View unanswered posts | View active topics It is currently Sat Jun 24, 2017 4:37 pm



Reply to topic  [ 6 posts ] 
 quick fuel 750 blow through carby. Poor running issues 
Author Message

Joined: Tue Nov 17, 2015 3:40 am
Posts: 3
Hey all
I have brought a new Quick Fuel 750BAN blow through carby. I am having issues with tuning it. If I put other carbys on that I have borrowed like a 800DP, it runs fantastic. But as soon as I put the 750 back on it idles poorly and is bad on light throttle surging at cruise. My afrs are steady in the high 12s and I have had it to 4 shops but no one can find an issue.

I can only have the 4 corner idle adjusters out 1/4 of a turn each or its way too rich. We have tried different air bleeds etc. Under power its fine though
Are these carbys known for this or are they usually very good.
cheers maca


Tue Nov 17, 2015 8:46 am
Profile
Site Admin
User avatar

Joined: Fri Feb 08, 2013 5:50 pm
Posts: 2302
A couple things that need to be addressed on them, especially on a blower carb. One is lower the idle jet shown on the link below. Assuming gas for fuel tart with .031, might be a tad lean but it will get you a response to see if you are in the right direction. Second is installing t-slot restrictors, start at .075.


viewtopic.php?f=25&t=18

t-slot restrictors
Image


Tue Nov 17, 2015 10:06 am
Profile

Joined: Tue Nov 17, 2015 3:40 am
Posts: 3
Hi jmarkaudio
Thanks for your help. My knowledge with carbs is basic so I may ask some silly questions. Yes its for pump gas

To lower the idle jet will I have to do this in both metering blocks? or just the primary one.
I will open it up and look as I am not sure if I will have to tap the hole as the quick fuel looks to have a lot of adjustable jets inside. I might get lucky and its already got screw jets in there.

Are the t-slot restrictors just a screw in and out deal? and what will they do? is this to try to fix my poor idle? I have never had a carby where I could only have the 4 corner idle screws all out a 1/4 of a turn. Is this 1/4 turn causing me some of my issues? or just fine
cheers


Tue Nov 17, 2015 8:21 pm
Profile
Site Admin
User avatar

Joined: Fri Feb 08, 2013 5:50 pm
Posts: 2302
It's a combination. Lowering the idle feed will stabilize fuel delivery, and your blocks are threaded for the upper location. Threading the t-slots will allow them to be tuned, the Quick Fuel baseplates have a larger t-slot than a Holley or BLP base. This bleeds too much air back at idle, further contributing to the poor idle. You have to get the combination of idle jet, t-slot size or size in combination with the t-slot jet, and the idle air bleed close for your idle and light throttle to work well. You will have to thread the body for t-slot restrictors as well, 8-32. If you are not up to it find a friend who can help you with the machine work.


Tue Nov 17, 2015 10:59 pm
Profile

Joined: Thu May 14, 2015 8:11 am
Posts: 149
following marks advice i lowered the idle feeds from up top to down low. with no other changes i went from having a lean part throttle surge with them up top to no surge with them down low. after some testing i was able to reduce the idle jet 3 thou. still no part throttle surge & leaner mixture.

the taps are cheap & if your gonna do this stuff worth the expense to buy


Wed Nov 18, 2015 5:46 am
Profile

Joined: Tue Nov 17, 2015 3:40 am
Posts: 3
do you think my surging and occasional missing could be a lean fuel problem even though the AFr gauge says its in the high 12s when its doing it?

The reason for all my questions is my engine seems to have a heat issue I cant find. It used to run at 160 but now after 25min it runs at 180 and starts surging and running very poorly. The only thing I have changed is the carby, fuel lines and pump, heads and cam. can is only a small street roller cam. heads went from cast to ally. fuel lines went from a single steel line to 2 1/2 inch ally lines as I plan on supercharging the engine but I am running it as a NA engine at the moment until I work out the heat and running problems.


Wed Nov 18, 2015 8:45 am
Profile
Display posts from previous:  Sort by  
Reply to topic   [ 6 posts ] 

Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group
Designed by ST Software for PTF.