I’ve been chasing a miss, had the tank out cleaned, full set of new lines. New filter. but under heavy load I’m getting a miss. I reckon it’s either a blocked main jet. But I’m not convinced it would get to 60 like that. Or the leccy fuel pump has had it. So what’s the difference between the £20 on eBay and the £135… what’s my Type 4 2.0 on webers need?
Enough. If it wasn't keeping up it would take minute to show. If it's immediate on heavy load it's not the pump.
Yep so climbing grizebeck hill which is 50mph WOT for about 3-4 mins it’s really struggling, but it’ll run round to 60mph pretty happily
I had a similar scenario occurring fairly regularly. A blocked idle jet or two on Webers gives a misfire on idle and up to midrange. In most town driving or part throttle situations the engine feels weak. Once fully on main jets... ie. 60mph...runs as normal. Its caused by dirt entering through the K&N style air filters and blocking the idle jets. Try removing the four idle jets and clean with carb cleaner. Blow through idle jet passageways also with carb cleaner. I made a copy of the 'jet doctor' fix. I have not suffered this issue since.
Struggling immediately or is it ok at first? Mine was absolutely fine for 1,000 miles, then halfway up a very long motorway hill showed I needed a tad more fuel pressure. It's all very well setting pressure at idle, but it's a bit meaningless really. Easy way to find out - lift off a bit, it should recover immediately. If you have a regulator, turn it up a bit, you can't believe everything you read.
What about your ignition .. could be a loose plug lead or an electronic module reacting to a Facet type ( pulsing coil clicky) pump. The wiring on a stock Type 4 is quite thin going to the coil compared with a Type 1.. connecting a pulsing fuel pump to the coil causes a drop of 0.5 to 1 volt every time the pump clicks, and that twitches the timing in the electronic module. Fix - power pump off a relay which takes a fused feed direct from the battery. Enable relay by whatever means you powered the pump before. And 60mph seems a bit slow anyway for a 2.0 type 4. ....80mph would be right. Your engine's performance has drifted off while you were sleeping....
Feel. It feels like a fuel problem. Sparks issue feel different. Stutter on light load is closed up points.
If your idle jets are blocked it’s nothing to do with dirt getting through air filters it will be something in the fuel system Most commonly rust from the fuel tank. You will be running on the main jets a lot earlier than you think in a bus. Do you have a link to the jet doctor fix please
I have a fuel injection fuel filter after the fuel pump so it's unlikely rust is coming from fuel tank. The idle jet draws air from the air filter cavity... and dirt off the air filter baseplate as standard. https://www.cbperformance.com/v/weberjetdoctor.html
Well everyday is a school day I’ve just learnt something new Thanks for the link Why is dirt getting in there in the first place though?
I think fine dirt gets through the K&N type filters and settles on the base plate of the air filter. The base plate is always grubby even though I clean it every time. The dirt mixes with the oil that seeps out of the filters, breather deposits etc. and because the idle jet air entrance is in the base plate of the air filter, the liquids provide the dirt a vehicle to move into the idle jet. My theory only! ...lol The idle jet isn't like a true idle jet. I believe it works like an emulsion tube, premixing air and fuel. Spend a bit of time cleaning the passageways, jets and caps. Top tip. lay a cloth under the carb and resting against the inlet manifold in case you drop anything...you will spend a long time looking for it!...ask me how I know...lol
I don’t know if it’s any help to you, but I had my £20 unbranded pump die on my twin carb type 4 this week, and the symptoms started as a misfire at speed, but rapidly turned into quite obviously under fuelling, then running on two as one carb dried up, and eventually grinding to a halt. If I sat there long enough with the pump running, it would eventually refill the carbs enough to do another mile or so, repeat to fade.
Hmm. Well I’ve pulled the idles out blown through the jets and the same on the mains. also the tiny holes in the top. Float levels look good. Still runs like a bag of soapy frogs. Is there an idle circuit in the carb that needs blowing through? I’m going to check valves and change the HT’s and plugs
Idle is a red herring. That would show itself as a lumpy idle and one barrel wouldn't respond to the idle mix screw, but foot down you wouldn't notice - not your problem. It's really obvious when you get a blocked idle jet. Mains rarely block as they are such big holes. From what you've said it's got to be lack of fuel to the carbs, or one of them. How are they plumbed? When I originally plumbed mine in series the second one suffered from lack of fuel so I changed that and T'ed to both. Might just have been the double banjo outlet for the second carb was too small, but I thought I'd cut to the chase.
They are t’d to each other. But they’ve been like that for at least a decade. Just with fresh hoses now.
Never assume there is no crud just because you have a stonking filter. Rubber crumbs off fuel pipe ends sliced off by the barbs can be as effective as rust.
