Carburetor issue

[DJs74]

Need some help from the carburetor guru's please!!

Recently there have been several threads about carburetors, sizes, CFMs, etc and a lot of good input... I have a specific issue I need some help with.

The carburetor is a Holley Street Avenger, 570 CFM, dual feed, vacuum secondaries, manual choke, 4 corner idle air mixture screws - brand new. It runs great and has no issues on performance or idle, only starting after initially run and warm.

For example: I get in it cold, a couple of pumps, starts fine and idles immediately. I run around a few miles with flawless performance, come back, turn it off, 5 minutes later (or even 1 minute later), reach through the window, hit the key - it fires before the engine even makes 1 full revolution but shuts off instantly. I have to get in, push the pedal to the floor as if its flooded and then it fires after several (too many) revolutions and then back to normal and idles fine. I also smell gas before I try to start it but there is no visible fuel anywhere under the hood or otherwise (more like vapor fumes). Its like it is flooded.

I've check and adjusted:
* float levels (they are half way up the clear sight glass)
* accelerator pump (0.015" feeler gage between the pump lever arm and adjusting screw @ WOT)
* manual choke is off and open
* air mixture screws @ all 4 corners are right - vacuum at idle is around 15"
* no vacuum leaks
* fuel line is stainless braided from the pump with all -6AN fittings (no hose / no clamps)
* fuel filter is at tank
* steel line from tank to pump

It almost acts like a blown power valve but shows no sign of vapor rolling when turned off and I have complete and responsive adjustment of the air mixtures screw so I've discounted the power valve + this particular model has power valve blow protection built in

Running a dual plane intake manifold, all vacuum lines on the carburetor are capped.

Idle circuit issue?
Engine heat issue?
Power valve even though it doesn't exhibit typical blown power valve symptoms?
float level need to be lower than mid glass?

I have a heat shield for mounting under a carburetor but I'm already borderline on my air cleaner height so I'm afraid adding it (plus another gasket) will cause hood clearance issues.


Thoughts and feedback is appreciated as always.


DJs74

 

[SHX669]

Fuel level should be at bottom of the glass or slightly lower -
SHX

 

[Eoth]

I think your stainless steel braided hose is heating up and vaporizing the fuel when it sits with a hot engine. Is there any way you can rig up a cheap rubber line to confirm?

 

[DJs74]

Hey Guys - sorry i was off for a while. Here in wonderful Winchester Virginia, it's Apple Blossom Festival weekend. We have 250,000 visitors from all over for country join us for three loooooong days so me and the family went to down to take in some of the festivities.

I will take a look at and make some adjustments to both the fuel level and bypass the braided line and see what happens.

thanks for the suggestions.

DJs74

 

[broncnaz]

Power valve is not the issue if it was you'd have issues at idle.
Maybe a heat issue fuel will evaporate or even boil in the carb once the engine is shut down. Although it still could be a idle mixture adjustment or idle speed issue.
You could even need to adjust the ignition timing you could have to much or to little.

 

[DJs74]

Power valve is not the issue if it was you'd have issues at idle.
Maybe a heat issue fuel will evaporate or even boil in the carb once the engine is shut down. Although it still could be a idle mixture adjustment or idle speed issue.
You could even need to adjust the ignition timing you could have to much or to little.

I agree on the power valve. Even though is has slight symptoms of power valve issues, it idles perfectly and as I mentioned earlier, the air mixture screws are very sensitive. Normally, when I've blown power valves in the past, I have limited to no impact with the air mixture screws

Timing is @ 34° so I could probably squeeze another degree or two out of it.

I think you, me and others are onto something with the heat - almost like the fuel is heating up and running down into it after it sits for a little bit, then the throttle has to be opened up (like when flooded) to get rid of the excess


thanks for your thoughts - I'm going to try to focus on the heat issue and see what I can do - maybe a different baseplate gasket??

thanks,

DJs74

 

[broncnaz]

34 degrees? is that at RPM's or at idle? If at idle then its probably way to much.

Heat can be a issue but Ive run holley's for many many years and never had that issue and I live in AZ where its hot. lol If you can find the 1/4" thick base plate gasket you should be able to rule out heat issues. I think felpro sells them most parts stores either have them or can get them.

 

[DJs74]

34 degrees? is that at RPM's or at idle? If at idle then its probably way to much.

Heat can be a issue but Ive run holley's for many many years and never had that issue and I live in AZ where its hot. lol If you can find the 1/4" thick base plate gasket you should be able to rule out heat issues. I think felpro sells them most parts stores either have them or can get them.

Sorry for just throwin 34° out. I run an MSD mechanical advance distributor, so my 34° is total at 3000 RPM - not sure what it is at idle

I will try a thicker more insulated type gasket and also mess around with the rear air mixture screws a little bit. This carburetor has 4 corner idle and the back on on the driver side is difficult to deal with because of the kickdown lever rod so I haven't done a whole lot with the back two


Thanks broncnaz!

 

[SHX669]

high float levels will usually make things run too rich ; I'd also lower the float levels .
I ran a Street Avenger for 4-5 years and had good success with it . It did pretty well on mild to not too wild off road angles also.
SHX

 

[Fairlane514]

I agree on the float level. It should be just below the sight screw threads.

 

[DJs74]

I agree on the float level. It should be just below the sight screw threads.

No threads / no holes on this model guys. I agree with you on the Holleys with the removable brass screw, the fuel needs to be at the bottom of the hole and I usually adjust the floats by rocking the vehicle so the fuel just trickles out of the holes.

This 570 avenger has clear sight windows (no screws) and Holley says the fuel level should be @ mid to just below mid level of the window,,, however, I am going to see what happens by adjusting the floats so that the fuel is at the bottom edge of the sight glass just to see what happens.

thanks,

DJs74

 

[SHX669]

Holley must have changed their float level instructions - my Street avenger owner manual says " if fuel level is above the bottom of the sight glass it's too high."
SHX

 

[broncnaz]

Sorry for just throwin 34° out. I run an MSD mechanical advance distributor, so my 34° is total at 3000 RPM - not sure what it is at idle

I will try a thicker more insulated type gasket and also mess around with the rear air mixture screws a little bit. This carburetor has 4 corner idle and the back on on the driver side is difficult to deal with because of the kickdown lever rod so I haven't done a whole lot with the back two


Thanks broncnaz!

You need to double check the initial timing 34 degrees is about all that you should run total. Initial timing affect total timing. Most of the time you can run 10-12 initial and the rest is mechanical.

With the 4 corner idle you need to adjust all corners to get your smoothest/highest idle. The secondaries idle system is part of normal idle so it has to be adjusted.

 

[aqua_wonder]

I found that Holley has 2 different set of instructions on adjusting float levels. The regular Street Avenger instructions state set floats with fuel at bottom of sight window. The Aluminum Street Avenger and Ultra Street Avenger state middle of sight window.