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#1 |
Registered User
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
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Re: Diagnosing a misfire
you are getting sound advice A 750 carb is big. My truck had a carter 750 i swapped an edelbrock 600 it feels faster. however your carb has as a stuck float or something. ive never had fuel come out of vacuum port. Never owned a holley carb though. Im no carbexpert. Ive had few problems maybe because I change my fuel filters often. I would check floats first
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#2 |
Registered User
Join Date: Apr 2015
Location: Weatherford Oklahoma
Posts: 53
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Re: Diagnosing a misfire
If all checks good on the floats and idle mixture screws, jet it down a couple of sizes. Holleys are really easy to tune, if you do jet it down you will need to readjust the mixture screws.
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#3 | |
Registered User
Join Date: Nov 2015
Location: Colfax California
Posts: 1,644
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Re: Diagnosing a misfire
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#4 |
Registered User
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
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Re: Diagnosing a misfire
My edelbrock 1405 ran rich the fuel pump pressure was toohigh I installed regulator. It ran so rich the idle mixture screws had noeffect i could close them and engine still ran. After installing reg. I was able to tune carb changing metering rods.You have a carb that is running rich clean floatbowls install fresh fuel filter and then trytuning carb.Big carbs and big exhaust is meant for full throttle high rpm work
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#5 |
Registered User
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
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Re: Diagnosing a misfire
We need more info 1did the carb ever run well? if it did then clean and rebuild adjust floats. 2 ha ve you changed anything else? on the carb or fuel delivery system? pump? regulator?? good luck might want to change oil if it has gas in it
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#6 |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,334
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Re: Diagnosing a misfire
That's a good point - check your oil to make sure it's not overfilled now (which would indicate a bunch of gasoline has made it past and into the crankcase).
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1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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#7 |
Registered User
Join Date: Nov 2015
Location: Colfax California
Posts: 1,644
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Re: Diagnosing a misfire
It started when I bought a new set of aluminum Ultra Gold full roller rockers because this new solid cam kept on beating my polylocks to the point where the set screw was stripped. I got the roller rockers and a nice set of polylocks to snug everything down but then the misfire started up. I checked lash to rule out the valves not closing all the way which makes the cylinder leak compression, and it's at .015" cold so I think that's where my problem is. The cam card from Comp says to set lash at .020", and bein this is my first solid cam I'm certainly no expert, but .005" less than the recommended lash is probably too tight.
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#8 | |
Registered User
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
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Re: Diagnosing a misfire
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#9 |
Registered User
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
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Re: Diagnosing a misfire
you have quite a ride brought a smile to my face. yeah my 750 was faster top end too not like yours though. looking forward to hearing the solution
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#10 |
Registered User
Join Date: Nov 2015
Location: Colfax California
Posts: 1,644
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Re: Diagnosing a misfire
I can just hear GrumpyOldMan now, "how do you like those HIGH PERFORMANCE parts now huh??" lol its comin, just wait
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#11 | |
Senior Member
![]() Join Date: Dec 2013
Location: Gods country East,Tn
Posts: 8,545
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![]() Quote:
![]() You've saved me money on haircuts because I keep pulling it out reading your engine build threads .... almost weekly ..... ![]() I've edited my signature below for your benifit !
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![]() 1967 Factory short bed - Old school '71 - 350 / 4bolt / 487 heads / Edelbrock C3BX Muncie M-22 4 speed / Hurst Comp plus Factory 12 bolt posi 3.73 / 255-70-15 Smoothed firewall / Factory cowl induction Power disc brakes / power steering / 3.5-5" drop |
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#12 | |
Registered User
Join Date: Nov 2015
Location: Colfax California
Posts: 1,644
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Re: Diagnosing a misfire
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#13 | |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,334
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Re: Diagnosing a misfire
Quote:
In useful news, I don't think it's a float level issue because they wouldn't be THAT high, but if you think about it, when you don't have clear sight plugs there's no way they intended it to be half way up the old original brass ones! It's supposed to be set to the BOTTOM of the sight plug, because that's where it would be dribbling out if you didn't have clear plugs (or any plugs installed). As others have said, fix what you know isn't right before chasing ghosts and valve lash. Get the fuel right first.
__________________
1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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#14 |
Registered User
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
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Re: Diagnosing a misfire
been trying to post not working operator error im sure... fuel coming out of vacuum port needs to be addressed maybe more than one thing is wrong but dont adjust valve train to oblivion carb is running rich not because of size
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#15 |
Registered User
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
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Re: Diagnosing a misfire
I guess i have to keep my post short I have a vacuum guage mounted inside cab. also a vacuum pump is handy for testing under the hood
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#16 |
Registered User
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
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Re: Diagnosing a misfire
I am impressed with the amount of work that you have done and hope i dont offend anyone but fuel from vacuum port needs attention maybe a holley expert would help you out. Its not the size of carb
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#17 |
Registered User
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
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Re: Diagnosing a misfire
just sittin here waiting for parts the vacuum pump has a gauge on it the vacuumgauge in cab helps me tunemy carb and save gas. torque wrenches are a must. I noticed you invest in tools so just thought id suggest . ive got a cool multimeter has digital tach even a temp probe
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#18 | |
Registered User
Join Date: Nov 2015
Location: Colfax California
Posts: 1,644
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Re: Diagnosing a misfire
Quote:
You're right on about the carb, I put a set of spark plugs in it 2 weeks ago and they looked just like the ones I pulled yesterday after only a few short trips to the store. These guys have seen me go from not being able to use a timing light to rebuilding a top end on my small block, and there's kind of an ongoing joke about how much unnecessary (and sometimes detrimental lol) wrenching I do on my truck haha I actually REPLACED HEAD GASKETS once about 4 months ago because I thought I blew one, and when I got it all back together it turned out to be one of my spark plug wires wasn't clipped in all the way on the distributor cap lol it's been fun. |
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#19 |
Registered User
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
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Re: Diagnosing a misfire
I reviewed thread and I would GUESS that when you installed valve train parts you got some debris in carb...as plugs became fouled it ran richer if you change plugs it will run better until they foul too
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#20 |
Registered User
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
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Re: Diagnosing a misfire
you could pop of gauge from under dash plug line then use gauge under hood. I use gauge under dash to select step up springs in edelbrock. I use manual to select rods and jets.BTW the more gas in manifold the bigger the backfire
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#21 |
Registered User
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
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Re: Diagnosing a misfire
they wouldnt pick on you if they didnt like you. thats what i was told about 50 years ago
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#22 |
Registered User
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
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Re: Diagnosing a misfire
Just thought i wouldmention this fuel in oil can ruin an engine even a small amount may not show up on dipstick. and your plugs? wow pardon me but sure you are not burning oil? Oil creates bluish smokeand fuel moreblack.
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#23 | |
Registered User
Join Date: Nov 2015
Location: Colfax California
Posts: 1,644
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Re: Diagnosing a misfire
Quote:
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#24 |
Registered User
Join Date: Jun 2016
Location: Phoenix AZ
Posts: 429
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Re: Diagnosing a misfire
Anyone ever try using this calculator to figure out which size carb your vehicle needs? Last time I checked, it said my stock 350 cid needs about 340cfm
http://www.carburetion.com/calc.asp |
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#25 | |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,334
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Re: Diagnosing a misfire
Quote:
A Chevy 350 -just- maxes out a 2GV, becasue adding a 4MV is worth 5hp (250hp vs 255hp). So I figure whatever a 2GV flows, that's what a normal 350 can use.
__________________
1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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