Hi all Well we went for a day out in our bus last weekend and my bus started backfire on overrun..I was tweaking the mixture screws a little bit the day before so first thought its too lean..so pulled over got all them screws a quarter of turn in and off we go..still poping and backfiring..and weak..so pulled over again and another quarter of turn in..so they all set somewhere between 3-3/5 turn..exactly the same as they were before..anyways..still same issue..then another thought it may be to rich as for the last few weeks it smells horrible of fuel when engine turned off..another thought its weak so one cylinder not working but ok We got back home and bingo..cylinder no. 2 not working..well not firing anyway..so compression test 116 engine cold..not great I no but thats how it was last few years so no change really..ok theres spark too so lets investigate further..took the dizxy cap off and found this.. The rotor arm bit got melted..anyone has any idea what could cause that? It happened to me first time..the engine never overheated temps and oil presure are spot on..got a new rotor arm but before it get fitted I need to find out the cause first... The story goes on as yesterday I was tweaking the mixture screws again and finnaly cylinder no 2 gotten alive..but whats strange only at mixture screws 4 turns out..ok I think lets have a drive..no backfire all cylinders work but...no power..what the hell I thought..so all screws back in at 3/5 turn out and it backfire again..weak too..I wll b pulling the engine in a couple of months cos I no something weird/bad is going on in it but still a mystery..was about to go to techenders next month but not sure if its a good idea tho.. Sorry for a long rant Wysłane z iPad za pomocą Tapatalk
I had a problem with the rev limiting rotor like yours, but you really don't need it unless you like screaming its nuts off. A regular rotor works fine and gives less to go wrong. The idea is that as the rotor reaches a certain speed it will cut the current. It's limited by a small spring but if the spring goes weak there will be a point where it's sparking a lot. That's why it's melted. It also looks like there's been a previous attempt to glue it back together.
Yeah I think I should have one that I took out of my beetle..Today I also found an exhaust leak nothing major tho but that could be a cause of lean mixture and results in misfire and poor running me thinks..will investigate this weekend Wysłane z iPad za pomocą Tapatalk
Rev limiting arms don't for so well on ours seem to make it much harder to put cap on so binned ours and went back to standard Sent from my SM-T580 using Tapatalk
Thoughts .. This might be cross-firing with a dud rev-limiting rotor arm. The centrifugal opening gap burns away maybe making a shorter path for the spark to jump to the 'next' or 'previous ' cylinder direct from the long point of the brass cross on top. So sometimes it fires the exhaust mixture rather than firing the compression mixture in the cylinder. Replace the rotor arm with a simple non rev limiting arm. Once sparks track across insulators they start to burn the surface, which then gets heated up, maybe melting things. Could be the rev limiting gap now has a burnt insulator and a stuck gap so the energy from the coil is spent melting things instead of making fat sparks. I think there is just meant to be a resistor from the centre contact to the tip of the rotor of a standard simple rotor arm. The smell of petrol could be the completely unburnt mixture from misfiring when it doesnt backfire as well as misfire. Something is strange though, you would have thought a duff rotor arm is likely to stop all cylinders working in an equal fashion. A three cylinder bus is a bit weak and weedy . Tweak your carburettors back where they were - the fuel smell may be misleading you into tuning it too lean. I would also pop the rocker covers and check that all the rockers are in line properly with the valves - I had a nightmare once where it backfired and shuddered like crazy when an exhaust rocker arm slid sideways. And another occasion where I failed to tighten up the rocker arm shaft bolts and it just came undone bringing my bus to being barely able to manage 10mph on the flat. I would also check idle jets for blockages - leading to a very lean idle / cruise on one cylinder if you have 4 barrels.
Just set carbs as they were, fit ordinary rotor arm, new dissy cap, check leads and plugs and give it a try this may give you a good idea of what is buggered
As above, bin the rev-limiting rotor. They don’t do anything and are just another potential point of failure.
Great advices guys thanks It absolutelly makes sense to me..it was misfiring for a bit of time and being shakey and erratic at idle may lead to that conclusion..for some reasons I always thought theres something wrong going on in ignition system..although I replaced cap rotor arm leads points and spark plugs a couple of times it didnt change anything..I even ran one of them new electronic dizzys off ebay but wasnt really happy with it so went back to points and my old og distributor..I definatelly can hear it doesn’t fire properly..I just know it..there must be somthing so I will try with std rotor arm first and see what happens..cheers Wysłane z iPad za pomocą Tapatalk
BTW I tweaked the mix screws back as they were before and it made a difference..still not great but no backfiring (fitted another rev lim rotor arm temporarily as I cant find the other one)..all valves are spot on I check them regulary.. Wysłane z iPad za pomocą Tapatalk
Got a new rotor arm from GSF and what a surrprice..its NOS£5.80 with discount so not a fortune toowill see how it goes tho.. Sent from my iPhone using Tapatalk
