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 Post subject: trouble balancing ONE carb!
PostPosted: Sun Apr 08, 2012 1:50 am 
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Joined: Mon Jul 26, 2010 6:24 am
Posts: 382
Location: Misawa Japan
ok, well i have triple DCOE 40's on my KGC10. I've been suspicious that there was a balance problem on this one carb for a long time, the number one spark plug is usually fouled when i pull it, and the rest are usually ok. today i relocated my fuel pump so that i could finally get around to testing it, and sho-nuff that intakes are NOT balanced. so i unhooked the linkages, and started tinkering and NOTHINg will correct it.

i need some guru's to throw out some good suggestions. I'm really stumped!!

these are pretty old DCOE's so they aren't as adjustable as the newer versions. i will post pics to show the intake numbers.

all the internals are matched, so they should be ok, BUT what i didn't think top do was swap the jets and stuff around from one side of the carb to the other to see if maybe i just have a bad component in there. i may run out and do that right quick..

Pics:
Image
this is the setting that the other two carbs are balanced at. (just over 2)

Image
This is the ONLY setting that the first velocity stack will adjust to for some reason.

can anyone PLEASE give some ideas. in the mean time i will swap the jets and stuff from one bank to the other and see if it happens on the second VS, and the first one is right. (confused yet?)


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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Sun Apr 08, 2012 2:00 am 
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Posts: 382
Location: Misawa Japan
BTW sapping the jets did NOT change the numbers at all :(


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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Sun Apr 08, 2012 2:34 am 
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Joined: Tue Oct 12, 2010 1:20 pm
Posts: 172
Location: UK
Might be worth checking that there isn't air being pulled in somewhere else, either carb to gasket, gasket to manifold or even manifold to head. Are they mounted solid or on rubber mounts ?
A bad leak can be heard through a bit of pipe, otherwise it's a matter of checking for tightness and flatness of mating surfaces.
Good luck !

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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Sun Apr 08, 2012 3:59 am 
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Joined: Mon Jul 26, 2010 6:24 am
Posts: 382
Location: Misawa Japan
I'm running the redline rubber o-ring gaskets, but tomorrow i plan on trying the "ether" method to see if theres a leak around the manifold, BUT it seems like if it was leaking air anywhere, then the WHOLE carb would be out of balance right?

maybe i should take the carb apart and double check everything. wonder if theres a gasket pinched or somethings just clogged up inside?

Thanks for the tip, i was just reading a tech guide that said an air leak was the easiest explanation for poor running conditions. i can't find anything in my tech guides about having one fouled plug though.


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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Sun Apr 08, 2012 4:22 am 
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Joined: Tue Oct 12, 2010 1:20 pm
Posts: 172
Location: UK
If you think of each choke as a seperate entity, a leak on one side of the carb would not effect the other. The air flow is adjusted seperatley so they are independent in that respect. As you say, a pinched or damaged gasket, a cracked mating face or a loose nut would be enough to allow the engine to suck air.
As for the plug, if it's got white/brown deposits thats running lean.
Once again, good luck. Air leaks are a pain.

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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Sun Apr 08, 2012 6:19 am 
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Joined: Mon Jul 26, 2010 6:24 am
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Location: Misawa Japan
nah, the plug is very dirty with soot. looks really rich


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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Sun Apr 08, 2012 7:40 am 
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Location: Sydney, Australia
How "strong" is the idle in general? Is it rock solid, or all wavery and delicate?

Because if say you have a "global" issue like weak ignition, it could amplify a little issue with one runner. You end up trying to diagnose that runner, but in reality, fixing the ignition (assuming that is what it is) will make 95% of the problem go away.

When I was chasing tuning issues with my Hako, I tried everything, but in the end the issue really was the cam timing was out. Once that was fixed, tuning and equalising the carbs was a snack :)

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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Sun Apr 08, 2012 8:42 am 

Joined: Sun Feb 08, 2009 3:07 pm
Posts: 191
Location: Norcal
If your butterfly valve is even slightly bent then it will cause the butterfly to sit at idle with a progression jet exposed, causing the mixture to be constantly rich on that single circuit. Possibly also your starter circuit as gummed up adding fuel to the mixture.


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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Sun Apr 08, 2012 9:11 am 
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Location: Sydney, Australia
wookieballa wrote:
I'm running the redline rubber o-ring gaskets, but tomorrow i plan on trying the "ether" method to see if theres a leak around the manifold, BUT it seems like if it was leaking air anywhere, then the WHOLE carb would be out of balance right?

Air leaks at the manifold to head face aren't uncommon either. Check that all the nuts holding on the manifold are present and correct/tight?

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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Sun Apr 08, 2012 3:40 pm 
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Joined: Mon Jul 26, 2010 6:24 am
Posts: 382
Location: Misawa Japan
funny you should mention the ignition, i just started my ignition upgrades.installed the pertronix points delete system, and it fired up like a champ. bought the blaster 3, but i sent it back because i would prefer the blaster 2 because it has the female connection not the male. i would rather not lose the ultra plug wires that I'm currently running.

i will check for leaks and tightness this afternoon. i know my timing is advanced a bit because of no vacuum advance, it has some weal low end power, but once you get up to around 2K its screams when its running right.

I'm pretty sure everything is ok, it has a nice solid idle, i have it set a little low (700ish) but i like it that way. its super quiet till you get into it a little. i think it surprises people that way LOL

im headed to work now, when i get home i will start tinkering. I've also emailed pierce manifolds to get their take on this. i will start looking into the starting circuit of the carbs too, maybe when i installed them i failed to clean something well enough.

Thanks for all the help so far!


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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Sun Apr 08, 2012 4:58 pm 
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Joined: Thu Jul 26, 2007 7:51 pm
Posts: 2200
Location: Sydney, Australia
Start balancing the carbs with a higher idle, like say 950 to see if that makes any difference. Also those manifold to head nuts are not torqued up very tight (IIRC 12ft-lbs or so), so don't lean into it too much :D

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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Sun Apr 08, 2012 5:59 pm 
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Joined: Mon Jul 26, 2010 6:24 am
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Location: Misawa Japan
ok i will try that.

wonder if my manifold to head gasket is bad. maybe thats where my trouble is coming in.

i will look into that too.


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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Sun Apr 08, 2012 8:20 pm 

Joined: Sun Feb 08, 2009 3:07 pm
Posts: 191
Location: Norcal
I'm sticking with my guess of bent shaft. It all adds up- weak suction on cylinder 1 means slightly open butterfly at idle, which means progression jet exposed at idle, which means rich circuit, which leads to fouled plug. I think a vacuum leak would have the opposite effect, leaning the cylinder, no?


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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Tue Apr 10, 2012 2:39 am 
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Joined: Mon Jul 26, 2010 6:24 am
Posts: 382
Location: Misawa Japan
well, I've gotten the carb clean, and installed again, it flows very close to the same air, BUT its not drivable at all. tried setting the timing back to baseline, and set the carbs back to a starting tune, and set the starting point on the idle mixture screw, at this starting point i foul the plugs on start up.

lean out the carbs by a half turn on idle mixture, still fouls plug

another half turn (at this point i have roughly a half turn left for adjustment) still fouling

1/4 turn and the plugs are looking much better, almost normal, BUT the car will NOT run at all.

when i first got these carbs they came from the original owner of the car, BUT the car has SU's on it, i assumed these carbs were on it till he want dot rebuild them, so he pulled the triple webers off and threw the SU's on to get by.
when i bought the car he gave the webers to my buddy who in turn gave them to me. i installed them, advanced the timing and it ran ok. now it will NOT run for shit.

i contacted Kev when i first got the carbs to see if he could give me a good baseline set of jets and venturi numbers to get the car running. i did not heed his advice and just ran what came in the carbs.

now that i think about it, i THINK the original owner said he originally had an L28 but blew it up. I'm wondering if he had these webers on there with bigger jets, and now I'm just flooding the engine with fuel.
My next grand idea is to find that email from Kev and buy the sizes he suggested to see if this corrects all my problems now.

anyone else have an L20 with DCOE 40's?
if you do, or know someone who does, what are your carb part numbers??

thanks guys!


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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Tue Apr 10, 2012 2:44 am 
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Joined: Mon Jul 26, 2010 6:24 am
Posts: 382
Location: Misawa Japan
heres my numbers BTW
Aux. Venturi: 35
Chokes: 32
Emulsion tube: F11
Air Corrector jet: 220
Main Jets: 140
Pump Jets: 45
Starter Jets: 100 F 5

can't remember what my idle jets are though.

its a normal L20, has a pertronix electric ignition kit (remove points, install pertronix kit in its place)
waiting for my Blaster II, and when that comes in I'm going to put in my MSD 6AL .
and when i cleaned the carbs, i found a wire down in one of the jet ports. not sure how it got in there, but the air compressor was a lifesaver lol


Last edited by wookieballa on Tue Apr 10, 2012 4:48 pm, edited 2 times in total.

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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Tue Apr 10, 2012 7:20 am 

Joined: Sun Feb 08, 2009 3:07 pm
Posts: 191
Location: Norcal
I'll look up what I have and post for comparison


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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Tue Apr 10, 2012 5:48 pm 
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Joined: Mon Jul 26, 2010 6:24 am
Posts: 382
Location: Misawa Japan
some new ideas i have:

1. plugs are too cold

2. pertronix ignition is the ONLY change I've made since last summer.
MAYBE that ignition system requires the timing to be retarded a hair? its still advanced because thats what i ran with the points system.

3. I suck at tinkering with carbs LOL

i'm going to roll out to the only parts shop that actually carries a wide range of plugs here and see if i can figure out a hotter plug, then go from there i suppose.
I'm pretty sure option 3 is the answer!

i still want to order different jets, but last year i was able to drive the car with no problems ponce i worked out the bugs, so i just can't see that the carbs are the problem.

wish my new coil was here, but until i work out these bugs, i don't need to add to the confusion.


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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Tue Apr 10, 2012 6:50 pm 
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Joined: Mon Jul 26, 2010 6:24 am
Posts: 382
Location: Misawa Japan
just checked my plugs, and I'm currently running NGK BPR6E-11's

so its already a pretty hot plug, but i wonder what the E means?


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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Tue Apr 10, 2012 7:09 pm 
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Joined: Mon Jul 26, 2010 6:24 am
Posts: 382
Location: Misawa Japan
ACTUALLY according to NGK's site this is the same plug that the 240Z's use, of course they don't list skyline's L20 :(


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 Post subject: Re: trouble balancing ONE carb!
PostPosted: Wed Apr 11, 2012 3:24 am 
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Joined: Mon Jul 26, 2010 6:24 am
Posts: 382
Location: Misawa Japan
just did compression test, all the numbers are within 5psi of each other ranging from 125-130psi.

as soon as i get some numbers for what others are running in their DCOE40's I'm going to order new internals, AND new plugs. I'm super irritated with this whole damn thing.

advancing and retarding is not changing anything at this point, and adjusting the mixture screw i get to where the plugs are no longer fouling, BUT at this point all the carbs have about 1/8th of a turn left on the mixture screws, and then they are fully closed, at that point it doesn't could the plugs, BUT it also will NOT idle at all, if i keep tapping the pedal it will run, but as soon as i let off it shuts off, I've even tried re-syncing the carbs at this point and bringing the idle up, but it does not stay running at all. if i go back to baseline on the mixture acre (1.5 turns to start with then adjust from there) the car starts fin and idles ok, but will not drive, just pops and sputters, and fouls the plugs.

at this point, I'm jut going to set the car on fire.. no wait, thats not what my plan is, I'm going to order the jets that are suggested to me. I've messaged Kev, but no reply yet. he sent me a good set of numbers, and i did NOT make the order, i just tried rolling with what my carbs came with, and that was ok last summer, but now i can't get it to run at all


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