Quetion For the Techs

[coreyhill]

Hay guys/gals

Just wanting to know if one could use V-maxs 1300 carbs on the VR 1200 motor? Also what is the biggest tire one could put on the rear of a VR1200?

This is for my custom build. Just trying to get a fill for some things I could do.

[bongobobny]

They are pretty much the same carbs but jetted differently due to the compression ratio and hotter cams. Also, the VMax has bigger valves...

 

Your restrictions on the rear tire are going to be the width of the swingarm and the total travel of the suspension in relation to the frame...

 

 

So, to answer, the carbs depend on what modifications you are planning for the motor, and the tire is dependant on what modifications you make to the suspension.

[Condor]

They also have the V-Boost manifold set up that can be wired for manual operation instead of running off the tach.. I think??...

 

OK found this on Wiki..

 

V-Boost is a system that opens butterfly valves in the intake manifold between the 1st and 2nd and between the 3rd and 4th cylinders starting from 5,750 rpm. The valves are opened gradually to match the rising engine speed with a signal provided by the ignition system. The valves are at the full open position at 8,000 rpm. A small black box sends a computed signal to a servo motor that pulls a wire to open the butterfly valves. The V-Boost system adds 10 percent to the top power rating of the base engine.^[10]

[CaseyJ955]

On the carbs there is a minute difference in the barrels as well as jetting, off the top of my head its 34 vs 35mm, so not much but not quite the same. Not sure if it would fit into the intake boots but being rubber they just might. The V4 seems to favor lean over rich, at least in Vmax guise. Im getting my best power out of my max with slightly leaner than stock jetting and free flowing exhaust and intake. I harvested a set of Vmax heads, cams, intakes and Vboost to install on my 1300 Venture but reconsidering since I already have a stonkin' Vmax. If you care for any measurements let me know.

 

With Vmax top end the stock limiting factor is restrictive exhaust, the Venture heads have notably smaller ports, runners and valves, not to mention less aggressive cams. I seriously doubt you will see any gains using Vmax carbs on a Venture mill. In fact maybe it will be counterproductive without careful jetting. Vboost can be added on the otherwise stock Venture but jetting needs change as after 6200 rpm each intake sucks through two carbs rather than one. Main jets should be downsized for this. When I tuned my Max I found the main jets that pulled the hardest and then tuned down from there for idle and midrange. For a bone stock Venture mill I dont believe free flowing exhaust will show any gains and if no vmax components are used yout close to stock jetting should be a great place to start. One thing you will want to take with you going forward is the fact that the stock airbox is quite restrictive, so much so that if you run the bike without it, its gonna run like ****, may not even idle. Since the stock airbox is so bulky and fugly you will probably ditch it for some sexy pod filters. Its still gonna run like **** for the same reason. The fix is a set of air correctors, cheap and easy to install little brass cogs not unlike main jets, they install in one of the small ports on top of the carbs. I sourced mine from Sean at Morleys Muscle but Danny at BRC carb shop is also excellent with these Yammy V4 engines.

 

A few others here have gone down the Vmax top end conversions and may have more info on proper tuning for your speciific goals. My experience is tuning my own Vmax and Venture, but I have not done the Vmax heads on a Venture...yet.

[CaseyJ955]

I forgot, if you do go with Vboost and dont want to manually control it, as I would not, you can use an Ignitek (and maybe other brand) aftermarket TCI. With a readily available Vmax map loaded it can control your Vboost, eliminating the stock Vmax Vboost control module which is finicky on a good day. I put an Ignitek on my Venture in anticipation of the Vmax heads later on and it does have some cool features. Aside from running resistorless COPs for a clean look and ditching the heavy bulky (and old) stock coils you can set a rev limit. It all comes down to how much you want to do, my guess is a stock Venture engine will be plenty potent but its not expensive or difficult to do Vboost and COPs. if you choose to.

[zagger]

I used stock 1200 venture carbs with the Vmax boost valves (fully open, they allow each cylinder to pull from 2 carbs). Rather than trying to install some automatic operation of the valves, I simply operate the boost valves with a bicycle shift lever mounted on the end of the left handlebar grip. Since the shift lever has 5 positions between fully closed and fully open, it is possible to just leave it partially open if that seems to help the engine. My venture runs best when the boost valves are left open just one "click". Unless the engine rpm's are quite high, the venture motor cannot use all of the extra air and gas provided by the boost valving in the fully open position. Fully open all the time doesn't seem to produce any obvious negative effects, it just doesn't help performance. I'm really not sure if the engine could ever use the total output of the boost valving since I really don't spend much time with the engine at max rpm's. It is kinda fun to mess around with, however. For my venture, I installed three different things to tune the air/fuel performance of the engine: flow restrictors inside each pod filter (just a washer with a machined ID), variable restrictors on the exhaust outlets (just a disk which can be tipped inside each muffler), and the Vmax boost valves between the carbs and the engine. Overall, it runs great with excellent acceleration and gas mileage in the mid-forties.

zag

 

[coreyhill]

Thanks Everyone for your post and advice. I'm just figuring some things out. Has anyone done a lot of mods to theses V4s? Like bored over, shaved heads, port&polshed, any major mods?

[CaseyJ955]

Thanks Everyone for your post and advice. I'm just figuring some things out. Has anyone done a lot of mods to theses V4s? Like bored over, shaved heads, port&polshed, any major mods?

 

I do believe there is a 1260cc bore, the 1300cc MKII Venture motor and there is an option to poke and stroke to 1500cc ($$$$$). There are probably others but these are more well known on the Vmax side of the fence. PWC is an outfit that does it if I recall. My favorite power mod would have to be one of those supercharger kits for Vmax. Comb ebay and vendors and the Vmax forum, they come up now and then. If I see one cheap enough ill snag one. It would be eye and ear candy for a bobber!!

 

The go to guy with tons of Vmax racing experience and many builds under his belt would be Sean at Morleys Muscle, he's a great source for parts too. Tell him what your power goals are and you will get straight answers and options. I dealt with him on my Vmax and have been delighted with the results.

 

Keep in mind that with a simple Vmax head/cam swap, int and exh tuning you can get up in the area of 160hp at the crank at ~10,000 rpm. There is more to be had but I'm cheap! I do have an extra Vmax pumpkin also if you want to gear down a bit. Its surprising what you can get from one of these lumps with little more than tuning.

Edited February 8, 2018 by CaseyJ955

[bongobobny]

Well, yes, sort of. PCW Racing still has my 1300 engine, it is now bored out 0.030 making it around 1350cc. It has the 1200cc VMax heads and the PCW cam installed along with the PCW stiffer valve springs. John has had some medical issues so he is down at present. I have the V Boost setup here at home, patiently waiting for the delivery of my engine and installation onto the frame. I was toying with the idea of FI but the company that was making them went out of business but Flying Fool has the blueprints and I am waiting on seeing what he does with them. I have a pair of Jardine mufflers and still want to buy a Marks collector if they are still available...

 

PS I have over 6 Grand into the engine...