Strange running problems

[djinuk]

I have a strange problem (i believe) with my R5. The carb is freshly rebuilt and cleaned, jetting is all standard etc. Mixture on idle is not correctly set however it will be next week, at the moment ive just got it set so that it idle's. Now the problem i am having is that the boost dosent feel like its pulling like it should and when changing gear with any power the car hesitates then a second later jumps into action. Now whats strange is i have noticed that these problems are not evident when the choke is on. I noticed this on my fun drive back from work yesterday during which time i forgot to turn off the choke. Car also feels like it boosts much stronger with the choke on, where as before it almost feels slightly like the car is pulling back when the turbo spools.

Now this may just be me but being my first turbo powered car it just seems somehow not right with regards to the above. Any ideas.

[guyus]

sounds like the car is under fueling quite badly or the turbo is sezed
the turbo runs off of exhaust gasses passing throught a turbine, if you have less fuel in the combustion chamber, it comes out of the manifold at less forse, there for the turbine wont turn as much as it should have and may stutter,( i would check the turbo play to see if its sezed could just be a nackkered turbo
if its all ok two things i would look at doing is turn the boost down till you get her set up and try not to run her as much or you can try and turn the mixture screw and get a bit more fueling in her but have a read up on this can be a right pain to get ith right with out any co2 meter or wideband kit if you start to get a lot of blackish wet soot comeing out of the exhaust , this is normly a tell tail sing of over fueling,

[djinuk]

ok man, turbo is only running 10psi (standard i believe) and to be honest so far ive not once drove the car hard. Am i right in saying screw the mixture screw out to increase fueling?. Ive gota photograph the turbo this weekend, as its smoking slightly , and i think there is some oil in the boost pipes, but it may be oil from previous turbo going wrong. There is slight play in the turbo side to side but i think thats the normal bit you tend to find.

[Chris Hebden]

Before you go hunting around for any problems, get that idle set up properly. Only take 10mins with a friendly MOT tester and his/her analyser.

[djinuk]

yea thats what im going to do i think, biggest problem for me is getting the time to go to one as most open monday to friday local to me , and obvioulsly im hard at work .. or at least im sat on rtoc at work but you get me :)

[Chris Hebden]

Theres loads open on a sat down Horkins lane i think it is ;)?!

[Mart]

the turbo runs off of exhaust gasses passing throught a turbine, if you have less fuel in the combustion chamber, it comes out of the manifold at less forse, there for the turbine wont turn as much as it should have and may stutter,

Fail.

DJ,

Hesitation between gear-changes is usually due to either the float chamber emptying, and thus no fuel when you come back on the throttle, or the float-chamber is 'flooding' and thus causing a dumping of the fuel when you're back on the throttle, or the accelerator pump/jet/circuit isn't working properly.

To eliminate the former, hook up a pressure gauge to the carb fuel inlet, and see what's going on there. If that checks out ok (should be ~4psi at idle, and boost pressure + ~4psi when on boost), then check the small filter in the carb inlet isn't caked in cr8p, that the float mechanism is working, the float itself isn't holed, that the needle valve is clear/clean, and that the main jet isn't blocked.

If it's flooding, it's usually either that the base fuel pressure is too high (but v rare to hear of the fpr causing that), a problem around the needle valve/float area, or the gasket/o-ring on the pump jet is allowing fuel to leak past, run along the pump jet 'arm', and drip into the venturi thus so, so a few things to check there.

If it's the accelerator pump cct, there's a few things to check, main point being correct travel of the accelerator pump arm (cue the 5mm drill bit test), that the arm itself is actually moving (the arm being found to be seized isn't unheard of), that the pump diaphragm hasn't split, the spring behind it collapsed, or that the pump jet (hook shaped arm when looking from above with the carb elbow removed) itself hasn't partially blocked up.

That should keep you busy for a while :D

Maybe before all that, check the dizzy cap & rotor arm, and plugs if needs be, to make sure it isn't just a weak spark causing the problem.

[Sparkie]

when changing gear with any power the car hesitates then a second later jumps into action..


your accelerator pump is either sticky, siezed or there is a blockage in the actual jet that squirts the fuel down the venturi.

take the carb top off, pull the brass jet out - make sure that you actually have the soft fibre seal on the bottom of it. then blow from the bottom of it to see if its free of swarf. then suck it to see if the ball bearing inside is free. then try and clean it out with carb cleaner?

also take make sure the accelerator pump mech is working and isnt oxidised up. - and you got the spring the correct way round and the diaphram isnt split. and the linkage to the throttle isnt being fouled by the breather pipe that goes under the carb.

[Sparkie]

you beat me to it Mart....:cooter:

[djinuk]

wow i will go through that list when i get home. I wound the noggin on teh acc pump all the way as per the carb refurb guide on here says. So first things im going to do is set that using the 5mm drill bit. After that i will go through the stuff you stated. Carb is fresh rebuilt but i will give it a check over anyhow. Thanks so much guys, i really appreciate the help etc.

just to add, sparkie you say remove the brass jet, is that the tiny one screwed in at a angle. And what does this "soft fibre seal" look like as i cant really remember seeing it

[MR TURBO]

I have a strange problem (i believe) with my R5. The carb is freshly rebuilt and cleaned, jetting is all standard etc. Mixture on idle is not correctly set however it will be next week, at the moment ive just got it set so that it idle's. Now the problem i am having is that the boost dosent feel like its pulling like it should and when changing gear with any power the car hesitates then a second later jumps into action. Now whats strange is i have noticed that these problems are not evident when the choke is on. I noticed this on my fun drive back from work yesterday during which time i forgot to turn off the choke. Car also feels like it boosts much stronger with the choke on, where as before it almost feels slightly like the car is pulling back when the turbo spools.

Now this may just be me but being my first turbo powered car it just seems somehow not right with regards to the above. Any ideas.

Sounds like just what i have but then i have one of those not so good grp A on mine.....I'm thinking its time to take it off revert back to standard carb and give the grp A a service.....I'm actually thinking about doing away with the grp A completely.....I seem to remember i have a bag of carbs somewhere

[Sparkie]

wow i will go through that list when i get home. I wound the noggin on teh acc pump all the way as per the carb refurb guide on here says. So first things im going to do is set that using the 5mm drill bit. After that i will go through the stuff you stated. Carb is fresh rebuilt but i will give it a check over anyhow. Thanks so much guys, i really appreciate the help etc.

just to add, sparkie you say remove the brass jet, is that the tiny one screwed in at a angle. And what does this "soft fibre seal" look like as i cant really remember seeing it


the brass jet im on about is the accelerator pump jet, the one that bends over the edge of the venturi like a little brass snake! when you pull it upwards, check the hole is comes out of, as there should be a seal there. if there isnt it will leak.