qud webers (help

hi guys i am new here and have a problem with my webers(quad 48 idf,s)
i have a holden 308(5 litre )heavillly modded around 450 hp
i have synchronized them all, float level is correct
the internals are as follows

40mm chokes
65 idle jets
f34 emulsion tubes
190 air correction jets
50 pump jet
160 main jets


at idle it pops and splutters,it will do this when acc slowly all the way to about 4500 rpm and then get a little better /ubbthreads/images/graemlins/banghead.gif,however if i throttle it hard it runs like a bullet and does not miss a beat. please help thanks glenn

 

[Neal]

I had a similar issue with my 48IDAs. My problem turned out to be an exhaust leak. Check your header gaskets.

 

[David Briggs]

Is this a new setup? Or was it running ok and developed a problem?

 

[Neal]

If no leak try bumping your timing up until the pop goes away.

 

[Steve Toner]

f34 emulsion tubes?

Have to check the book when I get home to see what these look like, but I thought Ford engines liked F5s, F7s, and I think there's one other that works well but I don't think it's the F34...

Idle jets may be a bit rich too (especially if you're not at sea level). It'll be running on just the mains by 4500 RPM, but if it's only a little better at part throttle operation at 4500, that's probably not your main problem...

 

[Steve Toner]

Re: quad webers (help

Oh yeah, make sure your fuel pressure is not too high as well. You really need a regulator in there to keep it down to something like 3 psi...

And what kind of a cam are you running to get 450HP out of a 308?

 

Re: quad webers (help

steve this setup was running on a mates car no problem so he says .
as soon as i put it on mine wam
this it what happened ...
the emulsion tubes i believe they are of an alfa,
i also forgot to mention when cruising at any spped it also backfires or pops through carbs and pops in the exhaust ocasionallly, i am at sea level
compression ratio tad over 10 to 1 ...i was running a barry grant 750 mighty demon before no problem at all
the cam specs are as follows

intake&exhaust 346
duration322
duration at 50 266

valve lift intake and exhaust 540,though

exhaust opens 82 close 60.5
intake opens 62 close 80.5

hope this helps thanks glenn

 

[David Briggs]

Re: quad webers (help

Should be ruuning on the mains by 3,000 rpm, transition from idle to mains should be complete by then, if you have any hesitation or misfire around 2,000-2,500, idle jets are too small, I agree with previous comment about emulsion tubes, that number is not right for down draft V8. You could have other problems but I would verify fuel pressure first, then bump mains by 10(if engine is too rich it should still run smoothly)air corrector really makes a difference at full throttle high RPM only, if too lean at high RPM then reduce the air corrector, if too rich increase slightly. Check for vacuum leaks around throttle plates and manifold. also you could have a small piece of debris in idle or main circuit, remove the idle jets and put air through them. Webers can be pretty far off but engine should still run smmothly. When I first cranked my engine it ran like crap, my thoughts were the Webers and then the MSD 7600, 2 very mysterious systems, I pulled the plugs and 2 of my brand new, out of the box Autolites, were obvuiously not firing, I threw them away, got some new ones, they died quickly also, Finally put in some Bosch +4(not exactly a racing plug but at least the Germans understand the need to keep the fires lit), ran fine after that but was way lean, fattened the mains and the idle and now it runs like fuel injection.
Good luck!

 

[Steve Toner]

Re: quad webers (help

On the emulsion tubes: These are the tubes I've found people referencing as using (working) with small block Ford engines: F5, F7, F2, F11, F16. The order that I have them listed is not meaningful. I *think* that my carbs (44IDF) as supplied by Inglese had F11s (for a 300HP 289), but all my jetting notes were in the car when it was stolen, so I can't be sure.

From looking at the Weber Tuning Manual, the F34 is not in "Current Usage" but it is very much like the F4, which is. And the F4 is shown as "for very large main fuel jets or for alcohol-based fuels."

40mm main venturi (choke) will punk out about 6000RPM for your engine displacement, according to the book. I haven't looked very closely at your cam specs, but it looks like one that will make its power higher in the RPM range, so the 40mm chokes may be limiting your top end. That's not the problem you're complaining about right now, but it may show up once the current problem is resolved.

Main jets look about right to me. Again, going by the book, they should be around 155-170 for a 40mm choke size. See this post for original 289 jetting for IDAs.

 

Re: quad webers (help

thanks steve unfortunately the link does not open when i try

 

[Steve Toner]

Re: quad webers (help

Oops! Try this .

 

Re: quad webers (help

guys i did have a blown header gasket ,i replace both but to no avail,
as far as fuel pressure goes i have set it at 3and a half pounds,my idle jets are 160,should i go up to next size
also if it is only one carb giving me grief now ,if i unscrew the idle jet a quater of a turn the popping almost disapears what do think

 

Re: quad webers (help

i might also it is just one carb,i moved from the left rear and put it on the right front and guess what the problem is now at the right front ,,need help guys i have no vacum leaks any where throttle shafts in cluded the same size idle jets to i dont know where to turn to please HELP HELP

 

[flatchat(Chris)]

Re: quad webers (help

Seems that carb has problem -- try it on a Ford motor,should run fine then /ubbthreads/images/graemlins/lol.gif er-- seriously, dismantle and meticulously clean, check and assemble lets know what you find?

 

Re: quad webers (help

flat chat i have done that several times ,will perservere
ps if you want a race i got an A9X for sale

 

[Jac Mac]

Re: quad webers (help

Had a Holley that nearly drove me insane with a similar problem,Finally threw the disassembled carb parts in a bowl of Duco thinners for the night, blew all passages out in the morning.Tiny piece of RTV was the problem.Thinners must have softened it enough to allow air gun to blow it out.
Cheers Jack. PS. How much of a head start does Flat Chat have to give you !!!

 

[Keith]

Re: quad webers (help

How right you are Jack! I had a Holley on a SBC in a street/strip Camaro that I parked one day facing down a fairly steep incline (nose down). Next morning when I went to fire it up - just got a dull clunk. Motor refused to turn and baffled everyone till someone noticed a drip of gas coming out of the front crankshaft oil seal! Yup! A tiny piece of Teflon sealing tape had lodged in the primary jet causing the carb to flood. As it was parked nose downwards, 1/2 the contents of the tank had filled the oil pan and the motor causing the engine to hydraulic. The previous day, the motor had popped and banged at part throttle and was OK at WOT.

Small pieces of debris like this can cause havoc. I learned from this that you only wind PTFE tape on to a thread for the absolute minimum distance to avoid bits breaking off when the union is tightened.

Hope this helps clear the Weber problem.

 

Re: quad webers (help

thanks guys i will check it in the morning ,i will let you know how i get on cheers glenn

 

Re: quad webers (help

hey guys still no luck .i am loosing my mind here, any other suggestions thanks glenn

 

[Mike Christian]

Re: quad webers (help

Turning the idle jet holder screw one quater turn loose and the problems goes away? - this seems to lead to the idle circuit and the jet/jet holder in that carb bbeing different from the others. That seems pretty localized. This might sound stupid, but the idle jets have O-Ring seals on them. Have you checked the condition of the seal on that jet? Have you checked the actual idle jet hole size to make sure it is correct for the jet marking? Have you cleared all holes in that idle jet?

Does that carb have any extra progression holes in the venturi than the other carbs? Some users of IDFs drill them these tiny holes under the butterfly to cure transition issues. If one of your carbs is different from the others...

Also, I recently tuned q brand new set of IDF carbs and the mixture screws right out of the box were different shapes. This cause all kinds of headaches trying to tune until we pulled all mixtures screws and compared them. With new/matching screws, the carbs dialed right in.

Just a few thoughts...

Mike