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The Jason Mod

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The Jason Mod

The theory behind this modification is simple. ALL engine tuners know that if you design an exhaust system with the cylinders that are timed 180 degrees from each other to dump into a common collector, there is sizeable increase in efficiency a.k.a. more horsepower. Well the same goes for a correctly tuned intake system. Just look at the V-MAX and you'll know what Yamaha did to increase it's potential. Simply put , this modification is a simple V-boost that works all the time.

HERE'S WHAT YOU DO

1st GEN.1200 - Disconnect the YICS hoses. Then using 1/4" fuel hose connect the two left cylinders together at the YICS spigots(1 & 2). Then do the same for the right side (3& 4).
1st GEN.1300 - Since you do not have YICS, the connections are made at the carb. sync pipes that stick out of the manifolds.You'll need 3/16" fuel hose and a 3/16" vacuum tee. The vacuum tee is because there is a vacuum line connected to manifold #2(left front), which goes to the ignitor box. Remove the rubber caps from the other 3 pipes. NOW using 2 1.5" pieces of hose connect the tee between #1 and #2 manifolds and attach to their pipes. Then connect the hose going to the ignitor so the hose basically goes up(yes the tee is upside down).NOW using a 3.5" hose connect the right two (#3 and #4) cylinders together.>>You're done...
2nd GEN. 1300 - The only difference between the 1st gen. and 2nd gen is the location of the vacuum hose to the ignitor. I think it is at the right rear manifold #3. So the location of the tee would be opposite.

RESULTS

Quicker throttle response at all rpms, especially down low.
More pull at small throttle openings allowing higher gear usage around town.
You'll be able to redline the bike at less than 1/2 throttle in the gears 1st, 2nd & 3rd.
Better gas mileage , usually 5 to 10%
The only negative, a slightly lumpy idle.

I HAVE HAD THIS MODIFICATION ON MY BIKE FOR 50k miles without a problem. Never fouled a plug. In fact my plugs were last changed with 25k miles on them, and they still were good! If your Venture ran good before, then it'll run great now! I could go into more detail as to why this works but lets not get too technical. MY DYNO results speak for themselves 93.2hp@7000rpm and 81.2 ft.lbs.@ 4600- 4900 rpm. You're WELCOME. I am at Americade every year and Hope to go to AMA Vintage Days 2001. Hope to see you all at one of these.

Bye the way mine is an 1987 VR with about 60k miles on it and it was just dyno'd again this past Spring. Please let me know how well this works out for you-all out there. I know it worked well for my local friends.

The 2nd gen. has vacuum hoses on cylinders 2 and 3 and plugs on 1 and 4. This doesn't quite jive with your instructions. Jim Venturer #006
By jason morris on Saturday, November 04, 2000 - 06:18 am: I made a slight mistake.I don't own a 2nd gen. , but friends do. So you'll need 2 vacuum tees , that's all, It'll still work!

Jason Morris

Here are a couple photos of the mod on a 1st generation by Yamahauler that may help.

Last update: 06:48 AM Monday, November 1, 2004

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