hello!
i rebuilt a 390 borde 0.30 over new Pistons and bearings new CAM Comp 264h
headers Edelbrock rpm intake mildly porten c4 heds hv oilpump hei ignition Holly 600dp.
now the problem i Did break in the CAM sound awsome when i rev it in neutral but under load IT has like 50hp nothing hapens i did set the timing 14 degres and have à total off 35. I have 10-1 compression on all cylinders i and the CAM is set right dubbel checkt. Any idies

sorry for My bad english live in sweden

 

I would think maybe distributor is off a tooth or so, but usually doesn't idle to good.

 

35° is reasonable. Just to clarify. This is "total" mechanical, initial plus distributor though measured with vacuum advance disconnected and plugged. Correct?

 

2x on the timing...it sounds reasonable if that's mechanical advance only, but way low if it includes vacuum advance.

How's the vacuum? I don't know specs on a 264h cam but vacuum should be steady and above 14 inches of Hg for a medium cam and 19 inches of Hg or more for a stock cam at idle. This info would help you know if you had valve timing or rocker adjustment problems.

Or if the car has been sitting a long time, check the exhaust for a mouse nest.

 

yes its correct
i have around 17 inches of Hg
i have plugged all vacuum and tried but nothing
the cam is very mild
exhaust is new

 

 

What is the vacuum advance connected to? There should be no vacuum on the vacuum advance at idle.

 

Connected to the intake
it advances when i connects It but shouldent there be some power anyway

 

Yeah, with 14 initial and 35 total (by around 3000 rpms) there should be decent power even with the vacuum advance disconnected.

There will be vacuum advance at idle unless the distributor is connected to ported vacuum.

I have a silly thing to check...pull all spark plugs and make sure they have all been firing. Might just have a wire not connected all the way. These V-8's will run okay with just 7 cylinders firing but power will be lower.

At some point may need to check valve lift to make sure the cam is still okay. Sometimes the break in does not go well on flat tappets.

 

It shouldn't matter where the vacuum advance is connected in operation, so long as there is plenty of mechanical advance measured when completely disconnected.

A cylinder compression test would be an easy test or maybe better, a leakdown test.

 

The vacuum advance on a Ford should not have ANY vacuum at idle. It should be connected to the carburetor, on a port called "ported vacuum".

For now, disconnect the vacuum advance completely, and plug the line.

Set initial to around 10-14 and take it for a drive. If it now has some decent power, go back and figure out where to connect the vacuum advance.

The problem is, with the vacuum advance on manifold vacuum, you are advancing the timing at idle. As soon as you try to accelerate, vacuum drops, timing drops way down, and you get no power.

 

Now i have something to check i Will switch bak to the original distributor and but new sparkplugs and wires and disconect vacuum. i Will report tomorrow.

 

Vacuum signals are basically identical throughout the RPM band except at idle, there's never any vacuum under load at either port so it doesn't matter. Where it will matter though, if the tuner mistakenly adds the vacuum advance as part of the total mechanical advance when setting the timing. This is a very common error, which is why I asked.

I agree he should disconnect and plug the vacuum advance and see how it runs. This is the way tuning is ordinarily done anyway. Get the mechanical timing setup where it runs best, then reconnect vacuum advance and dial that in.

Connecting vacuum advance to manifold source is very useful in modified "cammed" engines that have difficulty idling due to lower overall engine vacuum. It also helps the engine run a lot cooler in stop and go driving.

 

MercurySweden,

Before you spend money, might see if the plugs are firing or not.

Also, I think Krewat missed you confirming that you have 14 initial mechanical and 35 mechanical total timing. That should work and make decent power with or without vacuum advance. You can use full vacuum, ported vacuum or no vacuum and it should be good. You can use full vacuum and have nice power off the line depending on your mechanical advance curve. And 2x what Tester 9 said, first tune with mechanical advance (vacuum disconnected and plugged) and get it all good. Then come back and play with vacuum advance.


Leak down test is a good idea to see if rings or valve seats are bad though the rings may not be fully seated if the engine isn't fully broken in yet.

If the other things check out to be okay (like valve lift and spark plugs firing), you might borrow a carb that you know is good from a friend. Your fuel pressure should be around 4-6 pounds per square inch.

 

I did try ànother carb no improvment can IT be poor ground to the distributor i Will check IT tomorrow i broke 1 sparkplugg and the autoparts store is closed