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84 XL250R carb problems

By PrestonMiner,
in XR250R & XR400R

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Apprentice

PrestonMiner

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So I have a 84 XL250R and it’s acting like it’s too rich. Bogging with the twist of a throttle and a little backfire. But the air screw is only turned out .5 the way out. Any more and the big dies and slows down rpm and any more and it dies. The bike likes to run with the petcock halfway between off and on so maybe it’s the float bowl?? Can someone help me out and give some advice? Thanks.

 

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Grand Master

CRF2eR

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Make sure the rubber part of the intake manifold is still bonded to the aluminum part. After time, it can become loose and not seal anymore causing a vacuum leak which can make it run badly. My 84 xr250 had that problem when I bought it 10 years ago. Got a new manifold and it ran perfectly. Luckily new manifolds were still available from Honda back then. Not sure now. 

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Apprentice

PrestonMiner

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Make sure the rubber part of the intake manifold is still bonded to the aluminum part. After time, it can become loose and not seal anymore causing a vacuum leak which can make it run badly. My 84 xr250 had that problem when I bought it 10 years ago. Got a new manifold and it ran perfectly. Luckily new manifolds were still available from Honda back then. Not sure now. 

The intake manifold is in really good shape so it would have to be with the carb itself.
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Grand Master

Trailryder42

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The left carb does. For the way the carbs are timed with each other, the linkage between the two makes one carb lag behind the other in throttle opening amount. So I would think, given the small range that the pilot controls, the lagging(secondary) carb wouldn't need a pilot circuit because the engine and throttle setting of the primary carb is already beyond that throttle range.

The circuit of the secondary carb is probably plugged somehow. Look carefully.

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Apprentice

PrestonMiner

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The left carb does. For the way the carbs are timed with each other, the linkage between the two makes one carb lag behind the other in throttle opening amount. So I would think, given the small range that the pilot controls, the lagging(secondary) carb wouldn't need a pilot circuit because the engine and throttle setting of the primary carb is already beyond that throttle range.

The circuit of the secondary carb is probably plugged somehow. Look carefully.

Okay thanks! So I noticed the secondary carb float was sticking a little and fixed that. And I also heard that the carbs were stock with the needle at the second notch on the needle for emissions, should I lower it to the 3rd like recommended while I still have it off? I’m kinda confused because my bike was acting like it ran rich but minor to no backfire.

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Grand Master

Trailryder42

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10 hours ago, PrestonMiner said:

Okay thanks! So I noticed the secondary carb float was sticking a little and fixed that. And I also heard that the carbs were stock with the needle at the second notch on the needle for emissions, should I lower it to the 3rd like recommended while I still have it off? I’m kinda confused because my bike was acting like it ran rich but minor to no backfire.

What are you calling a "Backfire"? That term gets misused a lot. Do you mean you get a little popping out of the exhaust when riding along and you close the throttle? That usually indicates a lean/dirty pilot system, lean fuel screw setting, bad fuel screw oring, leak in the air diverter(air cut off) valve area.

Setting the needle clip to 3rd from top will richen it. Depends on how much jetting experimentation you want to do. Since the needle overlaps with both the pilot and main systems, it will effect both. Your engine was acting like it was running rich "in what throttle range"?

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Grand Master

Chuck.

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The twin carb XRs are a bit unique to bikes but 4 barrel carbs on cars operate the same way; two throats are low speed and two are 1/2 plus. The Honda just uses two separate carbs for the same compound action; controlled by the linkage. 

The XR versions had lean jetting issues that were easily fixed, don't know about the XLs.

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  • 2 weeks later...
Apprentice

PrestonMiner

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The twin carb XRs are a bit unique to bikes but 4 barrel carbs on cars operate the same way; two throats are low speed and two are 1/2 plus. The Honda just uses two separate carbs for the same compound action; controlled by the linkage. 
The XR versions had lean jetting issues that were easily fixed, don't know about the XLs.

So I took the carb off, cleaned it all, fixed the float and put it back on. Bike started up good but still doesn’t like when I twist it a little over half throttle. Full throttle, no problem, it rips. But it’s only a little after Half Throttle. The only sense I can make out of it is the missing pilot jet for the second carb. since it starts to be used after half throttle. Any suggestions on what I should do? Thanks.
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Rising Star

TexanCRF-250R

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Is this bike new to you?  Has it been sitting for a while or was it being ridden regularly before this problem surfaced?

When did it last run correctly? Any history on when or how this problem developed? This bit of background can help others better help you. 

I wouldn't be moving needle clip positions or changing jetting unless you recently made some sort of performance modification that would warrant doing so or changed the elevation where you ride. 

I'd look for something dirty (which you did with some success) or something that may have worn out or broken. 

Hope you find the problem. Good luck. 

Edited by TexanCRF-250R
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Apprentice

PrestonMiner

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Is this bike new to you?  Has it been sitting for a while or was it being ridden regularly before this problem surfaced?
When did it last run correctly? Any history on when or how this problem developed? This bit of background can help others better help you. 
I wouldn't be moving needle clip positions or changing jetting unless you recently made some sort of performance modification that would warrant doing so or changed the elevation where you ride. 
I'd look for something dirty (which you did with some success) or something that may have worn out or broken. 
Hope you find the problem. Good luck. 

This bike is very new to me, I’ve only had it for a month. Past owner seemed like he didn’t know what he was doing so that’s why I took the carb off and cleaned it all. The needles are left stock, as I want to see if the plugs still look rich after my cleaning.
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Community Regular

honda roboxl

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I maybe out in left field on this BUT I have a 1985 XL250R with the same carb etc. I had a issue on it with starting it cold after sitting for a couple weeks and a bog. Almost like when the second carb was opening up as they do not open at the same time... Anyway. I took off the bottom of the petcock bowl. 10MM and cleaned it out. There was a bunch of crap on the bottom of the bowl. After that. It always started easy and no bog. I know how stuff works and all. I was really surprised that it made any difference but it did. Since then. I can leave it all winter. Turn the gas on. Full choke and it starts with 2 kicks and does not miss a beat. Just fired it up 2 weeks ago after sitting over the winter. Been the same since I cleaned it.

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Grand Master

Chuck.

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I don't know the correct or mod jetting for the XL250s but I do have the 84 XR250R  jetting so comparisons to the XL might be a guide: The mod jetting was to correct too lean factory and did help running.

My 84 XR250R Modified jetting:
….................................. Old…...New
Main Primary:….......108…...102
Main Secondary:…..105…..108
Pilot: …......................... 45…... 50
Needle groove pri:… #2….. #1
Needle groove sec:... #2….. #1
Idle speed 1300rpm +/- 100
Float level 18mm
 

 

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