1980 XJ650 Carb Tuning

They work really well. I've had a carbureted vehicle sit for several years with E-10 in the gas tanks (treated before sitting) and it fired right up once the float bowl filled. I even burned through both fuel tanks without issue before putting new gas in. Granted a Quadrajet isn't a Hitachi, but it is just about as finicky.

 

Yup... I have to drive about 30 minutes to get non ethanol fuel and I just fill a couple of gas cans.
If you store your bike for periods of time things have changed over the years with ethanol fuel, now they say to drain the fuel tank and garbs then add two stoke oil or something of that nature to the tank to line the inners to prevent rust.

 

That looks like it is in fairly nice condition, how many miles ?
As you are learning it can get really costly fixing up these older bikes and the parts are getting to be a issue to find on the positive side I believe that it is a healthy fun addition.

 

The one i linked was my fathers bike which is long gone by now. He drag raced it in the philipines on a honda race team of all places. He removed the yamaha badges and wore a honda jacket i guess to disguise the bike. Said there was no other bikes at the time that could keep up with the thing. The bike im working on has just over 20k miles on it. And all i need is stock exhaust pipes and silencers in order for it to be back to the oem look.

 

Alrighty gents! I got the new valves and seats from Len yesterday and installed them into the carbs today. No leak from the carbs! I was able to wet set them all within 1mm of each other fairly quickly without spilling all the gas like before. I got the itch to see how they worked on the bike (No I haven't done the valves yet but I need more money next month to get those parts) because before they were awful. The bike took a minute to start this time, after a few tries I opened the throttle a bit on full choke and the bike fired up. I left it to idle in choke until it died once warmed, this was a good sign because before it ran on choke non stop. Turned it on again, slowly shut the choke off and eventually got it to idle without the choke. The revs hang only a little now, it returns to 1000 rpm in a few seconds. I rode it around the block as I usually do because before this was enough to completely ruin the spark plugs. The bike pops on deceleration, depending on how hard you engine brake, this is a new development but the bike no longer has hesitation or flat spots in the rev range. It pulls all the way through, which it never did before. Came back and let it idle again in the driveway because before it would eventually die when I did this. It would dip a little and come back up in rpms but it didn't die. Pulled the plugs to verify they weren't fouled and all of them were still new looking save for a faint haze around the outside ring. So this is a huge improvement from 3 months ago. The carb pilot mixture screws are exposed and no longer plugged so when I get off work I will make sure these are all set the same. Just looking at them they're all sitting in different positions from each other. I am also wondering if the open exhaust pipe is causing the popping on deceleration. This is why I will be trying to get the OEM or close to it exhaust pipes/silencers. Early next month I will take on the valves and see which ones need replacing, the bike doesn't idle rough and there are no ticking noises so hopefully any changes will be minor. Fantastic way to start today, confidence in this machine is slowly being restored.

 

Could be the exhaust, sucking air in causing the backfire, maybe some other members have been here before ? Glad to here that it's doing so much better!

 

Hogfiddles runs a shim pool on an exchange +postage basis. You won't need to replace all of the shims, just a few.

Popping on deceleration is normally indicative of a too-rich fuel mixture.
Check the valve clearances, note the size and location of the current shims, then contact Hogfiddles to get the shims you need. You will not be able to get a good fuel mixture if the valves are tight.

Another thing. It should never take several seconds for the engine to drop to idle (unless it's rolling). You may have a vacuum leak, or it may be hanging because of the carbs not being dialed in yet (you did a bench synch, correct?). You can't dial them in until you know that the valve clearances are in spec.

And another thing. Shim over bucket valves are supposed to tick. If they aren't ticking then the valve clearances are too tight.

I would recommend not riding the machine until you can get to the valves so you can sort the carbs properly.
You risk damaging the engine if you keep riding it as-is.

 

Of course K-Moe, I couldn't help myself honestly I needed some kind of validation that I was making progress! The bike is already taken apart again and back in the garage. Given the bike's past I would not be surprised if the valve clearances were never checked. The carbs were bench synced but I did not bother with the vacuum sync because I knew it was only going to be together for a short time, basically just verifying I had remedied the most serious issue with the carbs. I was planning on getting the tool to hold down the buckets, a new gasket, and some gasket sealer based off of a good guide that was posted by Fitz. I was planning on taking out each shim and trying to record what number it is (if its still legible). So no worries! I absolutely realize the bike wont run right with bad valve clearances and that's the next step for me which is backwards I know but I just had everything for the carbs first. In the meantime ill compile a list of tools/parts/consumables needed for the valve clearance job. That guide will be invaluable! Also I have to say JHC, I've never worked on a vehicle this extensively before, never tinkered with engine parts, and certainly never cracked open an engine but this has been an awesome learning experience.

 

The valve holding tool:

 

^ tool works well makes an easy quick job.
you will need digital calipers to measure the shims that the mark has been worn or faded
also metric feeler guages

 

I think i actually do have some wire on a spool around. I also have metric feeler gauges but will need digital calipers and hemostats. Just gasket and sealant as well as those rubber donuts on the bolts that hold the cover down. There isn't a ton of space between the valve cover and the frame, I'm guessing I can still remove it but very carefully. Will be interesting to see how crispy the old gasket will be!

 

There is plenty of room to remove the valve cover with the engine in the frame. You might need to remove the horn from the frame (I did to make it easier to pull the cover off).

 

K-Moe exactly, I saw the horn on there and it's gonna have to come off. Alright i'll give the valve clearance reading a shot this weekend, just need the calipers and hemostats. Will report with the findings!

 

Curious what you need calipers for? Also you said you wanted to make all the mixture screws the same. You can't do that by aligning the slots because the threads in the holes will not be the same. The only way to make sure they are the same setting, as a start point, is to turn them in to a light bottom and then turning them out the same amount of turns.

 

I was told to remove the shims and measure them with calipers in the event the numbers are worn off. I did reset the screws, one was higher than the others so i spun them all in and turned 3.5 turns out.

 

It's not too likely the numbers will be worn off but calipers would not be the best choice for fine thickness measurement. You would be better off with micrometers.

 

Ill see if i can spot those at the hardware store this weekend should i find any shims missing numbers.

 

Either works. The shims don't wear in the middle.
You'd be surprised how many shims got installed with the ink-stamped numbers facing up.
About 10% of my personal stock have my handwritten numbers on them.

 

Baseline is 2.5 turns out, with most ending up between 2.75 and 3.00 turns out.

 

Thanks K-Moe, will correct them a turn in tomorrow. 3.5 was what some of them took to spin back in. I have wire and feeler gauges so at minimum i should be able to read the shims tomorrow and post results.