Thread: new qtf 600 cfm

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I got this issue with this carb,it's brand new,first it won't go on idle circut,probably cause it's running rich so i've check my install multiple times i do have a 1 1\2 alum. spacer. if you let it sit after running for a few minutes after warm up it floods, so here the puzzling part, check the power valve appears to be fine (just using my mouth to suck on it) when running the bowls are dead center, when you let it sit a week it barely drops in the sight glass the accelerator pump also is still holding gas.anybody got an idea on what i could check next? THANKS also have pressure regulator set at 5lbs.

Originally Posted by craig akiyama

if you let it sit after running for a few minutes after warm up it floods

If Im reading you correctly, this sounds like heat soak, caused by motor heat transferring to the carb and boiling the fuel?

However, I believe you may have some tuning issues too. A few questions;
What motor?
How big is the cam?
What is the idle speed?
What is the idle vacuum?
How did you set your idle speed?
How did you set your idle mixture?
What number power valve do you have?
Have you checked for vacuum leaks?

Holley 108-12, Holley Carburetor Service Gaskets | Holley

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350 40 over 4 bolt been out of the garage once no front sheet metal yet heat soak not an issue never ran a long time at once edelbrock e force heads and air gap manifold speed pro cam hyd. 435 lift in. 454 ex. intake dur.283 ex.286 power valve 6.5 can't get on idle circuit and won't idle under 1000 no known vacuum leaks power breaks work and i'm embarrassed to say i don't have a vacuum gauge at the present time

Originally Posted by craig akiyama

350 40 over 4 bolt been out of the garage once no front sheet metal yet heat soak not an issue never ran a long time at once edelbrock e force heads and air gap manifold speed pro cam hyd. 435 lift in. 454 ex. intake dur.283 ex.286 power valve 6.5 can't get on idle circuit and won't idle under 1000 no known vacuum leaks power breaks work and i'm embarrassed to say i don't have a vacuum gauge at the present time

I'm going to give you some of the same info that I gave another rodder recently, but first off, let's identify the cam for other CHR members who are following along. I'm thinkin' it's a MC2203 with a 0.050" duration of 209/216, with really slow ramps (Hydraulic Intensity 74) with an intake lobe centerline of 107, exhaust lobe centerline of 117 and a lobe separation angle of 112.
You didn't tell us the static compression ratio of the motor, but I can tell you that the ideal SCR with that cam would be between 9.0:1 and 9.5:1. If your SCR is over that, the motor will have a tendency to detonate on pump gas due to excessive cylinder pressure. If your SCR is under that, the motor will tend to be a pig due to insufficient cylinder pressure.

If you don't have a vacuum gauge, then you have no idea of what power valve should be in the carb, so you need a vacuum gauge, but the first thing you need to do is to get some ignition timing in the motor because you are operating the motor too far into the power mode circuit of the carb by uncovering too much of the transition slot in the primary bores. The slots should be open only about 0.020". The top of the slot should be just visible above the throttle plate at curb idle.
Use this part to control the position of the secondaries....
Holley 26-137, Holley Secondary Idle Lever | Holley

For setting the ignition timing, first find top dead center with this tutorial.....
http://www.crankshaftcoalition.com/w...op_dead_center
Then determine what timing the motor wants.....
Don't be afraid to experiment with ignition timing. There is horsepower to be found there. First, find the limit of advance that the motor will tolerate using the available fuel you have access to. With the tight Edelbrock chambers, it will probably be around 34 degrees total, but you should experiment with this and keep detonation under control by reading the plugs.

You will want to keep an eye out for signs of detonation by examining the spark plugs regularly while using the best pump gas you can put in the tank. Your very next purchase, after a vacuum gauge, should be a 10X lighted spark plug loupe like this offering from Longacre....
http://www.longacreracing.com/produc...rk+Plug+Viewer
You'll need to be able to see way down on the insulator....either that or cut the plug apart.....
http://www.dragstuff.com/techarticle...lugs/rich1.jpg

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When reading plugs, make a full power run through the gears, then go to neutral and immediately chop the igniton. Any idling or low speed use after the full power run will re-color the plugs and you won't be able to read what the motor is doing at full bore acceleration. Let me say this again, with emphasis.....Choose a place where you can make a full-power run, then go to neutral, chop the ignition, coast to a stop, yank the plugs and inspect them right there. Or, you may want to yank 'em and number 'em, then install a fresh set of plugs that you have been carrying with you so you can examine the colored plugs at home later or back at your pit if you're at the drag strip.
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Find every bit of information you can that concerns tuning by looking at the spark plugs. I'll start you off with these....
Spark Plug Reading 101 by Mike Canter - Dragstuff
Spark plug reading
https://www.google.com/search?q=read...IQsAQIMw&dpr=1
https://www.ngksparkplugs.com/about-...d-a-spark-plug
https://www.google.com/search?q=read...urning+coolant
https://www.ngksparkplugs.com/about-...ut-spark-plugs
https://www.ngksparkplugs.com/about-...park-plug-faqs

When making changes, make only one change at a time and go over the results of that change. You may have to backtrack to your baseline before making another change.

The first indicator of detonation will be little black specks up on the insulator that look like someone sprinkled black pepper on them. That would be little droplets of oil that have been smashed from the top ring land by the sledgehammer blows of detonation. Next thing you will see on the insulators if you don't do anything to correct it will be little silver specks. That will be your pistons coming apart.
Once you have found the max timing the motor will like, experiment with the timing curve and where you put the initial timing at the crank.
http://www.firstfives.org/faq/timing...ed_engines.PDF
Now, of course you will need to know where top dead center is to begin with, so here's how to do that.....
http://www.firstfives.org/faq/timing...ed_engines.PDF

Try 12, 14, 16 or more degrees ignition timing at the crank.
If this will be a primarily race car, you may find that you can completely eliminate the centrifugal advance function of the distributor and hook 'er up direct with full ~34 degrees of advance without any centrifugal advance at all.
Locking out timing on HEI (here's how to) - NastyZ28.com

If you get to a point where excessive timing at the crank makes the motor kick back against the starter, cut into the hot feed wire that goes to the coil and install a momentary on-off switch that you can control from the dash. You can use a push-button NC (normally closed) kill switch for this function, one that will tolerate the amount of juice that goes through the wire to the coil. A 15+ amp switch should do the trick. Recommend this Cole-Hersee 35 amp unit.....
https://www.waytekwire.com/item/4415...JhbhoCslXw_wcB

Operation would be as follows.....
Push the engine off switch and hold it in with your left hand.
Turn the ignition start key on with your right hand.
Once the crank if spinning good, let go of both switches and the motor will be idling. No muss, no fuss.
If you can find a good starter support, you may want to install that also if you can get it to fit around/between the header pipes.

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Originally Posted by craig akiyama

when running the bowls are dead center.

The fuel level needs to be at the bottom of the sight glass. You should actually be able to remove the plug (or window) and fuel should barely be able to dribble out.

If your idle is at 1000rpm and your carb's idle speed screw is all the way loose (not touching the throttle blade stop), disconnect your vacuum advance and plug the carb port, if idle speed drops move the vacuum advance to the venturi vacuum port on the carb. If with vacuum advance disconnected your idle speed is still too high, you have a vacuum leak...

And, IMHO, what techinspector1 wrote above in post #5 should be BOOKMARKED on a page by itself so it can be referred to frequently. There is MUCH education in it!!!

Originally Posted by craig akiyama

heat soak not an issue never ran a long time at once air gap manifold
i'm embarrassed to say i don't have a vacuum gauge at the present time

Air gap manifold will not stop heat soak, as heat soak is a condition caused by heat transfer when the motor is turned off. The motor does not have to be run hot to cause heat soak, when the motor is turned off, there is a tremendous amount heat trapped in the metal surrounding the cylinders, aluminum transfers this heat quickly and heat rises. The aluminum heads and manifold are a conduit for heat soak by transferring heat from the motor quickly to the carb. And, the 1-1/2" aluminum spacer can increase heat soak. You can sometimes use a laser thermometer to see a heat soak condition.

BTW, why are you using a 1-1/2" spacer under the carb?

A VACUUM gauge is one of the most inexpensive and valuable tools you'll own...

did I miss it or ----what fuel pump do you have and what fuel pressure are you running?


Don't ever suck on a power valve to test it-that will only tell you if the diaphragm is leaking-------not what vacume holds it closed or whether it'll leak fuel pass it--and you certainly don't want any of todays fuel in your mouth, throat or lungs or spit it onto somebody close by trying to help you--- I once saw a guy do this and when he gagged spit it out onto a nearby standing friend (who was smoking) set the garage on fire--of course it did eradicate the problem they were having

holly fuel pump mech., set at 5 lb. holly reg.

today is my only day off and I will take this info gathered here and try to put it to use, thanks I'll be back

vacuum running at around 10 engine loops quit a bit, running very rich timing is a bit advanced with the port plugged, i just have a arrow doesn't show deg. guess i'll fool with that when the garage clears out.

TEST, don’t guess...
PROJECTS and TROUBLESHOOTING

OK timing is best set a little advanced where it was before vacuum up about 12 in. fouled my 3rd set of plugs the black smoke in the garage is hazardous, held my finger over vent tube and it took 20 sec. to die, i read about this test for power valves somewhere, qft says sight glass is to be half way, 5lb fuel pressure, choke backed off. still running the spacer plate. can't think of any other test to take. the engine was built at jms in irwindale. cam part no. cs1105r it was dinenod but i guess they don't use the carb we bought there. would it help now to know main jet size????