Damn Holley

MikeStang · October 29, 2014

Well I rebuilt my 770 street avenger and added some larger squirters.

Adjusted carb as normal and fires off perfectly and Idles 650-700 in gear but now when I shut it off it wants to sometimes diesel grrr.

Squirters don't seem to have solved the flat spot either.

And when it's warming up its got the "Cold Cam" syndrome but once it's warm it's smooth as butta.

Jets are stock 73/75 if I recall.

Upped squirters from 25 to 35.

Maybe I'll reset timing down 2 degrees and adjust carb / Idle again...wish I could get rid of the damn Cold rump ba dump crap.

I know that's a lean condition in the idle circuit..

MikeStang · October 29, 2014

Well I rebuilt my 770 street avenger and added some larger squirters.

Adjusted carb as normal and fires off perfectly and Idles 650-700 in gear but now when I shut it off it wants to sometimes diesel grrr.

Squirters don't seem to have solved the flat spot either.

And when it's warming up its got the "Cold Cam" syndrome but once it's warm it's smooth as butta.

Jets are stock 73/75 if I recall.

Upped squirters from 25 to 35.

Maybe I'll reset timing down 2 degrees and adjust carb / Idle again...wish I could get rid of the damn Cold rump ba dump crap.

I know that's a lean condition in the idle circuit..

1969_Mach1 · October 29, 2014

The most common size nozzle for street cars is 31. Sometimes the off idle flat spot is caused by the primary throttle plates being open too far at ide. When this happens too much of the transfer slot is exposed at idle. There should only be about 0.020" to 0.040" of the slot exposed below the throttle plates at idle. If too much slot is exposed at idle, then slightly off idle there is a flat spot because the air velocity is too low for the main circuit to start and the flow through the transfer slot is already at it's max. If you think that may be the case you need to open the secondaries more and close the primaries.

Also, be certain the accelerator pump linkage is adjusted correctly. The pink cam is most common and I think provides the most movement for a 30cc pump. Zero play in the linkage at idle and do not bottom out the accelerator pump diaphragm at wide open throttle.

Lastly, rough idle when cold can be a rich condition as well. Holley's performance carbs tend to not need much choke plate closure immediately after start up. I am not familiar with how to adjust the choke pull off on Holley electric chokes.

Edited October 29, 2014 by 1969_Mach1

1969_Mach1 · October 29, 2014

The most common size nozzle for street cars is 31. Sometimes the off idle flat spot is caused by the primary throttle plates being open too far at ide. When this happens too much of the transfer slot is exposed at idle. There should only be about 0.020" to 0.040" of the slot exposed below the throttle plates at idle. If too much slot is exposed at idle, then slightly off idle there is a flat spot because the air velocity is too low for the main circuit to start and the flow through the transfer slot is already at it's max. If you think that may be the case you need to open the secondaries more and close the primaries.

Also, be certain the accelerator pump linkage is adjusted correctly. The pink cam is most common and I think provides the most movement for a 30cc pump. Zero play in the linkage at idle and do not bottom out the accelerator pump diaphragm at wide open throttle.

Lastly, rough idle when cold can be a rich condition as well. Holley's performance carbs tend to not need much choke plate closure immediately after start up. I am not familiar with how to adjust the choke pull off on Holley electric chokes.

Edited October 29, 2014 by 1969_Mach1

barnett468 · October 29, 2014

hello;

check your timing . . i suggest you read the thread by juit on the first page of the forum if you are not completely familiar with the effects of ignition timing.

if you advance your timing slightly while the engine is idling and the rpm increases noticeably then you did not have enough timing at idle.

if you can reduce the rpm by turning the fuel mix screws in from the optimum position and reduce it slightly by turning then out from the optimum position it is impossible for it to be lean at idle.

what are your cam specs and carb jet sizes?

can you post a photo of a spark plug from a 45 degree angle?

.

Edited October 29, 2014 by barnett468

barnett468 · October 29, 2014

hello;

check your timing . . i suggest you read the thread by juit on the first page of the forum if you are not completely familiar with the effects of ignition timing.

if you advance your timing slightly while the engine is idling and the rpm increases noticeably then you did not have enough timing at idle.

if you can reduce the rpm by turning the fuel mix screws in from the optimum position and reduce it slightly by turning then out from the optimum position it is impossible for it to be lean at idle.

what are your cam specs and carb jet sizes?

can you post a photo of a spark plug from a 45 degree angle?

.

Edited October 29, 2014 by barnett468

SA69mach · October 29, 2014

I also suggest verifying your timing at idle. Dieseling is a classic indication of LOW timing at idle setting.

My 69 Mach 1 351 W had intermittent dieseling and it was due to ridiculously low idle timing settings. (one degree BTDC!!) Car ran nicely, so not much else to indicate the problem.

Now after a dyno tune it is about 12 degrees, runs like a champ, more power, better gas mileage, and NO dieseling.

I hope you find the problem.

I have had great results with the three Holley Street Avengers. My 770 is on a big block and like the other two 670's, ran near perfect out of the box. These days the testing and tuning out of the factory is fairly foolproof and you should be close to the mark for jetting and transfer slot adjustment......

SA69mach · October 29, 2014

I also suggest verifying your timing at idle. Dieseling is a classic indication of LOW timing at idle setting.

My 69 Mach 1 351 W had intermittent dieseling and it was due to ridiculously low idle timing settings. (one degree BTDC!!) Car ran nicely, so not much else to indicate the problem.

Now after a dyno tune it is about 12 degrees, runs like a champ, more power, better gas mileage, and NO dieseling.

I hope you find the problem.

I have had great results with the three Holley Street Avengers. My 770 is on a big block and like the other two 670's, ran near perfect out of the box. These days the testing and tuning out of the factory is fairly foolproof and you should be close to the mark for jetting and transfer slot adjustment......

MikeStang · October 29, 2014

Motor is a 408W, Camshaft is Hyd Roller, 228/236@50 563/571 lift on a 113 LSA

intake is Vic JR. W/ AFR 205 Nitrous ported heads, Holley 770 Street Avenger.

Motor made 550 Hp on the dyno and was tuned with my HP 950.

B4 I rebuilt the carb it was having float sticking issues so I went through it with a complete rebuild.

Before rebuild It smelled a bit rich and I checked timing and it was at 10 deg BTDC which is where it liked it on the dyno, total timing is 36 degrees if I recall which is where it made peak everything on dyno.

I knew I would have to tune it a bit when I went down to a 770 Vac sec carb and when I checked timing it was exactly where I left it 2 years ago from Dyno at 10 degrees, so I bumped it to 12 Degrees BTDC and the rich smell almost all but went away.

Now after rebuild of the 770 its still at 12 degrees but dieseling...

I just remembered I put some 89 Octane gas in it the other day :( that may be the issue

MikeStang · October 29, 2014

Motor is a 408W, Camshaft is Hyd Roller, 228/236@50 563/571 lift on a 113 LSA

intake is Vic JR. W/ AFR 205 Nitrous ported heads, Holley 770 Street Avenger.

Motor made 550 Hp on the dyno and was tuned with my HP 950.

B4 I rebuilt the carb it was having float sticking issues so I went through it with a complete rebuild.

Before rebuild It smelled a bit rich and I checked timing and it was at 10 deg BTDC which is where it liked it on the dyno, total timing is 36 degrees if I recall which is where it made peak everything on dyno.

I knew I would have to tune it a bit when I went down to a 770 Vac sec carb and when I checked timing it was exactly where I left it 2 years ago from Dyno at 10 degrees, so I bumped it to 12 Degrees BTDC and the rich smell almost all but went away.

Now after rebuild of the 770 its still at 12 degrees but dieseling...

I just remembered I put some 89 Octane gas in it the other day :( that may be the issue

SA69mach · October 29, 2014

The timing sounds right for that engine, and certainly not WAY off.

I once ran out of gas with that 351 and got 5 gallons of low grade fuel on the turnpike. Boy that engine dieseled for at least 30 seconds at the next gas station. So, yes, I believe low octane can affect, perhaps cause dieseling.

Considering your hi-po engine, I would agree that would be the likely culprit.

If your engine will start, idle and run, then it is less likely to be a jetting or mixture issue with the carburetor.

A leak, or a bad base gasket may be worth checking for, with a fuel smell.

Perhaps, due to the high hp engine and biggish cam, it would be worth a dyno tune if you have changed carburetors. It is not something I would want to tinker with, since if the engine goes 'boom' it is a big investment to blow up.

SA69mach · October 29, 2014

The timing sounds right for that engine, and certainly not WAY off.

I once ran out of gas with that 351 and got 5 gallons of low grade fuel on the turnpike. Boy that engine dieseled for at least 30 seconds at the next gas station. So, yes, I believe low octane can affect, perhaps cause dieseling.

Considering your hi-po engine, I would agree that would be the likely culprit.

If your engine will start, idle and run, then it is less likely to be a jetting or mixture issue with the carburetor.

A leak, or a bad base gasket may be worth checking for, with a fuel smell.

Perhaps, due to the high hp engine and biggish cam, it would be worth a dyno tune if you have changed carburetors. It is not something I would want to tinker with, since if the engine goes 'boom' it is a big investment to blow up.

barnett468 · October 29, 2014

Now after rebuild of the 770 its still at 12 degrees but dieseling...

i would set the gas level so it is just below the bottom of the inspection hole while it is idling. this can cure several problems with the holleys i guarantee you.

I just remembered I put some 89 Octane gas in it the other day :( that may be the issue

:saddam:

barnett468 · October 29, 2014

Now after rebuild of the 770 its still at 12 degrees but dieseling...

i would set the gas level so it is just below the bottom of the inspection hole while it is idling. this can cure several problems with the holleys i guarantee you.

I just remembered I put some 89 Octane gas in it the other day :( that may be the issue

:saddam:

1969_Mach1 · October 29, 2014

MikeStang,

You may get it to run okay. But that's not the best carb for that application. It may be difficult to tune out the stumble with that carb and your motor combination. To begin with, I would verify the primary throttle plate position is correct at idle. For your motor they are likely open to far to obtain idle which can cause engine run on (dieseling) and your off idle stumble.

I have no experience with Street Avenger Carbs simply because word-of-mouth in my area is to stay away from them for any application. Why, I don't know. I cannot afford to purchase something others have had bad experiences with. It seems to me they were not intended to be used with the weak signals from single plane intakes and large overlap camshafts. With a lot of valve overlap and a single plane intake I would expect some rough idle conditions, cold and/or hot.

If it's in your budget I would definitely consider replacing the Street Avenger with a Double Pumper series carb if you want a choke or HP series carb if you don't want a choke.

1969_Mach1 · October 29, 2014

MikeStang,

You may get it to run okay. But that's not the best carb for that application. It may be difficult to tune out the stumble with that carb and your motor combination. To begin with, I would verify the primary throttle plate position is correct at idle. For your motor they are likely open to far to obtain idle which can cause engine run on (dieseling) and your off idle stumble.

I have no experience with Street Avenger Carbs simply because word-of-mouth in my area is to stay away from them for any application. Why, I don't know. I cannot afford to purchase something others have had bad experiences with. It seems to me they were not intended to be used with the weak signals from single plane intakes and large overlap camshafts. With a lot of valve overlap and a single plane intake I would expect some rough idle conditions, cold and/or hot.

If it's in your budget I would definitely consider replacing the Street Avenger with a Double Pumper series carb if you want a choke or HP series carb if you don't want a choke.

barnett468 · October 29, 2014

put your finger over the vacuum port on the passenger side of the carb . . if there is noticeable vacuum then your butterflies are too far open as mentioned.

if this is the case, you can drill holes in the front plates or open the rear plates slightly and try that but because you will still be getting the same air flow i doubt it will change anything .

if your rpm increase with more initial timing then advance the distributor and then you can close the plates more. . this will make it idle smoother and run cooler at idle and may reduce or eliminate the dieseling if lowering the gas level has no affect.

.

barnett468 · October 29, 2014

put your finger over the vacuum port on the passenger side of the carb . . if there is noticeable vacuum then your butterflies are too far open as mentioned.

if this is the case, you can drill holes in the front plates or open the rear plates slightly and try that but because you will still be getting the same air flow i doubt it will change anything .

if your rpm increase with more initial timing then advance the distributor and then you can close the plates more. . this will make it idle smoother and run cooler at idle and may reduce or eliminate the dieseling if lowering the gas level has no affect.

.

MikeStang · October 29, 2014

Barnett -- Fuel bowl level is set correctly, checked it several times to be sure.

My next thought was opening the rear plates slightly as you suggested. I have never used this method but I don't feel like drilling any holes haha.

1969 Mach1 - Yeah I know this carb is not ideal for my motor as indicated by my Dyno with the 950 HP which had almost perfect AFR values and required no adjustment "I was running it on my 455 Pontiac before the Ford 408 lol"

I got the Street Avenger in a package deal of parts I bought so it cost me nothing really and because a friend had just put a 750 Vac secondary carb on his motor which is a close match to mine and it ran beautifully I decided I would give this 770 a try.... I have video of it idling in gear at 650 and its pretty damn smooth.

I can actually go down on the idle a bit more to try to close the transfer slots off some and give that a try.

The choke is set per Holley's directions and as such there is a gap between the blade and the housing when you tap the gas at first start up.

I also noticed that the choke does not stay on as long as it did before the rebuild and i put it back in the same spot that it was in to begin with.

hopped in it this morning and tapped the gas one time and hit the key, it ran on high idle about 10 seconds and then came off high idle and rpms were around 500 in Neutral and it was barley running, so I gave it some gas and was greeted with the usual bumpty bumpty till i got it to around 2000 rpms for about 6 seconds and then it smoothed out and idled about 750, then placed it in Reverse and took off lol.

I do like the way the carburetor runs however, its very peppy except from a dead stop when I nail it the engine will stumble for a split second then BAM the ass end is going to the right which pisses me off, but its not near as bad as it was, at least now when i stomp it below 60 and the tires break loose it doesnt go to far to the right that I cant control it, but still a scary feeling

MikeStang · October 29, 2014