Help 1982 Maxim Xj750 wil not start.

Hello everyone,

I have not posted in a long time. I ride a Yamaha Venture but my son bought a 1982 Yamaha Maxim a few years ago. It will not start.

He has never really rode it and it was about a year ago the last time it was ridden. Well I guess everyone knows what happened. It will not start. It will turn over but it will not fire or even try to fire.

I know nothing about working on a motorcycle but I took the carbs off. It was completely gummed up. I took the diaphragms and needles out and I cleaned the needles. I pried the float needles out and go new ones and cleaned the valves out. The replacement needles are for the 1982 maxim according to the retailer but they are very slightly longer. I don't know if this will affect anything or not. I cleaned the holes out on the main and pilot jet screws and the main jet nozzle. I don't know how to get the starter jets out or clean them and I don't know how to get the pilot jet out to clean it. I have not cleaned the cold start plungers either.

I have check for spark by holding a screw driver inserted into the spark plug wire next to a piece of metal and all 4 spark plug wires seem to getting power from the coils. The spark plugs are all covered with black dry carbon covering. I have checked the gap and blew as much of the carbon dust off as I could.

It ran when we parked it but now it will not even start to crank. It just turns over. When I spray started fluid into the carbs it will fire up for a split second and then will not fire again unless I use the starter fluid again.

I have the bike sold if I can get it running.

Does anyone out there have any suggestions? I don't have any testing equipment.

Thank you,
Harry

 

I'd recommend visiting the church of clean http://xjbikes.com/Forums/viewtopic/t=14692.html for info on how to clean the carbs out properly. They really do need to be as clean as all that, not just the bits you can see but also all the inner drillings you can't & the emulsion tubes etc so you need to follow the thread, even though it is very long (it's long for a reason). Also I'd recommend buying any spares from Chacal (the poster of that thread & our supporting vendor) as his parts are guaranteed to fit properly & they actually work unlike a lot of the Ebay specials etc.

The float needles you got sound like many "replacement" ones you get with cheap "repair" kits & the longer length will affect the amount of fuel in the bowl (float height) for the worse.

If you don't have the equipment or the inclination to do it properly I'd recommend selling it "as is" because attempting to do a "quick fix" on the carbs could not only yield no result, but easily make things worse by stripping screws or breaking float pillars.

You don't need a lot of kit (or even skill) to do the actual clean/rebuild, just patience, time, a set of JIS screwdrivers & some clear tube. but you do need to get the valves in spec (feeler gauges) and sync the carbs once it's running (manometer, you can make your own if you don't want to buy one, details are in FAQ as I recall.

 

Thank you very much for the help and the link. I will read it before I decide whether I should try to clean it or sell it as is.

 

Beyond cleaning, if you're replaced the float needles with non-identical ones, the float levels will need to be accrately wet-set or the bike will likely not run.

That and you'll need to do as accurate of a bench sync as possible. To get the bike running 100% properly, a vacuum sync would also be in order, but for that the valves need to be in spec.

 

Thank you. I have contacted the manufacturer of the float needles. They say they are the proper ones. The body of the needle is .25mm longer than the old ones. I did not replace the float valves. I think I will order a kit that contains the gasket, float needle, float valve and an "o" ring. I don't know what the "o" ring is for as I have not found an "o" ring in the carb.

 

The o-ring is for the pilot mixture screw, if it's tiny. There's one, with an equally tiny washer, on each pilot mixture screw. Quite often, they stay behind and have to be carefully extracted.

If the needle valves are different, then as I said, the float levels will need to be re-set. "Wet-setting" is the most accurate and foolproof way to do this.

Float levels: http://www.xj4ever.com/setting%20fuel%20levels.pdf

 

that o ring is literally the size of this --> o

 

Thank you both. I am still reading the link on rebuilding the carbs. Are the pilot mixture screws you are referring to the ones that you have to drill the tamper proof cap off?

 

The "o" ring that is in the kit is much larger than the "o" ring you are talking about. I will try to show a picture of the kit. Where do you get the tiny "o" ring you are talking about?

I don't know how to add a picture. I tried.

 

Could be fuel rail o ring possibly, you'd need 6 of those... Chacal has everything you could ever need for the XJ as I said, I recommend him because he's so supremely helpful also & will ensure you buy what you *need* not what he happens to have in stock that "will do the job" like some

Yes the pilot screws are the ones that sometimes are hidden under caps (sometimes not though, you may be lucky!) right next to the cold start plungers, facing upwards.

Oh, and if you add your pics to photobucket you can just copy/paste the IMG link from there to make pics show

 

Thanks! My carb does not have the tamper proof caps on it. I have a spare that does have the tamper proof caps. I took the pilot screw out of one of the carbs. I'm using it as a test dummy since I already broke one of the post that hold the float up when my socket slipped. I have it repaired with JB waterweld that says it is for repairing fuel tanks. If it doesn't hold I will replace it with one off the other carbs. I have not looked for the venders since I am trying to learn about rebuilding the carbs. Seems like every time I turn around I'm chasing another link to another part of the carb.

I don't have photobucket but it looks like I need to get an account there. I also either dropped the "O" ring or it did not have one. I don't know how important that tiny o ring is but I don't see it in the hole and it is not on the pilot screw.

 

THe o-ring could be down there even if you don't actually see it. Gently poke in there with a metal pick or even a tooth pick (like a round sturdy ones they have in restaurants), you could fish out the o-ring and the small washer at the same time!

 

Small washer? What small washer? I have the Yamaha XJ650 & 750 Fours for 1980 to 1984 Owners Workshop Manual. It does not show either one on page 126. That is how I found the pilot screw. I probed around with a pick and a flashlight but I did not see them but I will look again. I can not find Chacal's vendor store. Does he have a vendor listing?

 

The washer is as small as the o-ring. It sits on top of the o-ring so that the spring on the mixture screw doesn't damage the o-ring.

Dave F

 

Got it. The washer looked like a ledge and was hiding the "O" ring. I was looking for something about 1/4 the size than what they actually are. Now I'm going to do a search for Chacal and see if his site comes up.

After I pulled the carbs again I checked the gas level in the bowls and they are bone dry. The float valves that were .25mm to long must have kept the gas from entering the bowls. Yet when it was mounted on the bike it was leaking gas as gas was dripping off the left carb since it was on it's side stand.

The one carb I'm working on the starter jet hole in the bowl was blocked so I'm sure they all are. Since there is no way to remove the starter jet for the carb is there anyway to be positive it is cleaned out?

Thanks for the help. I'm starting to feel more comfortable now. The biggest problem I'm having is the terms used in the carb rebuild post I am reading. Since I have no knowledge of carbs it is taking awhile to figure some of this stuff out.

 

Probe the tube of a carb-cleaner spray-can in the starter jet hole in the bowl and give it a go. The juice should come out very strongly at the other end of the jet (long tube). If it doesn't, it is not clean enough.

Wear safety goggles, that juice is tough on eye balls!

 

Thanks but I have done that. I can get those clean. It is the brass probe that sticks into the bowl that I am talking about. I sprayed carb cleaner in iti but I can't tell if it is doing any good.

 

Try using either the smallest guitar metal string or a single wire from a wire-brush to poke in the tube to dislodge the crud.

 

Thanks again. I have a set of broaches that I am using. I can check everything with either a flash light or squirting carb cleaner through it and having it squirt out the other side. I read the link on the enrichment circuit and it gives some good information on how to clean it but it does not cover how to make sure it is clean. I guess there is really no way except put it back together and see if it works.

 

Re: Help 1982 Maxim Xj750 wil not start. (THANK YOU!)

THANK YOU! THANK YOU! THANK YOU!

It is running!!! Thank each and every one of you for your advice, links and support in my efforts to get this Maxim running. I could not have done it without your help.

You guys are a wealth of information! It is very generous of you to take time out of your busy schedule to help someone like me who does not know anything about fixing motorcycles.

Thank you again,
Harry