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excessive backfire and flames! also rocker arm knock

8K views 53 replies 8 participants last post by  chevykid90 
#1 ·
so i adjusted my valves again today, using the method of losening valve until noise is heard then tighten 1/4 turn. now the even (passenger side) was really easy. but when i tried to do the odd (driver) side there was a lot of noise i even tried tightening all the valves simultaneously but i could not get the noise to go away. the noise i am talking about is the ticking heard from the valves. before i adjusted them i had a slight backfire but nothing too big and not very often. now i have a backfire that happens a lot, and sometimes i cant even get up to speed because of it. and also there is an exhaust rocker arm for piston #5 that is hitting on the valve cover. but it only happens sometimes. doesnt happen when idling out of gear but happens when idling in gear. it will do it with slight throttle but not with full throttle. and i seemed to have noticed that when it starts ticking is when i have the backfire. i am starting to go kind of insane with this build. i just want the car to run right. btw, its a 454, with flat top pistons, performer RPM cam.
 
#27 ·
well took it up to the races tonight. about a 30 mile away all highway, and it didnt backfire at all the way up there. (of course i didnt race, was watching dirt track races) but in the way back when i would go down a hill then at the bottom get into it again it would backfire just a little bit. i think it did it only like twice.

what i am calling the shooters is the nozzles that "shoot" the fuel into the carb when you hit the gas.

right now i am running 66 jets in the primaries and 72 secondary.

and i still have a dead spot in my throttle, when i slowly press it starts to give it gas but when i give a little more it cuts out, if i hold it there it will come back after a second or two, but if i press it more it comes back immediately. this happens at any RPM, not just off an idle.
 
#28 ·
With those jets, it's gotta be on the lean side. That's your off-idle hesitation. I would pull the carb just to make sure you have the correct power valve put in some fatter jets and maybe some larger boosters. All these items will, chosen correctly, clean up the drivability of the 454.

What CFM holley buy the way? (probably a 750?)
 
#29 ·
yeah i have been trying to tune the carb but it was really hard with my valves not right it made it hard to tune. i have drilled the boosters too big i think, it shoots alot of fuel. but i will put a set of larger jets in and see what it does. i have jets from 66 to 76. i wouldnt think it would need more than 76's.

and yes its an old 4010/4011 750 CFM. its actually a marine carb. due to the position of the vents. they are bent over and not straight.
 
#30 · (Edited)
You may need a larger pump cam to go with that larger squirter. Have you tried moving the current cam to the second linkage hole, second cam hole?? to see if it helps.

72 front 76 rear would be a good place to start fot jets if this is a square bore carb( all barrels equal size)

Does this carb have a rear power valve??
 
#31 ·
i have thought about getting the cam kit just cant (actually my wife cant) bring myself to pay $35 for the kit.

and i have tried to move to the number 2 hole but that was before the valve adjustment and is made it worse, i will try again now that i have the valves done. just seems like its not getting the fuel when it transfers to the secondaries. maybe a spring change? it has vacuum secondaries.
 
#34 ·
There are two cam colors that can confuse people because there are close to each other in hue, red and pink. The red frequently is pale red and the pink often has a reddish tint to it, and without the two side by side some can't tell the difference. The red cam has only two holes in it while the pink cam has three, so check that out.

If it is the two hole red cam, it will be way too small, this is one of the smaller cams.
 
#37 ·
Nope, backfire is usually the accelerator pump shot not being able to cover the lean hole that occurs when you move the throttle open and the motor takes a big gulp of air. Will also often be accompanied by a stumble or stuttering acceleration, or the rpm won't recover unless you ease off the gas pedal..
 
#39 ·
so i put 72's in the primaries today and moved the cam lobe to the number 2 position and now its backfireing worse than before.... also i put the vacuum gauge back on and it is fluctuating a lot. could a valve tightened itself? also i noticed when i started it up it didnt want to run at all, i had to tighten the idle screw a few turns to get it to idle. about to go crazy... :smash:
 
#40 ·
ok, so it turns out that it just didnt like the number 2 position on the cam. now there is little to now backfire, and my "dead spot isnt as noticeable now. but there still are a few hear and there, especially when i really get on it, IE: getting on the freeway. just need a bigger cam??
 
#42 ·
Man I've been thinking about what i would do for a while n here is the best I can come up with.
1 Isolate problem by swapping pushrod and rocker with another
2 Be sure and look at everything and able to identifty top of rod vs. bottom
4 Adjust lifters by the t.d.c. method, do not start engine
5 Clay offending rocker and the one you swapped ( I realize we r dealin with hyd.cam)
6 Turn eng over by hand pull valve covers back off n look at clay
7 Dont forget to compare pushrods
Sometimes I wish I was there........
Obviously something is wrong with the geometry of valve train...
Could also be lifter
Sorry I didnt read to last page!!!
 
#43 ·
now that i have done the valves different i dont think the timing is what i set it at prior witch was 38 degrees at 2500 RPM, and initial was at 16.
i eased it up to 4500 RPM in first gear (TH 350) and had no backfire (kinda get a little ansy when i run up high like that, lol) its only when i really get into it quick when she wants to do it.

Topwrench, are you talking about putting a piece of clay on top of the rocker then turning the motor over by hand? (just want to make sure i am reading it right)

and honestly when i come to think of it now, when i was putting the motor together i had one bent P-rod and i replaced it with a spare i had. and now i am almost positive that is the one that is hitting is the one i replaced.

so next move is to buy all new P-rods. (should have done in the first place.)
 
#45 ·
chevykid90 said:
it was just the spring that came with the rebuild kit. not sure it had a color to it. was awhile ago when i did the carb. was thinking of buying a spring kit too.
Typically, secondary vacuum springs aren't supplied w/the rebuild kit. They are purchased as a kit, separately under Holley #20-13.

White - Lightest
Yellow- (Short Spring)
Yellow
Purple
Plain or silver
Brown
Black- Heaviest

Holley makes a "quick change" vacuum housing cover (#20-59) for changing out the secondary spring easier.
 
#47 ·
chevykid90 said:
i think your right, i just put the old spring back in. and if memory serves me right it was the silver (just metal) one. what spring should i go to next?
Purple would be the next lighter one to try. You need to get the accelerator pump cam right first, as changing the spring to open earlier without enough pump shot now will just make it worse, a bigger lean hole. From your description of running it up the rpm scale slow in first gear avoids the backfire, you definately need more pump shot. giving the mixture screws 1/4 turn richer may help too, they may be too lean.

Was there a pump cam on the 8700 Holley you bought, from your other thread?? Color?? Might be better than what you have, Orange would be a good one to try.
 
#48 ·
i thought of that already, but it came with a white one, which looks to be the same size very very similer. going to pick up a cam kit tomorrow, you think the best thing to do is just go one step higher in cam and repeat until no backfire? seems that would be the best way to go about it (like most anything with an engine). lol
 
#49 · (Edited)
Holley's instructions are on page 6 and 7 HERE.

ACCELERATOR PUMP:
The accelerator pump's purpose is to make up for the lag in fuel delivery to enable the engine speed to increase in response to throttle opening. Differences in vehicle weight, transmissions, and rear axle ratios affect the amount of fuel and the delivery rate that should be provided by the accelerator pump. This may necessitate the customizing of your accelerator pump to your vehicle and its use.

NOTE: The old saying “if a little is good, a lot is better” does not apply to the proper tuning of the accelerator pump. Your car’s performance can be just as bad if it receives “too much fuel too soon” as if it receives “too little fuel too late”.

Two factors that affect the accelerator pump’s delivery is the pump cam and the pump shooter (discharge nozzle). The pump cam determines the total volume of fuel and affects delivery rate; the pump shooter diameter affects delivery rate and helps determine the duration of the shot.

The cams will have 2 (some 3) holes in them. Besides the change to the fuel delivery curve made by changing holes, position #1 is used when the throttle blades at idle are "normal", position #2 is when the tune of the car requires an idle speed of >1000 RPM or so. Position #2 makes up for the additional throttle shaft rotation that's required for the higher idle speed. Cams w/position #3 are usually used on REO 50 cc pumps. Generally, vehicles which normally run at lower idle speeds (600-800 RPM) find this position more useful because they can have a good pump shot available coming right off this relatively low idle. Positions #2 and #3 delay the pump action, relatively speaking. These two cam positions are good for engines that idle around 1000 RPM and above. Repositioning
the cam in this way makes allowance for the extra throttle rotation required to maintain the relatively higher idle setting.

Pump arm adjustment and clearance should be checked and verified each and every time the pump cam and/or pump cam position is changed.
A 50cc accelerator pump conversion kit is available under Holley P/N 20-11 when maximum pump capacity is desired.

Holley says: "If you need more pump shot sooner, then a larger pump nozzle size is required. During acceleration tests, if you notice that the car first hesitates and then picks up, it’s a sure bet that the pump nozzle size should be increased. A backfire (lean condition) on acceleration also calls for a step up in pump nozzle size. Conversely, if off-idle acceleration does not feel crisp or clean, then the pump nozzle size may already be too large. In this case a smaller size is required."

The pump shooters have a number stamped on their casting which designates the shooter size in thousandths of an inch, i.e., a #25 shooter has a .025” discharge orifice. The smaller diameter nozzles lengthen the pump shot duration and are used with heavier vehicles or with vehicles equipped with lower numerical rear axle ratios.

Larger diameter nozzles (.035” - .037”) shorten the pump shot duration, but deliver a greater initial volume of fuel. These sizes should be used on applications where engine speed will increase rapidly (vehicles with good power-to-weight ratios). Best acceleration is achieved when the accelerator pump delivers the lean best power air/fuel ratio to the engine; not when the maximum volume of fuel is supplied.

If a shooter size greater than 0.038”-0.040” is required, a “hollow” discharge nozzle screw is advised. Above a 0.037” squirter size, a 50 cc REO pump may also be required, available under Holley P/N 20-11. Make squirter changes in 3-step increments- if you have a 28, go to a 31, etc.

Be sure the squirter you are using hasn't been drilled oversize! If it has, the number on it obviously will no longer apply.

The smaller sized accelerator pump squirters will cause the duration of the pump shot to be longer. Because the fuel cannot be compressed, the spring in the acc. pump lever compresses then this spring pressure continues to supply fuel through the squirter until the spring has extended back to its original length.

An important point should be kept in mind when tuning a double pumper: The secondary accelerator pump must supply fuel for a sufficient time so that the secondary main nozzles can begin to flow fuel to the engine after the secondary throttles are opened. If the nozzles do not start by the time the pump shot expires, bogging will result.

Also check the accelerator pump nozzles closely to see if they've been drilled oversize. You may have a hard time telling, if they did a good job so a numbered drill set or a wire spark plug gap measuring feeler gage would help to determine the size.

Here are a couple links you might find useful:

INSTRUCTION MANUALS BY P/N- http://www.holley.com/TechService/Instructions.asp

Exploded View and Nomenclature
Manual for Models

2010, 2300, 4010, 4011, 4150,
4160, 4165, 4175, and 4500- http://www.holley.com/data/Products/Technical/199R10014.pdf

TECHNICAL LIBRARY-
http://www.holley.com/TechService/Library.asp
 
#50 ·
ok after reading all that it makes a lot more sense to what everything actually does, and in relation to each other.

so should i then put in that smaller discharge nozzle you sent me and start tuning all over again with a new cam kit?

also it was stated about the number 2 hole being used with an idle >1000 RPM. my car does not like to idle at all below 1000, thats were she sits out of gear and when in gear will go down to about 700-800, i proly will know the answer to my question, but she really does not like the second hole so should i just stick with the first one? maybe i just didnt get the slack taken up enough on the pump arm?

i am almost thinking its going to be one of those things were you would actually have to be here in person to help adjust, seems like there are a lot of moving parts and they all must correspond with eachother just right to make it work well.
 
#51 ·
I would start w/the cluster that I sent, along w/a white cam to start. It's important to remove ALL slack between the linkage and the pump are at idle. There has to be at least 0.015" clearance at WOT so the diaphragm isn't damaged.

Then, using what you read above you can see what the cure is for whatever the problem you have w/an off-idle hesitation or whatever.

I don't recall how the timing curve is set up on your engine. You do need to be sure there isn't an excessive amount of transfer slot exposed at idle. This has been covered numerous times, but basically, it calls for the vacuum advance being hooked up to manifold vacuum so the idle speed is increased, this allows the curb idle screw adjustment to be used to lower the idle speed, this in turn lessens the transfer slot exposure.

If you have little control of the idle quality using the idle mixture screws, this is telling you the transfer slot is over-exposed. This will cause an off-idle stumble, too.
 
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