oxrabidus

I recently rebuilt a vortec 305, put a summit 1103 cam in it, it has stock heads, a procomp intake, a holley 4160 650cfm carb, and flat top pistons.

I have been having the hardest time trying to tune this thing. its running rich as hell, no matter how i do the idle fuel mix, it will stall on the highway. sometimes it bogs between part and full throttle. i dont understand it...

so this guy near me is selling a 350 out of a 91 vette, he says its an lt1 but it cant be, hes probably mistaken anyways....

so here is my question....

would it be easier for me to take the block and put the top end that i currently have on the 305 on the 350 block?
i was reading up and i found out that 650 may be too big for a 305, and with my cam it probably doesnt help. not that the cm is big but it just makes it harder to tune. i figured the extra cubes will help even the richness problem maybe.

i could just use the tpi and get all the other parts, but im ina tough situation, and cant afford it....

the cost of having my engine properly tuned by a shop is slightly more expensive than the cost of the whole 350. so being that the 350 is a cheaper option and that it came with 58cc heads i can just put the iron vortecs on no probles (and they probably flow better than the l98 alum heads anyways...)

i have tried to tune the carb and timing myself and sometimes it gts better sometimes worse... and i really wouldnt want to open it up to rejet it because ill probably mess something up.
i truly truly appreciate any help given
thanks
Miguel

camaronewbie

I'd say you just need to get what you have tuned - no way to know that another motor isn'y going to give you problems as well. It's kind of a "if you can't tune this one, what makes you think you could tune that one" scenerio - please don't take offense by that, not meaning to offend, just stating a fact of sorts - let's see if we can't get what you have tuned right. It's not rocket science, but does require alot of patience and fresh eyes.


What's your current timing at? Have you checked for vacuum leaks? Double triple quadruple checked the firing order? Tested plug wires for continuity? What's your fuel pressure set to? Are you using an in-tank electric fuel pump, external electric fuel pump, or a mechanical pump? You installed a vacuum-advanced distributor right?

I know all this seems basic - but usually it's the little stupid things that get overlooked - tell us everything you can about what you've done and let's see if we can get a grip on this tune.

oxrabidus

i dont know what the initial timing is at because i dont have a proper timing marker on it.
the firing order i have checked and rechecked. i have tested the wires, and used different sets, same thing with the plugs. its all getting voltage. im using a frankyl cheapo ebay dizzy cost me 65 bucks, its got a 65k coil, and comes with a preset performance advance curve.

i hooked up a vacuum gague to the carb to do the idle mixture, and did it as i was instructed by a holley video. got it up to 18 inches of vacuum at idle. the funny thing about that is that they said if you dont have a vacuum gague you just do it till you achieve the highest rpm at idle, which when i turned it and got the vacuum to go up the rpm dropped a bit, and vice versa.

i got it to where it would run really strong and seemed perfect. then the next day i drove it to my ladies house and driving along the engine just died.
i was on the highway, and it obviously die because the car jolted, then it came right back on a second or 2 later, i didnt even take it out of gear or anything. it just cut off then came back.

thats what i find weird... i try and tes and try and tes, get it to where it feels right then it keps on shutting off on me, then comes on... i dont understand it.

im using a stock replacement mech fuel pump with a return at around 6.5psi.

and another thing is i set the idle to around 750rpm. the next day i start it and with the choke closed it didnt go past 1000rpm, and when it opened it wend all the way down to 500 or so, and it was buckling and stalled...

thats what really confuses me, i fasten everything down and then just out of nowhere it comes undone. and im doing everything by the books i have bought to help me along...

what would cause it to cut off like it does? and why (if anyone else had this problem) does it all get weirdly messed up after you get it more or less right?

thanks

oxrabidus

another thing is when i first put the motor together, the heat from the headers would burn up 2 of the spark plug wires. i wrapped the headers and put protection on the wires, and found an exhaust leak from the connection to the y pipe. it was loose and 2 bolts had come off. fixed that and it made the hugest diffeerence.
id didnt buckle or hesitate from part to full throttle as much. and pulle a LOT harder.
just figured id throw that in there as well.

camaronewbie

OK - I'd say 1st thing is, fuel pressure is too high - most carbs want a max of 6 - I'd get pressure down to 5.5.

Can't do anything else without being able to check and adjust timing. Do you mean there's no tab or there's no harmonic balancer mark? Either way, going to have to fix that issue so that you can check timing. How did you verify firing order if you have no reference to where TDC compression stroke is on #1 cylinder?

firebird904

My dad ran one of those cheap ebay dizzy's on his s10 blazer and gave him nothing but trouble it would occasionally stall and just never ran right he got a re manufactured one from the part's store and it ran like a whole new truck.

oxrabidus

to check tdc i took out the #1 plug and put a screw driver in the hole, as well as take the valve cover off and turned the motor till the piston stopped moving and the intake valve on the #1 cylinder was on the opening ramp.

there is no mark on the damper and the engine had no marker on the block. there is a groove that seemed to line up with the cheapo marker that i bought. i marked it on the block.

i figured as well that it may be the distributor that was causing my problems.

i saw a summit replacement sbc dizzy for $89.00 it has no adjustable vacuum and medium weight springs. will a stock timing curve be fine for me? (once i get the base timing correct obviously.)

oxrabidus

oh and ill have to buy a regulator for the fuel pressure. they have one at autozone for 15 bucks, but i has no return? the max psi is 5.5lbs, do i need a return if the pressure is that low?

thanks again

oxrabidus

http://www.summitracing.com/parts/SUM-850001R/

this isthe dizzy i was talking about... its this one or the accel version that is 122 and doesnt include the coil.

camaronewbie

Well, until you are able to reference the timing in some matter, no distributor is going to make it better. If there is a cut line across the top of the balancer, that is your mark - but you say is't not lining up with a timing tab, or there is no timing tab?

You really don't have to know what exact number the base timing is 'set' at, but you must have something to help guage adjustment, so you can set it at point a and test, then change it to a point b and test again. Most carbed folks that I've seen start at about 10* BTDC and adjust up/down from there, most adjust up. I think mine is set at about 13* right now. But you're really going to have to have something in place to reference so you can see how much change you are making and in which direction. I'd go find myself a timing tab that bolts onto a timing cover bolt before I did anything.

oxrabidus

i did buy a timing pointer for my engine, and it does line up with the groove. I am gonna order some timing tape for the balancer so i can measure it accurately. judging by the way the numkbers look on the tape, and where the line is with the engine at idle with a timing light id say im at around 14* but thats just a rewally rough guess.

im gonna get that pressure regulator and a new dizzy this weekend and try that out.

i did have a feeling it was the dizzy though because like i said earlier id get it to where it ran strong as hell, then the next day id drive it and it would stall while running and run like poo...

when i have the parts and install them ill come back with what ive found.

thanks
miguel

camaronewbie

OK, sounds good. I'm sorry - I was under the impression that you had no timing tab or line at all, and therefore had no reference point in regards to timing. My bad.

When you get a timing tape and get it put on the balancer, you'll want to check your total timing as well as base timing. Base timing is at idle, total timing is at 3000rpms. You want total timing to be in the neighborhood of 32 - 36* BTDC. You probablyu won't see it with a standard distributor - usually folks have to change weights/springs inside to get as far as 32* by 3000rpms. But you adjust your base timing as high as you can to achieve as close to you can to the 32* @ 3000rpms, WITHOUT having spark knock at WOT. If you get spark knock at WOT, then you need to come back down 2 degrees and try again. All the while you'll need to adjust your idle setting at the carb - the higher you go on base timing, usually the higher the idle goes.

You check base timing above 10* (or whatever the last notch on your tab is) by setting the line on your balancer at say 4* BTDC, and then painting a very thin line on the balancer where the 0 mark is on the tab. Then you can read that second line you painted when adjusting timing - if the second line reads 10*, then you know it's at 14* - make sense? Kinda the same as making your own timing tape marks. You just don't want to do it too far, your get farther out of accurate the farther out you make marks on the balancer - that's why timing tapes are great for checking total timing.

Oh - you'll need to measure your balancer diameter, and get the right timing tape - there are several different sizes of balancers.

oxrabidus

im gonna get a set from msd that comes with 3 or 4 different sizes of tape.

its funny because when i was first trying to tune it myself, i gave it more and more initial advance, but it never would ping. it would backfire and stall but wouldnt ping.

another thing i noticed was when it would stall, sometimes it would come back on sometimes it wouldnt. but when it didnt there would be like a gunshot coming from the exhaust, i was told that it was unburned fuel that went out the pipes and when it cought oxygen it blew up in the pipes.

but im ordering that tape and distributor so i should be able to put it on this weekend.

a bit confused about what you said about marking the balancer? i figure rotate the engine till i find TDC for the #1 piston and place the tape to where 0 degrees was at the tab. or would this be the wrong way of doing this?

thanks again
miguel