I finally made it to New Mexico!... quick jetting question...

I came up from 4100' in Nebraska to 5000' or so in Albuquerque...

 

I am running the Mikuni 36mm pumper... I was not expecting to have to jet...

 

anyone come up a similar amount and have to re jet? seems kinda silly to me but neither my bike or the kids 85 wanna run off choke and/or past about 1/4 throttle...

Edited by delirious_nomad

PS wasn't trying to start another "jetting forum" just seeing if anyone else had experienced the same thing... I would be flummoxed if a 1000' rise on a trail made it behave as such...

I agree, you shouldn't need to rejet, unless your jetting for home is way off. You should always retune the fuel screw tho for the new elevation.

Did you drain the float bowl or idle the bike to run the gas out before the bikes sat for several weeks?

I live in New Mexico as well, work in Albuquerque. My bike (2001 XR400R) came from about 3500ft in Arizona and it runs perfectly here and I live up at 7450ft! Welcome to New MExico!

Unless someone else answers, I would START by tuning the fuel screw, and then dropping (leaner) a jet size on both plot and main and seeing what happens.

I live at sea level and raced my Xr400 at 6000 feet. It did run rich, so I pulled the quiet core for the race. (legal in the race.). Ideally, I should have done some jetting, but there was no time and it was good enough.

Either your jetting was way off or your carbs are plugged up.

I live at sea level and raced my Xr400 at 6000 feet. It did run rich, so I pulled the quiet core for the race. (legal in the race.). Ideally, I should have done some jetting, but there was no time and it was good enough.

Either your jetting was way off or your carbs are plugged up.

Well, I brought my plated XR600R here from sea level (LA CA) and it ran up here pretty good. I DID replace the main with one step leaner but that is it. It ran like a scalded monkey after that but did run fine with sea level jetting.

XR400s are known for jetting all over the map.

96-97 come stock with a 162 main.

98-04 come with a 138 main in Califronia.

XRs seem to run with almost any jetting.

I think the Mikuni is harder to get right. One problem I ran into was the tip of the fuel screw broke off into the carb body. I tried larger and smaller pilot jets, the fuel screw did nothing. Then I pushed out the broken tip and put in a new fuel screw. Now the carb worked as the hole was no longer plugged up. Searching for jetting advice, I ran into the issue a few times.

If you remove the fuel screw, there is a spring, washer, and oring. All may or may not come out when the fuel screw is removed. Make sure to have all the parts before pushing the bike around the garage or put the fuel screw bak in.

 

I live at 7000' and ride all over and never re-jet my pumper.  Runs like a beast on the beach and in Phoenix!

well what the F... the kids bike I can understand but the 400 ought to have been solid... it sat for a month or two prior to moving ( didn't have alot of time to ride with moving and all) it did start up fairly easily but fell right on its face when I dropped the choke...

 

I'll mess with the air screw but... I was to put it mildly shocked... lost a day of riding out west of town and was so wanting to get out...

 

I was working on leaning up the boys YZ85 after having Eric Gorr mill the cylinder base... so I was expecting that...

 

hey does that pumper lose it's prime or something?

I ride XRs from sea level to 6000ft. Usually 5k only needs a mixture screw adjustment unless it is a hot day then also drop the needle one clip.  Above 6k will require a main jet change. The Honda Service Manuals have a section and a chart for changing jetting for altitude and temperature, any dealer can provide guidance.

I ride XRs from sea level to 6000ft. Usually 5k only needs a mixture screw adjustment unless it is a hot day then also drop the needle one clip.  Above 6k will require a main jet change. The Honda Service Manuals have a section and a chart for changing jetting for altitude and temperature, any dealer can provide guidance.

 

not with a differnt carb they can't... 36mm Mikuni Pumper... XRs Only said I'd be good to go up to 11000 from 4100... something is amiss

Maybe change the gas in the tank to gas from albuquerque as in NEW gas? Maybe something that easy.

BTW, delerious, is your XR400R plated, or are you going to plate it now that you live here?

 

It's easy and if yours isn't plated and you want to plate it I can tell you exactly what you need.

The pumper losing its prime is not the problem.

 

What's a shock is that the bike started at all after setting for 2 months. The fuel turns to crap long before that and if the float bowl is left with fuel in it for that long, the small orifices and passages start to varnish over and become occluded. Todays fuel can lose its volitility(ability to give off sufficient vapors to create an ignitable mixture) rather quickly. It's the fuel in the float bowl that the engine has immediate use of when starting and it's the fuel in the bowl that goes bad the quickest.

 

If it's going to be as little as a couple of weeks between rides, keep the fuel in the tank treated with Stabil. After treating the tank fuel, drain and flush the float bowl so it has treated fuel in it.

 

it sat for a month or two prior to moving ( didn't have alot of time to ride with moving and all) it did start up fairly easily but fell right on its face when I dropped the choke...

 

hey does that pumper lose it's prime or something?

not with a differnt carb they can't... 36mm Mikuni Pumper... XRs Only said I'd be good to go up to 11000 from 4100... something is amiss

The Honda Service Manual provides guidance and a chart on calculating percentage jet changes based on temperature and elevation.  The method is based on air density and is also used by race tuners.  Keihin jets are sized based on flow so the method works. If the Mikuni jets are flow sized the method will also work. 

The pumper losing its prime is not the problem.

 

What's a shock is that the bike started at all after setting for 2 months. The fuel turns to crap long before that and if the float bowl is left with fuel in it for that long, the small orifices and passages start to varnish over and become occluded. Todays fuel can lose its volitility(ability to give off sufficient vapors to create an ignitable mixture) rather quickly. It's the fuel in the float bowl that the engine has immediate use of when starting and it's the fuel in the bowl that goes bad the quickest.

 

If it's going to be as little as a couple of weeks between rides, keep the fuel in the tank treated with Stabil. After treating the tank fuel, drain and flush the float bowl so it has treated fuel in it.

Depends on the quality of the fuel. I only use StaBil in vehicles I am not going to drive for MONTHS. As in more than 4 or so. I have found that at least up here, I can leave the same fuel in my tank in one of my bikes over the winter and only start it once a month or so and the next spring it still runs fine. So it can sit for four months easy. He might have other issues but I di suggest what you do, change the fuel and clear the carby!

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