59A-B Vacuum at dipstick tube
 

Hey fellas! I was running a good distance from home when my primary power valve let go ( Holley 94 ) but I had to get home. I remedied the power valve but now it's just not running like it was. Exhaust tone not the same, sleepy on accel from cruising speed and just doesn't have the power it did. I've set the distributor timing with the 3/8" method, checked my points gap, checked the timing, compression test shows 125-127 psi on all cylinders. BUT, vacuum gauge bounces between 14-19 Hg/in. at idle and now I'm drawing a vacuum at the dipstick tube. Any ideas on where to go from here? Thanks for your time, greatly appreciated!



Jim Sgrig

Re: 59A-B Vacuum at dipstick tube
 

Hi Jim. Glad you have posted here.

Jim asked me the same question via pm on the hamb but I couldn't really help. Any help you can offer is most welcome.

Jim, can you flesh it out a bit, what motor is it, what type of distributor, cam etc. What are we dealing with here.

Mart.

Re: 59A-B Vacuum at dipstick tube
 

The only way you would see vacuum in the crankcase is when the intake manifold gasket is bad leaking inward towards the valley or if the intake manifold has a bad runner with some type of hole. You don't mention is you have one on your engine but another item that would create a leak would be if there's a PCV involved that's not seating correctly creating a vacuum leak.
Ronnieroadster

Re: 59A-B Vacuum at dipstick tube
 

Yes, Thanks Mart!
'46 59A-B with stock distributor converted to crab cap, bored .040" over. Fairly sure it's a stock cam with adjustable lifters and milled stock heads, tri-power with Holley 94's that ran a treat before this issue. NO PVC system....

Re: 59A-B Vacuum at dipstick tube
 

My first thought is intake manifold gasket...but the fluctuating vac makes me scratch my head a bit. Really shouldn't pull vac at the dipstick if there's a proper crankcase vent elsewhere. Hmm-intake is still where I'd start my search I believe, at least after maybe pulling each plug wire off in turn while idling to see if there's a weak cyl.


Terry

Re: 59A-B Vacuum at dipstick tube
 

No PCV Ronnie....


Intake leak has crossed my mind, but would that give me the vacuum readings I'm getting?

Re: 59A-B Vacuum at dipstick tube
 

125-127 psi compression on all cyls. It all started after getting unmetered raw fuel through the vacuum port in the carb base....and driving home maybe 25 miles....

Re: 59A-B Vacuum at dipstick tube
 

How bout adding air via a compressor to the crankcase and listen to where it comes out . Dont have the engine running of course and dont put hi pressure air to it

Re: 59A-B Vacuum at dipstick tube
 

no PVC only place vac can come from is the intake so looks like its time to lift the valve cover

Re: 59A-B Vacuum at dipstick tube
 

I understand. What I was thinking is a possible vacuum leak at an intake port affecting a particular cylinder and it'd give an indication of the area to look for when pulling the intake.


Terry

Re: 59A-B Vacuum at dipstick tube
 

Since your running three deuces I have experienced when tuning three carbs the vacuum gauge needle bouncing similar to what your seeing. But the engine did not have any vacuum in the crankcase issue.

For an engine with no issues here's how I solved the bouncing needle issue. First thing that helped was a slight increase in the idle setting on the center carb. Next setting all three carbs so they pulled the same air at idle using a Unisyn gauge helped as well. And final adjustment adjusting all six idle air mixture screws to where the vacuum reading is the highest.

Another detail when additional air is getting into the intake plenum below the carbs the vacuum reading will go up along with the curb idle. The additional air will cause a lean condition thus some ignition misfiring will take place due to being to lean. Vacuum in the crankcase is causing a lean condition more air below the carbs into the intake runners finding the reason for this additional air will solve most of the problems.
Ronnieroadster

Re: 59A-B Vacuum at dipstick tube
 

Have you tried spraying a fluid around the intake. say carb cleaner, maybe WD 40 ?

Re: 59A-B Vacuum at dipstick tube
 

Sorry, I did forget to mention it idles fine....nice, quiet and smooth. I get what you're saying, I'm gonna give it a go and see how much difference each cylinder makes.

Re: 59A-B Vacuum at dipstick tube
 

Yes Bob....no difference in running. What I haven't done, is try spaying into the oil fill and see if that makes a difference. That would indicate a leak into the gallery....

Re: 59A-B Vacuum at dipstick tube
 

I'll definitely give that a go after I figure out this vacuum leak deal. It ran like a raped ape until the power valve/raw fuel deal. There's another symptom I forgot to mention, when it was leaking raw fuel into the intake, the valves started to rattle like mad when the power valve let go. Now that the power valve issue has been corrected, the valves are all silent, but now I have the driveability issue and vacuum at the dipstick tube.

Re: 59A-B Vacuum at dipstick tube
 

Yep....may be time for an "exploratory"....

Re: 59A-B Vacuum at dipstick tube
 

Bad power valve will leak fuel into the oil. Your vacuum readings sound like a valve, valve spring or guide. Backfire from engine will damage the power valve you had to replace.

Re: 59A-B Vacuum at dipstick tube
 

breather opening at front of oil pan plugged ?

Re: 59A-B Vacuum at dipstick tube
 

Vacuum brake routed correctly

Re: 59A-B Vacuum at dipstick tube
 

Pulled the intake…good seal all around. While grasping the valves and shaking side to side by hand on the intake valves that were at the bottom of the cam lobes and I get noticeable lateral movement and you can see the stem move while peering down the intake port. Seems excessive to me. Is there a spec for lateral movement or play? I’ve also noticed it has the 2 piece guides with the tulip valves. While prying down on the guides through the port, they move quite easily. Is this normal? It does have the adjustable lifters. How high are the guides supposed to sit above the floor of the port? I’ve go what looks like 1/8-3/16” above. Is THIS normal?
I want to thank everyone for their input up to this point, more would be greatly appreciated! Thanks fellas!