Weber 48 ida help

Ian Clark

Supporter
Hi Tom, just reading up the posting to your initial problem being of running rich, sooty plugs and black smoke in the exhaust. It sounds like you have made good progress with jet changes... good.

Running rich can mask other issues that weren't apparent before. Can you elaborate on coughing, sputtering in the 2>3k rpm range?

Is the engine falling flat as you move up the rev range? Does the engine reject the intake charge by popping back up the carbs? This will not sound as dramatic as backfiring in the exhaust, however it will hurt the throttle response.

Are you accelerating hard when coughing and sputtering happens?

A bit more info will help formulate additional suggestions.

Cheers
Ian
 
Hi,
Thanks for your help.
Its like a hesitation/missfire with popping/chuffing from the carbs. If I try to feather the throttle through its seems to go on for quite a while then it will suddenly clear and is great.
It definitely clears quicker if you plant the throttle.
I have attached the power run graph and cam spec if that helps.
I have also ordered the 34mm chokes. This will hopefully be a temporary fix for le mans classic is a more comfortable drive.
I'm running quite a mild cam so down the line I will replace for one with more lift and then look into the third progression hole.
Thanks
Tom
IMG-20220615-WA0000.jpegScreenshot_20220617-214253_Gallery.jpg
 
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Randy V

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Staff member
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You'r right, I am a carb specialist (weekly base) but agree a thirth hole conversion (drilling that 3th hole) on the older IDA's is a last resort.
48IDA carb's had one purpose back in the day's, Racing. Never ment to do cruising at 2000-3000 rpm. They suppose to run 6000-8000 rpm.

Weber IDF's are more suited for cruising rpm's
I don’t disagree regarding the suitability of the IDAs for street use. Particularly with high overlap cams.

My business was shut down when we picked up our toys and moved a thousand miles. I “used” to build and diagnose carbs in my old shop because it’s a dieing art. Mostly Holley (and clones), Autolite, Rochester, Carter (and clones) along with a smattering of Strombergs and motorcycle carbs.. Most of the Webers I dealt with were OEM installed units like the DGV and other 2-stage variants. And rarely, the DCOE IDF and IDA…
With the economy going the way it is, I am considering getting back into the game because the number of shops that work on them are few and far between..
Which reminds me - I have an oddball set of IDFs with airhorn mods in my shop (I own them) that I would sure like to identify. I’ll drop you a note in PM about those.
 
Tom,
swapping chokes means also rejetting of the carbs as there's a relation between choke size and jet size.

Assuming your carbs are synchronised (with proper vacuum gauges), what fuel pumps are you running?
 

Ian Clark

Supporter
Hi Tom,

JP has brought up a very important point about synchronization in Weber IDA carbs.

There are a few good posts on the forum about synchronizing the carbs (somewhere). The surging or sputtering will not be solved by changing chokes, jets or emulsion tubes. It's also common to have the engine run rich with out of sync carbs.

Not surprising it pulls well at WOT, you're past the idle to main transition sensitivity and the main power side of these carbs work fantastic.

Absolutely number one the linkages, throttle stops and airflow are equal in all four carbs before replacing parts. Also put in a new set of plugs, its' cheap insurance. Hope this helps

Cheers
Ian
 
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