Author Topic: Carburetor questions  (Read 7590 times)

ScotiaFE

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Re: Carburetor questions
« Reply #12 on: April 26, 2013, 06:18:01 AM »
No downside. Just less hood clearance.  ::)
An open spacer tends to work in the upper power zone.
A 4 holer tends to work in the lower power zone.
So a cloverleaf must work in the middle power zone. LOL
Actually test a few different ones. Some engines see pretty good size gains and then others loose.
It's a tunning gizmo.
Also a good heat sink, with some of the materials avalible, ie; wood and plastic

When my girls were young we used a 4 holer for tiddlywinks.

Woods

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Re: Carburetor questions
« Reply #11 on: April 24, 2013, 09:54:32 PM »
Post repair question, what is the down side of using an open carb insulator instead of the four port match to the intake ports?  Is this a bad thing?

Woods

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Re: Carburetor questions
« Reply #10 on: April 24, 2013, 09:47:16 PM »
Ok! back from a 12 day cruise in the Caribbean, thinking about my carburetor problem at least some of the time, and jumped right on the motor when I got home!

New gaskets, main body, jet plate and primary block installed.  After a quick check of all of the levels and adjustments we fire it up.  Bumber!! I think my A/R o2 meter has failed!!!  It doesn't jump around anymore?  As it warms up the readings fall into the 13.1 range and hardly changes at all.  I jetted the primaries up to 70's to bring it back in.  Must have been leaking gas somewhere but I couldn't see where.

Several running in trips and the WOT plunges to the 10.0 range have disappeared.  I think I'm down to the fine tweaks now and a much happier shade tree mechanic.

Thanks for the gaskets Barry!  We need to settle up.

« Last Edit: April 24, 2013, 10:03:30 PM by Woods »

Woods

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Re: Carburetor questions
« Reply #9 on: April 02, 2013, 04:38:38 PM »
What a surprise, I have discovered that right here in Jacksonville, Fl. we have a company, National Carburetors, that maintain an enormous amount of parts for all types of carburetors.  Stopping there at lunch today I was able to pick and choose exactly which gaskets and seals I need with out purchasing a complete rebuild kit X2 for my carbs.  They didn't know much about dual fours on an FE and the peculiar way we mount them but they have the parts!!! 

Woods

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Re: Carburetor questions
« Reply #8 on: April 01, 2013, 07:41:18 PM »
I have two major issues that I would like to cure.

#1 At WOT moving through the higher RPM's my AF/r starts drifting down from the 12.5's to the low 10's or "----" (off the bottom of the scale).  I have the weakest spring in the vacuum secondaries so you would think a reduction in size from the secondary plate from 76's to 74's would make a change.  I've tried it but no change.  Should I go deeper?

#2 Idle adjustment with a balance between the adjustable primaries and the fixed secondary idle circuits is a trick that I could us some advise on.  As best I can tell, secondary float bowl level is the only way to make some or minor adjustment.  is it true that float level is the only option? 

Given that the eight idle circuits of the 2x4 set-up of a pair of 750's are most likely under flowing on cfm, the intake runner closest to the individual intake runner would be the source of mixture to that cylinder. 

In the case of the cruise and WOT flows, cross blending has a greater chance of a more homogenized mixture.  Or is this incorrect, how can I best identify which one of the eight sources is creating such a giant change in AF/r?  As an example, lifting slightly off of WOT brings the AF/r back into the low 12's.  I would still have the pair of carbs near WOT just not completely planted.

As a catch up, this is a strokker 445 with 2x4's and iron heads. Isky 240/240@0.050 108 LCL.  10.2 cr


Woods

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Re: Carburetor questions
« Reply #7 on: March 31, 2013, 07:37:39 PM »
I think I have one possible answer, the power valve on the front carb was only finger tight.  Could have been leaking down.  I had change them to 6.5 from the 4.5 that were in originally last year.  Might have just vibrated to a looser condition?

Need gaskets to get everything back together so we are off the road and back on the hunt for parts.  Didn't look at the other one yet, I'll wait for parts before opening it again.

Woods

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Re: Carburetor questions
« Reply #6 on: March 29, 2013, 07:07:25 AM »
Different brands of gas make a difference it's true.  I can see vapors whiffing out of the secondaries after shut down so I suspect a leak down.  It's true, these carbs are very responsive to changes but I don't think I can adjust past a leak.  I just think I will go into them and eliminate as many variables as possible.  Barry, you told me once that dropping to #76's on the secondaries may be too much, is that still true?  If there is one thing I've learned with these 2x4 is that a good balance of the mixture to the eight paths has a significant effect.  Figuring out which port is out of line is tough!  When I go through them for a jet change I index all the settings, float level, butterflys and make equal adjustments as I tune.

Thank you for the help.  Do you still have my shipping address? 

Barry_R

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Re: Carburetor questions
« Reply #5 on: March 29, 2013, 05:29:11 AM »
Howza about I put a few gaskets in a box & send them to you?

I think - think - that fuel could be a big factor.  Have you tried a different source?  We get winter blend stuff up here that is unreal bad sometimes these days - blows to vapor in seconds if its warm.  It'll percolate in the bowls, overwhelm the venting, and flood the engine while its sitting.

FYI - up heree in sunny Detroit "winter" is the part of the year where the weather stinks, it's cold, wet and miserable and nobody wants to go outside.  Winter here generally lasts from October through April, then we get four months of humidity...

LargeRickhead66

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Re: Carburetor questions
« Reply #4 on: March 29, 2013, 01:27:15 AM »
Although the metering block to main body is a frequent problem with leakage internally. Maybe your problem is even easier, try dropping your float levels 2 flats on each float level adjustment nuts. This has worked for me in California with our "Special Blend" gas, maybe you are getting some of our stuff.
 As long as your fuel system/pump is up to snuff the slightly lower fuel level won't hurt anything anywhere.
As for the seconadry bowls going dry after it sits for a while, I would guess it percolates after it is shut down ( hot ). Do you have an insulator of some sort under the carbs?
Then again back to the metering blocks leaking at the main body, yup it could be that too. If the main body surfaces are not flat, even a gasket change will only work for awhile.
 When you have it apart, if you do, change the seconadary jets 2 sizes lower and watch your A/F ratio.
  Rick Wanner 

Woods

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Re: Carburetor questions
« Reply #3 on: March 28, 2013, 10:45:04 PM »
On cool days, not to many problems.  Warmer days at idle I can watch it slowly get richer.  I think it is leaking down until it doesn't idle any more.  Temp goes from 180-185 to 190-195 and it begins.  Timing is 18 initial, heavy silver/blue spring with the black pill for a total of around 38.  I just moved up to the blue spring from the lite silver and I think I need to change it back.  I have a A/R broad band 02 installed and can watch it.

I have been chasing the TOO Rich at WOT and still have a streetable driver.

How can I order some gaskets?  I would like to get the main body to base plate gaskets and some of the base plate to intake also.(takes 4 total I have thermal spacers)

do I order them by number or can you shoot me a total and I'll send you some cash?

Barry_R

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Re: Carburetor questions
« Reply #2 on: March 28, 2013, 10:27:44 PM »
Woods
Normally a leak down is a gasket issue - weeping through the metering block surface.
I can provide you some gaskets for the carbs... I have a hundred or so of each in stock.

The equal area is a reasonable place to start from, but although intuitively correct it's not truly accurate in terms of flow.  The differences are due to the wire draw nature of fluid flow through an orifice, along with the different heights of the passages relative to teh float level.  But a case where close is good enough.

Other than the leak down - what issues are you having?  Even if the carbs are not calibrated for the engine you're working on they should be reasonably close and certainly runnable.  Historically they have been on the 2-4 jet rich side of the curve but very responsive to changes and have a smooth linear fuel curve.

Woods

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Carburetor questions
« Reply #1 on: March 28, 2013, 09:43:15 PM »
If this is not the right section for this topic please just say so.

FE related because I'm working on a Barry R. 445 parts motor with 2x4 and Blue Thunder MR intake.

Are there any opinions from the carb. experts that the Sg/inch area of the various jetting paths for fuel should be balanced between the primary circuits and the secondary circuits.  For example total area of the primary jets plus the PVCR ports should equal the area of the secondary jets.  It is asserted that the tuning will be balanced and easier.

In my case I am working on the QF 750's that Barry provides and I think I have issues.  I have the printed build sheet that QF provided with the carbs and they were not built for my specific application.  Currently I have  #68 pri. jets with .052 PVCR, and #78 sec. jets.

Another question I have is how or why would the secondary bowls leak down when the car is parked and off.

A final question, which rebuild or gasket kit would I order for these Carbs?

Thanks for your help.