Pinto Kit car with bike carbs setup

[pringle1988]

Hello all im looking for some advice here.

I bought a kit car a couple of years ago now (pretty sure its a locost). It came with a 2L pinto lump in it running motorbike carbs which are mikuni and have 4 venturi? Basically 1 for each cylinder.
I have never been able to make this run correctly and seems to now be running on 3 cylinders. I have done some research and have been advised it is best to get these setup on a rolling road. Is this correct?
It also backfires now and again sometimes out the exhaust (with flames) and sometimes out of 1 of the trumpets of the carb.
Could the needles be the incorrect size? Sorry for the questions im pretty new to the world of carbs haha.

I have checked for a spark and made sure the timing is correct and these seem well. I can also see the fuel being drawn into the cylinders when I look into the carb.

Any help would be appreciated thanks

[pringle1988]

Thanks for all the replies everybody. I forgot to say I have done a compression test in the past and all cylinders came back pretty equal and within tolernaces for the engine.
Im going to do another compression test tonight and see what the results are along with rechecking for spark etc.

With regard to running on 3 at idle, this could be right, as soon as I press the accelerator even the slightest bit the engine goes from running like its trying to escape the car to pretty smooth although it sounds a little off beat still. I just put it down to faster engine speed smoothing out the bumpyness. The manifold for the exhaust has been completly custom made so not sure if this can cause it to sound a bit off beat?

Chester sports cars is a little far to go but Bogg Bros although quite far is a lot closer. Im based in Durham if that helps and worst comes to worse and have to get it looked at.

Thanks again.

[pringle1988]

LLantrisant said:

did the car every run roperly with those carbs?

what info did you got from the former owner?

valve clearances (sports camshaft fitted) and ignition timing are correct?

The car in my ownership has never run well, to be honest ive hardly used it though as I kind of got annoyed with it not running well. The former owner didnt give me any info on it. When I went to buy the car I was more into owning a kit car really and basically had rose tinted glasses on. Ive checked the timing and it is spot on but I havent looked at the valve clearances.

I dont know if this is a stupid idea or not as im a bit of a novice with carbs but if it was something to do with the idle jet as said above could I spray petrol into the carb to see if it the runs on all 4 at idle?

[pringle1988]

Thanks again everybody, Ive been back working on it again tonight.

I took each lead off individually and noticed it was actually on 2 cylinders only, untill I pulled the choke slightly. I now have adjusted the screw and have it running on 3. (The 3rd would always come on with throttle but not at idle). Its cylinder 4 thats my issue. Ive rechecked for a spark and thats good, but it does not fire at idle or with throttle.
I have noticed that the the black bit of plastic connected to the needle and vacuum vibrates and sort of chatters up and down. So I checked the vacuum seals at the top and all is good.
I have re done a compression test and im getting results between 130 and 110 PSI. To me this seems low but im used to more modern engines. Is this ok?
Does anybody have any access to a Mikuni carb diagram as I can see 3 screws but there are 4 carbs. To be honest its about time I seek professional help haha.