carb/timing help

[DirtDonk]

ACDelco PCV Valve - 19313320

It's a part for multiple GM products. But I use a '71 Corvette LT1 PCV on my '71 as well, so it's not out of line to cross lines. I tried one for a '74 Granada 302 and it bogged like you would not believe! I was only trying to find one with the 90 degree elbow already installed, rather than the straight-up models stock for the Bronco. That's when I found out they really could make a difference.
But it's hard to say the one you're using is "right" or "wrong" based on the applications. It fits some pedestrian models, but then again it's also for the '99 to '07 Corvettes. Should be a reasonably high-performance engine companion to yours.

This is why I may end up spending $100 (probably $200 by now though!) for a custom tunable PCV valve from the aftermarket. You can tune the open and the close times with a screwdriver. Pretty trick actually.
At least you could put it on multiple vehicles and not have to buy one again if you get another engine that needs it.
But it's a lot to digest (spend) on one part. Billet aluminum or not!

Paul

 

[bronco italiano]

That plug is rich.

Are you using plugs recommended by BP? Might try next step or two hotter see what that does.

so when you took it to the speed shop, did they give you a printout of fuel air ratio? Sounds like they just tuned it using their ear, as in, they don't work with carbs.

All the printout numbers are neat, but not really a thing. I think you need to find a tuner who works with carbs, who knows carbs. Did BP say it was tuned and ready to run, because if it came as a complete setup, and runs like that, they owe you an explanation and a carb set to work with your setup.

I just read up on that 670 carb, seems to me to be the absolute cheapest carb they could possibly make. 4 corner idle adjustment??? why? I recommend after you complain to BP, you call a known carb shop and ask what they can do for you.

Lastly, I can't say enough good things about carburetor unlimited in PHX area. http://carburetorsunlimited.com/ call them and he will answer

Bruce Benner may be "timing out", he was going to do a couple Q-jets for me. He got grumpy and then declined after I had already bought his Offy SBF intake for a qjet. Another member here recently had some issues with Bruce and not sure he followed though on some issues. Bruce is about 84 so he could have some health issues.

 

[Torkman66]

Although I have the Holley Warrior, I'm thinking about changing to the new Edelbrock AVS. Lots of folks have discussed how they run much better and eliminate all hesitation or bog at idle acceleration. Great for street/cruiser trucks but if you want max performance (HP) then I think the Holley is a better carb.

 

[steelworker77]

That 13 is pretty low, but in line with that cam and HP rating I would think.
Stock is 19 on the low end and 22 on the high end usually. I am a little bit surprised though, that it's that low even with your 18 degrees of advance.
Hmm, I wonder if there is a mis-matched timing mark and pointer situation. Very common with home built Ford engines, but not so much with pro-built stuff like BP.

Just for giggles, you could advance the timing at idle while watching the vacuum. See what it takes to get it up to, say, about 16 or 17 inches. That's about as much as I'd ever expect from a cam that big, but it might be possible to get there.
If it starts running worse while you're getting more vacuum, it's just too much. But if you can get a little more vacuum signal out of it (15 would be a good start!) with some more advance and not lose any drivability, it'd be worth it.
The builder says that 36 degrees total is fine, but I think you said you have it at 34. Am I remembering that correctly? If so, it sounds like you can throw at least a couple more degrees at it just to see if the vacuum goes up.
Only reason I'm on about the vacuum at all, is that higher vacuum signals usually benefit carburetor metering and adjustability.

Speaking of vacuum, is your current power valve the correct rating for that idle vacuum? Earlier it was mentioned that power valves are a common sore spot for being the wrong one for a particular engine build. If you have not done so already then, you might re-visit this aspect and compare your actual reading to what valve is installed.

Paul

14 was the absolute highest I was able to get out of it. Im just rich on the mixture screws to band aid the hesitation some. Came with a 6.5 pv which from what I am reading seems like it should be right for the vacuum. Maybe bump up to a 7 or 7.5 once everything is where it should be?

I may bump my idle up some from 750 to 800 or so. It has a decent amount of lope to it at 750 and if stepping on the hydroboost while cold can drag it down a fair bit. Assuming with a cam this size its normal for rpms to fluctuate a bit?

Accel pump stuff arrrives monday so I should know if that helps by the end of the day monday. Didnt get a change last night to screw with pcv to see if that made any changes. I am also gonna just unhook vac advance and see if any changes there at all just to rule that out.

The hesitation is right off idle like as soon as you get into the throttle and after its warm its not really even a hesitation more of gurgle if that makes sense. You can notice it the most in 4th gear lugging at like 12-1300 and just barely get into the throttle it gurgles alittle but pulls right through it.

If it was me driving it all the time I really wouldnt worry about it to much but its my wifes daily driver so I need it to run right, be able to idle for a bit without issues and not worry about any detonation.

 

[steelworker77]

It's a part for multiple GM products. But I use a '71 Corvette LT1 PCV on my '71 as well, so it's not out of line to cross lines. I tried one for a '74 Granada 302 and it bogged like you would not believe! I was only trying to find one with the 90 degree elbow already installed, rather than the straight-up models stock for the Bronco. That's when I found out they really could make a difference.
But it's hard to say the one you're using is "right" or "wrong" based on the applications. It fits some pedestrian models, but then again it's also for the '99 to '07 Corvettes. Should be a reasonably high-performance engine companion to yours.

This is why I may end up spending $100 (probably $200 by now though!) for a custom tunable PCV valve from the aftermarket. You can tune the open and the close times with a screwdriver. Pretty trick actually.
At least you could put it on multiple vehicles and not have to buy one again if you get another engine that needs it.
But it's a lot to digest (spend) on one part. Billet aluminum or not!

Paul

I have had a little bit of a slow return to idle ever since installing the motor. I really just chalked it up to the throttle linkage being old and sloppy and for the fact that you can pick up on the underside of the pedal and it will drop down. I have a cable setup I need to install.

So I unhooked the pcv left it open and capped the vac line off the carb. Didnt change the slight hesitation but it does return to idle immediately. I swung by napa and grabbed a pcv from a 1970 mustang with a 351W in it. Right back to the slow return to idle. It might hang at 1k for second and then slowly drop down to 775-800.

Today is probably 15-20* warmer outside and I can tell you the hesitation is noticeably better. That intake certainly does not like the cold temps. Im betting at 55* plus it might not even be there.

So gonna order an adjustable pcv setup and play around alittle with accel pump cams etc and go from there.

 

[DirtDonk]

I’m not an expert on hot cams, but from what I’m hearing from you, I think your idle should be at about 1000 RPM.
A 600 to 700 idle is for a stock, or near stock cam. Cams with low vacuum numbers like you’re seeing would probably work better at higher RPM.
Even at idle!

 

[steelworker77]

Got to spend some time on it yesterday some. Got m slow return to idle fixed (linkage rubbing on firewall). Played with timing alittle and vacuum and settled at 16* initial with 34 total and that seemed to make starting easiest as well as just overall response. Set my mixture screws for highest vacuum which was all 4 out 1/2 turn. Managed to get my vacuum up to 17" at 825-850rpms.

Also removed carb and verified I had the correct amount of transfer slot exposed. So I believe everything is good there as well as timing.

Had a bad hesitation off idle as I expected was going to happen. Installed a .035 accel pump nozzle and noticed it was ever so slightly better. Installed the blue pump cam in position #1 and wow massive difference. Hesitation is 95% gone and the bottom end feels much stronger. I think it alittle warmer weather it would have been completely gone (high was 16* yesterday). I did order a 9.5 powervalve to replace the 6.5 that is currently in it as the vacuum results were substantially better.

Making progress

 

[73azbronco]

You have an air gap intake. You have a circle track or race type carb.

It sounds like you have a camshaft for high rpm vs torque/towing.

These facts tells me you will have low vacuum and poor off idle response, just the nature of the beast with that setup. IOW, an engine not really meant to be in a heavy slow 4x4 unless you plan to run sand all the time.

What piston material do you have? Don't go too high on timing if you have hypertetic pistons.


Sorry to hear about Bruce, great guy, and last of the gentlemen racers who kept our old stuff running.

 

[steelworker77]

You have an air gap intake. You have a circle track or race type carb.

It sounds like you have a camshaft for high rpm vs torque/towing.

These facts tells me you will have low vacuum and poor off idle response, just the nature of the beast with that setup. IOW, an engine not really meant to be in a heavy slow 4x4 unless you plan to run sand all the time.

What piston material do you have? Don't go too high on timing if you have hypertetic pistons.


Sorry to hear about Bruce, great guy, and last of the gentlemen racers who kept our old stuff running.

I do have an air gap intake, correct. Forged pistons. Cam specs are 2000-6000 rpms and its only slightly bigger than the cam they use in their bronco edition 302 so I would think with the added displacement I should be fine. Just with the changes I have made so far the vacuum as well as off idle response has gotten substantially better so I would think it could still be improved on. I think with a little more tinkering its actually going to be pretty on point. Thanks

 

[knack]

Like pfc_mark mentioned, a wideband AFR monitor might do you some good. I installed one about a year ago. Mounted it next to the tach on my steering column. Great tuning tool! Wish I had added it years ago. I have a stock 302 with stock carb - still has points triggering the spark, but even that had some tuning problems that managed to fool me. Actually knowing fuel/air mix under different conditions made a huge difference.

 

[pcf_mark]

13-14" of vacuum is more like a performance set up versus the 19" factory. Not enough to be a problem you just need to tune around it. If you said 8-10" that would be a whole different problem. Your description of the issue in one of your comments is more like a dead spot not a lean pop or miss. It also sounds like more fuel from the accelerator pump helped. I would give it 2-4 degress of initial timing and see what that does. This extra timing will help prevent a stumble down low when combined with a larger and faster pump shot. If this works but you get knock at other rpm report back we can adjust the curve or total timing to prevent this.

 

[steelworker77]

13-14" of vacuum is more like a performance set up versus the 19" factory. Not enough to be a problem you just need to tune around it. If you said 8-10" that would be a whole different problem. Your description of the issue in one of your comments is more like a dead spot not a lean pop or miss. It also sounds like more fuel from the accelerator pump helped. I would give it 2-4 degress of initial timing and see what that does. This extra timing will help prevent a stumble down low when combined with a larger and faster pump shot. If this works but you get knock at other rpm report back we can adjust the curve or total timing to prevent this.

I am actually up to about 17" of vacuum now the way it is currently setup. I had tried 18 and 20* of initial and it seems to respond best @ 16*.

 

[pcf_mark]

Oh that is really good vacuum! Good that you tested timing - it is not sure fire fix but a test. I run a long vacuum hose so I can put the vacuum gage under the wiper and I can watch it from the driver's seat. Then with the truck warmed up try to get the flat spot to happen a few times and observe the vacuum right before and at the moment it happens. If you are moving the throttle slightly and the vacuum is not really changing much it would point to accel pump tuning. If the vacuum is dropping more than a point or two that is instructive. Either your main circuit is lean or your power valve is coming on too late letting it go lean.