My 1983 XJ750 Maxim Thread

Thought I’d consolidate any more posts about my bike into one thread, seeing that I probably will need about a million posts to get her rolling again.

On that note, I am having issues with cylinder 2, and would like some help. The issue was that cyl 2 was not getting hot (cool to the touch) when the bike was idling, and the bike was backfiring like crazy. That originally led me to believe that it the issue was the carbs.

I just finished rebuilding the carbs (church of clean levels), put them back on, and still no cyl 2 firing. Compression was 125 on that cyl when I checked it a week ago, but I didn’t do the oil test. I also think I left the other spark plugs in while I did each cyl, which probably gave bad readings. There is airflow though the carb, and I can feel on the intake boot that it is sucking air, but no flame.

I hardly know how carbouraters work, but if compression is too low, can that stop it from drawing anything from the carbs?

 

That happened to me once, i found that the spark plug in that cylinder was fouled. I cleaned and it got hot.

 

New compression numbers
Dry Wet
1: 125. 153
2: 118. 160
3: 125. 135
4: 125. 151

 

I had a backfiring issue out the tailpipe after rebuilding the carbs, the idle mixture screw on number 4 wasn't properly bottomed out before I turned it out again, causing a severely Rich mixture .

The newly installed o-ring got caught on the way down causing enough resistance to make me believe it was bottomed out.

First, I tried everything else including Grounds, new fuse centre, new coils, wires, caps, plugs. Resweat the, Suspicious, connections on the TCI, but I think it was ok to begin with.

That's when I thought to check the idle mixture settings again. Made sure they were where I found them and she started without incident. I found mine out 2 1/2 turns when I did the rebuild.

 

To lessen and prevent backfiring through your carbs. A carb synchronization should be done too. But still make sure your idle mixture screws are are where you found them. Check for vacuum leaks. Hopefully you changed the shaft seals on the carbs too. The devil's in the details. That's all I got. There are more knowledgeable people on this forum than me who can help too.

 

I kept the idle mixture screws set still. I do not think I changed the shaft seals. Where are those at? No vacuum leak either, and I have a carb tubing kit, and it was reading identical to the working cyls

 

New spark plugs, and all seemed fine. The problem stuck around even after rebuilding the carb, so I’m not sure the solution

 

Just did a valve check, and exhaust on cyl 1 is 0.001 inches out of spec too small, and cyl 3 is 0.001 inches out of spec large. I think compression may be fine, but I cant think of anything else that may be going on. Maybe something still wrong with carbs? Is there a way to check gas flow from carbs?

 

Since it's backfiring, are you sure it's not a spark problem instead of fuel? Did you ohm the resistor caps? Sometimes those things just go dead.

 

I sprayed starter fluid in the cyl, and it fired right up. I checked the ohms over the cable and they are in spec, and the caps are all good. Was going to replace ignition coils eventually, but they work fine right now. I wonder if it could be the fuel rail in the carbs is clogged. I did forget to check that

 

Check for gas in your #2 bowl.

 

I did take the bowl off and pour gas in the inlet, and gas flowed out bowl 2 when I was testing earlier, I just don't know if it is enough flow. Regardless, I'll check when I get home from work

 

I’m back with another question. Does anyone know if there are exhaust mufflers that work with the 4-1 system that is on my bike? It was out there by a PO, so I don’t know anything about it. My muffler fell off on the highway, and I couldn’t locate it, so I’m looking for any replacements. The outside diameter of my header collector is 2.25 inches, if that helps narrow down the search.