carb tuning advice

View previous topic View next topic Go down

carb tuning advice

Post  racinghabbit on July 18th 2017, 10:00 am

I took a couple trucks to a chassis dyno. when they make peak hp after jetting the carb up, it now seem to be rich at idle now. burns your eyes a little bit. just wondering if on engines that are race only if this common or if I just need to get back after the idle screws on the carb.
Thanks.
1050 dom & 770 holley vac secondary's are a couple carbs I'm seeing this on .
avatar
racinghabbit

Posts : 472
Join date : 2011-07-12

View user profile

Back to top Go down

Re: carb tuning advice

Post  tbirdmike on July 18th 2017, 11:33 am

jetting has very little effect on the idle circuit.

Might be that the main circuit is richer than it needs to be under light load now. If it where me I would take the main jet back down to where driveablility is good and open the PVCRs to compensate for WOT.
If you just race and thats it , then it doesnt really mater. I personally dont like motor being rich down low. Just reduces life of plug and dirties them up quicker.

tbirdmike

Posts : 27
Join date : 2015-07-21
Location : west michigan

View user profile

Back to top Go down

Re: carb tuning advice

Post  supervel45 on July 18th 2017, 12:50 pm

I would check the timing and float levels and see if they messed around with that also. Then I would count how far out the idle screws are turned out, record it, and go from there.

supervel45

Posts : 3047
Join date : 2013-09-04

View user profile

Back to top Go down

Re: carb tuning advice

Post  racinghabbit on July 18th 2017, 1:33 pm

ok. its not the floats or timing... these trucks are not street driven... race only... they never seemed rich until we jetted it up for max hp on the chassis dyno. a/r is around 12 ... but at idle its it seems rich like burns your eyes. I was not sure if that was common when you got to max hp or not.
avatar
racinghabbit

Posts : 472
Join date : 2011-07-12

View user profile

Back to top Go down

Re: carb tuning advice

Post  supervel45 on July 18th 2017, 2:28 pm

It sounds almost like a power valve going south to me. Jetting should not change it that much. If you close the idle screws does it help? If you close them all the way will it kill the engine? What is the idle RPM and is any fuel dripping out of the boosters?

supervel45

Posts : 3047
Join date : 2013-09-04

View user profile

Back to top Go down

Re: carb tuning advice

Post  BBFTorino on July 18th 2017, 11:56 pm

You may need to go with a smaller Idle Feed Restrictor.

BBFTorino

Posts : 401
Join date : 2015-12-31

View user profile

Back to top Go down

Re: carb tuning advice

Post  BOSS 429 on July 19th 2017, 9:09 am

rich out the pipe doesn't mean its wrong, go run it first ,then check the plugs
avatar
BOSS 429

Posts : 2145
Join date : 2009-08-10
Location : Ill

View user profile

Back to top Go down

Re: carb tuning advice

Post  racinghabbit on July 19th 2017, 10:38 am

no power valve in carb. its blocked off...

I'm going to try adjusting idle screws... the truck runs great above idle and there is no hesitation off idle...
avatar
racinghabbit

Posts : 472
Join date : 2011-07-12

View user profile

Back to top Go down

Re: carb tuning advice

Post  aquartlow on July 23rd 2017, 12:52 pm

If you can't get the needed info here(obviously lots of great folks here) to get the carb where you want it or where the engine likes it, try here:
http://racingfuelsystems.myfunforum.org

Hope this helps, learned quite a lot about carb tuning from that forum.
avatar
aquartlow

Posts : 117
Join date : 2010-02-05
Age : 49
Location : Summerfield, Fl

View user profile

Back to top Go down

View previous topic View next topic Back to top


 
Permissions in this forum:
You cannot reply to topics in this forum