I have that m90 on my 5.0 carb setup, it runs and everything, BUT, after hitting the throttle the rpms drop (OBVI) but when they drop it stalls right out unless i hit the throttle again... so it idles but then drops off.. what is causing this ??? any help would be greatly appreciated.. Thanks in advanced guys.....
ok heres a few questions
what size carb is it? and what brand with part number..
it may be rejeted and ajusted..
and what did you set the spark plug gap at? it needs to be at about .030-.035 ;)
and pictures please :D
oh and whats the timming set at are you useing a boost retard?
and whats the motor setup like
the carb was a 750cfm double pumper but i took the body off and used a 650 dp instead , i havent touched the plugs so im not sure on that . Im not using a boost retard but am thinking of that now (thanks) , the timing is set at 8 degrees advanced.. motor is a stock 85 Gt 5.0 (stang) e7's ported , eddy alum intake , longtube headers , stock cam , stock bottom end , flat top pistons , double roller timing chain , stock distributer , and its a 5 spd (for those who have to ask) PLUS the m90 .. any help would be great ...
when you say 8 degrees advanced do you mean 8 degrees before top dead center or 8 degrees after top dead center? you need to be at about 8 degrees before top dead center..
and as for the plug gap you better check and if at stock set the gap at .035 ..... if it's at .045or.055 the car will fall flat on it's face ..
Nick
sounds like it could also be too much gas at idle. The air helps mix it out and that will help stop it from stalling.
the gap is stock ,and the timing is 8 degrees after top dead center (advanced). i worked on it today and im still getting the same problem after i hammer the gas, the rpm's drop right off and stall on the decrease.
well like i said you have it all wrong
you need 8 degrees before top dead center..(retarded) and you need to gap the plugs at .035
oh and what plugs are you useing atuolite 25 next plug change go with 24's
Umm... are you guys living in a reverse universe or something? The last time I checked, "advanced" meant the spark happened
sooner, before the piston was all the way up (BTDC) and "retarded" meant it sparked
later, after the piston had passed the top (ATDC).
Blow thru or draw thru system???
Not all carbs can be used as a blow thru, the pressure pushes the fuel through the boosters back into the bowl.
sorry blown306 , ill try it...
get a wide band o2 sensor, check your A/F ratio, sounds like your running to rich,
some people are telling me to get a fmu, but im running carbed , so i know that wont work, today im going to try what blown306 has told me to do..anyone that has a idea or suggestion please leave info... thanks again guys..
retard the timing. You are running rich as anything.
:rollin: :rollin: a FMU will not work in your case
carbs don't use a return fuel line well if you use a three port carb regulator you can put a return line but it's not really needed your going to run about 14PSI and more pressure will blow the floats apart
and to lay to rest the whole advance/retard theory
in one way your right dude
and i'll try to explain this as easy as i can
it's something like when some people call a car engine a motor
a few exsamples
a boost retard.. retards the timming IE base timming is say 14 degreesBTDC and the retard is set at 1 degree per pound of boost.. if the motor"engine" makes a max of 6psi it will retard the timming 6 degrees which equals 8 degrees total timing but!!! thats the base total not the total timming @ 2500RPMS the ford ECM "A9L/A9P/A3M and so on adds if i remember corectly 22 degrees to the base timming which if you had 14 degrees of base would equal 36 degrees minus the boost retard of 6 which equals 30degrees..
anyway..
in this case there is no ECM theres a carb
which raises another question of which distributor he's useing if he's useing a dura spark type distributor then it has a cutrifical advance..which would be fine
but if he managed to get a TFi distributor to work. that might allso be a problem to.. it won't work right.with out an ECM two difrent types of distributors TFI uses a halafect pickup and a dura spark one uses a magnetic pickup..
oops back to the whole advance/ retard theory :sorry:
anyway most motor heads but not all of them say retard the timming and some say avdvance the timming depends on how you look at it ..
the reason why i say retard is because i'm a retard:raspberry :giggle:
no the reason why i say that is because i base it on how the cam,igntion timming and motor"engine" works
ie cam timming and ignition timming .. when you retard a cam the vavles open closer to top dead center and close closer to topdead center.. and when you advance the cam opens the valve sooner before top dead center and the valves close sooner to top dead center..
there are a few reasons why race shop do either one of these in a motor"engine"
when you retard the cam the motor"engine" will make more power in the lower rpm power band but loses some top end power
and when you advance the cam timming you gain power in the upper rpm power band but loses the lower rpm power gains..
but there is another reason why race shop advance cams..
sometimes the pistons used don't have the clearance for the cam they are useing and if it's only buy a very small amount you can advance the cam to gain the clearance back that you need.. ie by the time the piston hits top dead center the valve will be closed..
now igntion timming
now if the igntion fires @14 degrees BTDC it's firing 14 degrees before the piston hits TDC right and so then the timming is retarded and ie you set the timming @ 8 dgrees BTDC its closer to TDC so it's advanced..
now if you set the timming at
let say 14 degrees ATDC that would be advanced because the piston allready hit TDC.. and then if you set the timming @ 8 degrees ATDC that yes would still be advanced timming because it's still ATDC but it's a retarded timming. because it's closer to TDC.. sorry i can't help it if the igntion is dumb :crazy: :giggle:
i'll try and give it to you this way..
math..
.4-0 would be retarded and 0-4. would be advanced..
there for BTDC is "retarded" plugs fire before the piston hit TDC and ATDC is "advanced" the plug fires after the piston hits TDC..
thats where i get my advance/retard theory from..
i hope this clears things up ;)
Nick
All that's good Nick, but a few degrees of timing advance/retard ain't causing the problem.
That said, no I don't have the answer either....
Blown306 !!!!! you are the man !!!!!! I gapped the plugs .035 since they were .045 stock, and it worked awesome, problem solved , hammer the gas and it returns to idle without stalling out on me.... hell yeah ! thanks bud.... :)
:bowdown: BLOWN306....
:D anytime dude anytime :D any other questions just ask :cheers: :drink:
so have you takin it for a blast ? be carefull you don't know how meny pounds of boost it will make..
if it starts to clime over 7-9 psi get off the gas!! it will go BOOM!! with pump gas and no boost retard.. unless you have like 7.5to1 comp :giggle:
so if it makes over 6psi we will have to do some more talking ;)
Nick
i havent had it for a blast yet, im doing that tommorrow.. I dont even have a boost gage setup , i was told ill be lucky to make 7 psi with that on my car so i didnt think i would even need one.. and my comp is 8.5 to1... so i guess we're going to talk some more, lol..
dude your safer with the 8.5to1 but don't go stabing the throttle with out a boost gauge you never know what it's going to make for boost
i know that blower can make in the upwards of 15-17 psi on a 3.8 and yes it should only make about 7 psi on a 5.0 but you never know it might make 10 psi depending on the pulley setup..
so get a gauge or at least if you have an old cheap oil pressure gauge lieing around use that to see what boost it's making because if it makes 10 psi it could go BOOM! if it's to lean and/or if your useing low octane fuel. ie lower then 100 octane with out a boost retard..
Nick
Im making 10 psi but im running really lean .. what now blown306 ? boost retard ?
see so you do make 10 psi ;)
ok how do you know that your running lean? explain..
yes i would use a boost retard.. but the only right way to do this is to use the msd with a boost retard or instead of buying a 6AL and a boost retard buy the 6BTM .. it's a msd 6Al and boost retard in one..
then you can set your timming @ about 12-14 degrees BTDC and set the retard at 1to 1.5 and it will take 1to1.5 degree's of timming out per 1 pound of boost..
but you need to know for sure that you are running lean with a blower you should be runnning at about 11.5to1 "air fuel ratio".. lower..meaning like 10.5to1 would be rich and higher.. meaning 12.5to1 would be lean..
if it is running lean then you will have to rejet the carb..
let me know..
Nick
And that's where everything gets backwards.
You're saying the sooner a valve "does it's thing" before TDC, the more advanced it is, but the sooner a spark "does it's thing" before TDC, the more retarded it is? :grinno:
We all love HotRod magazine, right?
http://www.hotrod.com/techarticles/43300/ (http://www.hotrod.com/techarticles/43300/)
The general terms used in timing are advance, retard, initial timing and timing curve. To advance timing is to fire the spark plug sooner or more degrees before top dead center (BTDC). To retard timing is to fire fewer degrees BTDC (for example, moving from 12 degrees BTDC to six degrees BTDC).
And yes, I
DO always have to be right. :tg:
all of you guys have your timing degrees wrong. If you are 8 degrees advanced it means that spark is occuring 8 degrees before TDC. advanced=earlier spark before TDC. retarded=later spark after TDC. TDC= 0 degrees