General Technical Questions and Answers last answered over 1 year ago.
You may also want to visit the Wiki(pedia) for a more structured index of T25 repair, maintenance, technical and ownership topics
My camper has a Weber carb conversion and has been running OK for a few years but has now developed very bad hesitation when accelerating, tick over is OK. As you accelerate it sounds as if only two cylinders are working but further depression of the pedal allows you to go through the flat spot and then the engine pulls normally. The fuel filter at the tank and fuel line has been changed up to the pump. Also the carb has been stripped down and the jets cleaned and blown out.
Do any of you kind people have any ideas or suggestions on how I can isolate the problem.
If it was running very rich it could behave like this.
As you press the throttle the accelerator jet puts a squirt of fuel into the carb which tips it over the edge mixture wise, then as you press further the butterfly opens, more air is drawn in and with the accelerator jet not contributing additional fuel it 'clears its throat'
If you 'blip' the throttle does it die a little before it picks up?
I could be miles off base there though as these engines/carbs may be different to the ones I'm used to and I stand to be corrected
Not sure of your mechanical aptitude so please forgive me if this is patronising.
Could be worth checking and setting the mixture then. I've had good success with Colourtune (Its like a glass spark plug so you can see the colour of the flame in the cylinder).
Emissions could be an issue too so may be worth borrowing a gas analyser if you haven't got one (they're too expensive to buy just to do it once really) or see how much your local garage or MOT centre will charge you to set it up. It doesn't take too long to set the mixture so it shouldn't cost too much.
You don't need the full-on rolling road tune up, just enough to stop it coughing and spluttering.
Mixture should be the last thing you set though IMHO - Plugs, Points, Timing, Carbs. that's my little mantra
Just got up and remembered something I forgot to mention.
If this has an automatic choke make sure you confirm that it is 'coming off' properly once the engine warms. I had a Cortina once with an automatic choke on a Weber and it went stupid and would be half on all the time.
If it was running fine and this flat spot suddenly started out of nowhere, could be a bit of muck in one of the jets...
normal technique, rev it through the range of interest clapping the palm of your hand over the intake just before/as it goes throught hat throttle setting/revband (of course take air filetrs off first). Repeat... if you can identify eact spot, hold it at this throttle/rpm setting and do likewise, opening throttle fully from that point once hand over choke entry.
If it is falling over due to over-enrichment due to accelerator pump - and it wasn't doing it before > bad sparks, leads/plugs.
Finally traced the problem to accelerator pump diagphram. the original consisted of two layers of very thin floppy rubber sandwiched together with a metal disc. We obtained a replacemnt wich was considerably thicker and stiffer. This component also serves as a gasket between the two parts of the casting and I suspect the thicker material creates a better air tight seal.
During the investigation we found that the pump only operates on one venturi although their is a pump jet positioned over each. One of the jets is intentionally blocked (no hole drilled).
Hope others find this info useful, goes like a new van, many thanks for your assistance
During the investigation we found that the pump only operates on one venturi although their is a pump jet positioned over each. One of the jets is intentionally blocked (no hole drilled).
Normal for accelerator pumps to work just on the primary (small) choke... due it being smaller hence higher velocity to atomise said fuel...
