out the exhaust.

Running the bike without the mufflers is another good way to make it go crazy and do weird things. The bike NEEDS a certain amount of back pressure on the exhaust. Too much or too little and things start to go wrong.

 

I'll second that ... It is time for carb work. I suspect the float levels are too high and jetting is wrong. You said it " drinks gas" that is a sure sign the floats are too high . I bet if you pull the plugs they are black and sooty.

 

Yeah, if my paint job looked like my sparkplugs, I'd be a happy camper.

 

LOL! Quote of the year so far!! hahahaha

 

How about the MAC 4 to 1 exhaust? I'm already chasing down the air box and located one locally for $15, inquiring about the boots now, but 30 year old mufflers can't be helping and I'm liking the MAC set up for a new system, headers and muffler. Anyone getting good results with that system. I don't want to do any motor mods, but a new stock exhaust doesn't exist best I can tell.

 

You will definitely want to replace the airbox, as this is the cause of most of your problems. Keep in mind you may need to at least unbolt a few engine mounts and rotate the engine a bit to get the airbox in. The boots are readily available new. Don't waste your money on used ones that may be brittle and hard to work with.

While you have it all apart don't forget to clean the carbs as biff mentioned.

If the stock exhaust is real bad don't be afraid to replace it, just keep in mind some mild re-jetting/tuning will probably be necessary.

Oh, and check the valves, they're probably tight.

Some good tutorials here:

http://www.xj4ever.com/

Good luck and be patient.

 

I love the MAC exhaust on my 1100 see Len's thread on upping the jets for aftermarket exhaust. I do run the stock air box and filter and it works real well.

MN