Intake restriction?

[Numb Knuckles]

86 Venture Royale - It looks like the intake area in the air cleaner cover is about 1/4th the size of the area of the carb intakes. Is this an obvious restriction?

[pegscraper]

I say it is. And almost every motorcycle and ATV suffers from the same condition. It is kept small to keep intake air noise down, government regs and your average customer and such things. But if you don't mind a little sound of performance under a heavy throttle, easing the restrictions in the airbox and rejetting to match generally gives a good performance improvement. And BTW, easing the restrictions in the airbox does not mean simply installing K&N filters. Doing that by itself helps nothing because the airbox itself is a much bigger restriction. This is why you will read about people who have put the K&Ns in and didn't have to rejet, or otherwise felt no performance increase. Easing the restrictions in the airbox means increasing the cross section area through the whole intake path, and streamlining or even reducing the number of turns and twists through the intake path. I don't know what the 1st gen air path looks like, but I know that the 2nd gen airboxes and ductwork are a convoluted mess.

[Dave Insley]

In my previous VR's (86 and 88) I drilled two 5/8 inch holes in the side of the airbox, carefully ensuring no plastic drill chips entered (use an oily rag to collect the chips).

If you were to install a vacuum gauge inside the airbox you will see the carbs are being starved at higher rpm's. Opening 2 additional intake holes to the air filter improves performance and mileage (mileage about 12 percent) and additional throaty roar very slight. When Yamaha recognized this restrictive airbox situation, they properly designed the 2nd gen with easy breathing dual intake filters.

Try drilling the 2 holes...if you want, after monitoring a few tankfuls of gas for mileage and wish to revert to the restrictive throat only, simply place some duct tape over your drilled holes. I'll BET you won't because you'll have better high rpm/load performance. We've had over 30 members do this with good results./Bilko

[Numb Knuckles]

Thanks for the info. I just bought the bike, so I'll probably ride it a while and then drill the holes so that I can have the satisfaction of a noticeable improvement.

Gary

[Marcarl]

I drilled holes in mine, 5\8 times four in the lid of the box, one in each corner. Can't say it's better or worse but the carb sound is great when I open 'er up. Keep in mind that only one cylinder draws at a time, so if the intake is only 1\4 the size of the total of the carbs............