Topic: Aftermarket idle screw? Holes or no?

[evinrude7]

Are these aftermarket? Reading up on hondachopper.com suggests they are because of the pre-bored metering hole at the end.  Quick fix on the site suggests closing the hole w/ jb weld. Starting to wonder if this is the culprit for my deceleration pops.

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[TwoTired]

The holes are a limiter, so you can't totally close off the air supply to the pilot jet emulsion system.

Plugging them is not a "fix".  Possibly a band aid for a different problem, like no exhaust back pressure?


I will say that in an attempt to meet EPA standards, the CB550F used solid tipped air screws for a more precise lean mixture idle.  They also had a different tip angle and seat angle.

Why is it you want to change it?  Hearsay?  Infallible human opinion?   Do you have an actual adjustment problem to solve?  Does turning these in fully, not enrich the idle mixture enough?  What is you throttle response like in top gear at a crawl, when snapping the throttle to half way position?  Does it accelerate? Does it wheeze.  Can you give it more than 1/2 throttle and accelerate reliably?

Cheers,

[evinrude7]

The holes are a limiter, so you can't totally close off the air supply to the pilot jet emulsion system.

Plugging them is not a "fix".  Possibly a band aid for a different problem, like no exhaust back pressure?


I will say that in an attempt to meet EPA standards, the CB550F used solid tipped air screws for a more precise lean mixture idle.  They also had a different tip angle and seat angle.

Why is it you want to change it?  Hearsay?  Infallible human opinion?   Do you have an actual adjustment problem to solve?  Does turning these in fully, not enrich the idle mixture enough?  What is you throttle response like in top gear at a crawl, when snapping the throttle to half way position?  Does it accelerate? Does it wheeze.  Can you give it more than 1/2 throttle and accelerate reliably?

Cheers,

deceleration popping.  i've been chasing my tail on this issue for 3 years.  it seems to have fixed the issue.  3000 mile maintenance is all complete and spot on.  float heights and vacuum sync are all perfect.  1 and 3 carbs are set to 5/8ths from fully seated.  2 and 4 are set 1 turn out.  on your questions of throttle response at a crawl and giving it 1/2 throttle or more does it accelerate reliably.  i'm getting normal throttle response.  as for your question does turning the screws in fully not enrich the idle mixture enough.  no it didn't before i made this change.  now i can adjust the mixture noticeably with an 1/8th of a turn.  i could have an exhaust back pressure issue because i noticed a couple of the exhaust pipes were a bit rattley when i had them off this winter.  my guess is it was 1 and 3 which have been the offending ones all along.  as for your question about Infallible human opinion.  folks can be wrong but they can also be right.  what i do know right now is the bike isn't popping on deceleration and it hasn't run better. 

[pjlogue]

Check your exhaust gaskets.  Air getting in there can cause the popping on deceleration.  Decel causes a rich mix and can either not ignite or cause an incomplete burn because of lack of air.  With an air leak at the exhaust port enough air can get in to cause the popping at the hot un-burnt mix ignites.

-P.

[evinrude7]

Check your exhaust gaskets.  Air getting in there can cause the popping on deceleration.  Decel causes a rich mix and can either not ignite or cause an incomplete burn because of lack of air.  With an air leak at the exhaust port enough air can get in to cause the popping at the hot un-burnt mix ignites.

-P.

checked them.  retorqued the spigots that have new crush gaskets i put in this winter.  retorqued the header clamps.  still no change until i plugged those holes in the air screws.  i suspect i have less than ideal back pressure in the exhaust for 1 and 3.  i'll get to plug chopping next weekend. 

[HondaMan]

checked them.  retorqued the spigots that have new crush gaskets i put in this winter.  retorqued the header clamps.  still no change until i plugged those holes in the air screws.  i suspect i have less than ideal back pressure in the exhaust for 1 and 3.  i'll get to plug chopping next weekend.

If you have uneven baffle pressure in the pipes (and 4 pipes in place), then the carbs will mix unevenly despite their air screw settings. This is partly because the cylinders interact a little bit (as this is an engine comprised of 4 smaller engines, not one engine with one carb, a source of fear for Honda at the time!). If the last cylinder (in the firing order) fired a 'normal' cycle but the next one has less back pressure, the next one will pull more fuel as it has more flow than the last one had, at that speed. This extra fuel gets pulled during the overlap cycle and ends up being unburned, in the pipe.

[evinrude7]

checked them.  retorqued the spigots that have new crush gaskets i put in this winter.  retorqued the header clamps.  still no change until i plugged those holes in the air screws.  i suspect i have less than ideal back pressure in the exhaust for 1 and 3.  i'll get to plug chopping next weekend.

If you have uneven baffle pressure in the pipes (and 4 pipes in place), then the carbs will mix unevenly despite their air screw settings. This is partly because the cylinders interact a little bit (as this is an engine comprised of 4 smaller engines, not one engine with one carb, a source of fear for Honda at the time!). If the last cylinder (in the firing order) fired a 'normal' cycle but the next one has less back pressure, the next one will pull more fuel as it has more flow than the last one had, at that speed. This extra fuel gets pulled during the overlap cycle and ends up being unburned, in the pipe.

if i've vacuum synced the carbs should this not take care of the uneven back pressure?  yes i'm aware that uneven back pressure is not an ideal set up.  what are the consequences of running like this over time? 

[evinrude7]

none i guess.