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THANKS FOR YOUR ADVICE ON SYNC. THE TRIPLE WEBER SET ON MY CAR. THEY SOUND LIKE MUSIC TO MY EARS! HAVE TWO QUESTIONS
FOR YOU DR. WEBER. FIRST, AT IDLE ALL 3 CARBS BACKFIRE FREQUENTLY THRU THE AIR HORNS AND SOMETIMES TRY TO STALL. SECOND, WHEN I FLOOR IT AND LET GO IT TAKES A WHILE FOR THE RPM'S TO DROP BACK TO IDLE, STAYS ACCELERATED.(NOT WHAT I WANT TO HAPPEN ON THE STREET!).ANY ADVICE DR. WEBER?
 

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<b>Here's what I think it is.</b>

Well I'll give you a few hints but really I need more info to give you a more definite answer.
1 What size chokes are you using? (main venturi) it is the second little pipe thingy inside each barrel nearest the throttle plate.
2 What is the engine idling at? For initial tuning you need it below 900rpm or else the main jets becomes active and throws your tuning out.
3 Have you changed any jets yet?

Now I'll answer the easy question first. hahaha
The most likely reason for the idle to come slowly back down would be your throttle return springs (not the ones inside the carbs) but the ones that attach to the linkages. You need a fairly stiff spring to pull back on all the linkages. If you have one now physically attached to one of the throttle arms you may not be pulling all three arms back. ie one arm may be slipping a little on your main bar. Try putting another spring on the other arms. I personally run two return springs because one of my carbs is a little sticky and needs a little extra pull. Your pedal should be harder to push than your average carburated car. this is because you have three separate linkages to your carbs.
To test this as the car is still slowly idling down reach down and lift up on the throttle bell cranks one at a time. do not lift up on the individual arm links. If the car idles down faster when you do this then that suspected carb probably needs its own external return spring.

The backfiring problem could be several items but for an accurate answer I'll need that info from above plus any info on how the car drives under load.
backfiring through the carbs says to me that it is running lean. What colour are your plugs after idling or intown driving. Go for a drive and keep your rmps low 1-2000rpm.
Try an experiment again for the idle mixture screws. Set your idle under 900 (prefer 700) and back your idle mixture screws counter clockwise another 1/4 turns then put back to previous setting then turn them in 1/4 turns and note the difference (it may take whole turns to make a diff depending on the thread of the screws.) If you are idling over 1000 rpm then it is possible that you are engaging your main jet and that would account for the backfiring since I suspect your main jet is too small (120)
Try it. Once you get the idle mixture screw set you will never have to touch it again (make sure you record how many turns from seated once your test is done so you can set it again if it ever goes off again.)
Please let me know how it goes and try to give me more info. Maybe some more ideas will become evident with the new information.
ZR8ED.
 

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<b>Oops forgot one thing</b>

What is your distributer timing set at? Webers need to run quite different from your stock settings. I'll check what mine are set at and let you know for reference. I'm 99% sure I'm running 36 degrees total advance. BTW your vacuum advance probably won't work with your Webers especially with big cams and high flow cylinder head jobs.
ZR8ED.
 
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