Engine is rough when accelerating

S

Seattledavid

Member
I have 1930 Sport coupe with a 1928 engine and it runs rough and hesitates when accelerated. I did a compression check with the engine warm and it is
1. 60
2. 55
3. 55
4. 62

The carb is a zenith and was rebuilt. The valves have not been touched on this engine so wondering if that is the issue. Any input would be appreciated.

Dave
 
Seattledavid said:
I have 1930 Sport coupe with a 1928 engine and it runs rough and hesitates when accelerated. I did a compression check with the engine warm and it is
1. 60
2. 55
3. 55
4. 62

The carb is a zenith and was rebuilt. The valves have not been touched on this engine so wondering if that is the issue. Any input would be appreciated.

Dave
Click to expand...

Hi Dave, have you adjusted the carburetor's GAV to enrichen the mixture? Also, does advancing the spark lever help any?
 
How often has this monster been run ? The compression is good so the problem isn't valves unless they could be sticky from lack of use.

My questions are the same as Brents.
 
I have adjusted the mixture more rich and it doesn’t seem to help and the spark has been advanced also. It is quite possible the valves are sticky as this engine has only been run twice in who knows how long. The car was restored in the 60’s and sat for many years before I got it. When I first got it I did get it started but it had a leaky water pump so it didn’t run for long. Then it sat for a year before I really started to work on the entire car. I replaced the distributor and coil and the water pump. I pulled the pan and cleaned it out had the head manufluxed and the head made flat. I didn’t do anything to the valves though.

Dave
 
You might remove and clean out the intermediate and high speed jets in the carburetor as old gas may have gummed them up.
 
Try Marvel Mystery Oil in your gas. Should help free up any sticky valves. Also detergent oil would help.

Years ago I found a Model A that had been sitting in a barn in Up-State New York for years. Started right up but ran really rough. We cleaned the carburetor, new plugs and points, changed oil to 20w-50 HD, and added Marvel to the gas. After a good drive, you would never have known it was the same engine.

Don’t help the clutch problem, buts that’s another story.

Enjoy.
 
Dave
I think Brent gave you the correct advise. Unless you have a sticking valve the marvel oil won’t do anything. It sounds like you need more from the gav carb adjustment which is the dash Choke rod adjustment. Turn it a little clockwise maybe a quarter turn at a time and see if that helps. Too far will make it lope.
Gary noted the carb jets which if the main jet and/or cap jet get clogged can cause issues. Fuel sits at the tip of the jets and if sitting with today’s fuels can clog if sitting for a months or more.
From your description I think it’s your gav adjustment from inside the car, but acheck if the jets would also be in order.
Larry
 
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We had one like this and it turned out to be the float. The guy who rebuilt the carb put two washers under the float valve and that put the float way off. Just take a peak and look at the float and see if it is horizontal. We took out a washer and the car ran fine.
 
Mine ran the same why you describe. It sat for.a long time. Got it running and it was ran on 2 cylinders and was back firing found 2 exhaust valves stuck open. Got them unstuck and it ran on all 4 but missed when accelerating. Did all.them same things you tried. Figured it needed it anyway hoping it would be something easy. Tuned it up and went through the carb. I checked jet sizes. I found the GAV did nothing when adjusted. I tried the sea foam trick and that just made a lot of smoke. I decided to pull the head and lap.the valves in. I took the valve springs out and kept them.in order they were removed. Found the 2 stuck valves the springs were quite a bit shorter than the others. They must have taken set to that height. Did a.search on here and got spec's.and found the springs were half the pressure at height than they were supposed to be and the others were weak also. Found a set of springs that were right on for pressure. I lapped the valves In and adjusted them put it together and it's a totally different running engine. The GAV now works right. The engine needed everything I did to it anyway but a vacuum gauge would have told me it was valve related. I would do the valves and check your springs. It fixed mine.
 
Mine ran the same as you describe. I did all.the same things you tried. I tuned it up went through the carb and it still didn't run right off idle. The GAV had no effect when adjusted even after going through the carb. I shorted out cylinders at idle and they were all hitting but off idle 1 and 4 didn't.make no change. I took the valve springs out in order removed and found 1 and 4 exhaust valve springs noticably shorter than the others. I checked all spring pressures and those two were way low and the others weren't that great. I lapped.the valves in and installed a good set of springs that checked right on for pressures and it now.runs good. The GAV now makes a big difference when adjusting it. Mine set for a long time also and those springs on those valves must have taken set to where they were. The springs wouldn't keep up with the cam past idle speed. That's what fixed mine.
 
I should also mention that when I got the car it only ran on 2 cylinders and found 1 and 4 exhaust valves stuck. I sprayed carb cleaner and pb blaster on the valves and got them unstuck. I think that's why the springs went bad and took set to that height.
 
Jacksonlll said:
We had one like this and it turned out to be the float. The guy who rebuilt the carb put two washers under the float valve and that put the float way off. Just take a peak and look at the float and see if it is horizontal. We took out a washer and the car ran fine.
Click to expand...

I am going to look at the float again first to make sure it is not leaking since today the carb was leaking and it may be the float. I may need to bend the float also because I couldn’t get it horizontal with even one washer and even then it wasn’t perfectly horizontal.

Dave
 
bmodeltman said:
Mine ran the same why you describe. It sat for.a long time. Got it running and it was ran on 2 cylinders and was back firing found 2 exhaust valves stuck open. Got them unstuck and it ran on all 4 but missed when accelerating. Did all.them same things you tried. Figured it needed it anyway hoping it would be something easy. Tuned it up and went through the carb. I checked jet sizes. I found the GAV did nothing when adjusted. I tried the sea foam trick and that just made a lot of smoke. I decided to pull the head and lap.the valves in. I took the valve springs out and kept them.in order they were removed. Found the 2 stuck valves the springs were quite a bit shorter than the others. They must have taken set to that height. Did a.search on here and got spec's.and found the springs were half the pressure at height than they were supposed to be and the others were weak also. Found a set of springs that were right on for pressure. I lapped the valves In and adjusted them put it together and it's a totally different running engine. The GAV now works right. The engine needed everything I did to it anyway but a vacuum gauge would have told me it was valve related. I would do the valves and check your springs. It fixed mine.
Click to expand...


Thanks so much for your input. My Gav also seems to not have any effect. I’m thinking about doing the valves as they have probably been in there since the 60’s. Did you use modern or original valves??

I seem to go from one issue to another. I put a fuse on the starter and it kept blowing fuses so I bypassed it and today the starter quit so I’m getting a rebuilt one.

Dave
 
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