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| Back to this again. https://www.slantsix.org/forum/viewtopic.php?t=50578 |
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| Author: | Brussell [ Sun Dec 16, 2012 6:23 am ] |
| Post subject: | Back to this again. |
I'm having carb issues... car still won't rev above 3000 RPM, foot to the floor and it runs rich the entire time (confirmed by sensor, black smoke and soot etc coming out the exhaust). Plugs are covered in black soot as well. I pulled the carb off to clean it reset the float and no change. currently the jets are 54, with 8.5 pv on the 350 holley. No vacuum leaks that I can tell, running electronic distributor. I also pulled the manifold, and wiped a cloth in the intake head ports etc and the cloth turned black.... This is bad hey? Fuel filter looks clean. Could my problem be caused by crappy fuel, or even diesel fuel being mixed into the tank and run through the engine? If so would filling the tank up with known decent fuel and just running it through the car help? (I know this is a long shot). I was initially advised that jet sizes would start around 62, should I just try a set of 51's and see if it leans out? At the end on this one, cheers :/ |
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| Author: | robertob [ Sun Dec 16, 2012 6:42 am ] |
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Is your choke working properly? Is the power valve blown? |
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| Author: | Brussell [ Sun Dec 16, 2012 6:47 am ] |
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Powervalve still has movement was bought new a few weeks ago, I went up from the 6.5 that came with it. Choke is manual and is completely off. Car is running super rich from idle upwards |
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| Author: | Joshie225 [ Sun Dec 16, 2012 7:13 am ] |
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Is the carburetor dribbling fuel from the boosters? My gut feeling is that the wrong gasket is between the main body and metering plate. |
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| Author: | Brussell [ Sun Dec 16, 2012 7:17 am ] |
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I'll confirm tomorrow, I didn't think to check that gasket actually it would only fit one way. I just checked to make sure all of the holes lined up correctly, and that they weren't blocked off. |
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| Author: | olafla [ Sun Dec 16, 2012 9:08 pm ] |
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Brussel, you say you went up from the 6.5 power valve; to what? The power valve is activated when the vacuum drops below a limit that is relative to the number on the valve. That happens when you open the throttle wide enough for the vacuum to sink to that level. I am not familiar with Holley numbers, so correct me if I am wrong here, but if you went numerically higher - let us say to 8.5, will not the power valve be activated at a higher vacuum reading; i.e. sooner? In that case, the new power valve may just worsen your situation. I don't know your engine setup, but the 350 Holley may be a little too big for a stock SL6. The carb will read the vacuum 'signal' incorrectly, because of too low airspeed through the carb, and try to enrichen the mixture. Have you adjusted your valves recently? A good valve job may improve the situation dramatically. Olaf |
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| Author: | Brussell [ Mon Dec 17, 2012 2:52 am ] |
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Had a look today, looking down from the top with air filter off etc I couldn't see any crazy amount of fuel dripping out anywhere. |
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| Author: | Brussell [ Mon Dec 17, 2012 2:58 am ] |
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Hi, Yes olafla I believe you're correct I did change to a 8.5. I don;t think it's the cause of the problem though. I don't have access to a vac gauge. I was told the engine has previously been rebuilt... to what I have no idea, I just know a port job has been done, exhaust has been upgraded as has the ignition and so on. I think I'm getting into the ... strange ideas/something very simple area of the game? Cheers for the help so far, I'm learning more and more every day. |
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| Author: | Brussell [ Mon Dec 17, 2012 4:23 am ] |
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I will buy a vac gauge tomorrow, I've never used one before so this will be fun. Testing on a 2bbl 350 holley does anyone have any special tips? Or is it just fit it to the manifold and find the vacuum at idle, and at WOT etc? Cheers. |
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| Author: | DusterIdiot [ Mon Dec 17, 2012 5:45 am ] |
| Post subject: | Use... |
Quote: Testing on a 2bbl 350 holley does anyone have any special tips?
Plug it into the port under the fuel bowl for vacc. reading...that will read constant vacc, that the carb sees.-D.Idiot |
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| Author: | wjajr [ Mon Dec 17, 2012 6:59 am ] |
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You have performed some porting and freed up exhaust restrictions, but are you using a stock camshaft? Has compression been bumped up from stock? This carburetor is basically the front half of a 4160 four barrel, and could be on the too big side for a mostly stock engine causing low vacuum levels during operation. Without a good vacuum signal (high vacuum), carb has a hard time providing correct air fuel mixture. Causes for pig rich running and idle are: bad power valve or incorrect power valve, badly centered PV gasket; incorrect main jet; idle mixture circuit screwed up and or maladjusted; too large accelerator pump shot and or acc. pump syphoning when engine running; internal gasket mismatch; and various required controlled vacuum leaks plugged off in the form of PCV, vacuum advance, and cooling circuit for electric choke. Holley lists stock jetting as around 60 for 350 cfm two barrel carbs, I say around, because we don’t know the list number and model number of your carb. Stock power valve could be 2.5 to 6.5 standard flow, or other depending carb. Look for a plugged vacuum hole on choke side of carburetor that provided cooling to an electric choke that has been plugged, and unplug it. This will lean idle/transfer mixture. There are several power valves available: standard flow; high flow; and two stage (partial initial opening is at higher vacuum, and full opening is at much lower vacuum such as: # 125-201 first cracks opens @ 8 in Hg. and full open @ 5 in Hg.) I suspect a lot of your problems stem from a large vacuum drop once throttle plates crack open activating a power valve with too high vacuum kick in level such as anything above 2.5 or 3.5. In other words at 8.5 power valve is activated almost all the time while driving. When you get a vacuum gage, purchase an additional length of vacuum hose to be able to set gage on dash so you can get readings while driving. Every time that gage drops below 8.5 your power valve opens making a too rich mixture unless under WOT, or going up a steep hill. Generally to solve this problem, one may need to increase initial accelerator pump shot to cover flat spot at throttle tip in, increase main jet size, and drop power valve opening to much lower point of activation. What we are trying to achieve is to have engine running off of idle & transition circuits, and main jets most of the time, only opening power valve when under big load such as steep hill, or passing at WOT. Idle & transfer circuit provide fuel during small throttle plate opening cruise conditions Main jet comes on in addition to idle & transfer circuit during slightly wider steady throttle openings and during moderately higher vacuum levels at cruise than power valve rating to provide higher rpm operation at correct A/F mixture. Engine should be operating on idle/transfer & main jet circuits most of the time, only dipping into power valve enrichment during low vacuum conditions. |
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| Author: | Brussell [ Mon Dec 17, 2012 7:57 am ] |
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I didn't do the porting myself, the previous owner must have done it. I am unsure on any other changes to the engine as I haven't pulled it apart etc and would prefer not to. If it helps I have the #7448 Carb. Thanks for the input when I purchase the vac guage I will follow those steps, thankyou very much! I am unsure what type of powervalve is in the carb (standard, high or two stage) - I will try to find out. I can only find two ports on the carb, the vacc advance port, and the PCV port. The PCV is at the base of the carb, should I for the purpose of this plug the gauge into that port, and let the PCV hang freely? On the valve cover I have one of the older style caps with holes in the bottom to vent to atmosphere as well as the PCV. Or should I drill another port into the carb spacer? |
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| Author: | Brussell [ Mon Dec 17, 2012 5:58 pm ] |
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Hi, So I bought a vacc gauge, I put it on the same line as the vacuum advance line (Is this the incorrect line?), as I can only see that line and the PCV line. At idle I get 0" Hg, The highest reading I get is about 20" Hg this is just under 3000 RPM, and I have to rev slowly to get there. If I slam the foot to the floor she sounds like a bag of crap, and gets a lower reading of around 17/18" Hg. I also bought a fuel pressure gauge, and it's at approx 4.5 - 5 PSI. So that is sweet. I thought at wide open throttle the vacuum would be less? Heading back to the local shop to grab what I need to get a manifold vacuum line... |
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| Author: | Brussell [ Mon Dec 17, 2012 7:14 pm ] |
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Installed a port on the manifold to read vacuum, 17 - 18 " Hg, it decreases when I put my foot on the pedal, however it then goes back to 20, I did feel a difference in the Revs this time, it did seem to go a lot higher, however the tacho went higher and than sat back on 2000 rpm... I'm not sure if the tacho is faulty or what... It was purchased off ebay last year. I checked the dizzy hat, seems clean and rust free etc. I'm going to check the resistance of the leads... they are probably quite old. Cheers. This has all been completed whilst in netural with hand brake on as the car isn't registered. Edit - the leads are fine, as is the vacuum advance, did the suck air test and saw it move. It moved easily by a few mm. I'm going to go to the local shop tomorrow and put a set of 50's jets in the 350 A lot lower than current but at least it'll give me some indication as to what's happen as the level of vacuum seems to be decent? |
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| Author: | wjajr [ Tue Dec 18, 2012 6:01 am ] |
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Out of the box stock jetting for R7448 model 2300 is #122-61, Power valve #125-85, (standard flow calibrated to open when vacuum drops below 8.5†Hg.) Primary discharge nozzle size .031 Renew kit #37-749, Trick Kit 37-901, needle & seat 6-504 You should see a big drop in manifold vacuum from 20â€Hg into single digit numbers when at WOT. It is normal to see vacuum reading sliding up and down at vacuum advance tap and at manifold, this how distributor is able to automatically adjust timing going down the road. During small throttle openings such as level ground steady speed cruise timing advances to max or high vacuum condition, when accelerating or under load such as hill climbing, timing needs to be retarded to prevent detonation this happens when vacuum falls off causing vacuum advance to back off additional timing. Get the 61 jets installed, and see what happens. One reason engine won’t rev up is as soon as throttle is opened with 54 jets installed it goes lean. Lean engine won’t want to rev freely, will sputter perhaps spit back up through carb. Has the valve lash been checked? Incorrect valve lash will cause vacuum problems, and drivability problems. I said: [quote]I suspect a lot of your problems stem from a large vacuum drop once throttle plates crack open activating a power valve with too high vacuum kick in level such as anything above 2.5 or 3.5. In other words at 8.5 power valve is activated almost all the time while driving.[/quote] After seeing vacuum readings, disregard that advice. Once 61 jets are install I suspect your vacuum readings will change. |
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