Afr 22% On 1.9 Gti With Webers

[Saveit 0]

Hi,

 

I have a problem with my 1.9 gti with twin webers. I have bought the engine with the webers on from a former rally car, so i have not done any setting up myself. The car doesnt run properly though. It wont take the gas, and it splutters from the exhaust when touching the pedal. Is starts right away but it doesnt run properly. So i thought id do an AFR measurement with the wide band lambda from innovative motorsports. When idle it reads between 20 and 22% and wont settle on anything - it jumps around between those numbers. When pushing the accelerator it reads everywhere from 30-50%. The readings are made about 10 inches in to the back of the exhaust.

 

What does these AFR numbers tell you?

[petert 588]

All a bit too lean really, by heaps! You need to get it idling at around 13% before you go further.

[suth82 0]

Have you serviced the carbs? I would think that would be the first action after buying second hand. Much easier to set up with everything clean and fresh.

[Saveit 0]

Ah yeah thought so. But since the webers have been running on this particular engine before, it should be a matter of just adjusting them. But then again how can it be so far off if it has run before? Should i perhaps try refurbishing the carbs or something?

 

Do you recon that measureing about 10 inches in to the back of the exhaust is okay, or could this be some of the reason for low reading?

[madaxgt 0]

You need to ensure you have not got an exhaust leak as this will give an over-lean reading. But the running problems do suggest its too lean and misfiring a lot.

[Saveit 0]

But do you recon it is something that can be corrected by adjustment and refurbishment or what?

[suth82 0]

do you know the history of the carbs and engine? did you see them running before buying? If they were running fine before you swapped them into your car then we will need some more info before we can help:

 

firstly, what is your fuel pump/regulator setup?

[Saveit 0]

No i havent seen the engine runnin myself. But bought it from a guy who has just recently pulled it out from a rallye car because the shell was past its days.

 

I am running no regulator, just a solid state pump mounted fairly close to the tank running about 4-5 psi and capable of running 130 liters per hour. The fuel filter doesnt fill up fully for some reason, but i recon its just air in the filter?

[suth82 0]

I would not recommend running a solid state fuel pump with twin webers, especially with a race engine, it will not fluctuate to the demand like an interupter fuel pump.

 

My advice would be to buy a facet silver top fuel pump and adjustable regulator, plus a service kit for your carbs. Then you can think about setting them up properly.

[Saveit 0]

So finally the car is somewhat running. We had to replace the carbs to a rebuild set with same specs since the engine died after 1-2 seconds with either part or full throttle. We have checked everything from replacing pumps to filling up Cola bottles with gasoline to check fuel delivery. All seems to be good now.

 

BUT i am still getting a idle reading of around 1.40 on the lamda and a ratio of about 20:1. It is more steady now though than with the other set of carbs. When on the throttle the ratio changes to about 15:1 which is somewhat reasonable as far as i can tell. But what do i do about the lean mixture when idleing? Go up in idle jet size or? Ive tried to both loosen and tighten the mixture screw, but that doesnt seem to make much a difference. Unscrewed one of the idle screws with the engine running, and as soon as i took it off the engine was almost killed because of too much gasoline in that cylinder i guess?. So i cant see why it shouldnt be possible to get the mixture right when idleing if you can almost choke the engine by removing one of those screws - or is there something i am missing?