Low rpm problem

[Leonardo.IT]

Hello everyone!
I have a problem on my R4, a 1986 956cc.
When the engine is on and without choke it doesn't turn smoothly and usually turn itself off, even if it's warm.
The same problem comes when I drive with little throttle, even at "high" speeds.
First I changed all the electrical components, from the coil to the spark plugs.
Then I tried to change the carburettor with a refurbished one.
I also tried to change the head gasket, because I had a problem with the radiator switch and I thought that it could have been a cause.
The car when you hit the gas runs very well, and can even reach 140 km/h on the speedometer!
Anybody has experienced something similar before?
Any advice?
Thank you!

 

[malcolm]

I would check the vacuum hoses. The hose from the inlet manifold should have a restrictor inside with a 1mm hole. Or you could block that hose completely. Any splits in the hoses will make the car run weak at part throttle - pulling the choke out would balance that.

Next make sure the vacuum advance on the distributor works. Remove the distributor cap, and suck through the hose. The base plate on the distributor should twist and not release while you are sucking.

 

[Leonardo.IT]

Thank you Malcom!
The vacuum advance seems to work, but I'll double check it again.
The hose between the intlet manifold and the carburettor was in very bad condiction, the restrictor should be in the carburettor, in the hose or on the manifold?
I didn't know about this restrictor to be honest!
I'll try to block it as soon as possible.

Thank you!

 

[Leonardo.IT]

Here it is the little devil.
Fortunately I still had the old hose!!
Now the car seems to run smoothly, it just need a set up!
Thank you! Thank you so much!

 

[malcolm]

Excellent! Glad that worked.

 

[Ignas]

I have the same problem. But i checked the hoses, i have made a restrictor, but no changes. It seems, that it has no diference for the engine with that hose, or without. Is that normal? I double checked the carburator and all electrical components, but the engine doesn't run smoothly on low rpm.. Any ideas?

 

[mr-reno-139]

Worth checking manifold to head nuts as they come loose and leak air in may need new gaskets or just tightening

 

[mojobaby]

Hi Ignas, I had the same problem a few months ago, it was impossible to idle or drive at low revs.

It turned out that the 2 nuts holding my carburetor in place were loose and air was getting sucked in. So trying to set my mixture screw was impossible.

 

[Ignas]

Hi, today news:

1. I replaced new ignition contacts, the old ones were bad.
2. I checked manifold to head situation. One nut were missing, gaskets seemed to be ok so i left the old one cause it has a wire inside and looked strong.

But still no changes for engine work. I forgot to mention: engine work is not smooth even at high rpm.

 

[mr-reno-139]

It could be a bad spark plug if you take them all out compare the colour of tip
While they are out carry out compression test and hope they all read the same within 10 % difference

 

[Ignas]

I took a short video to show you how it goes. It's not good sound quality, but i hope you can hear 30s-48s i kept gas pedal steady, but engine works wavy. It still works quite steady as it works on low rpm.

I hope i can check compresion, when i have a tool, but for now i changed spark plugs and nothing happened. Thank you for your replies, please tell me what else i can check!

 

[Ignas]

By the way, I'm thinking to adjust valves tomorow. Does anybody know valves clearances?

 

[mojobaby]

Yes, its 0,15mm on the inlet valves and 0,20mm on the exhaust valves. These are the clearances for a cold engine.

Nice video but you have a crazy fly walking around