Low vacuum across all carbs

[lonestarmedic]

1986 Venture all stock. Has 80K miles. Cylinders showing 170 or better on compression. Using a Morgan Carbtune 2. All 4 carbs at the bottom of the glass. Just barely visible. Cleaned the carbtune and a few drops of light oil applied. Bike used to pull rods about halfway up. Running well. I inverted carbtune and checked. My bench sync is pretty good that way. Sprayed starter fluid around boots and intake with no change. Cannot figure why showing low. Starting to suspect gauge. Going to outfit a vacuum gauge with a restrictor valve and check. If I have compression and closed throttle plates I would think vacuum should be better. Any ideas or stop worrying?

 

[tugla]

whats your idle set at....does sound odd especially if starting and running decently. ive seen one or two at bottom of guage and kept syncing and it brought them all in..but all four....odd...
a/f screws all roughly the same???

 

[Mr. Max]

Do you have restrictors in carbtune hoses? They should be at cylinder end.. Does it show vacuum if you give little throttle?

 

[Damon]

Test your meter on a known good source. Is your V-Boost open all the time?

 

[dannymax]

Test your meter on a known good source. Is your V-Boost open all the time?

It's a Venture Damon.

 

[dannymax]

Have you tried backing out the left rear carb (#1) adjuster screw a half turn or so....see if you can get that rod to climb a bit?

 

[Damon]

It's a Venture Damon.

Ok I missed that LOL.

 

[MaxMidnight]

If the motor is running OK and the only issue is an indicated low reading then that would suggest to me that, as you have surmised, the gauges are giving a spurious value.
The Carbtune is a pretty simple piece of kit so little can go wrong with it. As Mr Max has suggested do you still have the restrictors in place?

 

[lonestarmedic]

Damon I have not been able to get my V-Boost to actuate

Restrictors are in place and next to the motor.

I did try to adjust #1 against the #2 cylinder. No real climb.

Next ideas are a known vacuum source to verify the Carbtune. Then rig a propane tester with a small flex end to direct towards the various spots.

Of special interest to me will be the shaft seals. The bike has 80K miles and is 30 years old. I tried to test them with starter fluid. No perceptible rpm increase.

It runs and idles pretty dang good. Pulls smooth and no surges.

Idle is setting at 975-1000 rpm.

Mixture screws are set at 2.25 turns out.

Only three thing I really know will effect the vacuum. Lack of compression, a vacuum leak, and the butterflies open too far. Those are stated considering idle is correct and motor is worn.

I will get this figured out. We went out 2 up and got 35mpg. And this is 400lbs of people and about 50 lbs of luggage. Thought perhaps I had missed some trick or adjustment.

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[Traumahawk]

Well normal rpm at idle is 1100 roughly. I wonder what would happen to the vacuum if you move it up?

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[lonestarmedic]

Traumahawk- Moves just slightly. Going to take momma and run the crap out of it this weekend. Couple 250 mile jaunts. If it is out of whack my gas mileage will tell. Ordered some fitting to tie the carbtune together on one vacuum source. Think I figured out how to make a small propane tester.

 

[Traumahawk]

OK thanks for the update......and keep us informed after the run.

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[lonestarmedic]

First test is tying all Carbtune ports to a common source. I tried my MityVac. The carb tune requires a continuous source! You pump with the MityVac and as soon as you stop the Carbtune rods drop to zero. And I mean pump like crazy. A stroke on the mighty vac at about 100 a minute. (I teach CPR so it equates for me). At the first few strokes one rod jumps very quickly followed by others. At low vac very uneven. At a higher pull they are more even but definately a spread of 5. Iay try my air conditioning vacuum pump with a bleeder valve in the line. So I can pull a low vacuum.

Off hand I would say that the Carbtune is most accurate at a high vacuum. Maybe in the 20 to 25 area. I do not trust it. Will see when I get a continuous source. Do not think bike would work. I bet a single cylinder could not stand all 4 ports at once!

 

[lonestarmedic]

My Morgan Carbtune looks to be worn out.

Ok, I put an old vacuum gauge on the bike and checked the vacuum at the ports. Now granted this gauge is not finely graduated. But I am reading about 9 inches of vacuum. Manual says I should have about 8.9 inches. So, the bike is sucking unk:
My Morgan Carbtune should read at least 20mmHg. The sucker is all the way to the bottom and only one or two of the rods are even bouncing a bit. I flip it upside down and two rods will balance. The other two will not. I think that the bore on the brass bushings is worn on the carbtune. So the rods will cock and drag in the bore. And the vacuum is going past the rods.

I have cleaned the rods and polished with steel wool. Cleaned the brass bushings with a q-tip soaked in blaster and WD-40. Tried waxing rods. Tride a few drops of very light oil on rods at bushings.

So, I am going to obtain a set of normal vacuum gauge synchronizers. And see what I can do there. And I am going to use the guage off my MightyVac to double check the old gauge I used last night. I think it is calibrated in mmHg.

My final thought is to purchase the DIGITAL synchronizer meter. But, I want the 6 cylinder one so that may have to wait until the money makes an appearance.

J.B.

 

[lonestarmedic]

Checked throttle shaft seals

Worked on bike and started chasing down my problems. So, I put it on the lift and checked the throttle shafts for vacuum leaks 2 different ways.

First I got a can of starting fluid and outfitted it with a straw tube from a can of WD-40. Used this ti spray against both shaft ends on all 4 carbs. No rise in RPM noticed that I could hear.

Second I stuck a hose over the end of a propane torch. Then necked the hose down until I had a piece of 3/16" hose on the end. Turned on the valve and verified gas coming out the hose. Placed the end of the hose next to all 8 shaft ends. no rise in RPM that I could hear.

Did find a bowl drain that was a bit wet. Time to order new O-rings.

So, I then used the same 2 techniques to check top of carb at airbox. base of carbs at top of boots, and the boots/runners at the cylinder heads. No noticeable rise in RPM.

Satisfied I do not have discernible vacuum leaks. Think my Morgan Carbtune is suspect.

J.B.

 

[Traumahawk]

You can get in touch with Morgan. ....if I remember right all of their products have a lifetime guarantee.

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[lonestarmedic]

Traumahawk I checkes the website and it is 12 months. I sent an email about 8-9 days ago and did not get an answer on what to do. Once I prove it, I will repair it with a .45 for all the trouble it has given me.

 

[Traumahawk]

How long ago did you buy it? Also the UK is roughly 6 hrs ahead of the US. I would try calling them. Your email couldve wound up as spam...you never know.

 

[Dragmaxster]

Traumahawk I checkes the website and it is 12 months. I sent an email about 8-9 days ago and did not get an answer on what to do. Once I prove it, I will repair it with a .45 for all the trouble it has given me.

As long as you have the date you sent it and it is ahead of 12 months you should have no problem- he is very easy to deal with and very understanding.

 

[lonestarmedic]

It is about 8-9 years old. A Carbtune 2 not the newer Pro.