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xr440 jetting in the tropics

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Hello,

 

I currently have a 1997 xr440 in the Dominican Republic.  I'm working hard to reduce the working heat from the bike - it gets dan hot here so I want to minimize impact on the engine.  So far, I've switch to 20w50, dpr9z sparkplugs and wrapped the headers, in addition to all the maintenance and rebuild work that was neglected for so long.

 

My question is jetting. The inside of my engine is black with carbon - partly due to the poor gas quality here but I also think due to incorrect jetting.  This is how I also received the bike. I pulled the carb and the jetting was 145/55.  This is my first time jetting a carb so I went bigger with 162/62, threw a new plug in and went for a ride.  Checked the plug after and it was covered with carbon so running rich.  Question is, should I go back towards 145/55 or start dropping down from 162/62?  Do bored-out xr440s require leaner jetting?

 

I ride at mostly sea level and high temperature/high humidity(and salt) environments with some runs up into the hills.

 

[edit]  forgot to add, it's been opened up with no snorkle, an Uni air filter and a basically a straight pipe that would not be even close to street legal in the US.[/edit]

Edited by Owchimata

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Higher velocity through carb creates more vacuum and may require smaller jets.  

 

Also high compression creates more heat.  You may want to shave top of piston to lower compression.

 

Carbon is normal with pump gas.  I use Techron.

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How did the bike start cold with the 55 pilot? For the high temps and humidity you have there I'm thinking the 55 might have been close, perhaps a 58. But the 145 main seems too lean.

How does the bike run out at half throttle and above with the 162 main? Is it blubbery or does it pull well with power?

In addition to everything you've done to combat heat, I also run the Two2Cool oil additive.

Edited by Trailryder42

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How did the bike start cold with the 55 pilot? For the high temps and humidity you have there I'm thinking the 55 might have been close, perhaps a 58. But the 145 main seems too lean.

How does the bike run out at half throttle and above with the 162 main? Is it blubbery or does it pull well with power?

In addition to everything you've done to combat heat, I also run the Two2Cool oil additive.

 

Higher velocity through carb creates more vacuum and may require smaller jets.  

 

Also high compression creates more heat.  You may want to shave top of piston to lower compression.

 

Carbon is normal with pump gas.  I use Techron.

 

ok, good to know.  The gas here usually contains  a lot of water, especially now during the rainy season.  Shaving the piston will be tough - precision machining in this country is a low priority.

How did the bike start cold with the 55 pilot? For the high temps and humidity you have there I'm thinking the 55 might have been close, perhaps a 58. But the 145 main seems too lean.

How does the bike run out at half throttle and above with the 162 main? Is it blubbery or does it pull well with power?

In addition to everything you've done to combat heat, I also run the Two2Cool oil additive.

Cold start with the 55 was all over the place though I do attribute a lot of that to the worn out rocker arms and cam lobes.  Start of sequence was a little strange.  Decompress and find tdc, put the choke on half and kick 10 times or so to start.  Bike wouldn't start or run on full choke at all with 145/55. I had to leave the idle high to the point of being able to ride in first gear easily while giving no gas and adjusting idle at all would often lead to a bike impossible to start. 

 

Post jetting, with the 162/62, idle is now low.  Start sequence changed to find tdc, put on full choke and kick until the engine almost starts on full choke then change choke to half or off and kick once or twice again to start.  After it's warmed up, only requires a light kick with no choke to restart.

 

With the 162 main sometimes at half throttle it runs great and other times sounds like it's drowning with the latter being much more common until I turned the fuel screw a full turn to the right.  Now, the drowning happens only after it's been running hard for a few hours.

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There's a key piece of info. Extremely worn valve train. Can the valve clearances be set to spec?

A full turn of the fuel screw clockwise would be leaner. How many turns out is it set now? You want it between 1-3 turns out, never more than 3 turns out.

Also, The fuel screw has little to no effect at half throttle.

162 main is too rich I think. Hot humid weather conditions displaces O2 in the air with water vapor which makes a given jetting richer than if it weather was cooler and dryer. So the big rich jetting isn't needed. I think I'd drop it 2 sizes to a 58, leave the needle in the 3rd from top position.

Put a pilot jet in it that gets you 2 turns out, or close to it, on the fuel screw for best idle and throttle response off idle. Example, if after going in that 1 turn on the fuel screw put the screw at 1 turn out from being seated, with the current 62 pilot, then go smaller on the pilot jet which, will require the fuel screw to need to come out more as you go leaner on the jet itself. If you can tune the pilot system with jet size and fuel screw so it runs its best at 2 turns out, then you have a full turn either way on the screw for tuning during changing weather and elevation conditions without needing to change the jet itself.

I would think the 62 pilot is too rich too. It sounds like the tweaking you've done so far is getting things a little better. Just need to do some more.

Cold start with the 55 was all over the place though I do attribute a lot of that to the worn out rocker arms and cam lobes.

With the 162 main sometimes at half throttle it runs great and other times sounds like it's drowning with the latter being much more common until I turned the fuel screw a full turn to the right. Now, the drowning happens only after it's been running hard for a few hours.

Edited by Trailryder42

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The valves can be set to spec.  I do them every 6 weeks or so - at one point, the old rocker arms were so worn the intake and exhaust rocker arm bolts vibrated free a few times(not both at once) during extended rides even after large amounts of red loctite applied.  Such is the price you pay when you spot weld the pads and then grind them by eye to keep the bike running.  Since new rocker arms and cam lobe clean up, this is no longer an issue.

 

I'd say right now, the screw is about 2.25 turns out, maybe more.  Think I'll replace it as it came with half the head missing.

 

Haven't touched the needle - when I rejet, I'll make sure it's the third from top position.  

 

Thanks for your detailed response, especially the effects of hot, humid weather - everyone who deals with heat seems to run XRs in the desert. . Service here is non-existent and/can be very iffy - there aren't a lot of people around here with specific XR knowledge and parts.

 

I'll order 158,160 mains and 58, 60 pilots, just to be on the safe side.

 

 

 

 

 

 

 

 

There's a key piece of info. Extremely worn valve train. Can the valve clearances be set to spec?

A full turn of the fuel screw clockwise would be leaner. How many turns out is it set now? You want it between 1-3 turns out, never more than 3 turns out.

Also, The fuel screw has little to no effect at half throttle.

162 main is too rich I think. Hot humid weather conditions displaces O2 in the air with water vapor which makes a given jetting richer than if it weather was cooler and dryer. So the big rich jetting isn't needed. I think I'd drop it 2 sizes to a 58, leave the needle in the 3rd from top position.

Put a pilot jet in it that gets you 2 turns out, or close to it, on the fuel screw for best idle and throttle response off idle. Example, if after going in that 1 turn on the fuel screw put the screw at 1 turn out from being seated, with the current 62 pilot, then go smaller on the pilot jet which, will require the fuel screw to need to come out more as you go leaner on the jet itself. If you can tune the pilot system with jet size and fuel screw so it runs its best at 2 turns out, then you have a full turn either way on the screw for tuning during changing weather and elevation conditions without needing to change the jet itself.

I would think the 62 pilot is too rich too. It sounds like the tweaking you've done so far is getting things a little better. Just need to do some more.
 

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When you replace the fuel screw, would be good to replace its o ring too. In fact, wouldn't hurt to verify that its current o ring is in good shape or if its even in there. If its in bad shape or missing, you'll never be able to tune the pilot system and it will have a bad effect on the rest of the throttle range too.

Be sure to check the tip of the screw to see if its pointed end is damaged or broken off. We've had guys around here whos screw tip was broken off and stuck up in the passage. Never could get the tuning right until they figured it out.

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