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| JG33Replica |
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Hi Have a problem with a 351 Cleveland breaking down. it is just like it is hitting the rev limiter. Every time at 5800 it breaks down. its running MSD 6al , MSD coil and MSD race series distributor. we have so far switched 6al and coil with brand new out of box items we had on hand and replaced dizzy cap with new one and no change. have set rev limiter at 7000 just to make sure it wasn't the limiter. Does anyone have any suggestions ? I am wondering could or would a fuel issue cause it to break down like this. The fuel pump is only a standard mechanical pump ( new )
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| XR9UTE |
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Valve springs can cause it. But if that's ok it could be spark advance. What total timing and what engine specs?
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| JG33Replica |
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well we were confident valve springs were ok but now we are not so sure. 351 Cleveland 30 thou, balanced , 10:1 comp ratio 2V heads ported valves intake 2V exhaust 4V , anti pump lifters , hardened manley push rods , crane roller rockers camshaft is mutha thumpa intake lift 519 exhaust lift 503 intake 234 duration @50 exhaust 249 @ 50 and is meant to be good for 6,100 , demon 750 , edelbrock airgap intake with K&N filter , 1" spacer , 302 rods with pistons to suit , MSD ignition system. We have changed 6al box, coil, distributor, leads, plugs and fitted larger fuel pump now have 6.5 psi fuel pressure , Running premium 95 fuel. Is there a way of testing if it is valve float or do we just remove springs a test pressures. there is not much left. I will disconnect the auto meter tacho just incase that is causing a break down some how , and try that in a minute. Engine is in XE Falcon Toploader, nine inch LSD, 3.5 gears.
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| rod hansen |
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It is probably valve bounce, what is the installed height valve spring pressure, it is easy to check fuel if it too lean, just run a hose to the air cleaner back to the cabin and connect a small propane bottle and when it starts to miss turn on the gas, if it is lean it will stop missing strait away, been using it for forty years.
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| XR9UTE |
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As Rod said you can at least get a rough idea of your installed heights without dissasembly. Even with a ruler. IF they aren't close it could very well be the problem.
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| JG33Replica |
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Forgot to mention we did chuck some larger jets in carb as well. As I said the car is my sons He is an apprentice engine machinist and built this himself. He was sure he had the spring heights and tensions correct but mistakes can happen. He is going to borrow tools and bring home , then we will remove some springs and check it all again. The propane idea is interesting as well. thanks for all the input keep the ideas coming and when we check it all out I will let you know what we find.
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| milo 302 |
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Has the cam timing been advanced,that could make it run out of legs earlier.
Or maybe the cam specs are slightly off,it is only 300rpm. |
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| JG33Replica |
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We have changed valve springs. My son Mikey as I call him brought the spring tester home from work and did all the spring tensions they were all within spec at the lower end. We had another set we tested and they were a bit harder but within the cam specs right at the top end so fitted them and it has made an improvement. revs to 6,500 now before it breaks down. when I say it breaks down it sounds exactly as though the rev limiter has cut in.Not sure about Timing was all dialled in properly with degree wheel and it was spot on a zero.
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| XR9UTE |
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And what is the limiter set to? If it makes power at 6100 do you need it to go past 6500?
Wouldn't be the first time I've seen MSD stuff not work properly either. |
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| JG33Replica |
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set it at max and also have another complete brand new in the box MSD set up. tried that and did exactly the same thing , that was the first thing we thought faulty ignition box or dizzy or coil. may not need to go further but just want to know what the problem is just incase it causes a larger one. we will try HP 750 holley maybe the Demon 750 has an issue.
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| sooty72 |
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When you say it breaks down at 6500, is this just free-revving the poor thing, or under load?
You may find it is just lifter pump-up, 6500rpm with a hydraulic flat tappet is about as far as you want it to go. And that cam will be pretty well out of breath by then anyway. Those Thumper cams are just noise-makers anyway, with that huge exhaust duration. I will sound good, but a race cam it is not. Best of luck. 
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| sooty72 |
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{USERNAME} wrote: It is probably valve bounce, what is the installed height valve spring pressure, it is easy to check fuel if it too lean, just run a hose to the air cleaner back to the cabin and connect a small propane bottle and when it starts to miss turn on the gas, if it is lean it will stop missing strait away, been using it for forty years. I'd hate to see what happens if it backfired with the Propane flowing into it.
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| sooty72 |
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Just thought of something - do you have this thing jacked up, with the back wheel off the ground when you are free-revving it? Or at least have someone holding on to the gear stick? If not, PLEASE do not stand in front of the car when it is revving up and down like that. Top Loaders are know to drop into gear all by themselves, at the most inappropriate of times.
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| JG33Replica |
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Yep I agree about the cam and yeah lifters could be pumping up even though they are anti pump. I did think of that but have not had it happen before so wasnt sure. Driving it under load hard on it up the road not free reving.
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| rod hansen |
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{USERNAME} wrote: {USERNAME} wrote: It is probably valve bounce, what is the installed height valve spring pressure, it is easy to check fuel if it too lean, just run a hose to the air cleaner back to the cabin and connect a small propane bottle and when it starts to miss turn on the gas, if it is lean it will stop missing strait away, been using it for forty years. I'd hate to see what happens if it backfired with the Propane flowing into it. |
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