confused need help with ignition problem

so I have a 1983 XJ750 Midnight Maxim, I'm assuming its an ignition problem at this point, but heres whats happening

so I start the bike it starts on the first crank as always and I get on it and ride it around for about 10 minutes or so and then it just losses all power and dies. I coast to the side of the road, try and start it over and over again for 10-15 minutes and it just turns over but it doesnt start. if I leave it alone for about 20 minutes it will start up fine and I can ride it again for a few minutes then it will have the problem again. this has been happening for weeks. every time I ride

I have pulled the carbs and cleaned them and that didn't do anything. pulled the air filter and that also didn't change anything. put brand new spark plugs in all around. no change. I talked to a mechanic and he told me it sounded like my coil was bad so I tested them and one was out of spec so I bought a new one and replaced that. no change.

at this point im clueless I have done everything I could think of. maybe I am getting a weak spark or something. I don't want to throw crazy ideas out there yet I want your guys opinions on it maybe one of you has experienced the same thing. any help would be greatly appreciated.

 

Could be a number of things. Does it just die or cough and splutter before it dies.

If it coughs and splutters then it could be running too rich. Check plugs and check float levels to start with.

If it just dies then that sound like the ignition module. Check ALL electrical connections for corrosion and clean if required. If the problem still exists then do a search for TCI repair. there is some info somewhere around here.

My moneys on a faulty module but there are plenty of other possibilities.

 

As I was reading my impression was 2 fold,
1) Ign Module
2) Wire problem/pickup/igniter trouble

Good Luck

 

Have a look here: TCI Fix guide

Sounds like a component is getting really hot, maybe the transistors in the TCI.

It would more likely run erratically (or not at all) if it was coil realted.

Only way to really find out if the TCI is bad is by swapping a known good unit.

 

I had an old VW once that did something very similar and it perplexed me for the longest time. It would run fine for days, sometimes weeks, and then all of a sudden it would just up and die. You could crank and crank and it wouldn't start right away, but if you let it sit for 20 minutes or so you'd be fine until the next occurrence. After trying a multitude of things, I figured out what it was. There was just enough sediment in bottom of the tank that every once in a while the fuel pump would suck it up and get clogged. After the car sat for a while the sediment would drain back out of the pump and you could run until it happened again. Too bad our bikes don't have fuel pumps. I think Kiwi is right.

 

Sounds to me like a fuel supply issue. Fuel Bowls getting just enough fuel to keep it running for a while. Check the petcock for a minor obstruction and or the fuel tube that goes up in the tank. It should be connected to the petcock. You may find some obstruction in there. How does inside of the tank look? When I am looking for problems I," KISS" Keep It Simple Stupid. I just have to keep this in mind. Once that is all eliminated then I dive into the more troublesome things.

 

Take your gas cap off the next time this happens and listen for rushing air. Sounds like your tank might not be venting properly, allowing a vacuum to build up and thereby starving the carbs for fuel.

 

I'm agreeing with Samsr and Mac. I think you have a fuel flow issue.

 

Put the Petcock on PRIME.
She if she goes.
Yes. You're vacuum valve is going.
No. You need to scope-out the Petcock Screen and all the Float Valve Filters.

Test the Petcock Vacuum Valve by disconnecting it from the Manifold and placing the line to your lips an taking a slight vacuum on the line ... the Gas should flow from the supply outlet pipe.

In the mean time.
Check the level of the battery.
Get a new Fuse panel in there ... the Old one is on life support.
Pull the Alternator Cover off and measure the length of the brushes. Look for the warning line on the brushes ... measure them; too 11mm min.

 

Any luck? Need more info .
Exactly what have you tried?

Does taking the fuel cap off work (silly vent thing!)?

Does she just die or splutter first?

 

she just dies... no sputtering, I am going to go out and try some of that stuff now, I'll keep you posted

the fuse panel seems to be alright thats one of the first things i checked its got the 4 glass vacuum fuses not the blade kind

 

Thanks.

Those fuse boxes end up giving trouble, only took me half an hour to convert to blade, well worth it. Have a look round the site plenty of fuse box replacement ideas.

 

alright so I pulled the gastank off the bike hung it over a bucket and set it to prime, the gas poured out. I then set it to on and no gas came out at all, I read about testing the vacuum valve. I put it to my lips and sucked and only a drop or 2 of gas came out so I think this means my issue is with my petcock, so whats the next step?

 

do I have to buy a new petcock?

 

You can get kits to repair them. Have a look with the search function and you should find threads about them.

Some people have converted to a manual petcock. You just need one that the holes line up to the ones in the tank.

Take the petcock out (drain the fuel first!) and check that it is not gumed up and that the in tank filter is clean.

You can drive the bike on prime, have a go and see if it still cuts out. If it does not cut out then you have found the problem.

 

I bought one of those repair kits, the quality is way below what you should expect, considering the cost.

In particular, the o-ring that should seal the lever to the tap body was rubbish.

Seemed to have reacted to the gas, when I had to dismantle the whole thing again the next day. What a PITA to get it back in there. You could see all the slack bulging out because the internal diameter of the ring had expanded so much.

 

yeah, before you go rebuilding the petcock or installing a new one that is not vacuum operated, like I did, run the bike on Prime and see if it cuts out. If not, then you know the issue is the petcock.

 

If the part you bought "swelled-up" when it came into contact with fuel ... I'd be looking for my money back.

Without making an indictment ... could you tell us where you bought your's. Other's might be able to side-step the problem.

 

K&L kit, from Sirius Consolidated, via ebay.

If you search - 'best place 2 buy petcock kit' - thread you'll read the posts I and others made at the time. Seems I wasn't the only one with a bad experience of those kits.

 

yeah its runs great on prime although now on prime when it warms up it runs around 3000 RPM's idle, i lowered the idle on it as much as I could so it would still start decent. I think its just running lean. is there any harm riding my bike around on prime?

 

No provided your float adjustments are good and you remember to turn it off when you shut down. You really don't want to run it lean if you can help it. Lean tends to burn valves. Get her richened up for the sake of the motor.