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Engine running crummy
#1
LHaving some issues with my newly rebuilt engine. I have a 72 Mach 1 completely rebuilt earlier this year. 351 Cleveland .040 over forged pistons, 10.3:1 cast iron closed chamber heads, Crane Gold roller rockers, Crower flat tappet cam 292/302 with .512/.538 lift, so nothing crazy. Carb is a Quick Fuel HR735 and I have a Blue Thunder aluminum intake. Transmission is a C6 with a trans go shift kit and the converter is 2500 stall. 3.50 Truetrac out back and I have 15 inch wheels. Had been running really great, would break tires loose with no problems till a couple weeks ago. It started missing and I heard it pinging a little. Also seems to be running rich. It was really spitting a lot of water from the tail pipes when warming up so I thought I had some water in my tank. I put fuel stabilizer in and that helped out with spitting unburnt fuel out but it’s still not running good. Thought maybe I got some bad gas so I got more 93 and put some octane booster in, still running lousy.
I checked the plugs and I had 5 of them carbon fouled and 3 looked good. I then removed the distributor cap and discovered it had 3 small cracks and one the plug wires wasn’t plugged into the cap very well. I thought for sure that was the problem but nope! It’s still running bad and I even put new plugs in when I changed the cap and rotor. I have made sure that the firing order is correct and all the wires are plugged in the cap and on the plugs. I thought the coil could be going bad but it checked out good.
Next I checked the timing and discovered it was at 22* advanced! Holy crap, no wonder I thought, it must have been loose and moved. I could move it, but the bolt wasn’t that tight so I still thought maybe it could have moved. I reset the timing to 15*BTC, this is where it was before I had problems, but it is still running really bad seems like it gets worse and worse. The shop that rebuilt the engine told me they set the timing at 15. Anyway, it starts easy and I can rev it up but when under a load it sputters and pops, sometimes when I turn it off it diesels.
 I must have a carburetor issue. I did check the fuel level in the site glass and it’s correct, but it does look like there’s some green crap on the brass floats. I also noticed that the fuel was pretty much gone from the site glass today and I had it running last night. Is that normal for it to leak down that much overnight? I haven’t noticed any gas in the oil. Could I have a sticky float or maybe a plugged air bleed? Thanks for reading and any help would be appreciated!

run_horse Run Horse Run!
John 72 Q Code
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#2
Green crap on the floats sounds like water.

The sputtering and popping might have blown the diaphragm in the power enrichment valve, causing the rich condition. One problem, possible water in the fuel, may have caused another.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#3
I'll try to help a little.

1st - The carb should not bleed off like that. Only a few ways that I know of for it to be losing fuel out of the bowls. Bad seal or crack in bowl or metering block. Your float could be set too low and you don't have enough to last overnight. Right after you shut the engine off do you see fuel in the sight glass - if not then you need to adjust your floats again. Leaking through the power valve. Weak fuel pump that is not providing enough pressure to keep the bowls fill. Green on the brass float would almost indicate a reaction to one of the additives you put in or water in the fuel.

2 - Carbon fool plugs are a sign of running rich which is caused by the carb out of adjustment, oversize power valve, weak spark or not enough air.
First try to adjust the carb following Holley's instructions for your model. Seeing that you had a larger cam put in the engine there is a good possibility that you need to go to a lower power valve. This is something that is overlooked way to often. To check the size you need you will need to see how much vacuum you are pulling at the manifold. Using a vacuum gauge see how many inches you are pulling at idle. Take that number and divide by two. ( Ex 10 in vacuum / 2 = 5). That is the power valve size you would need. Odds are you have the stock one that came in the carb from the factory which is a 65. Having the wrong power valve can cause it to be open at idle causing a rich mixture.

Weak spark is usually a coil issue. Sounds like you have already address those issues on the electrical side. You may have the wrong heat range spark plug causing some of your problems also. Need to check. Look on line for spark plug color diagnosis and also a heat range chart. To get a proper reading you are suppose to put in new plugs, drive 35mph and turn the engine off. I just put in new plugs and drive around the block and shut it down right before my house and coast into my drive. Be careful not to lock the steering.

3. Sputtering and dieseling. Timing, air fuel mixture or foul plugs once again. The normal timing for a stock 351 is 6 to 12 btdc with a total vacuum of 36* If the timing was at 22 at idle then added the vacuum advance you could have gone over 40* or more and have caused some engine damage. Try setting the timing at idle with the vacuum line disconnected and plugged to around 10* and see how the engine runs.. If ok then hook up the vacuum line and run the rpms up and see how it runs. Take a quick run around the block. See if worse or better. Either way this will give you a starting point to adjust your timing from. Try to find the optimal setting by adjusting just 1 or 2 * at a time.

Also wouldn't hurt to try and get a fresh tank of gas.

If all of the above fail then you may have to start tearing into the engine.

I would address one area at a time and not move on until I know I have eliminate all the possibilities in that area. Make notes of what you are doing and how it reacts.

Hope this helps a little.

Kilgon


"The only dumb question is the one not asked"
[+] 2 users Like Kilgon's post
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#4
Holy crap John, sounds like my issue all over again! In my case it WAS a cracked cap. I have found mine seems t like the Autolite 25's better, nice mid brown color, no fowling at all. My plugs are set at .045" because of the high volt coil and Pertronix II. Engine pulls like a train now.
You didn't mention what your idle vacuum was.  Your cam is a bit more aggressive than mine, but I would think your vacuum would be around 14-15" Hg. Mine is 17" Hg and I found on my 670 Holley, the 6.5 P/V worked best, didn't like an 8.5 at all, nor did it like a different pump cam other than what it came with. At least now I have a completely cleaned carb!! IF I did need to change carbs, I was thinking of going to an HR 735 as well, but I can't justify another 700 bucks Cdn to find out if it's any better.... can I borrow yours??!!!
Fuel; all your MI fuel is Ethanol laced, correct? Can you get non-ethanol and see how it runs on that?
 When I was at the Dearborn show, I was talking to a guy who said he was a high school science teacher. We got talking about Ethanol in gas. He asked what I knew about it other than it's bad news. He explained to me that ethanol does not absorb water out of the atmosphere, but it's the microbes in Ethanol (because it's plant based) that actually "eat" components of gasoline and excrete water (pee) and that is where the water actually comes from. Blew me away, sounds plausible, but I have not actually checked out his "theory". No doubt that statement will cause some comments!! 
 Hope you find the answer soon, very frustrating to say the least, I ought to know!
Geoff.

I learn something new every day!
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#5
Thanks for the replies guys!
I think I may have a blown power valve from what you guys are saying. No external leaking from carburetor. I have about 12-13 inches of vacuum at idle, so I have a 6.0 power valve. Should be right for my application. I have checked the level in the site glass and it is good while running and after I shut it off. I only noticed that the gas had leaked down after it sits overnight. I never noticed this before and didn’t think it should do this. My carb is only about 2 years old.
I just put new Autolite 25 plugs in and gaped them to .035. That’s what the engine builder installed, but I did notice that they didn’t gap them to .035, was more like .042. But that’s not the problem. I had checked the heat signs on the plugs before this started happening and they looked good. Timing marks on the ground strap looked good as well as the heat range also looked good.
As for the timing being so advanced, this must have just happened somehow. I did not drive it very far after I heard it pinging, I knew something wasn’t right so I got it right back home. Drove it for about 15 miles or so and babied it back home. I reset the timing to where it was. My engine is far from stock, so trying to start the timing at 10* BTC is not nearly enough. It has always run good around the 14-16 degree initial mark. I know to plug all the vacuum lines and how to set timing, but I guess I really don’t know what my total was. I never checked it, but it was really running great with no pinging at all. Also, my distributor is recurved. After I reset the timing I didn’t hear anymore pinging, but the engine was sputtering and popping so much that I really couldn’t give it to much gas. I didn’t even drive it very far, less than a mile and just brought it back home.
I just put in fresh gas the other day, so it’s not that. I actually thought at first it was the crappy winter blend gasoline, so I added some octane booster to it with the same results. I don’t think it’s the gas.

I started checking into the ignition first but I think I have eliminated that. Next thing to check is carb. I’m trying to go thru one thing at a time. Today I will pull the carb bowls off and see what’s going on inside. Can you tell if the power valve is bad by just looking at it?
Thanks again guys for helping me out with this!

run_horse Run Horse Run!
John 72 Q Code
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#6
Sounds like you got most of the bases covered. On checking the power valve the only sure fire way is to take it out and pull a vacuum on it and see if it holds. You may be able to see the diaphragm ripped if blown big time. Rule of thumb is if you run your idle mixture screws in all the way and the motor still runs then more then likely the power valve is blown. For the few dollars and minutes it takes to replace I would just go ahead and do it.

Once you get the engine running fine again check your timing with high rpms and see if your total is 36* This is the magic number for just about all street and high performance engines. Since you have a recurve this is probably around 2500 rpm so I would check at 3000 to be on the safe side. Also you should be able to see how fast its kicking in as you run your rpm up.

Good luck

Kilgon


"The only dumb question is the one not asked"
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#7
(10-12-2019, 11:49 AM)Kilgon Wrote: Sounds like you got most of the bases covered.  On checking the power valve the only sure fire way is to take it out and pull a vacuum on it and see if it holds.  You may be able to see the diaphragm ripped if blown big time.  Rule of thumb is if you run your idle mixture screws in all the way and the motor still runs then more then likely the power valve is blown.  For the few dollars and minutes it takes to replace I would just go ahead and do it.

Once you get the engine running fine again check your timing with high rpms and see if your total is 36*  This is the magic number for just about all street and high performance engines.  Since you have a recurve this is probably around 2500 rpm so I would check at 3000 to be on the safe side.  Also you should be able to see how fast its kicking in as you run your rpm up.

Good luck
Thanks Kilgon, I appreciate your help. I am looking for a pv now. I think I may try a 6.5 anyway seeing that my vacuum is a bit higher than it was before I had this engine rebuilt. But ya, I need to see what and where the total is. Thanks again!

run_horse Run Horse Run!
John 72 Q Code
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#8
(10-12-2019, 08:40 AM)Stanglover Wrote: Holy crap John, sounds like my issue all over again! In my case it WAS a cracked cap. I have found mine seems t like the Autolite 25's better, nice mid brown color, no fowling at all. My plugs are set at .045" because of the high volt coil and Pertronix II. Engine pulls like a train now.
You didn't mention what your idle vacuum was.  Your cam is a bit more aggressive than mine, but I would think your vacuum would be around 14-15" Hg. Mine is 17" Hg and I found on my 670 Holley, the 6.5 P/V worked best, didn't like an 8.5 at all, nor did it like a different pump cam other than what it came with. At least now I have a completely cleaned carb!! IF I did need to change carbs, I was thinking of going to an HR 735 as well, but I can't justify another 700 bucks Cdn to find out if it's any better.... can I borrow yours??!!!
Fuel; all your MI fuel is Ethanol laced, correct? Can you get non-ethanol and see how it runs on that?
 When I was at the Dearborn show, I was talking to a guy who said he was a high school science teacher. We got talking about Ethanol in gas. He asked what I knew about it other than it's bad news. He explained to me that ethanol does not absorb water out of the atmosphere, but it's the microbes in Ethanol (because it's plant based) that actually "eat" components of gasoline and excrete water (pee) and that is where the water actually comes from. Blew me away, sounds plausible, but I have not actually checked out his "theory". No doubt that statement will cause some comments!! 
 Hope you find the answer soon, very frustrating to say the least, I ought to know!
Geoff.
Hey Geoff, I remembered that you had a similar problem so that’s why I checked the distributor cap. I thought for sure when I found the cracks that’s was the problem. I was really baffled that it wasn’t, but I think it would have given me problems down the road.
 I am going to try a 6.5 power valve but looks like I have to order it. No one has the 4 door hi-flow valve Quick Fuel in stock. So I probably won’t be able to get it till Thursday. I will let you guys know what the outcome is. Thanks!

run_horse Run Horse Run!
John 72 Q Code
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#9
So I think I may know what caused my issue with hopefully just a power valve. A few weeks ago and I’m pretty sure right before I started having problems my engine wouldn’t turn off with the key. I got home one night and pulled into my garage and my car kept running with the key in the off position. It was about 10 pm and I was trying not to be real loud cause of the neighbors. The only way I could think of real quick to shut the engine off was to choke it out with a rag over the carb. It backfired a bit and I think that may have contributed to my problem? I hope this is all it is.

run_horse Run Horse Run!
John 72 Q Code
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#10
So I think I may know what caused my issue with hopefully just a power valve. A few weeks ago and I’m pretty sure right before I started having problems my engine wouldn’t turn off with the key. I got home one night and pulled into my garage and my car kept running with the key in the off position. It was about 10 pm and I was trying not to be real loud cause of the neighbors. The only way I could think of real quick to shut the engine off was to choke it out with a rag over the carb. It backfired a bit and I think that may have contributed to my problem? I hope this is all it is. We’ll see next Thursday or Friday. I just ordered a power valve from my local speed shop.

run_horse Run Horse Run!
John 72 Q Code
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