Need Help!

[02GF74]

For engine to speed up, it needs more air but that in itself is not enough as it needs fuel too in the correct ratio.

In the simplest form, carbs supply fuel according to amount of air drawn in.

I'm not familiar venture but assume it is similar to vmax else you would not be posting here.

Carbs connect to inlet manifold.
Other end of carbs connect to an airbox which has built in velocity stacks. These I believe sit inside the air filter and a lid sits on the air box.

How can putting an air filter into the air box or fitting the lid cause the engine to draw more air and subsequently speed up???

It does not make sense.

 

[MaxMidnight]

How can putting an air filter into the air box or fitting the lid cause the engine to draw more air and subsequently speed up???

The air filter arrangement differs from the Max as does the air filter.

Unlike the Max filter which is still open to atmosphere when placed into the air box it would appear that the Venture one would seal it.
Any blockage or restriction in the filter would cause increase manifold depression which would cause the slides to open? (speculation).

That's why I asked the question in post #5 and my comment in post #20.

 

[02GF74]

That is not my understanding of CV carbs work. Any restriction on the inlet side does not move the pistons, in fact it shoud do the opposite and stall the engine.

The air pilot and fuel pilot jet is all that keep the air/fuel mixture supplied until the butterfly is opened. Once the butterfly is opened, vacuum is routed to the pistons to raised them which in turn lets in more fuel by raising the needle in the main jet.

The OP said that the butterflies are not being moved which is why I believe some magic is happening.

A good explanation of how CV carbs works can be viewed here.

 

[Parminio]

Some people hate the Rochester Products Quadrajet, but I never found them difficult to rebuild or to tune properly. I am not a professional mechanic.

Same here. The only reason I ever went to Holley was I couldn't get the Rochester in a square bore.

 

[MaxMidnight]

That is not my understanding of CV carbs work. Any restriction on the inlet side does not move the pistons, in fact it shoud do the opposite and stall the engine.

The air pilot and fuel pilot jet is all that keep the air/fuel mixture supplied until the butterfly is opened. Once the butterfly is opened, vacuum is routed to the pistons to raised them which in turn lets in more fuel by raising the needle in the main jet.

The OP said that the butterflies are not being moved which is why I believe some magic is happening.

If we can agree that magic doesn't exist (? ) then something is causing the throttle slides to rise.

I take your point that opening the throttle will introduce the vacuum to raise the slides in a correctly set up system.
I'm speculating, and may be wrong, that significantly reducing the airflow through the filter (and where the filter seals the intake from atmospheric pressure) would also introduce a vacuum and could cause the slides to rise?

What we do know is that revs rise when the filter is put on. Therefore it would seem reasonable (to me at least) that that the filter is affecting the system.
I've made my suggestions as to what I would do and it is down to the OP to try it and either prove my theory wrong or not.
Either way they would either rule the filter in or out as a causal part.

 

[02GF74]

then something is causing the throttle slides to rise.

Maybe you're right but all that will do is allow more fuel in and chances are it will not be in correct ratio so engine will stall. If you watched the video above, you will see that the butterfly valve needs to open to get the air/vacuum circuit for the slides into play and OP said it does not move.

Have to say I'm stumped - there is something else going on here that we don't know about, trying to diagnose at a distance without seeing the bike isn't easy at the best of times.

It is somewhat suspicion that the bike idles at 2.5 k - is there a problem with the fuel enrichment?

 

[MaxMidnight]

I don't disagree with you but any port in a storm?

 

[JerrodR]

Got It!!! The Bar that the Idle Screw is on was bent up into my Throttle Linkage...

 

[JerrodR]

So my Idle Screw wasn't making Contact, but the Bar it goes through was back behind it where I couldn't see. Don't know how it got that way, but I bent it back down and she Idles Perfectly.

 

[COP RUNNER]

Awesome , Glad You Got It !

 

[desert_max]

I think I'd give the carburetor balance mechanism a good going-over. No stripped screws, things move when the balance screws are adjusted. Adjustment springs have tension and are not coil-bound. Same going-over for the carburetor enrichment mechanisms. Are the pistons all freely-moving fully-open and closed with the lever?

Use starting fluid to check for air leaks airbox to carbs, carbs to VBoost manifold, and VBoost manifold to cyl heads (O-rings). Check for proper slack in the throttle cables.

I think I'd pay attention to this wise counsel. I've encountered the behavior you describe and found it to be the rack being grossly out of synch. My trusty Carbtune Pro sorted it out. Not saying that's your problem, just that I have seen it firsthand.

<<Doh! Never mind. I see your issue was resolved.>>

 

[MaxMidnight]

Still don't understand why putting the air filter on caused the revs to rise.

 

[JerrodR]

Still don't understand why putting the air filter on caused the revs to rise.

Yeah me either, all I can tell you is thats what it does at this point lol. And I'm not sure if your Vmax would behave the same, I'm pretty sure the Heads and intake are different. I don't think you Guys have YICS, and I don't have VBoost.

 

[JerrodR]

Yeah me either, all I can tell you is thats what it does at this point lol. And I'm not sure if your Vmax would behave the same, I'm pretty sure the Heads and intake are different. I don't think you Guys have YICS, and I don't have VBoost.

The Guys in the Venture Forum say the Airbox is really important, and I guess they weren't kidding.

 

[Fire-medic]

The Guys in the Venture Forum say the Airbox is really important, and I guess they weren't kidding.

I ran into something similar on a Kawasaki 440 Standard, not an LTD. I got it for a song, non-operational, from the original owner, and while it took very-little to get it running, the forum for them said the same thing: "stay with an OEM intake, the airbox is very important to the bike's operation." Thankfully, the bike still had the OEM airbox, so that wasn't an issue. I had to replace the mechanical advance to get it to run properly. It was a neat little bike. Mag wheels, disc front brake, CDI ignition, chrome fenders and a belt drive.



Just in-case someone has one of these.

 

[JerrodR]

I ran into something similar on a Kawasaki 440 Standard, not an LTD. I got it for a song, non-operational, from the original owner, and while it took very-little to get it running, the forum for them said the same thing: "stay with an OEM intake, the airbox is very important to the bike's operation." Thankfully, the bike still had the OEM airbox, so that wasn't an issue. I had to replace the mechanical advance to get it to run properly. It was a neat little bike. Mag wheels, disc front brake, CDI ignition, chrome fenders and a belt drive.

View attachment 82540
View attachment 82541
Just in-case someone has one of these.

A lot of Bikes are. I have an 82 XJ-750 Maxim that I turned into a Cafe Racer during the Lockdown's, converted it over to a Mack 4 into 1 with Pod's and it was tricky. Ended up having to Jet it out to #130 and then Open the Pilot Screw's up an additional 4 turns to work the Dead spots out, took all Summer lol runs Great now though.

 

[JerrodR]

A lot of Bikes are. I have an 82 XJ-750 Maxim that I turned into a Cafe Racer during the Lockdown's, converted it over to a Mack 4 into 1 with Pod's and it was tricky. Ended up having to Jet it out to #130 and then Open the Pilot Screw's up an additional 4 turns to work the Dead spots out, took all Summer lol runs Great now though.View attachment 82587

Actually, I bought my Venture for the Breaks, Wheels and Engine with intentions to do a V4 Swap onto the XJ. Still think it would be awesome, but realized right away getting the 1200 on there would take more than I'm willing to do at the moment, so I decided to fix up the Venture. Still may throw at least the Wheels and Breaks on one Day, all depends I guess.