GMC Repair: Vacume Advance, impco propane, intake leaks

Question
Sir
I have a GMC 350 V8 running on Impco Propane equip. I realize that some things are different however I believe that my question is general. I rebuilt the engine several years ago and hopped it up. Don't know if these facts influence an answer but will include.  10.1 Compression- Crane RV Cam (mild.)H-266-2 (Can Timing at .050 ...Intake: (4deg) ATDC Close: 34deg ABDC)/ (Exhaust: 47deg BBDC Close: (11 deg.)BTDC. Intake Duration 210 degrees/Exhaust Duration 216deg -...(All parts rebuilt - running  Accell Performance Coil,Aurora 8.5 performance wires and Bosch plus 4 plugs. Engine has 30000 miles on new.
I have very little vacume at any RPM. I was doing small tune up and replaced the vacume line from Mixer (Carb) to the Distributor. Noticed lack of vacume.  Matter of fact had to put tongue on end of hose to determine if there was any at all.  
Q: What should I look for that would cause the lack of same and when should I expect the most draw. I thought that it should be a idle. I get about 8 -10 Mpg whether I am driving City of Highway (30 MPH or 80 MPH)
the engine is in a Starcraft 86 GM Van (weights 5400 net)so I accept lower Mpg but could be better.  
Sorry to give you all this gobbly gook but don't know what you need to give an assessment.
Earl
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Answer
I am in TOTAL SHOCK, I FINALLY got someone to give me some basic information as to their vehicle.

What i usually get is and these are the EXACT and ONLY information I get:

MY CAR WON'T START, WHAT'S WRONG.

That's it, NOTHING else. NO MAKE, MODEL, YEAR, ENGINE, NOTHING.

And they wonder why we get cranky in our old age.


Ok, back to your problem. As you ae aware, I'm sure, that there are numerous causes for LOW vacuum from intake leaks, to valve timing, etc,etc.

Did you test for full manifold vacuum at the intake at idle speed and what did you get ?. Should be close to 16 or 18" at idle.

Are you feeding your distributor direct manifold vacuum or a vacuum source ABOVE the throttle plate(s) (valve) ?.

Have you had this problem from day one or is it recent ?.



Let me know.



PLEASE keep your questions on the ALLEXPERTS BOARD because without it, Us volunteers would NOT be needed.

I do not have a staff of people helping me answer your questions, I do it all by my self, Therefore, Due to being retired and a computer on a dial-up connection that is so old it does not even have SPELL CHECKER, So please excuse the TYPO'S.

I do my best to respond to questions within 4 to 5 hours, But  due to the volume of questions I receive on a daily basis I answer them ASAP. If you require a faster response you can e-mail me directly at the below e-mail address as I check it more frequently.:

meperganfortis@msn.com

When you are asked to RATE THIS EXPERT the site only allows for about 10 (TEN) words. Therefore,  I never get to read your full response. You can e-mail me directly at the above said personal e-mail site. But make sure that you RATE ME before e-mailing me directly if you so desire to do so.

Sometimes when you have to replace a part, I will askyou  if I can have the old part, As I rebuild them and sell them for extra income. I will pay the shipping costs as long as it does not exceed $10.00.

Retired in New Mexico and teaching my son to learn the trade.

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