engine idle slow to come down

[Woodie]

Just to say hi, I was on the Midget board last yr but had to sell my 1970 last june. Well its june again and next friday I pick up a 77 B. The engine was rebuilt 700 miles ago, 2 thou overbored etcetc. Anyway I took it for a test drive today, and when I started the car the idle was very slow to drop down to 750. Same when I was driving, between shifts the idle stayed up. The car is running twin SU's with pancake filters. From the size i guess HS4s. The mechanic has just balanced and tuned them.

SO any ideas on where to start next week when I get the car to sort this idle issue. I ran twin HS2's on my midget and never had this problem.

Cheers

 

[JPSmit]

could it be something as basic as needing a new or stronger return spring?

 

[Woodie]

could be JP, I remember chatting on the SPridget board a few times.

SO how do you check those or do you just go buy new springs . ANd does it matter if I buy generic ones at CAnadian Tire

 

[JPSmit]

Canadian Tire is fine - Check it by popping the hood, and see if you can reduce the idle by hand on the mechanism - you should be able to see if it is binding or if the springs are missing - sounds more likely mechanical than anything else.

 

[Woodie]

OK I check the return springs and its definitely not them. Car idles when it settles at 700. But when I pull my foot of the gas it stays around 2000 rpm and gradually drops. These are twin HIF4 carbs, rebuilt and balanced.

SO I still have the no or slow return to idle, and when I turn the car off it runs on for a second or 2.

Any ideas???

 

[DrEntropy]

Throttle plate poppit valves. Solder those eeevile things SHUT!

 

[Woodie]

explain further please >>>>

 

[DrEntropy]

Throttle plates have a little valve in 'em, with springs the diameter of a human hair... it's a task, but pullin' the carbs, removing the plates and soldering the stoopid things shut will help eliminate your <span style="font-style: italic">g r a d u a l</span> RPM slow-down.

If you elect to try it without removing the plates, DRAIN the carbs well and use a BIG soldering gun. NO FLAME!!! :wink:


Elaborate enuff? :wink:

 

[Woodie]

yup I'll take a look tomorrow...thanks I will report back

 

[MGB922]

Woodie
When you say the spring are good does the throttle return completely to the idle stops immediately or could the cable be binding. If this is not the problem your getting too much fuel. Check the carbs, or have a garage that knows how to, with a gas analyser. A quick check can be to check your plugs. If they're black the carbs are too rich. If you're running rich when you shut the ignition off your anti runon valve will open dumping air into the manifold. A rich carb will be kepping the mixture going. Running rich for any amount of time will build up carbon in the chambers and hot carbon can act as spark plug to an extent. Sounds like the carbs are running rich. Another thing that comes to mind is if the chokes are set correctly. An activated choke will draw fuel. Moss motors has some good tech tips to diagnose carb problem. Find your carbs part list and they'll be next to the blowup picture.
Hope this helps.
Tim

 

[Woodie]

Tim thanks for the reminder on the spark plugs ..I will check them tomorrow.
These are HIF4 carbs, and I am used to HS2 carbs and was able to get those to sing. The PO said he had the carbs balanced and the mixture set by a garage. I have my doubts about that because of the amount of black soot on the white concrete patio stones the car sits on. I have read the instructions on setting and tuning the carbs, I just gotta find them on line again and save the link this time. As mentioned earlier the engine has 1050 miles on it after a rebuild done by a reputable local shop. Should I recheck the valves or leave them and do the timing and carbs.

 

[DrEntropy]

I'd say leave nothing to chance. Check valve lash before you start tweaking the carbs.

 

[PAUL161]

I agree with Doc, if your carbs have the butterfly's with the valve in them, close them up or replace them with the solid ones. As long as their in there, there's nothing you can do to totally eliminate the hesitant idle problem. The wifes car is as original from the factory and the rebuilt HIF carbs have the butterfly's in them. Hap rebuilt the carbs and done a beautiful job! He asked me if I wanted to leave the original butterfly's with the valves in there and I said yes, I wish I didn't. Jeff rebuilt the distributor. The engine runs perfect, but it's slow to idle back down, which is a pain when shifting gears. I'm going to pull the carbs when I get a chance and replace the butterfly's with the solid ones. PJ

 

[Woodie]

Ok,,I pulled the plugs last night, pretty black and sooty, SOOOO I will be doing a complete tune up in the next day or so. Valve lash, timing, checking the spark plug gap pulling the carbs and soldering the valves closed, reinstalling and resetting the carbs according to the manual. Oh that reminds me, the HIF4's have the lifter pins on them but the MG shop manual says nothing about using them. SHould I follow the manual or do like with the HS2's and use the pins to check mixture?? Once this is all done ... I will be back! (Thanks Arnold)

 

[GaryBeu]

I ~sorta~have this same problem. When I start the car idle is good at about 1,000. When I shift it does not come back down but stays at about 2,500. Coming to a stop, the only way to get it down is to leave the clutch engaged until almost at a complete stop...otherwise, you have to hold the brake and ease the clutch almost all the way out. We have HS4 carbs, springs are good, even manual closing of throttle won't bring it down. I THINK the choke is adjusted correctly. Do HS4's have that thing that needs to be soldered? May be valves? Jets sticking?