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.

Jason Morris

Now...here are some pictures and comments from my own installation of this mod. The 2nd gen. has vacuum hoses on cylinders 2 and 3 and plugs on 1 and 4. The vacuum hoses actually go to the AIS system so if have disabled the AIS system, you don't need to use the "tees".

Look carefully at this picture and you'll see that one nipple has a hose, the other a cap.

http://www.venturerider.org/jasonmod/jmod1.jpg

In this picture, I have removed the hose and the cap...now you can see the nipples.

http://www.venturerider.org/jasonmod/jmod2.jpg

You'll need a piece of 3/16" fuel line hose about 2 1/2" long with two clamps.

http://www.venturerider.org/jasonmod/jmod3.jpg

Simply insert this short piece of fuel line between the nipples.

http://www.venturerider.org/jasonmod/jmod4.jpg

That's it. Repeat on the other side and you are done. If you have NOT disabled the AIS system, you have to modify this procedure to include a tee. Simple use the Tee to connect the hose that was connected to the one nipple into this crossover. Same on the other side.

Don

My 1200 has a double-jason-mod. At first I did it 1st Gen 1300-style with some improvement, then later on I read that for the 1200 you were supposed to join the YICS outlets together, so I did that this weekend while changing out my breather gaskets. I don't feel a real big improvement since joining the bigger hoses, but I'm going to leave it that way. Both times I had to set my idle speed back down a few hundred revs. For me the improvements were better throttle response, especially off-idle, and the engine just seems to cruise more effortlessly.

Okay, GREAT info guys...

I have both front and rear AIS plugged (Plugging the AIS System) and I have done the "single" Jason Mod (The Jason Mod). Now, what if anything, do I do with the two hoses left over after removing them from their original plug on the manifolds? (I didn't catch that in the write up)

Do I then plug the two leftover hoses together with a union to make a "double" Jason Mod or just leave them hanging?

Thx,

Steve

They no longer do anything. You can just let them hang. Tape up the ends if you would like to...keeps them from getting any trash in them if you ever want to hook them back up.

Thanks Freebird. Just so I'll know... the opposite ends are connected to________?

They are connected to the diaphragm side of the AIS valves that you plugged. They cause the valves to open and close.

Thanks Freebird.!

On my proir bike (VTX) I removed this entire system see link: bareasschoppers.com/desmog/ (Go to Desomg and Pair Removal on left side of page if you want to see it) and put on blocking plates, thereby accomplishing the same goal. The reason for not only "plugging" that system was the possibility of condensation buildup re-entering the engine head.

Because this system is disconnected by plugging, I assume we have no possibility of condensation entering the manifold here. Or to be precise, all we have left are hoses into a diaphragm and then hoses on the opposite side not connected to anything. Is this correct?

Sorry to be a pest, just trying to understand the outcome of this mod.

Again, many thanks for all you help!

Steve

You still have the large hoses connected to the ports on the heads but due to the way they are designed, any condensation would run down and not up and into the heads. I have removed my entire system but that is on my '99 and I certainly wouldn't recommend it to anybody whose bike is still under warranty.

Don

Good info Don. I wish someone had pics of a 1200 mod, and 1200/1300 double mod. I'm getting confused as to which one works or is neccessary. Too much infomation to compute. Are the rubber caps the same one's that are removed to sync the carbs?? -Jack

Yes...same caps.

So.... now all I need to know is will adding the crossover hose work on a 1200, and is it absolutely neccessary to link the YICS hoses??

Ok..I admit it, I'm a Newbie to the Royal Star world.

So with that said: "what is this generation thing?"

I have a 97 RS, 1300cc. So am I a 1st generation RS or a 2nd generation Venture?

Question #2: I went home and looked at my bike only to discover that all 4 ports are capped. I don't see this ignitor hose anywhere.

Does this mean that someone has already disabled it? or could it be stock this way?

Question #3: with the absence of this "ignitor" hose on manifold #2 can i simply crosslink manifolds 1&2 and 3&4?

as always thanks for the help and input.

Ron

When people talk about 1st and 2nd Gens. They are talking specifically Ventures. The Venture was manufactured from 1983 to 1993 and then discontinued. They didn't discontinue the engine and it was in the V-Max and the Royal Star line. They started making Ventures again in 99 and 99 to present is the 2nd Gen Ventures. So I would guess that you'd fall somewhere into the 2nd Gen area.

With all 4 ports capped I'm going to assume that you don't have a cruise control. There is a hose that comes off my front left (as you sit on the bike) intake boot (#2 cylinder). This, I was told, goes to the Cruise control. I'm assuming that, if you don't have one, you don't have a cruise.

I'm thinking that, to do the Jason mod on yours, yes, you would just link the ports on #1 and #2 and then link #3 to #4. Now this is just a guess on my part, but for the most part that's the way it ends up.

Now on mine, with the cruise control hose, I would have to get a T so that I could hook 1 to 2 and then hook the cruise hose in there as well. But then you don't have to worry about that, now do you?

Well I did it and well the hardest part was getting that small piece of hose connected to both ports...they're rather close. I simply connected ports 1 with 2 (Left side) and 3 with 4 (the other side).

I still need more testing, but Trigger doesn't appear to slip the clutch as badly from a standing start and it's, also as if, I don't have to push her as hard out on the highway to keep her at or above the 65 mph mark. but then again maybe it's all in my head (but that's all that really matters now ... right:)).

anyway...no appearant downside to the "jason mod", but then again she's not popping wheelies at this point neither. It's all good!

Thanks again to all and enjoy!

(I'll post again after a good long ride)

Finally had a chance to top the tank off and roll off some miles....[drum roll please]....no change on mpg. Still holding at 42mpg.

verdict: I don't know if it really did any good. Actually thinking about putting the caps back on.

Hope this is helpful.

Finally had a chance to top the tank off and roll off some miles....[drum roll please]....no change on mpg. Still holding at 42mpg.

 

verdict: I don't know if it really did any good. Actually thinking about putting the caps back on.

 

Hope this is helpful.

Thats what I did. I saw no difference except a rough idol.

I had run the mod for several thousand miles then went back to stock. I didnt see any appreciable difference.

Same here. I've removed the AIS but I just capped all 4 ports and removed the mod.

The rough idle would be because you are throwing your carbs out of synch with this "mod". If there were an advantage to this, yamaha would have done it at the factory. The V-max V boost ™ system has nothing to do with what you guys are doing. The V boost ™ system works by changing the intake plenum working area at different rpm vs throttle load points.