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carbs again, not a problem but a question

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Woodie

Woodie

Jedi Warrior
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I ma running mis matched twin HS2's, Trevor know my issues. Well it was still backfiring just a little yesterday through the carbs, and the plugs were still pale tan, so I turned the mixture richer on both by 1 flat,,,reset the idle and hmm seems to be much better.

Ok, now the question, all this while no matter where the settings are, when I come to a stop and put it in neutral the idle instantly drops to about 1500 then takes about 5 or 6 seconds and slowly drops to 1000. Why is this?
 
Slow spring return rate?? With engine off does the carb come slam down to the idle position?

If you are running SUs I hope you are running like maybe 20 wt oil in the dash pots, heavy stuff will slow the fall of the idle as well.
 
That should really be OK Woodie.

I wonder if your have a bit of snugness in your linkage? Right at the bottom end.

Do the throtle plates slam shut when you release the linkage? You can test this by looking first without engine running.

For your next trick, with engine running, at maybe 2K force the throtle at the carbs to the idle positon, if you do not get the run on you know where the prob is.
 
Sounds like the needles may not be centered to the jets. Needle alignment is manually set and is very important to proper function. I think linkage can be eliminated since it only affects the butterflies. It sounds more like the pistons aren't settling the needles into the jets due to drag. I remember really having to pay careful attention to needle alignment when doing my last set. I would suggest starting there, my $.02

Also, if I remember correctly, a mismatched set makes no difference in terms of carb bodies or any other parts, but it is the needle combos that make all the difference. An improperly matched needle combo may be very difficult if not impossible to balance well. It affects the air/fuel ratio throughout the entire range of movement of the carb piston. Each needle should have an identifier stamped on it near the end with the set screw. Amything else would just be a matter of plugging off vacuum taps.

JACK
 
Jack, mismatched or unevenly worn jet/needles is what I have been thinking for some time, but I was really expecting to see more differnce in color of his #1 and #4 plugs.
 
Could very well be Trevor but I would think Woodie would have checked the needles and checked the fall of the pistons for free operation. Well maybe not.

When you turn loose of the piston Woodie it should seat with a thunk and be at the true bottom of its travel.
 
I know he has check the rate of the piston fall, but I do not think that he has replaced the needles and jets... Or even checked that the needles are the same profile.
 
And that is very probible, however that would effect the idle and the runability not his slow return to idle I should think. Bet, just bet he has a sticky return.
 
Ok guys now stop arguing,,, hahah anyway, I checked the thunk and that is good, but I did make a mistake on the 20/50 in the dashpots, it is actually 90 wt hypod oil. I used that on a local recommendation when I put the wrong stuff in my gear box. That is now removed from the gear box with 20/50 in. Anyway, the point is I checked the dashpot level today, and from the colour of the oil I remembered it is way heavy. I will change out tomorrow, and see what happens. I will also check the needle numbers tomorrow. Do I need to remove the needle to see the stamped number or is it visible with the needle mounted.

On a seperate note The local guys did not charge to drain and fill the diff. I only paid the 3.99 for the liter of 80w90 castrol hypod . Nice guys...
 
Yes, the first thing I'd check is a sticking throttle plate or needle sticking in the jet. However, what if ... at cruise he is rich on one carb because of a mismatched needle, then when he comes off cruise it takes a minute for the fuel mixture to balance via the crossover tube. I'd take the time to get matched needles that are appropriate for the car and be sure they are centered. Needles are cheap.
 
Hahahahahahhaha, got ya, that's it. Problem solved.
 
Trevor I thought of 1 rich and 1 lean carb, but the plugs are so close. So I will check needles carefully and the numbers too.

ANd Im watching ebay for a gunson colortune
 
jack what? the heavy oil...

I will change saturday and check the needles

why not today,??
Cause I just poured a shot of Crown Royal, getting ready to go see The Who tonight. Dinner first then the show then home, kids are at sitters for the night... imagine that !!
 
That heavy of oil will make a difference.
 
Will make all the difference
 
UPDATE
needles are the same, removed the dashpots (1 at a time) cleaned them out and refilled them with 20W50 instead of the 90wt. HMM seems to be much quicker to return to a steady idle, and it idles a bit slower too. I will readjust next weekend and recheck the plugs cause it is a bit jerky/misfiring before the engine is fully warm. I think still a bit lean and now with the pistons fully falling it is more noticeable when pulling away from a stop when the engine is cool.

I missed the nice set of HS2's on ebay on sunday, they sold for $80 or so, I had a bid in for them but got out bid, and stupid me fell asleep on the couch and did not check as the auction closed.
 
Obviously you have not had enough experence tuneing SUs. Should take a total of 5 min less removing and replaceing filters. Don't make a big deal of it, it isn't.
 
Actually I am not doing it sooner due to weather, rain for the next 3 days. All I need to do actually is open the bonnet and screw the mixture nuts down 1 flat. Don't even need to take off the filters.
 
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