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High idle. air leak or bad throttle return spring?

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Hi, I'm new here, I've been searching around here learning things for the last week and though I'd join. I got an 84 xr350 (dual carb) not running for $500 aud (380 usd). Apparently it'd been sitting for 4 years so I took off the carbie and gave it a clean since it was completely gummed up with old fuel I did notice that the primary carb wasn't returning fully and the spring was a little soft. I found that it didn't spark and cleaned up all of the connections with sand paper and got that working. Yesterday I managed to kick it over and get it started. It was a little rough at first, only just idling then over a minute it slowly revved up and was idling fairly high. When I touched the throttle it revved up a lot and stayed there I shut it off then because I had to go to work. Now today it started up after a few kicks and revved up again, I turned the idle screw so it'd idle lower and it worked a little. I then used my fingers to close the throttle manually on the carb. When I did that it settled right down, down enough for it to stall. I re-set the idle needle and made sure the throttle was closed and it started up and idled really nicely. I decided to actuate the throttle by hand directly on the carb and when I did it sounded like it was alright then I did it again and got some exhaust pops and sounded rather lean. I closed the throttle all the way but it was stuck idling high. That's as far as I got, I feel like I might have to replace the throttle return spring, but I might also have an air leak. It's really eager to rev up and is pretty unstable. This is my first bike so I'm not exactly a master but I kinda know a few things, mainly from RC cars and full size cars. Am I on the right track? Does anyone with more experience and the time to read this essay know what's up?

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20 minutes ago, 1gr8bldr said:

Could be throttle cable sticking???

I don't think so, it was free when I had it all disconnected, the primary carb slide thing (I'm not sure what it's called but it has a big needle in it and lets air in) doesn't close all the way unassisted. I just ran it and let it idle for a while and it slowly slowed until it stalled out. I couldn't get it going again after that. maybe it's a heat problem? I feel like there are multiple problems right now and it's hard to identify them when you don't have much experience with these issues.

Edited by Gandoolf

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I just checked to see what carb you have. The spring for the carb is not over the slide as most  but rather works a lifting shaft. That's the same carbs as my pet bike. I have taken that carb apart over 300 times.  That spring tension will not be the issue. It's fitment very likely is. It should close by gravity alone without the spring. 

Edited by 1gr8bldr

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33 minutes ago, 1gr8bldr said:

I just checked to see what carb you have. The spring for the carb is not over the slide as most  but rather works a lifting shaft. That's the same carbs as my pet bike. I have taken that carb apart over 300 times.  That spring tension will not be the issue. It's fitment very likely is. It should close by gravity alone without the spring. 

so take that assembly apart and put it back together? it was really loose when I had it all apart but as soon as I put that assembly on it it wouldn't fall closed anymore. would that be the only thing keeping it from dropping revs? it seems to be idling a little oddly, like it'll skip a little. that'd be a different issue though.

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Need to get the slide moving as it should then we can see if something else is needed. The fact that it has idle correctly at some point means that it is likely fine. It's hard to adjust an slide stop/idle when the slide is sticking. Did you take apart the top of the carb, where the lifter arm lifts the slide when you cleaned it?  If so, did you remove the arm from the slide? I once turned the mounts that attach to the slide 180 degrees and it was sticking like yours. I also reinstalled the spring in the wrong hooking points before. Also, if the spring does not coil correctly, it will bind up. All this I can do blindfolded now that I know what to look for but those first times are learning the hard way, for me usually

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15 minutes ago, 1gr8bldr said:

Need to get the slide moving as it should then we can see if something else is needed. The fact that it has idle correctly at some point means that it is likely fine. It's hard to adjust an slide stop/idle when the slide is sticking. Did you take apart the top of the carb, where the lifter arm lifts the slide when you cleaned it?  If so, did you remove the arm from the slide? I once turned the mounts that attach to the slide 180 degrees and it was sticking like yours. I also reinstalled the spring in the wrong hooking points before. Also, if the spring does not coil correctly, it will bind up. All this I can do blindfolded now that I know what to look for but those first times are learning the hard way, for me usually

Here's hoping it's fine, it gives me some hope that I'll have it running correctly hearing that you've had the same issues and that you've managed to remedy them. I did take the top of the carb apart and cleaned it, although I didn't thorougly clean where the arm pivots since I didn't have a toothbrush or anything to scrub it with, I was just using a rag. I remember that I put the squared off end of the spring on the carb and the rounded end onto where the throttle cable connects. I'll be able to look at it tomorrow, it's 11:40 pm here and I don't have lights in my shed so I'll take a look in the morning. I did notice that when it's idling, low or high, there's no smoke or anything, seems to be running really cleanly, apparently the previous owner had $1000 worth of work done to the motor having it rebuilt. seems like it's true, at least for now. Thanks for the help by the way, it's greatly appreciated!

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Might not be the exact carb, this is a spare I had lying around...but the spring fitment is likely the same. The coil of the spring also has to lay perfectly. You can press on it around the perimeter as you can reach it and it will sometimes pop, then you know it's seated. When its not seated correctly, the coils don't lay parallel but will have one going under the other and this will not allow it to push inward fully. If the screw that hold the lifting arm to the shaft was forced in without it fully inward, it will bind up. Inside where the plastic washer is, it should have plenty of play. If it's tight then its held off by the spring not coiling flat. Been there

20170327_095930.jpg

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12 hours ago, 1gr8bldr said:

Might not be the exact carb, this is a spare I had lying around...but the spring fitment is likely the same. The coil of the spring also has to lay perfectly. You can press on it around the perimeter as you can reach it and it will sometimes pop, then you know it's seated. When its not seated correctly, the coils don't lay parallel but will have one going under the other and this will not allow it to push inward fully. If the screw that hold the lifting arm to the shaft was forced in without it fully inward, it will bind up. Inside where the plastic washer is, it should have plenty of play. If it's tight then its held off by the spring not coiling flat. Been there

 

So I just spent 4 hours with it, I took the spring assembly apart and it feels loose, it's when I put the throttle cable on when it gets stuck. I cleaned the throttle cable out so that it has very little resistance, however, the cable is bent and slightly kinked in some areas causing a very slight binding, that's enough to stop the slide from fully closing. I'll get a new cable. The carb has spots for two cables though, I only have the pull and there's no space for another cable in my twist throttle on the handlebar. Should I worry about getting both push/pull cables and a new twist throttle? I also ran it until it got hot and stalled like last time, this time I had the throttle cable disconnected so it was fully closed, it wouldn't idle without the choke and when I pulled the spark plug it's really dirty and black, particularly for the short amount of time it's run. It did still spark while hot though so it's not the coil failing.

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Running it on choke will blacken the plug. A lot of people remove the dbl cable system but sounds like yours has had the throttle tube changed as well. There is a round pulley type wheel under a cover on the throttle, cable could be under it rather than riding it. Should be some adjustment on cable free play at the throttle. If it will not idle without the choke, a richer mixture, then this is a sign that the pilot jet is partly blocked.  The pilot jet has several holes, through the middle and the sides. If you don't have proper way to clean them you can buy new ones. You can run a single wire from a wire brush inside but it will never be a true size again, although, almost exact, if you ever want to compare jets relative to each other, it would give a scewed comparison. Once warm most bikes will stall out on choke at idle, to much fuel. I believe that motor is air cooled so don't let it run very long sitting still. Are you sure your spring is right. Mine has so much tension that it would take a knot in the cable to jam it up. It should have a prewind to it

Edited by 1gr8bldr

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2 minutes ago, 1gr8bldr said:

Running it on choke will blacken the plug. A lot of people remove the dbl cable system but sounds like yours has had the throttle tube changed as well. There is a round pulley type wheel under a cover on the throttle, cable could be under it rather than riding it. Should be some adjustment on cable free play at the throttle. If it will not idle without the choke, a richer mixture, then this is a sign that the pilot jet is partly blocked.  The pilot jet has several holes, through the middle and the sides. If you don't have proper way to clean them you can buy new ones. You can run a single wire from a wire brush inside but it will never be a true size again, although, almost exact, if you ever want to compare jets relative to each other, it would give a scewed comparison. Once warm most bikes will stall out on choke at idle, to much fuel. I believe that motor is air cooled so don't let it run very long sitting still

Yes, I'll check that, it's probably what it is, this throttle tube is missing the threaded metal piece that the adjuster threads into so it's not great anyway. I did clean all of the jets and the pilots with some copper that I puled out of some wire I had lying around, but being the genius I am I didn't clean out the petcock or the tank, so it's probably pulled something through, I'll take the carb all apart and clean it as best I can again, I don't have a compressor though so I have to rely on my brand new and unused wet/dry vac on blow haha. It is air cooled, I think the longest it ran was for 10 minutes from cold sitting, hopefully that's not too long.

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Usually cleaning the carb, if it's been sitting, requires the small holes in the mouth of the carb be checked as well. They tunnel back into the jet housings. 

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2 hours ago, 1gr8bldr said:

Usually cleaning the carb, if it's been sitting, requires the small holes in the mouth of the carb be checked as well. They tunnel back into the jet housings. 

I took the carb off and took it apart, all the jets were clean and debris free, there was plenty of fuel in the bowl and there were traces of fuel on the motor side of the carbie. I did however find a spot that there could be an air leak, both of the plastic caps on the top of the carb that cover up the slides have cracks in them, would that cause a problem? I also noticed that when the twist throttle is disconnected from the carb when closed/very slightly twisted it binds up a little, it feels like it's enough to stop the carb closing off fully.

Edited by Gandoolf

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I am not familiar with plastic caps on top, but it could be sucking air there.

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12 hours ago, 1gr8bldr said:

I am not familiar with plastic caps on top, but it could be sucking air there.

They're these ones here. you can't really see well in the photo but there are some small cracks just above the bolt holes. they're very thin but they go all the way through to the other side. is there anything I can do to seal them up? I'm also missing the side plastics, apparently that could also lead to it running lean because the air box lets too much air in.

DSC_0637.JPG

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OK, shaped just like mine but mine is metal. The "suck" pressure here is not a lot due to the air having to go around the slide and through the typical small hole in the carb slide that keeps it from making a vacuum on decent. They are likely cheap, but for now you could put some sort of sealer, like rtv blue.... or typical house caulk for now. But it is likely an insignificant amount. Side plates should not matter at idle as long as you have the filter in place. 

Edit, very little available for that carb    https://www.rockymountainatvmc.com/oem-schematic/5

Is your choke an air restrictor [butterfly] or an inricher? 

Edited by 1gr8bldr

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4 minutes ago, 1gr8bldr said:

OK, shaped just like mine but mine is metal. The "suck" pressure here is not a lot due to the air having to go around the slide and through the typical small hole in the carb slide that keeps it from making a vacuum on decent. They are likely cheap, but for now you could put some sort of sealer, like rtv blue.... or typical house caulk for now. But it is likely an insignificant amount. Side plates should not matter at idle as long as you have the filter in place. 

I wonder why they made these from plastic, it seems like metal would be a better choice. I have some araldite epoxy laying around, I know it doesn't go well with petrol but I don't think there'd be much getting to it since it'd be outside the carb. I know that original Honda replacements are really expensive, I think I saw $200 on a parts list, hopefully I'll be able to find some online. I noticed that one of the bolt holes holding the valve cover in is completely stripped out and the bolt could just fall out, could that be causing an air leak? all of the other bolts are fine and it seems to be held down pretty securely.

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11 minutes ago, Gandoolf said:

I wonder why they made these from plastic, it seems like metal would be a better choice. I have some araldite epoxy laying around, I know it doesn't go well with petrol but I don't think there'd be much getting to it since it'd be outside the carb. I know that original Honda replacements are really expensive, I think I saw $200 on a parts list, hopefully I'll be able to find some online. I noticed that one of the bolt holes holding the valve cover in is completely stripped out and the bolt could just fall out, could that be causing an air leak? all of the other bolts are fine and it seems to be held down pretty securely.

The valve cover is not under compression. No leak issue other than water getting in your oil if you pressure wash it...... but likely even though the one bolt is broken, it's probably sealed. I am assuming your valve cover bolts are not the heads bolts also

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I just looked at schematics of your engine. Your head bolts are under your head cover so your good. 230's are above the cover. Your fine on the broken bolt. If you ever take the motor down, you can back it out of the hole with a left hand drill bit.

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