yes another carb problem

advinnie · Posted: Mon May 18, 2015 12:43 am Post subject: yes another carb problem

Right I have a pair of Dell 40 carbs but I'm starting to getting pissed off with them. My problem is that on one carb both mixture screws end up being w.5 turns out from seated but on the other carb both mixture screws only need to be opened 1/4 turn from seat to gain the highest rpm. I have swapped the mixture screws from one carb to the other end all the jets as well but it has made no difference. Also after only two minutes at idle the manifold on the carb that is pissing me off is at a temperature that is to hit to touch while the other manifold is bearly warm. Both mixture screws on the bed carb when fully seated will kill its cylinder I just need to know what could be causing that carb to run at its fastest rpm when the mixture screws at only 1/4 open? I'm guessing it's running lean hench why that manifold is getting so hot so quickly. Also if I go to 4.5 turns out from seated on all four mixture screws (one at a time) the idle does start to run rough. Please help

modok · Posted: Mon May 18, 2015 12:48 am Post subject:

what procedure did you use to set the idle speed screws (to get both sides equal)??

advinnie · Posted: Mon May 18, 2015 2:43 am Post subject:

Hi there I used a snail gauge. I pre set the butterflies on the car mixture screws 3 turns out start the car let it warm up Then used the snail gauge so barrels 2 and 4 read the same, 6 on the gauge then checked the rear barrels and barrel 1 also read 6 but barrel 3 read 7 so opened up the bypass screw on barrel 4 So it read the same as its parter barrel 3 then used the throttle stop screw on the other carb so both them barrels read 7. Then I played with the mixture screws. Now all cylinders misfire and die when the mixture screws are turned on and seated (one at a time off cause) then slowly turned them out to get the highest rpm possible and a half turn more (richer) now on one carb the ment both mixture screws end up being 2.5 turns out but I'm the other carb as soon as you unseat the mixture screws the engine runs at its highest rpm. But all barrels will start to run rough when there mixture screws hit four turns out (to rich). Is this right?

modok · Posted: Mon May 18, 2015 2:51 am Post subject:

Might be ok
The idle mix screws on those don't adjust a lot, and are very fine thread, so it may seem odd, but if it's idleing steady and drives well then it's ok.
They made the idle screw design "foolproof"; you can't bottom them and get them stuck because the shoulder hits first, and if you have them 5 turns out it's still not so rich your killing the rainforest, but it has fooled many people over the years taht expect an real adjustment like olden days.

Most IDFS you'd be like 3/4 turns on one side and 1.5 on the other, and that's seem ok right? it's fine!!

advinnie · Posted: Mon May 18, 2015 3:22 am Post subject:

Cheers mate yes the engine runs fine at all rpm's no black smoke no coughing and banging nor backfiring through the carbs or exhaust I was just a little concerned about the mixture screws on one side both being turned out to 2.5 turns from seated but the other carbs mixture screws only having to be turned out 1/4 turn.
Also the fact that one manifold is to hit to touch after just 2 minutes while the other is still cool to the touch.

advinnie · Posted: Sat May 23, 2015 5:38 am Post subject:

But if an update. I have find that to get the engine to idle at 850rpm the throttle butterflies have all ready gone passed some I the progression ports so I have had to open up the air bypass screws to allow me to close the butterflies more so they are not passed the progression ports and now I have controll of the mixture screws.

[email protected] · Posted: Sat May 23, 2015 8:51 am Post subject:

what is your idle timing?
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advinnie · Posted: Sat May 23, 2015 9:00 am Post subject:

7 to 8 degrees BTDC

[email protected] · Posted: Sat May 23, 2015 9:19 am Post subject:

Timing is good.

Opening the bypass screws so you can back out the idle speed screws to close progression, is perfectly fine. Just re-set LBI afterward.

What oil and pump are you using? While it doesn't seem related, 20-50 is so thick it drags down idle speed significantly, and often creates this situation. I've seen engine's idle speed go up over 200 just by a change in oil.

advinnie · Posted: Sat May 23, 2015 11:25 am Post subject:

Oil is 15w-50.
Sorry I don't get what you mean by "just re-set LBI afterward."

[email protected] · Posted: Sat May 23, 2015 11:30 am Post subject:

LBI = Lean Best Idle = Idle Mixture

I'm pretty sure that 15-50 axle grease is part of your problem. What makes you think you need 50W in England? If it's an ambient 45C sure, but........

If you put in some 10-30 you'll likely experience a much faster idle speed, and higher idle vacuum.

advinnie · Posted: Sat May 23, 2015 2:12 pm Post subject:

Lean best idle or course. I only put that oil in because I was told by someone to use it for the first few hundred miles. So 10-30 than I will get some tomorrow.
PS you was right you posted on one of my other threads about high oil temperature and you said to change the 30mm oil pump to a 26 mm pump so I did and the oil temp dropped from 118 degrees Celsius down to 100 degrees CeCelsius, I don't know why that is but your advice was spot on cheers.

advinnie · Posted: Sat May 23, 2015 2:14 pm Post subject:

10-30 Semi synthetic, full or mineral?

[email protected] · Posted: Sat May 23, 2015 2:18 pm Post subject:

synthetic or not has nothing to do with the viscosity. I don't know what's available where you are, but Samba guys are reporting good results with Valvoline VR-1 10-30.

Please report back on the idle speed change after the switch. Change the oil, go for a drive, and note the idle speed upon returning home. Re-adjust idle speed and idle mixture if it's too high. Normally MPG also goes up after a change like this.
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advinnie · Posted: Sat May 23, 2015 2:25 pm Post subject:

Ok will do mate.

[email protected] · Posted: Sat May 23, 2015 2:28 pm Post subject:

Think of it this way.

Your old engine at 118C and a 30mm pump, has the same pressure as your new engine at 100C and 26mm pump, because the oil cooler becomes "active" sooner with the 26mm pump.

The same goes for changing viscosity. The engine is trying to achieve and maintain certain PRESSURES. It has to run higher temps to get the viscosity down when using 20-50, compared to 10-30. At operating temps the pressures of the 2 situations will be the same. It may be something like

120C with 20-50
and
100C with 5-30

get the same pressures. It's really tough to wrap your head around, but that's how that oil and oil cooler system behave.
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