1983 Venture runs bad with top cover on.

[lesdawg122]

Hey Guys and Gals,

Thanks for the warm reception. Okay lets see if I can stump the panel. I bought the bike

knowing it was running bad. I only gave him 1500.00 for her. Overall she is beautiful.

So I've been trying to figure out the reason she runs so bad. When I removed the top cover

I seen she needed a new air filter and also discovered the air box had been modified. The front side had been cut out completely. So I replaced the air and oil filters and changed the oil, seafoamed the gas, changed the plugs. I went ahead and fired her up without the top cover put on. She purred. So I rode her down the road and she did great. So I came back and put the cover on her and she started cutting out again. My two back cylinders have exhaust leaks right where the pipes go into the engine. A friend of mine said that was the prob. That the exhaust is being pulled into the carbs. Makes sense since the side covers are blocking any other route for the exhaust to go. So I went online to order new gaskets and silencer bands only to discover that they don"t make the bands anymore. So 1st question is where can I find the silencers and 2nd question is how hard is it to fix the leaks, and last question could the exhaust leak be causing the cutting out of the engine.

Thanks again for letting me join the group, I am looking forward to riding the ole girl.

[KenP]

I don't have my First Gen anymore, but I found the below site to be full of good info:

 

http://www.bergall.org/temp/venture/venture%20tips.html

[frankd]

By "top cover" do mean the top of the air box OR the tank cover (actually it covers the battery and air filter box)

 

If the front has been cut out of your air box, that will make it run much leaner (more air in the mixture) than when it left the factory. A normal 1st Gen. will run very lean with a modified air box, and with to air box top off, will be hard to get it to rev. up. Some riders used to drill a couple of 1/2" holes in the air box to improve gas mileage. When you say it doesn't run good, is it lean or rich? If it's lean it'll bog and back fire. If it's rich you may see black smoke out of the exhaust and the spark plug electrodes will be dark. To help, I need to know if it's rich or lean.

 

Frank D.

[Flyinfool]

What Frank said.

 

There is also the possibility that whomever cut out the front of the air box also rejetted to be able to use the extra air. With a whole side cut out of the air box it would have run terrible without rejetting. These bikes are very sensitive to changes in the air box.

[frankd]

I don't have my First Gen anymore, but I found the below site to be full of good info:

 

http://www.bergall.org/temp/venture/venture%20tips.html

 

Ken,

 

Thanks for this site....there is a lot of good info there.

 

Frank D.

[lesdawg122]

I mean its the outside cover that covers the air box, battery, and tank filler cap. There is no smoke, and it bogs down and backfires and hiccups in the carbs. Has anybody experienced

exhaust leaks that let gas fumes into the carbs?

[Prairiehammer]

I mean its the outside cover that covers the air box, battery, and tank filler cap. There is no smoke, and it bogs down and backfires and hiccups in the carbs. Has anybody experienced exhaust leaks that let gas fumes into the carbs?

 

No.

I've experienced some fair exhaust leaks on the rear headers on my '83, but I can't imagine that a leaky exhaust pipe would offer enough exhaust gasses to make any difference. Heck, most cars have an EGR valve that actually allows exhaust gases into the intake.

I believe your bog and hiccups in the carbs is due to the modified air box. Try sealing the air box with some duct tape and cardboard over the missing air box parts and see if it still runs badly.

[frankd]

You did say that the front of your air box was completely cut away, and that sounds like your problem. Like FlyinFool said, they are very sensitive to modifications in the airbox. I hope that somebody did NOT rejet the bike to compensate for the air box mods. I think you need a new, unmolested air box, but maybe you could temporarily replace the missing portion(s) with duct-tape and see how it runs.

 

The battery & airbox cover should make no difference in the way the bike runs, unless with the airbox mods. it just changed the path of the incoming air????? Try and get the airbox so that it isn't opened up and see how it runs.

[mbrood]

Constant velocity carbs function by a carefully designed air restriction intake to make the needed throat vacuum required to make the diaphragm effective and efficient. This also dictates the jet sizes to match the fuel mixture to the available air. Tearing open the airbox defeats the design of the carb. You want Webers, design for Webers. You want the Mikuni CVC, follow the design. Some small changes are always available as long as you meet the fuel/airflow requirements but there's no throttle cable control over that main intake needle, it's the vacuum developed to the diaphragm, dictated by a sealed airbox and a carefully matched opening in the lid.