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Old 04-26-2005, 06:57 PM
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help with engine tuning

well here i am again,a while back i wrote a thread saying i was finished with hot rodding after the price of gas went up. well guess what i am to addicted to quit. i sold my sb 400 i was building and wanted to buy a good running half ton p/u just to work out of. i found one for a reasonable price and guess what. i raised the hood and it had a freshly built 350 and 700r4 tranny.but im having trouble getting it to run right.i have only had it 2 days now so i haven't went over it very good yet.
its real lazy when trying to throttle it up from idle. acts like the booster pump in the carb is trying to flood it when you punch it from idle to half throttle, just a firm punch not a fast rap on the throttle. i noticed when coming home from work today while climbing a hill it was kinda popping at the exhaust a little ( not bad just a little).i have checked and recheck the timing and its good,vac adv is working.

the best of my knowledge here is what i have.

350 .030 over
keith black rotating assembly.
forged pistons
202 /160 titanium valves
weiand stealth intake
eldbrock carb (size unknown)
lunati 270 dur.cam (specs unknown) rough idle tho.
roller rockers
inital timing set at 10 deg. vacume adv. hooked to timed vac port of carb.
idle set with vacuum gauge

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Old 04-26-2005, 07:08 PM
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o, this thing has 273's in the rear with a 700r4,i plan to put 342's in next week.heres a pic of it
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Last edited by engineman302; 04-26-2005 at 07:40 PM.
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Old 04-28-2005, 12:52 AM
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Retarded?

Sounds retarded to me, I check idle timing with vac line disconnected when I use a timing light. Try watching the vac guage as you alter the timing.

Cheers from Aus!
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Old 04-29-2005, 04:16 PM
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nope not retarded,(at least not the truck any way), have set and reset the timing. engine was laboring real bad yesterday so i decided to run the over head and found all but 3 valves to tight, i hot set them while running and the engine come alive no more lazy engine. i still have a poping coming from the right bank ,it sounds more like its in the headers insted of the engine because when you get on it real hard it doesent stumble or hesitate or feel like the engine is missfiring in any way. you can hear both exhaust pipes good and the engine is running equaly balanced on both pipes.except for the poping.sounds like a fire cracker going off under the floorboard.


im wondering if i have a pin hole in the header flange letting a small amount of oxg. in and igniting any unburnt gas. just a thought.also i pulled a plug from that bank and a plug from the opp. bank and the right bank looks kinda lean compaired to the left bank, but i dont see how that could be with a single plane manifold.
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Old 04-29-2005, 05:15 PM
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You may have set the timing to the published spec's but the point that Rob was probably trying to make is that your engine probably could use even more inital advance.
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Old 04-29-2005, 09:12 PM
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Well, you have a slightly mis-matched setup there so tuning is more touchy that it normally would be. The 2.73 gears definitely don't match the semi-performance cam. The Stealth manifold is a pretty good choice for street strip and should not be causing your problem. The biggest suspect in my mind is that 'unknown' carb. Sluggish off-throttle response is a classic symptom of secondary butterflies opening too soon before engine RPM catches up with carb opening, killing venturi velocity and engine performance. Try tuning the carb for late secondary opening until you feel the engine holding back then zero in on the best timing.

Also, what 'correct' timing setting are you using? Once you modify an engine, factory specs are out the door. Try setting both distributor advance and idle feed screws by manifold vacuum. Max manifold vacuum at each device it the correct number.

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Old 04-29-2005, 09:48 PM
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try setting the timing by ear or vacuum the balancer might be spun
put a crayon mark across the balancer and check the rubber in between the 2 pieces

good luck
sr66
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Old 04-30-2005, 07:07 PM
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un beliveable

i got it fixed after four days of tunining. yall would not belive how bad this thing was miss tuned. i went ahead and put the 725 demon carb on, to eliminate the carb problem. that helped a lot, then i pulled the dist cap and found the dist wasnt even timmed to #1 cyl. i set the timing to manifold vac and it ended up being about 14 deg. the manifold is a single plane but it is supposed to be rated from idle to 6800 rpm?????? the fuel pump was failing at about 3200 rpm so it was leaning out and bucking and snorting. but the real problem was the valves were way too tight, i hot set them running and could hear the engine unloading as i backed them off. kinda suspected they were not set right because the cam is a small lunait 270 dur. cam and was loping like a big dog. the engine was laboring so bad it was funny. some of the valves i had to back off 1 1/2 turns to get them to clatter. any way i dont think it has 2.73 gears now because it will come alive now. he must have thought it did for no more power than it had.
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Old 05-01-2005, 07:30 AM
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Wow sounds like a final exam @ a mechanics school - every tuning flaw known to man built in! Check that rear end ratio to see for sure. Jack one wheel up leaving the other one on the ground. Rotate the free wheel 10 times, counting the spins of the drive shaft. Divide the driveshaft rotation count by 10, then divide it by 2 and that should be your ratio. Dividing by 2 is necessary since with one wheel stationary, the differential is in full operation and doubles the ratio. An easier way would be slide under the car and see if there is a metal tag attached to one of the bolts but that is usually missing on hot rodded rears.
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