Aisan Carb adjustments - Help! (1 Viewer)

[Pin_Head]

I am not that familiar with 79 and up carbs, but just from looking at the pictures on the SOR web site, there appears to be one. There are multiple vacuum fittings on the air horn of the later carbs, but if I had to guess, I would guess that the one facing straight forward is the one that operates the power valve.
The carb experts on the board would know for sure.

 

[762fmj]

I am glad this thread got started cause it's helped me a bunch. I have a Mark built (Mark's Off Road) 75 carb in my 80. It is awsome! I have done the fine tuning from feedback here.

Thanks guys for passing the knowledge

 

[badass]

You can cap off the brass tube on the front of the air horn and your engine will run, but it will rich and get poor fuel economy. It is supposed to be hooked up to the VSV that is operated by the engine control computer, but if that system is missing, manifold vacuum will be adequate.

The vacuum fitting by the idle mixture screw show in in the picture is appropriate for running a vacuum advance distributor, but not all tubes in this vicinity are. The vacuum port needs to enter the primary bore just above the throttle plate and not below it. You can check by sticking a piece of nylon fishing line in the hole and taking a peek inside to see where it comes out.

Pinhead, mine is not capped off and is just open, it does run real rich unless the the mixture screw is turned all the way to lean which i am sure is not normal. Can you please post a pic or explain in better detail what it is supposed to be hooked up to? BTW, mine still has the smog stuff intact.

 

[Pin_Head]

The idle mixture screw has nothing to do with the main jet richness, it only controls the idle mixture.

The power valve is an auxiliary main jet that supplies more fuel to the primary and secondary nozzles under pedal to the metal conditions, when the vacuum drops low in the intake manifold. It is supposed to connect to the VSV valve on the DS fender that is run by the engine computer. If this is gone or inoperative connect it to manifold vacuum, same as the PCV valve and the brake booster. You need to install a T fitting to tap into the vacuum.

 

[badass]

The idle mixture screw has nothing to do with the main jet richness, it only controls the idle mixture.

The power valve is an auxiliary main jet that supplies more fuel to the primary and secondary nozzles under pedal to the metal conditions, when the vacuum drops low in the intake manifold. It is supposed to connect to the VSV valve on the DS fender that is run by the engine computer. If this is gone or inoperative connect it to manifold vacuum, same as the PCV valve and the brake booster. You need to install a T fitting to tap into the vacuum.

right, i feel like i'm in math class.

 

[Pin_Head]

Would pictures help? I don't really have any, but maybe someone will post some up.

 

[badass]

Yes pics would help.

 

[Pin_Head]

Here you go:
Since you still have all the electronic control, it is the vacuum hose labeled #8 from the tube labeled #8 on the VSV to the tube labeled #8 on the top of the carb.

Taking Carburetor 101 would help too:
http://www.ih8mud.com/tech/carbinfo.php

 

[Cruiser_GT]

Yes pics would help.

Is this what you're looking for? ... '76 carb

 

[Perrymason]

Ok so my carb doesnt exacly look like the pics so i would appreciate some input if i am off base. I know my choke has been disabled hence the stupid wire thing. Not sure where the vacuum is?

 

[Degnol]

In your picture, the vacuum is to the right of the idle mixture screw.

 

[Perrymason]

K thanks.

 

[gwalt584]

adj

The idle mixture screw has nothing to do with the main jet richness, it only controls the idle mixture.

The power valve is an auxiliary main jet that supplies more fuel to the primary and secondary nozzles under pedal to the metal conditions, when the vacuum drops low in the intake manifold. It is supposed to connect to the VSV valve on the DS fender that is run by the engine computer. If this is gone or inoperative connect it to manifold vacuum, same as the PCV valve and the brake booster. You need to install a T fitting to tap into the vacuum.

Another Hijack, same topic:
mine is a 75 Aisan, just rebuilt. I capped off the brass connection (power valve)at the front of the airhorn. However, When I put manifold vac on it the engine would not run hardly at all. capped off it is fine. So what is wrong with the power valve that it runs so poorly with manifold vac to the power valve port?
This picture shows the open vac connections for the brake booster and the vac gauge, they are connected now, so no unpluged vac connections during the test.

 

[gwalt584]

Hello

Where's Pinhead and Jim when you need them??? LOL

 

[fjwagon]

I like this thread, good info. keep it going.

 

[Rajafarhan]

I need some help tuning the carb too...I'll get in touch later for that though

 

[PabloCruise]

Great thread, I missed it when it first came out.

 

[NorthFJ]

The area on the air horn that should have the power valve port has a brass plug, looks like factory to me?
76 but not sure if the carb is original...
Anyone else seen this?

 

[NorthFJ]

Just had it apart, almost seems to be ported back down through the body of the carb, right down the center???

 

[Pin_Head]

There is nothing wrong with the power valve because it runs poorly when you connect it to vacuum. Vacuum shuts the power valve, which is its default state until you floor it and manifold vacuum drops way low. Then it opens and richens the mixture when you need it.

The problem is why it runs crappy with the PV closed. You don't say what circumstances it is running when this happens, so it is hard to tell what the problem is. A better description of what you mean might help.