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Discussion Starter · #1 ·
I had this engine running back in December with the break in rockers on cause it was a new build. I just got back and swapped to 1.5 rockers and can’t get the car to idle under 1500 rpm. It has a small cam, blueprint heads, and a Holley 670 Street avenger on it. Ive checked for vacuum leaks and could not find any, the timing is set right and it will fire up as long as my idle screw is set at 1500+ rpm, the idle still bounces around a bit but is not really rough. Is this a carb issue?
 

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Besides rockers, what else was changed?
Could try the standard aerosol overhaul that all Holleys need occasionally---take out the idle mixture screws and blast carb cleaner in there.
 

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Discussion Starter · #5 ·
I changed the distributor to an msd unit from some eBay one which made it run smoother than it had on the EBay one. Tomorrow I’ll go get carb cleaner and try that trick and update it. Thanks for the idea.
 

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Discussion Starter · #6 ·
I retried to start it after making the carb more rich and it idles at 700 now but bounces around to 400 and 1200 then dies after like a minute. I’ll try spraying carb cleaner in the adjustment screws tomorrow and then see if that fixes it.
 

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Discussion Starter · #8 ·
Any tips, I did the usual checked the timing, reset it and then checked it again I picked up a higher quality distributor because I didn’t like the way the cheaper one looked. I think every plug is getting spark I can check that tomorrow too.
 

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Discussion Starter · #10 ·
What is you vacuum at idle and does it bounce a lot. Could you possibly have a rocker adjusted to tight?
I will check the vacuum tomorrow I know at 1500 I was getting over 20 on my gauge. I just redid the rockers yesterday because the engine was running rough and that solved that problem so I don’t think I have any rockers to tight would checking my idle vacuum help find out?
 

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Discussion Starter · #11 ·
I rechecked all the rockers and sprayed carb cleaner in sadly neither helped, I have the timing set to around 12 and it still wants to stall out at around 1000 rpm. Any other ideas? Thanks.
 

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What are the cam spec.s and compression ratio? Are the secondary throttle plates fully closed? History of carb.? (new. used, used by somebody else, used for racing, etc.?) Float fuel levels correct? Power valve not blown out? Proper amount of transfer slot exposed? Choke fully opening after warmup?
Ignition timing at idle? Is it advancing with RPMs? Vacuum advance disconnected and port plugged while tuning?
One way PCV valve not leaking?
Power brake booster not leaking?
HVA/C vacuum servos not leaking?
 

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Discussion Starter · #16 ·
Cams a lunati specs are; Advertised Duration (Int/Exh): 276/286; Duration @ .050 (Int/Exh): 221/230; Gross Valve Lift (Int/Exh): .454/.454; LSA/ICL: 112/106; compression I think is 10~10.1, the carb has vacuum secondary’s so they are hardly open at idle but I don’t know if I can even adjust that. Carb was used, but ran well 6 months ago during break in. The fuel levels are correct checked this AM. timing at idle is around 16 now. It advances through rpm and I set it at 36 at 3500. The vacuum ports on the carb and distributor are all plugged while I try and figure this out. Choke is good too.
 

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OK that is close to a stock 350 HP 327" cam... should have a lopey idle about 650 RPMs... don't expect it to idle smoothly down low... engine should explode into high power at about 2200 - 2500 RPMs as it 'comes onto the cam'... 10-12 degrees ignition advance at idle may work better... or not...
Might try putting a spark plug wire on a sparkplug outside the engine and see if losing spark at low RPMs...
While the engine was sitting, a clear waxy substance may have settled out of the gasoline and be blocking jets and idle passageways. It's difficult to see... Sea Foam / Super Tech Motor Treatment detergent added to the gas tank may help... $7 at Walmart, $12 at auto parts stores...
 

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Discussion Starter · #18 ·
Yeah I assumed it should idle lower and be lopey. I’ll check the spark tomorrow it has open headers but I can’t imagine that would affect my idle this much. I think the carb may be in questionable health but I’d rather knock everything out then buy a new one as my last effort.
 

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Back over tread ground but once again what is the vacuum gauge reading both in inches and steadiness.

The curb idle screw does or does not have idle or any speed control?

Is there a choke on this carb and if so does its fast idle cam release so idle can be set on the curb idle screw?

Holley’s typically have a secondary adjustment screw on the passenger side of the carb accessible from the underside of an external boss the secondary throttle shaft passes through.

Some Holley’s have an idle air adjustment screw under the air cleaner stud, have you checked for this or an open through psssage to the base passage below the stud?

Have you checked to see if the throttle plates are aligned such that when they should be closed they are or will? This will require backing off all stops to see if they close light tight when unimpeded by screw stops? We’re hunting for misalignments of plates to their bores or twisters in their shafts.

What about throttle shaft wear, this is a source of uncontrolled air if the shafts are loose in their bores.

Check the throttle plate for flatness a common problem on the Holley and its clones is bending the mounting wings which bows up the throttle plate mid section to where it leaks air. Assuming of course that the issue is a sneak circuit for air somewhere not that the engine itself is incapable of tacking over at less than 1500 RPM. The fine line here is air leaks don’t add fuel so if it’s getting air from somewhere that the carb can’t fuel it will stall out. A sign of this can be that closing the idle fuel adjustment kills the engine sooner than you would expect, while opening them may keep the RPM’s going up without flooding the engine with fuel.

What is the advance showing at this 1200 RPM idle? I’m kind of hunting for abnormalities in the advance that could be sourcing in how the module is timing itself as much as is the mechanical coming in too soon. If you haven’t, I’d torpedo all the advances so we can see what the base really is and whether the module is marching to a different tune than expected. Don’t forget to plug vacuum ports at their source when doing this.

You‘ve probably been over this ground already but if you don’t mind kindly humor me.

Bogie
 

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Besides all the other comments mentioned above on things to answer and also to answer, you might want to read the Holley 670 street avenger post on that carburetor and it might help give you some light on your carburetor. Does your carburetor have an electric choke on it?

If it does if the fast idle screw is adjusted to open the primary throttle around anything more then 1500 rpm when the choke is engaged then sometimes even when the plastic fast idle ramp is no longer engaged and the electric choke coil is full open and the choke plate is completely vertical and straight up and down and the fast idle ramp is all the way down like it supposed to be and the fast idle screw sometimes can still be making contact with the lowest part of the fast idle cam piece and you can chase your tail for a long time before you can see that and most of the time the carb has to be off or you have to use a mirror and get the right angle to see if its making contact or not.

I had a problem before where my idle kept not going to where I set it at and always kept seemingly getting stuck even though everything checked out. I then took the carburetor off and looked it all over and saw the screw would still make contact with the fast idle cam even though it was fully open on the choke. I had to lower my fast idle rpm setting just a hair so it would no longer make contact with it when it was fully open.

Also are you running your vacuum advance on full manifold or timed port? With that size of a cam you want as much timing as possible and you would want to use a vacuum advance limiter plate to limit it to around 12 to 14 degrees and add it to full manifold and it will allow you more timing and help with your idle. I have a hydraulic roller cam similar to your cam in specs wise and mine will not idle below 900 rpm in park and dropping into gear it goes down to about 700 and it does not like anything less as I have tried it.

I am running a Holley vacuum secondary currently that has the same parts as the 670 street avenger, and I had to enrichen mine to idle correctly and work right for my build and you might have to do the same for yours. The street avenger 670 is pretty lean out of the box especially for even a cam like that. Make a check list of all the things above and start checking all your things on the ignition side of things first and rule all that out before messing with the carb anymore before you might get it all out of whack and have to re adjust everything.
 
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