New guy with new bike

Ok guys I have been lurking around here for about two months now and its time to say hello. So hello all.

Now getting down to business. About two months ago I bought a '82 Maxim 750, many of the post on this forum helped me with that decision. To start with the bike ran great I couldn't ask for any better. The only thing I saw wrong with it was that it wouldn't idle above 900 rpms.

Then one day while riding through the mountains here in North Carolina I got behind several trucks pulling trailers down the mountain. I basically had to coast down the mountain behind them. Once down the mountain my bike began to run like sh!t. Every time I would twist the throttle it would spit and sputter and finally take off. When I finally got it home it died in my driveway.

About a week later I got the bike out again. When I would take off the bike would spit and sputter and just about die. I then took it for a lap around the block and everytime I would slow down to make a turn the bike would die. So I get it home and pull the plugs. They are all black. So I clean them and take the bike out the next evening. The bike's still not running like it was when I got it, but it is running better.

Well after its been sitting for a couple of weeks I finally get time to get it out again today. I decided to check the plugs again and they are all black once again. I put in new plugs and the bike fires up and seems to idle smoother. Still at around 900 rpms though. Take the bike for a spin and it is definately running better. Then it happens again. As I'm nearing the end of my trip the bike begins to spit and sputter when i give it gas. I'm going down the highway at full throttle in 5th gear and im only going like 45mph at 5000rpms. It does this until it finally dies. I then decide to turn the fuel to prime since the bike feels like its running out of fuel. I give it full choke and she fires right up. I ride the whole way home on prime and the bike runs good. I take another trip later today and the same thing happens again. After the ride I pulled one plug (only pulled one cause it was getting late) and the outside of the plug was black but the tip where it sparks was golden brown.

Sorry for the long post. Does anybody have any suggestions as to where to start?

Thanks
Adam

 

Well, I am almost a complete novice, but it sounds like maybe your choke is stuck open. What you describe is how mine runs when I forget to shut it off ;-)

 

Hi Max, your bike is bogging, which is a mixture problem, having said that, there could be numerous causes, from the slides sticking, split diaphrams, float levels, badly seating needle valves or the pilot mixture screws, which is where I would start, set them @ 2 1/2 turns out from bottom to start, see if that makes any difference.

 

*ignore the man behind the curtain (and this post)*

 

Black plugs = too much fuel. Odd that it runs better with the choke on.

Just to make sure, choke on = lever rotated to the left, 'tucked under' the grip; off = pushed all the way to the right (toward the front of the bike), sticking out.

My though process:
What causes too much fuel? Fuel is controlled by the carbs. Carbs have screws to adjust amount of fuel. That isn't likely to be changed by idling for a few miles. What about the rubber diaphragms? If they are damaged or are sticking they could let too much fuel flow, maybe? Stuck floats could do something similar?

Maybe choke cable is stuck/damaged? Make sure the brass pins on the carbs 'fall down' when the choke is 'off'.

Maybe it isn't too much fuel, but instead not enough spark? With all four plugs fouled at the same time I wouldn't expect both coils to fail at the same time. Maybe poor ground, ignition pickups, TCI? There are test procedures for all these parts.

All of these are just guesses. I have no practical experience to base any of this on. Simply (probably poor) academic knowledge of how these magical machines work.

I would be interested in hearing, from the more experienced XJ-ers, WHY my guesses are faulty (assuming they are).

Good luck!

 

There could be any number of things going-on. But, we'll try an Old School approach to see if we can improve upon your situation.

Locate the Pilot Mixture Screws on your Carbs.

They are all the same.
Located here:


Take a Glass Barrel Fuse
Tape one end so you don't get the ends confused.
On the end not taped ... make a Scribed Mark -- 9/32nds from the end.
This shall be your Pilot Mixture Screw "Depth Gauge"

Place the Scribed end of the Fuse into the hole housing the Pilot Mixture Screw.
Make the necessary adjustment to the Pilot Mixture Screw -- either UP (Out) or DOWN (In) to bring the Mark Scribed on the Fuse precisely LEVEL with the Top Surface of the Hole it is inserted into.

Lets see what happens to the Plugs after we do this.

 

Rick...your double post makes me think you are having similar 'database connection' issues I've had all night. Is this part of the new server?

 

this maybe a shot in the dark, but this helped me when i had an issue with idle and pickup after sitting when i got mine. it ran great for the first few rides then started acting up. i replaced the plugs and ran two cans of sea foam thru it. it's been a year and half with no problems since.

 

Are you saying that the bike runs just fine with the valve on "PRI"?

If so, there are two possibilities:

1 - You're running out of fuel. "PRI" and "RES" pick up fuel from near the bottom of the tank. "ON" gets fuel a couple inches from the bottom. So, if you're low on fuel "PRI" and "RES" would be expected to correct the issue.

2 - Problem with the vacuum petcock or the vacuum line to it. This could cause reduced fuel flow when "ON" or "RES".

 

When I started the bike again I put the valve on "PRI" gave it full choke and she started right up. I turned the choke off and rode the rest of the way home. The bike was definately riding more like it was when I bought it. It had plenty of power and good throttle response. I will definately check the vacuum petcock and line and see if that is the problem. If not I will start working on the mixture screws and see what happens. I will keep everyone posted on what my findings are.

 

Yes, I got the "Database" warning a couple of times clicking on the direct link in my Bookmark Toolbar.

When I opened a link that came in the Email ... the New Page wouldn't open.
I'd just have a Blank Screen.

 

Ok guys so heres a little update on the bike. I ran some seafoam through it last weekend. So far the bike runs 10 times better than it did before. I'm pretty sure it wouldn't hurt to clean the carbs. Im thinking about adding pods and new exhaust when I chop and bob this thing so im gonna wait before I tear into the carbs.