Can 1983 Honda VT-500 Meet the Vetter Challenge?

[redyaris]

Originally Posted by renault_megane_dci

Sorry if I didn't made myself clear.
I understood what you were saying previously, I just added an other option.

What if the cheapest solution was "more P&G" instead of constant throttle at a throttle opening that is not appropriate ?

It would also be a good test to narrow the problem to the carb.

To be honest my favorite solution would be to build a single carb manifold and use only one of your carbs.

More P&G is not raeally a viable option on a motorcycle due to the low mass 300kg as compaired to a car at 1200kg. better stream lining expands the viability of P&G but not any were close to a car. Varn and Yamaha 250 V-twins use Single carbs and I will have to look into what Yamaha does with there cooling of the rear cyclinder. It may be that for short trips in low ambiant temps the jetting is not an issue or Ymaha may have aranged the cooling to the rear cylinder to be better than the front cylinder I just don't know yet...

[Varn]

The low speed fuel screws are adjustable for a reason. So you can get the best running. Seems pretty obvious to me that you should try and adjust them to help with your rich mixture at low end. After all the screws affect low speed running mostly. To set them to a standard position means that you are hoping for the best but not actually tuning the mixture for best or most efficient running. I wouldn't worry about having marginal cooling if your gauge is reading normal. After-all you are only needing 50% of your normal amount of power.

I have adjusted single groove needles on many bikes. Some of them have the needle mounted in a clip that you can reverse or remove. If you want to lower a needle that sits in the slide without obvious means of adjustment try cutting the top of the hole of the slide letting the needle sit deeper in the piston. Many times a mm of adjustment is plenty. You just have to reverse engineer. Sudco may well sell alternative needles. You may have to measure the diameters every 10 mm and compare them to the charts on their web page.

Your bike probably won't be near stock as you are trying to do different things than it was designed for.

As for spark timing some advance from stock is a pretty standard way of improving response and economy. It can lead to trouble with high temps if you run it hard I doubt if you are. It moves the pressure peak up a bit.

[Varn]

As far as Yamaha v twin cooling, they use standard air cooling. Most use two side by side connecting rods on one journal. giving them about an inch or two of offset.

The rear cylinders run a bit hotter than the front but so what. Once you commit to liquid cooling you eliminate the differential in cylinder cooling.

When I made my Virago a single carburetor system I paid no mind to uneven cooling. The cylinders fire on opposite revolutions so the single carb is all that is needed. It runs fine and gets better mileage than it did when it was a twin carb bike.

[redyaris]

There is also a reasons for the manufacturers getting rid of the adjustability of the slow speed circuits and that is that most people fidle with them until they are poorly adjusted. Mine are properly adjusted at the manufacturers specifications, the throatle responce from idle is instentaniouse which is a good indication that they are adjusted properly. I am responding to a situation I encounted in the recent heat wave in the USA. It is not a trivial matter when riding accross the contenent. Even Honda recognized the problem, and made changes to the cooling system in 1985. I have been working on motorcycles and small engines for 30 years and have adjusted a carb or two...

[redyaris]

What I will try next is a 1986 larger radiator, a relocated fan with extra ducting and some form of heat sinks added to the system to increas surface area cooling. Replace the #38 with #35 slow speed jets and install #112 main jet in the rear cyclinder carb to match the #112 in the front cylinder carb. hopefully this is enough to get into the 80 - 90 mpg zone with consistancy.

I will also design and build a new front fender that improves the airflow around the front wheel and forks, and directs more air at the bottom of the radiator.

[renault_megane_dci]

Originally Posted by redyaris

More P&G is not raeally a viable option on a motorcycle due to the low mass 300kg as compaired to a car at 1200kg. better stream lining expands the viability of P&G but not any were close to a car.

Even if it is not as efficient, it might still be better than constant throttle in a rpm range that leads to a carburettion problem ...

[redyaris]

I am waiting for the smaller slow speed jets and the smaller main jet ordered from Honda. tomorrow I will work on a new under tray that is narrower than the original that would scrape on the ground on occasion when leaned over in a turn. I have plans to take this bike to the Los Vegas to Barstow Vetter Challenge in november to see if I have made major improvements or not.
I would rather solve the fuel metering problem on the VT500 with re jetting than try to compensate with P&G. This is all part of the process of development. Problems pop up and one has to solve them.

[redyaris]

Recieved ebay 1986 radiator today and with one extra row it has 8.3% more cooling seface. When trying to remove a threaded plug from the thermo switch hole I damaged the solder joint and had to resolder. After repairs I did a test fitup and everything is good. I also bought a small radeator from a VFR 750 at the wrecker, and am looking at how to add it to the system. The other option is to relocate the original 1983 radiator and run the coolent through both, this would be the best if I can find a good location. with 1.9 times the radiator area all cooling problems should vanish and the rejetting can procied, so that I can get close to the optimum 14.7 air fuel ratio and be in the 80 - 90 mpg zone. I am still waiting for the smaller jetting from Honda. I have also made a new undertray and will work on that tomorrow...

[redyaris]

The #35 slow speed jets are in and the rear cylinder carb now has a #112 main jet. the new under tray is fitted as is the new fairing sides. The 1986 radiator conversion will have to wait until I can get a used 1986 cooling fan. The O2 sensor/fuel-air guage will be installed in the next week or so and then I will do some test runs to check and see if the jetting gets me close to 14.7:1 air/fuel ratio.

Got air fuel guage and O2 sensor roughed in and tested today so if all goes well, I may be able to do a road test next weekend.

[redyaris]

Had the VT500 out for a short test drive with the cargo space open at the top so not very aero at the rear. The air/fuel guage works well, as does to the new bodywork. I will need to take a longer test ride after I instal the top of the cargo bay and then see what the fuel air guage tells me on a longer run. It was only 3*C out and my face was getting cold with my dirt bike helmit.