If you've put loads of miles on it since putting the carb on you may have worn the Acell pump cam. But it does sound like a clogged passage in the carb.
Someone above did say change the plugs. One thing to note is since mid 90's every plug manufacture has stopped ding a glaze coating on the inner porcelain, as EFI got more wide spread the glazing wasn't needed and it less to MFG with out it. Todays plugs foul easier when run on carbed motors.
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Ok, so of the things to check, I have:
Check low speed air bleed passages and accel pump and accel pump squirter for ethanol gunkiness
look for a larger vac leak somewhere else (i'm seeing some places that intake manifold bolts should be re-torqued every 30k?)
Check/reset timing - there is a chance that someone futzed with the timing, but I'm not sure. It would also be nice to get the vacuum advance working, if only for improved fuel economy on the 5hr+ drive home with a 12 gallon tank.
I have an inline fuel pressure gauge that I'll install to see what fuel pressure the carb is seeing as well.
Plugs have been changed, but might not be a bad idea to throw another set at it.
So. It stumbles when you get on the gas and you have the vacuum advance plugged?
Does it stumble if you stomp on it?
The vacuum advance is FOR part throttle acceleration. Disabling it will greatly reduce that and could easily create a stumble.
Clearly there are other issues going on, but the lack of vac advance is very likely adding to it.
aircooled said:So. It stumbles when you get on the gas and you have the vacuum advance plugged?
Does it stumble if you stomp on it?
The vacuum advance is FOR part throttle acceleration. Disabling it will greatly reduce that and could easily create a stumble.
Clearly there are other issues going on, but the lack of vac advance is very likely adding to it.
It stumbles and misfires at light to moderate throttle, if I stay in it, it will shake worse and worse, but still accelerating so I can't really do it for more than 10 seconds or so. If I get into the throttle, say more than 1/2 throttle down low, before the range where the issue presents, it will run right through that range without missing/stumbling. I have a couple videos from when i was trying to capture it on camera, the roll in and run through first gear i get into it around 1500 and it revs right through.
and a cold start, because i have it.
Well I got a bit more information about the motor, its a ford racing 302 with GT40P heads/headers (i'm told that he had to get "special" headers for them, so i'm assuming that means gt40p heads, he said they came off a v8 explorer), and an e303 cam.
according to this thread on corral, vacuum with gt40/40p heads and an e303 tends to be around 12-14", but it is not clear if these readings were in gear or in park/neutral.
Firm plan now is to check again for vac leaks, check/set timing. Hopefully I'll have some good news to report back in a couple weeks when I'm back with the car.
Well, I’m not proud to say that we threw a carb at it and changed the timing. The factory setting on the street avenger 670 was 65 mains/ 68 secondary jets, which is not too far from the old carb that had 68/70s in it. I put a new 4.5 power valve in it and moved the timing from the 10 degrees base setting to 18 degrees. I’m not sure if it was the timing or the carb/setting but it is back to running like before.
In case someone didn't mention it, take the distributor cap off, pull a vaccum on the advance can, and then plug it. Does the advance stay put or very slowly retract? Good.
My bet is that it falls back pretty quickly. If that's the case, replace the vacuum advance can.
It was the timing. :) 10° wasn't enough.
In reply to Curtis :
The vac advance isn’t hooked up. I’m leaving it that way for now since a) it appears locked up; I couldn’t move it when I had the cap and rotor off today, and b) it’s already got too much total timing and I need to get some different bushings for the msd Pro billet to get it to where it should be.
I will check the vacuum canister when I go back in to change the bushings, and a cap and rotor couldn’t hurt either.
In reply to snailmont5oh :
10 is supposed to be recommended 302 base timing, but I’m reading that a lot of people are running 18 with the gt40 heads and a e303 cam.
My old 302 never ran well with 10 base, 14-18 ran best.
Well, it made it the 260 miles from my parents in dfw to Houston without issue, and managed to get just under 18mpg on the way. The a/c worked well enough to keepme from sweating but not so well I was cold. The exhaust got a little loud above 70 so I tried to keep it under that, but with traffic running 80-85 I had to deal with the noise for a while to keep from being a rolling chicane.
Next steps will be bushings for the msd distributor and figuring out the vacuum advance.
Fits much better in the garage than the xterra.
Strizzo said:In reply to snailmont5oh :
10 is supposed to be recommended 302 base timing, but I’m reading that a lot of people are running 18 with the gt40 heads and a e303 cam.
The 10° recommended setting may be more about emissions than efficiency. A thorough perusal of the shop manual may reveal that even "pre-emissions" engines may have been tuned to prioritize emission standards at the expense of performance.
In reply to snailmont5oh :
My Volvo (96mm=3.78" bore, 2 valve SOHC) is pretty similar on idle ignition timing. It idled at 12 degrees stock as an emissions move, but it's much much happier at 18-20, especially with my somewhat larger than stock cam. If you don't care about emissions, 10-12 degrees is not enough timing for a super smooth idle.
Strizzo said:In reply to snailmont5oh :
10 is supposed to be recommended 302 base timing, but I’m reading that a lot of people are running 18 with the gt40 heads and a e303 cam.
My (extremely hackish) recommendation is this: 14° initial, 32-36° total mechanical, all in by 3k rpm, and maybe 15° or so vacuum, if the engine will allow it. And, try running the vacuum advance on full manifold vacuum. You'll probably have 28° advance at idle, which the engine should love.
snailmont5oh said:Strizzo said:In reply to snailmont5oh :
10 is supposed to be recommended 302 base timing, but I’m reading that a lot of people are running 18 with the gt40 heads and a e303 cam.
My (extremely hackish) recommendation is this: 14° initial, 32-36° total mechanical, all in by 3k rpm, and maybe 15° or so vacuum, if the engine will allow it. And, try running the vacuum advance on full manifold vacuum. You'll probably have 28° advance at idle, which the engine should love.
I have a spring and bushing kit on the way, should be here Monday. Re-checked the vac advance can and it does in fact move freely, so I’ve hooked it up to manifold vacuum. I’ll check the effect on timing tomorrow if I get a chance to run it, but I’m reading that the msd vacuum can only adds 10 degrees. We will see. For now here’s a pic from cars and coffee this morning:
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