2.0L pinto Engine Fuel Supply Pressure and Bypass line

[Alan c]

I overhauled (just cleaned) the weber carb and renewed the fuel lines (still have the stock mech fuel pump). I noticed the fuel line had a T piece to bypass back to tank with a restriction in the the return line part of T, obviously to provide a limited amount of bypass and maintain a pressure in the main supply to the carb.

I broke the T piece so had to buy a replacement, bought one specific for the 2.0 Pinto engine (so assume they are needed) no problem except when it arrived the bypass hole was a lot smaller (around 0.5mm vs 1.5mm) I fitted new one as supplied assuming old one had been tampered with as it looked as though it was drilled out. I figured it would by default increase the pressure to carb but assumed that would be OK.

Car ran great so was happy until MOT, when garage (who know me and car well) said HC emissions had shot up from previous year and it only just passed. They said no amount of mixture adjustment would get it down.

Reading up it appears fuel pressure can impact the HC reading assume by increasing fuel flow through carb due to high pressure - I have ordered a fuel press gauge so I can check I have right press for Weber carb (about 3psi).

Just thought I would ask if anybody else has been through this issue with wisdom to share (eg does anybody know what bypass hole size should be etc)

[boustrophedon]

Re: 2.0L pinto Engine Fuel Supply Pressure and Bypass line

Fit a fuel pressure regulator. I had to fit one to a 1.8 MGB engined car because there was no room for a mechanical pump with the aftermarket exhaust, so an electric fuel pump had been fitted near the fuel tank. Trouble was it worked fine at idle but the pressure was to high for the floats to reliably close the needle valve from high revs. MOT man was not happy with fuel flowing from the carb overflows into his pit.

One of these or the one with a built in filter. ​https://www.holden.co.uk/p/fuel_pressure_regulator_67mm

[Ye Ol Ripper]

Re: 2.0L pinto Engine Fuel Supply Pressure and Bypass line

Hi Alan
1)I would in the first instance advice you to look down the top of the Weber Carb , with the engine running check that there isn't a constant drip from a tube that runs in the venturi on either of the chokes.

That would indicate that the float level in the carb has either been set too high, the float is punctured or has got stuck . There is also the possibility that the needle valve has some dirt on the seat that will need to be cleaned with carb cleaner and a cotton wool bud.

2)If there is no dripping check your ignition timing as if the advance weights have stuck then the timing at idle could be over advanced , which is another cause of high HC.

3) If you have replaced the cam belt since the last mot , recheck your Cam timing is ok .

4) After which, check the resistance values of all your HT Leads , if you have a lead gone down, then that will also cause high HC readings.

5) With regards to the jet size ,I would initially leave as it is until you have been through my above recommendations . From memory 0.6- 0.8 mm seems to ring a bell , however you can simply insert a carb jet of that size inside the fuel hose if needed.

Hope that helps?

[Alan c]

Re: 2.0L pinto Engine Fuel Supply Pressure and Bypass line

Thanks all - will do the checks suggested and the pressure regulator is on the backup plan list.

[andyf]

Re: 2.0L pinto Engine Fuel Supply Pressure and Bypass line

I've never had a bypass fitted to my Pinto or my old 1600 sport escort, both being fitted with the same carb. I would check the float level, condition of the floats and the valve.

[Alan c]

Re: 2.0L pinto Engine Fuel Supply Pressure and Bypass line

I fitted a pressure gauge to fuel line it is exactly 3psi to carb which is what spec requires. I suspect this is achieved by the internal bypass on mech pump rather than bypass fitting. I think the old bypass fitting was oversize and causing a low press at the carb so when I had it set up on rolling road a few years back they re-jeted it to suit this low press. Now I have normal pressure I think it all needs re-setting. Rolling road here I come.

Thanks again all