Air/ fuel tuning

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The dyno figures were straight out the headers though ??
I seem to get 12.5 at cleanest going WOT.
I don't have a data logger or anything so that's watching gauge best I can As Well as the road




Sorry didn't read the last reply
I would not try WOT with 76 Jet after having dyno results that indicate it PMJs should be 82.
Even going winter to summer I wouldn't do it. It depends a bit on the carb how sensitive it is to air density changes. No choke tower will be more sensitive.

Test the leaner jets at cruise and gentle accelerations all you want. Go too lean under heavy load or throttle and you can cause damage.
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29156"]I would not try WOT with 76 Jet after having dyno results that indicate it PMJs should be 82.
Even going winter to summer I wouldn't do it. It depends a bit on the carb how sensitive it is to air density changes. No choke tower will be more sensitive.

Test the leaner jets at cruise and gentle accelerations all you want. Go too lean under heavy load or throttle and you can cause damage.[/QUOTE]
 
I'd still be cautious. Its too risky. Find a place they do standing 1/4 mile or longer and test WOT by jetting for the best mph through the finish lights. Or some fun on a chassis dyno. Start with the 82s and run by run take it down. If it starts to ping , back off the throttle immediately. If it loses mph or Hp and go back up in jetting. Also get the AFR curve - if its not flat in top gear WOT, that needs to be addressed.

Your question about secondaries effecting highway cruise. Since your 950 is customized, anything is possible. Typically the linkage is set up to open the secondaries when the primaries are 40-50% open. They should provide the same AFR as the primaries. They shouldn't be a crutch for enrichment. Their job is allow more airflow and higher pressure at high rpm.
If you want to prove it to yourself, disconnect the linkage and go for a cruise. I've disconnected them on the dyno just to see the difference AFR curves.
 
d1970 said:
yellow rose I know you are more educated on this subject then I am, I still like to learn more about this subject and I'm sure other guys can learn something to, could you please elaborate on how to read spark plugs with today's type of fuel
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I'll see if I have any used plugs in the shop and take some pictures.
 
yellow rose said:
I'll see if I have any used plugs in the shop and take some pictures.
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I don't know if this will be as practical as what you may have to show. But I rummaged around to see if Bruce Robertson's "Spark Plug reading Observations" is still downloadable and it is.
Anyone interested can go to this page, and click to download or open the file. ( Image gone means nothing as its pdf. Images are inside it)
Spark plug reading pdf - essential knowledge - read-only
 
i was thinking to buy these QFT metering blocks that have all screw in ifr and pvrc and etc.

Quick Fuel Billet Carburetor Metering Blocks 34-10QFT

can anyone tell me how to tell if it fits the main body ?
its a quickfuel main body but thats all i know
i read on the quickfuel website to make sure it same setup as current carb, but then after speaking with them they said it fits all 4150.??
 
ap6street said:
i was thinking to buy these QFT metering blocks that have all screw in ifr and pvrc and etc.

Quick Fuel Billet Carburetor Metering Blocks 34-10QFT

can anyone tell me how to tell if it fits the main body ?
its a quickfuel main body but thats all i know
i read on the quickfuel website to make sure it same setup as current carb, but then after speaking with them they said it fits all 4150.??
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It looks like the IFR is in the high position on those. I think BLP has them threaded for IFR high or low. Low position is more stable.

By "make the same", QF may mean starting with all the same restrictions and bleeds as your 950 currently has.
Since your 950 was customized, the blocks and air bleeds may already be tapped.
Might as well start with what you have. Open it up, take some photos and measure the all the restrictions and bleeds.
The cheapest way to measure is to use the shank of drill bits as gages. A real gage set is a bit more money.
In standard US sizes, a set of miniature sizes bits along with standard numbered bits will do the trick.

First thing to buy is a good book - this will show where each restriction is, differences in gaskets etc, and explain the concept behind each circuit in a 4150.
If you can get a good deal on any edition of Urich & Fisher's book, or Urich's 4150 book - which is a more stripped down verion of the bigger book.
Holley, carburetors and manifolds Mike Urich Bill Fisher | eBay-Aus

David Vizard's recent Holley book goes more in depth into the circuits. He writes well and also has good illustrations. Its more info thrown at the reader in less space so a little tougher as an intro. So that's an alternative book if its more readily available. (Just don't follow any recommendations in the book blindly. The SA format doesn't allow room for full explaination of why something wsa done or worked out in a specific situation that may or may not apply. I learned this the hard way...)
 
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I will definitely get a copy of that book.
I was just thinking it might be easier to muck around with those blocks as they are screw in rather than drill out holes especially if I'm not sure I am heading in the right direction.
 
ap6street said:
I will definitely get a copy of that book.
I was just thinking it might be easier to muck around with those blocks as they are screw in rather than drill out holes especially if I'm not sure I am heading in the right direction.
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I get that. But your blocks may already be done. Also the low IFR is going to be easier to tune, so if you're going to buy 'em, get them that option.
The main bleeds are in the main body - look and see if they are already screw in type. If not sure, post photos.
 
back on my tune.
have got most going very good.
idle:13.5
off idle:14
cruise:13.5
sounds really crisp and goes good .

only thing is the slightest opening of the throttle starts the pump shot, and brings it down to low 11 , maybe a 10.

pink cam #1 28nozzle. primary.
seems to want the instant fuel , but obviously not so much.

im gonna try a 25nozzle next.
the pink cam seems to have the slowest ramp.

ive tried several cams and #2 positions but i get a hesitation.??

is there a common choice for a decent cam motor , have 5" vacuum up to 11" at light cruise
 
thought i would update yes,
ended up tuning on the dyno.
we ended up with a 25 main air bleed and a 73 pmain jet.

i was more interested in idle and off idle tuning , but suprisingly this seems to get the tune pretty much spot on everywhere,

we made peak power at 12:1 afr though
ended up at 440rwhp from 417 but hard to tell the difference since then froom some street driving.


side note:
converter fell apart on the dyno , which ended up costing a fair bit from a simple quick idle tune up.
and since then my indy rockers let go , so have purchased the t&d series
 
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