No power at part throttle, carb edition

[Howlite]

Hello, this problem has been bugging me for the past month, ive got a barebone 88 dx accord that doesn't have ecu.
When pressing the gas pedal at a certain point i completely lose all power, and a faint sound can be heard, almost like it's misfiring, at this point if i press the pedal all the way it goes away.
The car does not drive as it used to, it feels way weaker than before.
The last two things i worked on were a distributor inner oil seal change and valve stem seal replacement.
I tried changing both fuel filters, spark plugs and i tried re adjusting the carb (stop screw, idle screw and especially af mixture screw)
The carb was rebuilt a few months ago.
I am at a loss, any help would be appreciated.

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[ShiRen]

Actually, it does have an ECU, it's just dumb as rocks.

Sounds like it's leaning out when the secondaries open. I expect a vacuum leak somewhere and it is unable to blend the throttles blades with the right amount of fuel. The way to fix this with the vacuum delete is just bending the accelerator pump tab, which you could do I guess.

[Howlite]

Actually, it does have an ECU, it's just dumb as rocks.

Sounds like it's leaning out when the secondaries open. I expect a vacuum leak somewhere and it is unable to blend the throttles blades with the right amount of fuel. The way to fix this with the vacuum delete is just bending the accelerator pump tab, which you could do I guess.

Update,
Yesterday i changed the pcv valve, checked distributor cap and rotor and reset af mixture but the issue was not fixed, today i noticed the car had a very bad misfire, after looking around i found out cylinder 4 spark plug was not firing, so i pulled out and cleaned all 4 spark plugs, cylinder 1 and 4 spark plugs had oil residue on them (seems like i did a really bad job on those valve stem seals).
I also checked for any vacuum leaks with carb cleaner but couldn't find any.
Lastly i redid my af mixture using a vacuum gauge this time.
Now the car jerks on throttle, it feels like the same thing happens as before but for a split second.
I am guessing the spark plugs are the problem as they are getting dirty, but wouldn't cleaning them fix the issue temporarily. Any ideas?

PS.
accelerator pump works and the tab is bend as specified in the manual

https://www.dropbox.com/scl/fi/1myfs...=qz9yarv1&dl=0

[Oldblueaccord]

Change out those plugs for fresh NGK's coppers gapped at .030. See what that does for you. Sounds like you got 2 cylinders using alot of oil.

Idle mixture screws are just that for idle mix nothing else.

[Howlite]

Change out those plugs for fresh NGK's coppers gapped at .030. See what that does for you. Sounds like you got 2 cylinders using alot of oil.

Idle mixture screws are just that for idle mix nothing else.

Gapped at .039 or actually .030?


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[Oldblueaccord]

Gapped at .039 or actually .030?


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I always go smaller gap not bigger. Less chance of misfires. Esp if you having and oil consumption problem.

[ShiRen]

Heck mine might be gapped near .02" I had a lot of issues with the spark not being adequate on this car. I run an msd box now and it made a world of difference, it's an old 6a unit I got off eBay for $50. Another big upgrade is the coil itself, but check the resistance of the windings, it may very well be bad, if it is you might as well swap it out for an off the shelf performance coil like an msd or accel coil.

Again, check the operation of the accel pump, a little jet should squirt from the back side near the top of the carb opening when you hit the gas, if not it's broken and needs to be fixed, and bending the tab slightly still might help it a bit if it's working. I believe I have some information on it on the vacuum delete thread

[Howlite]

Update
It took me a while because i had to remove the cylinder head in order to change valve stem seals to fix the oil issue.
I tried setting the gap to 0.03 but the same issue persists.
I also tried bending the accel pump tab in closer to the stop, so that it adds less fuel but still it didnt fix the issue.

After doing the valve stem seals, both the starter and the distributor decided to shit the bed, the starter randomly stops working and the distributor is making a faint sound and the tech sometimes jumps on idle, after fixing those ill check the fuel pump.

I also noticed that the spark plugs have white spots on them which indicates that its running lean, could this be why it loses power mid throttle ?

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[ShiRen]

You want more fuel not less fuel, the accel pump is pretty conservative

Yeah being lean will cause it. Check for vacuum leaks. Carb base gasket for sure

[Howlite]

You want more fuel not less fuel, the accel pump is pretty conservative

Yeah being lean will cause it. Check for vacuum leaks. Carb base gasket for sure

Update,
This issue is driving me crazy, i decided to replace the spark plugs but in the process i stripped one, so i had to pull the head to fix it.
I also checked the accel pump tab and bent it back to 12 - 12.5 mm (manual states 11.5 - 12 mm) but it still did not work.
I also cleaned and greased the distributor bearing as the tach was jumping on idle but still it did not fix the issue.
I will check for vacuum leaks for the tenth time if i don't find any I'll do a vacuum delete maybe that will help

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[Oldblueaccord]

Update,
This issue is driving me crazy, i decided to replace the spark plugs but in the process i stripped one, so i had to pull the head to fix it.
I also checked the accel pump tab and bent it back to 12 - 12.5 mm (manual states 11.5 - 12 mm) but it still did not work.
I also cleaned and greased the distributor bearing as the tach was jumping on idle but still it did not fix the issue.
I will check for vacuum leaks for the tenth time if i don't find any I'll do a vacuum delete maybe that will help

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Maybe film it might help us understand.

Do you feel like the mechanical advance is working? Check it with a timing light and see if the marks move with RPM.

The tach jumping on idle usually means the distributor is going bad. Im not sure why that is but everything I had read here on them thats the culprit.

The accelerator pump is just a mechanical squirter so cover the throttle transitions.

Does it squirt alot when you move the throttle by hand looking down the carb, motor off? It should be nice stream not spit and sputter.

...and as always float height is important.

[Howlite]

Timing changes with RPM, with and without vacuum advance connected.

as for the tach jumping, the distributor bearing dust cover plastic was deteriorating, so i removed the cover, cleaned the bearing and greased it, now it no longer jumps on idle or above 4k Rpm as before

The issue is way more noticeable when engine is cold.
Here is a video of the issue happening, i am holding the throttle at the same point after shifting, you can notice it in the video after shifting to 2nd gear just above 1k RPM
https://www.youtube.com/shorts/nXxdD8rCCVI

Here is a video of the accelerator pump squirt, full pump then about half pump.





Here is the float level


I also noticed while looking for vacuum leaks the secondary booster venturi was loose so i tightened it, the overall power and acceleration is better but the issue persists, here are some pictures of the screw perhaps someone might find it useful.

[Oldblueaccord]

OK

First off for some reason I thought you had done a webber swap I totally missed you have the stock carb!

The video of the accelerator pump squirt doesnt look good to me. You should get all kinds of squirts outta that thing dead cold with fuel in the bowl. 5 shots minimum.

The loose booster is a know thing good you got that together.

Check the book on the fuel level in the site glass. I dont know it.

Other than that the carbs age might be the culprit. The stumble as you add throttle is a classic case of the throttle shaft loose in the base plate bore from wear. The clearance in the shaft to bore lets air in. There are shops that can rebush them, I dunno about Honda carbs. My old International was quite bad and being standard shift it was right on the spot were you added gas as you shifted. I used plumbers putty on the non throttle linkage side as a band aid fix.


You have to explain the grey permatex all over everything on the base someday.

[Howlite]

Update,
The transmission rebuild took me some time but i am finally done with that, so last time i checked the fuel level and it was set correctly.
i am glad you mentioned the throttle shaft cause i had no idea there could be a vacuum leak from there, here is how the throttle shaft looks.

Here are two videos of the throttle shaft with the car off.

https://youtube.com/shorts/XLxof7E6m...ulGpEDa3xM-FH5

https://youtube.com/shorts/vbxea_ILa...wkpDzVSFo4Yhtp

And here is a video of the throttle shaft with the car on,

https://youtube.com/shorts/38VrmB1-r..._T1iPZSpHtQRNk

With the car on when i move it, the air suction sound from the carb increases, it somehow seems too small of a leak to cause that much Loss of power.

Anyhow i will try fixing it in the coming days and update you.

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[ShiRen]

Interesting. I've actually never checked that on any of the carbs that I've run. Never really had an issue that wasnt sorted with a little tuning though

[Howlite]

Finally fixed !!!
Here is what i did,
first i removed the throttle shaft but the wear did not look that bad,





So i put some rtv on the shaft where there is some wear, and i put some oil on the carb where the shaft sits, the idea is for the rtv to stick to the shaft not the carb, not sure if that works as intended.



There was some kind of fabric like oring on both sides of the shaft, i replaced those for regular orings that i had,
Here is a picture of the oring that was previously on it,



I did the same with rtv on the secondary shaft but i did not replace the old oring since it was still intact.
Next i noticed that the primary booster venturi would move with a bit of force, so i loosened its screw and moved the booster venturi for it to set right (it didn't feel centered before) then re-tightened it, here is where the screw is in case someone needs it.


I also re adjusted the accelerator pump but this time using a caliper, i think it was about 0.5mm off.
Lastly i changed the carburettor base gasket.

When i started the car, it would die unless i kept my foot on the pedal so i had to turn the idle stop screw in for it to hold idle, also the sound of air suction was way low after starting it the first time, i am guessing because there was no vacuum leak.

In the end i am guessing it was either the throttle shaft that was leaking, or the base gasket even though spraying carb cleaner on it would do nothing.

Thank you shiren and oldblueaccord for helping me on this, you guys are the ones keeping this forum alive.

[Oldblueaccord]

I Love it man thats great!