Case of the missing vacumm

[Marcarl]

It's an 88 Venture.

 

Owner is Trader.

 

Bought it from somebody in Chicago this year.

 

Ran like crap when he bought it. Smelled rich, but plugs don't show it. Wouldn't idle without the choke on.

 

Thought to do a carb tune on it yesterday.

 

Found #2 cylinder wasn't firing.

 

Cleaned the carbs with spray cleaner and a bit of air.

 

Eventually got # 2 to fire.

 

Still ran like crap.

Tried to do a carb tune. ( I have a homemade one that has 1 vacuum gauge with 4 shut-offs that works just fine when ever I used it before and tests out just fine right now).

 

Got no vacuum on # 2 or # 1 cylinders.

Could get vacuum to show on 3 and 4 but the screws had to be turned to their max.

Tried adjusting the throttle cables, worked better but didn't do anything for vacuum.

 

Checked for leaks in the manifold boots, around the intake, around the airbox, and anywhere else that might be of interest.

 

Called Squidley out of bed and found out what Lonna was up to,,, and it wasn't making cheesecake, so we talked instead,,,, thanks Lonna.

 

Went out and convinced Steve (Trader) that it was time to get a compression tester. I bought it, he paid for it and then left it here????????

 

Compression tested to 180 on all four cylinders. engine was warm, not hot.

 

Switched the vacuum lines form side to side to make sure things worked right. Expected to see #3 and #4 drop in vacuum, but 1 and 2 still didn't have any vacuum. Far as that goes, they seemed to maybe even have pressure because the needle seemed to keep wanting to go past the stop post.

 

Set the screws to where I thought they would be most beneficial, (no vacuum showing anywhere) put it all back together, fixed the battery lead and put the tools away.

 

End result: garage is cleaned up, bike runs without choke but still smells rich and idle screw is turned into the limit, Steve is on his way home and hasn't come back yet. I am now the proud owner of a brand new compression tester. AND WE NOW KNOW THAT 1ST GENS DON'T REALLY NEED VACUUM TO RUN!

 

Now the big question,,,,,,,,,,,WHY???????

[V7Goose]

Your carbs are plugged up very badly. The butterfly valves are being held so far open to try and get enough fuel to idle that there is no restriction on the intake. To make matters worse, the diaphragms may be damaged too, so that even opening the throttle is not getting enough slide movement.

 

That does not explain why you are only seeing zero on two carbs, since all four should have the butterflys just as far open, but it is at least a place to start. Could also be a problem with the carb linkage - maybe it has been really badly misadjusted so that the left bank is being held way too far open? Best way to check that is take off the air intake so you can see down through all four carbs at once (I do not even know if that is possible on a 1st gen). If you can do that, manually pull up the slide to see the butterfly valve below it and see if they are all closed. If the carbs are clean and properly adjusted, the butterfly valves should have such a small crack in them that they look closed at idle. Also look to see if they all four open at the same time with the throttle.

 

While you are in there with the tops of the carbs open, you can hold a piece of paper up to each carb top to see if it is really sucking air. Maybe you got a dead mouse jammed up against the intake valve?

 

Of course, a REALLY BAD intake leak would do the same thing, but you should be able to easily find that with starting spray.

 

Lastly, what about the possibility that the vacuum port is simply plugged? These things have a very tiny hole in them - try putting a hose on it and sucking through it.

Goose

Edited October 24, 2011 by V7Goose
more ideas

[Marcarl]

Your carbs are plugged up very badly. The butterfly valves are being held so far open to try and get enough fuel to idle that there is no restriction on the intake. To make matters worse, the diaphragms may be damaged too, so that even opening the throttle is not getting enough slide movement.

 

That does not explain why you are only seeing zero on two carbs, since all four should have the butterflys just as far open, but it is at least a place to start. Could also be a problem with the carb linkage - maybe it has been really badly misadjusted so that the left bank is being held way too far open? Best way to check that is take off the air intake so you can see down through all four carbs at once (I do not even know if that is possible on a 1st gen). If you can do that, manually pull up the slide to see the butterfly valve below it and see if they are all closed. If the carbs are clean and properly adjusted, the butterfly valves should have such a small crack in them that they look closed at idle.

 

Of course, a REALLY BAD intake leak would do the same thing, but you should be able to easily find that with starting spray.

Thanks Goose,,,, yes, the thought did run through my mind that it was running so crappy on the carbs that the butterflies had to be too far open. 3&4 could be closed enough to create some vacuum while it was running on 1&2. It was pretty hard to tell if it was running on 1 or 2 or 3 and which cylinders were firing when. As it is right now, we poured and good amount of cleaner in a full tank of fuel and he had a 5 hour run ahead of him. Maybe that will help,, maybe not, we'll see. looks like we need to do a carb cleaning on this one.

[V7Goose]

Everybody needs to remember that no fuel additive can clean the carb jets/passages unless the fuel is actually running through them. In other words, a partially plugged jet can be cleaned this way, but one that is completely plugged cannot. This is because the jet orifices do not actually sit submerged in fuel, so just putting cleaner in the float bowl is about as effective as putting it in a bowl on the floor under the engine.

 

I had a guy in here this weekend with an 08 for a valve adjustment, and I always take that opportunity to clean the carbs and check float adjustment. He regularly uses Seafoam, and at 35,000 miles, his float bowls were some of the cleanest I have seen. But he had one pilot jet that had gotten completely plugged sometime in the past, and it just stayed that way. He had no idea - the bike was running quite well (as these always will, even is one cylinder is completely shut off). But he seemed to be pretty impressed with the difference on his 500 mile ride home.

Goose

[Marcarl]

Everybody needs to remember that no fuel additive can clean the carb jets/passages unless the fuel is actually running through them. In other words, a partially plugged jet can be cleaned this way, but one that is completely plugged cannot. This is because the jet orifices do not actually sit submerged in fuel, so just putting cleaner in the float bowl is about as effective as putting it in a bowl on the floor under the engine.

 

Yep,, thanks for the reminder, but to get him home and the cost of a can of cleaner, you just never know, there might be enough flow that over a prolonged period of 5 hours running something might help things along,,, and he says when he got home he was quite pleased with the way it was running. Now did I say I cleaned the carbs,, like a bench cleaning,,,, nope,,can't do while they're not on the bench.

[V7Goose]

Yep,, thanks for the reminder, but to get him home and the cost of a can of cleaner, you just never know, there might be enough flow that over a prolonged period of 5 hours running something might help things along,,, and he says when he got home he was quite pleased with the way it was running. Now did I say I cleaned the carbs,, like a bench cleaning,,,, nope,,can't do while they're not on the bench.

I agree with you 100% - always worth a try. And I wasn't even trying to suggest that you personally needed the reminder - just thinking about all the various readers on this site and how often we recommend Seafoam or other gas additive for carb problems. Sometimes we get to thinking it can do it all, and it just cannot.

 

Glad his bike is running better.

Goose

[V7Goose]

By the way - best way to test the vacuum port is to just remove the cap or vacuum hose and spray the port with a little starting spray. If the port is open and cylinder firing, the speed will definitely pick up. Your friend can do this test himself very easily.

Goose

[Trader]

I think carl was using carb cleaner and propane to test for leaking boots. He did a really thourough job of testing it and it wasn't sucking anything anywhere it shouldn't!

 

Carl sprayed carb cleaner and blew compressed air into just about every nozzle, jet, and hose available to us with the diaphrams and slides out and the air box off.....and a few other places too!

 

the diaphrams are like new.

 

The idle mixture screws were about 4-5 turns out at first. We took them right out and sprayed cleaner and compressed air in the hole (what is the jet screw hole called anyway?) Then set them to 2 1/4 turns out.

 

In our "journey" we ended up with them at about 1 1/2 turns out.

 

The bike ended up sounding rough...but it would idle at 1000 rpm...where before it wouldn't idle at all without 1/2 choke and then at about 3000!!!!!!

 

The ride home was uneventful....no backfiring on decel...seems to have ok pick up...no hesitation when I open throttle but it did seem to be slow coming down to idle....a couple of times I had to blip the throttle to get it to drop the idle down.....it wanted to hang up around 2200 a few times.

 

I have a similar set up with the hoses and vacuume guage...tomorrow I'll hook them up and see if there is still no vacume.

 

I want to see how the plugs look after my 5 hour ride also.

 

I don't understand how it can run with no vacume???!!!