weber settings and backfire

[paul cass]

Hi Gary
I'm going to try your suggestion of running the engine at 1400 rpm and then play with the idle mixture screws. I was sent one of the synchrometer gauges but no info on how to use it. So my plan was to use it and see what the air flow is. I know that when I used it at idle all of the stacks read 5.5. Say that it now reads 7.5. I'm assuming that as I turn the mixture screw the reading will go up or down, and that I'm trying to adjust to a steady reading and where the engine noise sounds the best. I will have to do this one stack at a time. A motorcycle guy told me that he was able to adjust his mixture by adjusting the float level on his carb which was similar to a weber. Maybe I'm missing something here but I don't see how the float level could change the mixture. Unless maybe it was set too high and fuel would bleed over. Thanks for the help.
Paul

[Gaz64]

Technically if the mixture screws are at a base line setting, the airflow per barrel is adjusted first, while keeping the engine at say 1000, adjusting linkage as necessary to have all barrels flowing the same. The mixture screws alter engine smoothness, and each cylinder can "go away" with too much one way on the screw, and although there is air flowing though the mixture discharge port, the adjustable volume doesn't make significant difference to a synchrometer reading.

Get the carbs balanced correctly at idle, and check airflow balance at part throttle of 2000 or so rpm. Once balanced at idle, the carbs should be checked for mechanical balance at wide open throttle with the ENGINE NOT RUNNING.

Good baseline tune, good linkage, easy to adjust, can you give EFI smoothness.
I built a 2.1 Pinto a few years back with a pair of 44 IDFs for a friend, and even with a 250 @.050 cam, it had virtually no cam lope. I should have went up one grind.

Gary

[paul cass]

Hey Gary
Took the FIA out for a run this afternoon and boy what a difference. Ran almost exactly like when I had the carb. Occasionally I noticed that after stop and go I would have what seemed to be a cylinder go away. Blip the throttle and it usually cleared up. I'm running an 80's era Ford AOD that I manually shift. Stall convertor is 2900. A little different from a manual transmission. Had good idle, good performance on acceleration with no stumble. This under normal driving conditions. Once I got away from traffic I stomped the gas pedal and the FIA went like a rocket! When I got back to my shop I checked to see if there was any flooding after I shut down the engine. One carb had some slight flooding. I think that this is the one that had a different needle than the other 3. I won't have time to tinker again until Friday. But needless to say I was a very happy camper this afternoon. On the other post I mentioned that all of the floats were set at the wrong height. 4, 4, 3, and 5. Reset at 10 mm. Seems if you spend thousands of dollars on a set up the least they could is to set the floats correctly. Oh well. I'll further update later in the week.

[Gaz64]

Good to hear you are making progress Paul.

I would replace the needle and seats with the same type, then reset the float levels to 10mm.

Can you list your carb tune settings, choke, main jet, emulsion tube, air corrector, idle jet, pump jet, pump exhaust?

Or are they as factory set for a 44 IDF?

Gary

[paul cass]

Hi Gary
I don't have any specs on the Weber's. I've asked for that info, both from Top End and Red Line. Nothing from Top End and the guy with Red Line told me to take apart the weber and see what parts were in it. I plan to try again to get some info. See what happens.

[Gaz64]

Hi Paul,

Sounds like your 44s are still are factory settings.

Redline probably doesn't give a more appropriate setting for your engine capacity.

I know my 44s weren't big enough for my last setup, I wish I went to 48s.

Gary