High Idle

This is an awesome site! It has been very helpful. Thanks....

I just got this bike (XJ750 seca '81) about 2 weeks ago. My girlfriend’s dad gave it to me and it sat for about 2 years. At first it didn't start so I had to clean out the petcock and the carbs, get a new battery and sparkplugs, replace the fuse box, and I also changed the oil.

This got it going. It wasn't running too smoothly so I adjusted the fuel mixture on the carbs each at 2.5 turns out. Now it is running much better but when I put in the clutch or have the bike idling the RPM's jump between 3500 and 4000.

So now I have tried to adjust the idle and it doesn't do anything (I am positive that it is the idle). I can't figure out why the idle adjustment isn't working. Any suggestions?.....Thanks

 

Choke control?

 

Check the cable adjustors near the throttle to make sure they are not too tight.

 

I'd be willing to bet that you need to do a carb synch on the carbs. Carbs out of synch will cause a high idle.

Rex S.

 

I know its not the cable or the choke. I will do the carb sync once I get the tools and the XJCD. Any other suggestions in the meantime?

 

I would check the butterfly shaft seals for "old age".

Easiest to pull the outer E clip and remove the plastic washer to have a peek at the outer most o-ring on both outside carbs.

This could give you an idea if the other 6 o-rings ( 8 altogether ) need to be looked at.

I have some pictures of what my o-rings looked like in my gallery.

 

Today I rode the bike around and the idle seemed fine but to get the bike started I had to pour a little gas in the top of one of the carbs (that is the only way I can get it to start sometimes but, this makes it start right up). Anyways I checked out the O rings and they look a bit worn out.... I took a look at your pics thanks! Where did you get your O rings from? Do they need to be a specific type or can I just get some O rings that are the same size?

Also I saw the pictures about setting the float levels, which made me wonder if I could have messed up any adjustments (floats, jets, etc.) when I took the carbs apart and cleaned them out. So since I am going to take them out agian and change those O rings do you recommend changing/adjusting anything else on the carbs?

 

The o-rings are actually a quad ring, and I got mine thru a member that had spares. There may be other members that currently have some. Check previous links to find out where they came from, they have to be purchased in quantities of 50 if I remember correctly. O-rings may work but will have a smaller contact area for making an actual seal to the shaft.

Carbs are made to have the air flow thru specific passages. If you have worn out o-rings, needle valves adjusted wrong, fuel level too low or too high, or plugged passageways, things just won't work right.

You need to dismantle everything, check all the parts for wear, correct sizing of jets, and blow thru the passageways to make sure they are clear.

Here's a link to an article on Hitachi carbs...... http://www.drpiston.com/hitachicarbs.html

Do one carb at a time, take pictures or notes so you can get all the parts back in the correct place.

Old fuel turns into a real mess and can plug up the passageways quite well. After all the rubber parts are removed, you can use a carb cleaner, or a carb dip to try and loosen up the varnish. There is a very tiny oring and washer in the pilot screw adjustment. Try not to poke anything thru the passageways that may enlarge them, be gentle! There is a very small orifice in the bottom float bowl cover, it's in the passage the 1/8" brass tube slides into when the cover goes on the body (opposite side from the drain screw).

Once back together I made a rack to hold the carbs to adjust the float levels as you saw in my pictures. I found it easier than removing them from the bike all the time.

Hope this helps!

 

Thanks! Well I already did all of that and I cleaned them out really well. But I'll try getting the O rings... Does anyone have any of these butterly O rings I could buy from them?