Can not get pass 45 mph

Bob Johnson

Bob Johnson

Well-known member
I was helping a club member tune up his car. I took it for a test drive and at about 45 mph (broken speedometer so just a guess) the car would loose power. If I backed off the accelerator the car would have power again. It also happens in second gear at about the same rpms. I adjusted the timing and points, checked the fuel flow at the carburetor (good). Took apart the carburetor, blew out the jets and took out one red washer (there were 2) on the float bowl jet. Checked the filter in the carburetor (OK). Adjusted the ferrule at the carburetor end of the fuel line. Still had the problem. Any suggestions.

Bob
 
I will try to clarify the problem. It is not that the car reaches a top speed and can not go any faster. It is that the car looses power almost like the ignition is shut off or it has run out of fuel. Backing off the accelerator restores the power.

Bob
 
Check your Points, worked on a Coupe recently for a friend that was acting similar to what you are describing. Turns out the Points had closed up.

Please let us know when you resolve the problem.

Darryl in Fairbanks
 
Go through the basic adjustments first..

An Ignition issue can cause drivability also. Instead of guessing hook up a spark tester to ck the intensity and pulse.
 
Points were adjusted. I removed all the jets from the carburetor andblew them out. Also blew out the passages.

Bob
 
A friend of mine had a very similar problem last week. He tried a larger fuel line thinking it seemed to be fuel starved. He discovered that the elbow next to his gas shut off valve had become clogged. After several flushes of the fuel tank to get the rust out the problem went away with the rust.
 
I checked the flow of the fuel by removing the gas line from the carburetor. Then I turned on the gas valve at the tank. The flow was strong, no obstructions. The gas that came out was clean, no rust or other junk. The gas cap was on. I did not check with the gas cap off because the flow seemed strong enough.

Bob
 
Bill's comment was what I was thinking. If opening the GAV a half turn makes a noticable difference, that's a big clue.

And I would suggest you might want to try a bit more than blowing out passages... work with paper clips or fine wire (but not on the jets).

Good luck
 
I have read stories about Model As running 65 mph when they were new. Gasoline was 50 Octane back then.

Some tips to get your cruising speed up to 65 mph:
> Accounting for the 87 Octane modern gasoline, set the timing about 1/2 pin hole or more advanced. Iterate the advance at the pin hole until you find a sweet spot;
> Reduce the spark plug gap. I run TT10 plugs with a gap of 0.027".

My Coupe, running a 3.78 stock differential, no overdrive, a standard size Model B motor with a stock Model B cylinder head, a Zenith 2 carburetor with stock jets and 18" 1932 wheels with 30 psig in the tires will do 65 plus wide open with a passenger on-board. Compression readings are in the low 60s.
 
Many years ago, when good quality replacement points were difficult to find, I had this problem because the spring action on the points was too weak. It would run at slow speeds, but as the rpm's increased, the point spring did not close the points fast enough, and the engine would lose power and start to run roughly. Just check the points by pulling them open with your fingernail and see if it "feels" right.

W. Michael
 
I concur with Bill and Bruce . Drive the car down the freeway or similar type road and doing 45 open up the gav a little and see if it improves. If it does you know you're running a little lean. You may need some carb work and as Bruce said ckeaning passages , ensuring jets are of the correct size, flow testing jets are all part of a good carb rebuild.

Also making sure your ignition circuit and components are up to snuff. I would keep stock settings . Also, I would suggest making sure you manifold gaskets are good , replace if in doubt. I like the 1-piece steel clad felpro unit .
Preferably with manifold surfaced. Also make sure you carb is tight and not leaking air there either
Please let us know how it goes
Larry Shepard
 
You must log in or register to reply here.
Back
Top