Part-throttle lean condition, 53 R110, SD220, Carter YF


IHC in the early to mid-fifties.

Rookie
Rookie

Posts: 7

Joined: Sat May 05, 2018 6:28 pm

Post Sat Oct 12, 2019 6:53 pm

Part-throttle lean condition, 53 R110, SD220, Carter YF

Hello,

Has anyone struggled with a part-throttle lean condition? It has had it for as long as I have had the truck (20+ years). Extra initial timing helps (12 degrees). All advance in by 2400 rpm. I opened the jet from .104" to .107" (checked with gauge pins) and moved the metering rod up about 1/16" (I should have taken an actual measurement, next time the carb. is open). The metering rod is .040"/.060".

The accelerator pump gives a good shot through the range of throttle opening.

Off-idle response is noticeably better with the extra fuel. Light throttle and WOT are fine. However, there is a spot in between that is unhappy. Especially noticeable with the rpm drop when accelerating after the 1-2 shift.

The next thing that I plan to do is install a vacuum gauge to get an idea of how far the throttle is open when it feels lean.

Curious if anyone else has had a similar experience.

Thanks,

Bill

Golden Jubilee
Golden Jubilee

Posts: 4013

Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Sun Oct 13, 2019 9:37 am

Re: Part-throttle lean condition, 53 R110, SD220, Carter YF

Off idle bog is most often a timing issue and not carb. So just so I understand you correctly, you have confirmed that both the vacuum and mechanical advance are working correctly? You'll need an advance timing light or a digital advance meter with a pick-up and trigger on the crank to check.
Raising the float level a little is a quick and easy way to see if richening the mixture will help, without changing or drilling jets or metering rods.
Light trucks and cars lean out the mixture at part throttle to increase fuel mileage, but because lean mixture burns slower, than a stochiometric correct mixture, you need to light it off sooner, so a fair bit of advance is required when the carb transfers from the idle circuit to the main metering.
A too lean main metering will tend to backfire thru the carb, the mixture is lean enough to keep burning thru the exhaust stroke, and still be burning when the intake valve opens, and ignites the mixture in the intake.
I'd be looking hard at ign over carb.
User avatar

Golden Jubilee
Golden Jubilee

Posts: 4600

Joined: Thu Nov 29, 2012 11:47 am

Location: Bothell, Washington

Post Sun Oct 13, 2019 3:03 pm

Re: Part-throttle lean condition, 53 R110, SD220, Carter YF

^yup^ does your distributor move with vacuum advance? it should,

seen more than one of these distributors with hardware and mount bolts put on wrong, or missing specialty step washer,
Gentle Men! you can't fight in here! This is the war room!

Rookie
Rookie

Posts: 7

Joined: Sat May 05, 2018 6:28 pm

Post Sun Oct 13, 2019 9:19 pm

Re: Part-throttle lean condition, 53 R110, SD220, Carter YF

The ignition advance, both mechanical and vacuum, are working correctly. The vacuum advance pulls in as soon as the throttle is opened. The mechanical is clean and operates freely. All mechanical advance is in before 2500 rpm. I don't recall the amount of total advance. Around 30 crank degrees or so. I did try lighter advance springs, but it would ping on a hot day under load at lower rpm's. It does not run as well if I give it any more ignition advance that what it has.

Both light throttle and WOT are OK. Cruises fine and gets 14-15 mpg. This occurs at roughly 1/2 throttle opening. I don't have a vacuum reading, but I expect that the vacuum is low enough that the vacuum advance is not pulling. It would backfire through the carb. at this throttle opening before I provided the main metering with extra fuel. Extra initial advance helped but was not enough. There is still a slight stumble, but no where near what it was.

Thanks,

Bill

Rookie
Rookie

Posts: 7

Joined: Sat May 05, 2018 6:28 pm

Post Mon Oct 14, 2019 8:07 am

Re: Part-throttle lean condition, 53 R110, SD220, Carter YF

Also note that the increase in metering area did have a noticeable positive effect on response and acceleration throughout the range of throttle opening.

It did not always backfire through the carb. I started the tuning from scratch and set the metering rod depth and timing back to factory specs. The trucks runs the worst at this tune. Advancing the initial timing and moving the rod out of the jet some makes a substantial difference.

Bill

Golden Jubilee
Golden Jubilee

Posts: 4013

Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Tue Oct 15, 2019 10:11 am

Re: Part-throttle lean condition, 53 R110, SD220, Carter YF

Because Ign is the primary cause of these problems, I would move on to checking the whole ign system. Condenser, wires, coil and heat range and gap of plugs.
From there I'd look for vacuum leaks. One Carter has a problem with the joint between the throttle body and float body of the carb. I don't remember if it is the one you have or not, but the throttle body is held to the float body with 3 screws from below and they can loosen and cause all kinds of problems. You can check for it by grabbing the float body and try and turn it or move it while the throttle body is tight on the manifold. Is the manifold leaking at the head? cracks? is there a leak from vacuum accessories (wipers, 2 spd axle)? Does the manifold heat (heat riser) work?
Next is: was the carb assembled with mix-matched parts sometime in its past? was a rebuild done and the wrong gaskets used.
Only when every other possibility been check for and ruled out would I consider main mixture changes. The reason is simple, it is rarely the cause and much more likely the symptom. Once you change the mixture to compensate for another problem you mask the original problem making it harder to find and correct.
Carb's meter by volume of airflow thru the venturi, It should stay the same regardless of what is pulling the air thru the venturi, in short once the correct jet is used to get the mixture desired it should never need to be changed.
Unless you are working on something with wild cams and multiple carbs, it is unlikely that the stock jetting will be the cause of a drivability problem.

Rookie
Rookie

Posts: 7

Joined: Sat May 05, 2018 6:28 pm

Post Tue Oct 15, 2019 7:23 pm

Re: Part-throttle lean condition, 53 R110, SD220, Carter YF

New plugs gapped at .030"
New points/condenser gapped at .020"
New cap and rotor
Resistance checked on solid core wires, all OK

Wide open throttle acceleration is fine, no stumble, miss-fires, etc.

Valve lash set to .020"

No vacuum leaks

Vacuum at idle is a steady 20 in Hg

I am a machinist and I own a shop. I milled both the intake and exhaust manifolds. I also milled the mating surfaces between the manifolds, making sure that they are perpendicular to the head side.

New intake gasket, no leaks.

Carb. screws are tight as well as mounting studs/nuts. I have found no reason to believe that this is not the original carb. Parts are not mismatched.

Heat riser is currently wired closed (broken spring). All testing is done once the engine has been up to operating temperature (180) long enough for all parts to equalize.

I simply feels like the metering rod is too far down in the jet at 1/2 - 3/4 throttle opening.

Thanks,

Bill

Golden Jubilee
Golden Jubilee

Posts: 4013

Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Tue Oct 15, 2019 8:33 pm

Re: Part-throttle lean condition, 53 R110, SD220, Carter YF

Heat riser: by closed, do you mean it is directing exh at the carb base or do you mean it is directing away from the intake? While unlikely it could be a contributing to the problem, but not the primary cause.
What counts in carbs is the wet fuel level in the float bowl, not the actual position of the float itself. While the distinction is a small one, it can sometimes cause a problem. If the float is slightly heavy it will sit lower in the fuel raising the "wet float" level, conversely a light float will result in a lower fuel height.
A low wet level will tend to a lean condition.
It is why some carbs have a level plug, that the fuel level is supposed to be set to.
Dry setting of the float level is just an approximation of what the wet level will be inside the bowl.
If you are going to make changes in the carb, make one change at a time and document what/how you made the change so you can go back or note how the changes effected the running.
Before making "hard" changes to the jetting, I would suggest raising the wet level in the float bowl incrementally to see if it improves, without causing boiling over and flooding on hot shut down.
The metering rods are supposed to stay in the jet, the area of the jet is varied by the position of the rod in the jet. Manifold vacuum holds the rods down in the jet, leaning the mixture when manifold vacuum is high (part throttle) and spring loaded up when manifold vacuum in low (wide open throttle/ engine off). Unlike Holly's "all or nothing" power valve system, the metering rod can vary over a range rather than off or on.
I would also recommend fixing the heat riser, replacement springs are available, as the same engine was also used in ag equipment. Too much heat can reduce volumetric efficiency, too little can result in both carb ice and fuel condensing out of the intake stream.

Rookie
Rookie

Posts: 7

Joined: Sat May 05, 2018 6:28 pm

Post Tue Oct 15, 2019 11:13 pm

Re: Part-throttle lean condition, 53 R110, SD220, Carter YF

cornbinder89 wrote:Heat riser: by closed, do you mean it is directing exh at the carb base or do you mean it is directing away from the intake? While unlikely it could be a contributing to the problem, but not the primary cause.
What counts in carbs is the wet fuel level in the float bowl, not the actual position of the float itself. While the distinction is a small one, it can sometimes cause a problem. If the float is slightly heavy it will sit lower in the fuel raising the "wet float" level, conversely a light float will result in a lower fuel height.
A low wet level will tend to a lean condition.
It is why some carbs have a level plug, that the fuel level is supposed to be set to.
Dry setting of the float level is just an approximation of what the wet level will be inside the bowl.
If you are going to make changes in the carb, make one change at a time and document what/how you made the change so you can go back or note how the changes effected the running.
Before making "hard" changes to the jetting, I would suggest raising the wet level in the float bowl incrementally to see if it improves, without causing boiling over and flooding on hot shut down.
The metering rods are supposed to stay in the jet, the area of the jet is varied by the position of the rod in the jet. Manifold vacuum holds the rods down in the jet, leaning the mixture when manifold vacuum is high (part throttle) and spring loaded up when manifold vacuum in low (wide open throttle/ engine off). Unlike Holly's "all or nothing" power valve system, the metering rod can vary over a range rather than off or on.
I would also recommend fixing the heat riser, replacement springs are available, as the same engine was also used in ag equipment. Too much heat can reduce volumetric efficiency, too little can result in both carb ice and fuel condensing out of the intake stream.


Thanks for the suggestions.

Don't worry, I have made each change one at a time.

I do understand the functioning of the metering rod. The small end (.040") is still well in the jet at 0 vacuum. Getting the fatter diameter of the rod out of the jet sooner did help. The truck is responding well to more fuel. I did not mind opening up the jet .003" since the jets are still available. Would be simple to machine a new one anyway. I will not alter the metering rod at all except for it's depth in the jet. I have never tuned a Holley, I have always ran a Quadrajet in my Pontiacs.

I will raise the float a bit more and see. I did not think it would be necessary since WOT seems OK and I was running the float about 1/16" lower than it is now. Maybe WOT is lean also (but it does not fuss). The truck does not start easily after a hot soak. I made a stainless block-off plate for the heat riser this past summer. It did not help and it is time to pull it out since it is cooler out. Starts easier after a hot soak in cooler weather. I'll replace the spring this fall. The flap does not seal that well anyway. Heat would still be getting around it a little when it is closed. I have run it wired closed (no exhaust heat) for many winters without trouble. Actually the truck arrived, in the family, back in 1990 without the heat riser working. The stud for the end of the spring was gone. I finally repaired it when I had the manifold off this last time.

I probably won't tinker with the truck until next week.

Thanks,

Bill

Golden Jubilee
Golden Jubilee

Posts: 4013

Joined: Thu Nov 29, 2012 9:28 pm

Location: Lyman, IA

Post Wed Oct 16, 2019 7:15 am

Re: Part-throttle lean condition, 53 R110, SD220, Carter YF

Part or most of the trouble with hot soak is what we have for gas these days, it is mfg for pressurized fuel injection where the fuel line is under pressure from the tank to the engine. It vaporizes too easly from an open system and will cause hat start problems on a carb'd system.
Even in cool weather, mine will start ok if started with a few day of last running, but if they sit for more than a week need the system primed again.

Return to L, R and S

Who is online

Users browsing this forum: No registered users and 3 guests

cron
Powered by phpBB® Forum Software © phpBB Group
Designed by ST Software for PTF.