Engine Bog

[railroad]

There are several things that can cause and or cover up the remaining bog. If you knew your a/f ratio on the primary jets (51's) you could to step up a couple of sizes. This would mean the engine is richer prior to needing the pv enrichment. You can do this and cover the bog, but you could be running around rich in cruise situations. There are several methods of utilizing the shooters. If you put in smaller shooters the stream of gasoline is spread out over a longer period at a lower amount/time ratio. You are correct that you will not have the full shot available at part throttle. Depending upon the cam you have on the pump, #2 position can delay the shot to a later throttle opening. I agree the 2 stage pv's were designed for economy purposes. I would not hesitate to install a higher number pv. If you are patient ,as you seem to be, order the 10.5s Personally, I would not be satisfied until I felt a set of 9.5s, if they are even available. If the 10.5s open too soon, you might be able to feel a soft spot, probably not as noticeable as the bog. If you want to compare the timing on the shooters, you can set one carb on #1 hole and one on #2 and try to watch which comes in first and finishes last. I guess you could try them staggered if you have lotsa time. good luck, waiting....

 

[Bennett]

I'll try to explain .. as I understand the situation... this is as it applies to all carb systems... but it's especially true of tunnel-rams... when you advance the throttle the vacuum drops off which slows down the air velocity in the runners , the fuel/air charge drops to bottom ,resulting in a lean condition above that is normally covered up by the accelerator pump shooting in additional fuel until the boosters get enough vacuum signal to start supplying fuel , since the fuel the pv adds has to come thru the boosters , it's solely up to the accelerator pump to cover this "hole" in delivery. This is why a dual-plane short runner manifold is "better" for the street, less runner volume,less "hole". From a performance standpoint you can't beat a long runner manifold because of the ram-effect that's created. If you setup a tunnel-ram w/ individual port injection & just an air valve on top , you have the best of both.. long runners w/ fuel at the bottom where you need it... finger hurts again.... dave

I'm running #25 shooters now. In your estimation how much of a jump should I try?

 

[Bennett]

There are several things that can cause and or cover up the remaining bog. If you knew your a/f ratio on the primary jets (51's) you could to step up a couple of sizes. This would mean the engine is richer prior to needing the pv enrichment. You can do this and cover the bog, but you could be running around rich in cruise situations. There are several methods of utilizing the shooters. If you put in smaller shooters the stream of gasoline is spread out over a longer period at a lower amount/time ratio. You are correct that you will not have the full shot available at part throttle. Depending upon the cam you have on the pump, #2 position can delay the shot to a later throttle opening. I agree the 2 stage pv's were designed for economy purposes. I would not hesitate to install a higher number pv. If you are patient ,as you seem to be, order the 10.5s Personally, I would not be satisfied until I felt a set of 9.5s, if they are even available. If the 10.5s open too soon, you might be able to feel a soft spot, probably not as noticeable as the bog. If you want to compare the timing on the shooters, you can set one carb on #1 hole and one on #2 and try to watch which comes in first and finishes last. I guess you could try them staggered if you have lotsa time. good luck, waiting....

No 9.5 PV available. I'll order a 10.5 ad give it a try. I'll also order a couple of bigger shooters and give them a try as well.

 

[2old2fast]

Well ....I have a tendency to take big swings at things .... go at least # 35 & IIRC red cams give you the biggest shot..... If you buy the shooters w/out the nozzles [anti-pullover] you can drill them out....
To add a little background , I quit messing w/ the 390's about 8 years ago , so my memory is probably a little fuzzy, but I think going to #31 shooters didn't have a lot of effect...That's when I saw a pair of 450's on fleabay ,got 'em for $175 [I had more than that in parts for the 390's] basically did little more than bolt 'em on & never looked back !! They were that much better [to me]


dave

 

[railroad]

In case the 10.5s are a little early opening, http://www.summitracing.com/parts/HLY-125-95/

 

[Bennett]

What are the signs that I'm washing out my rings?

 

[railroad]

What are the signs that I'm washing out my rings?

I'll answer then ask, you will be blowing black smoke out the tail pipe, car will be sluggish until you get it up to speed, plugs will soot up and have more than normal black carbon. I guess in extreme cases, the oil will smell like gasoline. Why has this question come up? Some of the real racers can probably advise at what level of richness this may occur. I am familiar with the term and have seen carbs so far from right, they would barely run, but still have not seen a street engine get ruined in short before it was corrected.

 

[Screaming Metal]

What are the signs that I'm washing out my rings?

When its so rich that its loading up @ idle, then dies within seconds. Plugs will have a wet look. And when the gaskets on the lower plenum look like they're seeping a liquid....

 

[sstock]

I just got done tuning my tunnel, it was a chore, even with a single carb, changes to choke, idle mixture, main and secondry jets as well as power valve and power valve restriction channel, not to mention shooter sizes and accelerator pump upgrades. If I didn't have a wideband I would of gone crazy from pissing in the wind. Without one it is hit and miss but seldom hit.

 

[railroad]

I guess the further from stock the engine is, the more tuning knowledge is needed. I have a stock 1850 holley on a stock 302 mustang engine with a single 4 tunnel ram. It has a manual choke that is locked down. The only issues I have are a cold start, playing with the pedal about 30 seconds and my pipes are black. I guess I am a little on the rich side. A carb transitions from idle to mains to power valve to secondaries and another power valve if applicable. These transitions need to marginally overlap to a degree you either do not feel them or power just keeps increasing. I know you all already know this, but I am on my soap box. As one stage of fuel supply is maxed the next level of supply comes on line, if the timing or amount of fuel is off, you feel it. OK I feel better now. Send the bill to the usual address.

 

[Bennett]

Update.
The reason I asked the washing your rings out question was because I had a small puddle of liquid that had dripped out of my exhaust right behind the collector. The engine idles fine and doesn't load up. But this is what the plugs look like. Pulled 2 from each side. I think they look okay.

This was after I changed both shooters to #35s. The bigger shooters made a big difference in throttle response and minimizing the bog. The bog now comes in between 9 & 10 in/hg. The bog is very minimal now and I can get through it easily buy modulating (backing off & then re-apply) the throttle a bit.
I did purchase both 9.5 & 10.5 power valves but not sure I need to continue down that path further. I'm thinking maybe a couple of shooters 1 or 2 sizes bigger. I didn't do anything with the pump cam, still white in position 2.
I guess that's it from my end. Any suggestions?
Mike

 

[Bennett]

I have made many changes from the time we started this project and realize it might be hard to remember them all so I'll describe the project and give a re-cap.
350 Chevy, two 390 Holley's on a Weind tunnel ram. 400 trans, 3500 stall torque converter. 2:93 real and 31.5" tall M/T.
Performed a Tune up and set timing. Was very advanced, now 14* advanced.
Cleaned Rebuilt both carbs.
Had #49 main jets, now has #51
Had power valve plugs, now has 8.5 (started with 6.5 first also own 9.5s and 10.5s)
Had #25 shooters, now has #35s
Had white pump cam set in position #1, now set at position #2

I'm sure I'm forgetting some things but I suffer from CRS.

 

[railroad]

Plugs look perfect. Dripping is probably condensation. Put the 9.5's and have fun. Plugs look like your main jets are dead on. I do not remember what ign you are running, but the plug gap looks close for an electronic ign. Not critical to the issue at hand. I sense some fear of the higher number pv's. Leave your vacuum gauge hooked up when driving. You will see your cruising vac higher than the pv rating, letting you run on the main jets, as you load the engine the vac will drop and the pv will come in play like a switch. You are not increasing the richness of the carbs, just when it is used. After the new pv's are in put in a couple of fresh spark plugs and check them after some miles. I expect them to be the same. Imagine, no hesitation. I think you will be more excited than me.

 

[Bennett]

Plugs look perfect. Dripping is probably condensation. Put the 9.5's and have fun. Plugs look like your main jets are dead on. I do not remember what ign you are running, but the plug gap looks close for an electronic ign. Not critical to the issue at hand. I sense some fear of the higher number pv's. Leave your vacuum gauge hooked up when driving. You will see your cruising vac higher than the pv rating, letting you run on the main jets, as you load the engine the vac will drop and the pv will come in play like a switch. You are not increasing the richness of the carbs, just when it is used. After the new pv's are in put in a couple of fresh spark plugs and check them after some miles. I expect them to be the same. Imagine, no hesitation. I think you will be more excited than me.

Ya, I haven't upgraded my ignition yet. I'm still running a prehistoric ignition. Hopefully one of my next steps.
I'll give the 9.5s try and update later.

 

[2old2fast]

Good going! Sounds like you're zeroing in on it. If anything plugs look a little lean... if you richen the main pri. jets you also [slightly ]
richen the idle... might be you could increase shooters some more... now it's you're call... you can tell better than me at this point.
[another tuning " pro " is born]
dave

 

[Rogers23T]

I had this same problem in a '72 El Camino. The Distributor was the problem after I threw $200.00 dollars in tuning and adjusting everything!!!... I found the distributor had no advance in it it basically was locked out! You may have the same problem try to find a used or borrow a HEI and swap it out to see if its bad. I also believe the holley carbs call for 5-7 psi & vacumm should be around 14-17 for full advancement..Also would like to point out Carb Cleaner boggs engine while running ether (starting fluid) however makes the RPMs go sky high.

If you look at the plugs and find them to be clean and not fouled, the problem is in ignition advancement. Fouled plugs would tell; too much fuel or not enough spark, which could be bad cap & rotor. I can tell you its not a moduel or coil, when they go.. THEY JUST GO! You have no spark...

 

[Screaming Metal]

Don't do anything else to your carbs until after your Electronic Ign. install. Your running on the lean side, but thats good. Bigger squirters and a bigger pump shot (maybe 50cc pump) on at least one of the carbs.
Things will even get better with a hotter spark....

Its like putting on one coat of paint, looks damn good, until it drys, then you can see what has been missed or where its thin. That 2nd coat makes a world of difference.

 

[railroad]

I hope you are too busy cruising to report on your carb response and haven't thrown up your hands in frustration.

 

[Bennett]

I hope you are too busy cruising to report on your carb response and haven't thrown up your hands in frustration.

LOL...No we've just been very busy and the weather in New England hasn't been the best for cruising in a T-bucket and it looks like we are in for more of the same with Sandy and all coming our way. However we did get the bucket out and took it for a 40 -50 mile test ride. The 9.5 power valves didn't change things much. We are close but not quite there yet. I guess my next move is to change the prehistoric ignition system out...it's time to come into the 21at century. I may also bump up the shooters a bit as well but one thing at a time...you know me...controlled experiments and all. This may not happen until the spring as my wife has me focusing on another project (No laughing...her MGB). This will be the winter project...at least when she's looking. The cruising days are coming to a close in New Hampshire. It's time to get ready for winter here. My wife and I took a road trip today with one of our other toys (1955 R130 International truck) and picked up 2 ton of pellets. The high here was in the 50's and a rig with heat was well received by my wife. Oops that's not bucket stuff.
I want to thank everyone who provided me with advice regarding my T-bucket project! Your opinions are of great value to me and I've learned a lot from all of you! You have no idea how many post I've read on the side and I still have many questions to come.
Thanks, railroad, screaming metal, wild mango, 2old2fast, one finger john.....too many of you to mention, you are all great!
New members, you will enjoy this site.
Later,
Mike

 

[railroad]

Be sure to put your T to bed with gasoline treated with a shot of marine Stabil in the whole system, tank, lines, pump and carbs. I thought I had a lot to do, turn off the outside water hydrants, and put a lightbulb next to the water line in the shop/barn. I am sure the ign upgrade will be a big plus. If any other changes are made to the carb, I would richen up the main about 2 or 3 sizes. Good luck with the MGB, Sandy and the winter.