Pilot Jet Setting and Carb Sync

Hello,

I recently bought a 81 xj650 maxim. I bought it real cheap so I knew I was going to have to fix up a few things. The guy who sold it to me told me that everything was in real good shape on the bike (good compression and all that) on the bike except for a few carb related issues. He said the only two things that I would need to do to get it running perfectly(besides basic tuning) would be to get the carbs synced and to do the pilot jet setting. I figured I would bite the bullet and have a dealership do it because the bike was so inexpensive to begin with, and because I don't know enough to do it myself. But when I called them they said they don't do it for those older bikes anymore because it costs too much money and takes too much time(around $900, which i wouldn't pay for anyway).

So here I am, a guy who knows very little about motorcycles, and I need to do these two things myself now. I know there have been articles about carb syncing, which I suppose I will try to figure out, but as for Pilot Jet Setting... I have no idea how to do that. I thought it was a fixed thing, but I could be wrong.

Basically what's wrong with the bike is it doesn't idle well at all (it hunts and I have to keep the choke in just to keep it alive) and it doesn't respond well in the lower gears. Everything besides that is fine, which I suppose isn't really fine at all since, theoretically, one needs to go through the lower gears to get to the higher ones.

Any help on where to start would be appreciated. What things I need to buy, etc.

ps. i'm going to get the xj cd.


Thanks!

 

That dealer is full of shit. You *can* get it done at a dealer for a reasonable price. That being said I admire you're willingness to get your hands dirty.

On with the show. The XJ cd is a great resource - I've seen it but don't own a copy. I don't have a copy either... I do have various shop manuals so I just never had to bite the bullet and purchase it.

A carb sync. What this does is makes sure each carb sends the same volume of gas to the cylanders. Before you go down this road you want to make sure that your carbs are all equally clean. If this bike has sat for awhile then start at the very basics. Is the tank and mostly rust free? Does the bike have a fuel filter? What does the fuel in the bowls look like? What do the plugs look like?

Carb bowls - under each bowl you will see a slot-head screw and a little spigot. If you put a tube ( or a pop bottle onto the first one) and back the screw out a little bit gas will come out. Let it flow out a table spoon or so. Look in the bottom of the container for dirt and look at the gas. Does it look like gas should look like?

This will give you an idea ( and only an idea) of the general shape of the bikes carbs. To get a better picture you'd have to go in and have a look.

So the bike won't work properly at low rpms? His comment on pilot jet would make sense. I forget the RPM that the pilot jets get taken over by the larger volume mains... but it's pretty low. How does the bike behave above 5000 RPM?

The thing with jets and carbs - the smaller the opening the more affected they are by sitting gas (varnishing) and small particles (rust). It's quite possible that you will have to start by very carefully disassebling the carbs ( follow proper directions which I can't give you - XJCD and google might be your friends here!) and very carefully cleaning out the little passages. Remember that carbs have soft rubber bits that don't like cleaner and that the carbs have very soft bits of metal that are very sensitive to scratching.

Once you feel comfortable that your carbs are in good working order it's balancing time. You can create your own hose system or buy a tool to do it. The basic idea is that you balance the carbs in pairs first - making it so that each carb in it's pair has the same pull. Then when each pair is even, balance the pairs. This balances them.

The next step is to go and do fuel mixture. Changing the fuel mixture will effect the balancing so you might have to do a bit of a loop here - balance mixture balance mixture and so on.

Then you should be about right.

Setting jet heights is above me. If it was working properly before, and the carbs are as clean as they were before, and you haven't had significant changes in elevation I don't think you'd need to touch them - but maybe someone else could comment there.

So once thats done - set your idle speed for the last time ( changing the mixture will change the idle speed )...

It is definately a long process - but it's not $900... perhaps there is a knowlegable list member in the area that could mentor you a bit?

I realized I ignored your hunting comment - have you tried spraying something like wd40 around your carb boots when it is running? If it picks up you might find siliconing the boots will solve the problem.

Cheers,
woot.

P.S. We ride the same bike!

 

Well having to keep the choke in (I assume that means on) is clearly an indication of lean carbs. Carbs can be lean from the pilot mixture screws or a clogged fuel filter or dirty carbs. If there is a fuel filter change it , if there isn't, get one. For $2 , best carb protection on the market.
When it comes to carbs the XJCD is worth more than $10. I believe the '81 650 is not a YICS engine so you won't need a YICS tool. A colortune plug is the only way to get the settings right. Other than that you could open the pilot mixture screws 1/2 turn starting at the #1 cylinder and see if it runs better. Opening or turning counterclockwise will introduce more fuel into the mix. If you use a colortune plug which screws into the spark plug hole you can run the engine and look at the combustion. A steady blue color (actually a blue flame) is what you want. If the carbs are too lean then you will get a whiteish blue color or an intermitent flame. Too rich and it will be yellow. This is the only way to set the mixture for certain. You look at the flame and turn the screw in the needed direction in 1/4 turn increments.
A carb clinic in your area would be an invaluable asset. Experienced guys with the right tools and knowledge at your disposal. I think there is one in Vermont every year. I'll check on that. Meanwhile here is a link to DV's colortune web site. Read this several times to grasp it in detail and then buy a colortune plug and have at it.
http://www.surenet.net/~verhey/colourtune/Intro.htm

 

You might also check out the carb boots for cracks, tears and holes. If air is being sucked into the engine without going through the carb it will also cause a lean condition. It also causes the engine to hunt for idle. On bikes as old as ours bad carb boots are a pretty common thing to come across.

Keep digging, for every problem there is a solution.

 

Just to let you know, my bike is also an 81 XJ650, and I got mine for free from the brother-in-law who was about to take it to the junkyard. He could never get the carbs to synch (didn't know the procedure). I started by cleaning out the gas tank (lots of very fine sediment there), cleaning out the float needle screens (all were plugged solid) and then installing an inline fuel filter. Next came the visual throttle plate setup which allowed me to start the bike, and then synched it using a Carbtune II. Worked like a charm! (And I had no previous experience with carb synching). After a Dynojet upgrade, I bought the Colortune Plug and dialed in the pilot jets. Made all the difference.

Good luck - oh, and you can do it yourself.

 

You may want to check out this web site http://www.slygrin.net/xj750/html/carbs.html it’s about cleaning the Cleaning the Hitachi Carbs.

To fix the rubber boots from the air box to the carbs you may want to try using some siliconing as woot stated but before applying the silicone you may want to put alot of Vaseline Petroleum Jelly on the dried out rubber boots while they are off the bike. Let them sit like that for a day or so. This will bring back a lot of life back to the rubber. You can also get the carb boots that go to from the carbs to the engine from http://freedomcycle.ca/ for around $40 bucks.

 

Here's another link to reference for Hitachi carbs.... http://www.drpiston.com/ even though it's a Virago site he gets into carb operation details, repairs, and troubleshooting.
See the links on the left side for CV carburetors, and below that for Hitachi carburetors.

 

My xj650 H 1981 bike does not have YICS. I don't think any of the 81 650's did... for what it is worth


>THREADJACK<
Good to see freedomcycle.ca mentioned - good folks - they're actually building a new shop can't wait to get into it. How are they for shipping - I've only ever delt with them in person.