XR70 running rich

Hi,

Thanks for all the helpful info in this forum. With it I have been able to get a 2003 XR70R running again, which had sat stored with gas left in the entire fuel system for 8 to 10 years. The varnish was thick and hard and it took three efforts to get the carb completely cleaned. The tank was a mess too.

 

Anyway it now runs, idles and starts easily enough. It revs, but it is running too rich. There is a little black smoke when it is off of idle, and it does not develop full power. It can be ridden, but it is clear that it is not running correctly. This became especially clear when I shut off the fuel while it was running, and as it is becoming starved for fuel it runs great for a moment before it runs completely out.

 

I have two questions:

 

1. I understand that there is no way to adjust the mixture or the float. Is that correct? The float does not appear to be leaking. It has been dry inside each time I have checked it. Although, several times after getting the carb functioning again, fuel did come out of the over flow, but not continuously, just briefly then it quit.

 

2. When turned all the way in, the idle adjustment screw does not raise the throttle valve needle enough to keep it idling. It was necessary to adjust the throttle cable to raise the needle further to maintain idle. The cable is in about the middle of its adjustment, and I know the throttle valve is up off of the idle adjustment screw inside the carb body. Perhaps this is contributing to the rich condition and something else should be done to address the idle issue. Any advice on that?

 

I'm going out to check the valves now, while the engine is cold. That is the only thing I know I can do that hasn't been done, but I don't think it can have any affect on the mixture problem. Thanks for the help.

There is a fuel/air mixture screw and an isle adjustment on the carb.

I will guess one of two issues. The carb is not fully cleaned and/or the valves are out a bit. Ensure the valves are in spec, then go bacl to the fuel/air and idle adjustment. Try fuel/air out one and half turns to start. Idle screw out a turn. But honestly, make sure thenvalves are in spec first. And make sure you put some play back in the throttle. Basically, get everything set where it needs to be, then start troubleshooting one item at a time. If you adjusting more than one thing at a time, you wont know what fixedmthe problem or made it worse.

Let us know how the valves go.

I will guess one of two issues. The carb is not fully cleaned and/or the valves are out a bit. Ensure the valves are in spec, then go bacl to the fuel/air and idle adjustment. Try fuel/air out one and half turns to start. Idle screw out a turn. But honestly, make sure thenvalves are in spec first. And make sure you put some play back in the throttle. Basically, get everything set where it needs to be, then start troubleshooting one item at a time. If you adjusting more than one thing at a time, you wont know what fixedmthe problem or made it worse.

 

I'm with you on the carb (given the history of the bike) as well as the priority should be getting the basics in order.  But I'll guess something else: dirty air filter.

 

Remove the air screw and give the passage a good blast with carb cleaner from every direction you can.  And a lot of people overlook the valves.  Valve clearance if 0.002 inch on both intake and exhaust.

 

Also, some other things to consider.  Did the needle clip get put back in the correct groove - third from the top?  And one more: did the float get installed upside down?  I can't remember if it's possible on this carb, but it is on others.  Speaking of floats, I've never had one go out of adjustment.  I think it's rare that they do so I would put that way down on the list if the carb cleaning and valve adjustment don't get the bike back in order.  And one more: plugged spark arrestor, which could be possible if it's been running rich for a while.

 

To identify the carb adjustment screws, here's some info.  The throttle stop screw (aka, idle speed screw) will be located on the slide centerline and is perpendicular to the slide.  The air screw will be forward of the throttle stop screw and is about at a 45 degree angle from horizontal.

 

One other thing: are you sure you have the choke in the right position?

Edited by Punkinhead

Yep. That is one of things that didnt even think of but can cause all kinds of heart ache. Check thatfilter and ensure its clean.

Punkinhead,

Go over and check the post aboutnthe kickstarting issues. I think its titled clutch slipping or something.

Thanks for the replies. Rest assured, the carb is clean: ALL parts were removed, soaked in cleaner, all channels were blown out with cleaner and air. The first time we cleaned it, we didn't get it thoroughly cleaned. The second time we removed and cleaned it, it was completely clean, but then sediment from the tank and the dissolved filter screen on the petcock clogged it up immediately. That's when I realized the whole fuel system needed cleaning. 

 

As of the last installation of the carb, we verified the there was only clean, sediment free fuel flowing freely at the petcock, at the carb inlet and out of the carb bowl. That's when I noticed the bowl has a tendency to overflow periodically. I have since noticed it tends to do it at startup and then quits. it doesn't overflow when the fuel is on and it is just sitting not running. Only when I kick it in an effort to start it, then when it's running it stops overflowing. Maybe 1/2 a teaspoon of fuel accumulates under the bike.

 

The intake valve was .004", I reset it to .002". From what I've read .04" shouldn't be a problem. The exhaust valve was .002". Engine was cold.

 

About the fuel/air mixture screw: This screw is set at 1.5 turns out. The channel that this screw sits in flows to the slow jet, so doesn't this setting only affect mixture at idle? I turned it out several turns, and while the idle rpm increased slightly, it did not affect the problem with rich running at higher rpms.

 

I don't know if the float could be installed upside down. Aren't there two plastic tabs oriented perpendicular to each other near the float pin hinge mount that would prevent incorrect installation?

 

I suspect the rubber tip on the float valve pin is deformed. It is so tiny that while I did make sure the pin was clean, I did not know at the time to check closely the rubber tip for proper shape. 

 

In any event, to be sure we have all the bases covered, I have ordered a carb rebuild kit with a float valve, a new float, new jets and an air filter. Should be here next week. With the experience I have now it will require about 15 minutes to install all of that and see how it runs.

There are two screws on the side of the carb. If i remember, the rounded head screw with the visible spring is fuel/air. This will control running rich or lean at idle until you crack the throttle and it starts running off the needle and main jet, and then the main jet. Idle rpm is controlled by the other screw that has a flat head. Turning in should increase rpm, and out will restrict it. On the fuel/air, turned in will make it run ruch, and out will make it run leaner.

Here is a question that has gotten a few people, me included. Is your chocke lever up or down? Just confirm that up will have the bike chocked and down will have it off. I had it backwards when we got our 70 because it is opposite from some bikes.

As for fuel, a carb kit sounds like a good idea. The float needle could have gotten damaged or mis-shaped during that time. And putting in the float upside down can be done, but if i remeber right from experience, it flows out pretty good in that configuration. Just so you know, i still can get a drip from both of our bikes and the 50. Not often, but a little drip from time to time isnt the end of the world.

Yes, the choke had me confused until I took off the air cleaner housing and visually saw that it is backwards of what i expected. I thought it was fairly standard to have the choke handle indicate the position of the valve in the venturi.

 

The round head screw in the center of the carb body, perpendicular to the throttle barrel, simply raises the throttle barrel/needle assembly when it is turned in, thereby allowing more fuel to flow to the main jet when the throttle is closed, in the idle position. If I am understanding what I am seeing correctly, it is the equivalent of simply holding the throttle open just enough to keep the idle rpm where you want it. Turn the screw out, the barrel and needle move down, closing off the flow of fuel to the main jet somewhat, and thus reducing the idle rpm. The amount of air involved in all of this, at idle, is determined by the other flat head screw at a 45* angle. which affects the slow jet.

Carb rebuild kit is installed and it is running like brand new. The throttle cable adjustment is back to it's original position, the idle adjustment works as designed, and it develops good power through the rpm range. It moved my 200lbs fast enough enough that I started getting concerned about how fast I was zipping around with 15psi in the tires. 

 

We're sure that the main culprit was the float valve. The original one did not have the same consistent angle to it that the replacement did. I'd bet that a worn or damaged float valve is behind many cases of running rich on these engines. 

 

FYI: While the float itself can be installed upside down, it is not possible to do so when the float valve is installed. The way the valve mounts in the float hinge requires that the float be installed correctly in order for the valve to sit in it's channel in the carb body.

 

Thanks for all the help.

Be SURE the PILOT JET is clear, the hole is SMALL

Also the Pilot Jet Circuit must be clear, hard to do if it's really clogged bad from sitting a long time.

Pilot Jet is the Idle circuit, engine cannot and will not idle if it's not clear

........Just re-read above, carb "kit" includes new jets, problem solved.....

Also, a LOT of people don't understand how a choke works... you looking inside and seeing how it worked was smart

Edited by arthur6

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