Alright, so I finally got my rebuilt 302 idling right. No more valve problems, timing set, carb set. Time to test drive!!!

But there's a hiccup. It idles great. It accelerates great. It cruises great...but only if I keep the RPM below 1500. Get above 1500 and it's like I took my foot off the throttle. It falls on its face and won't go past about 950rpm no matter how far I put my foot in it. And it doesn't seem to matter if I accelerate slowly or quickly. Take the foot off the gas, shift gears, and we're good to go again until about 1500rpm.

But that means that I have to shift to second halfway through an intersection...and shift to third too early...I can hear it--not that it's grinding or anything, but it's just too soon. Same goes with overdrive. I have to shift in at about 40mph, where before I was shifting at about 55-60mph. This also means I have a top speed of a whopping 58mph!

What's changed from the old setup to now? Bored .030 over. Installed a Melling MTF-5 cam (talked to Melling btw and they were adamant that the MTF-5 was a direct swap for the stock cam and I could use the same distributor, lifters, valves, etc. (the valves were the issue at the time)) Re-set the carb after rebuilding it. Did a valve job, but skipped on port and polish for time and money reasons.

It starts great. I drove it around town a bit and it never gave me trouble. A handful of starts and stops running errands never gave me a bit of trouble starting back up again.

I swapped out the fuel pump, which I tested and was weak. But that didn't fix the problem.

I'm running with an Autolite 2100 1.08v carb...it's one of the smallest 2100's they made. I have every reason to believe it's the original carb, and it was great for fuel economy prior to the rebuild. But now I'm wondering if it can't feed the bored cylinders and new cam.

Thoughts?

Jim

 

More likely a plugged fuel line.

 

Ross...
New fuel filters and a new fuel pump. The fuel runs to the pump just fine. It's been several years back that a plumbed in new lines from the tank to the pump, and then from the pump to the carb. I guess I could check the pump to carb line. Don't know why/how it'd get plugged, but it's a possibility I suppose.

From what I've found online the 1.08v 2100 is rated at 287cfm. My thought was maybe 1500+rpm is getting beyond what it can handle. But I wouldn't claim to be an expert in carbs by any stretch.

I suppose I've got daylight left and it wouldn't take much to check that other line. ---Edit: Checked the other line. No restrictions. Unless I goofed something up when I rebuilt the carb...It's been several years since I rebuilt a carb on a car...couple since I did a snowblower and a lawn mower. Never have gotten them wrong before, but there's a first time for everything.

The other alternative is timing. I could probably push the timing a little more advanced. Is it possible it's not getting enough? With the new cam, despite what Melling's tech says, I'm not sure.

Jim

 

IMHO sounds like fuel problem more than a ignition one. Maybe something is clogged up inside the carb. My 2cts

 

If it were leaning out, you'd likely get popping and jerking. Any chance the choke is closing? Does it have a vacuum pull-off?

 

No popping and jerking. It's really like it just runs out of gas. It does have a vacuum pull off...but I don't know that it works. I don't think the choke is closing, but...maybe??? I'll have to see if it could.

Now I'm having nightmares that the dowel on the cam has sheered, or wasn't right and somehow the eccentric isn't doing it's job. I just had the timing cover off...I don't want to have to do that again!

 

Check your float level in your carb .

 

I'm guessing the distributor isn't advancing correctly, whether it's a mechanical advance issue or the vacuum isn't hooked up or working right.

 

Now that you mention ignition, it occurs to me that if the firing order were wrong, it might behave like that. As I recall, the firing order was switched on this engine?

 

Hey James,
First let me say that I like how you just go for it & you aren't shy about asking questions. You are getting there - it's great that it's up & running again. I would vote with Wayne on a vacuum problem. Is it possible that you didn't get the hoses back on there quite right?

Good luck over there!

Ben in Austin
1950 F1

 

You should get a vacuum gauge at hook it to a manifold vacuum source...tell us what the gauge is doing at idle.

One of the guys had a link for a great reference sheet on how to read a vacuum gauge. You can also set your timing with that gauge.

On fuel issues, a lot of guys miss the canister fuel filter that is in the fuel pump, but since you replaced the entire pump I'll assume that is new as well.

Also...I might've missed it in the other thread...what was the fix for your valve problem?

Dan

 

Ha ha! I've been on FTE for a lot of years, and helped others out with areas I had experience in. It's been a great community, so I don't feel a need to put on some kind of show. I run into something weird and why not throw it up here to see if any of the very knowledgeable guys here have any insights? Even if they don't it can get me thinking in different ways and find a solution. Since I've only been living where I am a couple of years I don't have a group of car buds to sit around the garage with a trouble shoot. My old car buddies are 6-20hrs drive from me. So, in comes FTE

Ross,
The firing order was switched with the new cam. Stock is 15426378. But the Melling MTF 5 uses the HO/351w firing order: 13726548. That's how it's hooked up currently. I would think it would idle like crap (it did before the shop told me "oh yeah, that cam uses the 351 firing order" ) if I'd gotten any of the wires crossed. It idles and accelerates great up to about 1500rpm. BUT maybe the dizzy's running out of advance by then? The thing is...if I run it over 1500 it falls on its face and drops down to 900ish rpm and it doesn't get any better until I leave my foot off the gas for a while (or shift). I would expect the engine to just crap out above 1500 and recover when you dropped below 1500 if it was the dizzy/advance.

So far as vacuum goes, on the 2100 there's only one vacuum port, and it's for the distributor...so there's no mixing them up...and I replaced that line just for cheap insurance.

(sidenote: I've got a Road Demon on my wife's merc and it's got three vacuum ports. I've spent more time than I'd like to admit going "now which one of these does what?")

I haven't measured vacuum from that port, but it's an idea.

Yep...been there. I could maybe bring it up above spec if that's really the issue, but if I didn't drain the bowl before when I had poor compression and needed a lot more fuel to make the same power, then I shouldn't be draining the bowl now. I might be over-reaching the ability of the venturri to feed air...with the cam's longer duration and greater lift, but then nobody else seems to think that's likely...so the hunt continues.

I haven't hooked up the vacuum gauge since I re-adjusted the valves (jam nuts is the solution we went with due to purpose/time constraints). When I had lashed them in with the non-jam nuts I was pulling a steady 19" vacuum. I probably should take another reading. If the rain quits I'll probably go out there and see what it does.

Here's the best pic of my carb that I have available. Ross' mention of the vacuum pull off has me interested. You can see it right behind the airhorn. I hate it. The little cylinder that sits there is constantly popping out. It fell off entirely when I was trying to get the engine to run with the wrong firing order and the wrong valves (the guys at the machine shop need to buy me a new bottle of advil ). The little arm it activates is loose too, and I can't seem to get it to tighten up. It leaves me wondering how good things can run if that little vacuum pot is always leaking from that cylinder coming off, and the arm has so much play in it.



It's scheduled to rain here all day...thunderstorms...but if it breaks for any length of time I'll head out and try a few things and see if I can find a fix.

Peace,
Jim

 

I looked it up, and that model carb doesn't use the kind of pull-off I was expecting. It's internal to the choke housing. Not sure what you are referring to in your picture? I doubt that's the issue.

 

Jim,

My bet is you have a main jet or jet passage plugged or partially plugged. I have seen it several times, especially on the Autolite carbs, as the jets are in the bottom of the fuel bowl. It is probably from while it was sitting and engine was getting rebuilt, it dried out and dirt or just bad fuel dried and plugged a passage. I suggest pulling the carb, pulling the jets, cleaning it with carb cleaner and compressed air. Buy a carb kit and install it at the same time as all else is new anyway. I will bet that will fix your problem.

As far as carb size with the engine being bored, new cam, etc... you only picked up about 3-4 CI (to early for me to do the exact math), not a difference the carb will see. The only time that carb would ever feel the the difference would be at high RPM.

Good Luck.

 

If you suspect the choke is misbehaving, wire it open. You don't need a choke this weather, anyway. Might stumble a bit when first started but after a minute you'll never need the choke. I would discount carb size issue, as stated, it ain't that critical. My SWAG is the drivability issue is a plugged fuel circuit in the carb. Put a vacuum gauge on it and see what it reads at various rpm.
Have you run it with a timing light while watching stability of the advance? Is the advance stable at the speed where you have problems or does the problem show up on non driving tests? What about the internal wiring within the distributor? That does not look like HEI.