OKC VentureMax Update

[GaryZ]

I have been playing around with the carb set-up on my VentureMax (1300 engine with Vmax cams and springs). The latest experiment is Vmax needles and .5mm spacers. I have not rode it much with this set-up yet;

 

Needs a little choke for cold starting

Idle appears to be lean (surges slightly at idle and pops during deceleration)

Pulls smooth and strong from 1500 rpm in second

Pulled a little "crisper" from 1500 rpm with stock needles

Pulls strong from 3,000 rpm (any gear)

Ran it up to 9,000 rpm in second and it wanted to keep going!

Edited August 14, 2010 by GaryZ

[dingy]

Probably the next thing to try would be rejetting.

 

Easy way to experiment with this is to reduce the size of PAJ2 or the main air jet. Either of these can be accessed without removing the carbs from the bike. Reducing these air jets helps richen the A/F ratio. PAJ2 is behind the diaphrams and Main air jet is in upper venturi.

 

Most straight forward way would be to increase the size of the main fuel jet. This is located inside the fuel bowl. Removing the carbs is required.

 

On the MKII's there is a 125 main jet. Increasing this to about 140 or 150 would be get rid of lean condition.

 

I have a 150 main jet and a 160 PAJ2 in mine. The PAJ2 was 180 in the 1st gens. I drilled my jets out. This is not the recommended way, but it does work. There is some discussion that drilling a jet tends to induce swirling in the fluid flowing through them. This has been shown to be detrimental in achieving maximum HP on a dyno, but for the hobbyist it is sufficient.

 

Gary

[jasonm.]

I going to clue you in...You need to find a dyno person with an EGA and a variable load dyno. For $100 usually they will eliminate the guessing. If you have not already. Go the Yamaha site and compare jet sizes from VMAX and you Venture engine. http://www.yamaha-motor.com/sport/myyamaha/prompt/L3Nwb3J0L3BhcnRzL2hvbWUuYXNweA==/Parts%20Catalog/starthere.aspx

One trip on the dyno will tell you if it's rich or lean and where. If it EGAs good at full pull 13:1 but is lean in the middle then it's strictly a needle adjustment..etc. BUT you MUST have the adapters to do this properly. Are you running Vboost too?

[GaryZ]

I going to clue you in...You need to find a dyno person with an EGA and a variable load dyno. For $100 usually they will eliminate the guessing. If you have not already. Go the Yamaha site and compare jet sizes from VMAX and you Venture engine. http://www.yamaha-motor.com/sport/myyamaha/prompt/L3Nwb3J0L3BhcnRzL2hvbWUuYXNweA==/Parts%20Catalog/starthere.aspx

One trip on the dyno will tell you if it's rich or lean and where. If it EGAs good at full pull 13:1 but is lean in the middle then it's strictly a needle adjustment..etc. BUT you MUST have the adapters to do this properly. Are you running Vboost too?

 

No Vboost . . . and no money to do a dyno

What adapters?

[GaryZ]

Update;

After reading an excellent article on CV carbs, I decided to remove the needle spacers to lean the mids. The difference is amazing! Crisp throttle when taking off from a stop, even when the engine is hot. It is crisp when lugging around corners in 2nd gear. The biggie is gas mileage. It has jumped from around 30mpg to over 37mpg!

 

Here's my set-up at this time:

1987 engine (1300cc)

1985 carbs

vmax needles

low speed screw 2 turns out

Dingy's universal TCI

 

I'm lovin' it!

[dingy]

Will you send me a link to carb article?

 

Gary

[VentureYZ]

What jets are you actually running in your carbs, main, pilot, air jets and needle shim.

[Keemez]

Will you send me a link to carb article?

 

Make that all of us. Just post it here public like, please.

[GaryZ]

What jets are you actually running in your carbs, main, pilot, air jets and needle shim.

 

The carbs are the originals on a 1985 VR and I switched the needles to ones from a vmax.

[GaryZ]

Make that all of us. Just post it here public like, please.

 

see attached file . . . Enjoy!

[bilko1]

Update;

After reading an excellent article on CV carbs, I decided to remove the needle spacers to lean the mids. The difference is amazing! Crisp throttle when taking off from a stop, even when the engine is hot. It is crisp when lugging around corners in 2nd gear. The biggie is gas mileage. It has jumped from around 30mpg to over 37mpg!

 

Here's my set-up at this time:

1987 engine (1300cc)

1985 carbs

vmax needles

low speed screw 2 turns out

Dingy's universal TCI

 

I'm lovin' it!

You could always stop by here, and tune mine.

[VentureYZ]

Quik question Gary,

 

In other words am I assuming you are using 34mm carbs with 117.5 main jet, 37.5 pilot,170 air jet and a 80 air jet. Dingy is just saying that the mains should go to a 145 or 150. Even reducing the air size also to make it run richer yet. A guy on the Venturers sit says put 150's in the front cylinders and 152's in the rear cylinders. These bikes are getting more confusing every day.

[GaryZ]

Quik question Gary,

 

In other words am I assuming you are using 34mm carbs with 117.5 main jet, 37.5 pilot,170 air jet and a 80 air jet. Dingy is just saying that the mains should go to a 145 or 150. Even reducing the air size also to make it run richer yet. A guy on the Venturers sit says put 150's in the front cylinders and 152's in the rear cylinders. These bikes are getting more confusing every day.

 

Others are apparently choosing to use vmax jetting (150s, 152s, etc). The vmax carbs are tuned for slightly larger valves, different air filter set-up, and v-boost. At this point I can only tell you that my set-up seems to be working great.

[yamihami]

Wow! amazing write up. Now I know why my bike doesn't need choke to start. At first I thought this was a very good thing. Now I know this is because my pilot circuit (jet) is probably(to rich) out to much. Just wondering if the POs played around with these settings and did they on all 4 carbs?

[Yamamike]

Quik question Gary,

 

In other words am I assuming you are using 34mm carbs with 117.5 main jet, 37.5 pilot,170 air jet and a 80 air jet. Dingy is just saying that the mains should go to a 145 or 150. Even reducing the air size also to make it run richer yet. A guy on the Venturers sit says put 150's in the front cylinders and 152's in the rear cylinders. These bikes are getting more confusing every day.

 

Correct me if I'm wrong but using different size jets front and rear is to allow for hotter running rear cylinders in an air cooled engine. I don't think this would apply to liquid cooled engines.

[jasonm.]

Quik question Gary,

 

In other words am I assuming you are using 34mm carbs with 117.5 main jet, 37.5 pilot,170 air jet and a 80 air jet. Dingy is just saying that the mains should go to a 145 or 150. Even reducing the air size also to make it run richer yet. A guy on the Venturers sit says put 150's in the front cylinders and 152's in the rear cylinders. These bikes are getting more confusing every day.

 

 

Going that high(150's) on the main jet is......insane. 1st the original Vmax uses 35mm carbs. You have 34s. Second you'd be increasing the available fuel flow by more that the size shows. Flow is the D squared. So increasing size nealy 50% is nuts! A stock 1300 runs 125's.So you have a Venture that pulls to 9000 nicely w/o Vboost. I would not go past 135 jet for your next step. But you already proved it was running rich by lowering the needles. FYI...it's worth the $$ to find a variable load Dyno operator w/EGA. My guy cost me $100 for 3 hours. The reason for the 3 hours was MY wrneching in between runs. No wrenching probably cost $30. You got $30 ? TO me time is $$. And this will same you BOTH. Guess....sucks and wastes time. This will give you direction on your next step.

Edited October 13, 2012 by jasonm.