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 Post subject: 40 IDF problems
PostPosted: Sun Jan 15, 2017 9:23 am 
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Joined: Thu Nov 24, 2016 9:48 am
Posts: 13
Location: Snohomish WA
I fixed the problem, I had to start with the air bypass screws 1/2 turn from seated. If you want to delete this feel free

I am close to the end of my rope so I am looking for advice to what I may have missed with my new motor / IDF’s. I hope I was able to communicate this well enough, posting from my phone, for others to understand.

2095cc 8.5:1 CR
78.8 crank
92mm B pistons
5.5 rods
Bugpack 4062 cam
40x35 ported heads, 62cc
.045 deck height
Cut to length cromoly pushrods set to lose zero
German 009 with points in it now but I have Petronix to put back in it
32* total advance
3psi fuel pressure
Dual 40 Weber IDF, not Empi. The jetting is off but I was trying to get a baseline to order jets

50 idle, 155 main, 32 venturi, 50 pump jet, f11 emulsion tubes and the floats are set to 10mm - 20mm.


I have really rough idle and when I pull any plug wire it makes a noticeable difference… with the exception of #2, I do get a good spark between the cap and wire. I noticed yesterday that the 1 &2 IDF is pulsing fuel out of the pump jet at idle unless I hold the throttle closed and have the throttle stop screw ¾ or less off of the stop. The mixture screw on that cylinder does not seem to make a difference and that The #1 mixture screw makes a difference but not as much as on 3 or 4.
The car sputters and #2 seems to make power sometime but not always when driving.

After alot of time eliminating problems I narrowed it to the carb so I pulled it, cleand it, checked the floats, bench set it and swapped it to the other side and the problem followed the carb.

I installed “idle jet fix tubes”
Used propane to check for vacuum leaks, hose with ball point pen end all over the carb and found nothing.
Swapped from a 50 idle jet to a 45 on the weak cylinder and I get lean pop (back to 50)
Synced / set carbs by process bellow without much luck
(I am showing lean idle because I can not get the idle up enough without turning the speed screws more then ½ turn)
The butterflies seem to be covering all the ports the same on both carbs

I have not played with the air corrector screws that are seated but I am about to try them at 1/2 turn out to start to see if it makes a difference.

I am looking for any advice or ideas if anyone has anything else to try.

Standard IDF Settings:
Speed screw ¼ to ½ turn in after contact with lever maximum.
Mixture Screw 1 turn out from lightly seated.

“Lean Best Idle” Procedures

After confirming the linkage allows the throttle lever to seat against the Idle Speed Screw. Back off the Idle Speed Screw, then turn the screw in until it contacts the throttle lever and turn it in ½ turn. Turn in the Mixture Screw in until it “LIGHTLY” seats, then back it out 1 full turn. Loosen the 8mm wrench size nuts on the “air bleed” screws, turn in the air screws until it seats then tighten the nut.
a. Start the engine, it will run slow and like a tractor. As long as it will stay running, the idle speed is not important at this point.
b. First, turn in the mixture screw until the engine runs worse, then back out the screw ¼ turn at a time. The engine should start to smooth out. Continue to back the screw out ¼ turn at a time until the screw does nothing or runs worse. Then turn it back in to the point where it ran best. You want to tune the engine by sound. Adjust each mixture screw to the best, fastest and smoothest running point. Do this procedure with each mixture screw.
c. Now you may adjust the Idle Speed Screw. It should be sensitive and only require ¼ turn in or out to achieve the idle speed you like.
d. These carbs are commonly used in pairs, this makes the synchronization important, be sure to bring the high flowing carb down to the low flow carb. Then bring them both up to “proper” Idle speed. The Idle Speed Screws are not opened more than ½ turn in.
e. After synchronizing multiple carbs, reconfirm steps b. c. & d


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 Post subject: Re: 40 IDF problems
PostPosted: Sun Jan 15, 2017 5:43 pm 
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dLk Redneck
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Joined: Tue Jan 22, 2008 5:58 pm
Posts: 9953
Location: Spring
Glad you got her fixed. :thumbs:

_________________
Ethan Dunlap
Concrete By Dunlap
Spring, Texas
" Just Happy To Own A Split"


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 Post subject: Re: 40 IDF problems
PostPosted: Mon Jan 16, 2017 1:16 pm 
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Joined: Thu Nov 24, 2016 9:48 am
Posts: 13
Location: Snohomish WA
Thank you, I did find that 99% of the info out there is about Spanish and Chinese IDF's, just like 99% of the carbs, making my Italian carbs a bit more difficult to troubleshoot.
ConcreteAce wrote:
Glad you got her fixed. :thumbs:


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