Carb throat balance when tuning now a rebuild saga !, those with Zenith carbs can learn from my bad fortune ? |
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Carb throat balance when tuning now a rebuild saga !, those with Zenith carbs can learn from my bad fortune ? |
porschetub |
Aug 29 2023, 11:25 PM
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#1
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Advanced Member Group: Members Posts: 4,706 Joined: 25-July 15 From: New Zealand Member No.: 18,995 Region Association: None |
Doing a tune on my Zeniths ,cant find an exact rpm range and done a ton of research ;
Bruce Anderson mentioned 1800 in his book, Factory says 1000 in the gary.suggate site factory manual, Haynes manual tells us 1000. So far I have tuned throats @ idle ,1000rpm ,1400 and 1800 on hand throttle and strangely I get the same balance any way ?. Now thinking its not an issue but would appreciate feedback from 6yl guys with carbs,TIA,cheers |
porschetub |
Sep 3 2023, 05:51 PM
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#2
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Advanced Member Group: Members Posts: 4,706 Joined: 25-July 15 From: New Zealand Member No.: 18,995 Region Association: None |
Thanks for all the replies and sorry for the delay, I can get them very close but critical to have idle screws even for normal idle and upping engine speed for balancing .
Spent a lot of time dialing the length of the drop links and have replaced many worn out ball cups ,strangely nearly all RH thread ones were worn out ? . When I first rebuilt these before I fitted the 2.2T motor I noticed both side cam rollers had seized @ some stage and there were area's on the rollers that had flat spotted and there was a lot of wear on the throttle cams which I have since replaced. Both the carbs were in very poor condition,I had no history when I bought this engine but the seller on behalf of the owner did say that "it ran like shit" this turned out to be a blessing as I knocked the price down and it turned out just to be the carbs and I had bought a strong engine. Working on more carb repairs as our crap fuel has buggered several parts just waiting to hear back from alfa 1750 on ebay,will update ,cheers. |
Retroracer |
Sep 4 2023, 09:32 AM
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#3
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Senior Member Group: Members Posts: 616 Joined: 7-July 13 From: Bend OR Member No.: 16,100 Region Association: Pacific Northwest |
Thanks for all the replies and sorry for the delay, I can get them very close but critical to have idle screws even for normal idle and upping engine speed for balancing . Spent a lot of time dialing the length of the drop links and have replaced many worn out ball cups ,strangely nearly all RH thread ones were worn out ? . When I first rebuilt these before I fitted the 2.2T motor I noticed both side cam rollers had seized @ some stage and there were area's on the rollers that had flat spotted and there was a lot of wear on the throttle cams which I have since replaced. Both the carbs were in very poor condition,I had no history when I bought this engine but the seller on behalf of the owner did say that "it ran like shit" this turned out to be a blessing as I knocked the price down and it turned out just to be the carbs and I had bought a strong engine. Working on more carb repairs as our crap fuel has buggered several parts just waiting to hear back from alfa 1750 on ebay,will update ,cheers. I usually increase the idle to 1200rpm or so for tuning, as it smooths out the pulsing of the readout. I have the overrun correction circuit disabled, as I suspect most do. As you point out, once achieved, the balance is pretty consistent across a range of RPM (which is of course the goal!) The accel pump cam rollers on my TIN40s (when I got them) had their bearings crumbling; so they would have flat spotted if I'd used them as is. Getting replacements seemed impossible at the time, so I modified some from McMaster-Carr ones to fit, which was tedious. If Alfa1750 has these available that would be good to know for sure. My carbs have been gone through recently - twice - as I foolishly let them stand over winter without flushing or draining them; and the the Ethanol based fuel wreaked havoc on the entire fuel system! Weeks later: new stainless fuel lines, new fuel pump, new fuel regulator - which leaked once plumbed in, so waiting on a replacement from PMB. The car's summer was spent up on jack stands; annoying... On a positive note, to help alleviate future embuggerance, a couple of local places here in Oregon, USA do sell Ethanol-free gasoline. That'll be the main fuel choice once I get everything running again. - Tony |
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