are you using 170 front and rear? stock is 175/178. i thought theyhad to stay unequal.

 

HOLY CRAP guys.... Every time I tear into this bike, I realize the previous owner is more of an idiot. He had the velocity stacks (intake trumpets, same thing) on reversed! And managed to round out one of the bolts...

So after I plugged up all the holes in the airbox to the carbs PAIR etc, drilled and easy-outed the bolt, I reversed the stacks, installed the K+N and removed the rubber snorkel. Bike runs MUCH better.....one small flat-spot at 4-5k and then pulls like a bandit....louder too. The jetting must be fairly close already because it really doesn't have any driveability issues, and it's much colder than normal right now so it should get better when we get some warmer weather.

 

Yes, I had it dyno tuned and that is how it was done. I questioned as to whether the rear should be richer due to the cylinder running hotter and was told "no". This guy has a great reputation, does a lot of race stuff with twins.

So that is why. I was going to change it, but he reckons not.

 

so in theory if one were to do the dual long runner mod, would they need to make their jets equal?

 

You make a good point.

The jetting thgeory with the VTR (and all twins I think) is that the rear cylinder runns hotter due to less airflow, and you run a bigger main jet to cool the combustion chamber down. This is not to be confused with the temp of the intake charge. This is what my dyno tuner disagreed with.

What you are suggesting could very well equalise the other settings such as needle shimming or position, and mixture screw position between each cylinder. It is reasonable to assume that with the same size stack it would make things more equal in this regard.

 

yes but without a wideband o2 sensor or egt sensors installed in each header we will never know. unfortunately only a burned valve or other internal damage will prove if we are right or wrong. but yes rear cylinders run hotter than fronts, but the intake air temp is always the same for both. thats my turbo talk and experience for you.

 

Another consequence of the different stacks is the effect on main jets. My stacks are billet ally, and the guy that designed them designed them on a flow bench. He had done a lot of development on the VTR, and found that the different stacks effected main jet sizes. Required main jets will be smaller when using his billet stacks. He had a full race motor that was using 182 keihin jets.

 

In reference to the rear cylinder running more rich to cool exhaust gas temperatures or egts. I find that using a laser temp gun is a good way to see the temp. differences from front to rear cylinder. At the time I am having issues trying to get the leaness out of my mixture. I have K & N filters and jaradine cans. I bought this bike at auction seems to run great however when I first got it, it hesitated when throttle was slammed. Upon disassembly I noticed it had stock jets 175 and 178 rear and someone had drilled a third hole in both front and rear slides. Also it looked like there were 2 small washers and a thinner one underneath the front needle and and 2 washers under the rear needle. I rejetted to 180 in the front and 185 rear took it to my friends smog shop and adjusted the mixture. The bike runs better and seems to have more power however later that evening at home I was reading the exhaust pipes temp. 2 inches from the cylinder noticed my rear cylinder was running 300 degrees hotter than my front cylinder. No matter how I adjusted the mixture of the front or rear the temperature was basically a 250-300 difference. Does anyone know if these exhaust gas temp. should be this far off?? Example front was 300 rear 620 degrees f. This seems too far off in my opinion- all readings were done at idle. Other than this 99 % of hesitation is gone but do get backfires every time when closing throttle abruptly but very little. Upon removal of spark plugs I noticed white ceramic insulater white in front cylinder and more white in rear cylinder. I have now decided to increase washers in front to 3 and 3.5 in the rear and am waiting for #48 pilots to come in so I can try this. Might get rid of my backfires and perhaps make it run a little less lean. Does any one have any advice??? Should I plug the drilled slide hole increase or shorten stacks?? Please let me know. thx.

 

Worth a read regarding your jetting questions. The holes drilled in the slides is indicative of a Dynojet kit.

https://www.superhawkforum.com/forum...-set-up-24769/

As far as the cylinder temps, I've never taken the time to check the temp between cylinders.

You'll probably get lots of advice to ditch the K&N and go back to a stock filter, seems not too many have had good luck with them.

Hope this helps a little.

 

Just wanted to chime in on my install of Dr.Honda's stacks. On my "Seat Of The Pants Dyno", I noticed an improvement. I would recommend them to anyone that would consider buying a set. I had them for a while and just now found the time to install them. Six spokers are the next mod on the way.

 

What are six spokers and where can I get a set of Dr. Honda's Velocity stacks? I found a website that sell velocity stacks but besides the different heights, is there an actual difference?

A&L Motorsports. Superhawk Parts

Those are the stacks I was thinking about getting.

 

Six spokes.





As far as the velocity stacks, you'll have to ask Dr. Honda if he is interested in making more. Check this thread:
https://www.superhawkforum.com/forum...y-stack-26914/

Order here:
http://www.a-lmotorsports.com/Catego...awk-parts.aspx