0" vacuum

S

stvaughn

New member
I have been trying to get a new engine running right for quite some time. I recently followed a thread concerning cam timing and I believe I may have the same problem, camshaft not timed correctly to the crank.

Details: Model A engine with a Lion III 6-1 head, FSI distributor, Weber carburator from Arizona A, camshaft is Specialty Motor Cars "3/4 Winfield A", T-5 transmission.

Problem: Engine starts and idles fine. Must be completely warmed up before it will drive without choke. Loses power after short drive. Gets hot.

Timing set a 0-5 degrees advanced. Advancing timing to +25 or so makes it run better but pings real bad. (no surprise there). Compression on all cylinders is 75 lbs.

Checking vacuum at the vacuum port in the side of the Weber yields 0" (zero) of vacuum at idle and 15" when running up engine. Needle stable at speed.

Need help, tired of struggling with this motor.

Steve
 
Where on the carb is the vacuum port? You want manifold vacuum, not the distributor advance port. Most carb ports are designed to provide a signal for something, not manifold vacuum.

If you have a vacuum wiper port on the manifold, that's where you can measure it.

The fact it idles make me wonder if you're heading down the wrong track, and the choke having to be on suggests a fueling problem.

Others more familiar with your stuff might be able to help a whole lot more :-)
 
I think I agree with Allen about fuel or maybe a vacuum leak as well. It will get hot if it's running lean and would also be temperamental till it's good and warm. Try to add some fuel with at least the GAV. You will also see an increase in vacuum with more timing advance.. What does it do when you advance the timing? The ping would also happen with advance and too little fuel.
 
can u elaborate on this
"Loses power after short drive. Gets hot."

Did you do this build? If not, what does the person who built it have to say? Almost nothing stock there for us to go on....
 
Allen has a good point the location of the vacuum port. A zero reading at idle means you have atmospheric pressure there, not manifold vacuum. What type of intake manifold do you have? I dont know any after market manifolds that have a vacuum port--you have to drill and tap one in.
How was your timing indicator set up for the FSI? I think maximum stock advance for them is 32* at about 1800. If you are indicating 25* max advance, but getting a ping (under load or stationary?) you are probably getting more advance than indicated. You should not get a ping at 25* advance. A quick and dirty check would be to try running it retarded on your indicator, see if there is improvement.
That said however, the other symptoms of smooth idle and overheating suggests retarded timing. For a quick check, try advancing the distributor, turning it clockwise. If the idle speed increases, you may be too retarded.
YOu can check the cam timing by removing timing cover with the engine in the car. Not too hard to do, but I would work on the timing first.
 
The vacuum port on a weber carb is before the butterfly so you have carb vacuum not manifold vacuum and won't ever get a correct reading on a gauge. You need to drill the manifold and tap for a fitting so you can get a true vacuum test.

Sounds like you have some head gasket or valve problems because the compression is low for a lion head. Even with a Snyder 5.5 on a new engine, I generally get 95# compression. If the valves are leaking, it will overheat quickly because the engine is working twice as hard to perform the same amount of work. I believe the same with a leaky head gasket but it would blow soon after it overheated.

Like PC/SR said, you can remove the front timing cover and check the timing marks for alignment.
 
You could check the valve timing by just using/inserting the timing pin and watching to see if #1 is on TDC with valves closed. But, I too, don't think that is your problem. Regarding the vacuum issue, where are you trying to pick up this vacuum ? It sounds like you're reading ported vacuum which means the port you're using is above the throttle plate when you need to use one below the throttle plate.
 
as the others said your checking the vacuum at the wrong port. the ports above the throttle plate is called venturi vacuum...below is manifold vacuum
its sounds like you need experienced help
 
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I have a Weber on my cart and the port is in the carb above the throttle plate. I figured this out when the vacuum wipers worked in reverse to what I am used to. At idle they won't work and running down the road they are slow till you throttle up then they work fast. Looking at it I realized the port was in the carb above the throttle plate. I don't use the wiper so it is not an issue but I will never be able to run a vacuum check on the engine with it like this, I will have to drill the manifold and tap it for a fitting to do that.
 
Thanks for the reply's folks. I really appreciate (and need) your help.

Some additional background. This engine was built by Ron Miller in Cincinattii 8-10 years ago. It took me five years to get in the car and start trying to get it running. It has been 3 years or so since I first tried to start it up. The first setup I used was a Holly 94 and one of Charlie Yapp's Scalded Dog intakes. I really liked that set up especially since the manifold is heated from the exhaust manifold like the original. Anyway, in my attempts to find a solution to the problem I changed to the Weber carb hoping the problem was in the carb. It wasn't. The fuel is fed from a rear mounted tank with a electric fuel pump. I have used everything from 1.5 lbs to 4 lbs. pressure with no improvement. I think the carb needs 1.5 lbs but don't remember for sure. I have tried a second fuel pump with a gas can in the cab just to eliminate a fuel feed problem. No improvement there either.

I checked the vacuum port and it is above the butterfly's so it is reading atmosphere and that explains the 0 reading.

In reference to the timing, I had two different "professional" mechanics attempt to make the engine run at two different times and both advanced the distributor to approximately 25 degrees initial advance in order to get it to run. This causes a great deal of pinging and I set it back up on 0-5 degrees when they left. I use a timing indicator that was set up at zero before I installed the engine using the Model A timing pointer in the cam gear indention as my zero timing mark. I have also reduced the total advance of the FSI unit to around 25 degrees just because my research indicated that 32 was too much.

I double checked compression today and it reads 85 lbs on all cylinders both hot and cold.

I played with it a little today to refresh my memory. The engine starts and idles fine. Playing with the throttle at the carb, the engine stumbles when trying to accelerate slowly. If I try to accelerate fast it will usually die. When bringing the engine up to 1800 or so rpm it accelerates sluggishly, acting like it just doesn't want to go faster. At steady rpm (1800) the exhaust "sputters" and the engine struggles to maintain speed. It never has overheated while I am playing with it in the shop, only when I drive it. Every once in a while when I am running the engine, it will spit out a cloud of white smoke. I do not believe it is oil and the oil level has never dropped.

Thanks for your help, I am getting really tired of wishing I could drive the A.
 
-White smoke usually means blown head gasket...water turns to steam which is white.
-Sounds very lean. A lean motor will ping (lean mix ignites earlier than it should) and run hot as hell
try with the choke partway closed to see if any different.
-i doubt there is any motor that will run right with 25* initial advance. You usually see
no more than about 6-8 on say a V-8. On an A, should oughta be prolly close to zero
 
Somebody (I think it was Bill Williamson, who doesn't seem to post anymore) mentioned re-jetting the Weber. FWIW
Paul in CT
 
Its a puzzle. I still lean to timing, although inadequte fuel as mentioned is a reasonable suspicion.
When I put in the FSI, I found that pointing the rotor directly at #1 connector like you do when timing a stock distributor, resulted in a substantial retard condition at TDC. I don't know when the module fires the spark but I had to advance it from the installation position pointing at the #1 connector, to get it to fire at TDC. That is why I asked about your timing indicator. If you did not put it in yourself, or even if you did, I would confirm the 0 advance mark being at TDC as determined by the timing gear, then time the distributor. Rotate the distributor body clockwise in very small increments to see if there is improvement.
The same problem with 2 different carbs would seem to rule out carb problems, but how about fuel flow, independent of pressure. What size fuel line do you have? Also retighten all the carb/manifold nuts.
 
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