Wr450 AIS problems

I bought a stock wr450 two years ago that I uncorked right away. I had the AIS blocked off properly and the right jetting to match. I think that somehow when i was switching between high and low elevation jets, the cap on the vacuum line came off without me realizing and I got it jetted to run pretty well. I have been riding it for awhile without knowing this but whenever it is running there is air being sucked in the vacuum line. When I put my finger over the hole the engine dies immediately. I can only imagine that running the bike without the cap on the vacuum line is a bad thing so my question is, What do I need to do to get it to run while the vacuum line is blocked off? Do i just need to get the jetting and fuel screw dialed in? Thanks in advance!


Cap it off. It can suck dirt in. Put the jetting back to how it was.


All AIS does (did) was 'inject' air into the exhaust for emissions. It in itself, does not affect jetting. But the vacuum port, if left open, is like always having the hot start 'engaged' except it is not sucking in filtered air, it is sucking dust and dirt.

I just took a look at the jets and the main is a 168 and the pilot is a 48. According to the wr jetting database that should be just about right. Any Suggestions?

45 pilot

R&D fuel screw

Smaller main, smaller pilot.

45 pilot

Probably a 160 main, depending on how large a opening you did to the air box.

I always ran a 168/45 on my '07 WR450. Ran it from 3,000-9,500 without any issues. Slight adjustment on fuel screw at the higher elevations. Southern Ca.

I had a Yosh slip-on exhaust, snorkel removed, grey wire removed, AIS removed.

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