Spluttering Flathead Help

Matt6494

Matt6494

Junior Member
Afternoon Flatheader's,

I'm after some advice on my 8CM.

It idles fine, but when you get on the gas it starts to splutter.

The engine is stock, with an electric fuel pump.

So far we've checked/replaced:

- Changed condenser
- Changed vacuum diaphragm in vacuum advance
- Set timing at 2° at idle
- Rebuilt carb (original Holley 885)
- Changed distributor cap and set points
- Checked compression
- Checked spark plugs

But no luck. Any other advice on what to change. Could the generator cause this if it's on the way out? Anything else to check/try?

Thanks
 
The generator shouldn’t be a factor if the battery voltage is good.
How far will the spark jump at the coil wire? When checking spark at the plug wires is the length it can jump comparable to at the coil wire?
Solid core wires or resistance cored wires?
Have you tried pulling the choke some to riches mixture?
Have you checked gas flow out of fuel pump?
 
Kurt has good points. I'd add that 4° is the stock advance 6° to 7° is better. Too much retarding causes power loss. What are you using for a condensor and do you have a VOM to do basic checks on it?


Glenn
 
Kurt in NJ said:
The generator shouldn’t be a factor if the battery voltage is good.
How far will the spark jump at the coil wire? When checking spark at the plug wires is the length it can jump comparable to at the coil wire?
Solid core wires or resistance cored wires?
Have you tried pulling the choke some to riches mixture?
Have you checked gas flow out of fuel pump?
Click to expand...

Thanks for the pointers Kurt, I'll try your spark check.

Unsure on the type of sparkplug wires, they looks reasonably new though.

It's got an 'auto choke' on the Holley 885 carb, not a manual one.

Gas flow out of the pump is ok as it goes via a glass bowl filter so can see it's keeping up.
 
glennpm said:
Kurt has good points. I'd add that 4° is the stock advance 6° to 7° is better. Too much retarding causes power loss. What are you using for a condensor and do you have a VOM to do basic checks on it?


Glenn
Click to expand...

Thanks Glen. I've been using the Vanpelt specs in terms of set-up which suggests 2°.

Why do you suggest 4° to 7°?

Using a Lucas DCB703C as a condenser which is 0.23 micofarad which I believe is within spec per the Vanpelt site above.

Not sure what you mean by VOM?
 
Matt6494 said:
Thanks Glen. I've been using the Vanpelt specs in terms of set-up which suggests 2°.

Why do you suggest 4° to 7°?

I assumed that you had an earlier engine, but probably an 8BA. A little advance will improve acceleration. Too much, it will be hard to start and may ping under heavy load. I'd try 4°

Using a Lucas DCB703C as a condenser which is 0.23 micofarad which I believe is within spec per the Vanpelt site above.

Good value

Not sure what you mean by VOM?

VOM = Voltage Ohm Meter
Click to expand...


Glenn
 
With an oscilloscope you can see which cylinder has the problem, without one your kind of guessing. I was a mechanic, but I wasn't allowed to bring any personal cars into the phone company's garage, they were pretty strict about that. So, if I was at home I would need to narrow it down to which cylinder was misfiring. The best way is to pull plug wires one at a time and see which cylinder has no effect. If the cylinder is good the rpm will drop when the wire is removed, if it doesn't drop its the cylinder with the problem. Since you replaced the wires the next thing I would do is perform a compression test.

Do not pull the wires on an engine that has an electronic ignition. If the spark cannot jump the gap, it will look for an alternative route to ground by back tracking through the electronic control module, at first you won't notice you damaged it but then the control module will fail months later. They make a special spark plug tool to ground the wire while doing a cylinder defect test on these vehicles.
 
Flathead Fever


Is this the tool?
 

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Flathead Fever said:
With an oscilloscope you can see which cylinder has the problem, without one your kind of guessing. I was a mechanic, but I wasn't allowed to bring any personal cars into the phone company's garage, they were pretty strict about that. So, if I was at home I would need to narrow it down to which cylinder was misfiring. The best way is to pull plug wires one at a time and see which cylinder has no effect. If the cylinder is good the rpm will drop when the wire is removed, if it doesn't drop its the cylinder with the problem. Since you replaced the wires the next thing I would do is perform a compression test.

Do not pull the wires on an engine that has an electronic ignition. If the spark cannot jump the gap, it will look for an alternative route to ground by back tracking through the electronic control module, at first you won't notice you damaged it but then the control module will fail months later. They make a special spark plug tool to ground the wire while doing a cylinder defect test on these vehicles.
Click to expand...

That is a tool I do not have. I've still got the standard distributor with points so can try the pulling plugs method, although it doesn't sound like it's running on less than 8 cylinders.

I've done a compression check, and all the cylinders were pretty close together, I think 90 was the lowest and 110 the highest.
 
Idles okay but "splutters" when opening the throttle. Hmmm. Maybe have another look at the carburetor. A rebuild kit will not fix a plugged fuel passageway. Who did the rebuild, and did they check and clean all fuel paths. A partially blocked primary jet path could give you spluttering.
 
Do you have a vacuum test gauge that you can plug into the intake manifold. They come with a chart that will point you in the direction of many engine problems. Regards, Kevin.
 
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