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 Post subject: 2nd Gear Stumble
PostPosted: Mon Jan 18, 2021 8:43 pm 
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Posts: 14
Hey all, I've got an odd problem that I've yet to solve, was hoping I'd get some suggestions here.

I've got a 1970 Cougar, 351C 2V, only gone around the block a few dozen times, and I'm slowly figuring out problems and issues but I'm working through it. Currently my biggest issue aside from some weak brakes, is a stumble as soon as it shifts to 2nd gear. I've got an AOD, with a shift kit, Lokar TV Cable and brackets. I had the initial timing around 14, with the vacuum advance hooked up, I've tried a few different springs and bushings, and it was bad enough that it would backfire out of the carb in 2nd, I've now advanced it to ~16 initial, with the vacuum advance connected at idle in park it goes up to 28-30, I've got 18" of vacuum, and the black bushing (18 Degrees), and the 2 heavy silver springs. It no longer backfires, but in 2nd it stumbles and is very unresponsive after the stumble. While driving it goes to about 10" of vacuum at light throttle in 1st, then drops to 5" or below at the same throttle in 2nd. I've checked the whole fuel system and I've got ~6psi at the carb on average.

I've tried a lot of different combinations of parts on the distributor, this is the happiest it's seemed so far, so I'm thinking it's my carb, or more specifically the power valve. I've got a Quickfuel 680, and I believe it comes with the 6.5 power valve, so I thought perhaps when it would swap to 2nd it was going below that threshold and making it too rich. I leaned it out quite a bit and it seemed to get better, still a stumble for sure but It's getting better. My primary Air/Fuel Mix Screws are only out 3/4 a turn, and the secondaries are only out 1 turn now.

I've got a kit of holley jets from around 66-99 I think, I was wondering if I should mess with that first, or if it sounds like a power valve problem, or if there's something else causing me to have such low vacuum at light throttle in 2nd. Any help would be great, I'll be gathering my specs since the engine has had some machine work and new cam and things. Thanks.


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 Post subject: Re: 2nd Gear Stumble
PostPosted: Tue Jan 19, 2021 7:58 am 
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Joined: Tue Nov 06, 2012 10:23 am
Posts: 1358
Location: Texas
Did you put an aftermarket cam in it? What distributor do you have - original with points or aftermarket? Just so you know, you do not set base timing with the vacuum advance hooked to the carb. Unhook the advance hose from the carb, put a vacuum cap on that port on the carb and then time it. Also, make sure you have the vacuum advance hooked to the correct port on the carb after you hook it up. Usually a Holley style carb there are 2 vacuum ports next to each other on the base plate front of carb on the passenger side. I believe the port closest to the front of engine is the "ported" port which is for vacuum advance. The other is "manifold" vacuum. Plug the manifold vacuum port off if you dont need it. Really without knowing about the cam its harder to know. I personally never used the vacuum advance. Even with the smaller cam I had with 219/219 .050 duration and .505/.505 lift - it would pop and bang if I ran vacuum advance.

Glad to hear another 70 Cougar is alive. I too have a 70 Cougar.
-Matt


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 Post subject: Re: 2nd Gear Stumble
PostPosted: Tue Jan 19, 2021 9:17 am 
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Joined: Mon Jan 18, 2021 8:10 pm
Posts: 14
I did set it with the vacuum advance off, sorry if I had worded it wrong, I'd meant that it was set at ~16 initial and it has the vacuum advance on.

Unfortunately I couldn't find my cam specs, its a custom grind from Brent who I found on here and helped me with a few suggestions. Machine shop threw out the box and I assumed I had the card or at least a picture but apparently not.

My issue has persisted with vacuum advance connected and not connected. Without the advance connected it had a rougher idle and backfired out the carb, with it connected it was better but still stumbles. I tried to get in-between with no vacuum advance and advancing the timing to see if the initial low rpm in 2nd gear was causing my initial timing to be slow, but it didn't help and caused pinging under throttle.


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 Post subject: Re: 2nd Gear Stumble
PostPosted: Tue Jan 19, 2021 9:37 am 
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As I finished my last post I decided to check another spot on my computer and found the picture I took.

Looks like its 225/233 .050 duration and .610/.617 lift and 113 LSA.

Engine was bored 20 over, and at Brent's advice we shaved a bit off the heads to lower the chamber size, I've got open 2V heads that now should be around 73cc.

The Distributor is an MSD, I believe the part number is 8350. I've got the black advance bushing on there, limits it to 18 degrees mechanical advance, and the 2 heavy silver springs. I've tried different bushings and springs and this has worked best so far, but I may change that advance bushing.


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 Post subject: Re: 2nd Gear Stumble
PostPosted: Tue Jan 19, 2021 10:55 am 
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Joined: Mon Oct 29, 2012 9:05 am
Posts: 2823
Have you checked your balancer marks against the pointer? Is it a factory balancer? Your timing shouldn't be that sensitive and cause backfiring.

Normally, when I set engines like these up, I will aim for 16-18 degrees initial with about 20 degrees of mechanical advance, all in by 2500-2800. With those two heavy silver springs, your advance probably doesn't come in until about 4000-4500.

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brent@lykinsmotorsports.com


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 Post subject: Re: 2nd Gear Stumble
PostPosted: Tue Jan 19, 2021 11:12 am 
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Joined: Mon Jan 18, 2021 8:10 pm
Posts: 14
It is the original balancer. The machine shop said they checked it all at TDC, and when I was checking my distributor I had the valve cover off and from the movement on the rockers it seemed accurate, I'll check again just to be safe.

I've got ~16 initial, and 18 mechanical, and I tried 2 blue springs which said that with the black bushing would come in at about 2500, but it had no real effect on the stumble which led me to thinking it was the carb.

I agree that the timing only being slightly off shouldn't affect it much, but I think it may be compounding with the carb, since I noticed no real difference in 1st gear between the different timing setups, it's only when it shifts into 2nd.

Is it normal to drop down to such low vacuum at light throttle? Idling it can get 12-15" on average, and in 1st it'll drop to ~10" with light throttle, but in 2nd it plummets to 5 or lower with the lightest touch of the throttle, and that's when its very unresponsive.


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 Post subject: Re: 2nd Gear Stumble
PostPosted: Tue Jan 19, 2021 7:43 pm 
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Joined: Tue Nov 06, 2012 10:23 am
Posts: 1358
Location: Texas
SoCal Cougar

I figured you my have typed it wrong but reminded you just in case ;) Well as far as balancer. My old 362C has the stock balancer. With the Comp 282s cam and Aussie 2v heads that thing seems to like 42 degrees total. Duraspark distributor "blue pickup" . I think these distributors weights are 15 or 18 degrees or something like that. Now could have the factory balancer moved-yes. Thing is when I would make any changes to it, the timing would never move the next time checked and I shifted 6400.

I have heard its common for MSD distributors to flake out so hopefully your not having that problem. I don't know what rear gears you have but remember, 1st gear has little load compared to 2nd Does this happen in every gear except 1st?

What do you have your spark plugs gapped at and what spark plugs are you running- brand/part#, heat range/gap? With a MSD distributor I can assume you have a MSD 6AL or another CDI box? When I first put my MSD 6AL I made the mistake of my plug gap being to wide. I thought I needed more gap for the higher energy spark. NOPE! I ran the plugs at .045. It just did not run good. I called MSD and they said no,no,no rookie, put it at .035. So I did and that helped a bunch . Now for plugs. The 362C with that comp 282s cam, Aussie 2v heads was around 10-10.25 compression. The Autolite 3926 plugs gapped at .035 gave me the best results. The engine in it now 359C has 11.1:1 compression and I run the Autolite AR3924 gapped at .035.
On the Autolite plugs the last 2 numbers tells you the heat range. the 3924 is a COLDER plug than the 3926. The "AR" stands for "Autolite Racing" which you don't want for a street engine. The strap is set back on this plug. Also, what coil do you have? Installed vertical or horizontal?

What torque converter do you have? That cam is kinda healthy for the street. I would say a stock convertor would not be ideal for that cam.

I know, alot of reading but I drive a truck all night so I have to put all my thoughts on paper before I go to work.
-Matt


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 Post subject: Re: 2nd Gear Stumble
PostPosted: Wed Jan 20, 2021 6:02 am 
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Joined: Mon Oct 29, 2012 9:05 am
Posts: 2823
Cam isn't anything wild at all, it's a street cam for sure, but due to the rpm range, a stock converter probably won't cut it. (I don't think it's a torque converter issue anyway.)

Does it only do it in 2nd gear?

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www.lykinsmotorsports.com
brent@lykinsmotorsports.com


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 Post subject: Re: 2nd Gear Stumble
PostPosted: Wed Jan 20, 2021 8:40 am 
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Joined: Tue Nov 06, 2012 10:23 am
Posts: 1358
Location: Texas
No, probably not a tq converter issue but just was just curious of what he had. That cam looks a little hotter than what you say it is and maybe with the second gear trans ratio and his rear gear and a stock converter it could be loading the engine in lower rpm more than needed. Just a thought. That's why I threw out a few different things that maybe he over looked. Simple things like spark plug gap and coil and coil mounted position etc.

SoCal Cougar its hard to figure this stuff out without hearing it or being there but damn it we are here for you brotha. One thing that would be helpful though is if you can have someone ride with you and video what's going on. Maybe video the vacuum gauge readings like you mentioned. Just upload it to Youtube and share it here and maybe it will be even easier to figure out. And hey, maybe you can give us a glimps of the Cat too.
-Matt


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 Post subject: Re: 2nd Gear Stumble
PostPosted: Wed Jan 20, 2021 9:07 am 
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Joined: Mon Oct 29, 2012 9:05 am
Posts: 2823
nova467spanker wrote:
That cam looks a little hotter than what you say it is -Matt


No sir, I'm saying it's a street camshaft and that's what it is. Nothing hot about a duration in the mid 220's with a 113 lobe sep. That cam only has 58° of overlap. 18" of vacuum is very mild.

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www.lykinsmotorsports.com
brent@lykinsmotorsports.com


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