Thread: Rochester jet size ?

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Originally Posted by Mike P

“……Well poo.......idle screws still have to be 4.5 turns out approx to idle without my hand over the carb.......still has a flat/dead spot off of idle……”


Bummer. It’s unfortunate you don’t have a carb number, but if you don’t you don’t.

First question I have is do you have an operational choke? The reason I ask is that it appears ion one picture that the fast idle cam linkage is missing. Are you bringing the engine up to full operating temperature before adjusting the idle and is that flat spot still there after it warms up? Some engines like a fair amount of choke until they warm up.

No operational choke, the average temp year round is 72 here, Yes the linkage is missing, I added a washer behind the idle cam and locked it down on normal idle. I m guilty as charged, did not fully bring it up to temp, will do that next time.

I’ve come across the bases with the holes a couple of times, it shouldn’t make a big difference. Like 34_40 I think I would probably plug them too but mainly just because I don’t like unfiltered air either.

Will probably plug them later, trying to see if I can make it run right with this carb as it might end up going away for a different one.

That being said, the first thing I would check would be the carb base to intake gasket. Over the years I have come across many base gaskets that don’t effectively seal the carb to the manifold. I just ran into this on the two outboard carbs I rebuilt for the Tri-Power, the gaskets in the kits did not completely seal the front of the carb. Because I’ve run into this before I always turn the carb upside down and lay the gasket on the base to verify the proper fit. The gasket I usually use if I need one is a Car Quest G7327 (it’s an old number but hopefully it will interchange).

Verified gasket fit and correctness......actually used a flat hone stone to clean up the carb base to true again and a flat file on the intake ....lightly....just enuff to true it up.......have not checked leaks yet with carb spray or other methods.

Although I’ve only seen the problem a couple of times another thing I would check is the PVC valve. The good one are calibrated differently. If someone threw a valve designed for say a 454 onto you engine with the smaller displacement there is a real possibility that you are pulling too much vacuum thru the valve.

Due to age and amount of cobbling on this engine it will definatly be checked/replaced........

While 4+ turns on the idle screws does sound a little excessive I’m not sure I’d be overly concerned about …….provided that is where they want to be after the engine is warmed up. If you turning them out to keep it running when it’s cold…..it could go back to my comments about needing the choke.

Will definately check this ,as I have the choke parts and a working cable.........once warm with a vac guage, I will set it and then if cold and it will not idle.....the choke will added back in.

The flat spot could be a couple of things. If it happens when you mash the gas pedal it sounds like the accelerator pump shot ……verify you have a good squirt that starts as soon as the throttle starts opening. If the shot starts late you may need to drop the accelerator pump a bit which can be accomplished the straightening the external pump linkage just a bit.

On the list of things to do, will verify what is happening in there and adjust as needed......

If the flat spot is just off idle with a slight pedal opening, you might try backing out the idle screws just a bit more and/or adding a couple me degrees advance to the timing.

Definatly want to check the timing as it has not been checked at all since I have had it......Yes the flat spot is just off idle, I can bring it up a few hundred rpms at the most...maybe 200 rpm increase, no tach yet, if done very slow and then it wants to bog/die out untill I let back off or punch it all the way down.

As far as the vacuum port on the front of the carb, it depends on the carburator I’ve seen them both ported and manifold in that location. Easiest way to check is pull the line and put your finger over the port. If you feel vacuum at idle it’s manifold if you don’t feel any vacuum until it reved up it’s a ported vacuum port…….the later 2Gs actually had two nipples in that location one manifold and the other ported.

Will definatly check this also ,as it does not burn the eyes out of my skull at idle now..... ..... I can fiddle with things more than a few seconds now as it does not load up and die at idle.....

Hope this helps.

.

Thanks....this helps a ton, I grasp the basics on a few things....when I do not have a full understanding it is hard to find a useful starting point to work from ....always helps when someone who has done it enuff to know the steps to check helps out...........I appreciate that very much!

I hate shootin in the dark when I know there is a easier way.....I usually get there, but it ends up being the long way around some times....

This gives me a good place to get the ball rollin from..........

Okay.....let it fully warm up and was able to get the idle screws in a little more to approx 3 turns out. Still starts and idles fine.

Once warm I pulled the pcv valve out of the valve cover and the idle shot way up........there is alot of vac on the pvc valve, I can put my finger over the valve and the idle goes back down.....actually goes lower than with it just stuck in the valve cover....when I take my finger off the bottom of the pcv it shoots way up in idle, when stuck back in valave cover it returns to a normal idle.

Not sure if that is correctly working or not ?


I pulled the vac line from the distributor at idle and it has lots of vac, idle shoots way up, so it is full maifold vac at idle, when I put my finger over the line it returns to normal idle...........did not seem to make any difference it timing by ear anyway...still need to verify with a timing light.

Fully warmed up at idle whe depressing the accelerator very very slowly it will gain maybe 2oo or so rpm then as I accel further it just starts to break up.............if I stomp it real quick it goes thru the dead spot and revs, but it is still a dead spot.........

I am thinking maybe the distributor advance weights are stuck and the vac caister might also be bad.....not really sure yet what is happening.........

Going to do a drive around the block after work today and see how it acts in actuall driving.......might even be the points as I have no idea how those act when starting to go bad.....first points style distributor for me, so I have no idea how they act.

I think getting a light on and checking the timing is a good plan! Also, and this is going waaaaaaaaay back to the Super Mod days (daze?) when we could only run 2 two barrel carbs, it took a bit of bending on the accelerator pump linkage rod to get the off-idle flat spot out of the little carbs..... Points should gap about .017 or 30 degrees of dwell if you have a tach/dwell meter. We also used to run really weak springs on the distributor advance weights. When you finally hit the right balance of timing, advance, and accelerator pump shot the carbs worked great!

Got a chance to fiddle with it more today after work........no timing light yet, but played with the timing a little and it is close.

I think I am really running lean .....bent the pump shot linkage a good bit and it helped a little, it shoots instantly now with any movement on the accel at all.

But the big tell tale sign was when pops came out and put his hand over the top of the carb and revved it up a few times and it completely cleared up the dead spot.....going to go back up to the .52 jets from the .48`s and see if that clears it up more....hopefully it helps....it had a small dead spot before the rebuild, so it might need even more jet...not sure.....hopefully will find the timing light in the garage soon and confirm timing.

Did take it for a drive around the block........ran fine other than the dead spot right at the rpms you need for working a clutch.......did wander all over the road though, definatly a lot of slop in the steering box...guess that is next after the engine situation gets fixed.

It was pretty fun to drive, even with the issues........never drove a 81 inch wheelbase Jeep or any Jeep for that matter.........like driving a lifted go kart........put a smile on my face anyway and that was the reason behind getting this thing in the first place.........can not wait to be able to drive it more than a mile in one shot........at least I can say I have actually drove it now....

shawn I think your float level is too low I would recheck that before going any farther I think the low float level is leaning out the transition circuit and your are trying to overcome that lean condition with the idle air control screws there are seven circuits in a carb the two circuits that will change the fuel mixture in all the other circuits are the choke and float circuits if you have driveability problems from the carb. it's always an a/f mixture problem that's why I think it's the float level effecting both the idle and transition circuits sometimes simple things can have you chasing your tail that's just my 2¢ worth .....ted

Thanks guys,

I changed the jets tonight after work back the 52`s .........very little change at all.....the dead spot is a little higher up in rpm now....maybe 200 more rpm tops, no tach........it is approx 600 idle and a very light minimal movement on the accel and it goes to maybe 900-1000 rpm now and then hits the dead spot....opposed to 850 with the 48 jets.

Question......when the choke is off/warmed up is the buttefly straight up and down or at a 45 degree angle........., because when I hold the choke butterfly at a 45 degree angle when it is warmed up, it runs like a top....no dead spot at all, no richness, no black smoke etc....runs like a normal engine.

Second question......this is a 63, with a approx 66 engine....would it have had a oil bath breather and would the carb that was set for a oil bath breather need that restriction to run properly.....just grasping at straws here with this one as I have no idea if a oil bath breather even has a significant amount more than normal filter/breather restriction.......

30 years ago I would have set the manual choke at a 45 and called it fixed......but, just can`t do that now anymore....

Although it seems to shoot the air right over the venturi`s /booster legs ...it does not bog or smoke.........could be they are not supposed to be straight up and down and setting the manual choke to hold the choke butterflies at a 45 is what is supposed to be happening..........as that lines right up over the center of the holes in the booster legs looking down into the carb........seems like that would give them the best signal possible and the air dumped off the lip of the choke butterfly straight thru the drop legs center ?

Might just have to get a air/fuel gauge so I know idle is not too lean and if running thru the rpms it is close to where it needs to be..............


The more I think about the flap off the choke dumping the air straight down thru the center of the hole in the legs, the more that seems right to me......trying to talk myself into it being right anyway........

Originally Posted by Dave Severson

I think getting a light on and checking the timing is a good plan! Also, and this is going waaaaaaaaay back to the Super Mod days (daze?) when we could only run 2 two barrel carbs, it took a bit of bending on the accelerator pump linkage rod to get the off-idle flat spot out of the little carbs..... Points should gap about .017 or 30 degrees of dwell if you have a tach/dwell meter. We also used to run really weak springs on the distributor advance weights. When you finally hit the right balance of timing, advance, and accelerator pump shot the carbs worked great!

Bending the pump shot linkage definately helped some as it was not shooting right away, it is now..........still digging for the timing light in the garage.

Thanks.....

Originally Posted by ted dehaan

shawn I think your float level is too low I would recheck that before going any farther I think the low float level is leaning out the transition circuit and your are trying to overcome that lean condition with the idle air control screws there are seven circuits in a carb the two circuits that will change the fuel mixture in all the other circuits are the choke and float circuits if you have driveability problems from the carb. it's always an a/f mixture problem that's why I think it's the float level effecting both the idle and transition circuits sometimes simple things can have you chasing your tail that's just my 2¢ worth .....ted

Checked the float level and it looked very very close.........plenty high to fill the accel pump well and everything else is in the bottom of the float area...both jets and the main valve are at the bottom....valve seems free and so is the spring loaded rod that sits on it......

Thanks

Originally Posted by shawnlee28

Checked the float level and it looked very very close.........plenty high to fill the accel pump well and everything else is in the bottom of the float area...both jets and the main valve are at the bottom....valve seems free and so is the spring loaded rod that sits on it......

Thanks

Shawn,
IMO, float level is right or wrong, but never "close". The flow through the jets is due to the head of fuel in the bowls, and a very small difference in level makes a big difference in flow. Get a carb kit, take the carb apart and clean it thoroughly, and then re-assemble it according to the instructions, paying close attention to getting the float level dead on.

Originally Posted by rspears

Shawn,
IMO, float level is right or wrong, but never "close". The flow through the jets is due to the head of fuel in the bowls, and a very small difference in level makes a big difference in flow. Get a carb kit, take the carb apart and clean it thoroughly, and then re-assemble it according to the instructions, paying close attention to getting the float level dead on.

Will check again......but I did get a rebuild kit and it came with gauge and it was within a 1/32second......maybe right under a 1/16th to the high side.....measuring in exactly the place shown to exactly the spot on the float and the float appeared to be almost exactly level after set, which is what the paperwork said it should be........when I say close, we are talking within a 1/32 .....about the thickness of the line on the gauge that was sent....very very close.

not more than a 1/16th.......

I am starting to think maybe some one has done something to this carb on the inside beyond what I can figure out, as it looked inside to have been taken apart quite a few times....just little nicks and dings in places that could only happen after it was taken apart, even has a helicoil in one of the threads from the base plate to the body.........to say this one has been apart a few times is a understatement.

I rebuilt and edelbrock 1405/quadrajet on my last build and it looked pristine inside, when done it ran perfect with a minimal of adjustement, engine fires up in a second after the rebuild...........this one looks like it has been apart and all the pieces were tossed in a spare bolt bucket and was shook back and forth 100 times........all the venturi legs look like they have dings in them and all the screw heads look like they have had the flat head on them 100 times taking it apart............someone could have drilled/plugged or swapped something inside I did not notice.


Not saying I do not make mistakes....I make plenty.......but I try to go right by the numbers on stuff I have not done a 100 times and take my time and pay attention looking for small details.......

I have only had one other carb act like this and it was literally a carb from the junk pile out back of someones shop....I was broke and young and had to have one to be able to drive to work......took it all apart with no kit/no gaskets or new parts and got it working minus the accel pump that was shot in it.....it acted like this one, but this one is worse than the carb that was getting no pump shot from a shot pump......


Granted it probably needs a valve job after 30 years with no leaded gas......but it feels like it has a decent amount of vac....runs fine and pulls hard once you are past the dead spot......fires right up and idles perfect, revs up as high as I feel taking it without a tach......as these motors top out at approx 4500 rpm, I am sure I have been revving it close to that.........it is just the pesky dead spot right where I need the rpm to use the clutch.....

I have turned the timing both ways as far as I dare and it made no difference in the dead spot..........

The only thing that makes any difference is to set the choke valve at a 45 degree angle and it runs like it should then....runs perfect, starts perfect,revs perfectly........that tells me it needs more fuel and with the 52 jets in it which are big enuff for a small v-8, I am not sure where I can get the needed fuel from or where it is missing from more correctly.

It could be that when it is rich/choke at a 45 it covers up the real problem.........maybe the vac advance is not working correctly or the mechanical is off...not sure if a rich condition would cover that up.

With the choke blade at a 45 I can punch it full throttle as fast as I can and it comes to life instantly up to as high as I dare rev it.......perfectly and crisply...no hesitation or anything all the way up.

If I got in it for the first time and had no idea the choke valve was at a 45, I would say the engine runs great! ...especially for a original mid 60`s motor......I would say it runs incredible!...............untill I saw the choke at a 45 and then it would be why is it like that....that does not seem right.....

Well, thats my saga on this one....all I can do is keep going down the list and eliminate things one at a time.

PS....the valves are fairly good as it does not suck a rag back in the exaust pipe....had a straight 6 with a bad valve and it would almost snatch a red shop rag out of your hand....

I appreciate the reply.....but I am thinking it is something else, I will definatly set it again as it only takes 5 mins or less to pop the top off the carb and do it.

Shawn,
It sounds like you've done the float level right. I wasn't questioning your ability, but some people who've not been inside carbs try to eyeball the levels and think that +1/4" is "good enough". I don't think your problem is in the jets. The jets & metering rods are set for 1) steady state cruise and 2) WOT power, both read by plug color, or maybe timing slips at the strip for WOT. What you describe is a transition mixture problem. With air flow restricted by having the throttle plate at 45 it's happy, but with it allowing full air flow it stumbles. That says that it's not getting enough accelerator pump shot in transition. IMO you may have a bad plunger (yes they can be bad out of the package, especially the type using a little circle of chamois leather), or the bore may be simply worn out or marred, or the linkage has been changed/messed with by some PO that didn't understand it. I'd focus on the accelerator pump and see if it gets happy with a stronger shot.

I think your right..........I think the pump shot well bore is just worn out, it appeared to have some wear, but since it did shoot out some gas I overlooked it......

It sends out a a slow arc .....not a nice crisp stream like 1405 edelbrock does....when I replaced the pump, it was nice and tight in the top half of the well above where the seal rides and was considerably larger and looser where the pump seal rides at......maybe 50 years of unkown/fuel and use was just too much for it...I heard ethanol likes to eat aluminum, maybe it accelerated the pump shot bore wear ?

I am thinking maybe just a rebuilt one might be best....hate to surrender and throw parts at it......but I have a pretty good idea the problem is with the carb. With my hand partially over the top of the carb it runs great.........

Thought about tossin the 1405 on there with a 20 dollar adapter plate just to confirm the carb issue......but then that is 20 that could go towards a new carb, along with the 50 I spent on the carb kit and jets and needles and floats....

If I knew the air/fuel ratio was not all messed up, I would drive with the choke part closed as this motor is all done at 4500 rpm anyway...the cfm calculators show about 230 cfm as the requirements of this motor at a 4500 top rpm and 225 cubic inches. Torque peak is under 2500 rpm........

Even thought about a one barrel as a replacement since I will be getting a new carb..........might drop the torque peak rpm even lower since that is what this ride will be doing is down low rpm stuff anyway.

I guess I could shim/stuff some stuff under the pump shot seal to just comfirm the problem, maybe wrap under there with some bread ties just as test to see if that cures it...then I would know the well is shot.

Shawn unless I've missed something, at this point I think continuing to concentrate on the carburetor is beating a dead horse.

Before you go any further in that direction, I think it's time to verify the the ignition is correct. Bad/worn/out of adjustment points, worn distributor shaft bushing, worn breaker plate, stuck advance weights and incorrect timing can all cause/contribute to the symptoms you are experiencing. While some of these have been mentioned as possible culprits I don't see where you have addressed any of them yet.

Mike's right, you need to have the ignition right before fine tuning your fuel/air issues.

Down but not out yet........

Getting the steering box pulled tomorrow and taking the box to a rebuilder.......hopefully will find the timing light and see what is happening...opened up the cap and it all looks new in there, so someone was tinkering before I got it.......

Going to get the front end aligned as one tire points way way out.....just a quick alignment as there will be lots of front end work close in the future, but the almost half a turn of steering play has got to go, so a box rebuild is first.

Hope to pull it off in one day...rebuilder says 3 to 4 hours turn around.....

Drove it to work all week long, but the steering concerns me, no need to push it....did not drive it today........less than 3 miles to work and the speed limit is 25 MPH 95 percent of the way. Seems to run well, more than enuff power, no smoke, shifts well..........ratlles like 50 buckets of bots on a steel bed......so I imagine all the body rubber is shot.

Thanks for all the help so far.....will update as soon as I get more info.......just got tired of troubling shooting and had to drive it a bit......big fun even with all the issues, first 4 wheel drive and first jeep........everyone sure likes it, got lots of comments.......lots of thumbs up.

I am pretty happy with it.......no doors and no roof is different.......I am liking it....pretty mild temps around here, I am sure it would be a different story in other parts of the country.

Just thought I would give a update..........have almost the entire interior down to bare metal........was just going to clean the inside up a little and put a new coat of bedliner down....... ..I restrained polishing the carb...but fell off the wagon on the interior... I wonder if runnin a die grinder and hammer and dolly out in front of a group of retial businesses downtown is pushing it....

I have been doing all the work out in front of the store in the parking lot about 8 foot from the front door of 3 businesses...

The first day was a little sand paper....the next day a litte aircraft stripper...the next day was rolocs and a paint stripper wheel on a cordless drill.......

Getting lots of looks anyway...just never been good at determining if they are good or bad...... .......I have been keeping the hammer and dolly work to a minimum as it is like beating on a empty 55 gallon drum with this old jeep.