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PostPosted: Sat Sep 17, 2016 2:26 pm 
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Joined: Thu Feb 26, 2015 9:49 pm
Posts: 213
As far as when it stumbles it is from idle to 1800 rpm level ground. at 1800 Im doing 40 mph and my foot is just resting on the pedal. As soon as I put a little pressure on pedal it smooths out. If Im on an incline it won't do it because I have to use a little pedal. So Id say its the idle circuit.


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PostPosted: Tue Sep 20, 2016 9:49 pm 
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Joined: Thu Sep 15, 2016 6:41 pm
Posts: 1
Hey barnfind,
I recently joined this forum and I recognize several very knowledgeable members from another excellent 351C forum that I've enjoyed for well over 10 years. Most of them have provided you with very good advice so far.

After reading all 18 pages of your engine build progress, I think you deserve a pat on the back for the determination you've shown to do things properly, despite any problems you've encountered along the way.

I'm also a proud owner of a 351C powered '70 Mach 1. Even after 33 years of ownership, I still don't have all the answers but I do have some thoughts about the problem you described in you recent posts.


You mentioned a "stumble" while driving at steady state low speed, RPM's, light load and throttle position that clears up when you accelerate. Could it also be described as "surging" at steady low speed? I think of stumble as a hesitation when the throttle is opened up. I believe Brent suggested the carb needs more initial squirter pump shot at throttle tip in which is correct and usually cleans up the stumble.

I've experienced surging at steady low speed cruise and found a couple of problems causing it. First of all, the vacuum hoses had become dry and cracked from heat and age which caused an intermittent vacuum leak. You've already checked for leaks but taking another look might help.

Another cause was some of the plug wires had developed resistance in ohms that was way too high in comparison to the others. The slight misfire kinda felt like surging at slow cruising speeds. New plug wires fixed it.


Just suggestions from my experience. Your results may and most likely will vary.

Good luck,
Dan.


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PostPosted: Wed Sep 21, 2016 9:43 am 
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Joined: Tue Jun 02, 2015 2:28 pm
Posts: 216
Not much help here(kind of) my motor has the same issue below 2000 rpms with no load it has a irritating skip if you just touch the throttle it will instantly go away.
I have battled with it for a very long time this is a list of what i have done in the past.
1.More expense plugs nope.
2.Plug wires nope.
3.dis. cap nope.
4. adj rotor for fazing dis. nope.
5.comp.CK 210 +- nope
6.Leak down 8% +- nope
7.Change intake from BT to eldenbrok 4v performer nope.
8.Went up and down with the timing manually so many times i cant count. nope.
9.Adj the timing from inside the car with the FI timing control. nope
9.Swap from FI back to carb after trying every AFR i could think of (keep a note book on it)
FI failed so I had to put it on to get home.950CFM nope
10.Install new pick up in MSD nope
11.Reinstall FI that failed again 8 weeks later.. this time put on a 750CFM nope
12.Needed to do some carb testing on the mud truck and my motor is the closest thing to it
So I installed the 1050CFM with anneal boosters on my motor..........

Let me just say this motor has never RUN this good from the day I put it together
I can drag it down to 900rpms in any gear and it wont skip a beat and pull from mid to top
like i have dreamed about..
Before anybody jumps on me I know this carb should be way to big for the motor and there is more than
likely something wrong with the 750-950 carbs the fact i have to give the carb back sucks and the
carb. is really mine on lone...

As of today the 750 is back on and runs poorly below 2000rpms..Tonight I retry the 950..and tune on that some more.. And yes i do have all the air jet and main jet kits.


Hope I didn't bore anybody the post is a bit long.


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PostPosted: Wed Sep 21, 2016 10:59 am 
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Joined: Tue Nov 06, 2012 12:02 pm
Posts: 276
I'm no expert on carbs. But if the thing ran the best with the 1050, I'd have just kept that on it.

Some people think the annular boosters are the cats meow. I've only ever used downleg so I can't comment.

If I had to make guess, I'd say something is funky with the transition circuit. That seems to be a problem with a lot of people, but once again, I'm no carb expert.


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PostPosted: Wed Sep 21, 2016 12:03 pm 
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Joined: Mon Oct 29, 2012 9:05 am
Posts: 2416
Yep, transition circuit or another size power valve.

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Brent Lykins, Lykins Motorsports
www.lykinsmotorsports.com
brent@lykinsmotorsports.com


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PostPosted: Wed Sep 21, 2016 12:32 pm 
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Joined: Tue Jun 02, 2015 2:28 pm
Posts: 216
I have tried many a power valve.. I did not just toss the carbs on hoping they would work and go to the next..
Lots of Sundays running my locale test coarse....Neighbors are starting to love me..
But as can happen many times.... I my have over tuned myself.. working with to many things at the same time .It can happen..

I will let you know how the 950 works out..

Transfer slots and the amount of air/fuel that flow throw them should be the most likely culprit.
The fact I know every thing else is working right my make things a little easier.

This is not my thread so I will bow out for now..............


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PostPosted: Tue Oct 25, 2016 10:42 am 
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Joined: Thu Feb 26, 2015 9:49 pm
Posts: 213
Lots of good info guys. Sorry I haven't been on the forum lately but my knee Dr ruined my knee doing a minor surgery and now I have to have it replaced, only working a couple of hours on the car a day and have been replacing the original 4 wheel manual drums over to big disc brakes all around.

I said the wrong word when I mentioned stumble, there is no stumble. Last year I had a real stumble and replaced the original squirter and pump on the 680 quikfuel, to the second to the largest pump cam. The quikfuel came with the second to the smallest. I think I went up 3 sizes. I also put the bigger squirter from a 570? holley I had. It ran great after that.
The problem with this new engine is hard to explain, passengers don't notice it. When Im driving 1000-1800 rpm with only slight pressure on the pedal there is this unevenness like the engine doesn't know whether to speed up or slow down. If I apply just a tiny bit more pedal it smiths right out but then I am going to fast say 50 on the city streets.

Before I put it on jack stands to start on the brakes I did one more tune on the 4 idle screws with a buddy of mine. We took it out for a drive and that seem to improve it. From a standing start on dry pavement ,I was trying to show off my new engine to my friend, I punched it. The tires were squalling and the rear axle started hopping and did a nice chirp when it shifted to second. I was expecting this new motor to have a lot more power than stock but it has even more than expected. I couldn't be happier with the finished product. Thanks so much Brent and the other guys who gave me advice. Brent, great cam choice. As soon as I am able to stop this car I am taking it to the strip and get some time slips. I also put some bigger tires and wheels 17x9 replacing the 14x61/2. That should hook up. I did a 100 yard dash against a new chevy pick up , he won because my tires spun all the way through 1st gear.


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PostPosted: Thu Mar 23, 2017 11:41 pm 
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Joined: Thu Feb 26, 2015 9:49 pm
Posts: 213
The car is running greatThe carb issue is no longer there . I guess I was able to tune it away the last time I set the idle mixture screws. But, the noise it makes before it warms up. I have reset the lifter preload twice and they are at 1/2 turn after I feel the slightest drag on the pushrod. Brent would it be safe to turn them slightly over half turn? It sounds like only 1 or 2 are clacking louder than the rest.
After its completely warmed up the individual clacking goes away and engine sounds good, idles good with no engine shake at all.


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PostPosted: Mon Jul 23, 2018 12:04 pm 
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Joined: Thu Feb 26, 2015 9:49 pm
Posts: 213
Hi guys, I haven't been on the site in a long time but Im having a new problem. My car won't pass emissions. They check it at idle and at 2500 RPM. It passes fine at 2500 RPM but not at idle. I even tried to tune the carb while it was attached to their exhaust gas analyzer at idle. The #s would not stabilize, basically to rich at idle. After adjusting the idle screws in enough to lean it out enough to get a passable exhaust reading it was idling so bad it couldn't pass. It seems to go back to the problem I had driving the car at idle to 1800. Im wondering if the idle air jets just need to be bigger so I can tune it with the idle screws. I have to turn them almost all the way in to lean the idle but then idle speed becomes very rough. I have rechecked my timing and its good so now Ill check my plugs for the hell of it. It passed last year only after I turned Idle screws in a little to raise AFR. Any Ideas?


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PostPosted: Mon Jul 23, 2018 12:25 pm 
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Joined: Mon Oct 29, 2012 9:05 am
Posts: 2416
What carb is it?

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www.lykinsmotorsports.com
brent@lykinsmotorsports.com


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