Jets
 

Here's the question , 540 cu in , 1050 Dominator no power valves. What size jets??? Had 90's around , ran ok(625 hp/5300rpm) , decent exhaust temps. Went to 88's and temps came down a bit. (gained 7 hp too , 632 hp)
When you back off the throttle it pops out the exhaust and the plugs are pretty black(rich). To me , the way I see it:crazy: is , it's still rich and dumping fuel into the exhaust , hence the popping when it ignites in the exhaust. Talked to Holley and they say go to 92 or 93 main jets:confused:
What'cha runnin???

Feel free to jump in here anytime:rolleyes:

What are your primary main jets? I have to 500hp 454's with Holley 750 dual pumpers. When I bought the boat the plugs were black and it popped through the carb occasionally at higher rpm's (say 3800 rpm and up). Long story made short, finally determined that the engines were run out, had them rebuilt. After getting everything back in, still had the same pop. Pulled the plugs and they were now all white. Had the carb rebuilt by the best in our area. Still popped. Also noticed that after about 3/4 throttles, didn't really have any change in power. Checked the main jets and found 70's in the primaries and 80's in the secondary just like Holley said it should have. Believing it was running to lean on the top end and being the shade tree mechanic that I am, decided to start stepping the secondaries up 2 steps at a time, each time the pop occurred at a little higher rpm's and the plugs got progressively "duller" white. Plugs continued turning darker with each jet change. Now (with 90's as secondaries), plugs are light brown and no pop at top rpm of 5000 rpm. Also, now I have continuous throttles from 3/4 to full throttle.

So what the hell am I saying? I believe someone had probably changed the jets (leaning them out) to keep the dam thing running when I bought it. Are you the original owner? Have you asked Holley what the standard jets sizes were for that carb, primaries and secondaries? Perhaps your primaries are to rich and when you back off the sticks it's still pumping to much gas (thorough the primary main jets) causing the pop in the exhaust. Just a though, especially since no one else has "jumped in" on your original post. Let me know.

Al

Al, thanks for your reply. A 454 with a 750 and 540s with dominators are two different animals. There is a big difference in jets with or without power valves too.
I am the original owner of the carbs and engines. We'll get this straightened out. I was just wondering if anyone else had this set up and knew the jets they had:)

A plug reading at your two critical throttle settings will be necessary to get it worked out. (set your 4 corner idle mix first, then verify float settings front and back - I know you already know this but a lot of tuning has been for naught cause somebody didn't verify these before attemting to jet). If you are NA then your air bleeds and such should be close enough.

#1) Figure out where your secondaries begin to open. Put a stop of some sort on the cable or somewhere so that you CANNOT get into the secondaries. Go out at full operating temp and do a plug run (fresh clean plugs, run at the throttle stop setting for 20 seconds, then pull the kill switches - yes, you CAN just back down, but I prefer to kill the ignition and pull the sticks all the way back - just my preference as idling can influence the reading). Jet for light tan or slightly leaner, depending on whether you are looking for best economy at high primary cruise.

NOW you got your primaries where you want them (you may even need to stagger the sizes in each barrel if you want to get picky).

#2) Do the same thing with WOT, 20 seconds if possible, or at least 10 full seconds. Kill the spark and check em. Jet again for light tan.

mcollinstn
The engine is on a dyno right now and have done just about like you said. After a pull , we try to kill it and the sucker becomes a diesel and continues to run...even under load. We can stop it but it takes quite a load to accomplish. Plugs come out relitively black , and with the exhaust popping on decelleration it certainly seems rich:confused: , yet a Holley is saying use bigger jets. we'll try this again since it only takes a few minutes to change jets and richer shouldn't hurt anything like lean can.

mo,

If it is trying to diesel, I would be concerned about one of two things:

1) Wrong heat range spark plugs (causing the electrode to glow and continue undesired ignition).

2) Exhaust seat too narrow, giving the valve nowhere to dissipate heat (causing the same issue).

Neither of the above issues will show up on EGT.

Good luck in troubleshooting her.

mc,
You're right , but , these engines where run all last season (all 15 hrs with the sucko summer we had) , and did not have the popping problem. Carbs where messed with last summer in an attempt to solve or at least put a band-aid on and idle problem.
Did have Autolite AR133 plugs last year now have AR132 (colder).
Original prob. was no idle. Cams were too big and had virtually no vacuum at idle ( 3 to 4 inches) and when put in gear wanted to stall , plus peak HP was in the 6500 range:mad: (too high). This was due to Comp. Cams recommendation:mad: New cams were degreed in and are doing 625 hp @ 5200 and have 13 inches of vacuum. Put a load on the engine at idle and produced almost 100 ft lbs of torque and only dropped 200 rpms so the idle problem is solved.
Still believe the problem is carb related , but could be wrong;) .
We'll get it:cool:

Regardless of how they ran last season, a motor that diesels has isolated hotspots in the combustion chamber that shouldn't be there.

It might only be a couple of cylinders doing it, but you got something glowing in there.

Ok,here is a far out theory.

You didn't tell if you pulled the heads for inspection before the dyno test.

If not,there is a chance it is plenty of soot in the chambers and on the pistons after
15 too rich hours,and the glowing soot now causes the diesel behaving.

My next attempt would be with smaller carbs, 800s or 850s and a misting or water into to carbs before pulls.

BT :cool:

38KV
Now there is a very good point. Perhaps it's time for a little water down the carb. That really works wonders to steam clean pistons and cylinder heads. I'll give it a try this week.

Good luck!:)

Now why didn't I think of that :rolleyes: :D

Good luck mo,

BT :cool:

Thanks

OK , did again yesterday

Good pulls , plenty of power , and no dieseling when shut off:) . Still pops , bangs and complains out the exhaust on deccelleration:(. Also idles fine:confused:
The saga continues:crazy:

I pull that Dominator off of there. So many people have had idling problems with them. The carb was designed to run on a Nascar car which has no idle concerns. With a 650hp 540 you'll need LESS than 850cfm.

Are you SURE your header gaskets aren't leaking?
Are you SURE your dyno headers aren't leaking near the heads?

Does this happen only on the Dyno or does it happen on the boat as well?

Starting to sound like it is pulling oxygen into the cylinders on decel and lean popping...

Leaking header gaskets , eh , maybe. Also slight leakage at the point where the thermocouples enter the headers for egts.
Don't want to put these in the boat yet due to this problem. I'm liable to blow my Formula Silent Thunder off the back of the boat:( . I was thinking on running my boat headers on the dyno just for a short period of time. Not too long , so my stainless elbows don't turn funky colors. The engine doesn't have to be warm to do it. It will do it at initial start up (65* room temp)
.
Last season when the cams were too big and in the boat , this did not happen. Last month , on the dyno ,pre cam change I don't remember it doing this.
Was also considering Cords suggestion of changing to a smaller carb , although I've never had an idle prob with Dominators.
You know MC, that leaky header theory could be pretty good. I remember years back when GM cars were equipped with A.I.R. and the control valve went south and didn't vent the air out of the exhaust on decel , they could put on a pretty good show;)

Not to mash Cord's idea, but all of the Dominators I've played with have idled better than most of the cheapo vacuum secondary fixed metering plate street Holleys out there (in their out of the box form).

All 4 corner Holleys have good idling manners (some may need the bleeds opened up some).

I'm not saying that the TYPE of exhaust is causing an issue. I am saying that a header air leak CAN do exactly what is happening to you. I had an inline Jeep with 6 into 2 headers that all bolted up with the intake manifold and headers and common gaskets and everything else. NEVER got all the header leaks taken care of no matter how many gaskets I used, how flat the weld rings on the header flange were, or how I shimmed the bolts... That booger would pop and blow flames on decel. Got to where I could "feel" it getting ready to blow a big flame and give it a tiny quick squirt of the accel pump right at the flame and blow a 7 footer out the right side pipe. If I timed it right, I could flatten the flame out against the driver's window of cars in the the right lane. Did it to a kid I went to HS with and it scared him so bad he drove into the ditch with his date. I had 4 buds piled into the CJ and it got all over school. Ah, so fun were those days.

Anyhow, ANY small air leak near the head flange WILL do what you describe.

Try whatever's quicker - careful torquing of new gaskets on the dyno headers - put your mani's on it, whatever.

If you DO run your mani's then don't do it dry - run water thru them. Not worth the cracking you'll likely get in the tailpipes.

What I figured on doing is hanging them on the engine and filling the with water with the hose on the bottom , then pinch it off with vice grips to hold it in. This will act like a heat sync and give me an extra margin of time and safety. Like I said , it will do this even at a cold start , so 10 seconds will be more than enough.
I had a 68 Camaro (new) and I had a problem with the A.I.R. system and blew a seam out of the muffler.:(

As for the Dominators , I 've never really had a problem with drivability. These were boogered up last season to try to mask the real problem but have been returned to normal parameters.

Leaking intake valves?

(caused by soot)

That was my problem a few years ago.

A main key point here is that it isn't backfiring or popping back thru the carb. It is popping out the exhaust.

Right;)

While I'm not sure your carb is the problem, Holley has a web site full of info. www.holley.com They make 1050's in lots of different configurations. Go to tech support. Look at the pdf chart to find your carb. It lists jet sizes, power valves, boosters, etc for each carb.

I'm using a 1050 on a 540 with no problems. With a Crane 651 hyd. roller, mine idles at 800 rpm all day. Throttle response is excellent. Mine was factory equipped with 88 jets and 6.5 power valves. It was a little lean so I went to 92 primary, 94 secondary. Hope this helps.

Pat,
Thanks , Already spend 1/2 hour on the phone with Holley;) . Got 92 around now. Also went over idle ckt (35 fuel and 52 air). Intermediate constant 43 , discharge tube 38 and air bleed 95. Main bleeds are.034 At this point it runs great and egts are fine and idles like a ***** cat (well , maybe a lumpy ***** cat). I think the carb problems are solved. And Holley was a GREAT help.
Just have to solve the popping out the exhaust and I really think mcollinstn is on to something with the leaky dyno headers:)

mcollinstn,
Your PM box is full:o. Now I have to give you a public thankyou.
Thanks for the heads up on the leaky header gaskets;)
Just got off the dyno with new gaskets and I also removed the probes for the EGTs and sealed those holes.
Quiet as a church mouse:) :) :)
I've had SO many problems with these engines I overlooked the obvious for the more complex. Shame on me.
Thanks again,
Cal (mopower)

PM box clean now.

You're so very welcome.

In lieu of flowers or praise, please send money or beer or passwords for celebrity porn sites.

:D :D :D