carb issues

7173Mustangs.com

Help Support 7173Mustangs.com:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

cdwininger

Member
Joined
May 9, 2011
Messages
19
Reaction score
0
Location
Evansville, IN
My Car
1973 Mach 1
1998 Mustang GT
I am having a few issues that I am hoping I can get some help with.

I have a 351c motor and am running an edlebrok model 1407 (750 cfm) carb.

In park the motor runs fine, and the vacuum gauge is reading 18. When I put it in gear it drops a couple hundred RPMS and I can't get my vacuum reading above 12. I just cant seem to get the carb adjusted properly to make it sound/run healthy when it is in drive.

I haven't found any vacuum leaks and I am not sure if the cam is stock or not. If it isn't stock, it is definitely very mild.

Just trying to figure out where I should start. I do not have a whole lot of experience with carbureted motors, just enough to be a little dangerous.

Thanks

 
All tuning with an auto has to be in gear.

Verify the timing.

With the car in gear foot on brake with a vac gauge hooked up.

Set your idle rpm. Then adjust the idle bleeds start at 1.5 turns out. Confirm turning the idle bleeds lightly to close will stall the engine. That means your butterflies are sitting open correctly.

Check vacuum reading. Then make slight adjustments of the bleeds equally till you get highest vac reading then richen it about 1/8 a turn.

You do not want the adjustment to the idle air bleeds to raise or lower the idle Rpms. So if you keep leaning it out and you hear the engine Rpms go up you went too far richen it back up.

Anytime you adjust idle Rpms you need to readjust the bleed screws. So there is a sweet spot for each timing and idle Rpms configuration but its not neccessarily the highest reading your engine might be able to make for vacuum, just optimal for the current settings.

Usually if you drop it in gear and the Rpms drops and the engine almost stalls you are too lean on the screws. Because the engine isn't getting enough to run on for the load this is because guys tune out of gear without engine load so they tune way too lean for the car to run correctly.

 
Sorry to highjack this thread, I have an 600cfm 1406 Ede on my mildly tuned 351 2V, is there any big different with an 750 cfm?

I'm just asking, because there is the possibility to get one.

I forgot to mention that I have the Ede Performer package, cam,intake,carb 1406,Dynomax headers

Thanks,

Oskar

 
Last edited by a moderator:
if both are 1460 model carbs one is 600cfm the other 750cfm.

they are basically the same except the 750 can flow more air.

usually in the same family of carbs they carry the same power valve and pump shooter sizes, sometimes the jets are larger by 1 or 2 sizes. many times from 600-850cfm the valves and jets are all the same and the carb can just flow more air even the ventries are the same.

the reason a smaller carb is crisper is because the intake restriction causes a rise in vacuum the engine produces.more vacuum increases fuel delivery signal from the carb so it can be richer.

the bigger the cfm to a point. is helpful at higher rpms. so if you are cruising around for 2 hours over 3500rpm then the bigger cfm is needed.

sometimes a cam requires more intake cfm.

problems, if you put a carb cfm that is too big for an engine it will always run lean. this is because the vaccum is lower, and the fuel signal is lower that forces you to basically jet up or increase power valve opening vacuum to compensate.

if you put a carb on a engine that is too small it will always run rich. the vaccum will be high and the engine will not be able to swallow enough air forcing you to either open the butterflies too far or requiring drilling holes in the butterflies to maintain idle speed without opening the butterflies exposing the transition circuit.

many people just assume bigger carb = more horsepower 600 is smaller then 750 so 750 means more.

the question is what problems are you having with the 600cfm you have now?

if you have closed chamber heads and a mild cam, 750 would be pushing too big on a 351 V2. the engine will run more rough at idle then after 2000rpms smooth out. you will have a lower vacuum so if you are running accessories that might start to cause issues. clevelands are sort of a weird beast too because they love to have more and more fuel poured down their throat.

clevelands were also designed as a higher rpm motor since it has some roots in nascar. so you have this situation where a cleveland will wake up at high rpms with a larger carb, but from a street car standpoint that isn't a good thing since you spend 99% of the time driving at 25-45mph street light to street light. in the street car case larger carb means worse idle, lower vaccum, worse MPG.

really it depends on what you want the car to be but also what the engine can tolerate.

for me i went from 600cfm to 750cfm in steps. my engine wouldn't run on the 600 properly at all i kept having to open the butterflies too much.

650 was better i had it for a while. but when i went to 750 suddenly the engine ran a lot better, it still needed alot of tuning but was more in the ballpark. i had bought a 670 holley but never tried it out since the 750 seemed to be a good fit. now i have a V4 converted V2 engine with open chamber heads lower compression that causes all kinds of weirdness so my issue was always with not enough air at idle and then too much air later on. i still have that problem and i did try modifying a 650 cfm carb to flow more at idle and it was a disaster. so i compromised with the 750 to take advantage of the idle flow but i had to de tune the top end in various ways to make it work.

personally i would like to have a 600 or even a 500cfm carb but on my engine parts combo it just won't work.

so again what problems are you a having with the 600 you have now, is it just old and you want to try a larger carb? are you just trying to get more HP from your car because you could advance timing and readjust the 600 to make up the difference.

 
19 is pretty steep for initial timing.

you might be getting a false reading if the mechanical advance is kicking in also your vacuum advance might be kicking in as well.

best way to get reading for initial timing.

disconnect the vacuum advance, cap the port on the carb.

next lower the engine rpms at idle till the engine almost wants to stall but runs smooth. then take a timing light reading.

that will give a true initial timing.

if you still get 19 somebody might of advanced too far. usually you see between 6 -16 initial timing.

 
if both are 1460 model carbs one is 600cfm the other 750cfm.

they are basically the same except the 750 can flow more air.

usually in the same family of carbs they carry the same power valve and pump shooter sizes, sometimes the jets are larger by 1 or 2 sizes. many times from 600-850cfm the valves and jets are all the same and the carb can just flow more air even the ventries are the same.

the reason a smaller carb is crisper is because the intake restriction causes a rise in vacuum the engine produces.more vacuum increases fuel delivery signal from the carb so it can be richer.

the bigger the cfm to a point. is helpful at higher rpms. so if you are cruising around for 2 hours over 3500rpm then the bigger cfm is needed.

sometimes a cam requires more intake cfm.

problems, if you put a carb cfm that is too big for an engine it will always run lean. this is because the vaccum is lower, and the fuel signal is lower that forces you to basically jet up or increase power valve opening vacuum to compensate.

if you put a carb on a engine that is too small it will always run rich. the vaccum will be high and the engine will not be able to swallow enough air forcing you to either open the butterflies too far or requiring drilling holes in the butterflies to maintain idle speed without opening the butterflies exposing the transition circuit.

many people just assume bigger carb = more horsepower 600 is smaller then 750 so 750 means more.

the question is what problems are you having with the 600cfm you have now?

if you have closed chamber heads and a mild cam, 750 would be pushing too big on a 351 V2. the engine will run more rough at idle then after 2000rpms smooth out. you will have a lower vacuum so if you are running accessories that might start to cause issues. clevelands are sort of a weird beast too because they love to have more and more fuel poured down their throat.

clevelands were also designed as a higher rpm motor since it has some roots in nascar. so you have this situation where a cleveland will wake up at high rpms with a larger carb, but from a street car standpoint that isn't a good thing since you spend 99% of the time driving at 25-45mph street light to street light. in the street car case larger carb means worse idle, lower vaccum, worse MPG.

really it depends on what you want the car to be but also what the engine can tolerate.

for me i went from 600cfm to 750cfm in steps. my engine wouldn't run on the 600 properly at all i kept having to open the butterflies too much.

650 was better i had it for a while. but when i went to 750 suddenly the engine ran a lot better, it still needed alot of tuning but was more in the ballpark. i had bought a 670 holley but never tried it out since the 750 seemed to be a good fit. now i have a V4 converted V2 engine with open chamber heads lower compression that causes all kinds of weirdness so my issue was always with not enough air at idle and then too much air later on. i still have that problem and i did try modifying a 650 cfm carb to flow more at idle and it was a disaster. so i compromised with the 750 to take advantage of the idle flow but i had to de tune the top end in various ways to make it work.

personally i would like to have a 600 or even a 500cfm carb but on my engine parts combo it just won't work.

so again what problems are you a having with the 600 you have now, is it just old and you want to try a larger carb? are you just trying to get more HP from your car because you could advance timing and readjust the 600 to make up the difference.
I do not have really problems with my 600, I just assumed that a bigger carb would bring me more HP.

Also I tried to tune my 1406 and I have still a pretty rich running engine.

 
it might, if the engine is being held back. What vacuum is it making now at steady idle?

option 2: lower your jet size, did you buy a calibration kit and give that a try?

 
it might, if the engine is being held back. What vacuum is it making now at steady idle?

option 2: lower your jet size, did you buy a calibration kit and give that a try?
what do you mean with "being held back"

vacuum I have no idea, never measured it.

I have an calibration kit and I already tried to lower the jet size, but still running rich and smoke a lot when WOT.

 
it might, if the engine is being held back. What vacuum is it making now at steady idle?

option 2: lower your jet size, did you buy a calibration kit and give that a try?
what do you mean with "being held back"

vacuum I have no idea, never measured it.

I have an calibration kit and I already tried to lower the jet size, but still running rich and smoke a lot when WOT.
Most 2v clevelands "unless built" Do not need over a 600cfm carb....Like Hcode is saying...Right carb for right motor...A 2v cleveland stock only used a 2 barrel carb.....Your 600cfm 4 barrel is already a big upgrade from the 2 barrel set up it originaly came with...Unless your motor is built and pumped up..." 300hp or more "..It will not need a 750 cfm carb unless your motor is being "held back" By lack of air flow due to carb being too small...I ran a 600 cfm carb on my 4v cleveland for years with out any issue...A 750cfm at the time would of been too much carb for my 4v cleveland stock...A 750 cfm is just too much unless you done some major mods to a 2v cleveland...upped the compression and put a big cam..stroker kit or had the heads milled and decked...Then yes..You mite wanna think about a bigger carb...Bigger carb can make your car slower if you do not have any idea of how she is built inside.

btw what year of 2v cleveland is she? and what color are your spark plugs? Pull one and see what color it is...If it is a nice coco brown your car is burning fuel just perfict...If it is white...Too lean...If they are black..They are getting too much fuel.

 
Last edited by a moderator:
throw a vacuum gauge on the engine to see where you are.

like hyena429 said pull your plugs and look at them, also what gap are you using.

also what is your total timing.

 
the reason i say check total timing is if for some reason the mechanical is messed up and holding back timing then you would be losing off the top end. the engine running too rich for the lower amount of timing and your getting smoke assuming no other problems. total timing should be around 32-38 degrees, some cars tolerate more. disconnect the vacuum advance when you start checking. and do not floor it just bring up the rpms fast enough to check the total timing then let off. usually i blip the throttle for a second to get a reading. I had to detune i was getting 58 degrees of mechanical which was insane. i had to modify my mechanical plate and add a stopper to hold it back to around 34.

a vacuum advance will throw off the reading and make you think you have like 60 degrees of timing so that is why you disconnect it and cap the port on the carb when you check.

you could also use a mr gasket 3000rpm distributor kit and lighten the mechanical advance springs. that would increase performance but you might need to compensate some more carb tuning.

basically you just want to make sure you have proper timing at WOT on the mechanical to rule it out as a problem for smoking at WOT.

also as a safety remember too much timing at wot will blow the engine.

 
19 is pretty steep for initial timing.

you might be getting a false reading if the mechanical advance is kicking in also your vacuum advance might be kicking in as well.

best way to get reading for initial timing.

disconnect the vacuum advance, cap the port on the carb.

next lower the engine rpms at idle till the engine almost wants to stall but runs smooth. then take a timing light reading.

that will give a true initial timing.

if you still get 19 somebody might of advanced too far. usually you see between 6 -16 initial timing.
I will give that a try over the weekend and see if what my "true" initial timing is and will report back. Thanks for the info

 
True initial timing was still at 19. I got the carb adjusted to where everything sounded great, but was still only running 13 on the vacuum gauge in drive and 18 in park. The car ran good during the test drive but occasionally the engine would cut out like it was wanting to stall, then it would start running fine again. I am starting to think maybe I have a fuel pressure problem. What should my fuel pressure be? Or is there some more carb adjusting that needs to be done?

 
Back
Top