miatalaw4u

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Dec 2, 2010
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I have a XR100r and a XR70r that are having the same issues.

The bikes start and run fine when not under full throttle or under a heavy load.

Today I pulled the Carb off the 70r and took it apart. I checked the jets, being that these bikes originally came from the mountains. Both jets we the factory numbered jets. I Cleaned them, along with the rest of the carburetor. I blew compressed air through all the ports and seen no blockage. I did notice that the hole in the slow jet was very tiny and I could hardly see light through it. I reassembled the carb and replaced the spark plug.
I cleaned the air filter also. The bike idles great but still will not rev great at WOT and under load.

I tried riding it with the choke partially on and the problem almost disappeared. This tells me that it is still a fuel / Carb issue.

Do any of you have any ideas? Do I need to soak this carb in cleaner over night? I took wire through all the ports and did not see any issues. Can the slow jet cause this issue or is it mainly for idling.
 

Patman

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It can be a real hassle tring to get those little carbs totally clean, perhaps a soak of a few hours would do it some good. Be careful pushing wire through the ports and jets it can easily scrape things up.
 

Patman

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If the bike is dead stock it should run fine with the stock carb brass unless it's really cool where you are. The little XR's do tend to be a bit lean so going up isn't a bad idea it just seems odd that the bike used to run fine and now it doesn't? Checking the valve clearances is easy to do and can't hurt (unless you botch it up).
 

miatalaw4u

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Dec 2, 2010
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I guess I will buy a tub of carb cleaner from autozone and pull the carb a part and let it soak while I check the valve timing.
From what I read, I need to pull the left side cover off to see the timing mark. Is there anything I need to know about removing that cover?

I will also see if the dealer has a larger jet. I only want to go up one size, right? Factory size is a 60 or 62, so I should be able to go to the dealer and ask for a 63.

Thanks for all the responses.
 

Patman

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A factory service manual would be very helpful for setting the valve lash. No there is nothing special about removing the vocer BUT.... you need to know the specifics of aligning the proper timing marks at the proper part of the cycle. It would also be quite handy for setting the float height on the carb and about a million other things. Biggest bang for the buck of anything you can buy for any bike.
 

miatalaw4u

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Dec 2, 2010
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whenfoxforks-ruled said:
Do not put the aluminum in the cleaner, it will turn dark/pickled. Just the brass parts!

I got my manual in the mail yesterday and it says to put it in carb cleaner. Are you saying it will mess up the aluminum carb if I soak it in it? Anyone else soak there aluminum carb in cleaner? If so were there and problems?
 

whenfoxforks-ruled

Old MX Racer
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Oct 19, 2006
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Verify what jets and other BRASS parts can be removed. The manual should show exactly what can be removed, some carbs are different. One of the many reasons to have a manual, for the specific bike. Some are pressed in, just shoot them, and the aluminum passages clear with a non chlorinated carb spray cleaner/ controlled air pressure. The brass parts go into the vat of cleaner. Turning aluminum,pickled is my speciality. And it ruins your carb cleaner. Aluminum is basically a filthy metal, and nothing will change this.
 

miatalaw4u

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Dec 2, 2010
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All the brass jets are removable. I have taken them off and cleaned them. I think the slow jet is partially clogged and I am thinking about replacing the #62 jet wit a # 63 jet.
I really think that there is a clog or restriction in the main carb housing. I blew air through it and it seemed ok. but after re-assembling the carb it was still having issues. That isd the only reason I was going to soak the housing. Does turning aluminum,pickled damage the carb or just discolor it. I'm not worried about the $15 can of carb cleaner being ruined.
I have two dirt bikes that I have to clean the carbs out of.
 

whenfoxforks-ruled

Old MX Racer
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Oct 19, 2006
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There is nothing I know of, except a fool with a grinder, that can screw up aluminum. It will just make it darker. The next bigger jet from a 62 is likely a 65. They do not go up by 1 number at a time. That number pertains to the orifice size. And it may be something up inside? The slow jet passage is bigger and does bottle neck at the carb bore. If you can force air through back wards would be the ticket? Thats just the way they are, I did not do it. Not to mention the design of the slow jet, that sucker is small! Try not to scratch the bore. It is smaller than the hole in the bore!
 

miatalaw4u

Member
Dec 2, 2010
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Thanks for all the comments. I will pull it apart tuesday and will get back on here and give all of you the results.
I think I will try to adjust the valves while I soak the carb. I will be using GUNK brand cleaner and it says it is safe for all metals.
 

Patman

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I wouldn't leave it in for hours on end either. Just give each port a really good blast of ait and make sure it's clear. I had a similar issue on our XR80 and after several passes with canned Berryman's carb cleaner I took the air gun and stuck the rubber nozzle against one of the port and it final blew out a little piece of crud on to the shop towel. Ran like a champ after that.
 

miatalaw4u

Member
Dec 2, 2010
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Finally got both of the carbs removed and cleaned out. Thanks for all the advice guys. The XR70 runs like a champ and the XR100 has a bog when you first twist the throttle, but once it starts going it runs great.
 
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