octane problem? or does carb need adjusting?

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The car was running a bit rough so i thought i'd check for vacuum leaks. i sprayd the intake and around the carb with no change...i was using a highly flamable cleaner...but when i sprayed into the throat of the carb it ran much smoother. Is it possible i'm not using a high enough octane (doesnt make sense since i have stock compression and am running a medium grade gas) or is something nt right in the idle circuit? I have to run the car with the idle mixture screw most of the way out or it will run rough. timing is 12 deg advanced (better than a lesser amount, but i can run it quite smooth up to about 25 deg. although i think thats too high)

i was thinking about hooking up methonal injection (just using a windshield wiper setup attached to a mister nozzle) I'll see if i can get anything rather cheap for an adjustable electric turn on switch to work with the RPMs of the vehicle.

is it possible i need to adjust the metering rod? more or less?
 
Howdy Dave;

First, it's very unlikely that a higher octane gas will solve a rough running engine problem. Higher octane simply slows the burning process during combustion.

It's hard to draw any conclusions from getting an increase in rpms from spraying carb cleaner into the carb. Most aerosol cleaners contain O2 as well as volitile mixes. It is best used for cleaning carbs, not tuning.

The best (maybe cheapest, The best way would be with an Air/Fuel Meter) way to assess you air/fuel ratio is to read your plugs. To fine tune you'll need several new sets of plugs of the appropriate heat range. It is easiest and most accurate to read a fresh set to assess each range of function of your carbs A/F mix. You'll need to start with a set for Wide Open Throttle (WOT). To do this, get your engine warmed up, put in the fresh plugs and do several WOT runs, shutting the engine off at the top end and coasting back to a slow speed and start over. After several runs, pull and read the plugs.

You can use the same set to assess mid range ratios, by driving around for a week in normal settings. After a weeks time, you'll be able to assess mid range.

The idle circuit is assessed by idling for an extended period, maybe 5 minutes.

Plug heat range and gap are also variables, especially in climates where summer highs and winter lows vary considerably.

I am not completely familiar with tuning the YF, but it will be a combination of needle rods seats, pumps, squirters and low speed air screw.

Don't fall for an ignition problem as the source of a rough running engine.

Adios, David
 
thanks for the reply David. I wasnt actually using the cleaner to tune the carb..i was checking for leaks and felt like spraying it into the engine...surprisingly it made a difference. I can adust the air/fuel mixture, but it seems to be an idle problem, which seemed to progress, but rather quickly. I used to have my timing way advanced (no where near the timing mark...almost 1/4 of the balancer past the mark :shock: ) and i just recently adjusted my timing properly with a light. It ran nice and smooth for awhile and then started to run worse...to where it is now..adjusting the air/fuel mixture screw doesnt help a whole lot..if i go by how smooth it runs i have to have the screw almost all the way out. the carb is pretty much new..i havent fiddled with it yet, but i think i will.

the thing about the YF is that i cant buy aftermarket parts for it...so i'm pretty much limited to the adjustment of the metering rod. I tried platinum plugs, and that didnt seem to make a difference (NGK Brand) i have the NGK V-Groove plugs. It seems that tuning the carb doesnt get rid of this problem. I'll have another go at tuning the carb (funds are quite limited as i had to get a new alt unexpectedly (lack of replacing the brushes :oops: easy to forget about it and cause more damage)

I'll try one more set of plugs though and try to tune it up better. thanks for the help
 
How long has it been since you changed the spark plug wires? Just a thought as you have been handling them quite a bit with all those plug changes.

It sounds like you are short on funds but I could almost guarantee you that an MSD would smooth that idle out, regardless of what the "real problem" is. Some on this board will say you are just compensating for a different problem that you should be fixing directly by using one, but like you said- there's no great supply of different metering rods, air bleeds, jets, etc. for you to play with the YF to that level. So I think there is some value in just letting an MSD take care of it for you.
 
mmm..yea..sorry, i should actually make a list of what i have in my sig. I do have the MSD blaster coil...would the MSD6 module make any difference? the wires are only a month old. And the MSD coil was a good upgrade. Thanks for the halp though, i appreciate it. If the MSD6 ignition module makes a difference then i'll probly look into that into that in a few weeks.
 
Yes, I was referring to the MSD Multi-spark Ignition box. My experience is mostly with the MSD-6A and MSD-6AL boxes. The fact you already run their coil makes it all the better.
 
allright, i'll look into the ignition module as well then. I have to run my car through Air Care (emmisions testing) in May so I'm trying to get the car running smooth and want to fix up my exhaust leaks and get it tuned the best i can. I advanced my timing today, without the gun though, but a guestimate would be around 25 deg. advanced...it runs smoothest here but is borderline to pinging, so i have to run without vac. advance untill i get the other problem(s) sorted out and can lower the timing again. I just dont get why spraying the carb cleaner made such a huge difference. And all the cylinders read 120 psi...which isnt high, but its even.
 
Have you tried changing your fuel filter, also just because one might buy gas from a reputiable place doesn't mean it is going to be good. I mean, I have gotten bad gas from filling stations I use all the time, ususally occurs when their tanks are getting low. Like you, I thought it was my ignition, and changed everything in it, ended up being bad gas. I saved all the old parts and not doing one weekend, put them all back in just to see...ran just as good, if not better. At least I have extras now. Add some additive like chem-tool or lucas, or drain it out. I know not fun, but you got to do what you got to do. Just something to ponder on. Good luck.

Kirk Allen '73 bronco
 
hmm...good call. I'll get a clear one so i can see if junk goes in. the tank hasnt been cleaned that know of. I'll try an additive to see how that works, then if it looks like the fuel filter is catching debris then i'll have to clean the tank. I have the gas stations pretty much figgured out as to which gas the car runs better on...i try to stick with the best, but sometimes i have no choice cause i need gas...and i did recently fill up at my least favorite gas station...but I put in premium and it sputtered a bit before that (probly about the last 1/4 tank) never though about it though, I'll keep an eye on it. Thanks.
 
PW, go to this website and then tell us which carburetor you have after looking at the exploded views.

I had the YFA at one time and experienced something very similiar to what you have described. My solution after a couple of rebuilds...a new carburetor.

Is this the replacement for the one you had drill out some jets?
 
yea, this is the replacement, good memory...its definately a YF though. I want to try to mod this one up too though, lol..but i'll wait till i find a used one for cheap. If it turnes out to be a bad carb then i'll bore this one out and re-jet it, only reason i scrapped the last one was cause 2 screws got stripped and would leak so I JB Welded it, a couple times...so i used it for my core charge on the new YF.
 
placid warrior":1eya2fpn said:
I have to run the car with the idle mixture screw most of the way out or it will run rough.
Click to expand...

If you keep turning the screw until it is almost all the way out, will it change the idle? If not, sounds like you need more fuel - almost as if the fuel jet is too small. :hmmm:

You might want to try lowering your intial advance and then re-tune the carburetor.
 
yea...the idle mixture screw is almost all the way out. The main jet squirts the fuel to accelerate right? will adjusting the metering rod change my idle mixture at all or is that also an acceleration thing? from my knowledge the metering rod allows u to adjust when the fuel gets shot...is that right? is there a way to richen the idle mixture aside from the mixture screw?
 
Dave you post some really good questions with regards to the YF/YFA, unfortunetly I don't have any concrete answers. I know that's not what you wanted to hear considering I took the whole weekend to answer. :? However, I always thought the same thing when speaking of the metering rod adjustment. Makes sense but as far as riching the fuel mixture, I would think that is determined by jet size. At least that is the case with other carburetors. Like anything else with a carburetor, the metering rod will only allow for "so much" fine tuning.

Again, sounds like to me your jet is too small. I say that because your mixture screw is just about completely unscrewed. You are trying to allow as much fuel to pass through as possible but you are reaching it's limits with the current jet size.

I don't know about YF/YFA rebuilds but I imagine it is the same with most over-the-counter brands and that is this, when rebuilt at the factory sometimes the wrong size jets can be installed. A simple oversight. This is what happened with my Webers'. It had a mixture of 4 cylinder jets as well as 6 cylinder jets. :shock: I had to install larger jets in order for it to work right. But with the YF, I don't where you can buy replacement jets. You may have to drill, again.

If I were you, I'd find out what size the current jet is in relation to a drill bit. Then I'd use a bit 1/64th larger to drill out the jet. Retune and ride it for awhile. Document the changes, if any, and then drill out another 1/64th. Do this until your idle mixture screw is no more, than say, three complete turns out. I know a 64th doesn't sound like much, but that's alot more gas you are giving the engine consider the intial hole size. They are quit small when you think about it.

Also, has far as your timing is concerned, when you say 25 degress, do you mean total or what?
 
thanks for the reply. As for the timing..yea thats total, I disconnected the vac advance completely so there was no advance or retard in the timing.

i didnt think that gas came out of the jet though untill u accelerated...when i watch from the top there isnt anything coming out, when i rev it up it squirts a quick shot of fuel in. is this the jet you are talking about? or do i have to change the size of the hole for the idle mixture? thanks again for your help.
 
A little carb 101
a-idle mix screw adjust fuel/air mix at idle only(+ just a little past)
b-pilot jet controls low speed fuel mixture
c-main jet in conjuction with middle circuit (needle on slide carbs)
controls mid range mixture(sometimes additonal jet)
d-main jet controls upper rpm demands
e-accelerator pump(squirter) helps jets for rapid acceleration, the rest of the time all fuel is delivered by carb's response to throttle position and vacumn. when throttle is steady squirter is not involved.
This is oversimplification as there have been many different ways carbs have been built. However it is a fair description of how carbs are operated.If at idle you can take the idle mix screw(not the idle speed screw) all the way out and it still runs there is a problem. Often a tiny piece of trash can find it's way into a jet causing symptoms like yours. Or a vacum leak or even having the wrong vacum hose connected to the dizzy. wrong plug gap or bad pcv valve will do wierd things too. Bad gas will also. if suspect water in gas, dry gas will often help run out the bad gas (or the poor man's version--rubbing alchohol)
 
PW, sorry, I just realized I had not posted the link for the exploded view. Try this:

http://www.carburetorfactory.com/expvw01.html

I'm pretty sure the jet that we are talking about is labeled 62 on that diagram. It's the only jet I found on my YF (or at least what looks like a jet).

You don't want to drill out the a/f mixture screw shaft. Doing that will cause irregular idle and possibly a fuel leak. :wink:
 
Thanks danwagon...thats the kind of info i was hoping for so i could understand it better. the car stalls with the mixture screw out so i guess its not plugged, i also checked for a leak and that was fine...plug gap is.50 with the MSD blaster coil....duraspark ignition module. PCV valve seems to be working as well. Your carb 101 helped me figgure things out a bit better, thanks.

Stang200: yea i wasnt sure about that..i knew it was removeable but i didnt think anything of it for idle or anything...if u look into the venturi there is a tiny tube type jet...which is the main jet that controlls the upper RPM demands. on my last YF this is the jet that i enlarged as well as adjusting the metering rod for a quicker shot...Thanks for pointing it out to me...i'll be sure to work on the proper jet now (heck i may even bore it out again now that i now that, lol) The one extra site u posted sure is great...i like the part where they mentioned the different size metering rods...anyone know if they still sell them or if other rods will work?

Thanks again for the great advice...helped me understand a few things. I cant wait to tear into the carb again :twisted:
 
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